rice grain yield and component responses to near 2°c of warming
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Field Crops Research 157 (2014) 98–110
Contents lists available at ScienceDirect
Field Crops Research
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ice grain yield and component responses to near 2 ◦C of warming
arooq Shaha,b, Lixiao Niea, Kehui Cuia, Tariq Shahc, Wei Wua, Chang Chena,iyang Zhua, Farhan Alid, Shah Fahada, Jianliang Huanga,∗
National Key Laboratory of Crop Genetic Improvement, MOA Key Laboratory of Crop Ecophysiology and Farming System in the Middle Reaches of theangtze River, College of Plant Science and Technology, Huazhong Agricultural University, Wuhan, Hubei 430070, ChinaDepartment of Agriculture, Abdul Wali Khan University Mardan, 23200 Khyber Pakhtunkhwa, PakistanCollege of Economics and Land Management Huazhong Agricultural University, Wuhan, Hubei 430070, ChinaNational Key Laboratory of Crop Improvement and Genetics, Huazhong Agricultural University, Wuhan, Hubei 430070, China
r t i c l e i n f o
rticle history:eceived 15 May 2013eceived in revised form4 December 2013ccepted 14 December 2013
eywords:enotypic variationlobal warmingigh temperatureicerain yield
a b s t r a c t
The paucity of studies regarding agronomic performance of rice cultivars under field-scale elevatedtemperature is seriously lacking our current understanding of the potential consequences of high tem-peratures. For quantifying the relative influence of H(D + N)T (high diel i.e. day plus night), HDT (highdaytime), HNT (high nighttime) and AT (ambient) temperatures on agronomic performance, grain yieldand its components, two field-scale experiments were conducted on a set of rice cultivars (includingvarious indica and japonica ecotypes). A newly developed system of blowers plus heaters was used toincrease the temperature of the field by approximately 2 ◦C. Starting from booting till harvest maturity,all genotypes were subjected to the above-mentioned four temperature treatments during both years.Among the tested treatments, H(D + N)T proved to be more devastating as it severely affected almost allthe investigated traits such as grain yield and its components, biomass and HI. Under our experimentalconditions, an increase of about 2 ◦C in H(D + N)T resulted in 16.3% and 26.6% yield reduction in bothindica and japonica ecotypes, respectively during 2009. In 2010, this yield reduction ranged from 21.3%for indica to 40.2% for japonica cultivars. The decrease in grain yield caused by HDT was 4.1 and 4.0% forindica and japonica ecotypes, respectively, in 2009. The grain yield reduction caused by HDT in 2010 was3.2 and 9.1%. Similarly, HNT decreased grain yield by 0 and 10.1% in 2009, and by 16.9 and 45.3% dur-
ing 2010 for indica and japonica ecotypes, respectively. HDT reduced aboveground biomass more thanHNT in 2009, while in 2010 there was no much difference between the effects of these two treatments.HNT resulted in more reduction of spikelet fertility and HI than HDT during both years. Japonica ecotypeappeared to be more sensitive to temperature increase than indica during both years in terms of grainyield and its components. In case of genotypic variation, the effect of temperature treatments on ther dep
studied traits was cultiva. Introduction
A recent increase in global warming has more frequentlyxposed crops to elevated temperatures which in turn have alreadyffset a significant portion of yield increase arisen from variousactors. This rising temperature is also posing great threats for pro-uctivity of rice. China is one of the most important rice producingountries (Dong et al., 2011) and Yangtze River Valley (YRV) signif-cantly contributes to ensuring its food security. Double season riceearly and late) and single season rice (middle season) are planted
idely in the middle and lower reaches of the Yangtze River, whichs of immense importance to the food security as it occupies 70% ofhe total rice growing area in China (Huang et al., 1998; Tian et al.,
∗ Corresponding author. Tel.: +86 2787284131; fax: +86 2787284131.E-mail address: [email protected] (J. Huang).
378-4290/$ – see front matter. Crown Copyright © 2013 Published by Elsevier B.V. All rittp://dx.doi.org/10.1016/j.fcr.2013.12.014
endant.Crown Copyright © 2013 Published by Elsevier B.V. All rights reserved.
2009). This particular area of YRV is prone to rice yield loss dueto high temperature especially in case of mid-season, though thetemperature may rarely increase more than 35 ◦C (Matsui, 2009).It implies that the critical maximum temperature for yield reduc-tion is much lower in this particular region compared with someother parts of the world like Australia (Tian et al., 2010), where anincrease of 40 ◦C may sometimes not cause yield reduction (Matsuiet al., 2007).
An important objective of conducting ecosystem warming tri-als is to obtain data for validating plant growth (Kimball, 2011).Till now, most of the research on global warming and rice is car-ried out in controlled experimental settings such as greenhouseand growth chambers, etc., and with the setting of temperature
increment above 4 ◦C, which in most cases may not exactly repre-sent the expected increase in the near future. The focus on relativelyhigher levels of temperature increases in majority of the studiesplus an environmental setup which does not ideally represent fieldghts reserved.
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F. Shah et al. / Field Crop
onditions fail to remove the uncertainty of the near future sce-ario. It implies that a system which can increase the temperaturet field level is required to assess the effects of global warmingn future rice production (Rehmani et al., 2011). To obtain thesebjectives and resemble a more realistic future scenario, we devel-ped a system which could increase the temperature under fieldonditions by almost 2 ◦C without causing much variation in othernvironmental factors like radiation and humidity, etc. This systems discussed in detail in the following sections. Besides, the effectsf daily mean, maximum and minimum temperatures are scarcelynvestigated individually in a combined study. Recently, Dong et al.2011) while focusing on all day, nighttime and daytime warming,ocumented that a temperature increase of less than 2 ◦C affectsice productivity in East China. They observed that the impact wasess than the previous projections. But the southern and centralarts of China, especially the Yangtze River basin, have totally dif-erent climate which is usually characterized by high temperatureith increased relative humidity. It is expected that in contrast toong et al. (2011), this part of region will be more severely affectedy a slight temperature increase and that a temperature increase of◦C will lead to more negative effects on rice productivity and qual-
tative traits than the previously projected simulations. Keeping thebove scenario in mind, our interests were to reveal the more real-stic impact of various higher temperature treatments (around 2 ◦C,
hich is the most idealistic target according to 2DS and 450 scenar-os by 2050 (IEA, 2013) on agronomic traits and yield of rice undereld conditions.
. Materials and methods:
.1. Crop husbandry
Field experiments were conducted at the experimental fields ofuazhong Agricultural University Wuhan of Hubei province, China,uring 2009 and 2010. Ten rice (Oryza sativa L.) genotypes rep-esenting a range of indica and japonica ecotypes from differentcosystems, morphology and place of origin in China were used in009. Details of the tested varieties are available elsewhere (Zhut al., 2013). These cultivars were selected on the basis of their fielderformance of previous trials of our group. The criteria used for theelection included grain yield, lodging resistance, plant height androwth duration. Due to variation in growth period from the rest ofhe cultivars, a japonica variety LimingB was not used in the anal-sis. During 2010, only six varieties were selected, i.e. three fromach ecotype based on their performance in 2009. The criteria usedor selection were the same growth duration and their responsive-ess to high temperature. Field preparation and crop managementere followed according to the standard practices suited to this
egion. Certified seed of all these cultivars (already germinated)as grown for the nursery on 11th May during both years. Twentyine and thirty days-old seedlings were transplanted at the rate ofhree seedlings per hill during 2009 and 2010, respectively. A planto plant (P-P) distance of 16.7 cm and row to row (R-R) distance of0 cm were maintained in the field in both trials. A three-way splitpplication of 180 kg N ha−1 was applied in the ratio of 40:30:30t transplanting, mid tillering and panicle initiation stages, respec-ively, during both experiments. Weeds were uprooted manuallyhenever found. Pests were also controlled intensively by sprayingesticides.
.2. Experimental design and temperature treatments
These trials were conducted in open top field chambers (OTC)ccording to randomized complete block design (RCBD) withplit plot arrangements and three replications. The plastic height
rch 157 (2014) 98–110 99
was kept at minimum level to avoid the problems associatedwith OTC trials (which in most cases may not ideally representnatural environment). Temperature treatments were assignedto the main-plots having an area of 30 m2, while varieties wereallotted randomly to the subplots (with 3 m2 area in 2009 and5 m2 in 2010). Temperature was increased by a newly developedsystem having a combination of blower and heaters (Fig. 1a), andsuiting rice field experiments. The blower model was CZR-LY90which was manufactured by Yong Qiang Ventilators Company(Fig. 1b); having a power of 0.75 kW with an air blowing pressureof 20 m3 min−1. The blowers were operated at full capacity all thetime. In this system, the blower was connected to a heater (Fig. 1c)which was surrounded by iron covering to avoid dissemination ofheat to the outside environment and protect it from rain. Four ironlegs were fixed to this system so as to keep it above the ground.The main-plots were surrounded by a constant height of 110 cmplastic sheets from start of heat treatment till harvest maturity tokeep the temperature constant within the main-plot and differentfrom the rest of the field (Fig. 2a). The front of the covering wasconnected to 10 m long PVC pipes with an inner diameter of 11 cm(Fig. 2c). Four such systems (blower + heater + pipe) were placedat the two opposite sides across the length of the main-plots(Fig. 2b). The shape and size of the heaters were designed by alocal company dealer such that these could be easily connectedto the blower and adjusted inside the iron covering used in thissystem. The power of the each individual heater was 1.5 kW.Small holes (approx. 0.8–1.0 cm in diameter) at different distanceswere made on the pipes so that the warm air (produced by theheater and pushed by the blower) can come out of the pipe andincrease the temperature of the plots. Four different temperaturetreatments were allotted to the main-plots i.e. high day plusnight H(D + N)T, high daytime (HDT), high nighttime (HNT) andambient (AT). For H(D + N)T treatment the heating systems werejust rested for 10–20 min at 7:00 AM and 7:00 PM during 24 hperiod. For HDT treatment the heating systems were turned onand off at 7:00 AM and 7:00 PM, respectively, and vice versa forHNT treatment. The AT plots were without any heating systembut were also surrounded with plastic like the other plots sothat greater uniformity in factors other than temperature canbe achieved with the rest of the field. The heat treatments wereemployed before booting stage as most of the damage to ricecaused by high temperature occurs after that. A HOBO MicroStation Onset Computer Corporation Data Logger–H21-002 withdifferent sensors (12-Bit Temp Smart Sensor S-TMB-017 whichcan measure temperature from −40 to 100 ◦C) was installed inthe field which could record temperature data during the wholeexperimental period. The sensors were fixed on wooden poles at aheight of 60–65 cm from the ground level to measure temperatureof the air within the canopy. As the temperature treatments werestarted just before booting stage, the height of the sensors was keptconstant at this level. For greater accuracy of data the sensors wereprotected from the sunlight, rain or other parts of the plants byusing Solar Radiation Shields (RS3) whose details are available at:http://www.instrumentchoice.com.au/instrument-choice/data-loggers/accessories/rs3-solar-radiation-shield-small (acessed on22-10-2013).
2.3. Antioxidant enzyme superoxide dismutase (SOD) activity andplant height
For enzymes extractions, 0.5 g of frozen leaves werehomogenized in 50 mM potassium phosphate buffer (pH 7.8)
containing 1 mM EDTA, 3 mM 2-mercaptoethanol, and 2% (w/v)polyvinylpolypyrrolidone in mortar and pestle. Then the activityof SOD was assayed following the method described by Bai et al.(2009). At harvest maturity, plant height was measured from the
100 F. Shah et al. / Field Crops Research 157 (2014) 98–110
Fig. 1. Different instrument used in the heating system (a) A pair of heating systems used to increase the temperature of the field. (b) Blower used to push hot air. (c) A heaterw
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hich was placed infront of the blower to heat the air.
ase of the plant to the tip of the uppermost reaching leaf duringoth years.
.4. Yield and its components
In both experiments eight hills from the central rows in eachubplot were sampled at maturity to determine grain yield, above-round total biomass, harvest index and yield components. Panicleumber of each collected hill was counted to calculate its numberer m2. Plants were then separated into straw and panicles. Strawas further divided into leaves and stems which were then ovenried at 80 ◦C to constant weight and their dry weights were calcu-
ated. The panicles were hand-threshed and filled spikelets wereeparated from unfilled spikelets through a seed blower. Threeub-samples each of 30-g filled spikelets and 5-g unfilled spikeletsere taken to count the number of spikelets. Dry weights of rachis
nd filled and unfilled spikelets were also determined after dry-ng them at 80 ◦C to constant weight in oven. Spikelets per panicle,pikelets per m2 and grain-filling percentage (100 × filled spikeletumber/total spikelet number) were calculated. Furthermore, at
arvest maturity, all the panicles from twenty five hills in centralows were harvested for yield data in 2009. During 2010, thirty hillsere harvested randomly from the central rows for yield deter-ination. These panicles were also hand threshed and the grainswere air dried for three days. The moisture content was testedthrough a digital moisture meter by randomly selecting three sub-samples and was then adjusted for the whole sample. The grainyield was adjusted to a moisture content of 0.14 g H2O g−1 freshweight.
2.5. Biomass and harvest index
For determining aboveground total biomass, the total drymatter of straw, rachis, and filled and unfilled spikeletswas summed up. Percent harvest index (100 × filled spikeletweight/aboveground total biomass) was also calculated at theend.
2.6. Data analysis
To test the significance of various treatments, data were statis-tically analyzed using analysis of variance (ANOVA; SAS statisticalanalysis system, version 9.2; SAS Institute, Cary, NC, USA). The
means were separated using Least Significance Difference (LSD) atan alpha level of 0.05. If there were no significant differences thenthe values were averaged and presented with standard errors aserror bars.
F. Shah et al. / Field Crops Research 157 (2014) 98–110 101
Fig. 2. Experimental plots with plastic used for keeping temperature within the plot constant (a). Blowers connected with pipes which were used for pushing the heated air(b). Pipes running within the main-plot lengthwise on each side (c). All these pictures are from field experiments.
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ig. 3. Mean daytime and nighttime temperatures under different treatments. H(Demperatures, respectively.
. Results
.1. Temperature increment
The apparatus used for increasing temperature in this study was
ble to increase the temperature of the air within the canopy bypproximately 2 ◦C compared with ambient (control). The maxi-um mean nighttime temperature reached to 30 ◦C (Fig. 3a) whilehe daytime mean maximum temperature exceeded 36 ◦C (Fig. 3b)
HNT, HDT and AT represent high day plus night, high night, high day and ambient
during 2009. In 2010, the mean maximum nighttime and daytimetemperatures reached to more than 33 ◦C and 36 ◦C, respectively.Maximum values of both night and daytime mean temperatureswere recorded during the period of 15–30 DAHT (days after heattreatment initiation), while minimum values of daytime were
observed at 32 and 59 DAHT in 2009 and 2010, respectively. Theminimum mean night temperature reached to almost 16 ◦C in 2009and below 15 ◦C during 2010, respectively. This figure further sug-gests that there were several peak values of mean temperature
1 s Research 157 (2014) 98–110
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Fig. 4. Effects of different temperature treatments on the activity of Superoxidedismutase (SOD) of the tested genotypes in 2009 and 2010. One unit of SOD activ-ity is the amount of enzyme required to result in 50% inhibition of the rate of NBT(nitro blue tetrazolium chloride) reduction measured at 560 nm. The abbreviationsDTWX, ZX232, CNSJ, DY5, ZH8 and J87-304 stand for varieties DongTingWanXian,ZhenXian232, ChengNongShuiJing, DangYu5, ZhongHua8 and Jing87-304, respec-tively. H(D + N)T, HDT, HNT and AT represent high day plus night, high day, high
02 F. Shah et al. / Field Crop
uring both years at different time intervals. As the temperatureresented here is the mean temperature, this implies that the actualaximum temperature within a certain day or night was even more
han the values presented in this figure.
.2. Superoxide dismutase (SOD)
Although during 2009, no consistent variation of SOD activ-ty in response to the three elevated temperature treatments wasbserved when compared with AT, it was significantly affected inwo out of the four varieties (for which SOD activity was measured).
hen averaged across all four cultivars, the activity of SOD was lessnder AT, followed by HDT, H(D + N)T and HNT, respectively (Fig. 4).
n 2010 the trend was relatively more obvious as the activity of SODas significantly less in four out of the six used varieties. Both cul-
ivars with no significant variation for SOD were indica i.e. ZX232nd CNSJ. Compared with AT, the activity under H(D + N)T was sig-ificantly higher in four (three japonica and one indica) cultivars.imilarly, HNT and HDT also resulted in increased activity in threend two varieties (which were japonica), respectively, when com-ared with AT. Generally the activity of SOD was not affected in
ndica varieties compared with japonica. The overall comparisonf the heat treatments revealed that the minimum mean values ofOD activity were in the range of 80–100 U g−1 recorded for AT tem-erature while the maximum was about 155 U g−1 observed under(D + N)T in variety DY5 (Fig. 4).
.3. Plant height at maturity
Plant height data at maturity is presented in Fig. 5. The datahow that during 2009 there was no noticeable variation caused byifferent temperature treatments among various genotypes. Theeight of only one indica variety ZX232 was significantly highernder HNT treatment than H(D + N)T, while for the rest the effectas not significant. Based on the genotypic variation DTWX had the
hortest plants among the tested varieties, while XWX1 and CNSJad the tallest ones. In 2010 a relatively more visible effect of differ-nt elevated temperatures was observed on plant height; as threeone indica and two japonica) out of the six tested varieties showedignificant variations. HDT tended to increase the plant height andhe plant developed under this treatment had the maximum heightor most varieties. No specific trend was recorded for the rest of theemperature treatments.
.4. Grain yield
Grain yield was lower under different high temperature treat-ents compared to ambient temperature for most of the genotypes
uring both years. Among the tested high temperature treatments,(D + N)T significantly reduced grain yield for the two ecotypesuring 2009 and 2010. This H(D + N)T associated reduction wasore prominent for almost all cultivars compared with only HDT
r HNT treatments in both years (Table 1). In 2009, the yieldas reduced by 4.08, 0 and 16.33% by HDT, HNT and H(D + N)T
reatments for indica cultivars, and by 3.99, 10.11 and 26.60% foraponica ecotype, respectively. During the second year of the trialhe yield was decreased by 3.23, 16.99 and 21.29% for indica ecotypend by 9.11, 45.36 and 40.18% for japonica varieties, respectively,ue to HDT, HNT and H(D + N)T. The effect of HDT on yield reduc-ion was not significant during both years, while that of HNT wasnly significant during 2010 for both ecotypes.
Considering the genotypic variation, the data reveal that XWX1
7.56 t ha−1) and ZH8 (7.14 t ha−1) had the highest mean grainields averaged across all tested temperature regimes, in indicand japonica ecotypes, respectively, during 2009. In 2010, theean grain yields of an indica variety ZX232 (4.75 t ha−1) and thenight and ambient temperatures, respectively. Means followed by different lettersare significantly different at a probability level of 0.05 according to least significantdifference (LSD) test and error bars represent standard error.
japonica cultivar DY5 (3.54 t ha−1) were the maximum when aver-aged across all four temperature treatments. Grain yield whencombined for both ecotypes during a particular year and under heattreatment is presented in Fig. 6. It is obvious from this figure thatthe yield of the first year trial was markedly higher than the sec-ond year. During 2009, the overall yield under AT was more than7 t ha−1 while in 2010 it was even less than 5 t ha−1 when averagedfor all the tested genotypes during a particular year. The mean yieldobtained under HDT and HNT treatments was almost the same in2009 but in the next year HNT showed a tremendous decrease interms of grain yield. The yield reduction due to H(D + N)T was max-imum during both years when compared with HDT and HNT. Likeother treatments during 2010 the yield under this treatment wastremendously lower than 2009.
3.5. Grain yield components
Data regarding panicle number per m2 are presented in Table 2.The data reveal that during 2009 in some indica varieties the pan-
icle number varied under different temperature treatments, whilethere was no significant variation among the japonica cultivars dur-ing this year. In this particular year, maximum number of paniclesfor indica cultivars were found under AT while the least number
F. Shah et al. / Field Crops Research 157 (2014) 98–110 103
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Fig. 5. Effects of different temperature treatments on the activity of Superoxide dismutase (SOD) of the tested genotypes in 2009 and 2010. The abbreviations DTWX, ZX232,DY5 ZH8 and J87-304 stand for varieties DongTingWanXian, ZhenXian232, DangYu5, JWR221, ZhongHua8 and Jing87-304, respectively. H(D + N)T, HDT, HNT and AT representh eans
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igh day plus night, high day, high night and ambient temperatures, respectively. Mccording to least significant difference (LSD) test and error bars represent standard
as observed in plants grown under H(D + N)T. The difference fromT temperature caused by elevated temperatures ranged from 1.26nd 4.11 under HNT to 10.22–8.05 under H(D + N)T, for indicand japonica ecotypes, respectively, during 2009. HDT caused aeduction of 7.51% and 6.46% in both indica and japonica ecotypes,espectively. Conversely, in 2010 more panicles were found underNT treatment, while less number of panicles was recorded underT for indica varieties. Like 2009, no significant difference among
he number of panicles per m2 was noticed in japonica cultivars.ithin the same ecotype, an indica variety XWX1 and japonica cul-
ivar J87-304 produced maximum i.e. 323.0 and 278.2 panicles per
2, respectively, in 2009. In 2010, an indica cultivar CNSJ and aaponica variety DY5 produced 279.8 and 222.4 panicles per m2,espectively which were the highest number within the same eco-ype. A comparison of the two years revealed that panicles number
followed by different letters are significantly different at a probability level of 0.05.
per m2 were considerably higher in 2009 when averaged across allvarieties and differenent temperature treatments.
In both experiments the number of spikelets per panicle ofboth ecotypes was not significantly altered by elevated temper-ature treatments (Table 3). An indica cultivar ZX232 resultedin maximum number of spikelets per panicle across differenttemperature treatments which ranged from 165.4 spikelets perpanicle in 2009 to 119.7 in 2010 within the same ecotype.Similary, among japonica cultivars JWR221 and ZH8 producedalmost the same number of spiklets per panicle i.e. 152.5 and153.6 during 2009 and 118.0 and 117.4 during 2010, respec-
tively. A comparison between the two years revealed that spikeletsnumber per panicle were markedly higher in 2009 comparedto 2010 when averaged across all temperature treatments andvarieties.
104 F. Shah et al. / Field Crops Research 157 (2014) 98–110
Table 1Effects of different temperature treatments on grain yield (t ha−1) of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 7.90 a 7.81 a −1.14 7.44 a −5.82 7.10 a −10.13SKC 7.96 a 6.69 b −15.95 7.63 a −4.15 6.43 b −19.22DTWX 6.26 ab 5.97 ab −4.63 6.82 a 8.95 5.19 b −17.09ZX232 7.15 a 7.17 a +0.28 7.36 a +2.94 6.03 a −15.66CNSJ 6.28 a 6.45 a +2.71 6.29 a +0.16 5.03 a −19.90Mean 7.11 A 6.82 A −4.08 7.11 A 0.00 5.95 B −16.32
2009 Japonica varietiesDY5 6.88 a 6.85 a −0.44 6.48 a −5.81 5.56 b −19.19JWR221 8.25 a 7.45 ab −9.70 6.76 b −18.06 6.52 b −20.97ZH8 7.55 a 7.83 a +3.71 7.17 ab −5.03 6.43 b −14.83J87-304 7.39 a 6.74 a −8.80 6.62 a −10.42 3.57 b −51.69Mean 7.52 A 7.22 A −3.99 6.76 A −10.11 5.52 B −26.60
2010 Indica varietiesDTWX 3.88 bc 3.46 c −10.82 5.32 a 37.11 4.78 ab 23.20ZX232 5.86 a 5.17 ab −11.77 4.56 bc −22.18 3.35 c −42.83CNSJ 2.61 b 3.45 a 32.18 3.02 ab 15.71 3.28 ab 25.67Mean 4.65 A 4.50 A −3.23 3.86 B −16.99 3.66 B −21.29
2010 Japonica varietiesDY5 4.95 a 4.60 ab −7.07 3.42 c −30.91 3.65 bc −26.26JWR221 5.94 a 5.81 a −2.19 2.96 b −50.17 3.27 b −44.95ZH8 5.91 a 4.85 b −17.94 2.80 c −52.62 3.12 c −47.21Mean 5.60 A 5.09 A −9.11 3.06 B −45.36 3.35 B −40.18
Within a column for each variety, means followed by different letters are significantly different at 0.05 probability level according to least significant difference (LSD) test.The abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, DongTingWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 andJing87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night, high day, high night and ambient temperatures, respectively.
Table 2Effects of different temperature treatments on panicles number per m2 of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 351.4 a 308.2 a −12.29 335.2 a −4.61 297.1 a −15.45SKC 290.0 a 260.9 b −10.03 275.2 ab −5.10 270.2 ab −6.83DTWX 297.1 a 269.3 a −9.36 312.0 a +5.02 278.9 a −6.13ZX232 280.0 a 251.4 b −10.21 250.9 b −10.39 240.7 b −14.04CNSJ 292.9 ab 308.4 a +5.29 319.3 a +9.01 269.8 b −7.89Mean 302.3 A 279.6 AB −7.51 298.5 A −1.26 271.4 B −10.22
2009 Japonica varietiesDY5 302.8 a 236.4 b −21.93 266.6 ab −11.96 266.3 ab −12.05JWR221 212.8 ab 176.4 c −17.11 223.0 a +4.79 180.7 bc −15.08ZH8 204.3 a 231.6 a +13.36 213.9 a +4.70 198.1 a −3.03J87-304 283.1 a 293.9 a +3.81 258.6 −8.65 277.1 a −2.12Mean 250.8 A 234.6 A −6.46 240.5 A −4.11 230.6 A −8.05
2010 Indica varietiesDTWX 226.3 b 263.8 ab +16.57 318.5 a +40.74 291.3 ab +28.72ZX232 212.2 a 230.2 a +8.48 200.02 a −5.74 224.4 a +5.75CNSJ 273.5 a 264.1 a −3.44 306.6 a +12.10 274.8 a +0.48Mean 237.3 B 252.7 AB +6.49 275.1 A +15.93 263.5 AB +11.04
2010 Japonica varietiesDY5 207.5 a 226.5 a +9.16 227.4 a +9.59 228.3 a +10.02JWR221 218.8 a 214.2 a −2.10 202.7 a −7.36 201.5 a −7.91ZH8 210.1 a 206.5 a −1.71 200.1 a −4.76 203.9 a −2.95Mean 212.1 A 215.7 A 1.70 210.4 A −0.80 211.3 A −0.38
Within a column for each variety, means followed by different letters are significantly different at 0.05 probability level according to least significant difference (LSD) test.T ngTinJ , high
nimocait
he abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, Doing87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night
Total number of spikelets (filled and unfilled) per m2 was alsoot significantly affected by various temperature treatments dur-
ng both years except H(D + N)T in 2009. While fewer spikelets per2 were found for H(D + N)T treatment which caused a reduction
f 12.61% in indica ecotype and 13.68% in japonica ecotype when
ompared with AT (Table 4). During 2009, HDT and HNT causedreduction of 8.19 and 0.22% in total number of spikelets per m2
n comparison with AT. Similarly in 2010, HDT, HNT and H(D + N)Treatments led to a decrease of 0.0, 12.2 and 9.9 percent compared
gWanXian, ZhenXian232, ChengNongShuiJing, DangYu5, JWR221, ZhongHua8 and day, high night and ambient temperatures, respectively.
to AT in japonica ecotype, while for indica ecotype the number ofspikelets under all three elevated temperatures was greater thanAT but not significantly. Based on the genotypic variation, XWX1and J87-304 produced 47.3 and 37.0 thousand spikelets per m2
when averaged across different temperature treatments, which
were the maximum values within indica and japonica ecotypes,respectively, in 2009. Likewise in 2010, DTWX and ZH8 prouduced29.8 and 25.8 thousand spikelets per m2 which were the maximumvalues when averaged across all temperature treatments among
F. Shah et al. / Field Crops Research 157 (2014) 98–110 105
Table 3Effects of different temperature treatments on spikelets per panicle of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 145.0 a 150.0 a +3.45 152.8 a +5.38 140.0 a −3.45SKC 170.8 a 154.8 a −9.37 156.6 a −8.31 151.9 a −11.07DTWX 124.5 a 127.0 a +2.01 129.0 a +3.61 124.5 a 0.00ZX232 164.3 a 163.1 a −0.73 169.9 a +3.41 164.3 a 0.00CNSJ 146.3 a 150.5 a +2.87 153.1 a +4.65 148.4 a 1.44Mean 150.2 A 149.1 A −0.73 152.3 A +1.40 146.4 A −2.53
2009 Japonica varietiesDY5 120.4 a 128.8 a +6.98 118.8 a −1.33 112.1 a −6.89JWR221 135.0 a 169.0 a +25.19 149.6 a +10.81 157.0 a +16.30ZH8 161.4 a 152.3 ab −5.64 160.4 a −0.62 140.4 b −13.01J87-304 150.3 a 142.9 a −4.92 119.5 a −20.49 120.3 a −19.96Mean 141.8 A 148.2 A +4.51 137.1 A −3.31 134.9 A −4.87
2010 Indica varietiesDTWX 106.4 a 100.1 a −5.92 109.5 a +2.91 114.3 a +7.42ZX232 120.4 a 126.5 a +5.07 124.6 a +3.49 107.4 a −10.80CNSJ 74.0 b 86.4 a +16.76 73.4 b −0.81 92.8 a +25.41Mean 100.2 A 104.6 A +4.39 102.5 A +2.30 104.8 A +4.59
2010 Japonica varietiesDY5 100.5 b 115.6 a +15.02 106.8 ab +6.27 108.0 ab +7.46JWR221 116.8 a 119.0 a +1.88 115.4 a −1.20 120.7 a +3.34ZH8 125.2 a 123.8 a −1.12 112.4 a −10.22 108.3 a −13.50Mean 114.2 A 119.5 A +4.64 111.5 A −2.36 112.4 −1.58
Within a column for each variety, means followed by different letters are significantly different at 0.05 probability level according to least significant difference (LSD) test.The abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, DongTingWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 andJing87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night, high day, high night and ambient temperatures, respectively.
Table 4Effects of different temperature treatments on total number of spikelets per m2 of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 50.9 a 45.8 b −10.02 51.1 a +0.39 41.5 b −18.47SKC 49.4 a 39.8 a −19.43 43.1 a −12.75 41.0 a −17.00DTWX 36.9 ab 34.2 b −7.32 40.3 a +9.21 34.7 a −5.96ZX232 45.9 a 41.1 ab −10.46 42.3 ab −7.84 40.4 b −11.98CNSJ 42.8 ab 46.4 a +8.41 48.5 a +13.32 40.0 b −6.54Mean 45.2 A 41.5 B −8.19 45.1 A −0.22 39.5 B −12.61
2009 Japonica varietiesDY5 36.4 a 30.5 a −16.21 31.7 a −12.91 32.5 a −10.71JWR221 28.7 a 29.7 a +3.48 33.3 a +16.03 28.2 a −1.74ZH8 33.0 a 35.1 a +6.36 34.2 a +3.64 27.6 b −16.36J87-304 42.3 a 41.9 a −0.95 30.8 a −27.19 33.1 a −21.75Mean 35.1 A 34.3 A −2.28 32.5 AB −7.41 30.3 B −13.68
2010 Indica varietiesDTWX 24.2 a 26.6 a +9.92 35.0 a +44.63 33.5 a +38.43ZX232 25.5 a 29.4 a +15.29 25.0 a −1.96 24.2 a −5.10CNSJ 20.3 a 22.9 a +12.81 22.5 a +10.84 25.5 a +25.62Mean 23.3 A 26.3 A +12.88 27.5 A +18.03 27.7 A +18.88
2010 Japonica varietiesDY5 21.6 a 26.2 a +21.30 23.4 a +8.33 24.7 a +14.35JWR221 26.0 a 27.7 a +6.54 23.3 a −10.38 24.3 a −6.54ZH8 31.2 a 27.3 ab −12.50 22.6 b −27.56 22.1 b −29.17Mean 26.3 A 27.0 A +2.66 23.1 A −12.17 23.7 A −9.89
W tly diT ngTinJ , high
icr
sitHb(
ithin a column for each variety, means followed by different letters are significanhe abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, Doing87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night
ndica and japonica varieties, respectively. Similar to other yieldomponents, the data about total number of spikelets also showededuction in 2010 when compared with 2009.
Except an indica variety SKC and a japonica cultivar DY5, thepikelets fertility of all other varieties was reduced under H(D + N)Tn 2009 (Table 5). The percent spikelet fertility of all japonica cul-
ivars and only one indica ZX232 was significantly decreased by(D + N)T during 2010. The overall reduction percentages causedy H(D + N)T were 15.9 and 16.3% (in 2009), and 12.2% and 30.2%in 2010) for indica and japonica ecotypes, respectively. HDT ledfferent at 0.05 probability level according to least significant difference (LSD) test.gWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 and
day, high night and ambient temperatures, respectively.
to a decrease of 4.4% and 2.6% in 2009 and 1.1% and 5.6% during2010 for indica and japonica ecotypes, respectively. The reductioncaused by HNT for indica ecotype was 4.9% and 7.2% while thatfor japonica type varieties was 7.2% and 18.9% in 2009 and 2010,respectively.
Grain weight data of the two years are presented in Table 6.
Although the weight of the grains ripened under AT treatmentwas higher than grains matured under different high temperaturetreatments, significant differences were found for only four vari-eties (XWX1, SKC, ZX232 and J87-304) during 2009. The effect of
106 F. Shah et al. / Field Crops Research 157 (2014) 98–110
Table 5Effects of different temperature treatments on spikelets fertility percentage of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 83.8 a 81.8 ab −2.4 75.1 b −10.4 66.2 c −21.0SKC 81.6 a 76.7 a −6.0 83.2 a +2.0 74.8 a −8.3DTWX 93.1 a 87.5 a −6.0 91.3 a −1.9 83.9 a −9.9ZX232 81.9 a 78.9 a −3.7 78.1 ab −4.6 73.0 b −10.9CNSJ 77.8 a 75.2 a −3.3 70.4 a −9.5 54.2 b −30.3Mean 83.7 A 80.0 A −4.4 79.6 A −4.9 70.4 B −15.9
2009 Japonica varietiesDY5 81.3 a 84.9 a +4.4 75.1 a −7.6 70.4 a −13.4JWR221 85.0 a 82.1 ab −3.4 76.4 ab −10.1 71.7 b −15.6ZH8 87.1 a 83.5 ab −4.1 83.5 ab −4.1 81.0 b −7.0J87-304 86.1 a 80.4 ab −6.6 80.3 ab −6.7 61.3 b −28.8Mean 84.9 A 82.7 A −2.6 78.8 AB −7.2 71.1 B −16.3
2010 Indica varietiesDTWX 79.8 a 77.7 a −2.6 72.2 a −9.5 70.0 a −12.3ZX232 92.4 a 89.8 a −2.9 81.1 ab −12.2 69.8 b −24.5CNSJ 65.5 a 67.5 a +3.1 67.3 a +2.7 68.7 a +4.9Mean 79.2 A 78.3 A −1.1 73.5 AB −7.2 69.5 B −12.2
2010 Japonica varietiesDY5 93.6 a 77.4 b −17.3 73.1 b −21.9 67.7 b −27.7JWR221 92.7 a 92.7 a 0.0 81.2 b −12.4 62.9 c −32.1ZH8 92.1 a 89.5 a −2.8 69.0 b −25.1 61.4 b −33.3Mean 91.7 A 88.7 A −3.3 74.4 B −18.9 64.0 C −30.2
Within a column for each variety, means followed by different letters are significantly different at 0.05 probability level according to least significant difference (LSD) test.The abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, DongTingWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 andJing87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night, high day, high night and ambient temperatures, respectively.
Table 6Effects of different temperature treatments on thousand grain weight (g) of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 22.54 a 21.89 b −2.9 22.52 a −0.1 21.64 b −4.0SKC 22.83 a 22.80 a −0.1 23.06 a +1.0 22.16 b −2.9DTWX 20.88 a 20.41 a −2.3 20.18 a −3.4 20.71 a −0.8ZX232 22.52 a 22.23 a −1.3 22.58 a +0.3 21.83 b −3.1CNSJ 22.67 a 22.51 a −0.7 22.21 a −2.0 22.30 a −1.6Mean 22.29 A 21.97 AB −1.4 22.11 A −0.8 21.73 B −2.5
2009 Japonica varietiesDY5 24.27 a 23.66 a −2.5 23.74 a −2.2 23.93 a −1.4JWR221 28.41 a 28.43 a +0.1 28.75 a +1.2 28.21 a −0.7ZH8 28.42 a 28.18 a −0.8 28.20 a −0.8 27.87 a −1.9J87-304 21.33 a 21.32 ab 0.0 20.45 b −4.1 21.15 ab −0.8Mean 25.61 A 25.40 A −0.8 25.29 A −1.2 25.29 A −1.2
2010 Indica varietiesDTWX 19.50 a 19.01 ab −2.5 18.86 b −3.3 17.78 c −8.8ZX232 20.35 a 20.37 a +0.3 19.60 ab −3.7 19.18 b −5.7CNSJ 21.86 a 21.37 a −2.2 21.85 a 0.0 21.19 a −3.1Mean 20.57 A 20.25 AB −1.6 20.10 AB −2.3 19.38 B −5.8
2010 Japonica varietiesDY5 22.39 a 21.95 a −2.0 21.74 ab −2.9 20.27 b −9.5JWR221 26.02 a 25.61 ab −1.6 25.32 ab −2.7 24.68 b −5.1ZH8 25.54 a 24.95 ab −2.3 23.90 c −6.4 24.10 c −5.6Mean 24.65 A 24.17 AB −1.9 23.65 B −4.1 23.02 C −6.6
W tly diT ongTinJ , high
vsvbrsaHca
ithin a column for each variety, means followed by different letters are significanhe abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, Ding87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night
arious elevated temperatures was more pronounced in 2010 asignificant effect was observed for five out of the total six culti-ars. The weight of only three cultivars was significantly decreasedy H(D + N)T, while grain weight of one cultivar was significantlyeduced under HNT and HDT each, during 2009 (Table 6). In theecond year of the trial, except an indica cultivar CNSJ the yield of
ll remaining five cultivars was significantly reduced by H(D + N)T.DT resulted in lighter grains but the difference was not signifi-ant for all genotypes while HNT decreased the grain weight forn indica (DTWX) and one japonica (ZH8) varieties significantlyfferent at 0.05 probability level according to least significant difference (LSD) test.gWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 and
day, high night and ambient temperatures, respectively.
during 2010. All together, HDT decreased the grain weight by 1.4and 0.8% in 2009, and 1.6 and 1.9% in 2010 for indica and japon-ica ecotypes, respectively. Similarly, HNT caused a reduction of 0.8and 1.2% in 2009, and 2.3 and 4.1% in 2010 for indica and japonicatype cultivars, respectively. The weight reduction due to H(D + N)Ttreatment was 2.5 and 1.2% in 2009, and 5.8 and 6.6% in 2010 for the
indica and japonica ecotypes, respectively, when compared withAT. The grain weight data further suggest that during 2009 thegrains were comparatively heavier than those matured under theclimatic conditions of the year 2010.
F. Shah et al. / Field Crops Resea
Grain yield during 2009 and 2010
Year
20102009
Gra
in y
ield
(t
ha-1
)
0
2
4
6
8
AT
HDT
HNT
H(D+N)T
Fig. 6. Comparison of grain yield (t ha−1) among different temperature treatmentsduring 2009 and 2010. Values were obtained by averaging the yield of all indicaaAt
3
Tcnrot1DtwtwOa1WAbatr
ttpoai(pattni2dh(
nd japonica cultivars under a particular heat treatment. H(D + N)T, HDT, HNT andT represent high diel (day plus night), high daytime, high nighttime and ambient
emperatures, respectively.
.6. Total aboveground biomass and harvest index
Data regarding total aboveground biomass is presented inable 7. The data show that H(D + N)T and HDT showed signifi-antly reduced total aboveground biomass for five out of the testedine varieties in 2009. In contrast, HNT did not lead to any obviouseduction in terms of aboveground biomass. Maximum reductionf 27.1% and 19.8% was observed under H(D + N)T and HDT, respec-ively. While among the japonica ecotype the maximum decrease of3.3% was found for JWR221 under H(D + N)T and 19.2% for varietyY5 in case of HDT. The overall reduction caused in indica eco-
ype was 10.0% and 14.4%, while that occurred in japonica ecotypeas 6.3% and 10.9% under HDT and H(D + N)T treatments, respec-
ively. Surprisingly, no difference in total aboveground biomassas observed under different temperature regimes during 2010.nly for variety ZH8 all the three elevated temperatures HDT, HNTnd H(D + N)T reduced the total aboveground biomass by 16.7%,9.7% and 19.7%, respectively, which differed significantly from AT.hile in CNSJ (an indica) cultivar the aboveground biomass under
T was significantly less than HNT and H(D + N)T. Abovegroundiomass was greater in 2009 when averaged across all varietiesnd temperature treatments in comparison with 2010. Moreover,his difference in aboveground biomass between the two years waselatively more visible for indica ecotype.
In case of harves index (%), the effect of different temperaturereatments was not much different from those observed for otherraits (Table 8). H(D + N)T treatment showed comparatively moreronounced effect on harvest index during both years. In 2009, thebserved reduction percentages compared to AT were 3.9%, 5.2%nd 15.2% for indica ecotype, while 0%, 14.3% and 19.2% for japon-ca ecotype under HDT, HNT and H(D + N)T treatments, respectivelyTable 8). Similarly in 2010, when compared with AT, the reductionercentages were 2.2%, 11.5% and 17.3% for indica and 2.2%, 31%nd 42.3% for japonica ecotype under the three elevated tempera-ures HDT, HNT and H(D + N)T, respectively. It is obvious from therials of both years that HNT and H(D + N)T treatments had moreegative effects on the harvest index compared with HDT. Within
ndica ecotype, maximum HI (%) was 49.4; found for SKC during
009 and 34.9 for ZX232 in 2010 based on the average value acrossifferent temperature regimes. Similarly, for japonica ecotype theighest HI (%) value was 42.9 (observed for ZH8) in 2009 and 31.0in case of variety DY5) during 2010, when averaged across allrch 157 (2014) 98–110 107
temperature treatments. HI (%) was also relatively greater in 2009when compared with 2010.
4. Discussion
Rice plant height is an important morphological trait whichis linked with grain yield (Yang and Hwa, 2008). The findingsregarding plant height imply that except HDT, the other two ele-vated temperatures did not affect plant height (Fig. 5). The HDTassociated increase in the plant height of some varieties can beattributed to the rapid elongation of internode. Internode elonga-tion is greatly linked to the internal hormones like ethylene andgibberellins (Qi et al., 2011). The no visible effect of HNT on plantheight is in accordance to the findings of Mohammed and Tarpley(2009a). They reported that in a japonica cultivar “Cocodrie” HNTtreatment did not significantly affect the morphological traits ofrice including plant height. Similarly, HNT did not affect the plantheight in soybean (Seddigh and Jolliff, 1984). In contrast to suchfindings, Cheng et al. (2009) found that plant height significantlyincreases in rice when grown under HNT.
Superoxide dismutase is one of the key enzymes for scav-enging reactive oxygen species (ROS).The significantly reducedSOD activity observed for some of the varieties grown underAT when compared with all three elevated temperature treat-ments during 2010, implies that elevated temperature enhancedthe activity of antioxidative enzymes under high temperatures.The most probable reason is that under high temperatures anincrease in the activity of ROS occurs. In such circumstances, plantsusually respond with greater production of SOD to combat theheat induced injuries. Such increase in response to various abi-otic stresses in rice plant has been also reported in earlier studies(Shah et al., 2001). The second year’s data further suggest thatjaponica type varieties were relatively more sensitive to such ele-vated temperatures in terms of causing a decrease in SOD activitythan indica which was significantly reduced in all three japonicavarieties in contrast to only one indica. Moreover, the activi-ties of such enzymes under H(D + N)T, HDT and HNT need to befocused in future research as the current study could not unravel aspecific trend in response among these elevated temperature treat-ments.
Assessing the impact of climate change provides better under-standing of global warming effects on grain yield formation whichin turn serves as a practical reference for measures needed to betaken (Chen et al., 2011). Rice grain yield is determined by fourparameters; number of panicles per plant, number of spikeletsper panicle, grain filling rate and total grain weight (Kim et al.,2009). Our trials confirm that a temperature variation of about2 ◦C can lead to significant yield losses. Grain yields of both indicaand japonica ecotypes were reduced by different elevated tem-peratures. Maximum decrease in grain yield was recorded underH(D + N)T during both years, while the effect of HDT and HNT dur-ing 2009 was not significant. In the next year, HNT also resultedin much lower yield than HDT which was almost similar tothat caused by H(D + N)T when averaged for both ecotypes. Theobserved significant difference of H(D + N)T treatment comparedwith the other treatments is due to the fact that the continuousheating for the diel (24 h) treatment resulted in relatively moreincrease in the accumulative temperature compared to HDT andHNT. This increase in temperature might be one of the reasons forsuch a huge decrease observed under H(D + N)T treatment com-pared to the rest of the treatments. Nighttime temperature plays apivotal role in determining the grain yield of rice (Peng et al., 2004).Our results confirm this hypothesis as nighttime elevated tempera-
ture was more detrimental for rice crop in terms of yield especiallyfor the tested japonica varieties. The greater yield reduction ofthe tested japonica varieties (Fig. 6) may be ascribable to their
108 F. Shah et al. / Field Crops Research 157 (2014) 98–110
Table 7Effects of different temperature treatments on aboveground biomass (t ha−1) of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 19.8 a 17.4 b −12.12 19.6 a −1.01 16.2 a −18.18SKC 18.2 a 14.6 ab −19.78 17.2 ab −5.49 13.27 b −27.09DTWX 16.8 a 15.0 a −10.71 16.9 a +0.60 14.9 a −11.31ZX232 18.0 a 16.0 b −11.11 17.1 ab −5.00 16.4 ab −8.89CNSJ 17.2 a 18.0 a +4.65 18.7 a +8.72 16.4 a −4.65Mean 18.0 A 16.2 B −10.00 17.9 A −0.56 15.4 B −14.44
2009 Japonica varietiesDY5 17.7 a 14.3 b −19.21 15.9 ab −10.17 15.4 b −12.99JWR221 16.6 ab 14.6 b −12.05 18.9 a +13.86 14.4 b −13.25ZH8 17.6 a 18.4 a +4.55 19.2 a +9.09 16.5 a −6.25J87-304 18.2 a 18.5 a +1.65 17.1 a −6.04 16.2 a −10.99Mean 17.5 A 16.4 AB −6.29 17.7 A 1.14 15.6 B −10.86
2010 Indica varietiesDTWX 12.2 a 12.5 a +2.46 16.3 a +33.61 14.8 a +21.31ZX232 11.5 a 13.8 a +20.00 11.9 a +3.48 12.5 a +8.70CNSJ 12.0 b 13.3 ab +10.83 14.3 a +19.17 14.4 a +20.00Mean 11.9 A 13.2 A +10.92 14.1 A +18.49 13.9 A +16.81
2010 Japonica varietiesDY5 11.5 a 14.2 a +23.48 14.6 a +26.96 14.2 a +23.48JWR221 16.9 a 17.4 a +2.96 17.0 a +0.59 18.5 a +9.47ZH8 20.3 a 16.9 a −16.75 16.3 b −19.70 16.3 b −19.70Mean 16.2 A 16.2 A 0.00 16.0 A −1.23 16.3 A +0.62
Within a column for each variety, means followed by different letters are significantly different at 0.05 probability level according to least significant difference (LSD) test.The abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, DongTingWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 andJing87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night, high day, high night and ambient temperatures, respectively.
Table 8Effects of different temperature treatments on harvest index (%) of the tested genotypes in field experiments during 2009 and 2010.
Cultivar AT HDT Diff (%) HNT Diff (%) H(D + N)T Diff (%)
2009 Indica varietiesXWX1 48.5 a 47.2 a −2.68 44.2 a −8.87 36.9 b −23.92SKC 50.6 a 47.6 a −5.93 48.1 a −4.94 51.3 a +1.38DTWX 42.7 a 40.8 a −4.45 43.9 a +2.81 40.9 a −4.22ZX232 47.0 a 45.0 a −4.26 43.6 a −7.23 39.3 b −16.38CNSJ 43.9 a 43.6 a −0.68 41.4 a −5.69 29.9 b −31.89Mean 46.6 A 44.8 A −3.86 44.2 AB −5.15 39.6 B −15.02
2009 Japonica varietiesDY5 40.6 a 42.3 a +4.19 35.6 a −12.32 35.2 a −13.30JWR221 41.2 a 47.5 a +15.29 38.8 b −5.83 39.7 a −3.64ZH8 46.5 a 45.1 a −3.01 42.1 b −9.46 37.8 c −18.71J87-304 42.6 a 38.8 ab −8.92 29.8 b −30.05 26.5 b −37.79Mean 42.7 A 43.4 A +1.64 36.6 B −14.29 34.5 B −19.20
2010 Indica varietiesDTWX 30.9 a 31.4 a +1.62 29.3 a −5.18 28.7 a −7.12ZX232 41.8 a 38.8 a −7.18 33.5 ab −19.86 25.8 b −38.28CNSJ 24.1 a 24.7 a +2.49 23.2 a −3.73 25.7 a +6.64Mean 32.3 A 31.6 A −2.17 28.6 AB −11.46 26.7 B −17.34
2010 Japonica varietiesDY5 39.5 a 35.3 a −10.63 25.6 b −35.19 23.8 b −39.75JWR221 35.6 a 37.6 a +5.62 28.4 b −20.22 20.4 c −42.70ZH8 36.1 a 36.0 a −0.28 22.8 b −36.84 19.9 b −44.88Mean 37.1 A 36.3 A −2.16 25.6 B −31.00 21.4 C −42.32
W tly diT ongTinJ , high
rctiT(rd2t
ithin a column for each variety, means followed by different letters are significanhe abbreviations in first column stand for varieties XiangWanXian1, SanKeCun, Ding87-304, respectively. H(D + N)T, HDT, HNT and AT represent high day plus night
elatively more sensitivity to temperature increment than indicaultivars. Such a reduction in yield with an increase in tempera-ure has been already reported in various investigations especiallyn response to nighttime temperature increment (Mohammed andarpley, 2009a,b; Peng et al., 2004; Prasad et al., 2006). Peng et al.2004) reported a decrease of 15% in grain yield for each 1 ◦C
ise in minimum temperature. A comparison of the two yearsata revealed significant yearwise variation as the yield during009 was markedly higher than 2010. Several reasons can explainhis variation. Firstly the mean temperatures especially duringfferent at 0.05 probability level according to least significant difference (LSD) test.gWanXian, ZhenXian232, ChengNongShuiJing DangYu5, JWR221, ZhongHua8 and
day, high night and ambient temperatures, respectively.
nighttime were higher in 2010 than 2009 (Lanning et al., 2011),which might be one of the major causes leading to such variation.Another reason could be that differences of other climatic factorslike radiation, humidity, etc. during these two years. Our other stud-ies (in an experimental area not far from the location where thesetrials were conducted) also revealed that during 2010 the yield of
both early and late season rice varieties was different from 2008and 2009 (Wu et al., 2013). While making an attempt to identify thereasons for such yield reduction it was found that the radiation dur-ing this particular year was markedly lower than the earlier years
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uring the rice growth period. That study also attributed thebserved yield reduction partially to decrease in the incident radi-tion.
Some genotypes showed variation in the number of paniclesith a rise in the temperature especially in indica ecotype. Similar
esults have been reported in an earlier investigation by Baker et al.1992) who found an increase in the number of panicles with anncrease in minimum (nighttime) temperature. Besides, some of theultivars also showed an increase in the number of panicles whenrown under ambient treatment. As the trend observed for thisrait was not consistent during both years and across the genotypesTable 2), such results could not be used to derive any conclusionbout the effect of high temperature on the number of panicles. Noverall significant effect of different temperature increments wasbserved on the number of spikelets per panicle (Table 3). Although
negative linear relationship between spikelets m−2 and daily min-mum temperature has been reported by Peng et al. (2004), theylso did not find any relationship between spikelets per panicle andaily maximum or minimum temperatures. Conversely, the grainumber in wheat are shown to be sensitive to heat stress, as theumber of grains per ear at maturity declined with increasing tem-erature (Ferris et al., 1998). Among the tested cultivars, the indicaenotypes produced greater number of grains per panicle than theaponica type.
The reduction in total number of spikelets per m2 of bothcotypes during 2009 (for all three elevated temperatures) andaponica ecotype during 2010 (for HNT and H(D + N)T treatments)an be partially attributed to the number of panicles for a particularreatment combination. The reduced number of total spikelets per
2 during 2010 compared with 2009 can be explained in terms ofhe reduced solar radiation as discussed above. Moreover, in thetudy of Peng et al. (2004), they also found a significant reductionn the total number of rice spikelets with a decrease in daily solaradiation.
Among the yield components, the most pronounced effect ofemperature increase was found on the fertile spikelets percentage.s was expected, different temperature treatments significantlyeduced the number of fertile spikelets. A similar reduction inhe percent spikelets fertility in response to different tempera-ure increments has been reported earlier in several othere studiesJagadish et al., 2007; Matsui et al., 1997a,b; Prasad et al., 2006).mong different temperature treatments, H(D + N)T treatment was
ound to be the most detrimental one for rice in terms of reducinghe fertility percentage of spikelets, while different trends amongarious genotypes were observed in case of HDT or HNT treatments.he response of the varieties to different temperature incrementsn terms of spikelet fertility also varied according to the geno-ypes. Existence of such variation in different genotypes has alsoeen already reported in various investigations such as Prasad et al.2006). These findings regarding spikelet fertility imply that tem-erature plays a vital role in determining the ratio of fertile andterile spikelets.
Different elevated temperatures also tended to reduce therain weight. During 2009, among all treatment combinations, therain weight of only indica ecotype was significantly decreasedy H(D + N)T compared with AT and HNT. The next year resulted
n more pronounced result as in both ecotypes H(D + N)T treat-ent resulted in significanlt reduced grain weight when comparedith AT (Table 6). In accordance to our findings, a reduction in
he grain weight of the rice found in Japan has been attributedo an increase in the temperature especially during the ripeningeriod (Morita, 2008). Similarly, a reduction in grain weight has
lso been found in wheat when grown under high mean tempera-ure (Ferris et al., 1998). One possible reason for the reduced graineight under high temperature may be the fact that high tem-erature leads to loss of sink activity due to earlier senescence ofrch 157 (2014) 98–110 109
panicle as has been reported by Kim et al. (2011). Among differ-ent varieties the two japonica type (DTWX and ZX232) with largegrains produced significantly heavier grains under all temperaturetreatments.
Aboveground biomass is mainly determined by photosynthesisand respiratory losses and both these traits are sensitive to tem-perature (Yoshida et al., 1981). Both increase and decrease of ricebiomass under high temperatures has been reported in earlier lit-erature. A reduction in biomass was observed under H(D + N)T andHDT treatments (but not in case of HNT) compared with AT dur-ing 2009. In linearity with these findings, a reduction of biomassfor rice has also been reported by Peng et al. (2004) in responseto an increase in minimum temperature. They found a decrease of10% in total above ground biomass for each 1 ◦C rise in daily min-imum temperature. Our findings regarding the effect of maximumtemperature on biomass are in contrast with theirs, as they did notobserve any relationship between maximum temperature and totalaboveground biomass. The no effect of different high temperaturesduring 2010 is consistent with the results of Prasad et al. (2006) whodid not find any significant relation between temperature incre-ment and vegetative biomass of various rice genotypes. Significantnegative relationship of harvest index with minimum tempera-ture has been documented by Peng et al. (2004). The decrease inharvest index at elevated temperatures was mainly due to lowergrain yield caused by decreased spikelet fertility. Surprisingly, HDTincreased the harvest index percentage compared to H(D + N)T andHNT. The HDT associated increase in harvest index can be attributedto the decrease in biomass of most cultivars grown under this treat-ment. Similarly, the HNT related decrease in HI can be ascribed tothe relatively greater biomass and reduced grain yield than HDT.Prasad et al. (2006) also found a similar decrease in the harvestindex of different rice genotypes when grown under high tem-perature. Like grain yield, the aboveground biomass and HI of thejaponica ecotype were more sensitive to elevated night and dieltemperatures.
5. Conclusion
Significant efforts are required to enable rice plant to copewith the menace of high temperature stress. In our trial, H(D + N)Ttreatment showed more deleterious effects than the HDT andHNT due to relatively higher accumulated temperature. Underour experimental conditions, an approximately 2 ◦C increase inH(D + N)T led to 25.1% reduction in grain yield; which was sig-nificantly higher than 18.0% and 5.1% caused by HNT and HDT,respectively, compared with ambient. Although there was enoughtrait to trait variation among the genotypes, HNT seemed to bemore devastating than HDT in terms of grain yield in this study.Indica ecotype was relatively more tolerant to high tempera-ture than japonica. The ecotype and cultivar specific responsesdemonstrate that there are marked ecotypic and genotypic vari-ations among the tested genotypes which can be exploited inthe future breeding programs to develop heat tolerant vari-eties.
Acknowledgment
We thank the funding provided by the Major InternationalJoint Research Project (No. 31361140368) by the National Nat-ural Science Foundation of China, the Key Technology Program
Fund for Agro-scientific Research in the Public Interest of China(No. 201103003). Thanks are also extended to the Higher Edu-cation Commission of Pakistan for sponsoring PhD of the firstauthor.
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