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Ecological Engineering 58 (2013) 52– 56

Contents lists available at ScienceDirect

Ecological Engineering

j ourna l ho me pa g e: www.elsev ier .com/ locate /eco leng

hort communication

iological soil crusts decrease soil temperature in summer andncrease soil temperature in winter in semiarid environment

o Xiaoa,b,∗, Huifang Wangb, Jun Fanb, Thomas Fischerc, Maik Vested

Beijing Research & Development Center for Grass and Environment, Beijing Academy of Agriculture and Forestry Sciences, Beijing 100097, PR ChinaState Key Laboratory of Soil Erosion and Dryland Farming on the Loess Plateau, Institute of Soil and Water Conservation, Chinese Academy of Sciences,angling, Shaanxi 712100, PR ChinaBrandenburg University of Technology at Cottbus, Faculty of Environmental Sciences and Process Engineering, Central Analytical Laboratory,onrad-Wachsmann-Allee 6, 03046 Cottbus, GermanyCEBra-Centre for Energy Technology Brandenburg e.V., Friedlieb-Runge-Straße 3, 03046 Cottbus, Germany

r t i c l e i n f o

rticle history:eceived 21 November 2012eceived in revised form 9 April 2013ccepted 8 June 2013vailable online 6 July 2013

a b s t r a c t

In hot and wet conditions in summer, the biological soil crusts (BSCs) decreased soil temperature by upto 11.8 ◦C, 7.5 ◦C, 5.4 ◦C, and 3.2 ◦C at surface, 5 cm, 15 cm, and 30 cm, respectively; while in cold and dryconditions in winter the BSCs increased soil temperature by up to 1.2 ◦C, 1.2 ◦C, and 1.1 ◦C at 5 cm, 15 cm,and 30 cm, respectively. The daily mean soil temperatures of the BSCs in a whole year were averagelyincreased by 0.57 ± 0.04 ◦C, 0.31 ± 0.04 ◦C, and 0.22 ± 0.04 ◦C at 5 cm, 15 cm, and 30 cm, respectively. The

eywords:oss crustydrological functioncological restorationesertification controloess Plateau of China

effects of the BSCs on soil temperature were positively correlated with air temperature and soil moisture,and decreased with soil depth from surface to deep soil. We concluded that BSCs relieved the extremehot and cold soil micro-environments in desert ecosystem to some extent. Therefore their effects on soiltemperature are positive for improving water and nutrient availability and biological community struc-ture, thus decreasing susceptibility to desertification. These results would be helpful for understandingthe ecological and hydrological functions of BSCs in semiarid environment.

woadseoh(oaa

Biological soil crusts (BSCs), which are defined as the complexosaic of soil, green algae, lichen, moss, micro-fungi, cyanobacte-

ia, and other bacteria by Belnap and Lange (2003), are extensivelyeveloped and are widely distributed in hot, cool, and cold aridnd semiarid regions (Belnap and Lange, 2003). The ecologicalunctions of BSCs and their potential effects on desertification arettracting more attention (Xiao et al., 2007a,b, 2011), and recently,hey have been recognized as a major influence on desert terres-rial ecosystems (e.g., Belnap, 2006; Bowker et al., 2011; Maestret al., 2011). However, their effects on soil temperature, whichlay very important role in many ecological processes in soiluch as water movements (e.g., evaporation and condensation),hemical reactions and biological interactions (Belnap, 1995), are

eldom reported. The only results came from the following stud-es: Belnap (1995) found that cyanobacteria-lichen crusts increasedoil surface temperature by up to 10 ◦C in summer and 14 ◦C in

∗ Corresponding author at: Beijing Research & Development Center for Grassnd Environment, Beijing Academy of Agriculture and Forestry Sciences, No. 9,iddle of Shuguang Garden Road, Haidian District, Beijing 100097, PR China.

el.: +86 10 51503436; fax: +86 10 51503297.E-mail addresses: xiaoboxb@gmail.com, xiaoboxb@126.com (B. Xiao).

tBsgwtoe75

925-8574/$ – see front matter © 2013 Elsevier B.V. All rights reserved.ttp://dx.doi.org/10.1016/j.ecoleng.2013.06.009

© 2013 Elsevier B.V. All rights reserved.

inter; George et al. (2003) indicated that daily soil temperaturef cyanobacteria crusts was consistently higher than lichen crustsnd bare soil (<1 ◦C); Xiao et al. (2010) reported that in wet con-itions moss crusts slightly decreased soil temperature 0.4 ◦C aturface, 0.9–1.5 ◦C at 5 cm, 0.8–1.1 ◦C at 10 cm, and almost no influ-nce below 10 cm. Above results were not consistent with eachther and possibly caused by the differences of BSCs types, whichad significant different functions in soil heat transport processXiao et al., 2010). Also, the contradictive results mainly dependedn manual observations in short time by field geothermometers,nd thus to some extent the conclusions were accidental, unstable,nd unsolid.

To provide more insight into this issue, we conducted a long-erm monitoring experiment for soil temperature with and withoutSCs on semiarid environment on the Loess Plateau of China. Thetudy was conducted in a representative watershed named Liudao-ou (38◦46′–38◦51′ N latitude and 110◦21′–110◦23′ E longitude),hich has 409 mm average annual precipitation (about 80% of

hem occur in summer) and 1337 mm average annual water evap-

ration (Cha and Tang, 2000). Natural moss-dominated BSCs arextensively developed on the watershed with coverage reaching0–80% (Xiao et al., 2010). A southeast facing slope with less than% slope grade and well-developed BSCs was selected as the study

B. Xiao et al. / Ecological Engineering 58 (2013) 52– 56 53

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ig. 1. Change of the gaps of daily mean soil temperature between the BSCs and thef the control.

ite (38◦47′43′′ N, 110◦21′29′′ E) for this experiment. The BSCs areainly constituted of mosses Bryum arcticum (R. Brown) B.S.G. andidymodon vinealis (Brid.) Zander, and generally are 15–20 mm in

hickness, 10–15 mg cm−2 in biomass, and 170–200 plants cm−2 inoss density. The soil in the study site was Ust-Sandiic Entisols in

AO soil taxonomy, and its texture was sandy loam with 81% sand,4% silt, and 5% clay.

Two treatments including the BSCs and the control (BSCs wereemoved) were set in the experiment, and each treatment had twoeplications. According to the experimental design, four locations

n the study site were randomly selected for the BSCs and the con-rol treatments. For the BSCs treatment, all litters were carefullyleared off but the BSCs were perfectly kept; while for the con-rol, the BSCs layer and about 20 mm upper soil were completely

s2ct

ol at different soil depth. TBSCs = soil temperature of the BSCs; TCK = soil temperature

emoved by hand. The measurement included the following threeections. (1) The soil temperature at surface (sensors were levellyalf embedded in soil), 5 cm, 15 cm, and 30 cm were measured byemperature probes (CS109, Campbell Scientific, Inc.), which wasevelly inserted into soil at specified depth in soil profiles. (2) Theoil moisture at 5 cm, 15 cm, and 30 cm were measured by waterontent reflectometers (CS616, Campbell Scientific, Inc.) installedn the same way as the temperature probes. (3) The air tempera-ure at 200 cm above ground was also measured by a CS 109 probenside a radiation shield. In sum, there were four soil temperature

ensors and three soil water sensors at each location; and totally8 sensors (four locations for the two treatments with two repli-ations) with one more air temperature sensor were installed inhe experiment. All the sensors were connected with a data logger

54 B. Xiao et al. / Ecological Engineering 58 (2013) 52– 56

F ent soT ture o

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ig. 2. Change of 10 min mean soil temperature of the BSCs and the control at differCK = soil temperature of the control; �BSCs = soil moisture of the BSCs; �CK = soil mois

CR 1000, Campbell Scientific, Inc.). The parameters were measuredutomatically every 10 s and the data were stored in 10 min tablesnd daily tables, respectively. The measurement performed morehan one year from August 2, 2011 to September 14, 2012. The totalainfall during this period was 578.1 mm, including 164.3 mm in011 and 413.8 mm in 2012. The most rainfall occurred from Juneo September, accounting for 88% of the total rainfall. Meanwhile,he heavy rainfall event exceeding 30 mm occurred five times andccounted for 37% of the total rainfall.

The change of daily mean soil temperature between the BSCs

nd the control at different soil depth was presented in Fig.1. In this figure, the change of soil temperature was closelyorrelated with or driven by air temperature because they hadery similar wave shapes. However, it is hard to identify the

asit

il depth in hot and wet conditions in summer. TBSCs = soil temperature of the BSCs;f the control. The soil moisture at surface was come from the soil moisture at 5 cm.

ifferences between the BSCs and the control because the rela-ive small gaps between them were almost covered by the intenseuctuation ranged from −20 ◦C to 30 ◦C. Therefore, we presentedhe change of the gaps between the BSCs and the control in Fig. 1.rom this figure we clearly found that the effects of the BSCs onoil temperature in a whole year can be divided into two oppo-ite periods: the BSCs increased daily mean soil temperature byp to 2.3 ◦C from middle September to next May (about 250 days),hich corresponded to non-rainy season in the study region; while

he BSCs decreased daily mean soil temperature by up to 3.3 ◦C in

nother period (about 110 days), which corresponded to rainy sea-on in summer. However, as a whole we concluded that the BSCsncreased soil temperature because the daily mean soil tempera-ures of the BSCs in the first period (about 250 days) were averagely

B. Xiao et al. / Ecological Engineering 58 (2013) 52– 56 55

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ig. 3. Change of 10 min mean soil temperature of the BSCs and control at differeCK = soil temperature of the control; �BSCs = soil moisture of the BSCs; �CK = soil moi

ncreased by 0.80 ± 0.03 ◦C, 0.66 ± 0.02 ◦C, and 0.59 ± 0.02 ◦C at cm, 15 cm, and 30 cm, respectively; while in the second periodabout 110 days) they were averagely decreased by 0.73 ± 0.11 ◦C,.68 ± 0.07 ◦C, and 0.65 ± 0.05 ◦C at 5 cm, 15 cm, and 30 cm, respec-ively. The daily mean soil temperatures of the BSCs in a wholeear were averagely increased by 0.57 ± 0.04 ◦C, 0.31 ± 0.04 ◦C,nd 0.22 ± 0.04 ◦C at 5 cm, 15 cm, and 30 cm, respectively, whichccounted for 5.3%, 2.8%, and 2.0% of the daily mean soil tempera-ures of the control.

Besides above daily mean soil temperature, we studied thehange of 10 min mean soil temperature in couple of days in sum-er (Fig. 2 and Fig. S2, in hot and wet conditions) and winter (Fig. 3

nd Fig. S3, in cold and dry conditions), respectively. The resultonfirmed that the BSCs decreased soil temperature in summery up to 11.8 ◦C, 7.5 ◦C, 5.4 ◦C, and 3.2 ◦C at surface, 5 cm, 15 cm,nd 30 cm, respectively; while in winter the BSCs increased soilemperature by up to 1.2 ◦C, 1.2 ◦C, and 1.1 ◦C at 5 cm, 15 cm, and0 cm, respectively. These results were reasonable because the soileat was originally came from solar radiation, and usually trans-

erred from surface to deep soil. The gaps of the soil temperatureetween the BSCs and the control were driven by air temperaturend soil moisture in summer, while they were only driven by airemperature in winter because the soil moisture was very low. In

et2w

l depth in cold and dry conditions in winter. TBSCs = soil temperature of the BSCs;of the control. The soil temperature data at surface were missed.

ther words, the gaps were positively correlated with air tempera-ure and soil moisture, meaning that the BSCs decreased more soilemperature in hot and wet conditions. Additionally, the effects ofhe BSCs on soil temperature decreased with soil depth, indicat-ng that the BSCs had stronger impacts on surface and shallow soilemperature than deep soil.

In conclusion, the presence of the BSCs decreased soil tem-erature in hot and wet conditions in summer and increased soilemperature in cold and dry conditions in winter. This conclusions well consistent with the results from Belnap (1995), Georget al. (2003), and Xiao et al. (2010), who reported similar resultsut with more or less differences in the extent of influences. Theeceasing soil temperature of the BSCs in hot and wet conditionsas possibly caused by the following three mechanisms: (1)SCs prevented the formation of dry layer at soil surface (whichould significantly slow down soil evaporation) and subsequentlyesulted in faster soil water evaporation rate and longer timet constant rate drying stage (Zhang et al., 2008; Xiao et al.,010; Kidron and Tal, 2012; Chamizo et al., 2013); More water

vaporation took more heat out of soil and resulted in low soilemperature; (2) BSCs had higher soil moisture (Almog and Yair,007; Xiao et al., 2007a; Kidron and Vonshak, 2012), and thus soilith more water needed more heat to increase its temperature

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6 B. Xiao et al. / Ecologica

ecause of the high heat capacity of water compared with air andolids (Abu-Hamdeh, 2003; Guan et al., 2009); and (3) the mulchffects of BSCs with rich organic materials (living components andheir residue, especially for moss stems and rhizoids), which acteds a poor conductor of heat to prevent heat flow into soil becausehe heat flow was dominantly directed from surface warmer layerso deep cooler layers in summer (Abu-Hamdeh and Reeder, 2000;an Donk and Tollner, 2000). Correspondingly, the increasing soilemperature of the BSCs in cold and dry conditions was possiblyaused by: (1) the mulch effects of BSCs, which acted as a pooronductor of heat to prevent heat flow out of soil because the heatow was dominantly directed from deep warmer layers to surfaceooler layers in winter (Abu-Hamdeh and Reeder, 2000; van Donknd Tollner, 2000), especially in dry conditions; (2) the dark colorf BSCs in winter (Moss dominated BSCs were generally in blackr gray color in dry conditions and in light green color in wetonditions), which absorbed more solar radiation compared withdjacent uncrusted soils (Belnap, 1995; Xiao et al., 2010). Althoughurther research is necessary to clear the reasons, the positiveffects of BSCs on soil temperature in semiarid environmentere confirmed and quantitatively evaluated in this study. Theecreasing temperature in summer and increasing temperature ininter relieved the extreme hot and cold soil micro-environments

n desert ecosystem to some extent, which is definitely positiveor improving water and nutrient availability and biological com-

unity structure, thus decreasing susceptibility to desertification.hese results would be useful for understanding the ecological andydrological functions of BSCs in semiarid environment, and coulde helpful for the management of BSCs and desertification controln the Loess Plateau of China and similar regions all over the world.

cknowledgments

This study was funded by the National Natural Science Founda-ion of China (No. 41001156), the Beijing Nova Program (2009B25),nd the Open Fund from the State Key Laboratory of Soil Erosionnd Dryland Farming on the Loess Plateau (No. K318009902-1316).e also thank the Shenmu Experimental Station of Soil Erosion and

nvironment for logistical support.

ppendix A. Supplementary data

Supplementary data associated with this article can beound, in the online version, at http://dx.doi.org/10.1016/j.ecoleng.013.06.009.

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neering 58 (2013) 52– 56

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