Grain protein accumulation in relation to grain yield of spring wheat

(Triticum aestivum L.) grown in open-top chambers with different

concentrations of ozone, carbon dioxide and water availability

H. Pleijela,*, L. Mortensen1,b, J. Fuhrerc, K. OjanperaÈd, H. Danielssona

aSwedish Environmental Research Institute, IVL, P.O. Box 47086, SE-402 58, GoÈteborg, SwedenbNational Environmental Research Institute, NERI, Fredriksborgsvej 399, DK-4000, Roskilde, Denmark

cInstitute of Environment and Agriculture, IUL Liebefeld, CH-3003, Bern, SwitzerlanddAgriculture Research Centre of Finland, Institute of Resource Management, MTT, FI-31 600, Jokioinen, Finland

Received 24 March 1998; accepted 28 October 1998

Abstract

The present investigation was undertaken in order to study the in¯uence of ozone, carbon dioxide and water availability on the

relationship between grain protein and grain yield in wheat (Triticum aestivum L.). Results were combined from spring wheat,

®eld grown in 16 different open-top chamber experiments, from four different countries. Protein concentration of the grain

was negatively (linear) associated with grain yield. This relationship was symmetrical for yield reductions and yield

stimulations, despite the fact that the major cause for increases in yield (elevated carbon dioxide concentrations) was different

from that causing crop loss (elevated ozone concentrations). The relationship between off-take (the amount of protein taken

away from the farmland per unit area) of grain protein and grain yield was clear and highly consistent, but not linear. Yield

loss in relation to the reference used (open-top chamber with non-®ltered air) was associated with a larger negative change in

protein off-take than the positive change in protein off-take corresponding to a yield increase of the same size. The water

treatments used in some of the experiments in¯uenced yield and protein content to a very limited extent. It is concluded from

the present study that the change of the grain protein from factors such as ozone and carbon dioxide can be explained largely

by a simple relationship between grain protein and grain yield at a certain level of nitrogen availability to the plants. # 1999

Elsevier Science B.V. All rights reserved.

Keywords: Carbon dioxide; Europe; Grain yield; Ozone; Protein; Water; Wheat

1. Introduction

Present ambient-elevated ozone (O3) concentra-

tions have been shown to reduce the grain yield

(GY) of wheat (Triticum aestivum L.) and other crops

(Fuhrer, 1994), and globally increasing carbon dioxide

(CO2) concentrations tend to stimulate crop yield

Agriculture, Ecosystems and Environment 72 (1999) 265±270

*Corresponding author. Tel.: +46-31-460-080; fax: +46-31-482-

180; e-mail: hakan.pleijel@ivl.se1Present address: FIRST, Bredgade 43, DK-1260 Kùbenhavn,

Denmark.

0167-8809/99/$ ± see front matter # 1999 Elsevier Science B.V. All rights reserved.

P I I : S 0 1 6 7 - 8 8 0 9 ( 9 8 ) 0 0 1 8 5 - 6

(Kimball, 1983). Also quality aspects of yield may be

in¯uenced by the atmospheric change. A negative

relationship between cereal GY and grain protein

concentration (GPC) has been observed (Evans,

1993). This phenomenon has been called `growth

dilution,' and exists also for nutrients other than

nitrogen. If the nitrogen availability is constant,

GPC becomes higher if GY becomes lower because

of some external factor. Plant breeders have been

relatively unsuccessful in combining high, genetically

based performance for the two traits, high GYand high

GPC (Kibite and Evans, 1984; Borghi et al., 1986). In

several studies, GY reductions caused by ozone were

accompanied by an increase in GPC (e.g. Fuhrer et al.,

1992; Pleijel et al., 1991). Elevated CO2 concentra-

tions, on the other hand, led to a growth stimulation

and an increased carbon content in relation to nitrogen

of plant tissues in several experiments (Bowes, 1993;

Mooney and Koch, 1994; Manderscheid et al., 1995).

As a consequence of the lower GPC associated with a

stimulation of GY by elevated CO2 concentrations,

other quality aspects of wheat grain may be affected,

such as poorer dough and decreased loaf volume

(Blumenthal et al., 1996). If growth stimulation is

caused by increased nitrogen availability, the growth

dilution rule does not hold. Addition of nitrogen

stimulates both GY and GPC (BaÈnziger et al., 1994).

A large number of open-top chamber experiments

with ®eld grown spring wheat including GY and GPC

measurements have been undertaken in Europe during

the last decade. The chamber treatments have included

increased or decreased ozone concentrations,

increased CO2 concentrations and manipulations of

plant water availability. These treatments caused yield

stimulations as well as yield reductions (for references

see Table 1). In the present study the results of 16

experiments with similar basic design were combined,

in order to ®nd out if a consistent quantitative relation-

ship between GPC and grain protein off-take (the

amount of protein (kg) taken away at harvest from

Table 1

Experiments, country, year, cultivar used, nitrogen application rate (kg haÿ1), number of replicate chambers per treatment (n), the treatments

used, and reference in those cases where results from the experiments have been published earlier

Experiment Cultivar Nitrogen

application

rate

n Treatments AOT40 of

highest ozone

treatment

Reference

SE87 Drabant 120 7 CF, NF, NF� 2036 Pleijel et al. (1991)

SE88 Drabant 120 5 CF, NF, NF�, NF�� 7813 Pleijel et al. (1991)

SE94 Dragon 120 3 NF, NF�, NF��, NF���, NF�700,

NF��700, NF���700

11 974 Pleijel et al. (1997)

SE95 Dragon 120 5 NF, NF�, NF520, NF520 2500 Pleijel et al. (1998)

SE96 Dragon 120 6 NF, NF700, NFH, NFH700 Unpublished

DK89 Ralle 150 5 CF, NF, NF� 19 053 SkaÈrby et al. (1993)

DK91 Ralle 150 5 CF, NF, NF� 18 511 Mortensen and Engvild (1995)

DK94 Minaret 150 3 NF, NF520, NF700 ± Unpublished

DK95 Minaret 150 3 NF, NF520, NF700 ± Unpublished

CH86 Albis 75 4 CF, NF, NF� 22 850 Fuhrer et al. (1989, 1990)

CH87 Albis 90 4 CF, NF, NF�, NF�� 33 058 Fuhrer et al. (1989, 1990)

CH88 Albis 112 4 CF, NF, NF�, NF�� 30 789 Fuhrer et al. (1989, 1990)

CH89 Albis 25 6 CF, NF, NF�, NF�� 22 449 Fuhrer et al. (1992)

CH90 Albis 30 6 CF, NF, NF�, NF�� 22 165 Fuhrer et al. (1992)

FI92 Satu 110 5 CF, NF, NF� 13 744 OjanperaÈ et al. (1994);

Pleijel et al. (1997)

FI93 Satu 115 5 CF, NF, NF� 4609 OjanperaÈ et al. (1994);

Pleijel et al. (1997)

SE, Sweden; DK, Denmark; CH, Switzerland; FI, Finland.

CF, charcoal-filtered air; NF, non-filtered air; NF�, NF��, NF���, non-filtered air with increased concentrations of ozone; 520,

approximately 520 ppm CO2; 700, approximately 700 ppm CO2; H, doubled water availability. For those experiments where elevated ozone

concentrations were used the AOT40 (Accumulated exposure Over the concentration Threshold 40 ppb) is given in ppb hours (Fuhrer, 1994).

266 H. Pleijel et al. / Agriculture, Ecosystems and Environment 72 (1999) 265±270

the farmland per unit area) with GY over the range of

environmental conditions used in the open-top cham-

ber experiments with spring wheat.

2. Materials and methods

All experiments were performed with open-top

chambers (OTCs) and ®eld grown spring wheat. Sev-

eral of the experiments with only elevated ozone

treatments formed part of the European Open-top

Chamber Programme. All experiments with elevated

CO2 concentrations were part of the EU funded

ESPACE-wheat programme. Table 1 shows that most

of the experiments have been described earlier in the

literature. Table 1 also includes information concern-

ing the country and year of the different experiments

as well as on cultivars, nitrogen applications, number

of replicates and the treatments used. Air ®ltration

(CF) was used in most of the ozone experiments in

order to reduce the ozone concentration of the air.

Ozone was generated using pure oxygen in all

experiments with elevated ozone treatments with

the exception of SE87 and SE88 where the ambient

air was used. The crude protein concentration of the

grain was determined using the Kjeldahl method

for nitrogen and multiplying the result by 6.25. The

only exceptions to this were the experiments DK94

and DK95 for which protein was determined using

X-ray emission (PIXE) (Johansson and Campbell,

1988).

The values for GY (dry weight per unit area), GPC

(%) and the off-take of grain protein per unit area (dry

weight per unit area) from the chamber treatments of

the different experiments were normalised using the

non-®ltered chamber treatment (NF) of each experi-

ment as the reference. The three parameters are

expressed as a percentage of the value for the NF

treatment of the particular experiment and parameter.

Since different application rates of nitrogen were used

in the different experiments (Table 1), as well as the

interannual variation in crop performance, these are

also normalised by using the NF treatment of each of

the 16 experiments as the basis for comparison. The

NF treatments were not included in Figs. 1 and 2. For

the relationships obtained, linear and non-linear

regressions were performed and the distribution of

residuals was considered (Statgraphics 5).

3. Results

A clear negative relationship between GPC and GY

was obtained (Fig. 1). High ozone treatments gener-

Fig. 1. Grain protein concentration (GPC) plotted against the unit

area grain yield (GY). Both parameters are expressed as the

percentage of the value for the non-filtered open-top chamber

treatment of each of the 16 experiments included in the study.

Fig. 2. Unit area off-take of grain protein plotted against the unit

area grain yield (GY). Both parameters are expressed as the

percentage of the value for the non-filtered open-top chamber

treatment of each of the 16 experiments included in the study.

H. Pleijel et al. / Agriculture, Ecosystems and Environment 72 (1999) 265±270 267

ally had lower GY and higher GPC, and high carbon

dioxide treatments generally had higher GY and lower

GPC; compared with the plants grown in the non-

®ltered air chambers. The elevated water treatments

used also had a small positive in¯uence on GY and a

small negative effect on the protein concentration.

Fig. 1 shows that the signi®cant linear regression

line nearly includes the 100 : 100 point, although the

NF points per se were excluded from the calculation of

the regression. Thus, the effect on the protein con-

centration associated with a change in yield compared

with NF, is symmetrical and linear for positive and

negative effects on GY caused by the treatments used

in the experiments of this study. This symmetry exists

regardless of the fact that the major cause of decreased

yield (elevated O3 concentrations) in the data set was

different from the major cause of increased yield

(elevated CO2 concentrations). Non-linear regression

was tested, but resulted in a line which was very close

to linear and the non-linear model did not have a

higher correlation than the linear.

When grain protein was expressed on off-take per

unit area basis, protein was positively associated with

yield (Fig. 2). In this case the data were ®tted with a

non-linear regression model. Unlike Fig. 1, the dis-

tribution of residuals of a linear model revealed that

the relationship was not linear in this case, and the

correlation was improved by using a non-linear model

(from r2 � 0.91 to r2 � 0.94). In Fig. 2 the regression

line comes very close to the 100 : 100 point if a non-

linear model is used, but not with a linear regression

model. In addition, extrapolation of the non-linear

regression nearly included the 0 : 0 point, which

was not the case for the linear model.

4. Discussion

Over the range of OTC treatments which were used

in the present study there was a consistent and linear

negative relationship between the GPC and GY. The

character of the in¯uencing factor (ozone, carbon

dioxide or water availability) seems to be of limited

importance. An important question is how such a

pattern can be explained.

An analysis of GY and GPC data from eleven

genotypes of wheat was performed by Kibite and

Evans (1984). They found that a strong inverse rela-

tionship between GY and GPC existed, as was also

found in the present study. Furthermore, these authors

concluded that this relationship was not primarily

driven by genetic factors, but by environmental fac-

tors. Dilution of protein by non-nitrogen compounds

in the grain seemed to be the primary cause for the

negative association between the two traits GY and

GPC. This view is supported by experiments using

modi®cations of the sink/source relationships of

wheat. Borghi et al. (1986), for instance, found that

a reduction of the sink led to a signi®cantly higher

GPC of the remaining sink. In addition, they suggested

that GPC is very strongly source controlled. The sink

will accept virtually any amount of N which is trans-

locatable from the rest of the plant during grain ®lling.

This view is supported by the very ef®cient N-redis-

tribution during grain ®lling found in wheat in other

studies. For example, Osaki et al. (1991) found that the

N-redistribution rate (de®ned as: (amount of N of

leaves at maximum shoot growth ÿ amount of N of

leaves and stems at harvest)/(amount of N of leaves at

maximum shoot growth)) of wheat was as high as

81.1%. Most of the nitrogen present in the plant will

thus be distributed to the grain during grain ®lling. If

the conditions for grain ®lling are very favourable, the

grain protein concentration will become lower,

because large amounts of carbohydrates are passed

into the grain. The duration of grain ®lling has been

shown to be of crucial importance for the ®nal yield

and the duration of grain ®lling is strongly related to

¯ag leaf duration (Evans, 1993). Ozone has been

shown to shorten the ¯ag leaf duration in several of

the experiments used in the present study (Grandjean

and Fuhrer, 1989; OjanperaÈ et al., 1992; Pleijel et al.,

1998). A longer leaf duration caused by elevated CO2

treatments was observed in those experiments where

large positive effects on the GY were obtained (SE94,

DK94, DK95, data not shown).

It is, however, evident from Fig. 2 that, although an

increase in the protein percentage of the grain is

associated with the ozone-induced reduction of GY,

the unit area production of grain protein is reduced by

ozone, but the opposite is the case for CO2. Conse-

quently, when the conditions for carbon assimilation

became more favourable than in the NF treatment (at a

certain application rate of nitrogen), both the unit area

off-take of grain protein and grain carbohydrates

increased, with both these parameters decreasing

268 H. Pleijel et al. / Agriculture, Ecosystems and Environment 72 (1999) 265±270

when carbon assimilation was impaired by ozone.

Thus, there does not seem to exist a simple competi-

tion for organic carbon between protein and carbohy-

drate accumulation in the grain under the

circumstances of the experiments included in the

present study. The likely reason is that in favourable

growth conditions, which permit a large uptake of

nitrogen from the amount of nitrogen available, this

nitrogen is ®rst invested in a large capacity for carbon

assimilation. Later, during grain ®lling, this nitrogen is

redistributed to grain. This is consistent with the

results of BaÈnziger et al. (1994), who studied the

possible competition between grain protein and grain

carbohydrates in fertilisation experiments. They found

that a direct competition between protein and carbo-

hydrates for organic carbon was not signi®cant.

In the case of grain protein off-take, the relationship

with grain yield was not linear. The loss of grain

protein production per unit area caused by a certain

yield loss by ozone, is larger than the gain of protein

per unit area linked to a yield increase by elevated CO2

of the same size. This is a consequence of the non-

linearity of the relationship. The non-linearity can be

viewed as a saturation effect which exists because at a

realistic level of nitrogen application, the off-take of

protein cannot continue to increase endlessly when the

yield is increased. The nitrogen will become a more

and more scarce resource for the plant as the yield

increases.

To conclude, changes in grain protein from factors

such as ozone and CO2 can largely be explained by a

simple relationship between grain protein and GY at a

certain level of nitrogen availability to the plants. The

crop loss caused by present ambient concentrations of

ozone may to some extent be compensated for by

higher GPC, although the off-take of protein per unit

area is likely to decrease along with the crop loss

because of ozone. Farmers are paid for the protein

concentration of the grain. The effect of elevated CO2

on GPC may lead to an increased application rate of

fertilisers.

Acknowledgements

The Swedish and Danish experiments with elevated

CO2 concentrations formed part of the EU ESPACE-

wheat research programme. The author thanks the

anonymous referees` for their improvements on the

earlier version of this paper.

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