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Journal of Resources and Ecology >

2023 , Vol. 14 >Issue 1: 167 - 176

DOI: https://doi.org/10.5814/j.issn.1674-764x.2023.01.016

Ecosystem Assessment

Impacts of CO2 Enrichment on Water Use Efficiency in Terrestrial Ecosystems: A Meta-analysis of Experimental Manipulations

  • ZOU Jingru , * ,
  • LI Shuai
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  • College of Geography and Environmental Science, Henan University, Kaifeng, Henan 475004, China
*ZOU Jingru, E-mail:

Received date: 2021-05-20

  Accepted date: 2022-04-27

  Online published: 2023-01-31

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Abstract

Elevated CO2 (eCO2) has important impacts on plants, especially on water use efficiency (WUE). A meta-analysis was performed to determine the responses of WUE to enriched CO2. We summarized 242 studies on WUE research under ambient and enriched CO2 conditions that were published between 1989 and 2019. Our results showed that WUE had positive responses to elevated CO2 with an increase of about 46% and high heterogeneity. Elevated CO2 increased leaf, grain, biomass and whole plant WUE by 76%, 9%, 30% and 37%, respectively. The effect size on leaf WUE was higher than the other three WUE types, and the effect size on whole plant WUE was higher than grain WUE (P<0.05). In another respect, the response of WUE in forests was higher than in cropland (P<0.05). Regarding different experimental methods, WUE had a stronger response to elevated CO2 by the method of climate-controlled chamber than by the methods of OTC (Open Top Chamber) or greenhouses (P<0.05). However, the effect size obtained by the method of greenhouse was higher than that obtained by the methods of either OTC or climate chamber for whole plant WUE (P<0.05). Furthermore, our results found WUE had a positive linear relationship with the magnitude of CO2 enrichment (P<0.05). Meanwhile, the effect size of elevated CO2 on grain WUE had a positive linear relationship with the duration of CO2 enrichment. This study found that the impacts of CO2 enrichment on WUE are unique and specific for different WUE types and the various experimental conditions.

Key words： elevated CO2; water use efficiency; forest; cropland; Open Top Chamber

Cite this article

ZOU Jingru , LI Shuai . Impacts of CO2 Enrichment on Water Use Efficiency in Terrestrial Ecosystems: A Meta-analysis of Experimental Manipulations[J]. Journal of Resources and Ecology, 2023 , 14(1) : 167 -176 . DOI: 10.5814/j.issn.1674-764x.2023.01.016

1 Introduction

WUE (water use efficiency) has a well-established relationship with vegetation production, and the changes in WUE have effects on terrestrial ecosystem carbon cycling. Moreover, the changes in water conditions caused by WUE could result in effects on vegetation production and carbon cycling. The global atmospheric CO2 concentration is predicted to double (to about 700 ppm) by the year 2100 (IPCC, 2007). Elevated CO2 might have significant effects on plant WUE, and a change in WUE might lead to significant plant responses to the enriched CO2 (Rogers et al., 1994).
Many studies have shown that elevated CO2 has positive effects on WUE (Robredo et al., 2007; Tuba and Lichtenthaler, 2007; Bender and Weigel, 2011; Dalling et al., 2016). The research by Dalling et al. (2016) indicated that WUE of four forest species increases with elevated CO2. Some other studies also found that higher CO2 concentrations improve WUE in the cropland (Tuba and Lichtenthaler, 2007; Bender and Weigel, 2011; Dahal et al., 2014). Elevated CO2 generally enhances WUE by increasing plant growth and reducing stomatal conductance or water use (Leakey, 2009; Dahal et al., 2014), and it can mitigate the stress-induced decrease of WUE by climate change and other conditions, such as cold temperature, drought and others (Leakey, 2009). Fur thermore, Perry et al. (2013) reported that WUE under stress conditions is lower than under normal conditions in response to elevated CO2 in some species. Centritto et al. (1999) demonstrated that elevated CO2 had a stronger impact on WUE in well-watered conditions and did not improve stress tolerance.
Different types of WUE with diverse scales (leaf, yield, canopy, whole plant WUE and others) are reported in various studies, and this variation could increase the inconsistency of values among the studies (Blum, 2009). Li et al. (2013) reported that elevated CO2 increased WUEinstantaneous and WUEintrisinc by 64% and 56% under drought, compared with the improvements of WUEyield and WUEbiomass by 5.9% and 13.4%, respectively. Conley et al. (2001) indicated that grain WUE had positive responses to enriched CO2 by 9% and 19% in wet and drought conditions, while the corresponding data were 16% and 17% for whole plant WUE. Generally, WUE in individual leaves is different from WUE measured on large scales (Morison, 1985). However, similar patterns of changes between instantaneous and whole plant WUE were found under CO2 enrichment by Norby and O’Neill (1989).
WUE in response to enriched CO2 has a relationship with ecosystem types. The plants in different ecosystems have different structural characteristics and growth habits, which result in diverse growth patterns in relation to CO2 enrichment (Lee and Jarvis, 1995; Mbava et al., 2020). The effect on WUE from CO2 enrichment was shown to be vegetation dependent (Norby and O’Neill, 1989; Guehl et al., 1994). Furthermore, different CO2 enrichment methods are used to study the impact of enriched CO2 on WUE, and this variability also increases the lack of uniformity among studies. For example, Long et al. (2006) and Ainsworth et al. (2008) found that seed yields had stronger positive responses to elevated CO2 by the method of Free-air CO2 enrichment (FACE), compared with the enclosure methods.
The results of previous studies on WUE under CO2 enrichment have high variations, and so it is difficult to make general conclusions about the response to enriched CO2. Several studies on the responses of WUE to elevated CO2 have used meta-analysis methods (Wand et al., 1999; Jiang et al., 2020). Wand et al. (1999) indicated that leaf WUE increased in response of elevated CO2, while Jiang et al. (2020) found that elevated CO2 had a positive impact on leaf WUE with either high phosphorus or low phosphorus supply. However, the mechanisms of WUE responses to elevated CO2 are not well known. Considering the lack of uniform factors among studies, the results at the different scales or under other specific conditions should be carefully evaluated (Hatfield and Dold, 2019). In this study, we used the meta-analysis method to obtain quantitative statistical means among studies and discuss how WUE responds to CO2 enrichment. We collected data from studies focusing on the effects of CO2 on WUE, and analyzed the data with a meta-analysis method to obtain quantitative results about the responses in terrestrial ecosystems. Several questions should be resolved in our research: 1) How does enriched CO2 impact WUE? 2) How does enriched CO2 impact WUE in different research scales, ecosystem types or CO2 enrichment methods? 3) How is the effect size of CO2 on WUE related to the experimental CO2 concentration or enrichment time?

2 Materials and methods

2.1 Data sources

Meta-analysis was a quantitative synthesis of the published literature which attempted to determine the patterns and mechanisms of the effects of enriched CO2 on plant WUE in terrestrial ecosystems, and 242 observations from 29 published papers were included in our analysis (Table 1).
Table 1 Studies included in the meta-analysis
Ecosystem Location CO2 enrichment
method		 Reference
Cropland Australia Climate chamber Shabbir et al., 2019
Cropland Australia FACE O’Leary et al., 2015
Cropland Brazil FACE Ghini et al., 2015
Cropland Canada Climate chamber Dahal et al., 2014
Cropland China Climate chamber Li et al., 2003
Cropland China Climate chamber Li et al., 2013
Cropland China Climate chamber Liu et al., 2020
Cropland China Climate chamber Pan et al., 2020
Cropland China OTC Li et al., 2019
Cropland China OTC Qiao et al., 2010
Cropland Denmark Climate chamber Kaminski et al., 2014
Cropland Hungary Greenhouse Varga et al., 2017
Cropland Portugal OTC Moutinho-Pereira et al., 2009
Cropland UK Greenhouse Centritto et al., 1999
Cropland USA Climate chamber Ephrath et al., 2011
Cropland USA Climate chamber Hui et al., 2001
Cropland USA FACE Conley et al., 2001
Cropland USA FACE Ruiz-Vera et al., 2013
Forest Brazil Climate chamber Oliveira and Marenco, 2019
Forest France Greenhouse Picon et al., 1996
Forest India OTC Hebbar et al., 2020
Forest Malaysia Climate chamber Ibrahim et al., 2010
Forest Panama Greenhouse Dalling et al., 2016
Forest Switzerland OTC Bucher-Wallin et al., 2000
Forest USA Climate chamber Norby and O’Neill, 1989
Forest USA OTC Leavitt et al., 2003
Grassland Czech Republic Greenhouse Holub et al., 2019
Grassland The Netherlands Climate chamber Schapendonk et al., 1997
Wetland Spain Climate chamber Mateos-Naranjo et al., 2010
An exhaustive search of the journal articles about WUE and CO2 enrichment before 2019 was conducted through the platform of Google Scholar (Google Inc. Mountain View CA, USA) using the following key-words: Elevated CO2, WUE, and FACE (free air CO2 enrichment). We also searched the related studies in the reference lists of the journal articles that were retrieved from Google Scholar. The articles which were ultimately selected for the analysis had to provide data about WUE under both ambient and elevated CO2, and use a paired-sample or chrono sequence design. Independence of data in the research is required for carrying out a meta-analysis. When more than one vegetation type was assessed in one study, the results were considered independent among the vegetation types so the data could be included. However, the data with more than one sampling date was not independent, so we only extracted the data from the last sampling date.
For each selected study, we collected information on biome type, treatment techniques, experiment duration, the control and treatment means, sample size, and variance. To conduct the meta-analysis, we also need means, standard deviations, and sample sizes for the values of WUE for both the treatment and control groups. So only those studies which provided all of this useful information were used in our research. We derived means and standard deviations when they were reported directly, and digitized the data from graphs when it was presented in the figures. Furthermore, if mean and standard error (SE) were reported for the treatments, we calculated the standard deviation (SD) from SE by using Metawin 2.0 software.
Three categorical variables (WUE types, CO2 enrichment method, and ecosystem types) were chosen to potentially explain heterogeneity in the effect size of CO2 on WUE. For each categorical variable, if less than eight studies or observation were available, the results were discussed if the studies originated from at least three independent articles (Wittig et al., 2009). The data of WUE of different types, including leaf WUE, grain WUE, biomass WUE and whole plant WUE, which were extracted from the selected studies had various definitions and were calculated using different formulas. Leaf WUE was calculated as net photosynthesis divided by transpiration or stomatal conductance, while instantaneous WUE or intrinsic WUE were categorized into leaf WUE. Biomass WUE and grain WUE were estimated as total aboveground biomass and grain yield divided by evapotranspiration, respectively, while whole plant WUE was calculated as the ratio of total biomass to total water use.
Data on WUE in response to elevated CO2 was divided among the enrichment methods, which was done in order to compare outdoor facilities (FACE and open top chamber (OTC)) with climate chamber and greenhouse studies. For ecosystem types, our analysis focuses on the studies in forest, cropland, wetland and grassland. Moreover, we chose two continuous variables to examine the heterogeneity among studies: magnitude of treatment (+ppm above the standardized concentration of the control treatment) and duration of treatment (in years).

2.2 Data analysis

The lnR (natural log of the response ratio) was used as an index of the estimated magnitude of the CO2 enrichment effect (Curtis and Wang, 1998; Hedges et al., 1999). The lnR could quantify the effect size of an experimental treatment and was calculated as: lnR=ln(T/C), where T is the treatment mean and C is the control mean. Moreover, it could be reported as the percentage change in response to elevated CO2 (i.e., (R-1)×100). Meta Win 2.0 software was used to quantify the means and variances of lnR of the treatment and control (Rosenberg et al., 2000), and sample size was taken as the weighting function in this process. When lnR is greater or less than zero, it represents the increased or decreased effect size of the treatments, respectively. Moreover, the heterogeneity of lnR was quantified to examine whether all studies share a common magnitude of effect size from the treatment. We calculated the total difference in lnR among studies (QT) and the differences among groups (QM) to test the heterogeneity. Finally, the lnR data were grouped according to the categorical and continuous variables in order to determine the factors and mechanisms which affect the treatment effect on WUE. We conducted our analysis using random-effect models. In the random-effect model, the difference between studies was assumed to arise not only from sampling error, but also from a random component in effect size from the treatments among studies (Rosenberg et al., 2000).
We estimated the frequency distributions of the treatment effects (lnR) on WUE, leaf WUE, whole plant WUE, grain WUE and biomass WUE to confirm that they show normal distributions by Sigma Plot software before our meta-analysis (Fig. 1, Fig. 2). Furthermore, a fail-safe number (Rosenthal’s method at α=0.05) was estimated to evaluate the publication bias within each group (Table 2). The values with significance indicate no publication bias for the study groups.
Fig. 1 Frequency distribution of the effect size (lnR) on WUE with elevated CO2 for all studies

Note: The solid line is the fitted Gaussian (normal) distribution of the frequency data.

Fig. 2 Frequency distributions of effect size (lnR) of elevated CO2 on (a) leaf WUE, (b) whole plant WUE, (c) grain WUE and (d) biomass WUE

Note: The solid lines are the fitted Gaussian (normal) distributions of the frequency data.

Table 2 Rosenthal’s fail-safe numbers for assessing publication bias with three categorical grouping variables: WUE types, CO2 enrichment method and ecosystem types
Variable Rosenthal’s fail-safe number Variable Rosenthal’s fail-safe number
Overall 36114.6* OTC 136.5*
Leaf WUE 13753.7* Climate chamber 350.8*
Forest 589.3* Grain WUE 289.9
Cropland 8026.6* Biomass WUE 87.2*
Grassland 35.2* Forest 2061.5*
Greenhouse 536.5* Cropland 19150.6*
OTC 98.6* Grassland 35.2*
Climate chamber 8383.8* Greenhouse 2341.5*
Whole plant WUE 1507.0* OTC 552.1*
Forest 395.2* Climate chamber 11565.9*
Cropland 339.6* FACE 269.8*
Greenhouse 291.7*

Note: * means the significant level is 0.05.

3 Results

Elevated CO2 generally increased WUE compared with ambient CO2 (Table 3). The average effect size (ln response ratio) for the studies indicated that elevated CO2 increased WUE by about 46% on average (40%-52%, P<0.05, Table 3). However, the heterogeneity analysis showed that the responses were somewhat inconsistent, and high heterogeneity existed among the studies, as indicated by the significant QT value among these studies (P<0.05, Table 3). The heterogeneity existed between groups when the studies were separated by the three categorical variables (WUE types, ecosystem types, and elevated CO2 methods) and the two continuous variables (magnitude of CO2 concentration and duration of treatment) that were used to study the effect size on WUE (Table 4).
Table 3 Results from the meta-analysis of the effects of elevated CO2 on WUE
Variable Effect size df QT P
WUE 0.38±0.04 241 339.7 0.00003*

Note: A random effects model was selected to carry out the meta-analysis, and assess whether QT is significant. * means the significant level is 0.05.

Table 4 Results of the heterogeneity analysis among groups for WUE
Group df QM
WUE types 3 1334.0*
Ecosystem types 3 238.66*
eCO2 methods 3 391.14*
Magnitude of treatment 1 68.84*
Duration of treatment 1 4.45*

Note: * means the significant level is 0.05.

Elevated CO2 increased all four WUE types (leaf WUE, whole plant WUE, grain WUE and biomass WUE) by 76% (68%-85%), 37% (27%-48%), 9% (2%-16%) and 30% (7%-57%), respectively. The effect size of eCO2 on WUE was significantly higher in forest (lnR=0.52, 55%-84%) than in cropland (lnR=0.34, 34%-46%). The effect sizes on WUE in grassland (lnR=0.49, 15%-133%) and wetland (lnR=0.22, -58%-168%) were not significantly different from those in forest and cropland, which might be the result of the lower numbers of studies that were analyzed.
The effects of eCO2 on WUE were different in the studies with different CO2 enrichment methods. The effect size was significantly higher in the studies using climate chambers (lnR=0.50, 56%-74%) than in those using OTC (lnR=0.22, 9%-44%) or greenhouses (lnR=0.27, 23%-39%). However, the effect size by the method of climate chamber was marginally higher than that by the method of FACE, but not significantly (lnR=0.30, 17%-56%, P>0.05).
The response of WUE had a positive effect with the magnitude of CO2 enrichment (P<0.05), while it had no relation with the duration of CO2 enrichment (P>0.05, Table 5).
Table 5 Relationships between the effect size of elevated CO2 on WUE and two continuous experimental variables
Variables Range Mean Intercept Slope P
Magnitude of
treatment (ppm)		 107-800 362.33 0.17 0.0006 0.00001*
Duration of
treatment (yr)		 0.03-13 0.51 0.39 -0.0150 0.39

Note: * means the significant level is 0.05.

Table 6 Heterogeneity of leaf WUE, grain WUE, biomass WUE and whole plant WUE
WUE type df QT
Leaf WUE 134 1802.26*
Grain WUE 55 582.59*
Biomass WUE 8 16.65*
Whole plant WUE 41 492.29*

Note: * means the significant level is 0.05.

Moreover, our results showed that high heterogeneity existed in the effect sizes on the four WUE types (Table 6). We separated the studies into two categorical variables (ecosystem types and elevated CO2 methods) and two continuous variables (magnitude of CO2 concentration and duration of treatment) for leaf WUE and whole plant WUE, and into the two continuous variables for grain WUE (Table 7).
Table 7 Results of the heterogeneity analysis among groups for leaf WUE, grain WUE, biomass WUE and whole plant WUE
WUE type Group df QM


Leaf WUE

 Ecosystem types 3 187.1064*
eCO2 methods 3 660.0788*
Magnitude of treatment 1 188.3747*
Duration of treatment 1 504.4072*


Grain WUE


 Ecosystem types - -
eCO2 methods 3 6.3199
Magnitude of treatment 1 19.0557*
Duration of treatment 1 10.4979*


Biomass WUE


 Ecosystem types - -
eCO2 methods 1 1.4799
Magnitude of treatment 1 0.9590
Duration of treatment 1 1.0385

Whole plant WUE

 Ecosystem types 1 58.7418*
eCO2 methods 2 200.9703*
Magnitude of treatment 1 105.4783*
Duration of treatment 1 20.1892*

Note: * means the significant level is 0.05.

The effect sizes of eCO2 on leaf WUE showed no significant differences among the four ecosystems. The effect size on whole plant WUE in forest (lnR=0.36, 31%-57%) was higher than that in cropland (lnR=0.25, 18%-41%), but without significance (P>0.05).
For the different CO2 enrichment methods, the effect size on leaf WUE was higher in the studies using the method of greenhouse (lnR=0.68, 69%-133%) than in those using the methods of climate chamber (lnR=0.57, 65%-89%), OTC (lnR=0.32, 3%-84%) or FACE (lnR=0.52, -0.08%-183%), however, the differences are all non-significant (P>0.05). In addition, the effect size on whole plant WUE was significantly higher in the studies using greenhouse (lnR=0.49, 47%-81%) than in those using climate chamber (lnR=0.24, 18%-37%) or OTC (lnR=0.17, 4%-35%) (P<0.05). The effect size on whole plant WUE in studies using climate chamber was not different from those using OTC. The analysis of the effect size on whole plant WUE by the method of FACE was not assessed in our results.
Furthermore, the effect sizes on leaf WUE and whole plant WUE had positive relations with CO2 enrichment magnitude (leaf WUE: lnR=0.0009x+0.25, P<0.05; whole plant WUE: lnR=0.0007x+0.051, P<0.05), while neither WUE type had any relation with CO2 enrichment duration based on the analysis results (Table 8). On the contrary, the effect size of eCO2 on grain WUE had no relation with eCO2 magnitude, however it had a positive correlation with eCO2 duration (lnR=0.074x+0.049, P<0.05, Table 8).
Table 8 Relationships between the effect sizes of elevated CO2 on WUE and the continuous experimental variables for the different WUE types
WUE type Variable Range Mean Intercept Slope P
Leaf WUE Magnitude of treatment (ppm) 120-800 374.35 0.25 0.0009 0.00007*
Duration of treatment (yr) 0.03-13 0.44 0.58 -0.03 0.22
Grain WUE Magnitude of treatment (ppm) 185-600 370.59 0.07 0.0000 0.78
Duration of treatment (yr) 0.2-3 0.54 0.05 0.07 0.03*
Whole plant WUE Magnitude of treatment (ppm) 107-620 341.62 0.05 0.0007 0.0003*
Duration of treatment (yr) 0.03-0.9 0.41 0.30 0.0090 0.93

Note: * means the significant level is 0.05.

4 Discussion

Our meta-analysis results showed that WUE had positive responses to CO2. The positive impact of elevated CO2 on WUE has been reported by many studies (Robredo et al., 2007; Tuba and Lichtenthaler, 2007; Bender and Weigel, 2011; Dalling et al., 2016; Rahman et al., 2020). However, there was high heterogeneity in the effect size of elevated CO2 on WUE among the studies. Our results indicated that different WUE types had different responses to elevated CO2. Leaf WUE showed a more sensitive response to elevated CO2 than the other three types. The response of leaf WUE is usually documented by instantaneous gas exchange measurements, and enriched CO2 tends to increase leaf photosynthetic rates and decrease transpiration rates of plants (Kang et al., 1999; Li et al., 2003). Besides, elevated CO2 has negative effects on stomatal conductance by inducing stomatal closure, which also leads to an increase of leaf WUE (Yu and Wang, 2010). Jiang et al. (2020) found that elevated CO2 increased leaf WUE by about 60% under high phosphorus treatment by using a meta-analysis method, and Wand et al. (1999) found elevated CO2 increased the leaf WUE by 72% in C4 grass species by the same method, both of which are close to our result (about 76%). Considering the alleviation by plant respiration, nutrient limitation and other factors, the rising photosynthetic rates and short-term increase in leaf biomass may not result in an increase in the whole plant or over the long term (BassiriRad et al., 2001). Therefore, the effect sizes for whole plant, grain and biomass WUE should be weaker than the leaf WUE, indicating that it is difficult to extend the short-term measurements of individual leaves to the responses of whole plants or ecosystems over longer time periods (Morison, 1985; Norby and O’Neill, 1989). Although the instantaneous measures of carbon assimilation and transpiration only roughly predicted the equivalent whole-plant responses, Norby and O’Neill (1989) found that instantaneous WUE had the same change trends as the whole plant WUE in response to elevated CO2. Furthermore, our results indicated that the grain WUE had a weaker response (2%-16%) to elevated CO2 than plant growth and other physiological processes, and this can be confirmed by other studies. Using modelling methods, Han et al. (2021) showed that the grain WUE of maize increased by 1.5% or 2.2% with elevated CO2 in an agro-pastoral ecotone of Northwestern China. Our results for the grain WUE also coincided with the value range of a study (7%-21%) in maize crop in the Shannxi Province of China (Saddique et al., 2020).
Two ecosystem types (cropland and forest) were the main ones included in our analysis. Our results suggested that there was a higher effect size of eCO2 on WUE in forest than in cropland. A non-significantly higher effect size in forest than cropland was found when the WUE was separated into leaf WUE and whole plant WUE, and this might be due to the high in-group heterogeneity caused by the small sample number. Compared with the forest ecosystem, the significantly lower effect size on WUE in the cropland ecosystem indicated that elevated CO2 might have a weaker effect on plant growth in the cropland than in the forest. Norby et al. (1996) have suggested that highly productive systems should have a strong biomass response to enriched CO2. Zhu et al. (2011) reported that WUE had stronger positive responses to CO2 in the areas where forests were mainly located. In the Tibetan Plateau, Lin et al. (2020) indicated that CO2 concentration had positive relationships with WUE, and a higher impact on the WUE in the forest ecosystem compared with other vegetation ecosystems. The vegetation type, water and nutrient conditions might contribute to the differences in WUE responses to elevated CO2 between cropland and forest ecosystems (Yu et al., 2008; Beer et al., 2009). Moreover, the high canopy closure in the forest ecosystem could reduce the amount of radiation reaching the ground, resulting in decreased soil evaporation, and raising the impact of elevated CO2 on WUE (Beer et al., 2009).
Our results showed that the methods of CO2 enrichment contributed to variations in the effect size on WUE by eCO2. The environmental conditions of Free-air CO2 enrichments and OTC differ from those in enclosure studies (climate-controlled glasshouses and chambers), such as growing space, microclimate and so on, which might cause different physiological processes related to water use (Ainsworth et al., 2008). Our results indicated that the effect size on WUE obtained with the method of enclosure systems was higher than that with the method of OTC. This result has been supported by many other studies (Long et al., 2006). Long et al. (2006) demonstrated that the enhanced yield under enriched CO2 with fully open-air field conditions was 50% less than that with enclosure conditions. Furthermore, our results showed that the microclimate environment should be different between the greenhouses and climate-controlled chambers, which might result in the higher effect size of enriched CO2 on WUE in climate-controlled chambers. However, there was no significant difference among the CO2 enrichment methods for leaf WUE, while the effect size by the method of greenhouse was higher than that by the methods of OTC and climate chamber for whole plant WUE. Our results suggested that the response of whole plant growth might be limited by the spatial size in OTC and climate chambers compared with greenhouses.
The leaf photosynthesis rate was positively related to elevated CO2, with higher values at higher CO2 concentrations (Succarie et al., 2020). Rahman et al. (2020) demonstrated that an increasing CO2 concentration was the main factor leading to the enhanced WUE in a long-term study. However, it might represent acclimation to long-term CO2 enrichment (Xu et al., 2013). Our results indicated that the effect size on leaf WUE had a positive linear relationship with the magnitude of CO2 enrichment, while it had no relationship with the duration of CO2 enrichment. This might have connections with the responses of leaf photosynthetic activity to elevated CO2. A model described by Comins and McMurtrie (1993) demonstrated that the carbon allocation to leaves in the long term was less than that allocated to stem growth under elevated CO2. The decreased carbon allocation to leaves could result in a compensatory increase in carbon allocation to roots (Norby et al., 1996). This mechanism was consistent with our results on the relationships between the responses of whole plant WUE and the magnitude of CO2 enrichment. Furthermore, the effect size of CO2 on grain WUE had an accumulative effect of increasing with the duration of CO2 enrichment.

5 Conclusions

Water use efficiency (WUE) is an important value which can connect plant growth with water resources. Studies on the responses of WUE to CO2 have advantages for understanding the plant growth and carbon allocation in vegetation under elevated CO2. The results from our meta-analysis indicated that elevated CO2 had positive effects on WUE, and leaf WUE had a more sensitive response to elevated CO2 than other types of WUE. The effect size of elevated CO2 on WUE was smaller in the cropland ecosystem than in the forest ecosystem. The enclosure CO2 enrichment method might increase the effect size of CO2 on WUE and limit the effect size on whole plant WUE. Furthermore, the effect size on leaf WUE had a positive linear relationship with CO2 concentration, while it did not have an accumulative response to CO2 enrichment for the long term compared with the accumulated increasing effect size for grain. The responses of whole plant WUE to elevated CO2 also had positive linear relationships with CO2 concentration. The factors that cooperate with rising CO2 in affecting WUE are complex and differences in those factors among specific studies could lead to the diverse conclusions in different studies. Regarding the relations of WUE with nutrient and water resources, we will investigate some general patterns in the responses of WUE to CO2 under different nutrient and water conditions in our future studies.

References

Publishing order | Descend order by publishing year | Descend order by cited within
[1]
Ainsworth E A, Leakey A D B, Ort D R, et al. 2008. FACE-ing the facts: Inconsistencies and interdependence among field, chamber and modeling studies of elevated [CO2] impacts on crop yield and food supply. New Phytologist, 179(1): 5-9.

DOI PMID

[2]
BassiriRad H, Gutschick V P, Lussenhop J. 2001. Root system adjustments: Regulation of plant nutrient uptake and growth responses to elevated CO2. Oecologia, 126(3): 305-320.

DOI PMID

[3]
Beer C, Ciais P, Reichstein M, et al. 2009. Temporal and among-site variability of inherent water use efficiency at the ecosystem level. Global Biogeochemical Cycles, 23(2): GB2018. DOI: 10.1029/2008GB003233.

DOI

[4]
Bender J, Weigel H J. 2011. Changes in atmospheric chemistry and crop health: A review. Agronomy for Sustainable Development, 31(1): 81-89.

DOI

[5]
Blum A. 2009. Effective use of water (EUW) and not water-use efficiency (WUE) is the target of crop yield improvement under drought stress. Field Crops Research, 112(2-3): 119-123.

DOI

[6]
Bucher-Wallin I K, Sonnleitner M A, Egli P, et al. 2000. Effects of elevated CO2, increased nitrogen deposition and soil on evapotranspiration and water use efficiency of spruce-beech model ecosystems. Phyton-Annales Rei Botanicae, 40(4): 49-60.

[7]
Centritto M, Lee H S J, Jarvis P G. 1999. Interactive effects of elevated [CO2] and drought on cherry (Prunus avium) seedlings I. Growth, whole-plant water use efficiency and water loss. New Phytologist, 141(1): 129-140.

DOI

[8]
Comins H N, McMurtrie R E. 1993. Long-term response of nutrient-limited forests to CO2 enrichment, equilibrium behavior of plant-soil models. Ecological Applications, 3(4): 666-681.

DOI

[9]
Conley M M, Kimball B A, Brooks T J, et al. 2001. CO2 enrichment increases water-use efficiency in sorghum. New Phytologist, 151(2): 407-412.

DOI

[10]
Curtis P S, Wang X Z. 1998. A meta-analysis of elevated CO2 effects on woody plant mass, form, and physiology. Oecologia, 113(3): 299-313.

DOI PMID

[11]
Dahal K, Knowles V L, Plaxton W C, et al. 2014. Enhancement of photosynthetic performance, water use efficiency and grain yield during long-term growth under elevated CO2 in wheat and rye is growth temperature and cultivar dependent. Environmental and Experimental Botany, 106: 207-220.

DOI

[12]
Dalling J W, Cernusak L A, Winter K, et al. 2016. Two tropical conifers show strong growth and water-use efficiency responses to altered CO2 concentration. Annals of Botany, 118(6): 1113-1125.

PMID

[13]
Ephrath J E, Timlin D J, Reddy V, et al. 2011. Irrigation and elevated carbon dioxide effects on whole canopy photosynthesis and water use efficiency in cotton (Gossypium hirsutum L.). Plant Biosystems: An International Journal Dealing with All Aspects of Plant Biology, 145(1): 202-215.

DOI

[14]
Ghini R, Torre-Neto A, Dentzien A F M, et al. 2015. Coffee growth, pest and yield responses to free-air CO2 enrichment. Climatic Change, 132(2): 307-320.

DOI

[15]
Guehl J M, Picon C, Aussenac G, et al. 1994. Interactive effects of elevated CO2 and soil drought on growth and transpiration efficiency and its determinants in two European forest tree species. Tree Physiology, 14(7/8/9): 707-724.

DOI

[16]
Han Z B, Zhang B Q, Yang L X, et al. 2021. Assessment of the impact of future climate change on maize yield and water use efficiency in agro-pastoral ecotone of Northwestern China. Journal of Agronomy and Crop Science, 207(2): 317-331.

DOI

[17]
Hatfield J L, Dold C. 2019. Water-use efficiency: Advances and challenges in a changing climate. Frontiers in Plant Science, 10: 103. DOI: 10.3389/fpls.2019.00103.

DOI PMID

[18]
Hebbar K B, Apshara E, Chandran K P, et al. 2020. Effect of elevated CO2, high temperature, and water deficit on growth, photosynthesis, and whole plant water use efficiency of cocoa (Theobroma cacao L.). International Journal of Biometeorology, 64(1): 47-57.

DOI PMID

[19]
Hedges L V, Gurevitch J, Curtis P S. 1999. The meta-analysis of response ratios in experimental ecology. Ecology, 80(4): 1150-1156.

DOI

[20]
Holub P, Klem K, Linder S, et al. 2019. Distinct seasonal dynamics of responses to elevated CO2 in two understorey grass species differing in shade-tolerance. Ecology and Evolution, 9(24): 13663-13677.

DOI

[21]
Hui D F, Luo Y Q, Cheng W X, et al. 2001. Canopy radiation- and water-use efficiencies as affected by elevated [CO2]. Global Change Biology, 7(1): 75-91.

DOI

[22]
Ibrahim M H, Jaafar H Z E, Harun M H, et al. 2010. Changes in growth and photosynthetic patterns of oil palm (Elaeis guineensis Jacq.) seedlings exposed to short-term CO2 enrichment in a closed top chamber. Acta Physiologiae Plantarum, 32(2): 305-313.

DOI

[23]
IPCC. 2007. Summary for policymakers. In: Solomon S, Qin D, Manning M, et al(Climate change 2007: The physical science basis, contribution of working group I to the fourth assessment report of the intergovernmental panel on climate change. Cambridge, eds.). UK: Cambridge University Press.

[24]
Jiang M K, Caldararu S, Zhang H Y, et al. 2020. Low phosphorus supply constrains plant responses to elevated CO2: A meta-analysis. Global Change Biology, 26(10): 5856-5873.

DOI

[25]
Kaminski K P, Kørup K, Nielsen K L, et al. 2014. Gas-exchange, water use efficiency and yield responses of elite potato (Solanum tuberosum L.) cultivars to changes in atmospheric carbon dioxide concentration, temperature and relative humidity. Agricultural and Forest Meteorology, 187: 36-45.

DOI

[26]
Kang S Z, Zhang F C, Liang Y L, et al. 1999. Effects of soil water and the atmospheric CO2 concentration increase on evapotranspiration, photosynthesis, growth of wheat, maize and cotton. Acta Agronomica Sinica, 25(1): 55-63. (in Chinese)

[27]
Leakey A D B. 2009. Rising atmospheric carbon dioxide concentration and the future of C4 crops for food and fuel. Proceedings of the Royal Society, 276(1666): 2333-2343.

[28]
Leavitt S W, Idso S B, Kimball B A, et al. 2003. The effect of long-term atmospheric CO2 enrichment on the intrinsic water-use efficiency of sour orange trees. Chemosphere, 50(2): 217-222.

PMID

[29]
Lee H S J, Jarvis P G. 1995. Trees differ from crops and from each other in their responses to increases in CO2 concentration. Journal of Biogeography, 22(2/3): 323-330.

DOI

[30]
Li D X, Liu H L, Qiao Y Z, et al. 2013. Effects of elevated CO2 on the growth, seed yield, and water use efficiency of soybean (Glycine max (L.) Merr.) under drought stress. Agricultural Water Management, 129: 105-112.

DOI

[31]
Li F S, Kang S Z, Zhang J H, et al. 2003. Effects of atmospheric CO2 enrichment, water status and applied nitrogen on water- and nitrogen-use efficiencies of wheat. Plant and Soil, 254: 279-289.

DOI

[32]
Li P, Li B Y, Seneweera S, et al. 2019. Photosynthesis and yield response to elevated CO2, C4 plant foxtail millet behaves similarly to C3 species. Plant Science, 285: 239-247.

DOI

[33]
Lin S, Wang G X, Hu Z Y, et al. 2020. Spatiotemporal variability and driving factors of Tibetan Plateau water use efficiency. Journal of Geophysical Research: Atmospheres, 125(22): e2020JD032642. DOI: 10.1029/2020JD032642.

DOI

[34]
Liu J Z, Kang S Z, Davies W J, et al. 2020. Elevated [CO2] alleviates the impacts of water deficit on xylem anatomy and hydraulic properties of maize stems. Plant, Cell & Environment, 43(3): 563-578.

[35]
Long S P, Ainsworth E A, Leakey A D B, et al. 2006. Food for thought: Lower-than-expected crop yield stimulation with rising CO2 concentrations. Science, 312(5782): 1918-1921.

DOI

[36]
Mateos-Naranjo E, Redondo-Gómez S, Álvarez R, et al. 2010. Synergic effect of salinity and CO2 enrichment on growth and photosynthetic responses of the invasive cordgrass Spartina densiflora. Journal of Experimental Botany, 61(6): 1643-1654.

DOI PMID

[37]
Mbava N, Mutema M, Zengeni R, et al. 2020. Factors affecting crop water use efficiency: A worldwide meta-analysis. Agricultural Water Management, 228: 105878. DOI: 10.1016/j.agwat.2019.105878.

DOI

[38]
Morison J I L. 1985. Sensitivity of stomata and water use efficiency to high CO2. Plant, Cell & Environment, 8(6): 467-474.

[39]
Moutinho-Pereira J, Goncalves B, Bacelar E, et al. 2009. Effects of elevated CO2 on grapevine (Vitis vinifera L.): Physiological and yield attributes. Vitis, 48(4): 159-165.

[40]
Norby R J, O'Neill E G. 1989. Growth dynamics and water use of seedlings of Quercus alba L. in CO2-enriched atmospheres. New Phytologist, 111(3): 491-500.

DOI

[41]
Norby R J, Wullschleger S D, Gunderson C A. 1996. Tree responses to elevated CO2 and implications for forests. In: Koch G W, Mooney H A(Carbon dioxide and terrestrial ecosystems. London, eds.). UK: Academic Press.

[42]
O’Leary G J, Christy B, Nuttall J, et al. 2015. Response of wheat growth, grain yield and water use to elevated CO2 under a Free-Air CO2 Enrichment (FACE) experiment and modelling in a semi-arid environment. Global Change Biology, 21(7): 2670-2686.

DOI

[43]
Oliveira M F, Marenco R A. 2019. Photosynthesis and biomass accumulation in Carapa surinamensis (Meliaceae) in response to water stress at ambient and elevated CO2. Photosynthetica, 57(1): 137-146.

DOI

[44]
Pan T H, Wang Y L, Wang L H, et al. 2020. Increased CO2 and light intensity regulate growth and leaf gas exchange in tomato. Physiologia Plantarum, 168(3): 694-708.

DOI

[45]
Perry L G, Shafroth P B, Blumenthal D M, et al. 2013. Elevated CO2 does not offset greater water stress predicted under climate change for native and exotic riparian plants. New Phytologist, 197(2): 532-543.

DOI

[46]
Picon C, Guehl J M, Aussenac G. 1996. Growth dynamics, transpiration and water-use efficiency in Quercus robur plants submitted to elevated CO2 and drought. Annales Des Sciences Forestières, 53(2-3): 431-446.

DOI

[47]
Qiao Y Z, Zhang H Z, Dong B D, et al. 2010. Effects of elevated CO2 concentration on growth and water use efficiency of winter wheat under two soil water regimes. Agricultural Water Management, 97(11): 1742-1748.

DOI

[48]
Rahman M, Islam M, Gebrekirstos A, et al. 2020. Disentangling the effects of atmospheric CO2 and climate on intrinsic water-use efficiency in South Asian tropical moist forest trees. Tree Physiology, 40(7): 904- 916.

DOI

[49]
Robredo A, Pérez-López U, de la Maza H S, et al. 2007. Elevated CO2 alleviates the impact of drought on barley improving water status by lowering stomatal conductance and delaying its effects on photosynthesis. Environmental and Experimental Botany, 59(3): 252-263.

DOI

[50]
Rogers H H, Runion G B, Krupa S V. 1994. Plant responses to atmospheric CO2 enrichment with emphasis on roots and the rhizosphere. Environmental Pollution, 83(1-2): 155-189.

PMID

[51]
Rosenberg M S, Adams D C, Gurevitch J. 2000. MetaWin: Statistical software for meta-analysis. Version 2.0. Sunderland, USA: Sinauer Associates.

[52]
Ruiz-Vera U M, Siebers M, Gray S B, et al. 2013. Global warming can negate the expected CO2 stimulation in photosynthesis and productivity for soybean grown in the Midwestern United States. Plant Physiology, 162(1): 410-423.

DOI PMID

[53]
Saddique Q, Khan M I, Habib ur Rahman M, et al. 2020. Effects of elevated air temperature and CO2 on maize production and water use efficiency under future climate change scenarios in Shaanxi Province, China. Atmosphere, 11(8): 843. DOI: 10.3390/atmos11080843.

DOI

[54]
Schapendonk A H C M, Dijkstra P, Groenwold J, et al. 1997. Carbon balance and water use efficiency of frequently cut Lolium perenne L. swards at elevated carbon dioxide. Global Change Biology, 3(3): 207-216.

DOI

[55]
Shabbir A, Dhileepan K, Zalucki M P, et al. 2019. Biological control under a changing climate: The efficacy of the parthenium weed stem-galling moth under an atmosphere enriched with CO2. Biological Control, 139: 104077. DOI: 10.1016/j.biocontrol.2019.104077.

DOI

[56]
Succarie A, Xu Z H, Wang W J, et al. 2020. Effects of climate change on tree water use efficiency, nitrogen availability and growth in boreal forest of Northern China. Journal of Soils and Sediments, 20(10): 3607-3614.

DOI

[57]
Tuba Z, Lichtenthaler H K. 2007. Long-term acclimation of plants to elevated CO2 and its interaction with stresses. Annals of the New York Academy of Sciences, 1113(1): 135-146.

[58]
Varga B, Vida G, Varga-László E, et al. 2017. Combined effect of drought stress and elevated atmospheric CO2 concentration on the yield parameters and water use properties of winter wheat (Triticum aestivum L.) genotypes. Journal of Agronomy and Crop Science, 203(3): 192-205.

DOI

[59]
Wand S J E, Midgley G F, Jones M H, et al. 1999. Responses of wild C4 and C3 grass(Poaceae) species to elevated atmospheric CO2 concentration: A meta-analytic test of current theories and perceptions. Global Change Biology, 5(6): 723-741.)

DOI

[60]
Wittig V E, Ainsworth E A, Naidu S L, et al. 2009. Quantifying the impact of current and future tropospheric ozone on tree biomass, growth, physiology and biochemistry: A quantitative meta-analysis. Global Change Biology, 15(2): 396-424.

DOI

[61]
Xu M Y, Wang A X, Ni H W. 2013. Effect of elevated CO2 concentration on leaf photosynthesis in Sanjiang-Deyeuxia angustifolia. Advanced Materials Research, 726-731: 305-309.

[62]
Yu G R, Song X, Wang Q F, et al. 2008. Water-use efficiency of forest ecosystems in Eastern China and its relations to climatic variables. New Phytologist, 177(4): 927-937.

DOI PMID

[63]
Yu G R, Wang Q F. 2010. Ecophysiology of plant photosynthesis, transpiration, and water use. Beijing, China: Science Press. (in Chinese)

[64]
Zhu Q A, Jiang H, Peng C H, et al. 2011. Evaluating the effects of future climate change and elevated CO2 on the water use efficiency in terrestrial ecosystems of China. Ecological Modelling, 222(14): 2414-2429.

DOI

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