Abstract
Elevated atmospheric CO2 concentrations ([eCO2]) and soil water deficits significantly influence gas exchange in plant leaves, affecting the carbon-water cycle in terrestrial ecosystems. However, it remains unclear how the soil water deficit modulates the plant CO2 fertilization effect, especially for gas exchange and leaf-level water use efficiency (WUE). Here, we synthesized a comprehensive dataset including 554 observations from 54 individual studies and quantified the responses for leaf gas exchange induced by e[CO2] under water deficit. Moreover, we investigated the contribution of plant net photosynthesis rate (Pn) and transpiration rates (Tr) toward WUE in water deficit conditions and e[CO2] using graphical vector analysis (GVA). In summary, e[CO2] significantly increased Pn and WUE by 11.9 and 29.3% under well-watered conditions, respectively, whereas the interaction of water deficit and e[CO2] slightly decreased Pn by 8.3%. Plants grown under light in an open environment were stimulated to a greater degree compared with plants grown under a lamp in a closed environment. Meanwhile, water deficit reduced Pn by 40.5 and 37.8%, while increasing WUE by 24.5 and 21.5% under ambient CO2 concentration (a[CO2]) and e[CO2], respectively. The e[CO2]-induced stimulation of WUE was attributed to the common effect of Pn and Tr, whereas a water deficit induced increase in WUE was linked to the decrease in Tr. These results suggested that water deficit lowered the stimulation of e[CO2] induced in plants. Therefore, fumigation conditions that closely mimic field conditions and multi-factorial experiments such as water availability are needed to predict the response of plants to future climate change.
Highlights
Global atmospheric carbon dioxide concentration ([CO2]) has accelerated at an unprecedented pace of about 2.4 μmol mol−1 per year during the last decade, and presently, it is 413 ppm (IPCC, 2019; NASA, 2020). [CO2] is projected to be between 421–946 ppm by 2,100 depending on continued emission scenarios
Our meta-analysis demonstrated that the % increase in photosynthesis rate (Pn) by e[CO2] treatments depended on the fumigation method; Pn was stimulated to a greater magnitude when plants were exposed to e[CO2] in an open environment than in a closed environment, especially when compared to the growth chamber
Our meta-analysis demonstrated that e[CO2] generally augmented Pn, but the magnitude of the increase varied depending on the CO2 fumigation method and light conditions
Summary
Global atmospheric carbon dioxide concentration ([CO2]) has accelerated at an unprecedented pace of about 2.4 μmol mol−1 per year during the last decade, and presently, it is 413 ppm (IPCC, 2019; NASA, 2020). [CO2] is projected to be between 421–946 ppm by 2,100 depending on continued emission scenarios. An increase Pn and WUE are necessary for improve carbon-water cycle and plant productivity in terrestrial ecosystems. Understanding how soil water deficit affects “CO2 fertilization effect” on plant is of great significance to projecting the potential risk of climate change on global bio-environment equilibrium. E[CO2] and drought stimulate or inhibit plant growth by changing leaf gas exchange including net photosynthesis rate (Pn), transpiration rate (Tr), stomatal conductance (Gs), and leaf-level water use efficiency (WUE), which result in a significant impact on the global cycling of carbon-water in terrestrial ecosystems (McLaughlin et al, 2007; Lawson and Blatt, 2014). Short-term water stress results in stomatal defense and increased WUE, which is associated with delayed drought (Ameye et al, 2012). Drought stress results in stomatal and non-stomatal limitations; for instance, a reduction in Pn may occur as a result of conditions favoring ribulose 1,5-bisphosphate (RuBP) oxygenation rather than carboxylation, resulting in a reduction of chlorophyll content (Farquhar and Sharkey, 1982; Ameye et al, 2012; Drake et al, 2017; Birami et al, 2020)
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