Atmospheric CO2 concentrations are rising and projected to reach ∼800 μmol mol-1 by 2100, while soil salinity is expanding globally, yet their combined impact on crops remains unclear. In particular, the interactive effects of elevated CO2 and salinity on maize (Zea mays L.) physiology and development are poorly understood. The physiological and anatomical responses of maize to elevated CO2 (800 μmol mol-1) and NaCl stress (0-150 mmol L-1) were investigated through a controlled factorial experiment. Results showed that elevated CO2 increased net photosynthetic rate, water-use efficiency, and biomass accumulation, partially mitigating salt-induced reductions in growth and photosynthesis under moderate NaCl stress, while mitigating salt-induced growth inhibition through three key mechanisms: (1) reinforcement of antioxidant defenses and improve water use efficiency by upregulating superoxide dismutase and peroxidase, (2) osmotic adjustment via leaf non-structural carbon accumulation especially under moderate salinity, and (3) high salinity caused structural deteriorations such as thinner leaves, lower stomatal density, and reduced vascular bundle size, while elevated CO2 counteracted salinity-induced structural degradation, maintaining leaf thickness and vascular bundle integrity while modulating stomatal patterning and opening. However, growth and physiological function were still markedly hindered under severe salinity. Our multi-trait analysis demonstrates that rising CO2 may partially compensate for salinity impacts in maize, providing critical insights for predicting C4 crop stress resistance under future climate scenarios.

The frequency and intensity of drought are projected to increase globally, threatening plant growth. However, the role of elevated CO2 (e[CO2]) in plant drought recovery, particularly with respect to photosynthesis and water use efficiency (WUE), remains unclear. The study investigated the impact of e[CO2] (800 mu mol mol(-1)) on the gas exchange parameters, stomatal morphology and distribution, and leaf tissue structure of tobacco plants under various water levels (full irrigation [FI], mild water deficit [MI], moderate water deficit [MO] and severe water deficit [SE]) within growth chambers. The results revealed that stomatal limitations significantly reduced CO2 assimilation under MI to MO, whereas non-stomatal limitations became more prominent under more severe deficit. Moreover, the instantaneous water use efficiency (WUEn) and intrinsic water use efficiency (WUEi) of tobacco plants grown under e[CO2] were approximately twofold greater than those of plants grown under ambient [CO2] (a[CO2]). Moreover, e[CO2] led to distinct adjustment strategies in response to varying water availability, thereby alleviating the adverse effects of water deficit on plants. These findings indicate that e[CO2] enhances leaf water use efficiency in tobacco plants by modulating stomatal behaviour and increase our understanding of the potential mechanism through which the CO2 fertilization effect improves plant drought resistance.

IntroductionSoil phosphorus (P) deficiency limits plant growth and productivity in grassland ecosystems and may moderate the growth-promoting effects of “carbon dioxide (CO2) fertilization effect”.MethodsTo evaluate the interactive effects of these two factors on the growth and physiology for annual ryegrass (Lolium multiflorum Lam.), plants were grown in controlled growth chambers with a range of P supply (0.004, 0.012, 0.02, 0.06, 0.1 and 0.5 mM) under two levels of CO2 (400 and 800 μmol mol-1, respectively).ResultsElevated [CO2] dramatically increased the aboveground biomass and net photosynthetic rates of annual ryegrass by 14.5% and 25.3% under sufficient P supply (0.5 mM), respectively, whereas decreased the belowground biomass and net photosynthetic rates under lower P supply of P0.004, P0.02, and P0.06. Two-way ANOVA results showed that CO2 × P (p < 0.001) significantly affected stomatal traits, leaf photosynthesis and biomass. The stimulation of growth and photosynthesis by elevated CO2 concentration (e[CO2]) was reduced or highly suppressed, indicating that the sensitivity of annual ryegrass to P deficiency was enhanced under e[CO2].DiscussionThese results indicated that P limitation may offset the positive effects of e[CO2] on plant growth by altering stomatal traits, leaf photochemical processes and biochemical composition in annual ryegrass.

Background Understanding the mechanisms of crops in response to elevated CO 2 concentrations is pivotal to estimating the impacts of climate change on the global agricultural production. Based on earlier results of the “doubling-CO 2 concentration” experiments, many current climate models may overestimate the CO 2 fertilization effect on crops, and meanwhile, underestimate the potential impacts of future climate change on global agriculture ecosystem when the atmospheric CO 2 concentration goes beyond the optimal levels for crop growth. Results This study examined the photosynthetic response of soybean ( Glycine max (L.) Merr.) to elevated CO 2 concentration associated with changes in leaf structure, non-structural carbohydrates and nitrogen content with environmental growth chambers where the CO 2 concentration was controlled at 400, 600, 800, 1000, 1200, 1400, 1600 ppm. We found CO 2 -induced down-regulation of leaf photosynthesis as evidenced by the consistently declined leaf net photosynthetic rate ( A n ) with elevated CO 2 concentrations. This down-regulation of leaf photosynthesis was evident in biochemical and photochemical processes since the maximum carboxylation rate ( V cmax ) and the maximum electron transport rate ( J max ) were dramatically decreased at higher CO 2 concentrations exceeding their optimal values of about 600 ppm and 400 ppm, respectively. Moreover, the down-regulation of leaf photosynthesis at high CO 2 concentration was partially attributed to the reduced stomatal conductance ( G s ) as demonstrated by the declines in stomatal density and stomatal area as well as the changes in the spatial distribution pattern of stomata. In addition, the smaller total mesophyll size (palisade and spongy tissues) and the lower nitrogen availability may also contribute to the down-regulation of leaf photosynthesis when soybean subjected to high CO 2 concentration environment. Conclusions Down-regulation of leaf photosynthesis associated with the changes in stomatal traits, mesophyll tissue size, non-structural carbohydrates, and nitrogen availability of soybean in response to future high atmospheric CO 2 concentration and climate change.

Use of brackish water is becoming more and more important in agricultural irrigation, and it has not been effectively utilized. The effects of brackish water on the soil salt and water movements and the emergence rate of cotton with different salinities of brackish water (0 g/L (control group—CK), 2, 3, 5 and 7 g/L) through film hole irrigation were examined. The results showed that: (1) the cotton emergence rate significantly decreased under the salinity of brackish water more than 5 g/L, whereas the brackish water salinity of 0–5 g/L barely affected the cotton seedling growth; (2) the leaf net photosynthetic rate (Pn) and transpiration rate (E) gradually decreased with the increasing salinity brackish water; (3) the soil salinity increases with the increase of salinity brackish water; and, as time increased, soil salinity gradually moved downward. The results suggested that high salinity of brackish water may have impacts cotton seedling growth. The results may have important significance on cotton plantations with brackish water film hole irrigation.

利用可精准控制CO2浓度的大型气候箱设置2个CO2浓度400和800μmol/mol,研究CO2浓度升高对大豆(Glycine max(L.)Merr.)、冬小麦(Triticum aestivum L.)、草地早熟禾(Poa pratensis L.)、黑麦草(Lolium perenne L.)和高羊茅(Festuca arundinacea Schreb.)生理特性及叶片水分利用效率的影响.结果表明,大气CO2浓度升高对大豆、冬小麦、草地早熟禾和高羊茅叶片的净光合速率没有产生显著影响,但却使黑麦草叶片的净光合速率显著增加43％(P<0.05).升高CO2浓度增加冬小麦、黑麦草和高羊茅的最大羧化速率,而对大豆和草地早熟禾的最大羧化速率和最大电子传递速率没有产生显著的影响.另外,提高大气CO2浓度导致黑麦草蒸腾速率的降低;同时,草地早熟禾、黑麦草和高羊茅的水分利用效率分别提高161％、175％和74％.不同作物水分利用效率对升高CO2浓度的响应存在明显差异,3种草坪草的适应能力均高于大豆和冬小麦2种作物.研究结果有助于深入理解CO2浓度倍增下不同农作物发生光合下调现象的潜在机理,为未来大气CO2浓度升高情形下生态系统适应性管理提供理论支持.

Background: Grasslands are one of the most representative vegetation types accounting for about 20% of the global land area and thus the response of grasslands to climate change plays a pivotal role in terrestrial carbon balance. However, many current climate change models, based on earlier results of the doubling-CO2 experiments, may overestimate the CO2 fertilization effect, and as a result underestimate the potentially effects of future climate change on global grasslands when the atmospheric CO2 concentration goes beyond the optimal level. Here, we examined the optimal atmospheric CO2 concentration effect on CO2 fertilization and further on the growth of three perennial grasses in growth chambers with the CO2 concentration at 400, 600, 800, 1000, and 1200 ppm, respectively. Results: All three perennial grasses featured an apparent optimal CO2 concentration for growth. Initial increases in atmospheric CO2 concentration substantially enhanced the plant biomass of the three perennial grasses through the CO2 fertilization effect, but this CO2 fertilization effect was dramatically compromised with further rising atmospheric CO2 concentration beyond the optimum. The optimal CO2 concentration for the growth of tall fescue was lower than those of perennial ryegrass and Kentucky bluegrass, and thus the CO2 fertilization effect on tall fescue disappeared earlier than the other two species. By contrast, the weaker CO2 fertilization effect on the growth of perennial ryegrass and Kentucky bluegrass was sustained for a longer period due to their higher optimal CO2 concentrations than tall fescue. The limiting effects of excessively high CO2 concentrations may not only associate with changes in the biochemical and photochemical processes of photosynthesis, but also attribute to the declines in stomatal conductance and nitrogen availability. Conclusions: In this study, we found apparent differences in the optimal CO2 concentrations for the growth of three grasses. These results suggest that the growth of different types of grasses may respond differently to future elevated CO2 concentrations through the CO2 fertilization effect, and thus potentially alter the community composition and structure of grasslands. Meanwhile, our results may also be helpful for improving current process-based ecological models to more accurately predict the structure and function of grassland ecosystems under future rising atmospheric CO2 concentration and climate change scenarios.