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To probe the mechanism of action of NaCl in regulating drought adaptation in Medicago sativa, we pretreated M. sativa with different concentrations (0, 50, 100 and 200 mM) of NaCl, then studied the effects of NaCl pretreatment on water content, chlorophyll content, photosynthetic function, and membrane peroxidation of M. sativa plants subjected to drought stress. Although pretreatment with different concentrations of NaCl significantly increased the Na+ content in the aboveground of M. sativa, it had no significant effect on the activity of PSII and PSI. However, different concentrations of NaCl pretreatment significantly increased the water content of the aboveground of M. sativa under drought stress, alleviated the degree of photoinhibition of PSII and PSI, and maintained the flow and stability of donor and acceptor electrons in PSII. NaCl pretreatment promotes the increase of non-photochemical quenching (NPQ), which relieves oxidative damage in the leaves of M. sativa under drought stress, playing an important role in maintaining the activity of PSII and PSI. In conclusion, pretreatment with a certain concentration of NaCl can help M. sativa leaves maintain relatively high-water content and alleviate the photosynthesis inhibition of PSII and PSI under drought stress, thereby improving the drought resistance of M. sativa.

The effects of arbuscular mycorrhizal fungi Glomus mosseae (+AMF) on the growth, nutrient uptake and leaf photosynthetic characteristics of alfalfa (Medicago sativa) under salt stress were studied. In alfalfa, 100 mM salt stress had no obvious effect on plant growth, nutrient content and photosynthetic capacity, however, 200 mM salt stress significantly inhibited biomass accumulation and NPK uptake. In addition, 200 mM salt stress led to decreased photosynthetic carbon assimilation capacity and lower PSII and PSI activity levels. Cultivation of alfafa with +AMF promoted biomass accumulation and uptake of nutrients, increased its underground growth, and promoted accumulation of P over N and K. +AMF increased PSII and PSI activities in alfalfa leaves under salt stress, and increased the electron transfer ability of PSII donor and acceptor sides. +AMF not only made alfalfa have relatively high stomatal conductance under salt stress, but also significantly enhanced its ability to utilize CO2.

The effects of elevated CO2 concentration on photosynthetic gas exchange parameters and chlorophyll fluorescence parameters in leaves of Calamagrostis angustifolia seedlings under drought stress were studied through control of different CO2 concentrations (370 and 700 μmol·mol−1) with an artificial OTC climate chamber. The results demonstrated that: Under non-drought conditions, although the stomatal conductance (Gs) and transpiration rate (Tr) decreased slightly as the CO2 concentration increased, while the net photosynthetic rate (Pn) increased significantly, resulting in a significant increase in leaf water use efficiency (WUE). However, the effect of elevated CO2 concentration on PSII reaction center activity was insignificant under non drought conditions. Under severe drought stress, the amount of active reaction centers per unit area and the proportion of PSII absorbed light energy for photosynthetic electron transfer increased, while the proportion of PSII absorbed light energy for heat dissipation decreased, providing energy guarantee for effective fixation of CO2 as dark reaction. In conclusion, elevated CO2 concentration could improve the water use efficiency of C. angustifolia seedlings under normal water and drought stress, and the elevated CO2 concentration could improve the drought resistance ability of C. angustifolia seedlings through PSII function improvement under severe drought stress. [ABSTRACT FROM AUTHOR]

Drought stress led to a decrease in PSII photochemical activity in tobacco leaves and the blockage of electron transfer, especially from QA to QB on PSII acceptor side. In addition, drought stress caused a dramatic increase in H2O2 and MDA contents. However, the overexpression of 2-Cys Prx significantly reduced the H2O2 accumulation in tobacco seedlings and alleviated the degree of oxidative damage under drought stress. It also improved stomatal limitation and net photosynthetic rate of tobacco seedlings and reduced its PSII photoinhibition under drought stress which promoted the ability of PSII electron transfer. [ABSTRACT FROM AUTHOR]

In this paper, the effects of different CO2 concentrations (400 and 800 μmol·mol−1) on photosynthetic gas exchange and chlorophyll fluorescence of mulberry (Morus alba L.) seedling leaves under drought stress were studied using an artificial climate chamber. The results showed that under non-drought conditions, the stomatal concentrations (Gs) and transpiratration rate (Tr) of mulberry seedling leaves decreased slightly with increased CO2 concentrations, but the net photosynthetic rate (Pn) increased significantly. Under mild drought stress (5 days of drought), higher CO2 concentrations significantly affected the photosynthetic gas exchange of mulberry seedling leaves, but had little effect on chlorophyll fluorescence. Under severe drought stress (10 das of drought), increased CO2 concentrations not only alleviated drought stress by increasing the WUE of mulberry seedling leaves, but also significantly increased its PSII photochemical activity, which promoted electron transfer on the PSII acceptor side. In conclusion, increased CO2 concentrations could raise the WUE of mulberry seedling leaves under normal water conditions and drought stress, and this effect was more significant under drought stress. Under severe drought stress, increased CO2 concentrations improved the drought resistance of mulberry seedlings by improving their PSII function. [ABSTRACT FROM AUTHOR]