Continuous High Temperature Affects Chlorophyll α Fluorescence of Alhagi sparsifolia at Southern Taklamakan Desert

Climate change affects organism habitats through direct temperature warming and increased frequency of extreme weather events. High temperature modifies the structure and damages the photosystem II (PSII). Temperatures higher than the optimal level for plant growth result in the deterioration of the structure and function of photosynthetic proteins, consequently leading to a decrease in photosynthetic efficiency.

PSII, with its oxygen-evolving complex (OEC), is one of the three major stress-sensitive sites in the photosynthetic machinery. Chlorophyll α fluorescence kinetics are an informative tool for studying the effects of different environmental stresses on photosynthesis and can thus be employed as the main method in the investigation of the function of PSII and its reactions to changes in the environment and growth conditions. PSII contains a number of sensitive proteins. High temperature can decrease the electron transport capacity in the acceptor side of PSII as well as the activity of the OEC.

Alhagi sparsifolia is an important species for wind prevention and sand fixation in the forelands of the Taklamakan Desert. However, the effects of high temperature on desert plants remain widely unknown.

To investigate how PSII in A. sparsifolia, LI Lei et al. set a series of temperature and time gradients in the early August 2011. Chlorophyll α fluorescence induction kinetics were investigated at different time stresses of 5, 20, 40 and 60 min at temperature gradients of 38°C–44°C at 2°C intervals. A pronounced K-step was found, and the values of the maximum quantum yield for primary photochemistry, the quantum yield of electron transport, the density of reaction centers and the performance index on absorption basis were lowest after 60 min at 44°C, thus indicating that the oxygenevolving complex was damaged, the inactivated reaction centers increased, and the activity of the photosystem II (PSII) reaction center in leaves was seriously limited.

Therefore, researchers suggest that under normal temperature (below 42°C), the PSII of A. sparsifolia would be unaffected. When such temperature is maintained for 40 min, the activity of PSII would be limited, and when retained for 60 min, PSII may be severely damaged. The result was published in Acta Physiologiae Plantarum in February 2014.