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Abstract

Light energy partitioning, photoprotection and influencing factors of photosystem II in an exotic species (Salix psammophila) in Mu Us sandy land.

Abstract

With the technique of in situ continuous monitoring of chlorophyll fluorescence, the energy distribution of photosystem II in Salix psammophila and its response to environmental factors were explored in the semi-arid area of Mu Us sandy land. The dynamic effects of environmental factors on energy distribution of the photosystem II and their photosynthetic physiological adaptation strategies were revealed in the daily and seasonal scales, in order to provide theoretical guidance for vegetation restoration management and species selection in the study area. Method: Chlorophyll fluorescence was continuously measured in situ and fluorescence parameters were calculated using Kramer methods of light energy allocation. Result: At the diurnal scale, photochemical efficiency φ PSII and regulated heat dissipation φ NPQ were directly related to photosynthetically active radiation (PAR), and also influenced by air temperature (Ta), relative humidity (RH) and vapor pressure deficit (VPD). The non-regulate heat dissipation φ NO was relatively stable. At the seasonal scale, at the early stage of the growing season (May-June), φ PSII and φ NPQ partitioning is relatively uniform, φ NO was higher and remained stable. Maximum quantum yield of PSII photochemistry (Fv/Fm) declined. In the mid-growing season (July - September), August φ PSII significantly decreased and φ NPQ rose. At the end of the growing season (October), φ PSII was lowest, φ NPQ was highest, and φ NO value was higher and more stable. Fv/Fm declined. Conclusion: On the daily scale, the energy partitioning of photosystem II is mainly affected by PAR and Ta, while it is less regulated by RH and VPD. At the seasonal scale, energy partitioning is mainly regulated by the phenological period. Fv/Fm is significantly correlated with PARmax (R2 = 0.13, P < 0.01), Ta variation (R2 = 0.16, P < 0.01) and soil moisture content (SWC) (R2 = 0.19, P < 0.01), indicating that high radiation, extreme temperature and drought are the main environmental stress factors limiting the photosynthetic physiological state of Salix psammophila. Energy partitioning is likely to be caused by the difference between the short-term regulation mechanism such as photosystem II lutein cycle and the long-term regulation mechanism such as chlorophyll. The results enrich the physiological plasticity theory of desert plants in response to environmental fluctuations and provide a scientific basis for vegetation restoration in semi-arid regions.