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Abstract

This study has surveyed three plots with different groundwater depth (GWD) along the lower reaches of Tarim River in Northwest China. Chlorophyll fluorescence of Populus euphratica (P. euphratica) was investigated to understand the effects of increasing GWD on its photochemical efficiency and activity. Our results showed that the actual photochemical efficiency of photosystem II (PSII) in light-adapted leaves, the electron transportation rate, and the fractions of absorbed light energy used in PSII photochemistry rose first but declined thereafter with the increase in GWD, which was accompanied by an initial declining and then increasing of non-photochemical quenching. However, the maximum efficiency of PSII in dark-adapted leaves is maintained at optimal values. The photochemical activity in moderately drought-stressed P. euphratica is slightly higher than that in relatively well-watered one and significantly decreases with the continuously increasing GWD. Although the ability of P. euphraitca to use light energy significantly declines, with an elevated excess excitation energy, the photosystem can still maintain a normal function. These data suggest that decline in photochemical efficiency and activity due to decreased water availability may not play an important role in the degeneration of P. euphratica at the lower reaches of Tarim River.

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