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EFFECTS OF GROUNDWATER DEPTH ON PHOTOCHEMICAL PERFORMANCE  OF POPULUS EUPHRATICA IN ARID REGIONS OF CHINA

CHENGGANG ZHU¹, YANING CHEN^1*, WEIHONG LI¹, JIANXIN MA¹ AND XIAODONG MA²

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.

Abbreviations: E_max: maximal electron transportation rate; ETR: electron transportation rate; F_m: maximum fluorescence of dark-adapted leaves; F_o: minimal fluorescence of dark-adapted leaves; F_s: actual fluorescence of special time in light-adapted leaves; F_m′: maximum fluorescence of light-adapted leaves; F_o′: minimal fluorescence of light-adapted leaves; F_v/F_m: maximum photochemical efficiency of PSII in the dark-adapted leaves; F_v/F_o: potential activity of photosystem II; GWD: groundwater depth; I_k: semi-saturation light intensity; LWP: leaf water potential; NPQ: non-photochemical quenching; PAR: photosynthetically active radiation; PSII: photosystem II; q_P: photochemical quenching coefficient; P% : fractions of the excitation energy absorbed by the PSII allocated to PSII photochemistry; D%: fractions of the excitation energy absorbed by the PSII allocated to thermal dissipation; X%: fractions of excess excitation energy in the excitation energy absorbed by the PSII; SWC: soil water content; Φ_PSII: actual photochemical efficiency of photosystem II in light-adapted leaves.

¹State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography,

Chinese Academy of Sciences, Urumqi 830011, Xinjiang, China

²Xinjiang Normal University, Urumqi 830054, Xinjiang, China

*Corresponding author’s e-mail: Chenyn@ms.xjb.ac.cn; Phone (fax): 086-991-7823169