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利用Li-6400光合作用系统,在自然条件下对塔里木河上游地区天然灰杨的净光合速率(P_n)、气孔导度(G_s)、胞间CO_2的浓度(C_i)、蒸腾速率(T_r)和水分利用效率(WUE)等生理指标进行测定。结果表明,灰杨的P_n、T_r日变化均呈“双峰”曲线,并且存在“光合午休”现象;G_s日变化呈“双峰”曲线,C_i与WUE均在8:00达到最大值,随后逐渐呈下降趋势。上午灰杨P_n降低主要是由于气孔限制造成光抑制所致;下午P_n再次降低,主要是由于外界光强下降所致。
The net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO_2 concentration (C_i) and transpiration rate (T_r) of natural aspen population in the upper reaches of the Tarim River under natural conditions were calculated using Li-6400 photosynthesis system Water use efficiency (WUE) and other physiological indicators were measured. The results showed that the diurnal variations of P_n and T_r showed “double peak” curve, and there was a phenomenon of “midday depression”. The daily variation of G_s showed a “double peak” curve with C_i and WUE at 8: 00 reached the maximum, then gradually showed a downward trend. The decrease of P_n in the morning was mainly due to the photoinhibition caused by stomatal limitation. The decrease of P_n in the afternoon was mainly due to the decrease of external light intensity.