毛竹(Phyllostachys pubescens)叶光合作用的气孔限制研究

运用Farquhar和Sharkey(1982)提出的两个判据——细胞间隙CO_2浓度(C_i)和气孔限制值(L_s),从几个不同的侧面研究了毛竹光合作用的气孔限制。虽然观测到气孔导度(G_s)与光合速率(P_n)随着气温、光量子通量密度的降低和叶水分胁迫的加剧而大体上平行地下降,但是在低的环境温度、低的光量子通量密度和严重的水分胁迫下,气孔导度的下降不是光合速率下降的主要原因,因为这时C_i在上升,而L_s下降。然而,在低的空气湿度和轻微水分胁迫下,C_i的下降和L_s的上升都证明,这时气孔导度的下降是光合速率降低的主要原因。

STUDIES ON STOMATAL LIMITATION OF PHOTOSYNTHESIS IN THE BAMBOO (Phyllostachys pubescens) LEAVES

Net photosynthetic rate (P_n) measurements were made on the leaves of Phyl-lostachys pubescens using an ADC portable gas analysis system under differentcombinations of air temperature, photon flux density (PFD), air humidity andleaf water potential. Analysis of stomatal limitation of photosynthesis was carriedout with two criteria suggested by Farquhar and Sharkey (1982), i.e., intercellularCO_2 concentration (C_i) and stomatal limiting value (L_s), which were,calculatedaccording to Berry and Downton's method (1982).When air temperature was decreasing from autumn to winter, P_n, stomatalconductance (G_s) and L_s were declining simultaneously, while C_i was increasing.The seasonal changes in these parameters indicated that the decrease in P_n maynot be due to stomatal factor.As air humidity decreased, P_n and G_d declined proportionally, and in themeantime C_i decreased and L_s increased, showing that the decrease in P_n wasdue mainly to the decrease in stomatal conductance.At low PFD the decrease in P_n was accompanied by a decrease in G_s and L_s,and an increase in C_i. In this case P_n was limited obviously by energy supplyrather than by CO_2 supply.Leaf P_n and G_s declined sharply after detachment. At first, while waterstress was developing, C_i declined and L_s increased. However, as the water stressbecame severe, C_i began to increase and L_s decreased. It seems that stomatalclosure is the major limiting factor of P_n under mild water stress, but under severewater stress the main limitation of photosynthesis is in the photosynthetic capacityof mesophyll cells.From these results, we conclude that stomatal conductance limits P_n in somecases. However, it is not always the predominant limiting factor of photosynthesisthough parallel changes in P_n and G_s are often observed.