RESPONSE OF PHOTOSYNTHETIC RATE AND STOMATAL CONDUCTANCE OF RICE TO LIGHT INTENSITY AND CO2 CONCENTRATION IN NORTHERN CHINA

Abstract

The response of photosynthetic rate and stomatal conductance of rice (Oryza sativa var. Japonica) to changes in light intensity and CO2 concentrations was studied using a Li-6400 in Northern China. In general, photosynthetic rates increased with light intensity and CO_(2) concentrations and could be expressed by a Michaelis-Menten function. Apparent quantum yield increased with CO_(2) concentrations but decreased slightly when CO_(2) concentrations exceeded 800 mol·mol~(-1). Similarly, apparent carboxylation efficiency increased with light intensity but decreased slightly when light intensity exceeded 1600 mol·m~(-2)·s~(-1). The response of stomatal conductance to light intensity can also be expressed by a Michaelis-Menten function, whereas the response to CO_(2) concentrations can be expressed by a hyperbola. If the combined effects of light intensity and CO_(2) concentrations are considered, the photosynthetic rate can be estimated by a Michaelis-Menten equation with a maximum photosynthetic rate of 71.74 mol·m~(-2)·s~(-1). Apparent quantum yield was 0.0560 mol CO_(2)·mol~(-1) photons and carboxylation rate was 0.1031 mol·m~(-2)·s~(-1)/mol·mol~(-1). The response of stomatal conductance (G_(sw)) to light intensity can be expressed by a Michaelis-Menten function too, but the response to CO_(2) concentrations (C_(s)) can be simulated by the equation: G_(sw)=G_(max,c)/(1+C_(s)/C_(s0)) where G_(max,c) is maximum stomatal conductance of stomatal response to CO_(2) under a defined light intensity and C_(s0) is a constant, because the stomatal conductance decreases with increases in CO_(2) concentrations, stomatal conductance can be estimated by G_(sw)=G_(max)(PFD/PFD_(c))/[(1+PFD/PFD_(c))(1+C_(s)/C_(s0))]+G_(ct) in response to the combined effects of CO_(2) concentration and light intensity (I). The potential maximum stomatal conductance, G_(max), can reach 0.6709 mol·m~(-2)·s~(-1) under saturated light levels and CO_(2) near 0 mol·mol~(-1). Ball-Berry model and its revised form can still be used to express the coupled relationship of stomatal conductance and photosynthesis. The simulation precision will be improved if saturation vapor pressure deficit, D_(s), at the leaf surface was used in the Ball-Berry model instead of relative humidity.