Development of an Analytical Model of Whole Leaf Photosynthesis for Soybean.

Abstract

The goal of this research was to develop an analytical model of whole leaf net photosynthesis, capable of predicting photosynthetic rates as a function of incident light intensity, leaf temperature, and CO(,2) and O(,2) concentrations. This modelling effort is aimed at providing a tool for use in ecological studies, and is used here in an attempt to elucidate the phenomenon of photosynthetic acclimation to different growth temperatures in soybeans (Glycine max L.). Soybeans were grown under two growth temperature regimes, and a large amount of gas exchange data were collected for plants grown at each temperature. Gas exchange data were gathered using an open, flow-through CO(,2) measurement system. Sufficient data were collected to permit the determination of the parameters of the photosynthesis model, WHOLEPHOT, developed by Tenhunen et al. (1976a,b; 1977). The predictive ability of the model was tested against an independently obtained set of gas exchange data, and WHOLEPHOT was found to systematically underestimate measured rates of net photosynthesis. A closer examination of this model lead to re-evaluation of certain underlying assumptions, and to the development of a second model. This model, based on Michaelis-Menten kinetics, but relaxing the assumption, implicit in WHOLEPHOT, that RuBP is always nonlimiting, was tested against the same independent data set as WHOLEPHOT, and provided a clearly superior fit to the measured data. Under the growth conditions employed, soybeans were found to acclimate only slightly to the changed temperature regimes. Low-temperature grown plants and slightly greater maximum rates of CO(,2) uptake under optimal conditions, but this advantage was not clearly manifested under ambient conditions.