Ecological Studies on the Photosynthesis of Winter Cereals : IV. Model simulation of dry matter growth of six-rowed barley

Abstract

A model for simulation of dry matter growth of six-rowed barley was built and formulated with a simulation language DYNAMO, for the purpose of studying the ecophysiological relationships between photosynthetic function and crop growth including production of grains. General structure of the basic model are outlined as follows (see also Fig. 1 and Fig. 2). 1. Photosynthesis and respiration of various organs: It is assumed that all the cars distribute in the top layer of the canopy, and that the other organs with photosynthetic ability (leaf blades, leaf sheaths and a part of culms) distribute uniformly in the layer beneath the ears. The daily gross photosynthesis of the canopy was calculated by the equations (2) and (3), which were obtained by modifying the equation of KUROIWA (1961). The parameters relating to the photosynthetic and respiratory functions were determincd based on the observed data (Fig. 3-Fig. 12). 2. Distribution and redistribution of photosynthate to various organs: In the basic model, dates for germination and heading were fixed to November 5 and April 24, respectively. Time trends in the distribution ratios in Fig. 13 were used in every simulation run to calculate allocations of photosynthate to various organs. Redistribution, or import of stored organic matter from other organs; was assumed to occur only in ears (Fig. 14). 3. Death of various organs: Life spans of the plant organs except for ears and roots were assumed to be longer in winter than in spring (Fig. 15). Death rate of each organ was obtained with the exponential delay function of the DYNAMO language. Model simulation of the plant growth was made for the period of 175 days from the 30th day to the 205th day after the germination (Nov. 5), and gave the following results. 1. Results of the basic simulation run showed the normal growth pattern in total dry weight and ear dry weight of six-rowed barley, suggesting that the greater parts of the parameters used in the basic model may be appropriate. 2. Sensitivity analysis of the model was made by changing parameters relating to the photosynthetic functions and initial values. The results of analysis are summarized as follows: 1) There existed the optimal LAI value for the grain production. 2) Contribution of photosynthesis by ears, leaf sheaths and culms to grain production of barley was rather great. Improvement of photosynthetic ability of these organs resulted in increase of grain production. 3) This model showed sensitive reaction when the parameters relating to the light-photosynthesis relationship were changed. 4) When the inhibitory effect by low temperature on photosynthesis was reduced, the LAI tended to be over-optimal in spring. 5) When the life span of photosynthetic organs was prolonged at the later growth stages, the grain production was increased conspicuously. 6) The effect of changing SLA on the grain production was slight. 7) It was suggested that there exist suitable soiling period for barley to give considerable amount of green fodder without reducing the grain production.