Estimation of Climatic Productivity by Phytometers (1)

Abstract

A Clement's phytometer, combined with growth analysis technique, was applied to the estimation of climatic productivity, which was tentatively defined as the maximum net assimilation rate per unit photo-synthetic system (leaf area, land area, etc.) of a plant in a given climatic condition.In this experiment, isolated young rice plants, grown up to a definite leaf stage in full nutrition, were used as test plants. The main measure of climatic productivity adopted was the dry matter production rate per dry weight of leaf blade, EB, which was found to be a sensitive and reproducible indicator over a wide range of climatic conditions.As shown in Fig. 3, the plot of EB in g·g-1·day-1 versus daily solar radiation in ly·day-1, I, gave saturation curves, showing linear ascending part approximated byEB=0.00177(I-20) (A)A marked dependence of EB on temperature was observed under sufficient radiation, showing the high Q10 value of 6 at lower temperasures (see Fig. 4). This fact indicates the risk of the calculation of dry matter production from the short term measusrements of photosynthesis and respiration.There seems to be a limit of photosynthetic activity imposed by the capacity of roots. Young rice plants ceased to increase EB under favourable climates when the dry matter production rate per root weight reached to 1.3-1.4g·g-1·day-1 (see Figs. 3, 4, and 5). Rise in air temperature or decrease in solar radiation was accompanied by relative reduction of root system (see Tables 1, 2, 3, and Fig. 2).In plants with full developed roots, the relationship between daily maximum air temperature, Tmax, and EB under sufficient radiation, EB·sat, was approximated byEB·sat=-0.000891 T2max+0, 0811Tmax-1.137 (B)Combining this with equation (A), we obtainIsat=-0.503(Tmax-45.5)2+421 (C)where Isat means the daily solar radiation necessary for saturation of EB, If I is larger than Isat, the equation (B) is adopted, while in the opposite case, equation (A) can be used. Thus the seaasonal change of climatic productivity can be expressed as functions of solar radiation and air temperature.The lower limit of air temperature for net assimilation of young rice plants was inferred to be 17°C in daily maximum or 7°C in daily minimum (see Figs. 4 and 5).