Studies on Plant Response to Rainfall

(I) Effect of Rainfall on Dry Matter Production of Plant Leaves

Abstract

Effect of rainfall (mist) on dry matter production in the leaves of kidney bean (Phaseolus vulgaris L.), sweet potato (Ipomoea batatas Lam.) and maize (Zea mays L.) was investigated. The rate of dry matter accumulation was measured by using the improved half-leaf method. The results were as follows.
1) On rainy days, dry matter accumulation rates of these crops exposed to rainfall showed 30-50% lower values as compared with those of crops protected from rain by a plastic roof, though the light intensity in the former was greater 10% than that in the latter.
2) The mist treatment in growth chamber also decreased the rates of dry matter accumulation of crop leaves. The effect of mist treatment was rather smaller on maize than on kidney bean or sweet potato. From the response curves of accumulation rates to various intensities of light, it was noticed that light compensation point of these crops was about 1000-1500lux, but it became higher up to 2000-2500lux with mist treatment.
3) The effects of mist treatment on environmental factors such as air- and leaf-temperature and light intensity in the growth chamber were markedly small. Therefore, it can be considered that the effect on dry matter production rate is apparently an effect of rainfall (mist) itself rather than an effect of environmental conditions produced by mist treatment.
Two reasons may be suggested to explain these phenomena. First, the layer of rain water on the leaf surface prevents the exchange of gases, and the photosynthetic activity of the leaf is suppressed. Second, carbohydrates may be leached from leaves by rainfall.