Studies on Plant Response to Rainfall.

Abstract

The present investigation was designed to examine the differences between the effects of rainfall and those of submergence. The growth response and injury of kidney bean plants were examined after the artificial rainfall (mist), root submerging and whole plant submerging treatments. Plants were exposed to mist (Precipitation: 5mm/h, Diameter of water drop: 0.24mm) or submerged in the growth chamber (20°C, 12hr light+12hr dark) for 5 days.(1) Growth response and injury immediately after the treatments:Considerable differences in growth response and injury were observed with the three treatments. In general, the inhibitory effects on growth and injury immediately after the treatments were marked on the shoot by mist, on the root by root submergence and on both the shoot and root by whole plant submergence.Mist treatment decreased the area, dry weight and chlorophyll content of the leaves, but it increased the fresh weight of the stem and elongation of the root (longest root). The greatest wilting response was observed one hour after the end of mist exposure.Root submergence decreased elongation, fresh weight and dry weight of root, but increased the dry weight of the stem. Wilting was not observed.Whole plant submergence decreased markedly elongation, fresh weight of the leaf and root, dry weight of the shoot and root, and chlorophyll content of the leaf. Wilting was observed, but its degree was weaker than that of mist.(2) Growth response and injury 12 days after the treatments:Mist treatment caused growth inhibition, but the degree of inhibition was weaker than that immediately after the treatments. The aftereffect of mist remained on fresh weight of leaf and dry weight of shoot and root to some extent. Foliage leaves that opened after mist treatment were injured strikingly.Root submergence decreased root length, leaf area, fresh weight (leaf, stem) and dry weight (shoot, root) to some extent, but foliage leaves were not injured.Whole plant submergence decreased elongation, fresh weight and dry weight of shoot and root to a great extent. Foliage leaves were injured, but less severely than by mist.These results suggest that the exposure to rainfall not only causes weak effects of submergence, but also has a different action on the plant.