Diurnal Expansion and Contraction of Leaves and Fruits of English Morello Cherry1

Abstract

Changes in leaf thickness and fruit diameter were measured in growth chambers under varying conditions of light, humidity, temperature, and soil moisture for potted trees of English Morello cherry (Prunus cerasus L. grafted on Prunus mahaleb root stock). Decrease in leaf thickness of well-watered plants was induced by illumination following a period of darkness. In the light, leaf thickness decreased when vapour-pressure deficit (VPD) was rising or high. The magnitude of diurnal change in leaf thickness was related to amount of change in VPD of the air. Leaf thickness increased in the dark when stomata were closed. When changes in VPD were minimized, leaves under 8-h days and 16-h nights still decreased in thickness during the day and expanded at night, but the degree of change was not as great as when VPD also fluctuated diurnally. When severe internal water deficits developed in trees during prolonged droughts the correlations of changes in leaf thickness with VPD and light intensity were low. Marked decline in leaf thickness resulted with little re-expansion in the dark at low VPD. Soil irrigation resulted in rapid hydration and expansion of leaves. Changes in fruit diameter in contrast were positively correlated with VPD fluctuations and were not influenced by photoperiod.