Photosynthesis, Light Acclimation of Photosynthesis and Chlorphyll Fluorescence of Lemon in Response to Water Stress and Shading

Abstract

The combined effects of water and light on net photosynthesis (A) of rooted cuttings of lemon (Citrus limon L. Burm.f. Eureka) were investigated to determine if the effects of water stress and shading are interactive. Treatments investigated included sufficient water +full light (control), water stress + full light, sufficient water + shade and water stress + shade. Under ambient conditions, the main effects of water stress significantly decreased A, g_s, and chlorophyll content. It increased C_i. Mean effects of shading decreased A and NPQ. It significantly increased F_m, and F_v/F_m. Water×light interactions were not significant for A, g_s, C_i, chlorophyll content, F_o, F_vF_m, qP and NPQ. But they were significant for F_m, and Yield. Under controlled environment, the mean effects of water stress on A were as for ambient conditions, but the effects of shade were reversed. Water×light interactions significantly influenced A at irradiance of 50 and 300μmol m^-2 s^-1 but not at 600 μmol m^-2 s^-1. At 300 μmol m^-2 s^-1, shaded sufficiently watered plants had significantly higher A than plants grown under the other water×light combinations. Water stressed plants grown in full light were photoinhibited at 50-600μmol m^-2 s^-1. Water stress and shading effects on A are interactive if leaf environment is controlled.