Leaf water potential (ψleaf) and chlorophyll fluorescence (Chl. F) transients were determined in coconut seedlings in the field under intermittent irrigated (non-stress) and un-irrigated (stress) conditions. Stress was imposed by withholding irrigation to the seedlings. With reduction in ψleaf, associated with the increase in soil water deficit as well as micrometeorological variables, the Chl. F traits showed variation. Re-irrigation of the seedlings, although showed recovery of the leaf water status, did not show recovery to the PS II system as revealed by Chl. F values. The reduction in various fluorescence derived ratios viz, Fv/Fm and Fm/Fo as well as t½ (the half rise time from Fo to Fm) implied the blockage of electron flow on the waterside of the PS II and damage to the photochemical apparatus with stress. Observations during different treatment periods clearly revealed that in coconut PS II is highly sensitive to agro-meteorological variables and prolonged drought lead to permanent damage to photosynthetic apparatus. Hence, maintenance of water status of both soil and leaf is highly crucial to protect the PS II system in coconut seedlings during summer months.
Chlorophyll fluorescence, leaf water potential, perennial tree, PS II, stress
