Diurnal variation studies in leaves of custard apple (Annona squamosa) cv. Arka Sahan

The plant canopy regulates the exchange of carbon, water and energy between the ecosystem and atmosphere and provides a habitat for a wide variety of ecospecies. Understanding the canopy processes with respect to diurnal variation is important for carbon sequestration predicting the effects of global changes in climate and atmospheric chemistry on the functioning of horticultural ecosystems. Diurnal net photosynthetic rates (Pn) of custard apple cv. Arka Sahan were determined in a new orchard of two years age during September, 2010. There was a pronounced fluctuation in Pn for the whole plant along with variations in the other parameters such as stomatal conductance, transpiration rate, leaf temperature, internal CO₂ concentration from 8.00 am to 6.00 pm. Peak Pn occurred before solar noon, remained static for 1 h - 2 h and then declined. Pn showed highly significant and positive correlation with stomatal conductance, (gs) (r = 0.852*) and relative humidity (rh) (r = 0.963**). Intrinsic water use efficiency was maximum in the morning, minimum during mid day and increased in the evening. The results from the study may be to study the carboxylation efficiency of custard apple plants under vertisols which is a new introduction to Jhalawar district of Rajasthan, India