Photosynthetic characteristics and productivity of the coconut palm

Abstract

Among the tree crops in the tropics the coconut palm occupies an important position as a food, oil, and fibre crop. Productivity of crop species depends on the combined effect of their genetic constituion, climate, nutrition and other biotic factors. To increase the productivityof coconut palm it is necessary to have a basic understanding of physiological processes such as assimilation of carbon and growth in relation to climatic factors. In-situ photosynthetic measurement of coconut seedlings using Li-COR 6500 portable photosynthesis system revealed that their maximum photosynthetic capacity is attained at photosynthetic photon flux densities (PPED) ranging from 1400-1700 moles photons m-2 s-1. The rate of apparent photosynthesis (A) of the coconut palm varies between 2-15 m mol CO2 m-2S-1 depending on leaf age, nutritional status and climatic factors. The rate of leaf respiration was closely similar in young and older leaves ranging from - 2 to 1 m mol CO2m-2S-1. The measured light-use efficiency of the coconut palm was found to be 1.2 g MJ-1 and the conversion efficiency of solar energy was approximately 2.4 per cent. Water deficit is the major constraint causing wide fluctuations in photosynthesis. due to height of trees, the leaves in the canopy are exposed to high wind velocity as well as water and thermal stressess. As a result, under soil water defict conditions coconut palm reduce excessive water loss and gaseous echange by mid-day closure of stomata and maintain stomatal conductance at a lower level. However, the rate of apparent photosynthesis and the ratio of intercellular to ambient partial pressure of CO2 (Pi/Pa) are not decreased proportionately with the stomatal conductance.