EFFECT OF SOIL PHYSICAL AND WATER STRESS ON BIOCHEMICAL ASPECTS OF COCONUT SEEDLINGS (Cocos nucifera L.) IN SRI LANKA

Abstract

Soil physical and water stress conditions adversely affect the biochemical aspects of coconut production. Field experiments were conducted in Madampe and Andigama soil series, to investigate the ATPase activity, starch conversion to glucose and accumulation of proline in leaves, absorption cells and respiratory organs of coconut roots and their interrelationships with respect to soil physical and water stress. After one and half years of the establishment of coconut seedlings in different horizons of both series, the moisture contents at three depletion levels viz.10 kPa to 30 kPa, 10 kPa to 100 kPa and 10 kPa to 1500 kPa were maintained using tensiometers and neutron scatteringtechnique in order to create moisture stress around root zone of coconut seedlings during the dry period. Detailed soil physical analysis showed that soil compaction limits the aeration and available water retention in soil horizons of both series. Evaluation of biochemical properties showed that the highest ATPase activity and starch conversion to glucose in leaves and absorption zone of coconut roots was observed in the B horizon of Madampe series at field capacity moisture level (10 kPa to 30 kPa suction), while the lowest activity was observed in the A horizon of Madampe series and B horizon of Andigama series at high water stress condition (100 kPa to 1500 kPa suction). However, the highest ATPase activity and starch conversion rate was observed in respiratory organs in A horizon of Madampe series. Moreover, the starch and proline accumulation in different parts of coconut seedling positively related with soil physical and water stress conditions (100-1500 kPa) prevalence in ‘A’ and ‘B’ horizons of Madampe and Andigama series respectively.