Tolerance ofAlbizia zygia (DC) Macbride, a Shade Tree for Cocoa, to Soil Acidity and Water Stresses

Abstract

This paper reports the results of the study carried out to assess the tolerance to soil acidity and drought of Albizia zygia (DC) Macbride, which is one of the West African native tree species growing wild and used to provide shade for cocoa, with a high potential for amelioration of degraded cocoa soils. The results of the present study indicate that A zygia is tolerant to soil acidity. The species also exhibited characteristics of drought avoidance. Stomatal control was found to serve as a protective mechanism against excessive water loss when the seedlings were exposed to drought. The relationship between leaf water content and xylem pressure potential also indicated an ability of the species to maintain a given level of water tension throughout a certain degree of tissue dehydration. The high root : shoot ratio obtained for A zygia in this experiment suggests that the species is adapted to a resource limited environment. The increased magnitude of instantaneous relative growth rate in well-watered plants compared to water-stressed plants also indicates the overriding effect of changes in the instantaneous unit leaf rate on growth in A zygia subjected to different watering regimes.