Growth and mineral nutrition of the native trees Pollalesta discolor and the N-fixing Inga densiflora in relation to the soil properties of a degraded volcanic soil of the Ecuadorian Amazon

Abstract

Land reclamation in the humid tropics, using native tree plantations, requires a better knowledge of plant-soil interactions, and of patterns of growth of several poorly known species. We examined the establishment and mineral nutrition of two early-successional native tree species, Inga densiflora (N-fixing) and Pollalesta discolor, in relation to properties of a degraded Hydrandept volcanic soil in Ecuadorian Amazon. Initial content of organic matter was the most significant soil variable in explaining the growth of pure stands of both species and was strongly related to effective cation exchange capacity (ECEC) and to net total N mineralization. Leaves of Pollalesta discolor had greater concentration of nutrients than Inga densiflora, which led to a litter-layer rich in nutrients. Deficient concentrations of foliar P, detected on plots with low soil organic matter, were linked to poor growth of Inga densiflora, and indicate that this species may be P-limited. The inclusion of Inga densiflora did not stimulate the growth of Pollalesta discolor in mixed stands. This study indicates that soil organic matter management is an important issue on these degraded volcanic soils. We suggest that a reduction of the pool of labile organic matter appears to hamper tree productivity through a nutrient shortage. The high variability of the degraded soil studied proved to be an obstacle to tree growth and establishment.