Patterns of nutrient immobilization and release in decomposing forest litter in Central Himalaya, India

Abstract

(1) Decomposition of leaf litter from ten woody species was studied using litter bags incubated for a two-year period in five forest ecosystems in Central Himalaya. In addition, Quercus leucotrichophora leaf litter was placed in each forest site to provide uniform substrate quality. (2) The annual weight loss ranged from 47% to 100% among species. Differences between sites and species were significant. (3) Most of the species exhibited two phases in their nutrient dynamics, a net immobilization phase followed by a net release phase. Net immobilization of N and P occurred in all litter species except Mallotus philippensis, Lyonia ovalifolia and Quercus leucotrichophora, while Ca and K exhibited only a release phase except in Pinus roxburghii and Myrica esculenta, where net immobilization of Ca occurred for a short period. The periods of net immobilization of various nutrients overlapped to a considerable extent. (4) Material with higher initial C: nutrient ratios had a longer duration of immobilization and, in turn, a slower release phase. Linear regression analyses between concentrations of pairs of nutrients during decomposition indicated positive relationships between N and P and between K and Ca, and negative relationships between combinations of N or P and Ca or K. (5) The critical C:N ratio (at which net release of N occurred), varied from 15:1 to 55:1. The species having higher N contents (1.20-3.04%) had higher weight loss rates and species having low N contents (0.85-1.01%) exhibited lower rates. (6) Species having more than 17% initial lignin accumulated more N whereas species with a lower (<17%) lignin content showed little or no accumulation of N. (7) Mean annual temperature, altitude and lignin content were the principal regulating factors for weight loss and nutrient mineralization.