Litterfall and nitrogen-use efficiency of plantations and primary forest in the eastern Brazilian Amazon

Abstract

Aboveground fine litterfall and decomposition are critical processes for transferring nutrients from forest biomass to soils, and the conversion of Brazilian terra-firme forest to tree plantations with varied litterfall characteristics has altered soil nitrogen (N) dynamics and stores at the Curuá-Una Forest Reserve, Pará, Brazil. In this study, we investigated the relationship between soil N stores and aboveground litter inputs by measuring fine litterfall, litter N inputs, forest-floor mass and turnover, foliar N concentrations, and within-stand nitrogen-use efficiency (NUE) for one year under four plantations and adjacent undisturbed forest. The plantations consisted of replicated plots of Pinus caribaea var. hondurensis (36-year old), Carapa guianensis (36-year old), Euxylophora paraensis (23-year old), and a Leguminosae combination ( Parkia multijuga, Dinizia excelsa, and Dalbergia nigra, all 36-year old). Fine litterfall ranged from 8.0 ( Euxylophora paraensis) to 10.3 t ha −1 year −1 ( Pinus caribaea), forest-floor mass from 7.2 (forest) to 11.0 t ha −1 ( Pinus caribaea), total fine litterfall N inputs from 43 ( Pinus caribaea) to 134 kg ha −1 year −1 (legumes), and foliar N concentrations from 9 ( Pinus caribaea) to 18.8 mg g −1 (legumes). Relative to adjacent terra-firme forest, total N stores in surface mineral soils, forest-floor mass, and fine roots (live+dead) ranged from a net decrease of 25.6% under Pinus caribaea to a net increase of 14% under Euxylophora paraensis. The replacement of terra-firme forest with plantations of tree species with varied phenologies and resource requirements altered soil N stores, but these changes were not related to total fine litter N inputs, needle and foliar N concentrations, or within-stand nitrogen-use efficiency.