Restoration of N dynamic in the soil of a tropical rainforest in México

Background/Question/Methods Restoration of tropical rain forest areas has been an interesting issue in the last years. The accelerate land-use change affects the distribution and pool of soil nutrients. In this scenario is a necessity to evaluate the potential of reforestation programs to restore biogeochemical process of soil. We asked the following question: What is the effect of reforestation on nitrogen cycle in soil of areas converted to pastures in the tropical forest? In this study, nature and size of soil nitrogen (N) pools and turnover were compared in pasture, mature forest and reforested sites in a humid tropical region, near to The Tropical Biological Station Los Tuxtlas of Mexico. Total N, microbial biomass N, mineral (ammonium and nitrate) N, dissolved (total and inorganic) N pools and potential N transformations were measured in samples collected in open-pasture, closed-pasture, one-year reforested plots, and mature tropical rain forest sites along slopes (256-195 masl).

Results/Conclusions Soil total N decreased in the following order mature forest > close-pasture > open-pasture ≈ reforested sites. After one-year of reforestation the concentrations of inorganic N (NO₃ plus NH₄), microbial biomass N, and the potential N transformations in the soil did not change. On the other hand, mature forest registered the greatest total and inorganic dissolved N concentrations, whereas pastures and reforested sites had the lowest dissolved N concentrations. Concentrations of total and dissolved N, and inorganic N in all sites were the greatest in the lower slope position. Our study on the consequences of the land cover change and reforestation on soils, following the discontinuation of cattle grazing, suggest that the restoration of N pools appear start with changes in dissolved forms of the nutrient.