Nitrogen cycling in tropical dry forests is sensitive to changes in rainfall regime and nitrogen deposition

Abstract

The impacts of changes in rainfall regimes and atmospheric nitrogen (N) deposition on the biogeochemical cycles of tropical dry forests (TDF) remain unclear. To analyze whether amounts of mean annual rainfall (1240 mm year−1 in subhumid vs. 642 mm year−1 in semiarid forests) and rates of atmospheric N deposition affect the N cycle in TDF, we examined N concentrations in (i) green leaves, (ii) forest floor and mineral soil layers, and (iii) soil microbial biomass, as well as (iv) δ15N natural abundance in green leaves and (v) rates of soil enzyme activity and (vi) N losses in two sites (one subhumid and another semiarid) of Yucatan. The semiarid site had higher N concentrations in leaves and both soil layers than its subhumid counterpart. Natural abundance δ15N in the vegetation suggests a more open N cycle with lower rates of rainfall, which was corroborated by N losses as nitrous oxide (N2O) being twice as high in the semiarid compared to subhumid site. A more open N cycle subject to greater losses in response to N addition in the semiarid site, but not in the subhumid site, reinforce that rainfall amounts strongly affect N cycling in TDF.