Precipitation regimes influence differently the biogeochemical cycles of the tropical dry forest

Tropical dry forests (TDFs), comprising ∼40 % of all tropical forests, are crucial for global biogeochemical cycling and a leading driver of global interannual variation in net carbon dioxide exchange. Their sensitivity to precipitation variability affects microbial activity, nutrient mineralization, and organic matter decomposition, yet their responses to environmental change remain insufficiently understood. This study evaluates how different precipitation regimes—annual precipitation, seasonal precipitation, and El Niño events—on the biogeochemical cycling of carbon (C), nitrogen (N), and phosphorus (P) in TDFs. Using long-term datasets on biogeochemistry and plant diversity (both taxonomic and functional), we isolated precipitation effects through a multi-ensemble approach. Our results highlight the role of plant biodiversity–soil interactions in shaping population, community, and ecosystem level responses. Annual precipitation emerged as a key driver of functional trait expression and C cycling. This resulted in a negative trend for most C and N metrics, while the ratio of soil basal respiration to microbial C showed a positive trend. Seasonal precipitation explained much of the variation in N cycling, with wet seasons linked to elevated N metrics and dry seasons associated with higher dissolved organic C and microbial biomass. Post-El Niño recovery of soil C and N required at least two years. While P cycling was influenced by annual precipitation, the effect was not significant. These findings advance our understanding of TDF vulnerability under climate change, emphasizing how changes in rainfall regimes may reshape biogeochemical processes. Notably, our results suggest that TDFs may shift from C sinks to sources under scenarios of intensified drought and incomplete ecosystem recovery after stronger and more frequent drought events.