Stochastic Dynamics of Gross Soil Nitrogen Transformations in Amazon Forests—High Local Variation but Lack of Basin-Wide Patterns

Tropical forests play a critical role in global climate regulation by taking up and storing significant amounts of carbon. Soil nitrogen (N) dynamics is the key to understanding forest productivity. However, we have only a very rudimentary understanding of in situ soil N transformations in the Amazon Basin, the largest intact tropical forest. This study investigated gross soil N dynamics across 12 locations in the Brazilian Amazon Basin using ¹⁵N labeling to quantify gross N transformations in situ. Our results revealed significant variation in both gross N mineralization and nitrification at the local and basin-scales. Unexpectedly, no spatial patterns were observed across locations, nor were gross N rates correlated with any measured soil properties. Our results suggest a stochastic and unpredictable nature of gross N transformation rates in the rainforests of the Amazon basin. These findings highlight the need for a more nuanced understanding of N cycling in tropical forests, which could improve ecological models and inform strategies for managing these ecosystems in the face of climate change and deforestation.