Soil invertebrates facilitate plant nitrogen assimilation in a tropical seasonal secondary forest

Nitrogen (N) is an essential nutrient for plant growth, and its availability frequently constrains primary productivity during forest recovery¹. Soil invertebrates play a crucial role in N mineralization during litter decomposition²; however, whether they regulate downstream plant N assimilation remains unclear. To address this knowledge gap, we carried out a 15-month invertebrate exclusion experiment in a tropical seasonal secondary forest, using N-stable-isotope (¹⁵N) tracers to track N transfer from ¹⁵N-labeled-leaf litter to plant leaves in the presence or absence of soil invertebrates. We found invertebrates increased ¹⁵N atom excess in plant leaves by 59.4% by enhancing ¹⁵N release from ¹⁵N-labeled-leaf litter by 6.3%. This study provides direct evidence that soil invertebrates represent an underappreciated pathway linking biodiversity, primary productivity, and nutrient cycling. As active regulators of plant nutrition and N turnover, soil invertebrates are crucial for plant growth and carbon sequestration¹, especially in secondary forests that are increasingly becoming the predominant forest type in tropical regions³.