Replicated Data for: Nitrogen and potassium limit fine root growth in a humid Afrotropical forest

This data on fine root growth response to nutrient additions was collected as part of the RELIANCE project in Uganda involving an ecosystem-scale full factorial nutrient (N, P, K) manipulation experiment. We established 32 (eight treatments (control, N, P, K, NP, NK, PK, NPK) × four replicates) 40 × 40 m plots, and nutrients were added at 125 kg N ha−1year−1, 50 kg P ha−1year−1 and 50 kg K ha−1year−1. The dataset includes fine root biomass, fine root production, and fine root turnover rate. Abstract: Nutrient limitations play a key regulatory role in plant growth, thereby affecting ecosystem productivity and carbon uptake. Experimental observations identifying the most limiting nutrients are lacking, particularly in Afrotropical forests. We conducted an ecosystem-scale, full factorial nitrogen (N)-phosphorus (P)-potassium (K) addition experiment consisting 32 40 × 40 m plots (eight treatments × four replicates) in Uganda to investigate which (if any) nutrient limits fine root growth. After two years of observations, added N rapidly decreased fine root biomass by up to 36% in the first and second years of the experiment. Added K decreased fine root biomass by 27% and fine root production by 30% in the second year. These rapid reductions in fine root growth highlight a scaled-back carbon investment in the costly maintenance of large fine root network as N and K limitations become alleviated. No fine root growth response to P addition was observed. Fine root turnover rate was not significantly affected by nutrient additions but tended to be higher in N added than non-N added treatments. These results suggest that N and K availability may restrict the ecosystem’s capacity for CO2 assimilation, with implications for ecosystem productivity and resilience to climate change.