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.

养分限制在植物生长中发挥着关键的调节作用，从而影响生态系统的生产力和碳吸收。缺乏确定最具限制性养分的实验观察，特别是在非洲热带森林中。我们在乌干达进行了生态系统规模的全因子氮 (N)-磷 (P)-钾 (K) 添加实验，该实验由 32 个 40 × 40 m 样地（八个处理 × 四个重复）组成，以调查哪些（如果有）养分限制细根生长。经过两年的观察，添加氮在实验的第一年和第二年迅速降低了细根生物量高达 36%。添加钾使第二年的细根生物量减少了 27%，细根产量减少了 30%。随着氮和钾的限制得到缓解，细根生长的迅速减少凸显了在昂贵的大型细根网络维护方面的碳投资的减少。没有观察到细根生长对磷添加的反应。细根周转率不受养分添加的显着影响，但添加氮处理的细根周转率往往高于不添加氮处理。这些结果表明，N 和 K 的可用性可能会限制生态系统吸收 CO ₂的能力，从而影响生态系统的生产力和对气候变化的适应能力。