Tropical forest productivity is increasingly reported to be nutrient limited, which may affect its response to seasonal droughts. Yet experimental evidence on nutrient limitation from Afrotropical forests remains rare. We conducted an ecosystem-scale, full factorial nitrogen (N)–phosphorus (P)–potassium (K) addition experiment in a moist forest in Uganda to investigate nutrient controls on fine litter production and foliar chemistry. The eight factorial treatments were replicated four times in 32 plots of 40 × 40 m each. During the three-year nutrient additions, we found K and P limitations on leaf litter production, exhibiting strong links to ecosystem responses to seasonal drought. Specifically, leaf litterfall consistently decreased in dry seasons with K additions, whereas P additions caused a reduction only during prolonged drought in the first year. Leaf litterfall was not significantly affected by N additions. Furthermore, K additions delayed the timing of leaf litterfall peak, underscoring the crucial role of K in regulating stomatal aperture and signalling during water-stress conditions and suggesting a prolonged leaf lifespan. Foliar N increased with N and P additions whereas K was the most resorbed nutrient. We conclude that the productivity and resilience of tropical forests, particularly under drier conditions, may depend on terrestrial K and P availability.

越来越多的报道称热带森林生产力受到养分限制，这可能会影响其对季节性干旱的反应。然而，关于非洲热带森林养分限制的实验证据仍然很少。我们在乌干达的潮湿森林中进行了生态系统规模的全因子氮 (N)-磷 (P)-钾 (K) 添加实验，以研究对细小凋落物产生和叶面化学的养分控制。 8 个因子处理在 32 个小区（每个小区 40 × 40 m）中重复四次。在三年的养分添加过程中，我们发现钾和磷对落叶层产量的限制，这与生态系统对季节性干旱的反应有密切的联系。具体而言，添加钾后，旱季落叶量持续减少，而添加磷仅在第一年的长期干旱期间导致减少。添加氮肥对落叶没有显着影响。此外，钾的添加延迟了落叶高峰的时间，强调了钾在水分胁迫条件下调节气孔孔径和信号传导的关键作用，并表明叶片寿命延长。叶面氮随着氮和磷的添加而增加，而钾是吸收最多的养分。我们的结论是，热带森林的生产力和恢复力，特别是在干燥条件下，可能取决于陆地钾和磷的可用性。