The abiotic and biotic factors that regulate stability in species-rich forests are poorly resolved, and this limits the ability to predict how climate change and other perturbations impact forest dynamics. Phosphorus limitation and nitrogen deposition are important factors affecting the dynamics and functioning of tropical and subtropical forests, but how long-term temporal stability of tree communities is affected by availability and heterogeneity of soil phosphorus and nitrogen remains unclear. We collected annual dynamic data of 20,768 regenerating saplings, which were censused from 2008 to 2019 in a subtropical forest, to investigate how soil nutrients affect the temporal stability of productivity at both population and community levels. We found that concentrations of soil inorganic phosphorus were significantly and positively correlated with sapling richness and phylogenetic diversity, leading to significantly higher species asynchrony and community temporal stability. By contrast, higher concentrations of organic phosphorus weakened community stability via a negative effect on species richness. Structural equation models provide further strong evidence that increasing concentrations of soil inorganic phosphorus strongly promoted community temporal stability via increased species diversity, species asynchrony and population stability, while organic phosphorus displayed opposite effects. Meanwhile, soil concentrations of available and unavailable forms of nitrogen showed much weaker and negative associations with community stability. Synthesis. Using a 12-year data set of sapling demography from a subtropical forest of south China, our study demonstrates that soil phosphorus is an important determinant of the long-term stability of sapling dynamics and consequently the whole-community structure, and the composition of soil phosphorus pools predicts the temporal stability and diversity of tree communities in phosphorus-limited forests.