Tropical tree growth is correlated with soil phosphorus, potassium, and calcium, though not for legumes

Tropical forest productivity is widely assumed to be limited by soil phosphorus (P), but biogeochemical processes that deplete P also could deplete base cations, suggesting multiple resource limitation. Limitation by several resources could arise from species and functional diversity and from variation among groups in resource requirements, including ecophysiological strategies that minimize P limitation. We hypothesized that tree growth is positively related to soil base cation and P availability and negatively related to local competition; Fabaceae growth is weakly correlated with soil resources if fixed N is used indirectly to acquire other resources; growth of species with low wood density is more strongly related to soil resource availability than that of species with high wood density. Diameter growth and soil resource availability were measured in five mapped stands situated across natural soil resource gradients in lowland wet tropical forest (La Selva Biological Station, Costa Rica). Soil resource availability, and associated uncertainty, was estimated for each tree using a Bayesian multivariate spatial regression model, with individual tree growth being a function of diameter, local neighborhood, and soil resources. Separately, site-level mean tree growth and resource availability were modeled using linear regression. Individual diameter growth and site mean basal area increment correlated with soil base cations and P, but rarely with N; individual growth correlated negatively with neighborhood index for only three species. Growth of Fabaceae was unrelated to soil resources at both individual and site levels. When species were categorized by wood density, growth was related to soil P or base cation availability, with the strongest correlation between the lowest-density species and soil P. Several resources may limit tropical forest productivity, because tree growth was similarly correlated with soil P and base cations, but functional groups responded differently. Negligible growth relationships with soil resources in Fabaceae suggest that N fixation may alleviate mineral nutrient limitations. Correlations of soil P with growth of species of low wood density and base cations with species of higher density suggests variation in resource demands among functional groups. Thus, tropical tree growth may be limited by base cations and/or P, with degree and type of resource limitation dependent on functional or taxonomic group.