Exploring the maintenance of biodiversity in highly diverse ecosystems such as tropical forests is crucial to understand how these systems might respond to environmental change. In successional tropical forests, environmental factors such as light and soil resources (e.g., N, P, K, Ca, and micronutrients) can have an important effect on tree species survival. This effect is particularly important in the seedling community of the forest understory given that those individuals with the greatest probability of survival will establish in the forest community, influencing biodiversity and community composition in these ecosystems. We ask (1) whether soil resources have an effect on seedling survival and (2) whether the role of soil resources on seedling survival changes with forest age along forest stands of different ages. We use seedling survival data from 2012 to 2016 from the Luquillo Long-Term Ecological Research station in El Verde, Puerto Rico. To address our questions, we modeled seedling survival using a generalized logistic mixed effect model with soil resources, seedling size, and irradiance as covariates. Soil resources included macronutrients (N, P, K), micronutrients and pH.
Results/Conclusions
We found positive and negative effects of various soil nutrients on seedling mortality. Larger seedlings growing in soils with high magnesium had greater survival while individuals growing in soils with high aluminum, phosphorus, and pH had reduced survival. These findings highlight potential effects of specific soil resources on seedling survival. High concentrations of aluminum could result in phytotoxicity, by reducing and inhibiting cell elongation and division, especially in root tips. Magnesium and phosphorus are necessary nutrients that may have significant role in seedling mortality during tropical forest succession. The negative effects of these necessary nutrients on survival indicate possible unknown interactions among soil resources, light and conspecific density. Sites with higher soil phosphorus might result in higher competition among individuals resulting in higher mortality. We also found a significant effect of forest age on seedling survival, with lower survival in older forests than early successional sites. The results of this project highlight potential understudied effects of soil nutrients in forest community development. These patterns will be explored further by also looking at growth responses of seedlings to these nutrients. In addition, the interaction among soil nutrients and conspecific density will be explored further to understand mortality patterns.