Responses of Tropical Tree Seedlings to Nutrient Addition: A Meta-analysis to understand future changes in Tropical Forest Dynamics

Abstract

Purpose of the Review: The escalating impacts of human activities and climate change, particularly increased nutrient leaching and deposition, could significantly alter the productivity, structure, and function of tropical vegetation. To better understand how nutrient deposition affects regeneration in tropical ecosystems, we synthesised studies that added N, P, NP, or NPK to the seedlings of tropical tree and shrub species. Recent Findings: In the tropics, nutrient limitation leads to multiple resource constraints. Our systematic review and hierarchical meta-analyses aimed to: (1) test the effect of nutrient addition on the growth rate and biomass allocation of seedlings of tropical species; (2) examine seedling responses across climate-defined groups; (3) quantify the effects of experimental methods and wood density on species’ responses to experimental fertilisation. Summary: Overall, nutrient addition increased seedling shoot biomass by 26% and growth rates by 14%. Pot and transplantation experiments demonstrated stronger positive effects than in-situ observational studies. Nutrient combinations yielded the highest growth rates (NPK: 27%, and NP: 18%), and N was critical for shoot biomass (N: 38%, and NP: 48%). The responses of shoot biomass indicated co-limitation of N and P, but also high variability in seedling responses to individual nutrients. Temperature and precipitation had indirect regulating effects, while seasonality showed the strongest impact in seasonally dry sites (38% growth rate and 70% shoot biomass). Species showed individual responses to nutrients, influenced by biotic and abiotic interactions. Finally, we suggest tracking additional parameters, like forest successional status, that may intensify nutrient deposition effects on tropical soils due to climate change.