Isolating the effects of precipitation, soil conditions, and litter quality on leaf litter decomposition in lowland tropical forests

Global change drivers such as climate change influence decomposition by altering extrinsic site conditions and intrinsic litter traits. This study aimed to quantify the relative importance of these two pathways for litter decomposition in tropical forests. The effects of soil nutrient availability, mean annual precipitation (MAP), and leaf litter chemistry on decomposition were isolated by measuring mass loss of leaf litter from 10 tropical tree species transplanted to 19 sites along independent gradients of soil fertility and precipitation in Panama. Across species, litter nitrogen (N) content ranged from 7.1 to 13 mg N g(-1) and phosphorus (P) from 0.077 to 0.56 mg P g(-1). Across sites, soil N content ranged from 1.7 to 5.5 g N kg(-1), soil P from 77 to 1500 mg P kg(-1), and MAP from 1900 to 2700 mm. Variation in leaf litter mass loss was explained largely by litter species identity (55 %). Site only explained a small, but significant, amount of variance (6.5 %); soil C:N ratio explained this response. Notably, neither litter nutrient content nor MAP were significant predictors of litter decomposition. Changes in tree species composition may influence decomposition rates more than changes to site conditions.