Solubility of leaf litter carbon and nutrients from 41 lowland tropical forest woody species

Background/Question/Methods Predictors of decomposition rates and nutrient release patterns have received a great deal of research attention and, in general, predictors are most often emphasized in context of their effects on soil fauna and biotic decomposition. Abiotic leaching has been less well-studied but could result in carbon and nutrient fluxes that may drive some plant-soil-microbe feedbacks in lowland tropical forests. Here we test if the solubility of carbon and nutrients of initial leaf litter can be predicted by leaf litter traits (e.g., litter toughness, total element concentrations etc.).  In addition, we investigated whether carbon quality of leachate (defined by specific ultraviolet absorbance at 280 nm, SUVA₂₈₀) was related to total carbon solubility and leachate pH.  Leaf litter was collected weekly in aboveground litter traps on Barro Colorado Island, where the majority of leaf litter falls during the dry season.  Three replicate samples of each species litter were extracted using a standardized procedure (1:50 litter to solution ratio and 4-hour extract time) to determine the solubility of carbon, phosphorus, nitrogen and cations. Results/Conclusions On average, across the 41 species, 34% of the total litter phosphorus, 5% of the nitrogen and 1-8% of the carbon was soluble during the 4-hour extract. Soluble and total element pools were positively correlated for manganese (r²=0.36), nitrogen (r²=0.35), phosphorus (r²=0.54), potassium (r²=0.79) and sodium (r²=0.51), but no relationship was found for carbon or calcium.  SUVA₂₈₀, an index of carbon aromaticity, was negatively correlated with leachate pH (r²=0.41) and was weakly but positively correlated with total carbon extracted. Litter toughness was not related to solubility of any of the nutrients. In summary, for many nutrients, total litter concentration of the nutrient predicts the quantity of nutrient released in leachate, suggesting that nutrients in the 41 tropical woody species investigated here have similar solubility. Phosphorus solubility is especially high suggesting leaching of initial litter may be an important flux of phosphorus to either soil or microbes on the litter.