Convergence and divergence of nutrient stoichiometry during forest litter decomposition

Background and aims General theory of forest floor dynamics indicates convergence of properties during detrital decomposition. This study examined the hypothesis that nutrient stoichiometry, i.e. the relative amounts of nutrients, converges during litter decomposition. Methods Douglas-fir (Pseudotsuga menziesii (Mirb.) Franco) and red alder (Alnus rubra Bong.) foliar litters that decomposed in their respective forests were analyzed for N, P, Ca, Mg, K, S, Mn, Fe, Zn, and Cu. A novel approach quantified the stoichiometric difference as the angle between nutrient vectors. The approach was also used to synthesize data from 11 previously published studies representing a broad array of litter types and locations. Results The stoichiometries of the Douglas-fir and red alder litters converged during the first 2 years of decomposition, but diverged in the subsequent 4 years. This temporal trajectory was explained by two competing sets of processes: stoichiometric convergence occurs when different litters decompose in the same environment, and divergence occurs when the same litter decomposes in different environments. Manganese, Fe, and Ca were important contributors to stoichiometric differences. Conclusions Stoichiometric convergence processes often dominate over divergence processes. Consideration of multi-nutrient stoichiometries may enhance the understanding of the functions of litter, including rates of decomposition and relative rates at which nutrients are released.