Role of precipitation partitioning in litter biogeochemistry

Abstract

Passage of precipitation though the plant canopy can conceivably affect litter decomposition in two ways; reduction in quantity of precipitation and alteration of throughfall chemistry. In many ecosystems, interception ratios are of the magnitude to possibly reduce decomposition rates due to moisture limitations. Simulations indicate that these are especially likely to limit decomposition at higher temperatures, lower monthly precipitation rates, and in the presence of evergreen canopies. However, this review has not located any experiments that directly test the hypothesis that canopy interception can reduce litter decomposition. There have been many observational surveys and experiments with different objectives, such as evaluation effects of climatic change and at least three have noted decreased decomposition rates with partial exclusion of throughfall. Canopy removal by clearcutting or thinning generally reduce decomposition rates because of temperature and moisture effects. The most definite effect of throughfall chemistry on litter decomposition is its effects on immobilization of N and P in litter during the early stages. The two studies that directly address the effects of throughfall on litter decomposition showed that simulated throughfall containing inorganic nutrients increased the uptake of N and P and speeds up the rates of net mineralization but only one showed a difference in mass loss. Studies using fertilization of litter have shown mixed results in its effect on decomposition rate. There is an extremely diverse array of organic substances in throughfall that could hypothetically cause priming effects or even inhibitory effects (e.g. polyphenols). However, these substances are also present in freshly senesced litter and maybe in higher concentration in litter. However, experiments using realistic concentrations characteristic of throughfall appear to be lacking.