Rainfall manipulation effects on litter decomposition and the microbial biomass of the forest floor

Abstract

Simple structures aimed at regulating the amount of rain water dropping into the forest floor were installed to determine the impact of rainfall on leaf litter mass loss, respiration rates, microbial biomass C (C mic) and metabolic quotient ( qCO 2). The rainfall manipulation treatments were (I) fully covered (100% reduction); (II) partially covered (50% reduction) and (III) control (fully exposed). Using the litterbag technique, the mass losses of covered Quercus serrata, Quercus acutissima, Acer rufinerve and Pinus densiflora leaf litter were reduced ( P<0.01) by 19–26% compared to fully exposed litter. A positive linear relationship ( r=0.90; P<0.0001) between litter C mic and mass loss was noted across all litter types and covering regimes. The mass losses in fully exposed litter were attributed to the leaching effect of rainfall coupled with the synergistic actions of microbes and soil fauna, as suggested by their respiration and microbial biomass. In the covered litter, C mic was generally reduced ( P<0.01) while fully and partially exposed litter were comparable ( P>0.05). On the other hand, respiration rates and qCO 2 were variable and showed no consistent treatment effect except for respiration rates at 3 months. Similarly, soil respiration rates and C mic were not consistently affected by cover treatments. Evidently, the zero-rainfall condition negatively affected some biological processes in the litter layer but sporadically affected soil processes. The absence of rainfall, even if the soil moisture content was maintained, could affect organic matter turnover in the forest floor.