Response of microbial respiration from fine root litter decomposition to root water content in a temperate broad-leaved forest

Microbial respiration from plant litter decomposition is sensitive to soil water status; however, its response to water status remains ambiguous, particularly in the litter of fine roots. We investigated the effect of fine-root water content on microbial respiration after 468 days of decomposition in forest soil for two diameter classes (0-0.5 and 0.5-2 mm) of Quercus serrata and Ilex pedunculosa in central Japan. Direct measurement of microbial respiration from root litter resulted in a range of 0.015-3.52 nmol CO2 g −1 s −1 . Microbial respiration in both diameter classes and species decreased linearly with decreasing root water content. These changing patterns of microbial respiration did not differ significantly between the diameter classes of either species, indicating that microbial respiration was regulated by the moisture of root litter, and not by characteristics associated with diameter class or species. In contrast, the carbon to nitrogen ratio and mass loss of the root litter differed significantly between diameter classes in both species. These findings suggest that along with chemical and morphological properties of fine root litter, the changes in root water content should also be considered as a viable factor in microbial activity variations. Drying-wetting cycles of fine roots could lead to sensitive responses of microorganisms during the short term, leading to variation in the decomposition rate of fine root litter over the long term. This study provided insight into the potential impact of microbial physiological performance on heterotrophic respiration and fine root decomposition under the varying root water content.