CO2 efflux from decomposing leaf litter stacks is influenced by the vertical distribution of leaf litter water content and its temporal variation

Abstract

We evaluated the temporal changes in the vertical distribution of leaf litter respiration (RLL) due to changes of leaf litter water content (WLL) within the leaf litter layer (L layer) using in situ direct measurements. To investigate the vertical distribution of RLL and WLLwithin the leaf litter layer over a time-series, we measured the RLL and WLL of 10 separate layers in vertical leaf litter stacks fixed to the forest floor using wire pins. Measurements were conducted for 30 stacks in a temperate broad-leaved secondary forest between May 2008 and January 2009. In the warm season, high RLL was observed at high WLL, while low RLLwas observed at low WLL. RLL was comparatively lower during the cool season than during the warm season regardless of the magnitude of WLL. The temperature sensitivity of RLLdiffered depending on WLL; temperature increases under low-moisture conditions had small effects on RLL, while under higher-moisture conditions, RLL was more responsive to temperature increases. Small differences in position within the leaf litter stack affected the vertical variation of WLL and, consequently, there was large distribution in RLL during the wet period and small distribution in RLL (totally small values) during the dry period. Thus, CO2 efflux from the net L layer was strongly affected by RLL distribution induced by the local wetting within the L layer. In estimating CO2 efflux from the L layer using water content of the L layer, monitoring of the water content of the L layer, which takes into account the vertical distribution in WLL within the L layer, is necessary.