Biodegradation and chemical characteristics of hot-water extractable organic matter from soils under four different vegetation types in the Wuyi Mountains, southeastern China

Abstract

Water extractable organic carbon (WEOC) is the most active soil organic carbon and plays an important role in global C cycling. Our aim was to investigate the biodegradability and the chemical characteristics of hot-water extractable organic matter (HWEOM) from soils under different vegetation types, including evergreen broad-leaved forest (EBF), coniferous forest (CF), dwarf forest (DF) and alpine meadow (AM), across an altitude gradation in the Wuyi Mountains of southeastern China. We quantified the biodegradability in a 90 day incubation experiment by measuring the loss of hot-water extractable organic carbon (HWEOC) and calculated the sizes of labile and stable HWEOC pool and the respective decomposition rate constants by a double exponential model. We used UV and fluorescence spectroscopic techniques to characterize the structural properties of HWEOM and measured the contents of carbohydrates, phenols and hydrophilic carbon of HWEOM solution. The extent of HWEOC biodegradation was higher in EBF and DF soils with about 20% HWEOC loss, and the labile C accounted for 13–15% of the total HWEOC. HWEOC from CF soils was the least degradable with only 12% HWEOC loss. The estimated mean residence time of the labile HWEOC pool was 8–10 days, whereas that of the stable HWEOC pool ranged from 3 to 6 years. The biodegradability of HWEOC increased with decreasing soil C/N ratio, aromaticity and humification indices, proportion of phenols and increasing proportion of hydrophilic carbon.