Early decomposition and transformation of organic matter in natural and disturbed boreal forests

Abstract

The state of boreal larch forests near the southern permafrost margin in eastern Eurasia varies considerably, even on a local scale, as a result of anthropogenic disturbances (e.g., clear-cuts and fires) and uneven permafrost distribution. This study aimed to investigate whether various ecosystem conditions affect litter decomposition and organic matter (OM) transformation. Here, we present the results of a field experiment in natural and disturbed larch stands utilising the Tea-Bag Index approach (TBI). We investigated the decomposition in four larch stands in different states (post-fire, clear-cut, permafrost and control). Besides standard TBI indexes, we studied the transformation of OM composition by thermochemolysis–gas chromatography mass spectrometry. Mass loss differed depending on litter quality rather than forest disturbance type or permafrost. No significant differences were found between stabilisation (S) and decomposition constant (k) in disturbed and unaffected forests, whereas soil properties were differently related to decomposition parameters at the study sites. Our results on molecular composition before and after the incubation suggest site-depending, mainly microbial transformation of green tea in various forest conditions. Rooibos did not undergo a considerable microbial transformation. We showed that S and k might not be sensitive to various ecosystem conditions (e.g., disturbances and permafrost). However, the transformation of OM may vary, even on a local scale, having significant implications for carbon sequestration in soil. Our study shows that not a mass loss but a transformation of OM might depend on various conditions of the larch ecosystem at the southern margin of permafrost distribution in eastern Eurasia.