Methanogenesis rather than carbon dioxide production drives positive priming effects in anoxic sediments of saline lakes

Abstract

Priming effect is an essential mechanism regulating global organic carbon storage. The generation of priming effects has been exclusively investigated in anoxic sediments of freshwater lakes and in oxic sediments of saline lakes. However the differences in priming effect generation between oxic and anoxic saline lake sediments remain unclear. Here, we investigated the effects of algal and grass organic matter additions on priming effects under oxic and anoxic conditions in saline lake sediments. Sediment microcosms from three saline lakes with different salinities were amended with algal (¹³C-labeled Chlorella vulgaris) and grass (¹³C-labeled Festuca ovina) organic matter and incubated under oxic and anoxic conditions for 7 days to estimate priming effect intensities for CO₂ and CH₄ production. The results showed that algal and grass organic matter additions promoted higher CO₂ production under anoxic conditions than under oxic conditions, with grass organic matter inducing more CO₂ production than algal organic matter. Under oxic conditions, both algal and grass OM additions induced positive priming effects for CO₂ production, while negative priming effects were observed under anoxic conditions. In contrast, positive priming effects for CH₄ production were found in all anoxic microcosms. Our study highlights the importance of OM mineralization and positive priming effects for CH₄ production in anoxic sediments of saline lakes, which should not be overlooked given the high global warming potential of CH₄ and the increasing anoxia in global lakes due to climate change.