Antagonistic effect of changing salinity and dissolved organic carbon on N₂O production via different pathways in saline lakes

    Saline lakes are experiencing significant changes in salinity and organic matter content due to climate change. However, the specific impacts of these environmental changes on the production processes of nitrous oxide (N₂O)—particularly nitrification and denitrification—in saline lake sediments are still poorly understood, leading to significant uncertainty in current estimates of greenhouse gas (GHG) emission from these ecosystems. To address this gap, the present study used the isotope pair labelling technique to quantitatively assess the effects of climate-induced changes in environmental variables such as salinity and organic matter and their combined influence on N₂O production rates and production pathways from lake surface sediments. The results showed that saline lake sediments act as hotspots for N₂O production, with nitrification making a significant, although previously underestimated, contribution to the total N₂O flux; Salinity was found to limit N₂O production through both nitrifying and denitrifying processes in lake sediments, although dissolved organic carbon (DOC) in the sediment could mitigate the limitation caused by salt. In low-salinity lakes (salinity < 35 g/L), N₂O production, which mainly comes from denitrification, was significantly suppressed by salinity increase due to the increased sensitivity of denitrifying microbes to salinity change. Conversely, in high-salinity lakes (salinity > 35 g/L), where salinity stress remained pronounced, an increase in DOC appeared to play a crucial role in increasing N₂O production by triggering both denitrification and heterotrophic nitrification processes. Consequently, future investigations on GHG emissions from lakes should prioritize the evolving environmental dynamics driven by climate change and provide new insights and a solid scientific basis for predicting and managing future changes in these critical ecosystems.

Key words: N₂O production pathways, saline lakes, climate change, salinity, dissolved organic carbon.