Predominance of positive priming effects induced by algal and terrestrial organic matter input in saline lake sediments

Abstract

Priming effect (PE) is a key biogeochemical process regulating organic carbon mineralization. However, the impacts of climate change-related factors on PE remain largely unclear in lakes with a large salinity range. The patterns of PE induced by algal (13C-labeled Chlorella vulgaris) and terrestrial grass (13C-labeled Festuca ovina) organic matter (OM) at 8 °C and 18 °C were investigated in lake sediments with a salinity range from 0.7 to 376.3 g L−1. The results showed that the intensities of early (7th day) and late (42nd day) PEs in the studied lake sediments ranged −51.0%–3833.7% and −55.2%–1874.5% of basal respiration, respectively; positive PE predominated over negative PE. Climate-related factors (e.g., salinity, temperature, OM types) exhibited significant influences on the intensity and/or direction of PE. Positive PE was more likely to occur in the sediments of hypersaline lakes than in freshwater/saline lakes, while negative PE showed an inverse trend. PE intensity induced by algal OM was significantly different at 8 °C and 18 °C, but no temperature influence was observed for that induced by grass OM. The effect of temperature increase on PE induced by algal OM was negative and positive in the early and late stages of incubation, respectively. The types of OM (algal OM vs. grass OM) supply significantly (P < 0.05) affected PE intensity except for the late PE intensity at 8 °C. Overall, these results suggest that organic carbon mineralization in lake sediments may be enhanced by positive PEs induced by the increased input of both allochthonous and autochthonous OM, and the autochthonous OM-induced PE is more susceptible to climate warming than that by allochthonous OM. These results help understand the carbon cycle in lakes under global climate change.