Has Submerged Vegetation Loss Altered Sediment Denitrification, N2O Production, and Denitrifying Microbial Communities in Subtropical Lakes?

Abstract

Loss of submerged vegetation has become one of the most serious ecological issues in shallow lakes worldwide. However, there is limited understanding of the effect of vegetation loss on sediment nitrogen (N) cycling processes and microbial communities, which are closely linked to the N removal function of aquatic ecosystems. Here we investigated the sediment denitrification and N2O production rates of 10 macrophyte-rich and 12 macrophyte-free lakes in subtropical China. We determined the abundance of diversity of nirS- and nirK-encoding denitrifiers in sediments using quantitative polymerase chain reaction and clone libraries. The results showed that denitrification and N2O production rates in vegetated lakes were slightly but not significantly lower than those in nonvegetated lakes. Sediment denitrification rates in vegetated lakes were positively correlated with water NO3− concentration but not significantly related to submerged vegetation and denitrifier communities. Similarly, the presence of submerged macrophytes had no significant effect on denitrifier diversity and abundance. Water N content and sediment moisture were the main factors affecting the composition of denitrifying communities. Moreover, no significant correlation was found between community similarity and geographical distance among lakes. Overall, our findings suggest that submerged vegetation degradation in Yangtze lakes has no significant effect on sediment denitrification rates and denitrifying community structure. Abiotic factors, especially water N level and sediment moisture, play a critical role in controlling N removal capacity of lake sediments.