Nutrients dynamic and temperature sensitivity of emergent plant litter decomposition in an inland freshwater wetland: perspective of microbial community structure and function

Abstract

Among the most crucial biogeochemical processes in wetlands, the decomposition of emergent plant litter, significantly influences the dynamics of eutrophication, health and integrity of the ecosystem. However, the mechanisms that govern wetland nutrient and litter decomposition interactions are still not well understood. Here we carried out four different treatments to investigate the effect of different temperature (20 and 35 °C), ammonia nitrogen (NH3-N) concentration (0.8 and 1.2 mg/L) and sediment on the changes of the water quality, organic matter composition and bacterial community succession in the leaf litter of lotus (Nelumbo nucifera). The results revealed that, all four water quality indexes chemical oxygen demand (COD), NH3-N, total nitrogen (TN), total phosphorus (TP) initially showed an increasing and followed by a subsequent decrease over the 4 days of decomposition, and the concentration at the end of the test were higher than the initial value. More organic matters, nitrogen and phosphorus were obviously released from 35 ℃ treatments, while the increase of NH3-N content inhibited the release of nutrients, and there was an adsorption effect of the sediment on nitrogen and phosphorus. Excitation emission matrix parallel factor analysis identified the presence of difficult biodegradable aromatic hydrocarbon structures of humus under the 35 ℃ treatments, and the litter decomposition at low NH3-N concentrations and sediment treatments released more dissolved organic matter (DOM), especially the involvement of sediment promotes the production of amides and proteins. At 72 h, the decomposition of plant litters under 35 ℃ and low NH3-N content improved the microbial diversity, and the main microorganisms included Proteobacteria (96.82 %), while the 20 ℃ and sediment were more suitable for the growth of Bacteroidota (25.20 %) and Firmicutes (9.91 %), respectively. Canonical correspondence analysis suggested that differences in bacterial abundance and diversity significantly correlated with COD and NH3-N, and the relationship between bacterial diversity and environmental parameters was affected by decomposition phases. Moreover, the microbial differences between the early and late stages of decomposition were significant. Thus, we provide evidence that the complex litter decay in wetlands is the result of dynamic effects of nutrients and environmental conditions, accompanied by bacterial diversity succession.