Effects of Climate Change and Nitrogen Addition on Carbon Loss in Alpine Wetland of Qinghai–Tibet Plateau

Abstract

Soil microorganisms and soil organic carbon (SOC) play important roles in ecosystem cycling, but there is a lack of clarity about the effects of nitrogen addition on soil microorganisms and SOC, as well as the key microbial taxa that influence SOC. This study was conducted in the alpine wetland of Xiaopo Lake in the Qinghai Lake basin, using NH4NO3 as the nitrogen source, three nitrogen addition gradients (N2: 2 g/m2, N5: 5 g/m2, N10: 10 g/m2), and a blank control treatment (N0: 0 g/m2), with three replicate experiments for each treatment. The main findings were as follows: (1) Both increased soil temperature and decreased precipitation reduced SOC content. SOC content gradually decreased with increasing nitrogen concentration; SOC was reduced by 3.36–29.54% and 8.57–26.66% at 0–15 cm and 15–30 cm soil depths, respectively. (2) Proteobacteria, Chloroflexi, Acidobacteria, and Actinobacteria were the main dominant species, and their changes determined the changes in the entire bacterial community. The relative abundance of Proteobacteria and Actinobacteria decreased under nitrogen addition; Acidobacteria increased significantly; and Chloroflexi did not change significantly. The overall abundance and diversity of soil bacteria showed an increasing trend. The number of soil bacteria is a key factor affecting SOC content, and an increase in the number and diversity of soil bacteria enhances their decomposition capacity, and thus, reduces SOC content. (3) Increased soil temperatures and decreased precipitation are associated with decreased SOC and are the main climatic factors affecting SOC. This study provides a reference for the rational utilization and management of wetland ecosystems under climate change.