Effects of Nitrogen Deposition on Leaf Litter Decomposition and Soil Organic Carbon Density in Arid and Barren Rocky Mountainous Regions: A Case Study of Yimeng Mountain

Abstract

The ecological impact of nitrogen (N) deposition has gained significance since the advent of the industrial revolution. Although numerous studies have examined the impact of N deposition on soil organic carbon (SOC), certain arid and barren rocky mountainous regions, which experience more pronounced N limitations, have been overlooked. This study was conducted in the Yimeng Mountains, examining eight treatments created by four N addition levels (0 kg N ha−1 yr−1, 50 kg N ha−1 yr−1, 100 kg N ha−1 yr−1 and 200 kg N ha−1 yr−1) and two tree species (Quercus acutissima Carruth. and Pinus thunbergii Parl.). The research revealed variations in the effect of N addition on leaf litter decomposition and SOC density (SOCD) between different tree species. Notably, N addition stimulated the decomposition of leaf litter from Quercus acutissima Carruth. However, the decomposition of Pinus thunbergii Parl. leaf litter was enhanced at N addition levels below 100 kg N ha−1 yr−1, while it was hindered at levels exceeding 100 kg N ha−1 yr−1. In the Quercus acutissima Carruth. forest, the N addition levels of 50 kg N ha−1 yr−1, 100 kg N ha−1 yr−1 and 200 kg N ha−1 yr−1 resulted in decreases in SOCD by 10.57%, 22.22% and 13.66%, respectively, compared to 0 kg N ha−1 yr−1. In the Pinus thunbergii Parl. forest, the N addition levels of 50 kg N ha−1 yr−1, 100 kg N hm−2 ha−1 and 200 kg N ha−1 yr−1 led to increases in SOCD by 49.53%, 43.36% and 60.87%, respectively, compared to 0 kg N ha−1 yr−1. Overall, N addition decreases the SOCD of Quercus acutissima Carruth., but it increases the SOCD of Pinus thunbergii Parl., attributed to the alteration in soil enzyme stoichiometry and nutrient cycling by N addition. This study fills a theoretical gap concerning leaf litter decomposition and SOC sequestration in arid and barren rocky mountainous regions under global climate change.