Nitrogen and phosphorus addition-induced soil and microbial ecological stoichiometry regulated carbon decomposition and accumulation and reduced soil carbon content in Tibetan alpine meadows

Abstract

Nitrogen (N) and phosphorus (P) additions to grasslands increase aboveground plant biomass and modify plant community composition, thereby affect plant-derived organic carbon inputting to soil and soil C cycling and storage. However, the effects of nutrient additions on SOC decomposition and soil C sequestration have no census and their underlying mechanisms are poorly understood. This study aimed to explore the mechanisms underlying SOC decomposition and SOC content decline in the topsoil of Tibetan alpine meadows after nine-year field N and P additions. Soil and microbial stoichiometric characteristics were measured and priming effects (PEs), substrate decomposition, as well as microbial C use efficiency (CUE) by adding 13C labeled substrate (glucose or vanillin) were analyzed. N and P additions differentially affected the magnitude and direction of PEs and SOC decomposition, accelerated substrate mineralization of glucose by 33-45% and that of vanillin by 11-45%, but decreased microbial CUE of glucose by 9-15% and that of vanillin by 11-48%. This was associated with the N and P additionsinduced lower soil ecological stoichiometric ratios and higher microbial C:N:P ratios compared with Control. Therefore, these comprehensive effects of N and P additions on decomposition of SOC and plant-derived C substrates reduced SOC sequestration and thus SOC content. Long-term N and P additions would weaken soil functioning as C pool of Tibetan alpine meadows.

Microbial Necromass, Lignin, and Glycoproteins for Determining and Optimizing Blue Carbon Formation

“…The results are consistent with the idea that bacterial necromass C is less recalcitrant and thus more degradable. 3,51 Therefore, the increased LAP activities contribute to the observed decrease in microbial necromass. The lignin phenol content increased with NAG activities and Fe SRO contents (p < 0.05) (Figure S5).…”

“…This may be due to the allochthonous environment of coastal wetlands, and allochthonous materials leave potential impacts on carbon-nutrient cycling by stoichiometry control. 3 During these processes, the nutrient availability greatly influences microbial activities. High-salinity sampling sites (S. salsa soils and mudflat soil) showed higher AP contents, lower N:P ratio, and microbial N limitation (Tables S2 and S3).…”

“…1,2 The sources of soil organic matter (SOM) in coastal wetlands are complex and can stem from both autochthonous (produced within the wetlands) and allochthonous (transported from the uplands and marines) sources. 3 Coastal wetlands have specific soil conditions that differ from other terrestrial ecosystems, such as low oxygen, high salinity, fluctuating hydrological, and redox conditions. 4,5 With the projected 5% reduction in the areas of river delta by the end of the 21st century, 6 coastal wetlands are expected to undergo seawater intrusion, altered hydrological conditions, increase in salinity levels, and changes in vegetation composition.…”

“…Anaerobic conditions favor the growth of certain microbial groups, such as sulfate and Fe-reducing bacteria, which can promote the reduction of Fe minerals. 37−39 Since allochthonous particle deposition and mineral protection act as key biogeochemical controls in the accumulation of SOM in coastal wetlands, 3 further investigations are needed to determine whether redox fluctuations can undermine or promote the capacity of Fe minerals to protect SOM.…”