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
additions-induced 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.