Effects of nitrogen and phosphorus additions on decomposition and accumulation of soil organic carbon in alpine meadows on the Tibetan Plateau

Abstract

Nitrogen (N) and phosphorus (P) additions to grasslands increase aboveground plant biomass and modify plant community composition, thereby affecting plant‐derived organic carbon (C) input to soil and soil C cycling and storage. However, the effects of N and P additions on soil organic C (SOC) decomposition and sequestration are not fully understood and their underlying mechanisms are poorly known. This study aimed to explore the mechanisms underlying SOC decomposition and SOC content decline in the topsoil of alpine meadows on the Tibetan Plateau after 9‐years of field N and P additions. Stoichiometric characteristics of soil and microorganisms and their effects on microbial decomposition, including priming effects (PEs), C substrates decomposition, and microbial C use efficiency (CUE), were investigated by adding 13C labeled substrate (glucose or vanillin). Results showed that N and P additions differentially affected the magnitude and direction of PEs and SOC decomposition, accelerated mineralization of glucose and vanillin by 33–45% and 11–45%, respectively, but decreased microbial CUE of glucose and vanillin by 9–15% and 11–48%, respectively. These effects were caused by differential increase in microbial activity and acceleration of microbial decomposition due to N and P additions, and induced lower soil ecological stoichiometric ratios and higher microbial C:N:P ratios. The above effects led to different magnitudes of decomposition and accumulation of SOC and plant‐derived C substrate and thus decline in SOC content depending on N and P additions. We found that long‐term N and P additions would weaken soil functioning as a C pool for alpine meadows on the Tibetan Plateau.

Long‐term cultivation of Miscanthus and switchgrass accelerates soil organic carbon accumulation by decreasing carbon mineralization in infertile red soil

“…In this study, the significant effect of DON on the decomposition of input biomass was an indication of this relation. Phosphorus concentration can affect C m in P‐limited environments (Li et al, 2021). Phosphorus additions lead to increases in abundances of bacteria and fungi, which accelerate decomposition of both easily degradable C and recalcitrant organic C (Diamond et al, 2019; Riggs & Hobbie, 2016).…”

“…In this study, the significant effect of DON on the decomposition of input biomass was an indication of this relation. Phosphorus concentration can affect C m in P-limited environments (Li et al, 2021).…”

Nitrogen and phosphorus additions accelerate decomposition of slow carbon pool and lower total soil organic carbon pool in alpine meadows

“…This seemingly contradictory was partially due to the N and P additions-induced shift from recalcitrant SOC pool into labile SOC pool (Table 1) which was decomposed easier and fast than slow C pool (Luo et al, 2019). Besides, N and P addtions increased AGB ( (Kuzyakov, 2010;Li et al, 2020;Song et al, 2018) and increased decomposition of plant-derived C substrates (Li et al, 2020 submitted). N and P additions reduced cumulative SOC decomposition when there was no plant litter (Table 1).…”

“…This was ascribed to positive priming effects (PEs) on native SOC decomposition by enhanced input of plant-derived C substrates (Kuzyakov, 2010;Li et al, 2020;Song et al, 2018) and thus lowered SOC accumulation and SOC pool. N and P addditions reduced fungal diversity and modified soil microbial composition and activity (Chen et al, 2019;He et al, 2016;Yue et al, 2015), which may promote SOC decomposition and lead to lower SOC stocks in alpine meadows (Li, Hou, et al, 2018;Luo et al, 2019Luo et al, , 2020.…”

Soil Fungal Composition Drives Ecosystem Multifunctionality after Long-Term Field Nitrogen and Phosphorus Addition in Alpine Meadows on the Tibetan Plateau

“…As many studies have shown the acidification by nutrient additions [ 6 , 26 , 27 , 28 , 29 , 30 , 31 ], our results showed that N and P addition reduced soil pH. The decline in pH could be explained by (1) plants growing rapidly and producing a large amount of organic acids, such as malic acid and citric acid; (2) soil microorganisms producing a large amount of H + , NO 3 − , and NH 4 + through ammonification and nitrification while plants and soil microorganisms were unable to absorb enough H + , NO 3 − , and NH 4 + , resulting in the accumulation of these irons in the soil and a decrease in pH [ 32 , 33 ].…”