Nitrogen Additions Promote Decomposition of Soil Organic Carbon in a Tibetan Alpine Meadow

Abstract

Core Ideas Litter addition increased C decomposition. Litter properties were more important than abiotic soil properties in controlling C decomposition. N addition would increase decomposition of SOC with added litter and decrease SOC accumulation by altering litter quality. In grassland ecosystems, nitrogen (N)‐induced changes in plant community often affect grassland soil organic carbon (SOC) decomposition and accumulation. However, there is no consensus on the biological and chemical mechanisms that underlie the response of SOC decomposition to N‐addition. In this study, we did a litter addition experiment to study the decomposition of SOC with added litter of six dominant plant species collected from N alone or N combined with phosphorus (N+P) fertilization treatments in a 7‐yr field experiment. The experiment showed that there were no consistent responses of plant chemical properties to N alone or N+P addition. Fertilization altered plants species' dominance in community, in particular the grass Elymus nutans. Litter addition significantly increased C decomposition, with the highest decomposition rates of SOC with added litter of all six plant species in N+P treatment. In general, both plant litter properties of organic C, total N (TN), lignin concentrations, and soil properties of SOC and TN, but not soil microbial biomass C, were the main factors determining cumulative decomposition of SOC with added litter. Litter properties were more important than abiotic soil properties in controlling C decomposition. This study indicated that fertilization with N alone or N+P can increase decomposition of SOC with added litter and lower SOC accumulation through changes in plant species' dominance and chemical properties of litter. In terms of maintaining high SOC and increasing soil C, N fertilization, whether in N alone or N+P, should not be used in these alpine meadows.

The Roles of Bacteria in Soil Organic Carbon Accumulation under Nitrogen Deposition in Stipa baicalensis Steppe

“…This finding is in agreement with our results. On the other hand, N addition has been found to reduce the SOC content and increase the decomposition of SOC vis changes in belowground chemical properties and aboveground plants in a Tibetan alpine meadow [18]. The SOC concentration in the 0-10 cm soil layer showed no response to N addition in a semiarid grassland [19].…”

“…The critical N load is estimated to be between 8 and 10 g N m −2 year −1 [16]. Conversely, the SOC content was reduced following N addition in a Pinus tabuliformis forest [17] and Tibetan alpine meadow [18], especially in the 10-20 cm soil layer [19]. Research has found that N addition tends to enhance SOC mineralization [20].…”

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

“…Nutrient supply, especially nitrogen (N) and phosphorus (P) availability, strongly affects C cycling and storage in grasslands ecosystems (Li et al, 2018; Luo et al, 2020; Ramirez, Craine, & Fierer, 2010; Riggs & Hobbie, 2016). N and P additions increase the aboveground plant biomass (Borer, Grace, Harpole, MacDougall, & Seabloom, 2017; Isbell et al, 2013; Li et al, 2014), and increase or decrease biomass allocation to roots (Fornara & Tilman, 2012; Li, Li, et al, 2018). These modifications in plant biomass would, in turn, affect C input to soil and SOC dynamics, however, the effects of N and P additions on SOC decomposition and soil C sequestration had no apparent interrelationship???…”

“…N and P additions accelerated SOM decomposition and reduced SOC content in the topsoil of alpine meadows on the Tibetan Plateau (Li et al, 2018; Luo et al, 2019, 2020). The litter quality and various biomass allocations to aboveground plant and roots in different grassland ecosystems may result in varying soil C sequestration and SOC storage due to N and P additions (Fornara & Tilman, 2012; Li, Li, et al, 2018; Soudzilovskaia et al, 2007). Besides these reasons, the inconsistent effects might be due to the differential response of the various microbial compositions (Leff et al, 2015; Riggs & Hobbie, 2016; Zhang, Chen, & Ruan, 2018), and thereby SOM decomposition and accumulation (Chen et al, 2014; Leff et al, 2015; Li, Hou, et al, 2018; Riggs, Hobbie, Bach, Hofmockel, & Kazanski, 2015) to N and P additions.…”

“…Anthropogenic drivers, such as atmospheric deposition and nutrient addition, increase the availability of N and P in grasslands, including alpine meadows (Galloway et al, 2008; Liu et al, 2013). Previous studies from alpine meadows on the Tibetan Plateau showed that input of N and P modified litter quality through increasing aboveground plant productivity and altering plants species' dominance in community, particularly the grass, Elymus nutans (Li et al, 2014; Li, Li, et al, 2018). These modifications can affect the availability of organic C and the decomposition of SOM, thus reducing SOC content (Li, Hou, et al, 2018; Li, Li, et al, 2018; Luo et al, 2019, 2020), with the lowest SOC content under P additions, as compared to N and NP additions (Li, Hou, et al, 2018).…”