Nitrogen Addition Affects Ecosystem Carbon Exchange by Regulating Plant Community Assembly and Altering Soil Properties in an Alpine Meadow on the Qinghai–Tibetan Plateau

Abstract

Nitrogen (N) deposition can affect the global ecosystem carbon balance. However, how plant community assembly regulates the ecosystem carbon exchange in response to the N deposition remains largely unclear, especially in alpine meadows. In this study, we conducted a manipulative experiment to examine the impacts of N (ammonium nitrate) addition on ecosystem carbon dioxide (CO2) exchange by changing the plant community assembly and soil properties at an alpine meadow site on the Qinghai–Tibetan Plateau from 2014 to 2018. The N-addition treatments were N0, N7, N20, and N40 (0, 7, 20, and 40 kg N ha–1year–1) during the plant growing season. The net ecosystem CO2 exchange (NEE), gross ecosystem productivity (GEP), and ecosystem respiration (ER) were measured by a static chamber method. Our results showed that the growing-season NEE, ER and GEP increased gradually over time with increasing N-addition rates. On average, the NEE increased significantly by 55.6 and 65.2% in N20 and N40, respectively (p < 0.05). Nitrogen addition also increased forage grass biomass (GB, including sedge and Gramineae) by 74.3 and 122.9% and forb biomass (FB) by 73.4 and 51.4% in N20 and N40, respectively (p < 0.05). There were positive correlations between CO2 fluxes (NEE and GEP) and GB (p < 0.01), and the ER was positively correlated with functional group biomass (GB and FB) and soil available N content (NO3––N and NH4+–N) (p < 0.01). The N-induced shift in the plant community assembly was primarily responsible for the increase in NEE. The increase in GB mainly contributed to the N stimulation of NEE, and FB and the soil available N content had positive effects on ER in response to N addition. Our results highlight that the plant community assembly is critical in regulating the ecosystem carbon exchange response to the N deposition in alpine ecosystems.

Nitrogen addition affected the root competition in Cunninghamia lanceolata–Phoebe chekiangensis mixed plantation

“…It is widely recognized that N deposition can influence tree growth (Zhao and Zeng, 2019; Cao et al, 2023) and the structure of forest ecosystems. In particular, N inputs to forest ecosystems can alter soil resource availability and the intensity of interspecific competition (Elias and Agrawal, 2021; Han et al, 2022), thereby significantly affecting species coexistence and, ultimately, forest productivity. The effects of N deposition on interspecific interactions vary among species.…”

Soil habitat condition shapes Tamarix chinensis community diversity in the coastal saline-alkali soils

“…High soil salinity inhibits the growth of plants with low salinity tolerance and decreases the diversity of the T. chinensis community ( Qu et al., 2017 ). Soil nutrients promote plant growth and development and determine the species composition of T. chinensis communities, whereas appropriate soil nutrient content increases plant diversity ( Han et al., 2022 ). Numerous studies have examined the independent effects of soil texture, water content, salinity, and nutrients on plant community diversity.…”