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- Title
Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes.
- Authors
Bing Song; Jian Sun; Qingping Zhou; Ning Zong; Linghao Li; Shuli Niu
- Abstract
Increases in nitrogen (N) deposition can greatly stimulate ecosystem net carbon (C) sequestration through positive N-induced effects on plant productivity. However, how net ecosystem CO2 exchange (NEE) and its components respond to different N addition rates remains unclear. Using an N addition gradient experiment (six levels: 0, 2, 4, 8, 16, 32 gNm-2 yr-1) in an alpine meadow on the Qinghai-Tibetan Plateau, we explored the responses of different ecosystem C fluxes to an N addition gradient and revealed mechanisms underlying the dynamic responses. Results showed that NEE, ecosystem respiration (ER), and gross ecosystem production (GEP) all increased linearly with N addition rates in the first year of treatment but shifted to N saturation responses in the second year with the highest NEE (-7.77±0.48 μmolm-2 s-1) occurring under an N addition rate of 8 gNm-2 yr-1. The saturation responses of NEE and GEP were caused by N-induced accumulation of standing litter, which limited light availability for plant growth under high N addition. The saturation response of ER was mainly due to an N-induced saturation response of aboveground plant respiration and decreasing soil microbial respiration along the N addition gradient, while decreases in soil microbial respiration under high N addition were caused by N-induced reductions in soil pH. We also found that various components of ER, including aboveground plant respiration, soil respiration, root respiration, and microbial respiration, responded differentially to the N addition gradient. These results reveal temporal dynamics of N impacts and the rapid shift in ecosystem C fluxes from N limitation to N saturation. Our findings bring evidence of short-term initial shifts in responses of ecosystem C fluxes to increases in N deposition, which should be considered when predicting long-term changes in ecosystem net C sequestration.
- Subjects
MOUNTAIN meadows; NITROGEN; PLANT productivity; MICROBIAL respiration; RESPIRATION in plants
- Publication
Biogeosciences, 2017, Vol 14, Issue 17, p3947
- ISSN
1726-4170
- Publication type
Article
- DOI
10.5194/bg-14-3947-2017