Responses of ecosystem respiration and its components to fertilization in an alpine meadow on the Tibetan Plateau

• Positive effects of fertilization on respiration rates.
• Response of aboveground biomass to nitrogen addition contributes to the patterns of respirations.
• Apparent negative relationship between soil temperature and respirations was modulated by aboveground biomass.

Nitrogen (N) deposition alters composition and productivity of plant community, plant litter quality and quantity, composition and activity of soil microbial community. All these changes would influence ecosystem and soil CO2 emissions. We established a fertilization experiment in an alpine meadow in hinterland of the Tibetan Plateau to detect the responses of ecosystem and soil respiration to fertilization and further explore forces driving changes of CO2 fluxes. The fertilization experiment was conducted in 2008, in which five treatments were manipulated, i.e. three N levels of 0, 5, 10 g N m−2 yr−1 (coded as Control, LN and HN, respectively), and two N levels combined with constant level of 5 g phosphorus (P) m−2 yr−1, respectively (coded as LN + P and HN + P, respectively). Ecosystem respiration (Rec), aboveground plant respiration (Ra), and soil respiration (Rs) were measured in growing season of 2010 the third year of the experiment. N addition alone did not affect Rec, Ra or Rs. However, combination of N and P increased Rec, Ra and Rs mainly in later period of the growing season. Similarly, N addition did not affect aboveground biomass, but combination of N and P increased aboveground biomass. Rec, Ra and Rs were positively correlated with aboveground biomass, but were not correlated with belowground biomass, indicates enhancement of aboveground biomass by nutrient enrichment could contribute a large part of variation of ecosystem and soil respiration, especially at the end of the growing season. It is suggested that apparent negative effect of soil temperature on ecosystem and soil respiration could be confounded by the effect of aboveground biomass, especially under nutrient enrichment.

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