Responses of CO2 efflux from an alpine meadow soil on the Qinghai Tibetan Plateau to multi-form and low-level N addition

Abstract

Aims To assess the effects of atmospheric N deposition on the C budget of an alpine meadow ecosystem on the Qinghai-Tibetan Plateau, it is necessary to explore the responses of soil-atmosphere carbon dioxide (CO 2 ) exchange to N addition.Methods Based on a multi-form, low-level N addition experiment, soil CO 2 effluxes were monitored weekly using the static chamber and gas chromatograph technique. Soil variables and aboveground biomass were measured monthly to examine the key driving factors of soil CO 2 efflux.Results The results showed that low-level N input tended to decrease soil moisture, whereas medium-level N input maintained soil moisture. Three-year N additions slightly increased soil inorganic N pools, especially the soil NH 4 + -N pool. N applications significantly increased aboveground biomass and soil CO 2 efflux; moreover, this effect was more significant from NH 4 + -N than from NO 3 − -N fertilizer. In addition, the soil CO 2 efflux was mainly driven by soil temperature, followed by aboveground biomass and NH 4 + -N pool. Conclusions These results suggest that chronic atmospheric N deposition will stimulate soil CO 2 efflux in the alpine meadow on the Qinghai-Tibetan Plateau by increasing available N content and promoting plant growth.

Contrasting effects of ammonium and nitrate inputs on soil CO2 emission in a subtropical coniferous plantation of southern China

“…We did not observe a significant decrease in soil CO 2 flux at the high N treatments, suggesting that the subtropical plantation is in the early or medium stages of N saturation (Aber et al 1998). Generally, the promoting effect has a short duration (e.g., less than 1 year) and shifts to the neutral and inhibitory effects (Bowden et al 2004;Fang et al 2012). In our study, we found that each N treatment significantly increased soil CO 2 flux in the first 6 months of N addition , while the promotion was only observed at the low-NaNO 3 treatment after 1-year N addition (Fig.…”

“…However, the effects of increased N deposition on soil CO 2 flux are high variable, including promotion (Cleveland and Townsend 2006;Contosta et al 2011), inhibition (Mo et al 2008;Janssens et al 2010), and no change (Allison et al 2008), depending on the level and the form of N addition (Fang et al 2012), on the duration of N addition (Hasselquist and Högberg 2014), and on distinct stages of N saturation (Sutton et al 2011). In addition, these studies have been conducted using a type of N fertilizer (e.g., NH 4 NO 3 or urea) (Mo et al 2008;Phillips and Podrebarac 2009), and the contrasting effects of oxidized NO 3 − and reduced NH 4 + have rarely been investigated (Lu et al 2011a).…”

“…In addition, these studies have been conducted using a type of N fertilizer (e.g., NH 4 NO 3 or urea) (Mo et al 2008;Phillips and Podrebarac 2009), and the contrasting effects of oxidized NO 3 − and reduced NH 4 + have rarely been investigated (Lu et al 2011a). Recently studies found that the NO 3 − and NH 4 + might have totally different impacts on ecosystem processes due to plant's preferable uptake, competition between plant and microbial communities, and different action in soils (Gavrichkova and Kuzyakov 2008;Fang et al 2012).…”

Construction and progress of Chinese terrestrial ecosystem carbon, nitrogen and water fluxes coordinated observation

“…Oxidized NO 3 -and reduced NH 4 + inputs contrastingly affect soil greenhouse gas exchange fluxes. The promotion or inhibition on soil greenhouse gas fluxes are stronger from NH 4 + -N fertilizer addition than from NO 3 --N fertilizer addition (Jiang et al, 2010;Fang et al, 2012;Wang et al, 2014). Also, the responses of soil greenhouse gas fluxes to N addition dose exhibit a nonlinear curve.…”

“…Low dose of N addition inhibits soil CO 2 and N 2 O emissions, but promotes soil CH 4 uptake, whereas high doses of N inputs have contrary effects. Overall, these contrasting responses depend on the different stage of N saturation in terrestrial ecosystems (Fang et al, 2012. Furthermore, the environmental mechanisms driving the responses of soil greenhouse gas fluxes in the northern and southern forests of China to N enrichment are contrasting.…”