Nitrogen Critical Loads for an Alpine Meadow Ecosystem on the Tibetan Plateau

Zong, Nan; Shi, Peili; Song, Minghua; Zhang, Xianzhou; Jiang, Jing; Xi, Chai

doi:10.1007/s00267-015-0626-6

Cited by 67 publications

(68 citation statements)

References 74 publications

(110 reference statements)

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“…1). This threshold for triggering changes in ecosystem C fluxes is comparable to that in another alpine meadow on the mid-southern part of the Tibetan Plateau (Zong et al, 2016). Considering that atmospheric wet N deposition ranges from 0.87 to 1.38 gN m −2 yr −1 on the eastern Qinghai-Tibetan Plateau (Lü and Tian, 2007), our estimate of N critical load suggests that the ecosystem C cycle may be largely affected under future N deposition in the alpine meadow of the Qinghai-Tibetan Plateau.…”

Section: The Time and N Threshold For The Saturation Responsesmentioning

confidence: 62%

Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes

et al. 2017

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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 CO 2 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 gN m −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 µmol m −2 s −1 ) occurring under an N addition rate of 8 gN m −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.

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Section: The Time and N Threshold For The Saturation Responsesmentioning

confidence: 62%

Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes

et al. 2017

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“…In addition, the meadow has also been invaded by Anaphalis xylorhiza due to overgrazing degradation. The total atmospheric N deposition at this site is approximately 10 kg N ha −1 year −1 (Zong et al., ).…”

Section: Methodsmentioning

confidence: 99%

The effects of warming and nitrogen addition on ecosystem respiration in a Tibetan alpine meadow: The significance of winter warming

Zong

Shimin

Duan

et al. 2018

Ecology and Evolution

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In recent decades, global warming has become an indisputable fact on the Tibetan Plateau. Alpine ecosystems are very sensitive to global warming, and the impact may depend on the degree of atmospheric nitrogen (N) deposition. The previous studies have paid more attention to year‐round warming, but the effect of winter warming has been unstudied. In this study, a manipulative experiment was conducted, consisting of warming and N addition. It was carried out since 2010 in an alpine meadow, and three types of warming treatments were set up: no warming (NW), year‐round (YW), and winter warming (WW). Warming significantly increased air and soil temperature, but decreased soil moisture. Under no N addition, YW showed significantly decreased ecosystem respiration (Reco) in 2012, and WW decreased Reco in 2014. Under N addition, neither YW nor WW had significant effects on Reco, indicating that N addition compensated the negative effect of warming on Reco. Annually, YW and WW decreased ecosystem carbon (C) emissions, and the extent of the reduction was even larger under WW. Under no N addition, both YW and WW significantly decreased aboveground biomass. Moreover, especially under no N, YW and WW significantly decreased soil inorganic N. WW also had negative effects on soil microbial biomass C. Structure equation modeling showed that soil moisture was the most important factors controlling Reco, and soil inorganic N content and microbial biomass C could explain 46.6% and 16.8% of the variation of Reco. The findings indicate that soil property changes under warming had substantial effects on ecosystem C efflux. The inhibitory effects of winter warming on ecosystem C efflux were mainly attributed to the decline of soil N and microbial biomass. Thus, the effects of winter warming on ecosystem C emissions in this semiarid alpine meadow are not as serious as expected and largely depend on N deposition.

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“…In addition, the alpine meadow in this region has been invaded by Anaphalis xylorhiza due to overgrazing in recent decades. The atmospheric N deposition rate is approximately 10 kg N ha −1 year −1 at this site (Zong et al., ).…”

Section: Methodsmentioning

confidence: 96%

“…Soil nutrient availability can directly affect plant biomass production and root growth patterns (Sun, Cheng, & Fan, ; Sun & Wang, ), and the determination of plant nutrient contents is fundamental for rangeland management (Arzani, Sour, & Motamedi, ; Stevens & Gowing, ; Sun & Wang, ), as livestock development is generally limited by forage nutritional yield (Abdala‐Roberts, Parra‐Tabla, Campbell, & Mooney, ; Ren et al., ). Due to the harsh climate on the plateau, plant growth in alpine ecosystems is severely restricted by soil nutrient availability, so alpine plants are more sensitive to exogenous nutrient inputs (Bowman, Gartner, Holland, & Wiedermann, ; Bowman, Murgel, Blett, & Porter, ; Zong et al., ). Therefore, alpine ecosystems may respond differently than other ecosystems to nutrient input after clipping defoliation.…”

Section: Introductionmentioning

confidence: 99%

Nitrogen addition stimulated compensatory growth responses to clipping defoliation in a Northern Tibetan alpine meadow

Zong

Shi

2018

Grassland Science

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Grazing and clipping defoliation are the most important human disturbances in natural grasslands. Compensatory growth is a common response to clipping defoliation, which is of great significance for forage production and livestock husbandry development. However, how clipping intensity affects plant compensatory growth and how nitrogen (N) addition regulates this response in alpine ecosystems are still unclear. A manipulative experiment including two clipping intensities (light and heavy) crossed with N addition was conducted in an alpine meadow ecosystem to examine the effects of how N addition regulated plant compensatory growth induced by clipping defoliation. Selective clipping was used to simulate animal feeding, that is, only grasses and sedges were clipped. Under the N addition treatment, the relative growth rate of grasses and total biomass after clipping were significantly higher than those under the no N addition treatment. The total community biomass showed over‐compensatory growth in light clipping under N addition treatment, while it showed equal‐compensatory growth under the other treatments. The over‐compensatory growth in light clipping under the N addition treatments mainly resulted from the stimulated growth of grasses. Regression analysis showed that the relative growth rate and biomass of grasses were positively correlated with soil inorganic N content, but increasing N availability was not conducive to the growth of sedges and other forbs. Divergent responses of different plant functional groups to clipping and N addition would lead to changes in community structure and functioning. Both community biomass and compensatory growth tended to increase first and then reach a stable state with the increase in soil N availability. Our results show that although light clipping could largely stimulate forage production under N addition, excessive clipping cannot lead to a continuous increase in compensatory growth of plant biomass, even under N addition conditions, in this semiarid alpine meadow ecosystem.

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Nitrogen Critical Loads for an Alpine Meadow Ecosystem on the Tibetan Plateau

Cited by 67 publications

References 74 publications

Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes

Initial shifts in nitrogen impact on ecosystem carbon fluxes in an alpine meadow: patterns and causes

The effects of warming and nitrogen addition on ecosystem respiration in a Tibetan alpine meadow: The significance of winter warming

Nitrogen addition stimulated compensatory growth responses to clipping defoliation in a Northern Tibetan alpine meadow

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