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Contribution of the vegetation layers in the nitrous oxide emission from alpine Kobresia humilis Serg. meadow ecosystem on the Tibetan Plateau

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Du Y. , Cao G. , Deng Y. , Sun G. , Cui X.

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2010

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tom Vol. 58, nr 1

115-124

EN

Nitrous oxide (N[2]O) was one of the major atmospheric greenhouse gases. Its budget was poorly understood in alpine meadow, a dominant vegetation type on the Tibetan Plateau. To characterize a Kobresia humilis meadow on the plateau, N[2]O emission rates were monitored from June 2003 to June 2006 in the study area located at 3280 m a.s.l. Nine plots with 1 m x 1 m each were divided into three treatments, i.e. intact herbaceous community (HCK), removal of aboveground plant biomass (CBK), and removal of both above and belowground plant biomass (BSK), to estimate contribution of plants, r hizosphere and bulk soil to the total N[2]O emission. N[2]O emission from plant aboveground biomass was calculated by flux difference between HCK and CBK, denoted as F[(HCK-CBK)], from rhizosphere by F[(CBK-BSK)], and from bulk soil was the flux in BSK treatment. Static chambers (height 50 cm, area 0.5 x 0.5 m2 )were used for gas collection. N[2]O emission rate was significantly correlated with soil temperature at 5 cm depth in both HCK and BSK (P <0.001). Both treatments demonstrated a seasonal peak rate in growing season and minimum rate in dormancy period. The mean emission rates in the three years were 39.7[plus or minus]2.9 and 30.6[plus or minus]2.5 [mu]g m[^-2] h[^-1] in HCK and BSK, respectively, with the former significantly higher than the latter (P <0.05). In CBK, however, the emission rate did not show consistent correlation with soil temperature, especially in growing season. Its three-year mean emission rate was 36.2[plus or minus]3.3 [mu]g m[^-2] h[^-1]. In the K. humilis meadow, bulk soil contributed much more than plants and rhizosphere. The mean emission rate was 3.5[plus or minus]2.9, 5.7[plus or minus]3.8, and 30.6[plus or minus]2.5 [mu]g m[^-2] h[^-1] (P <0.001) from plants, rhizosphere and bulk soil, and these accounted for 9, 14 and 77%, separately. Our results implied that N[2]O emission rate decreased little with grazing as indicated by the difference between HCK and CBK in K. humilis meadow (P <0.05). N2O emission from alpine meadow could not be ignored in addressing regional greenhouse gases budget on the Tibetan Plateau, considering the vast area and much higher radiative forcing of N[2]O.

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Simulating N2O emission from Kobresia humilis Serg. alpine meadow on Tibetan Plateau with the DNDC model

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Du Y. , Cui X. , Cao G. , Zhao X. , Yang G.

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2011

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tom Vol. 59, nr 3

443-453

EN

Field measured N2O emissions in two years were used to parameterize and validate a process-based model, DNDC, for an alpine Kobresia humilis meadow on the Tibetan Plateau in China. Although this model failed to capture the N2O fluxes in some time periods in the spring or autumn, the modeled results showed overall a good performance in terms of simulating the seasonal variation of N2O fluxes and quantifying the annual total emissions. The relative deviation on the annual basis was about 12.4% and -15.9% for the two years, respectively. The modeled data showed that nitrification contributed about 53% of total N2O production, slightly higher than denitrification. The modeled fluxes were sensitive to soil organic content (SOC), pH, and temperature, but less sensitive to variation of precipitation, soil ammonium and nitrate contents. Further modifications for the model were suggested to focus on the process of soil freezing and thawing as well as the crop growth sub-model that would improve the model's performance for quantifying N2O emission from the alpine meadow.

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Response of alpine plant community to simulated climate change : two-year results of reciprocal translocation experiment (Tibetan Plateau)

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Zhang F. , Li Y. , Cao G. , Wang S. , Zhao X. , Du M. , Wang Q.

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2011

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tom Vol. 59, nr 4

741-751

EN

The great sensitivity of the response of alpine plant community to climate change makes the identification of these responses important. In 2007, we conducted a reciprocal translocation experiment on 100 x 100 x 40 cm coherent turf and soil along an elevation gradient of 3200.3800 m on the south slope of Qilian Mountains northeast of the Qinghai-Tibetan Plateau. The aim was to understand the warming/cooling effects on the alpine ecosystem where treatments were simulated by donor elevations below/above receptors. Translocated vegetation comprised the Kobresia meadow at 3200 m, deciduous shrub meadow at 3400 m, forbs meadow at 3600 m, and sparse vegetation at 3800 m. The 5 x 5 cm grid method (50 x 50 cm, 100 grids) was used for surveying plant species absolute abundance in translocated quadrats. Results showed that species richness and Shannon-Weaver index of Kobresia meadow increased significantly (P <0.05) when translocated to 3400 m. Shannon-Weaver index of shrub meadow declined, while shrub species abundance responded slightly both to warming and cooling treatments. Both species richness and Shannon-Weaver index of forbs meadow and sparse vegetation were enhanced evidently at 3200 m and 3400 m. Four groups were identified by non-metric multidimensional scaling based on receptor elevation. Responses of the alpine plant community and the function group appeared to be specific to climate magnitude and specific to function type, respectively. Correlation indicated that climatic factors played a much more important role than soil in the response of the alpine plant community. Four vegetation types were sensitive to climate change, while Kobresia meadow behaved flexibly. Global warming would depress sedges but favor legumes and graminoids.