Xilin River Basin Research Articles

CH4 uptake flux of Leymus chinensis steppe during rapid growth season in Inner Mongolia, China

The influence of near ground atmosphere CH4 concentration, soil water content, soil Eh, plants, soil temperature, and pH on CH4 uptake flux of Leymus chinensis steppe during rapid growth season was studied using field in-situ measurement in Xilin River basin of Inner Mongolia, China. The results showed that CH4 uptake flux was positively correlated with near ground atmosphere CH4 concentration and soil Eh but negatively correlated with soil water content. Precipitation may decrease the CH4 flux by increasing the soil water content. The average fluxes of three treatments during the observation period were 1.52 (natural conditions, 1.51 (aboveground plants were excluded), and 2.00 mg m−2 d−1 (all plants were removed), respectively. The difference between the CH4 flux of natural condition treatment and that of removing aboveground plants treatment is small, whereas the flux of removing all plants treatment is larger than the other two treatments. This means that the contribution of aboveground plants to CH4 uptake flux is smaller than that of roots or roots-removing process. CH4 uptake flux is not sensitive to soil temperature and the narrow-ranged soil pH (6.36–7.86). The Leymus chinensis steppe acts as a sink for CH4, and thus more studies should be focused on its affecting factors and related mechanisms.

Spatial-temporal variation in soil respiration and its controlling factors in three steppes of Stipa L. in Inner Mongolia, China

Grassland is the largest terrestrial ecosystem in China. It is of great significance to measure accurately the soil respiration of different grassland types for the contribution evaluation of the Chinese terrestrial ecosystem’s carbon emission to the atmospheric CO2 concentration. A three-year (2005–2007) field experiment was carried out on three steppes of Stipa L. in the Xilin River Basin, Inner Mongolia, China, using a static opaque chamber technique. The seasonal and interannual variations of soil respiration rates were analyzed, and the annual total soil respiration of the three steppes was estimated. The numerical models between soil respiration and water-heat factors were established respectively. Similar seasonal dynamic and high annual and interannual variations of soil respiration were found in all of the three steppes. In the growing season, the fluctuation of soil respiration was particularly evident. The coefficients of variation (CVs) for soil respiration in different growing seasons ranged from 54% to 93%, and the annual CVs were all above 115%. The interannual CV of soil respiration progressively decreased in the order of Stipa grandis (S. grandis) steppe > Stipa baicalensis (S. baicalensis) steppe > Stipa krylovii (S. krylovii) steppe. The annual total soil respiration for the S. baicalensis steppe was 223.62–299.24 gC m−2 a−1, 150.62–226.99 gC m−2 a−1 for the S. grandis steppe, and 111.31–131.55 gC m−2 a−1 for the S. krylovii steppe, which were consistent with the precipitation gradient. The variation in the best fitting temperature factor explained the 63.5%, 73.0%, and 73.2% change in soil respiration in the three steppes at an annual time scale, and the corresponding Q10 values were 2.16, 2.98, and 2.40, respectively. Moreover, the Q10 values that were calculated by soil temperature at different depths all expressed a 10 cm > 5 cm > surface in the three sampling sites. In the growing season, the soil respiration rates were related mostly to the surface soil moisture, and the 95.2%, 97.4%, and 93.2% variations in soil respiration in the three steppes were explained by the change in soil moisture at a depth of 0–10 cm, respectively.

Effects of grazing on leaf traits and ecosystem functioning in Inner Mongolia grasslands: scaling from species to community

Abstract. Understanding the mechanistic links between environmental drivers, human disturbance, plant functional traits, and ecosystem properties is a fundamental aspect of biodiversity-ecosystem functioning research. Recent studies have focused mostly on leaf-level traits or community-level weighted traits to predict species responses to grazing and the consequent change in ecosystem functioning. However, studies of leaf-level traits or community-level weighted traits seldom identify the mechanisms linking grazing impact on leaf traits to ecosystem functioning. Here, using a multi-organization-level approach, we examined the effects of grazing on leaf traits (i.e., leaf area, leaf dry mass and specific leaf area) and ecosystem functioning across six communities of three vegetation types along a soil moisture gradient in the Xilin River Basin of Inner Mongolia grassland, China. Our results showed that the effects of grazing on leaf traits differed substantially when scaling up from leaf-level to species, functional group (i.e., life forms and water ecotype types), and community levels; and they also varied with vegetation type or site conditions. The effects of grazing on leaf traits diminished progressively along the hierarchy of organizational levels in the meadow, whereas the impacts were predominantly negative and the magnitude of the effects increased considerably at higher organizational levels in the typical steppe. Soil water and nutrient availability, functional trade-offs between leaf size and number of leaves per individual, and differentiation in avoidance and tolerance strategies among coexisting species are likely to be responsible for the observed responses of leaf traits to grazing at different levels of organization and among vegetation types. Our findings also demonstrate that, at both the functional group and community levels, standing aboveground biomass increased with leaf area and specific leaf area. Compared with the large changes in leaf traits and standing aboveground biomass, the soil properties were relatively unaffected by grazing. Our study indicates that a multi-organization-level approach provides more robust and comprehensive predictions of the effects of grazing on leaf traits and ecosystem functioning.

Correlations between leaf and fine root traits among and within species of typical temperate grassland in Xilin River Basin, Inner Mongolia, China.

Correlations between leaf and fine root traits among and within species of typical temperate grassland in Xilin River Basin, Inner Mongolia, China.

Changes in carbon and nitrogen of Chernozem soil along a cultivation chronosequence in a semi‐arid grassland

SummaryChanges in the carbon (C) stock of grassland soil in response to land use change will increase atmospheric CO2, and consequently affect the climate. In this study we investigated the effects of land use change on soil organic C (SOC) and nitrogen (N) along a cultivation chronosequence in the Xilin River Basin, China. The chronosequence consisted of an undisturbed meadow steppe, a 28‐year‐old cropland and a 42‐year‐old cropland (abbreviated as Steppe, Crop‐28 Y and Crop‐42Y, respectively). Crop‐28Y and Crop‐42Y were originally created on the meadow steppe in 1972 and 1958, respectively. The soil samples, in ten replications from three depth increments (0–10, 10–20 and 20–30 cm), were collected, respectively, in the two cropland fields and the adjacent undisturbed steppe. Bulk density, SOC, total N and 2 m KCl‐extractable mineral N including ammonium and nitrate were measured. Our results showed that the greatest changes in the measurements occurred in the 0–10 cm soil depth. The SOC stock in the upper 30‐cm soil decreased by 9.83 Mg C ha−1 in Crop‐28Y and 21.87 Mg C ha−1 in Crop‐42Y, which indicated that approximately 10 and 25% of the original SOC of the steppe had been emitted over 28 and 42 years, respectively. Similarly, the total N lost was 0.66 Mg N ha−1 and 1.18 Mg N ha−1, corresponding to approximately 9% and 16%, respectively, of the original N at the same depth and cropping duration as those noted for SOC. The mineral N concentration in the soil of both the two croplands was greater than that in the steppe soil, and the ammonium‐N was less affected by cultivation than the nitrate‐N. The extent of these changes depended on soil depth and cropland age. These effects of cultivation were much greater in the top 10 cm of soil than in deeper soil, and also greater in Crop‐42Y than in Crop‐28Y. The findings are significant for assessing the C and N sequestration potential of the land use changes associated with grassland conversion, and suggest that improved management practices are needed to sequester SOC and total N in the cropped soil in a semi‐arid grassland.

Drivers of soil net nitrogen mineralization in the temperate grasslands in Inner Mongolia, China

Soil net nitrogen mineralization (NNM) of four grasslands across the elevation and precipitation gradients was studied in situ in the upper 0-10 cm soil layer using the resin-core technique in Xilin River basin, Inner Mongolia, China during the growing season of 2006. The primary objectives were to examine variations of NNM among grassland types and the main influencing factors. These grasslands included Stipa baicalensis (SB), Aneulolepidum Chinense (AC), Stipa grandis (SG), and Stipa krylovii (SK) grassland. The results showed that the seasonal variation patterns of NNM were similar among the four grasslands, the rates of NNM and nitrification were highest from June to August, and lowest in September and October during the growing season. The rates of NNM and nitrification were affected significantly by the incubation time, and they were positively correlated with soil organic carbon content, total soil nitrogen (TN) content, soil temperature, and soil water content, but the rates of NNM and nitrification were negatively correlated with available N, and weakly correlated with soil pH and C:N ratio. The sequences of the daily mean rates of NNM and nitrification in the four grasslands during the growing season were AC > SG > SB > SK, and TN content maybe the main affecting factors which can be attributed to the land use type.

Short-term responses of a Stipa grandis/Leymus chinensis community to frequent defoliation in the semi-arid grasslands of Inner Mongolia, China

Grassland degradation due to over-grazing causes severe ecological and economical problems in the semi-arid grasslands of Inner Mongolia, PR China. The development of sustainable management systems is required, but basic information regarding the degradation process in its formation and development is rare. In 2004 and 2005 a cutting-frequency experiment was conducted in the Xilin River Basin, Inner Mongolia, subjecting a non-degraded grassland area to 3 different cutting frequencies: single defoliation at the end of growing season and defoliations every 6 and 3 weeks. It was hypothesised that the productivity of the S. grandis/L. chinensis community will be reduced by frequent defoliations. The cumulative dry matter yield increased with increasing defoliation frequency from 204 to 277gDMm−2 in 2004 and from 87 to 158gDMm−2 in 2005. The low aboveground biomass productivity in 2005 resulted from the low amount of precipitation, which was only 50% of the long-term mean. The nitrogen yield increased from 2.9 to 6gNm−2 in the frequently defoliated treatments in 2004 and from 1.2 to 2.8gNm−2 in 2005. Total leaf area was significantly reduced by frequent defoliation, but specific leaf area increased both in S. grandis and L. chinensis. Root mass (0–15cm) was on average 929gOMm−2 in 2004 and 882gOMm−2 in 2005 and, as well as species composition, not significantly influenced by frequent defoliations. It was concluded that frequent defoliation positively affected the productivity of the S. grandis/L. chinensis community, and that the annual amount of precipitation essentially determined the biomass production of this grassland ecosystem. Because the community increased its productivity after frequent defoliation in the 2 experimental years, it was suggested that the community is resistant to defoliation stress in the short-term.

Impact of grazing intensity on herbage intake, composition, and digestibility and on live weight gain of sheep on the Inner Mongolian steppe

High grazing pressure during the last decades caused severe ecological problems in the steppe of Inner Mongolia, China. The objective of the present study was to determine the effects of grazing intensity of sheep on herbage mass (HM) and intake, chemical composition and digestibility of herbage, and on live weight gain (LWG). A grazing experiment with six different grazing intensities (1.5, 3.0, 4.5, 6.0, 7.5, and 9.0 sheep/ha) was conducted in the growing season of 2005 in the Xilin River Basin. HM decreased from 1.5 t DM/ha at the lowest grazing intensity to 0.6 t DM/ha at the highest grazing intensity. NDF content of the herbage was high (> 700 g/kg DM) and relatively constant, whereas acid detergent lignin (ADL) content increased with grazing intensity and with proceeding grazing season. Digestibility of organic matter ingested (DOM) tended to decrease with grazing intensity as well as intake of organic matter (OMI) and of digestible organic matter (DOMI) per sheep ( P = 0.090 and P = 0.065, respectively), whereas LWG per sheep decreased with increasing grazing intensity ( P = 0.018). DOM and OMI were negatively related to ADL content. However, herbage intake and LWG per ha increased with grazing intensity ( P < 0.001) and reached their maximum at 9 and 7.5 sheep per ha, respectively. This observation confirms the current farmers' practise of high grazing pressure ignoring long term grassland productivity and ecological problems. Therefore, the studies are continued to provide further information on long term effects. This study could show pronounced effects of grazing intensity on animal and grassland productivity and the suitability of the methods applied to measure intake and digestibility of herbage in a large scale grazing experiment with sheep.

China's grazed temperate grasslands are a net source of atmospheric methane

A budget for the methane (CH 4) cycle in the Xilin River basin of Inner Mongolia is presented. The annual CH 4 budget in this region depends primarily on the sum of atmospheric CH 4 uptake by upland soils, emission from small wetlands, and emission from grazing ruminants (sheep, goats, and cattle). Flux rates for these processes were averaged over multiple years with differing summer rainfall. Although uplands constitute the vast majority of land area, they consume much less CH 4 per unit area than is emitted by wetlands and ruminants. Atmospheric CH 4 uptake by upland soils was −3.3 and −4.8 kg CH 4 ha −1 y −1 in grazed and ungrazed areas, respectively. Average CH 4 emission was 791.0 kg CH 4 ha −1 y −1 from wetlands and 8.6 kg CH 4 ha −1 y −1 from ruminants. The basin area-weighted average of all three processes was 6.8 kg CH 4 ha −1 y −1, indicating that ruminant production has converted this basin to a net source of atmospheric CH 4. The total CH 4 emission from the Xilin River basin was 7.29 Gg CH 4 y −1. The current grazing intensity is about eightfold higher than that which would result in a net zero CH 4 flux. Since grazing intensity has increased throughout western China, it is likely that ruminant production has converted China's grazed temperate grasslands to a net source of atmospheric CH 4 overall.

Using a hybrid fuzzy classifier (HFC) to map typical grassland vegetation in Xilin River Basin, Inner Mongolia, China

Community ecologists and vegetation scientists in grassland research have a strong interest in quantifying biotic communities in detail. However, a satisfactory classification with fine biotic details has been challenged by the coarse resolutions of Landsat images, although they are easily accessible. In this paper, a hybrid fuzzy classifier (HFC) for vegetation classification with Landsat ETM+ imagery on the typical grassland in Xilinhe River Basin, Inner Mongolia, China has been developed. Three vegetation classification systems were created from different aspects: the botanical system (Bio‐classes, also as the final mapping units for vegetation cover), the combined botanical and spectral system (Bio‐S classes), and the spectral system (Spec‐classes). The HFC designed a fuzzy logic to measure the similarity between Spec‐classes, extracted by the unsupervised classification, and Bio‐S classes, built from the field samples, when considering the spectral variations of samples within the same Bio‐class. Then, Bio‐S classes, which served as a bridge for assigning Spec‐classes to the target Bio‐classes, were merged to restore Bio‐classes for the final mapping. To assess the classification accuracy, the HFC was compared with a conventional supervised classification (CSC). The overall result of the HFC was much better than that of the CSC, with an accuracy percentage of 80.2% as compared to 69.0% for the CSC.

Slope aspect has effects on productivity and species composition of hilly grassland in the Xilin River Basin, Inner Mongolia, China

In order to investigate the productivity of hilly grassland of the Xilin River Basin as affected by slope aspect (North versus South), aboveground green biomass (AGB) and species composition were studied at four hill sites in 2005. Additionally, a detailed investigation combining vegetation parameters, physical and chemical soil characteristics was carried out at different slope positions (base, middle, and top) of north and south slope aspect on one of the hills in 2004 and 2005. Northern slopes exhibited a higher productivity and species diversity compared to southern slopes. Plant available soil K, P and N were not limiting the productivity at south- relative to north-oriented slopes, whereas soil available water was the primarily limiting factor for plant productivity, which was supported by results of leaf carbon isotope discrimination of main species. A negative correlation between productivity and relative abundance of C 4 plants indicates that the relative biomass of C 4 plants can be used as a water-stress indicator.

Isotopic carbon composition and related characters of dominant species along an environmental gradient in Inner Mongolia, China

Carbon isotope composition ( δ 13C value) provides a useful measure of integrated water-use efficiency (WUE) of plants and can be used to rank the drought tolerance of different species. We determined the δ 13C values, leaf water content (LWC) and free proline content of 52 plant species selected from eight plant communities along a moisture gradient in the Xilin River Basin, Inner Mongolia. The δ 13C values and WUE of C 3 plant species tended to increase as the occurrence frequency and relative biomass of the species increased in the entire basin. The mean foliage proline concentration of all species in a community was higher when the habitat was drier and the mean LWC of plants decreased with increasing soil aridity. Significantly positive relationships existed between the foliar proline concentration and occurrence frequency and relative biomass of the species, respectively. Our results indicated that inter- and intra-species variations in WUE might significantly influence the outcome of competitive interactions and played a large role in determining species composition of plant communities. In addition, proline accumulation in leaves might strengthen competitive ability of plants growing in drought prone habitats.

Spatial variability of soil properties affected by grazing intensity in Inner Mongolia grassland

Analysis of the spatial variability of soil properties is important to interpret the site-specific ecosystems not only with respect to process investigations but also to model upscaling. This paper aims to study the effects of the grazing intensity on soil physical and mechanical properties and their interactions in a Leymus chinensis steppe of the Xilin River Basin, Inner Mongolia, China. The investigated sites were subjected to five grazing intensities (ungrazed since 1979, ungrazed since 1999, winter grazing, continuous grazing and heavy grazing). Soil water content (SWC), hydraulic conductivity ( K), water drop penetration time (WDPT), shear strength (SS), soil organic carbon (SOC) concentration, bulk density (BD), and soil texture were measured at a grid with 15 m sampling distance on the surface soil during the period of 2004–2005. The data were analyzed using descriptive statistics and geostatistics. The correlation and interaction between soil properties were analyzed by the methods of Pearson correlation, partial correlation and multiple regression analysis. The results showed that spatial distributions of soil properties could be well described by spherical or exponential models. The ranges of spatial dependence were the highest for WDPT and the lowest for SS. Grazing decreased SWC, SOC and WDPT but increased BD and SS. Multiple regression analysis showed significant correlations among SWC, K, WDPT, SOC and BD; as well as between SS and silt content. Soil compaction induced by sheep trampling, especially in the heavily grazed site, inclined to a homogenous spatial distribution of soil properties, which will possibly enhance soil vulnerability to water and nutrient loss, and consequently reduce the plant available water and thus grassland productivity.

Variations in δ13C values among major plant community types in the Xilin River Basin, Inner Mongolia, China

The δ13C values of 51 plant species selected from eight plant communities along a moisture gradient were measured. Our results showed that all the community types that we investigated are dominated by C3 species in the Xilin River Basin. Large variations in the average 13C natural abundance of different communities were detected, and the magnitude of δ13C values showed the following trend: typical steppe (–23.0‰) &gt; degraded steppe (–23.5‰) &gt; sand dune (–25.0‰) &gt; restoring degraded steppe (–25.8‰) &gt; meadow steppe (–26.4‰) ≥ saline meadow (–26.5‰) &gt; swamp meadow (–28.2‰). The major determinants of the biomass-weighted δ13C values in a given community were the presence or absence of C4 plants, the intrinsic variation among species and the variation of the same species growing in different habitats with different soil-moisture regimes and disturbance history. These results suggested that different habitats support dominant species with different water-use efficiencies and a trend in the community-level δ13C values was observed, as ascribed by the contribution of C4 plants and/or the variations among species or the response of water-use efficiency of the same species to different soil moisture conditions.

NEW METHOD FOR MEASURING EVAPOTRANSPIRATION AND CO&lt;inf&gt;2 &lt;/inf&gt;ABSORPTION IN GRASSLAND CO MMUNITIES USING LI-6262 CO&lt;inf&gt;2&lt;/inf&gt;/H&lt;inf&gt;2&lt;/inf&gt;O ANALYSER

Aims Our objective was to develop a new method for simultaneously measuring evapotranspiration and CO2 absorption in plant communities using the LI-6262 CO2/H2O analyzer for regional integration of water and CO2 dynamics. Methods We measured evapotranspiration and CO2 absorption of some plant communities in the typical steppe of the Xilin River Basin, China. Important findings Our method enabled us to concurrently measure evapotranspiration, photosynthesis and respiration, the important ecological processes of communities and therefore obtain a series of valuable measurements of community characteristics. Our method is precise, the instruments are easily portable, and the method is adaptable for plant communities of steppe, sand lands and wetlands. The method has important practical value for study of the impacts of global change on ecological functions of steppe.

Comparison of CO2 effluxes and their driving factors between two temperate steppes in Inner Mongolia, China

Soil respiration is a key component of the global terrestrial ecosystem carbon cycle. The static opaque chamber method was used to measure the CO2 effluxes from soil of a semiarid Aneurolepidium chinense steppe and a Stipa krylovii steppe in the Xilin River Basin of Inner Mongolia, China from March 2002 to December 2004. The results indicated that the soil respiration rates of the semiarid Aneurolepidium chinense steppe and the Stipa krylovii steppe were both relatively high from mid-May to mid-September of each year and remained low during the rest of the year. The minimum value of soil respiration occurred in December or January and negative effluxes of CO2 appeared for several days during the non-growing season of individual years at the two sampling sites. A high annual variation was found in the two steppes with the coefficients of variance (CV) being over 94%, even high to 131%. The annual sums of soil CO2 efflux of the Aneurolepidium chinense steppe varied between 356.4 gC m−2 yr−1 and 408.8 gC m−2 yr−1, while those of the Stipa krylovii steppe in the three years were in the range of 110.6 gC m−2 yr−1 to 148.6 gC m−2 yr−1. The mean respiration rates of the Aneurolepidium chinense steppe were significantly higher than those of the Stipa krylovii steppe in different statistical periods with the exception of the non-growing season. About 59.9% and 80.6% of the soil respiration variations in both steppes for the whole sampling period were caused by the changes of temperature and soil water content. In the Aneurolepidium chinense steppe, the soil respiration rate has significant or extremely significant positive correlation (r = 0.58–0.85, p < 0.05 or p < 0.01) with air temperature and ground temperature of the topsoil except in 2002; the unique contributions of temperature change to the soil respiration variation of the three years were 53.3%, 81.0% and 58.6%, respectively. But, for the Stipa krylovii steppe in the same time interval, the soil water content (especially that of the 10–20 cm layer) has a greater effect on the change of soil respiration, and the unique contributions of the change of the 10–20 cm soil water content to the variations of soil respiration in 2002 and 2003 were 60.0% and 54.3%, respectively. In 2004, in spite of the higher contribution of temperature than soil water content, the contribution of ground temperature at a depth of 10 cm was only 46.2%, much weaker than that of any single year in the Aneurolepidium chinense steppe.

IMPACT OF EXTREME DROUGHT ON NET ECOSYSTEM EXCHANGE FROM LEMUS CHINENSIS STEPPE IN XILIN RIVER BASIN, CHINA

Background and Aims Many reports on global change have predicted major change in the temporal and spatial pattern of precipitation, which may have significant effects on temperate grasslands in arid and semi_arid regions. The responses of grasslands to environmental changes, especially amount and timing of precipitation, can be very different. Some studies indicate that drought may result in degradation of ecosystem function in NEE, even changing the ecosystem from a carbon sink to a carbon source. Methods In order to quantify net ecosystem carbon exchange in Leymus chinensis steppe and its response to precipitation, we used the eddy covariance technique to measure carbon dioxide flux during the 2005 growing season in Xilin River Basin of Inner Mongolia Plateau in 2005. Only 126 mm precipitation fell during this growing season, far less than average; therefore, the steppe was in an extreme drought condition. Key Results The daily pattern of CO_2 uptake in this drought year was consistent bimodal, with peaks at 8∶00 and 18∶00. In normal years, the bimodal pattern occurred only when soil water stress occurred. Maximum half_hourly average CO_2 uptake was -0.38 mg·m~ -2 ·s~ -1 in 2005, which was half that in typical growing seasons. Moreover, the ecosystem was a CO_2 source most of the growing season, releasing about 0.05 mg CO_2·m~ -2 ·s~ -1 at nighttime. Conclusions The seasonal pattern of CO_2 uptake closely followed that of aboveground biomass and was strongly affected by soil temperature and soil water content. The ecosystem emitted 372.56 g CO_2·m~ -2 during the growing season in 2005. The partial explanation is that much plant litter accumulated on the ground surface due to enclosure of the grassland since 1979, and this litter decomposed and resulted in a net release of CO_2 to atmosphere.

Effects of grazing on photosynthetic characteristics of major steppe species in the Xilin River Basin, Inner Mongolia, China

Species composition and photosynthetic characteristics of dominant species of ungrazed plot (UG), overgrazed plot (OG), and restored grazed plot (RG) were determined in the Xilin River Basin, Inner Mongolia, China. Both heavily grazing and restoration significantly affected the composition of different species and life forms. Leymus chinensis, Stipa grandis, and Cleistogenes polyphylla, three dominant perennial grasses in UG plot, contributed 58.9 % aboveground biomass to that of whole community, and showed higher net photosynthetic rate (PN), transpiration rate (E), and intrinsic water-use efficiency (WUE). In OG plot, relative biomass of L. chinensis and S. grandis significantly decreased, while relative biomass of three shrubs/sub-shrubs, Caragana microphylla, Artemisia frigida, and Kochia prostrata, obviously increased. Heavy grazing significantly decreased PN, E, and WUE of L. chinensis and S. grandis, while shrubs/sub-shrubs showed significantly higher photosynthetic activity and WUE than the grasses. After 18-year restoration, photosynthetic activities of L. chinensis and S. grandis were significantly higher than those in the OG plot. The proportion of L. chinensis, S. grandis, and C. microphylla significantly increased, and relative biomass of C. polyphylla, A. frigida, and K. prostrata markedly declined in RG plot. We found close relationships between physiological properties of species and their competitive advantage in different land use types. Higher photosynthetic capability means more contribution to total biomass. The variations in physiological characteristics of plants could partly explain the changes in species composition during degrading and restoring processes of Inner Mongolia typical steppes.

Uncertainties in up-scaling N 2O flux from field to 1°×1° scale: A case study for Inner Mongolian grasslands in China

Since N 2O emissions cannot be measured easily at large scales, global emission estimates inevitably involve problems with scaling. To date, up-scaling processes depend highly on the models and database. Because of the limitation in resolution of the databases, which provide input parameters to drive the model's regional simulations, the uncertainties generated from the up-scaling processes must be quantified. In this paper, the uncertainties in up-scaling N 2O emissions from the field scale (∼1 km 2) to 1°×1° scale (∼10,000 km 2) were quantified in a case study from the Xilin River basin of Inner Mongolia, China. A revised process-based DNDC model was applied in the study for quantifying N 2O fluxes with a high-resolution (1 km 2) soil database constructed with remote sensing data and GIS technique. The results showed that the uncertainties coming from spatial scaling effect is 63.6%, and from the partitioning of sensitive model parameter (SOC) is 86.4%. We found that inclusion of spatial heterogeneity of soil factors resulted in lower regional N 2O emission estimates. Utilization of the spatial structural information based on soil type was more effective for reducing the spatial scaling effect in comparison with the variability information calculated from Monte Carlo method.

Methane emission from small wetlands and implications for semiarid region budgets

Despite considerable research, large uncertainties exist in the various area‐scales budgets of CH4 flux between soils and the atmosphere. We postulated that small wetlands greatly contribute to the CH4 budget in semiarid regions, where wetland contributions are often assumed to be insignificant. To test this hypothesis, small riparian mires of the Xilin River basin in Inner Mongolia were selected as a case study for weekly measurements of in situ CH4 flux. Average CH4 fluxes were 234.3 and −1.9 mg CH4 m−2 d−1 for the riparian mires and the upland grassland, respectively, during July–October 2003. Although the riparian mires cover only 0.4% of the Xilin River basin, their total CH4 emission was about half of the amount of CH4 consumed by the upland grassland with 89.7% land cover ratio. Our results indicate that estimated CH4 budgets for semiarid regions should include an assessment of small wetlands.