Soil Erosion and Vegetation Succession in Alpine Kobresia Steppe Meadow Caused by Plateau Pika——A Case Study of Nagqu County, Tibet

This paper evaluated the impacts of mounds created by the plateau pika （Ochotona curzoniae） on the vegetation composition, structure, and species diversity of an alpine Kobresia steppe meadow in Nagqu County, Tibet Autonomous Region, China. Based on mound height or the depth of erosion pit, we defined five stages of erosion and compared the floristic features of communities at these stages with those in undisturbed sites. In the study area, the mounds and pits covered up to 7% of the total area. Lancea tibetica, Lamiophlomis rotata, and Potentilla biflarca were the dominant species in erosion pits, and Kobresia pygmaea, the dominant species in undisturbed sites, became a companion species in eroded areas. In the process of erosion, the original vegetation was covered by soil ejected by the pika, then the mounds were gradually eroded by wind and rain, and finally erosion pits formed. The vegetation coverage increased with increasing erosion stages but remained significantly lower than that in undisturbed sites. Improved coverage eventually reduced soil erosion, and pit depth eventually stabilized at around 20cm. Aboveground biomass increased with increasing erosion stage, but the proportion of low-quality forage reached more than 94%. The richness index and Shannon-Wiener index increased significantly with increasing erosion stage, but the richness index in mound and pit areas was significantly lower than that in undisturbed sites.

Dynamics of Above-and Below-ground Biomass and C,N,P Accumulation in the Alpine Steppe of Northern Tibet

The temporal dynamics of the biomass, as well as the carbon （C）, nitrogen （N）, phosphorus （P） concentrations and accumulation contents, in above- and below-ground vegetation components were determined in the alpine steppe vegetation of Northern Tibet during the growing season of 2OLO. The highest levels of total biomass （311.68 g m-2）, total C （115.95 g m-2）, total N （2.60 g m-2）, and total P （0.90 g m-2） accumulation contents were obtained in August in 2010. Further, biomass and nutrient stocks in the below-ground components were higher than those of the above-ground components. The dominant species viz., Stipa purpurea and Carex moorcrofli had lower biomass and C, N, P accumulations than the companion species which including Oxytropis. spp., Artemisia capillaris Thunb., Aster tataricus L., and SO on.

Plant diversity-productivity patterns in the alpine steppe environment of the Central Tianshan Mountains

The biodiversity-productivity relationship is an important topic in the research of biodiversity and ecosystem function. The plant diversity productivity pattern is commonly unimodal and positively correlated. This paper researches the characteristics of plant diversity-productivity patterns in the Bayanbuluk alpine steppe in the central Tianshan Mountains, Xinjiang, China, and analyzes the effects of environmental factors on the distribution of plant communities, species composition, plant diversity and productivity in the steppe. The results show a positive correlation between plant diversity and productivity. DCCA (detrended canonical correspondence analysis) ordination reveals a significant relationship between the effects of air temperature, soil moisture content, available soil nitrogen, relative humidity and pH value on the distribution and composition of plant communities. There are significant correlations between the soil moisture content, relative humidity, pH value, air temperature and species richness and the aboveground biomass of Gramineae and Cyperaceae, and also significant correlations between the relative humidity, pH values and the total aboveground biomass of plant communities.

Changes in plant species composition and diversity of alpine Kobresia (Kobresia pygmaea) steppe meadow at different stages of desertification in the North Tibetan plateau

The impacts of desertification on the vegetation composition, structure, and species diversity of alpine Kobresia steppe meadow were evaluated in an area of severe desertification in Anduo County, Tibet Autonomous Region, northern China. We investigated and analyzed the floristic features of communities at four different stages of desertification (slight desertification [SLD], moderate desertification [MD], severe desertification [SD], and very severe desertification [VSD]). The composition and structure of the alpine Kobresia steppe meadow at the SLD site differed significantly from that at the MD, SD, and VSD sites. Species that were more drought resistant and inedible by livestock were the dominant species at the SD site. No plants were found in the shifting dunes of the VSD site. Species diversity also decreased with increasing desertification. The SLD site had the largest mean number of species and individuals and the largest richness index; the MD grassland had the largest Shannon-Wiener index and evenness index, but the smallest Simpson’s index. The vegetation cover declined from 91.8% to 34.8% as desertification increased from SLD to SD, and reached 0% in VSD areas with shifting dunes.

Profile of Methane Concentrations in Soil and Atmosphere in Alpine Steppe Ecosystem on Tibetan Plateau

The methane concentration profile from -1.5m depth in soil to 32m height in air was measured in alpine steppe lo-cated in the permafrost area. Methane concentrations showed widely variations both in air and in soil during the study period. The mean concentrations in atmosphere were all higher than those in soil, and the highest methane concentration was found in air at the height of 16m with the lowest concentration occur-ring at the depth of 1.5m in soil. The variations of atmospheric methane concentrations did not show any clear pattern both temporally and spatially, although they exhibited a more steady-stable state than those in soil. During the seasonal variations, the methane concentrations at different depths in soil were sig-nificantly correlated (R2>0.6) with each other comparing to the weak correlations (R2<0.2) between the atmospheric concentra-tions at different heights. Mean methane concentrations in soil significantly decreased with depth. This was the compositive influence of the decreasing production rates and the increasing methane oxidation rates, which was caused by the descent soil moisture with depth. Although the methane concentrations at all depths varied widely during the growing season, they showed very distinct temporal variations in the non-growing season. It was indicated from the literatures that methane oxidation rates were positively correlated with soil temperature. The higher methane concentrations in soil during the winter were deter-mined by the lower methane oxidation rates with decreasing soil temperatures, whereas methane production rates had no reaction to the lower temperature. Relations between methane contribution and other environmental factors were not discussed in this paper for lacking of data, which impulse us to carry out further and more detailed studies in this unique area.

Rangeland degradation assessment in Kyrgyzstan:vegetation and soils as indicators of grazing pressure in Naryn Oblast

Rangelands occupy more than 80% of the agricultural land in Kyrgyzstan. At least 30% of Kyrgyz pasture areas are considered to be subject to vegetation and soil degradation. Since animal husbandry is the economic basis to sustain people＇s livelihoods, rangeland degradation presents a threat for the majority of the population. We present for the first time an ecological assessment of different pasture types in a remote area of the Naryn Oblast, using vegetation and softs as indicators of rangeland conditions. We analysed the current degree of utilization （grazing pressure）, the amount of biomass, soil samples, and vegetation data, using cluster analysis as well as ordination techniques. Winter pastures （kyshtoo） are characterized by higher pH values （average of 7.27） and lower organic matter contents （average of 12.83%） compared to summer pastures （dzailoo） with average pH values of 6.03 and average organic matter contents of 21.05%. Additionally, summer pastures show higher above- ground biomass, and higher species richness and diversity. Our results support the hypothesis that winter pastures, which are located near settlements, suffer from over-utilisation, while the more distant summer pastures are subjected to much lower grazing pressure,

Variation in carbon,nitrogen and phosphorus partitioning between above-and belowground biomass along a precipitation gradient at Tibetan Plateau

Precipitation is a potential factor that significantly affects plant nutrient pools by influencing biomass sizes and nutrient concentrations. However, few studies have explicitly dissected carbon(C), nitrogen(N) and phosphorus(P) pools between above- and belowground biomass at the community level along a precipitation gradient. We conducted a transect(approx. 1300 km long) study of Stipa purpurea community in alpine steppe on the Tibet Plateau of China to test the variation of N pool of aboveground biomass/N pool of belowground biomass(AB/BB N) and P pool of aboveground biomass/P pool of belowground biomass(AB/BB P) along a precipitation gradient. The proportion of aboveground biomass decreased significantly from mesic to drier sites. Along the belt transect, the plant N concentration was relatively stable; thus, AB/BB N increased with moisture due to the major influences by above- and belowground biomass allocation. However, P concentration of aboveground biomass decreased significantly with increasing precipitation and AB/BB P did not vary with aridity because of the offset effect of the P concentration and biomass allocation. Precipitation gradients do decouple the N and P pool of a S. purpurea community along a precipitation gradient in alpine steppe. The decreasing of N:P in aboveground biomass in drier regions may indicate much stronger N limitation in more arid area.

Effects of Enclosure on Plant and Soil Nutrients in Different Types of Alpine Grassland

Enclosure is one of the most widely used management tools for degraded alpine grassland on the northern Tibetan Plateau, but the responses of different types of grassland to enclosure may vary, and research on these responses can provide a scientific basis for improving ecological conservation. This study took one site for each of three grassland types(alpine meadow, alpine steppe and alpine desert) on the northern Tibetan Plateau as examples, and explored the effects of enclosure on plant and soil nutrients by comparing differences in plant community biomass, leaf-soil nutrient content and their stoichiometry between samples from inside and outside the fence. The results showed that enclosure can significantly increase all aboveground biomass in these three grassland types, but it only increased the 10–20 cm underground biomass in the alpine desert. Enclosure also significantly increased the leaf nutrient content of the dominant plants and contents of total nitrogen(N), total potassium(K), and organic carbon(C) in 10–20 cm soil in alpine desert, thus changing the stoichiometry between C, N and P(phosphorus). However, enclosure significantly increased only the N content of dominant plant leaves in alpine steppe, while other nutrients and stoichiometries of both plant leaves and soil did not show significant differences in alpine meadow and alpine steppe. These results suggested that enclosure has differential effects on these three types of alpine grasslands on the northern Tibetan Plateau, and the alpine desert showed the most active ecological conservation in the responses of its soil and plant nutrients.

Stipa steppes in scantily explored regions of the tibetan Plateau:classification,community characteristics and climatic distribution patterns

Aims As a unique geographical unit of the earth,the tibetan Plateau is extensively covered by various Stipa communities.However,their vegetation features have not been reported systematically till now,especially in some scantily explored regions.In this study,we endeavor to reveal the community types,quantitative charac-teristics and climatic distribution patterns of Stipa steppes in these areas based on primary relevés obtained from fieldwork.Methods We collected a total of 223 plots in 79 study sites in the Changthang Plateau and the Yarlung Zangbo Valley,ranging from 79°E to 91°E.the categories of Stipa formations were identified according to the classification scheme in Vegetation of China and then verified by Nonmetric Multidimensional Scaling.We performed detrended correspondence analysis and detrended canonical correspondence analysis to hunt for the alteration of Stipa communities along the precipitation gradient.Quantitative characteristics including species richness,coverage,biomass as well as importance values(IV)of dominant species were calcu-lated and visualized,respectively.Important Findings Stipa steppes in scantily explored regions of the tibetan Plateau are classified into 11 formations but major formations are rather limited in number.Formation(form.)Stipa purpurea is the most widespread Stipa assemblages not only in scantily explored regions but also across the whole tibetan Plateau.the characteristics of Stipa com-munities,including coverage,species richness,productivity and IV of dominant species,demonstrate the features of typical alpine steppes on the tibetan Plateau.Precipitation proves to be the prime climatic factor controlling the distribution patterns of Stipa assemblages.Form.Stipa subsessiliflora var.basiplumosa and form.Stipa glareosa normally distribute in arid habitats,but rainfall for the former is of greater variance.Form.Stipa roborowskyi and form.Stipa capillacea favor moderately moist environment.Form.Stipa purpurea and form.Stipa roborowskyi can tolerate a fairly broad range of precipitation.

Above-and belowground trait linkages of dominant species shape responses of alpine steppe composition to precipitation changes in the Tibetan Plateau

Aims Human activities and global changes have led to alterations in global and regional precipitation regimes.Despite extensive studies on the effects of changes in precipitation regimes on plant community composition across different types of grassland worldwide,few studies have specifically focused on the effects of precipitation changes on high-altitude alpine steppe at community and plant species levels in the Tibetan Plateau.Methods We investigated the effects of growing-season precipitation changes(reduced precipitation by 50%,ambient precipitation,enhanced precipitation by 50%)for 6 years on plant community composition in an alpine steppe of the Tibetan Plateau by linking above-to belowground traits of dominant species.Important Findings We found that reduced precipitation shifted community composition from dominance by bunchgrass(primarily Stipa purpurea)to dominance by rhizomatous grass(primarily Leymus secalinus).Roots and leaf traits of L.secalinus and S.purpurea differed in their responses to reduced precipitation.Reduced precipitation enhanced root vertical length and carbon(C)allocation to deep soil layers,and decreased the leaf width in L.secalinus,but it did not change the traits in S.purpurea.Moreover,reduced precipitation significantly enhanced rhizome biomass,length,diameter and adventitious root at the rhizome nodes in L.secalinus.These changes in traits may render rhizomatous grass greater competitive during drought stress.Therefore,our findings highlight important roles of above-and belowground traits of dominant species in plant community composition of alpine steppe under precipitation change.