Effects of grazing on carbon and nitrogen in plants and soils in a semiarid desert grassland,China

Grazing can modulate the feedback between vegetation and soil nutrient dynamics（carbon and nitrogen）,altering the cycles of these elements in grassland ecosystems.For clarifying the impact of grazing on the C and N in plants and soils in the desert grassland of Ningxia,China,we examined the plant biomass,SOC（soil organic carbon）,total soil N and stable isotope signatures of plants and soils from both the grazed and ungrazed sites.Significantly lower aboveground biomass,root biomass,litter biomass and vegetation coverage were found in the grazed site compared to the ungrazed site,with decreases of 42.0%,16.2%,59.4% and 30.0%,respectively.The effects of grazing on plant carbon,nitrogen,？15N and ？13C values were uniform among species.The levels of plant carbon and nitrogen in grasses were greater than those in the forbs（except for the carbon of Cynanchum komarovii and Euphorbia esula）.Root 15 N and 13 C values increased with grazing,while the responses of root carbon and nitrogen to grazing showed no consistent patterns.Root 15 N and 13 C were increased by 79.0% and 22.4% in the grazed site compared to the ungrazed site,respectively.The values of SOC and total N were significantly lower in the grazed than in the ungrazed sites for all sampling depths（0–10 and 10–20 cm）,and values of SOC and total N at the surface（0–10 cm） were lower than those in the deeper soils（10–20 cm）.Soil ？15N values were not affected by grazing at any sampling depth,whereas soil ？13C values were significantly affected by grazing and increased by 19.3% and 8.6% in the soils at 0–10 and 10–20 cm,respectively.The soil ？13C values（–8.3‰ to –6.7‰） were higher than those for roots（–20.2‰ to –15.6‰） and plant tissues（–27.9‰ to –13.3‰）.Our study suggests that grazing could greatly affect soil organic carbon and nitrogen in contrast to ungrazed grassland and that grazing appears to exert a negative effect on soil carbon and nitrogen in desert grassland.

Analysis of the Species Dominance & Dominant on the Karst Mountain Grassland Plant Community

[Objective] The aim was to study the species,quantity and community traits of dominant plant in karst mountain grassland plant community so as to provide support for the vegetation restoration in karst mountain grassland.[Method] Standard plot sites investigation method was used study the quantity traits of different plant communities of different altitudes and slopes.[Result] The IV SDR4 were the highest in the all plot sites of plant community on the kasrt mountain grassland,but the IV SDR4 were showed a trend of decreasing with the increasing of the altitude.The dominant quantity was increasing with the altitude upward,so the altitude was the mostly factor for plant community construction.[Conclusion] Altitude was the main factor to influence the community structure of plant.

Effects of converting natural grasslands into planted grasslands on ecosystem respiration： a case study in Inner Mongolia, China

With increasingly intensifying degradation of natural grasslands and rapidly increasing demand of high quality forages, natural grasslands in China have been converted into planted grasslands at an unprecedented rate and the magnitude of the conversion in Inner Mongolia is among the national highest where the areal extent of planted grasslands ranks the second in China. Such land-use changes（i.e., converting natural grasslands into planted grasslands） can significantly affect carbon stocks and carbon emissions in grassland ecosystems. In this study, we analyzed the effects of converting natural grasslands into planted grasslands（including Medicago sativa, Elymus cylindricus, and M. sativa＋E. cylindricus） on ecosystem respiration（F（eco）） in Inner Mongolia of China. Diurnal F（eco） and its components（i.e., total soil respiration（F（ts））, soil heterotrophic respiration（F（sh）） and vegetation autotrophic respiration（F（va））） were measured in 2012（27 July to 5 August） and 2013（18 July to 25 July） in the natural and planted grasslands. Meteorological data, aboveground vegetation data and soil data were simultaneously collected to analyze the relationships between respiration fluxes and environmental factors in those grasslands. In 2012, the daily mean F（eco） in the M. sativa grassland was higher than that in the natural grassland, and the daily mean F（va） was higher in all planted grasslands（i.e., M. sativa, E. cylindricus, and M. sativa＋E. cylindricus） than in the natural grassland. In contrast, the daily mean F（ts） and F（sh） were lower in all planted grasslands than in the natural grassland. In 2013, the daily mean F（eco）, F（ts） and F（va） in all planted grasslands were higher than those in the natural grassland, and the daily mean F（sh） in the M. sativa＋E. cylindricus grassland was higher than that in the natural grassland. The two-year experimental results suggested that the conversion of natural grasslands into planted grasslands can generally increase the F（eco） and the increase in F（eco） is more pronounced when the plantation becomes more mature. The results also indicated that F（sh） contributed more to F（eco） in the natural grassland whereas F（va） contributed more to F（eco） in the planted grasslands. The regression analyses show that climate factors（air temperature and relative humidity） and soil properties（soil organic matter, soil temperature, and soil moisture） strongly affected respiration fluxes in all grasslands. However, our observation period was admittedly too short. To fully understand the effects of such land-use changes（i.e., converting natural grasslands into planted grasslands） on respiration fluxes, longer-term observations are badly needed.

Soil and Vegetation Seasonal Changes in the Grazing Andean Mountain Grasslands

Andean grasslands ecosystems are fragile environments with rigorous climatologic conditions and low and variable food for the grazing. The Apolobamba area is located in the Bolivian Andean Mountains. Its high grasslands provide a natural habitat for wild and domestic camelids such as vicuna(Vicugna vicugna) and alpaca(Lama pacos). The botanical diversity plays an essential role in maintaining vital ecosystem functions. The objectives of this research were to determine the seasonal changes in soil properties, to study the vegetation changes during the wet and dry seasons and the influence of soil properties and camelid densities on the vegetation in the Apolobamba grasslands. Four zones with different vicuna populations were selected to be studied. The following soil parameters were determined: total organic carbon, total nitrogen, available phosphorous, cation exchange capacity, exchangeable cations, pH and texture. The vegetation season changes were studied through botanical identification, above-ground biomass, plant cover and species richness. Results showed that some soil properties such as C/N ratio, CEC, silt and clay percentages kept stable against the seasonal changes. Generally, soil nutrients were relatively higher during the dry season in the surface and subsurface. The results did not point out the predominant vegetation growth during the wet season. The seasonal vegetation growth depended on each species. Thegood soil fertility corresponded to the highest plant cover. Soil fertility presented no influence on the above-ground biomass of the collected species. The negative influence of camelid grazing on soil properties could not be assessed. However, overgrazing could affect some plant species. Therefore, protection is needed in order to preserve the biodiversity in the Andean mountain grasslands.

Reasonable management of perennial planting grassland contributes to positive succession of soil microbial community in Sanjiangyuan of Qinghai-Tibetan Plateau,China

Grassland reconstruction is a major approach to alleviate the‘black beach’in Sanjiangyuan of the Qinghai-Tibetan Plateau.It is vital to understand how to manage the planting grassland after reconstruction.And which artificial grassland management pattern is more likely to restore the degraded grassland of‘black beach?’To provide the scientific basis for the restoration of‘black beach’,we investigated the changes in vegetation characteristics,soil physicochemical properties and soil microbial community structure of planting grassland under different management patterns,and explored the effect of the management patterns on community succession of planting grassland.In this study,vegetation characteristics and soil physicochemical properties were measured by field investigation and laboratory analyses,respectively.Soil microbial community composition was determined by high-throughput sequencing techniques.The results showed that there were significant differences in vegetation characteristics,soil physicochemical properties and soil microbial community structure of the planting grassland under different management patterns.Actinobacteria and Basidiomycota were mainly controlled by vegetation plant species diversity,aboveground biomass(AGB)and soil organic carbon(SOC).Shannon-Wiener index,AGB and SOC peaked and the relative abundance of amplicon sequence variants annotated by Actinobacteria and Basidiomycota were significantly enriched under the management pattern of the planting once treatment.Additionally,the soil had the highest bacterial diversity and the lowest fungal diversity under the planting once treatment,becoming a‘bacterial’soil.These vegetation characteristics and soil environment were more conducive to overall positive community succession,indicating that the planting once treatment is the most reasonable management pattern for restoring the‘black beach’.