| As effective recovery measures, the enclosure has been widely applied in degraded grassland management in China. Since Ecological Engineering launched in three headwater river source,2.92×104hm2grassland have been get recuperate and built up strength due to the successful implementation of "Returning Grazing-Growing" Project in Qinghai. Analysis such as plant, soil and material recycling in fencing alpine meadows, are not only very important to the regional sustainable utilization of grassland and protection but also to the restoration and reconstruction of degraded grassland.Based on the national macro-control measures, filed investigation including individual and community’variation were compared between fencing and grazing Kobresia pygmaea meadow in the region.Plant and soil carbon/nitrogen storage and distribution were analyzed as well.Moreover, dynamics of soil respiration by enclosed chamber method (TRGA) and estimates of carbon balance were studied in the paper. The main results obtained as follows:(1) Fine herbages showed a tendency of undersizedness in long term grazing. Functional biomass and seed weight decreased significantly, poisonous plant were not obvious. The variability of reproductive weight and reproductive shoot number per plant was small and little plasticity.(2) The plant vegetation group changed with enclosure of grassland. The community structure exhibited simplification and species richness, evenness and diversity decreased in long term fencing, but ecological dominance increased.(3) Total carbon and C:N radio were significantly higher in fenced and ungrazing grassland than those in free grazing grassland.In addition,the storage of soil organic carbon per unit area varied in the order of FU5>FU10>FG, which the order of carbon and nitrogen’contribution was soil>roots>plants. Therefore fenced to exclude grazing by Tibetan sheep and yaks was an alternative approach to sequester C to the soil in Kobresia pygmaea meadow systems.The varieties of total nitrogen storage appeared corresponding tendency,which grazing lead to nitrogen loss.(4) The seasonal dynamic of community above-biomass were not same in fencing and grazing in the whole growing season. The general trend was the "low-high low","S" shape change. Above-biomass showed a trend that FU5was greater than FU10and FG. The self-healing effect of fencing remained not only high above-biomass but also maintained high litter fall and decomposition rate, which appeared double peak curve maximum in green-up period and minimum in the brown-off period. Net Primary productivity of dry material were259.81g·m2·a-1,292.84g·m2·a-1,216.77g·m2·a-1respectively in FU10, FU5and FG. Contribution rate of root system of plant community was maximum and litter fall was minimum.(5) The soil respiration of diurnal and seasonal rate changed little in growing season, which showed soil respiration rate was higher in fencing than that in free grazing grassland. The daily soil respiration rate which was mainly affected by temperature appeared single peak curve that showed afternoon; Composite model which was set by soil respiration rate, soil moisture content and temperature (atmospheric temperature and soil temperature) could explain better the variations of soil respiration rate; The variation range of Q10ranged from1.28to2.34,which was sensitive to temperature in green-up period and late growth stage, and decreased in growth peak period, it was an important factor that grazing increased the sensitivity of soil respiration on soil temperature.(6) Net ecosystem productivities of FU5, FU10and FG was82.67g C·m2·a-1,84.91g C·m2·a-1,80.86g g C·m2·a-1respectively. Roots accounted for the largest share in carbon input components. Fencing or not, Kobresia pygmaea meadow was a carbon sink in three headwater river source regions. In addition, the capacity of carbon sequestration of FU was greater than FG; However, the capacity of carbon sequestration was not obvious when the enclosure was more than5years. |
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