| The influences of different enclosure years(that were respectively zero, one, six and nine) on grassland community characteristics, species diversity, pasture mass index, soil conventional nutrients, and soil fraction of active organic carbon(soil readily oxidizable carbon, soil particulate carbon and nitrogen, soil light fraction organic carbon and nitrogen, microbial mass carbon and nitrogen) of Seriphidium transiliense desert grassland were studied, and analyzed the degree of coupling of vegetation and soil, the degree of correlation and regression between enclosure years and each index of vegetation, soil with gray system. The response of each index of vegetation and soil to enclosure was discussed and found a suitable enclosure year in order to provide a scientific basis for the management and rehabilitation, and the improvement techniques for the degraded grassland of desert in this area. The main results were as follows:(1) The total coverage, density and biomass of S.transiliense desert grassland presented the fluctuation of “down-up-down” with the increase in the time of enclosure, and reached the highest in six years of enclosure; Fencing enclosure was conducive to S.transiliense, Kochia prostrate growth and recovery; The species diversity index of community had increased compared with the control area after the enclosure, and presented the trend that increased first and then decreased and further increased with the increase in the time of enclosure.(2) Overall, the content of soil TC showed an upward trend with the time of enclosure in 0-20 cm, and the difference of enclosure 9 years and control area was significant. The control area was significantly higher for enclosure 6 years in 20-30 cm, and the content of total carbon of enclosure 9 years was minimum in 30-50 cm, and lower significantly than other three treatments. Soil carbon density showed “enclosure 9 years>the control> enclosure 1 year> enclosure 6 years” in 0-5cm, but it were significantly different both enclosure 9 years and enclosure 6 years, while effects of enclosure on soil carbon density and stocks were not significant in other soil layers.(3) Soil organic matter, total nitrogen and alkali solution nitrogen substantially showed a trend of “first down then up” with the extension of fencing time in the surface, and reached the highest value in enclosure 9 years, and soil organic matter, total nitrogen of enclosure 9 years were significantly higher than enclosure 1 year in 0-5cm(P<0.05); The available potassium and available phosphorus showed a trend of “first down then up then down ”, and reached the maximal value in enclosure 6 years, and available potassium was significantly higher than enclosure 1 year in 0~5cm, 20~50cm(P<0.05), and available potassium was basely higher than other treatments in 0~50cm(P<0.05); The total phosphorus and potassium had no obvious changing. Soil organic matter, total nitrogen and available nutrients presented a phenomenon of surface aggregation.(4) Soil active organic carbon and carbon pool management index showed “enclosure 9 years> the control> enclosure 6 years>enclosure 1 year”, and enclosure 9 years was significantly higher than other treatments, and the difference of amount of active organic carbon of enclosure 9 years was significant with enclosure 1 year. Soil nutrients showed a significant or extremely significant correlation with soil active organic carbon, activity of carbon and efficiency of carbon. The influence of enclosure on soil active organic carbon, soil carbon pool management index of grassland of S.transiliense desert mainly occurred in 0-5cm.(5) Soil carbon and nitrogen of particulate, light fraction and microbial showed the trend of “decrease-increase” with the extension of enclosure time, and soil carbon and nitrogen of particulate of enclosure 9 years and the control were significantly higher than enclosure 1 year and enclosure 6 years, while Soil carbon and nitrogen of light fraction of enclosure 9 years and the control were significantly higher than enclosure 6 years, and Soil microbial carbon and nitrogen of enclosure 9, 6 years and the control were significantly higher than enclosure 1 year in 0-5cm. Soil distribution ratio of carbon and nitrogen of particulate were maximum. Soil carbon and nitrogen of particulate, light fraction and microbial showed a significant or extremely significant correlation with Soil organic carbon, total nutrients.(6) The larger of degree of weighted correlation of each of soil index was available phosphorus or potassium with coverage, density, biomass of grassland community, and especially the restrictions of available phosphorus supplied. The larger of degree of coupling of vegetation and soil was enclosure 1 year, while minimum was the treatment of control. Preliminarily estimated by regression analysis, grassland productivity and soil nutrients would gradually recover in enclosure 5~6, 8~15 years respectively, while the downward trend would occur if enclosure continued. |
PDF Full Text Request