| In order to provide a scientific basis for the restoration and sustainable development of sandy desert grassland,the influence of enclosure years(including 0 year,3 year,5 year and 8 year)on grassland community characteristics,stability,plant diversity,soil nutrients and active organic carbon and nitrogen(soil readily oxidized organic carbon,particle organic carbon and nitrogen,microbial biomass carbon and nitrogen)in sandy desert grassland were studied,and the sensitive indicators for evaluating recovering effect were selected by the multi-factor analysis and regression between enclosure years and index of vegetation and soil characteristic,then find the optimal period of enclosure.The main results are as follows:(1)The species richness,Simpson index and Shannon-wiener index showed a trend of "up-down-up" with the increase of enclosure years,while the Pielou evenness index showed a decreasing trend.Constructive species Seriphidiam santolinum have important proportion all the time with in the enclosure.The important values of Ceratocarpus arenarius were decline and the importance values of Salsola collina Pall were increased with increase of enclosure years.The community stability showed that 8-year enclosure was superior to 5-year enclosure,that 5-year enclosure is greater than 3-year enclosure,and better than grazing.Therefore,the species diversity and stability are promoted with the increase of enclosure years.(2)The content of total carbon in the soil increased by 1.34%~173.15%,and the content of organic carbon showed a trend of "up-down-up" after cultivating grassland.Total nitrogen decreased by 8.33%~34.38%,0-50 cm soil layer total phosphorus and total potassium increased.The content of available phosphorus decreased,while the content of available potassium and available nitrogen was not significant.The ratio of soil carbon to nitrogen was a trend of first increased then decreased.The ratio of carbon to phosphorus showed a “V” shape changes.Compared with the control,the ratio of nitrogen to phosphorus was decreased by 27.14%~ 68.24%.(3)The content of soil readily oxidized organic carbon in the 0-20 cm soil layer increased,and the soilreadily oxidized organic carbon and distribution ratio of 0-5 cm soil layer from high to low was enclosure 5 years,enclosure 3 years,enclosure 8 years and the control.The particle organic carbon showed an increasing trend,and the particle organic nitrogen distribution ratio was decreased.The light organic fraction carbon and nitrogen that were increased by 72.47%~118.22% in the 0-5 cm soil layer.The soil microbial biomass nitrogen,carbon and its distribution showed a trend “first up then down” with enclusure years increasing.The content of POC increased and the content of MON was decreased after enfencing.LFOC,LFON,MOC and MON were more sensitive than other indexes in the index of active organic carbon.(4)The results showed that the total phosphorus,total potassium and total carbon in the soil were the largest in En2~En5.The maximum value of soil microbial biomass nitrogen and microbial biomass nitrogen distribution ratio were in En2~En5,that the nutrients cycling dynamics reaches the maximum value.While the grassland productivity is the best in En2~En3.If the enclosure is continued,the vegetation productivity will decrease. |
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