| The influence mechanism of grazing disturbance on grassland and the reasonable selection of grazing system are the urgent needs of multi-disciplinary research and production practice.The grassland degradation caused by overgrazing is the result of unbalanced energy flow and material circulation of grassland ecosystem caused by grazing pressure.Although remarkable progress has been made in recent years on how different grazing systems affect the vegetation characteristics of grassland and the physical and chemical properties of soil,it is still unclear how grazing systems affect the coupling relationship between grassland vegetation and soil.Based on this,the research in the Ma Qu County of Tibet Plateau chose typical sample area(fencing,seasonal grazing and grazing)under different grazing system,through field observation and experimental analysis.And we use the different grazing system of alpine meadow vegetation and soil and their coupling relations research as the breakthrough point,to improve the mechanism of the effects on grazing.And finally to provide the theoretical basis for rational selection and science management of grazing system.The main conclusions of this study are as follows:(1)Grazing system significantly changed the characteristics of vegetation community composition,quantity and diversity of alpine grassland.Grazing caused the increase of compositae and legume in alpine grassland community,decreased the quantity of high-quality herbage and increased the quantity of poisonous grass.Compared with the fencing area,grazing caused the increase of compositae and legume in alpine grassland community,decreased the quantity of high-quality herbage and increased the quantity of poisonous grass.Grazing also reduced the amount of annual and biennial herbs and increased the distribution of semi-shrubs.The vegetation coverage of fencing,seasonal grazing and annual grazing plots were 86.48±19.90%,74.15±13.70%,0.75±8.83%,the height was 26.43±3.65cm,17.27±4.95cm and 14.05±3.71cm,and the density was 294.95±41.81 plants/m2,241.10±91.66 plants/m2 and 137.40±37.10 plants/m2.The vegetation diversity index of seasonal grazing plots was higher than that of other two plots.(2)Grazing system significantly changed the soil physicochemical properties of alpine grassland(P<0.05).The bulk density of the enclosed samples was 0.78±0.06 g/m3,significantly lower than the two grazing samples(P<0.05),while the soil moisture content was 23.94±2.15%,significantly higher than the other two(P<0.05).The content of organic carbon,total phosphorus,total potassium and nitrate nitrogen in the surface of alpine grassland(0-10cm)was significantly reduced by grazing(P<0.05),while the content of total nitrogen in the surface of alpine grassland was significantly increased by seasonal grazing(P<0.05).(3)High throughput sequencing method was used to determine the community structure of soil bacteria and fungi.With OTU as the classification unit,the amount of bacteria and fungi species in the grazing plots was less than that in the fencing and seasonal grazing plots.The richness of proteobacteria was the highest in the sample plots,accounting for 21.9%,23.3%and 22.7%respectively in the fencing,seasonal grazing and grazing plots.Compared with fencing plots,the evenness and richness of soil microbial species decreased with grazing intensity.(4)RDA ranking shows that soil total phosphorus content is the most important factor affecting the distribution pattern of community species under grazing.Soil factors accounted for 50.2% of the variation of community species distribution,with soil chemical properties accounting for 10.5% of plant population variation and physical properties accounting for 21.9% of community species distribution.Verruciformes have the strongest correlation with environmental factors and can be used to indicate environmental changes. |
PDF Full Text Request