Effects Of Simulated Trampling And Rainfall On Soil Physicochemical Properties And Microorganism Abundance In Alpine Meadow

Grazing is the most direct and effective way to grassland utilization,in which grassland ecosystem was acted by livestock trampling,ingestion and excretion.Compared with others,the action of trampling has long,lasting and remarkable effects that is far-reaching and profound on the grass and play a leading role in grassland degradation and health maintenance.At the same time,due to global warming and drying,the lack of water supply and evaporation intensification in growth season,as well as the seasonal variation of rainfall and the variation in the interannual variability which further aggravates the degradation of grassland.However,the effect mechanism of trampling and rainfall on the grassland ecosystem in Qinghai-Tibet Plateau and the interaction between trampling and precipitation on the soil-grass system were not clear.Therefore,in this experiment,Tianzhu alpine meadow was taken as the research object.The response of soil physical,chemical and microorganism abundance to trample and precipitation was discussed by simulating the trampling effect of main animal species: yak and Tibetan sheep in Qinghai-Tibetan Plateau.In order to explore the mechanism of livestock trampling on grassland under different precipitation,and to clarify the differentiation effects of yak and Tibetan sheep trampling on grassland soil.The purpose is to provide new ideas and scientific basis for the health management of natural grassland,reasonable collocation of grassland grazing livestock,and restoration of degraded grassland.The main results are as follows: 1.The soil compactness and bulk density in 0-15 cm soil layer are increasing with the increased of simulated trample intensity and simulated precipitation.And the compaction of the surface layer(0-15 cm)soil by the severe trampling of yak and Tibetan sheep were significantly greater than that of mild trampling and CK treatment.When the soil moisture content is higher than the water shortage treatment,the effect on soil compaction should be more significant and the compactness of high water treatment is significantly increased.At the same time,the compaction under livestock trampling of the soil causes the water permeability of the grass to decrease,and the increase of the trampling and precipitation intensity was significantly negatively correlated with the soil saturated hydraulic conductivity.Under the same grazing pressure,soil compaction and bulk density of the yak trampling test area were greater than that of the Tibetan sheep,while the saturated hydraulic conductivity was less than that of the Tibetan sheep.The compaction of the yak trampling on the grassland was greater than that of the Tibetan sheep.2.The soil chemical characteristics of grassland had different response to simulated and precipitation.The total nitrogen(TN)and phosphorus(TP)content of soil showed the change rule Tibetan Sheep Light Trampling(TSLT)>Tibetan Sheep Moderate Trampling(TSMT)>Tibetan Sheep Heavy(TSHT),Yak Light Trampling(YLT)>Yak Moderate Trampling(YMT)>Yak Heavy Trampling(YHT)with the increase of simulated trample.With the increase of soil moisture content,TN and TP in grassland decreased after the first increase.The value of TN and TP was the highest in the average level of rainfall,and the main effect is 0-20 cm soil layer.With the increase of trample intensity the soil available nitrogen(AN)and available potassium(AK)showed increasing trend,while the available phosphorus(AP)decreased.The soil available nutrient reaches the maximum under the condition of lower level of rainfall.The more water content in the soil,the smaller the available nutrient.The available nutrient content in 0-30 cm was significantly reduced by the increase of soil moisture in alpine meadow soil.The variance analysis showed that the effect of precipitation on soil nutrients is greater than that of livestock trampling.Simulated trampling and rainfall interacts with the AN content in 0-20 cm soil layer,which had no significant effect on AP and AK.Simulated trampling and precipitation on soil total potassium and organic matter had no significant difference.3.Trampling and precipitation affected the soil bacteria and fungi of the soil layer in 0-10 cm,and the soil actinomycetes of soil layer 0-20 cm.With the increase of trampling intensity,the number of soil bacteria first increased and then decreased,light trampling is beneficial to the propagation of soil bacteria,while the number of fungi and actinomycetes decreased with the increase of trample intensity.The number of the three major microorganisms increased with the increase of soil water content,and the number were highest in high rainfall.With the same grazing pressure,the number of microorganisms in yak area was less than that in Tibetan sheep trampled area,but the difference was not significant.The reduction in the number of microorganisms affects the respiration of grasslands to some extent,soil respiration rate was significant decreased by simulated trampling.Compared with CK,the respiration rate of one and two growing seasons decreased by 37.54% ~ 67.91 and 22.90%~41.23% respectively.Soil respiration rate is positively correlated with soil moisture content in which under high level of rainfall is significantly greater than that lower and average water treatment.The simulated trampling reduced the microbial activity and air permeability of grassland soil significantly.To sum up,herbivore trampling accelerates grassland soil compactness,reduces soil permeability and microbial activity.When soil moisture content is high,the consolidation of the soil is more significant.The severe effects of yak on grassland soil are greater than that of Tibetan sheep.Therefore,from the ecological and economic benefit of grassland ecosystem,the grazing should be reduced when after the rain or the soil is wet,to reduce the consolidation under high moisture content and the damage to the soil structure.Moreover,implement measures to optimize the structure of livestock,increasing the proportion of Tibetan sheep grazing and reduce the proportion of yak appropriately,to reduce the grassland grazing pressure and to make the grassland ecological get rest,realize the sustainable using of grassland.