Response Mechanism Of Stipa Breviflora To Grazing In Desert Steppe

The Eurasian grassland is the largest and relatively perfect grassland area in the world,and the Stipa is the most important species in the Eurasian steppe.Analysing the mechanism of Stipa plant ecological adaptation under disturbance of livestock can help us to understand the self-regulating process of grassland plant and its ecological response mechanism to grazing.It can not only explain the maintenance mechanism of plant population from ecological theory,but also the grassland degradation process and grassland degradation,which provides theoretical support for the best grazing and utilization of grassland.Therefore,this study used the long-term grazing control experiment of desert grassland in Right Banner,Xilin Gol League,Inner Mongolia,using the platform to study the edificators of Stipa breviflora as the research object,and analyzed the individual traits of heavy grazing,moderate grazing,and non-grazing,reproductive characteristics,habitat,population distribution pattern and population dynamics.The results showed:1 The phenotypic characteristics of S.breviflora were not only affected by grazing,but also influenced by the age of self-growth and the interaction between the them.The performance of seedling phase and ageing phase plants was basically not affected by grazing.The difference was mainly reflected in 3 age stages: young phase,adult phase and pre-aging phase.The phenotypic plasticity index further showed that individual traits(leaf height,leaf dry weight,length to width ratio)of S.breviflora were influenced by the age of the plants.The thickness of leaves of S.breviflora showed the highest tendency of heavy grazing,followed by moderate grazing,and lowest in no grazing treatment.The heavy grazing treatment of the lower epidermis cell area was significantly less than that of moderate grazing treatment and no grazing treatment.Grazing reduced the C content of S.breviflora leaves,but heavy grazing increased N content in leaves,and N: P was always less than 8.The age,leaf dry weight,leaf length and leaf area of S.breviflora were important factors affecting leaf height,and there was a trade-off relationship between leaf curl and leaf height.2 The reproductive individuals under no grazing treatment were significantly higher than the moderate grazing treatment and heavy grazing treatment.Compared with the no grazing and heavy grazing treatment,the weight of the moderately grazing S.breviflora was increased by approximately 82.99%.The number of reproductive branches,reproductive branches,vegetative branch weights,number of vegetative branches,and plant age were important signs affecting the seed number of S.breviflora.For seed density and seed bank in soil,the highest values were observed for the no grazing treatment,followed by the moderate and heavy grazing treatments.Theseed density for germination ofsoilseed banks was nearly one-fourth ofseed density during the growing season.In addition,grazing treatments affected the phenotypic characteristics of seeds and reduced the lower limit of the weight of germinable seeds.Awn removal significantly increased germination.The longest germination time was observed for seeds that entered the soil at an angle of 0°.3 The results of plant-derived mound showed that there were obvious phytogenic hillock in individuals with young plants in heavy grazing,and the length,width and seed number of phytogenic hillock in moderate grazing and no grazing were significantly higher than heavy grazing.The result of the path analysis model showed that the height of the phytogenic hillock significantly affected the number of seeds,whereas the length of the phytogenic hillock from the heavy grazing treatment significantly affected the number of seeds.The distribution of soil aggregates in the desert grassland of S.breviflora was influenced by the interaction between aggregate size and grazing intensity.In the same grazing treatment,the content of 100-250 ?m plant sedimentary aggregates was the highest,while that of bare land soil in <50 ?m aggregates was the highest.The structure of the soil aggregate destruction rate of heavy grazing was greater than the moderate grazing treatment,and the grazing under the bare land soil aggregate structure structural destruction rate is higher than the phytogenic hillock soil aggregate structure destruction rate.Heavy grazing treatment showed that soil N,C,P,and K all increased first and then decreased with the increasing of phytogenic hillock.4 The adult phase and the pre-aging phase of S.breviflora were relatively higher,which the no grazing treatment for pre-aging phase plant weigh was more than 0.4.The individual weights of the heavy grazing seedlings were significantly higher than that of the moderate grazing treatments and non-grazing treatments,and increased by 651.06% and 168.30%.The results of pair-correlation function showed that the population of S.breviflora in heavy grazing treatment was randomly distributed in the small-scale range,and the cluster distribution was increased with the increase of the scale.The results of distribution function of the distances to the nearest neighbour function showed that the scale of 3 cm–18 cm showed strongly cluster distribution.Moderate grazing treatments are clustered on small scales and randomly distributed with increasing scale.Compared with no grazing treatment,the spatial correlation was greater than 40 cm.Under heavy grazing treatment,the young plant clusters and the adult plant clusters were spatially correlated in a range of less than 12 cm,and the moderate grazing treatments were spatially correlated in a range of less than 20 cm.5 The annual dynamics of plant populations in the desert steppe indicated that the annual fluctuation range of the biomass of the no grazing communities was the largest,followed by heavy grazing,and the minimum for moderate grazing.The ratio of biomass of each grazing treatment of S.brevifolia was the highest.The interactions of grazing treatments,different years,and grazing treatments with years all affected the biomass of the S.brevifolia population.In no grazing,the precipitation and total precipitation of the plant growth season are important indicators affecting the biomass of S.brevifolia population;while the precipitation during the returning green period is a non-important indicator,this result also applies to the moderate grazing treatment.In heavy grazing treatments,only the precipitation in the green period is an important indicator that affects the biomass of the S.brevifolia population.Further research found that the S.brevifolia population status in early years affected the population in subsequent years,and grazing weakened the relationship.