Effects Of Different Managements Oncommunity Structure And Ecological Functions In A Typical Steppe

The ecological functions of grassland have seriously degenerated due to long-term overuse on the Loess Plateau.Short-term grazing exclusion is a favor of improving plant community structure and ecological functions,but there is controversial about the effect of long-term grazing exclusion.Additionally,there are trade-offs between multiple grassland ecological functions.Therefore,understanding that different managements mediate ecological functions is essential to optimizing management.Here,we selected open grazing,long-term grazing exclusion(35 years),and fenced mowing grassland in Yunwu Mountain National Nature Reserve.We researched the response patterns of plant community structure,species diversity,grassland productivity and stability,soil organic carbon(SOC)and water content(SWC)on different managements by monitoring species composition,above-ground net primary productivity,litter mass,SOC and SWC.Meanwhile,we analyzed the multifunction trade-off relationships.It could provide a reliable basis for grassland optimization in semi-arid region of the Loess Plateau.The main conclusions as follows:(1)The community structure existed significantly different under diverse grassland managements.Species numbers were 31,25,and 35 at open grazing,grazing exclusion,and fenced mowing grassland,respectively.The dominant species were Stipa przewalskyi,which accounted for 33.30%,45.23%and 43.31%of the net primary productivity,respectively.The competition effect of dominant species and litter accumulation were the important factors affecting plant community structure.The relative biomass of dominant species(Stipa przewalskyi)was negatively correlated with the biomass of smaller individual plants.And plant functional groups had shown diverse trends with increasing litter mass,observing decreasing(perennial forbs and perennial rhizome grasses,P<0.05),increasing(shrubs and semi-shrubs,P=0.001),and no change(annuals and biennials,perennial rhizome grasses,P>0.05).(2)There were significant differences in plant diversity,above-ground productivity and stability,SOC and SWC under different managements.Long-term grazing exclusion increased obviously grassland productivity,SOC and SWC,but suppressed plant diversity and grassland community stability compared with open grazing.Additionally,plant diversity was significantly negative with litter mass(P<0.001).The SOC stocks(0-100 cm)were12.0±2.0,19.2±2.9,19.9±2.4 kg C m~-22 in open grazing,grazing exclusion and fenced mowing grassland,respectively.And the soil water stocks were 104.1±13.6,158.8±10.2and 114.8±9.3 mm,respectively.Meanwhile,SWC was positively correlated with litter mass(P<0.001),indicating that litter could effectively ameliorate soil water-holding capacity.(3)Trade-off analysis of multifunction showed that the plant diversity was higher,but the SOC and grassland productivity were at lower level at opening grazing.On the contrary,long-term grazing exclusion increased obviously SOC and grassland productivity,but impressed species diversity.Fencing mowing could effectively improve species diversity,but not benefit for grassland productivity and SWC.Therefore,opening grazing and long-term grazing exclusion could not achieve a win-win situation for species diversity and SOC.And short-term mowing can achieve the dual objectives,but is not conducive to soil water maintenance.Therefore,long-term grazing exclusion cannot be beneficial to plant diversity and SOC simultaneously.We suggest that introducing disturbances are necessary to safeguard biodiversity.Short-term mowing could achieve a win-win situation for species diversity and SOC,but continuous mowing was not conducive to soil water maintenance.Therefore,it is essential to optimize grassland management with dual objectives of biodiversity and soil carbon sequestration on the Loess Plateau.