Effects Of Enclosure On Plant Community And Organic Carbon Distribution In Desert Steppe Ecosystem

In order to clarify the effect of enclosure on vegetation and organic carbon distribution in the desert steppe ecosystems in Ningxia,The desert steppes of unenclosed(FYO),6-year enclosed(FY6),9-year enclosed(FY9)and 13-year enclosed(FY13)were selected as investigative plots by adopting spatial sequences instead of time series.The plant community structure,organic carbon and ?13C value of plants and their litter,distribution of soil organic carbon and its ?13C value in different soil profile and different particle size of aggregate,were studied.The response of plant community structure,organic carbon differentiation characteristics of plant-soil system to enclosure was discussed.The results were as follows:(1)The increase of plant height,aboveground and underground biomass and litter accumulation were promoted in desert steppe in Ningxia because of enclosure.The dominant species changed,the proportion of perennials increased,the plant community stability improved with extension of enclosure years.But they appeared transition in 9-year enclosed grassland.(2)With extension of restoration years,soil particles gradually converged to large aggregates and soil structure were improved.The water stability aggregates of various soil layers were dominated by<0.25 mm particles.The contents of water stability aggregates at 10?20 cm and 20?40 cm depth upped to the highest in 9-year enclosed grassland.The MWD decreased first and then increased with extension of enclosed years,and fell to the lowest in 9-year enclosed grassland.The percentage of aggregate destruction was higher in 9-year enclosed grassland..With deepening of soil layers,both dry and wet sieving MWD increased,while the percentage of aggregate destruction decreased.(3)The organic carbon contents and storages of aboveground parts of plants and litters showed as increase-decrease with extension of enclosure years.The plant roots,soil and total organic carbon storages appeared as increase-decrease-increase trends,and declined in 9-year enclosed grassland.(4)The aggregate associated organic carbon was most distributed in in<0.053 mm grain size.The 0.053?0.25 mm fraction of aggregate contributed most to total soil organic carbon,and the contribution of larger particle size fraction increased with depth.The contributions of different carbon sources to the total organic carbon storage of the desert steppe ecosystems showed as:soil>belowground plants>aboveground plants>litter.(5)The stable isotopes ?13C values of the aboveground plants,Lespedeza potaninii and Stipa breviflora litters gradually tended to positive with extension of enclosed years.The Lespedeza potaninii and Stipa breviflora ?13C value increased first and then declined.The soil organic carbon ?13C value was more negative in 9-year enclosed grassland.the aggregate soil organic carbon ?13C value of the same particle size tended to positive with depth under different years of enclosure.The ?13C values of 0.25?2 mm particle fraction were more negative,and the than those of other particle fractions.