Characteristics Of The Organic Carbon And Turnover In Grassland Of Different Fenced Years In Southern Ningxia

Fencing is regarded as a reliable method to restore degraded grassland on Chinses Loess Plateau?CLP?.In order to study the soil organic carbon?SOC?,SOC fractions and allocation of recent photoassimilate carbon in grasslands of CLP,we selected 4 fenced pastures which have been constructed at 1?1a?,5?5a?,10?10a?and 30?30a?years ago to study the allocation of recent photoassimilates in plant-soil system by using ¹³C pulse-labeling.It can help us understand the mechanism of carbon fixation and the cycling of recent photoassimilates in ecosystem.The results showed that:1.Fencing enhanced the above-and below-ground biomass.In this study,plant biomass of 30a was significantly higher than the other grasslands?P<0.05?.Root biomass had a properties of surface-aggregation,root biomass of 0-20 cm accounted for 70.66%,76.36%,84.02%and 75.63%of root biomass of 0-40 cm in 1a,5a,10a and 30a respectively.The root shoot ratio decreased with increased length of time the grasslands were protected from grazing.2.Amount of SOC,soil dissolved carbon?DOC?and microbial biomass carbon?MBC?increased with increased length of time the grasslands were protected from grazing.SOC had a properties of surface-aggregation.Fencing increased the amount of SOC and soil active carbon,benefit for carbon fixation.3.In this study,soil humus,humic acid and fulvic acid increased with increased length of time the grasslands were protected from grazing.The ratio of humic acid fulvic acid was highest in 10a indicated higher humification level.4.In this study,the recovery of ¹³C in shoots and roots was lowest in 1a.5 years after exclusion,the recovery of ¹³C in soil was decreased with increased length of time the grasslands were protected from grazing.Fencing increased the allocation of recent photoassimilates to plant,the rate of carbon fixation to soil decreased with increased length of time the grasslands were protected from grazing.5.30 days after labeling,amount of ¹³C-DOC and ¹³C-MBC increased with increased length of time the grasslands were protected from grazing.The renewal rates of MBC?DOC and SOC was all highest in 1a indicated higher ¹³C turnover rate in belowground C pool.6.Loss of recent photoassimilates from shoots and total respiration was significantly highest in 1a?P<0.05?.Fencing decreased the loss of recent photoassimilates.Grassland which excluded for 10 years had longest mean residence time?MRT,14.3 days?.Grasslands excluded for 10 years benefit for carbon fixation.