| Grazing exclusion measures are more effective grassland management in the Loess Plateau.In order to explore the relationship of root parameters and soil organic carbon during different vegetation successional period in grassland,we selected different enclosed plant communities as the research object in Yunwu Mountain.By analysing C,N,P ecological stoichiometry among aboveground part,litter,roots and soil and soil carbon fractions in typical communities in 0~100cm soil layers,we wanted to explore relationship between roots and soil carbon fractions,and provide scientific basis for grassland restoration and management.The main conclusions were as follows:(1)The range of root biomass during different enclosure years was 410.38~1494.92 g/m~2,mean 856.23 g/m~2.The root biomass decreased first and then increased.The lowest community root biomass was enclosed fifth years.The vertical distribution of root biomass in different communities was same,decreased by the exponential function.Root cellulose and lignin content were 21%,8%respectively,and the content in early stage(1~10years)was higer than the late period(15~30years)during vegetation succession.Lignin/N ratio increased with soil depth during vegetation succession.The average root C concentration was438.43 g/kg during six grassland communities of succession stage in the study areas.Root C concentration was no significant difference between the different exclosure grassland communities.Fencing measures had no significant effect on root C concentration.The average concentration of root N and P were 6.31 g/kg,0.92 g/kg respectively.(2)The C,N and P average content in aboveground part in research areas was 419.44g/kg,13.04 g/kg and 1.83 g/kg respectively.With the progress of enclosed,the C content of the aboveground parts and litter showed an increasing trend,but the growth rate was slow.The content of N and P showed a decreasing rule.Except the enclosed 30 years Stipa bungeana and Stipa grandis communities,the N and P content of plant litter were significantly lower than the aboveground part.The average value of C:N and C:P for the different years of closure was 33.79 and 307.04 respectively.The change trend of C:N and C:P in the above-ground part of the planting years was opposite to the N and P.The differences in C:N,C:P were mainly caused by differences in N and P.The average value of litter C:N and C:P was 23.76 and 181.21 respectively.Litter C:N,C:P gradually increased with the increase in the number of years.The average N:P of the aboveground parts of the plant was 8.71,and the average of the litter N:P was 7.81.With the increase of the enclosure years,litter C:N,C:P were gradually increased.Both N:P of aboveground parts and litters showed an upward trend with the increase years of enclosure.The main limiting element for plant community growth in this area was N.Aboveground part C was negatively related to root N and cellulose.Litter N was significantly positively related to root N.Litter C:P was significantly negatively correlated with root P.It showed that the ratio of the absorption and utilization of nutrient elements in the leaves and roots of plants was consistent.(3)Long term grazing exclusion maked content of SOC and soil organic fractions increased significantly.The MBC,DOC,and humic carbon in the enclosed 30 years communities were significantly higher than those in the 15 years.Humin acid carban becomed more.The vertical distribution patterns of SOC and soil organic fractions were similar.The top layer of 0~20cm soil contents were the higest and then gradually decreased.Soil organic matter mineralization was smaller in 0~20 cm layer.Enclosure increased the MBC content in 20~40 cm soil layer significantly.(4)The content of of soil TN and TP increased with increasing fencing years.Soil C,N,P showed a significant positive correlation with each other.In general,grassland enclosure was beneficial to the improvement of soil quality.Soil N,P content in the surface layer(0~20cm)was significantly higher than the lower layer(20~100 cm).The soil average C:N and C:P was 11.04 and 19.68 respectively.Soil C:N showed a significant correlation with soil SOC and TN.Soil C:N and C:P were greatly influenced by C in different enclosed years.Soil N:P was lower,with a mean value of 2.94,and grassland productivity in this area was mainly limited by N.Soil SOC,TN,and TP showed similar trends in the vertical distribution,increasd from bottom to top.(5)The root C content was positively correlated with MBC.The root biomass would significantly increase MBC.The root C:N was negatively correlated with soil TN..There was a negative correlation between the root C:P was and soil C:P,and a positive correlation with soil N:P.The composition and biomass of plant roots significantly affected soil organic fractions and ecological stoichiometry. |
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