| Mechanisms of carbon accumulation in severely degraded soil have been highly focused for it’s great carbon sequestration potential.Vegetation is gradually restoring by building measures of ecological restoration in red soil erosion area in Subtropical China.The Dicranopteris dichotoma is a typical understory vegetation,and the soil carbon sequestration is rapidly increased,however the influence of Dicranopteris dichotoma on soil carbon sequestration is still unclear.Thus the study of the stability of organic carbon covered by Dicranopteris dichotoma is useful for understanding of the mechanism of carbon sequestration in degraded soil.The research selected the typical sequence of vegetation restoration(Y0-without building measures of ecological restoration,Y13-have built measures of ecological restoration for 13 years,Y31-have built measures of ecological restoration for 31 years)as the object of study in Hetian town,Changting county,Fujian province.We implemented three kinds of treatment(NRd-Not removed Dicranopteris dichotoma;Rd-Removed Dicranopteris dichotoma;CK-Control)at experimental plots,and were carrying out experiments of the effect of Dicranopteris dichotoma on the stability of soil organic carbon.It demonstrated thatThe quantity and proportion ratio of CK soil Dissolved Organic Matter(DOM)were significantly lower than that of NRd(P<0.05)and Rd decreased significantly(P<0.05),it means that the Dicranopteris dichotoma had effected the the quantity of soil DOM;By comparison,the SUVA and HIXem and HIXsyn of NRd DOM was significantly higher than that of CK in Y13 and Y31,however E2:E3 value was contrary to that,which showed that the soil DOM structure that was covered by Dicranopteris dichotoma contained more aromatic nucleus and had higher aromaticity and humification degree,and the molecular of DOM was more larger.In addition,the SUVA and HIXem and HIXsyn of Rd DOM was significantly decreased,it meant that Dicranopteris dichotoma had a positive impact on the the complexity of DOM structure,and this effect was a long slow process.we aslo found same results by analysis of emission and synchronous fluorescence spectrum,it is also same as analysis of Fourier infrared transmission spectrum.Thus,the soil that covered by Dicranopteris dichotoma could offer enough carbon source to microorganism,and maintained the balance of carbon cycle,and DOM had a stable structure that was easily adsorbed by soil colloid,which had a positive effect on the stability of soil organic carbon.Compared to CK,NRd content of water-stability of aggregate(>0.25 mm)was higher(P<0.05),indicating that NRd soil structure was more stable than CK,Soil aggregate of mean weight diameter(NWD)or geometric mean diameter(GMD)and SOC were significantly correlated(P<0.05),and NRd soil aggregates MWD and GMD were significantly higher than those of CK(P<0.05),but Rd and NRd had no significant difference,indicating that soil aggregate state,degree of aggregate that covered by Dicranopteris dichotoma were higher than those in bare land,therefore stability of organic carbon was relatively more stable than that in bare land.NRd and Rd soil aggregates coarse particulate organic carbon(cPOM)and fine particulate organic carbon(fPOM)had higher C/N and lower δ15N than the occluded micro-aggregate fraction(mM)and the occluded silt&clay faction(s+cM)(P<0.05),indicating that the stability of mM and s+cM was much more stable.NRd(Y13 and Y31)the different size aggregate had higher C/N and lower δ15N than CK,and relative SOC stability of CK was significantly lower than that of NRd(P<0.05),which demonstrated that the stability of SOC covered by Dicranopteris dichotoma was much more stable.We also found that NRd(except Rd and CK)relative SOC stability was increasing with vegetation restoration,therefore,Dicranopteris dichotoma might be the key factors of affecting the SOC stability in process of vegetation recovery,it also might be the major contributor of the accumulation of SOC.CK soil MBC and MBN and PLFAs was significantly lower than that of NRd,and Rd soil MBC and PLFAs decreased significantly(P<0.05),it showed that the quantity and community of soil microorganism was much more abundant,and microbial activity was aslo much higher.Compared to CK,NRd soil gram positive bacteria/gram negative bacteria(GP/GN),cyclopropyl to cyclopropyl precursor ratio(cy/pre)and saturated straight chain fatty acid/mono unsaturated fatty acids(sat/mono)were significantly decreased,fungi/bacteria(F/B)and arbuscular mycorrhizal fungi(VAM)was significantly increased(P<0.05),indicating that the soil ecosystem that covered by Dicranopteris dichotoma stability of organic carbon was relatively more stable than that in bare land.NRd soil environment of nutrient was significantly better than CK,and Rd was significantly worse;NRd(except for Y0)soil temperature and pH was significantly lower than CK(P<0.05),while the soil moisture has no significant difference between treatments. |
