| In grassland ecosystem,the carbon pool is mainly stored in soil.It is of great significance to study the components and their stability of soil organic carbon in grassland ecosystem.Inner Mongolia grassland is an important ecological security barrier and carbon sink base in northern China.In past decades,due to global changes and excessive utilization,a large area of grassland has undergone varying degrees of degradation in Inner Mongolia.In-depth revealing of soil carbon components and their stability characteristics in different degraded communities has important application value for adaptive management of grassland ecosystem with the goal of restoring degraded grassland and increasing sink.In this paper,the typical steppe in Inner Mongolia was taken as an example.Based on the plant community changes in aboveground biomass and diversity,four degraded community types were divided:non-degraded,mild,moderate and severe.The contents of soil total carbon,organic carbon,inorganic carbon,microbial biomass carbon,particulate organic carbon,mineral-bound organic carbon,readily oxidized organic carbon and other components in different degraded types were measured.Soil p H,total nitrogen and microbial biomass nitrogen were measured.Based on the proportion of particulate organic carbon,readily oxidized organic carbon and microbial biomass carbon to total organic carbon,the stability of soil organic carbon in different degraded types was discussed.The main results and conclusions are as follows:1.The community aboveground biomass was 100.25-153.40g·m-2in the study area.During 0-30cm soil layer,p H is 7.05-8.48,total nitrogen content is 0.76-1.87g·kg-1,total carbon content is 10.50-19.86g·kg-1,inorganic carbon content is 5.56-12.50g·kg-1.Soil p H(8.26)of the non-degraded community in 0-30 cm soil layer was significantly higher than that of the degraded communities,and that of the non-degraded,mild and moderate degraded communities increased significantly with the deepening soil layers.The total nitrogen content was the highest in the moderately degraded community(1.49g·kg-1),and the total nitrogen content in each community decreased significantly as soil depth deepened.Total carbon content(13.40g·kg-1)and inorganic carbon content(7.17g·kg-1)in severe degraded communities were significantly lower than those of the other communities,and only severe degradation decreased with soil depth increased.Soil p H,total carbon and inorganic carbon showed the order of non-degradation community>mild degradation community>severe degradation community,and moderate degradation community was more complex.2.The microbial biomass nitrogen of each community was 10.18-44.00 mg·kg-1,and the microbial biomass carbon was 464.01-696.64 mg·kg-1.Microbial biomass nitrogen(34.99 mg·kg-1)in 5-30 cm soil layer was the highest in moderate degradation.The microbial biomass carbon of non-degraded communities(618.35 mg·kg-1)was significantly higher than that of moderate(545.38 mg·kg-1)and severe degraded communities(516.57 mg·kg-1).3.The organic carbon of each community was 4.05-9.02 g·kg-1,the particulate organic carbon was 0.48-3.68g·kg-1,the mineral-bound organic carbon was 2.7-7.79g·kg-1,and the easily oxidized organic carbon was 2.41-7.74 g·kg-1.In 0-30 cm soil layer,organic carbon and mineral-bound organic carbon were the highest in moderate degraded communities,which were 7.60 g·kg-1 and 6.48 g·kg-1,respectively,indicating that moderate grazing was beneficial to grassland ecosystem carbon pool.The particulate organic carbon(3.20g·kg-1)in the non-degraded community was significantly higher than that in the degraded communities;the easily oxidized organic carbon(3.61g·kg-1)of severely degraded communities was significantly lower than that of the other types;The order of microbial biomass carbon,particulate organic carbon and readily oxidized organic carbon content from high to low was:non-degradation community>mild degradation community>moderate degradation community>severe degradation community.There was a significant positive correlation between organic carbon and active organic carbon,and the sensitive of degradation components were as follows:microbial biomass carbon(MBC)>particulate organic carbon(POC)>easily oxidized organic carbon(ROC)>organic carbon(SOC).4.The proportions of soil microbial biomass carbon,particulate organic carbon and readily oxidized organic carbon were 7.48%-13.88%,10.03%-63.60%and 11.93%-43.64%,respectively.In 0-30 cm soil layer,the proportion of microbial biomass carbon distribution in non-degraded communities(12.05%)was significantly higher than that in mild(9.15%)and moderate degraded communities(7.59%);the proportion of particulate organic carbon(54.16%)in the non-degraded community was significantly higher than that in the degraded community,and the proportion of easily oxidized organic carbon(33.70%)was significantly higher than that in the heavily degraded community(20.28%),indicating that the soil carton stability of the degraded community was high,but the proportion of soil microbial biomass-based carbon distribution was the highest in the moderately degraded community. |
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