| Plants are important for maintaining the structural and functional stability of ecosystems.The impact on soil is one of the key issues in ecological research.However,the wide variety of plant species and the large differences in their respective properties and sizes make it difficult to grasp accurate contribution values.Introducing the concept of plant functional groups can simplify the complexity of plant species and make it easier to understand the relationship between plant and soil interactions.In this study,16 species of pasture from four functional groups were used as experimental materials in the small mound soil of the Loess Plateau.In order to understand the microbial effects on soil organic carbon sequestration after pasture planting,we conducted the effects of different pasture functional groups(C3,C4,leguminosae and asteraceae)and planting densities(low planting densities:1,2 and 4 holes/pot,high planting densities: 8,12 and 16 holes/pot)on soil physical properties,nutrient and microbial residual carbon distribution characteristics in pot tests.The main findings of this study are as follows:(1)The above-ground biomass of asteraceae was the highest,and the below-ground biomass of leguminosae was the lowest.The root to crown ratio of C3 plants was the highest.The above-ground and below-ground biomass of plants was greater at high planting densities than low planting densities,and the above-ground biomass of plants was lowest in the D1 treatment.The root-to-crown ratio of plants was greater at high planting densities than low planting densities.(2)Soil water content was greater in C3 and C4 plants than in legumes and asteraceae.Soil water content was greater at low planting densities than high planting densities.Soil mechanical stability agglomerates were dominated by 0.25-2 mm agglomerates,followed by > 2 mm agglomerates,with the smallest proportion of < 0.25 mm agglomerates.The proportion of > 2 mm agglomerates was smallest in C3 plants at low planting densities.The proportion of 0.25-2 mm agglomerates was greater in C3 and C4 plants than in leguminosae and asteraceae,except for the D8 density treatment.The proportion of clusters < 0.25 mm was smallest in C4 plants at high planting densities.(3)Soil organic carbon in the root zone and non-root zone was greater in legumes and asteraceae than in C3 and C4 plants.The root zone of asteraceae and the non-root zone of C3 plants had the lowest soil total nitrogen.Soil nitrate-nitrogen was the highest in the root and non-root zones of legumes.Soil nitrate and fast-acting phosphorus were highest in the root and non-root zones of asteraceae,while C4 plants had the highest soil total phosphorus in the root and non-root zones.Soil organic carbon and total soil nitrogen in the non-root zone were greater at high planting densities than low planting densities,and soil nitrate-nitrogen was the highest under D1 and lowest under D16.(4)The carbon content of microbial and bacterial residues in the root zone and non root zone soils of C3 and C4 plants is higher than that of leguminous and composite plants.The fungal residue carbon and the ratio of fungal to bacterial residue carbon in the root zone were:asteraceae > leguminosae > C3 > C4.Soil fungal residue carbon and fungal to bacterial residue carbon ratios in the non-root zone were the lowest in C4 plants.Soil fungal residue carbon and fungal to bacterial residue carbon ratios in the root and non-root zone were the highest at D12.Soil microbial and bacterial residue carbon in the root zone increased with planting density and then decreased.The carbon of soil microorganisms and bacterial residues in the non-root zone was the highest in D2.(5)Soil microbial carbon and bacterial residues carbon in the root zone was strongly correlated with soil physicochemical properties.There was strongly significant positive correlations between soil microbial and bacterial residues and soil total nitrogen and phosphorus in the root zone.There was strongly significant positive correlations between soil fungal residues and soil organic matter,ammonium nitrogen and available phosphorus in the root zone.Soil microbial carbon and bacterial residues carbon in the non-root zone were strongly significantly correlated with root crown ratio,soil water content,0.25-2 mm aggregates,and total phosphorus.Soil microbial carbon and bacterial residues carbon in the non-root zone were highly significantly and positively correlated with root to crown ratio,soil water content,0.25-2 mm aggregates and total phosphorus,and highly significantly negatively correlated with above-ground biomass,< 0.25 mm aggregates,organic carbon,total nitrogen,ammonium nitrate nitrogen and available phosphorus.In this experiment,the response of plant biomass,soil physicochemical properties and microbial residual carbon accumulation characteristics to pasture functional groups and planting density were analysed.We found that increasing planting density was beneficial to soil quality.leguminosae and asteraceae planting were good to the accumulation of fungal residual carbon.C3 and C4 plants increased soil bacterial residual carbon.Soil water content,agglomerates,total nitrogen and total phosphorus were the main physicochemical factors influencing the accumulation of soil microbial residual carbon. |
