| Soil microorganisms, an important factor in the driving cycle of matter and energy, can influence soil quality, cropping productivity and environmental sustainability. Different plant species affect soil organic carbon stocks or changing the short-term carbon cycle by the differences in quantity and quality of root exudates and litter, thereby affect the microbial community structure and functions. Accordingly, we speculate that planting forages can regulate orchard soil microbial community and functions, and the effects may be related to the variety of forage species. In this paper, we evaluated soil microbial community structure and carbon utilization ability of apple orchard intercropping with three different forages, which including native wild grasses, red clover (Trifolium pretense L.), ryegrass (Trifolium repens L.) and conventional tillage (CK). We analyzed the relationship between chemical composition of the different forage shoots and the chananges of soil microbial community structure and carbon utilization ability in the decomposition process. And evaluated the growth of potted Malus baccata seedlings that affected by the decomposition of three different forage shoots. The main results are as follows:(1) Compared the relative abundance of dominant bacterial phyla in different soils, native grasses soil had large relative abundance of Acidobacteria, but small relative abundance of Nitrospirae and Verrucomicrobia. The red clover soil had large relative abundance of Nitrospirae and Verrucomicrobia, but small relative abundance of Planctomycetes. The ryegrass soil had large relative abundance of Nitrospirae, Chloroflexi and Verrucomicrobia, but small relative abundance of Acidobacteria. The conventional tillage soil had small relative abundance of Nitrospirae, and large relative abundance of WPS-2(Unnamed), obviously higher than that of the other three forages planted soils in20cm-40cm depth; Compared the abundance of dominant bacterial genus in different soils, there were more large abundance bacterial genera in native grasses and conventional tillage soils than those in red clover and ryegrass soils. Conventional tillage soil had less large abundance bacterial genera than the other three forages planted soils. As mentioned above, the composition of apple orchard soil bacteria community had been affected by intercropping three different forages.(2) Compared the relative abundance of dominant fungi phyla in different soils, the fungi relative abundance of ryegrass and conventional tillage soil obviously greater than those of natural grass and red clover soil, especially reflected in the40cm-60cm soil depth. The native grasses soil contained large relative abundance of Zygomycota, while the ryegrass and conventional tillage soil contained large relative abundance of Ascomycota and Basidiomycota. The proportion of these three fungi phyla in red clover soil was similar with that of natural grass, but slightly with lower relative abundance. Compared the abundance of dominant fungi genera in different soils, Red clover soil had more large abundance of dominant fungi genera at20cm～40cm and40cm～60cm depth. There was no obviously large abundance fungi genus in conventional tillage soil at40～60cm soil depth. As mentioned above, the composition of apple orchard soil fungi community had been affected by intercropping three different forages.(3) Different forages had been increased the content of apple orchard soil organic matter, especially reflected in the40cm～60cm depth soil of red clover; The microorganisms in red clover planted soils had strong carbon utilization abilities at all three soil depths, obviously stronger than those of the other two forages planted soils. The microorganisms in native grasses soils had strong carbon utilization ability at10cm～20cm depth, but weak carbon utilization abilities at0cm～10cm and20cm～30cm depths. The microorganisms in ryegrass planted soils had weak carbon utilization abilities at all three soil depths. The microorganisms in conventional tillage soils had stronger carbon utilization ability than the other three forages planted soils at0cm～10cm depth, but weak carbon utilization abilities at10cm～20cm and20cm～30cm depths. As mentioned above, apple orchard soils’ intercropping with three different forages had been affected the carbon utilization ability of microorganisms in apple orchard soil.(4) The chemical composition of different forage shoots compositions were quite different. There were significant (P<0.05) differences of C/N values between three different forage shoots, in descending order of red clover, native grasses and ryegrass; The shoots of native grasses and ryegrass contented more polysaccharides, however the shoots of red clover contented more lignin, lipids and N-bearing.(5) The community structure of soil fungi changed a lot by decomposition of native grasses and red clover shoots, but the community structure of soil bacterial only changed a little. However, the community structure of soil fungi changed a little by decomposition of native grasses and red clover shoots, but the community structure of soil bacterial changed a lot; According to soil amino sugar content, decomposition of native grasses shoots had significantly (P<0.05) inhibited the proliferation of soil fungi. While the decomposition of red clover shoots significantly (P<0.05) promoted the proliferation of soil fungi. The effect on the proliferation of soil fungi by decomposition of ryegrass shoots was not significant (P>0.05). The decomposition of each of three forages shoots had significantly (P<0.05) promoted the proliferation of bacteria. Compared the three forages, the impact by decomposition of red clover shoots was the maximum, and the impact by decomposition of ryegrass shoots was the minimum. As mentioned above, the decomposition of different forage shoots had been affected soil microbial community and biomass of apple orchard.(6) The soil microbial carbon utilization abilities were increased by decomposition of three forage shoots. The impact by decomposition of red clover shoots was the maximum and that of ryegrass shoots was the minimum. In addition, the decomposition of each of three forages shoots had increased the activities of cellulase, invertase,β-glucosidase and urease.(7) The decomposition of forage shoots, inoculation with corresponding soil microorganism, had no significantly (P>0.05) impacted the PS II maximum photochemical efficiency of potted Malus baccata seedlings. And no significantly (P>0.05) promoted the growth of potted Malus baccata seedlings. The decomposition of ryegrass shoots, inoculation with ryegrass soil microorganism, had obviously inhibited chlorophyll synthesis of potted Malus baccata seedlings. |
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