| With the global warming by carbon emission, carbon fixation in forest soil has become an essential issue. Biochar is evaluated as a means to improve soil physicochemical properties and to mitigate climate change, which has received widespread attention. However the effects of biochar on soil microbial community received much less attention than its effects on soil physicochemical properties and crop growth. Since biochar applying to agricultural soils were widely studied, this study focus on understanding how biochar application to polar plantation soil influences soil microbial traits with their seasonal variations. A field controlled experiment was designed to understand biochar with the seasonal variations in microbial biomass and metabolic diversity of microbial communities in carbon resources with four different treatments, i.e. Control(0), T1(40t·hm-2), T2(80t·hm-2) and T3(120t·hm-2) of biochar, which aims for providing scientific basis for understanding how biochar effect the circulation of C, N in soil ecosystem and the ecological safety of the application of biochar in forestry. The result showed as follow:(1) Comparing biochar with control, biochar treatments improved p H value, MBC/MBN and had negative effect on moisture and MBN(p<0.05). Through stepwise regression analysis(SREG), p H has been found to be the main reason for the reduction of MBN observed from soils when biochar is added. Communities physiological profiles(CLPP) that were assessed using Biolog Eco Plates TM displayed that biochar improved microbial metabolic activity, whereas it had not obvious effects on functional diversity assessed by Shannon diversity index('H) and evenness(E). It was suggested by principle component analysis(PCA) that high level of biochar could potentially change microbial metabolic patterns.(2) Biochar treatments had effect on the seasons variations of soil moisture, pH values. Soil moisture reached the peak in summer, and it was decreased by the application of biochar. There were seasonal variations in soil p H, meanwhile, soil p H was increased by the application of biochar. Biochar and seasons variations, as well as their interactions had effects on MBN, while MBC only showed significant difference with seasonal variations. The seasonal variations of MBN saw a “Z” shape and higher in winter and spring than summer and autumn; whereas the seasonal variations of MBC saw a “N” shape: spring > winter > autumn > summer.(3) The AWCD values of soil microbial communities in different seasons were around 1.0, indicating that they had a strong ability of utilizing carbon resources. The utilization of carbon sources of soil microbial communities has significant difference during the seasonal variations, and AWCD in autumn was the highest. The application of biochar can also improve the metabolic activity of microorganisms. In general, the function of microbial communities is stable, and their diversity is not easy to change. Compare with the difference brought by seasonal variations, the difference brought by different levels of biochar has not significance. The result of PCA presented spring and summer were obviously separated, while autumn and winter were clustered but separated from spring and summer.Overall, this study indicates that biochar decreases the moisture of loam soil and improves soil p H, meanwhile it decreases MBN through altering the microbial communities, while its effects on MBC are not significant. Besides that, biochar has not significant difference on functional diversity, but its effects on microbial metabolic patterns are uncertain. Before these uncertain effects can prove to be ecologically secure, the spread of the application of biochar is waiting for further study. The stability of biochar leads to the laggard effects of biochar on soil ecosystem, therefore it is necessary to have long-term study on a fixed site. |
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