生物炭用量对塿土微生物量及碳源代谢活性的影响

目的研究果树树干、枝条制成的生物炭添加4～5年后，其添加量对土微生物量及碳源代谢活性的影响，为生物炭改良土的合理应用提供数据支撑和理论依据。方法基于陕西关中土的长期田间试验，采用氯仿熏蒸—浸提法及Biolog-ECO检测法，研究了生物炭不同添加量 (0、20、40、60、80 t/hm2) 下冬小麦不同生育期土壤微生物量C、N、P、C/N的动态变化及土壤微生物的碳源代谢活性。结果当生物炭添加量为40～60 t/hm2时，显著提高了土壤微生物量碳；当生物炭添加量 ≥ 40 t/hm2时，显著提高了土壤微生物量C/N；添加生物炭对土壤微生物量N、P没有显著影响。当生物炭添加量为20 t/hm2时，显著增加了土壤微生物量碳的季节波动；当生物炭添加量为40～60 t/hm2时，显著增加了土壤微生物量C/N的季节波动；当生物炭添加量为20～60 t/hm2时，显著降低了土壤微生物量P的季节波动；添加生物炭对土壤微生物量N的季节波动没有显著影响。添加生物炭对土壤微生物碳源代谢活性没有显著影响，但高量生物炭的添加有降低土壤微生物整体代谢活性的趋势。当生物炭添加量为60 t/hm2时，显著降低了土壤丰富度指数，显著提高了均匀度指数；当生物炭添加量 ≥ 60 t/hm2时，显著降低了Shannon-Wiener指数、Simpson指数。添加生物炭对土壤微生物利用糖类、氨基酸类、多聚物类、多酚化合物类、多胺类碳源的利用率没有显著影响，但生物炭添加量为60 t/hm2时，土壤微生物显著降低了对羧酸类碳源的利用率；糖类、羧酸类、氨基酸类是土中微生物比较偏好、利用率较高的碳源。结论生物炭添加4～5年后，在第7季作物冬小麦生育期内，其不同添加量对土壤微生物量及微生物功能多样性的影响依然有显著的差异。生物炭添加量为40 t/hm2时，可以显著提高土壤微生物量碳和C/N，显著降低土壤微生物量磷的季节波动；生物炭添加量大于40 t/hm2时，土壤微生物的整体代谢活性，表征土壤微生物功能多样性的丰富度指数、Shannon-Wiener指数、Simpson指数，土壤微生物对糖类、氨基酸类、多胺类碳源的利用率均呈现降低趋势。因此，生物炭添加量必须控制在合理的范围内，避免对土壤产生不良影响。

Effect of biochar addition on soil microbial biomass and metabolic activities of carbon sources in Lou soil

ObjectivesThe residual effect of different biochar after 4 to 5 years’ application was investigated, in order to provide data and theory references for suitable use of biochar in Lou soil amendment.MethodsA field experiment was carried out on Lou soil of Guanzhong Plain, Shaanxi Province. The tested biochar was made from trunk and branch of fruit trees, and was once added into soil in 5 levels (0, 20, 40, 60 and 80 t/hm2). Five years later, the soil microbial biomass C, N, P contents and the C/N ratio were analyzed; the microbial carbon metabolic activities were studied by the chloroform fumigation–extraction and biolog-ECO plates.ResultsWhen the biochar addition was 40–60 t/hm2, the soil microbial biomass C increased significantly. When the biochar addition was above or equal to 40 t/hm2, the soil microbial biomass C/N ratio increased significantly. The biochar addition had no significant effect on soil microbial biomass N and P contents. When the biochar addition was 20 t/hm2, the seasonal fluctuation of soil microbial biomass C increased significantly. When the biochar addition was 40–60 t/hm2, the seasonal fluctuation of soil microbial biomass C/N increased significantly. When the biochar addition was 20–60 t/hm2, the seasonal fluctuation of soil microbial biomass P decreased significantly. The biochar addition did not influence the seasonal fluctuation of soil microbial biomass N significantly. The biochar addition had no significant effects on carbon source metabolic activities. However, the addition of high amount of biochar had a tendency to reduce the overall carbon source metabolic activities of soil microorganisms. When the biochar addition was 60 t/hm2, the richness index decreased significantly, while the evenness index increased significantly. When the biochar addition was above or equal to 60 t/hm2, Shannon-Wiener index, Simpson index decreased significantly. The biochar addition had no significant effects on the utilization rates of soil microorganisms to use C sources such as carbohydrates, amino acids, polymers, aromatic chemicals and amines. When the biochar addition was 60 t/hm2, the utilization rate of soil microorganisms using carboxylic acids decreased significantly. Carbohydrates, carboxylic acids and amino acids were the preferable carbon sources with higher carbon utilization efficiency for soil microorganisms.ConclusionsThe biochar addition rate significantly affects the soil microbial biomass and microbial functional diversity even after 4 to 5 years’ application. When the biochar addition was 40 t/hm2, the soil microbial biomass C and C/N increased significantly, and there is no significant seasonal fluctuation in soil microbial biomass P. When the biochar addition was above 40 t/hm2, the overall carbon source metabolic activities of soil microorganisms, richness index, Shannon-Wiener index and Simpson index indicating soil microbial functional diversity, and the utilization rates of soil microorganisms to use C sources such as carbohydrates, amino acids, and amines shows a decreasing trend. Therefore, biochar application must be controlled within a reasonable range to avoid adverse effects on soil.