Soil nitrogen transformation and functional microbial abundance in an agricultural soil amended with biochar

ABSTRACT Biochar soil amendments are attracting attention as one strategy to improve soil microbially ecological environment and regulate the soil nitrogen cycle. This study aimed to evaluate the effects of biochar application on agricultural soil improvement, nitrogen (N) mineralization and nitrification. The experiment was carried out on a typical farmland containing black soil and saline-alkaline soil in Northeast China. Four treatments were undertaken, including the control-treated black soil farmland (CS), the biochar-treated black soil farmland (BCS), the control-treated saline-alkali soil farmland (SAS), and the biochar-treated saline-alkaline soil farmland (BSAS). Basic physical and chemical properties, enzyme activity, and the contents of ammonium-nitrogen (NH4+-N) and nitrate-nitrogen (NO3--N) in the soil were subsequently determined. The co-occurrence networks of bacterial communities of the biochar and control treatment groups were constructed based on high-throughput sequencing data of the 16S rRNA genes. The results showed that the BCS and BSAS treatments significantly increased the contents of soil organic matter, total nitrogen, total phosphorus, and available phosphorus. The application of biochar significantly increased the NH4+-N contents in the black soil and saline-alkaline soil by 81.78 and 80.08 %, respectively, while significantly reducing the soil NH4+-N/NO3--N content, which promoted the transformation of NH4+-N into NO3--N. Subsequently, the released NH4+-N was transformed into NO3--N through nitrification. After the biochar application, the NO3--N contents in the black and saline-alkaline soils could be fixed. The biochar application significantly increased the abundance of gdh, AOA-amoA, AOB-amoA, nirK, nirS, nosZ, and nifH genes, with no significant difference in the abundance of napA genes being found among different treatments. Microbes playing a key role in the co-occurrence network were Proteobateria, Acidobacteria, Bacteroidetes, Actinobacteria, and Chloroflexi. As compared with the CS and SAS treatments, under the BCS+BSAS treatment, the connectors, module hubs, connectedness, and clustering coefficient showed larger parameters, and the networks were more complex. The application of biochar gradually increased the nodes, edges, and average degree of the bacterial co-occurrence network, thus indicating that the interaction between microbial groups in the black and saline-alkaline soils post biochar application may be important in the biogeochemical cycle process in farmland soil.

摘要 生物炭（biochar）土壤改良剂作为改善土壤微生物生态环境、调控土壤氮循环的策略之一，正受到广泛关注。本研究旨在评估生物炭施用对农田土壤改良、氮（N）矿化与硝化作用的影响。试验于中国东北典型黑土与盐碱农田开展，共设置4组处理：对照黑土农田（CS）、生物炭改良黑土农田（BCS）、对照盐碱农田（SAS）以及生物炭改良盐碱农田（BSAS）。随后测定了土壤的基本理化性质、酶活性，以及铵态氮（NH4+-N）与硝态氮（NO3--N）含量。基于16S rRNA基因高通量测序数据，构建了生物炭处理组与对照组的细菌群落共现网络。研究结果显示，BCS与BSAS处理显著提升了土壤有机质、全氮、全磷与有效磷含量。生物炭施用分别使黑土与盐碱土的铵态氮含量显著提升81.78%与80.08%，同时显著降低了土壤NH4+-N/NO3--N比值，促进了铵态氮向硝态氮的转化。后续释放的铵态氮可通过硝化作用转化为硝态氮，而生物炭施用后可固定黑土与盐碱土中的硝态氮含量。生物炭施用显著提升了gdh、AOA-amoA、AOB-amoA、nirK、nirS、nosZ与nifH基因的丰度，而不同处理间napA基因丰度无显著差异。共现网络中的关键微生物类群为变形菌门（Proteobacteria）、酸杆菌门（Acidobacteria）、拟杆菌门（Bacteroidetes）、放线菌门（Actinobacteria）与绿弯菌门（Chloroflexi）。相较于CS与SAS处理，BCS+BSAS组的连接节点、模块枢纽、连通度与聚类系数参数均更大，网络结构更为复杂。生物炭施用使细菌共现网络的节点数、边数与平均度逐步提升，表明生物炭施用后黑土与盐碱土中微生物类群间的互作，可能在农田土壤生物地球化学循环过程中发挥重要作用。