深翻秸秆还田在我国东北地区已得到了广泛的应用，可以显著增加土壤有机碳储量，改善底层土壤养分循环功能。土壤微生物普遍被认为是这一过程的关键，但其在深层土壤改良中的作用仍研究有限。本研究于2018年开始，以东北地区棕壤为研究对象，以常规耕作（CT，翻耕深度15 cm）为对照，分析了秸秆浅混还田（SCT，翻耕深度15 cm）、深翻处理（IT，翻耕深度35 cm）和深翻秸秆还田（SIT，翻耕深度35 cm）对土壤微生物群落网络和多养分循环功能的影响。结果表明，深翻秸秆还田改善了土壤多养分循环指数，提高了表层和底层土壤有机碳、全氮、有效氮、有效磷和有效钾等养分含量。与传统耕作和秸秆浅混还田相比，深翻秸秆还田通过减少微生物网络平均连通度和节点数，增加平均路径长度和模块化程度，创造了一个结构相对松散但具有高集中度集群的网络结构。同时随机森林分析发现，平均路径长度和聚类系数是影响土壤多养分循环功能的主要因素。综上，深翻秸秆还田将是改善棕壤养分循环和微生物群落结构的一个有效措施，以上结果也为该地区关于微生物驱动秸秆分解策略提供了重要信息。

本研究通过84天的室内培养试验来揭示秸秆和养分（氮(N)、磷(P)和硫(S)）联合供应下土壤新碳生成的潜在微生物机制。结果表明，与对照土壤相比，单独添加秸秆刺激微生物进行养分开采，这与C:N和C:P酶活的比例降低了8-16%相吻合。随着养分补充水平的增提高，公主岭土壤新碳生成量从1155.9增加到1722.4 mg kg^-1，海伦土壤则从725.1增加到1067.5 mg kg^-1。回归树分析表明β-葡萄糖苷酶（BG）、酸性磷酸酶（AP）、微生物量碳（MBC）和酸杆菌对公主岭新碳生成的相对影响分别为27.8、18.5、14.7和8.1%；对海伦新碳生成的相对影响分别为25.9、29.5、10.1和13.9%。路径分析表明酸杆菌通过调节BG、AP和MBC直接或间接对土壤新碳生成产生积极影响，其中MBC的获取更多受到AP的调节。海伦土壤的新碳生成强度低于公主岭土壤，并且海伦土壤的新碳生成与AP活性直接相关，表明土壤属性（例如SOC和pH值）对土壤新碳生成的重要性。综上，本研究揭示了添加秸秆的土壤中新碳生成与NPS养分补充的响应关系，且土壤新碳生成主要依赖于酸杆菌和变形菌的生长代谢及对BG和AP的调控。

Certain agricultural management practices are known to affect the soil microbial community structure; however, knowledge of the response of the fungal community structure to the long-term continuous cropping and rotation of soybean, maize and wheat in the same agroecosystem is limited.  We assessed the fungal abundance, composition and diversity among soybean rotation, maize rotation and wheat rotation systems and among long-term continuous cropping systems of soybean, maize and wheat as the effect of crop types on fungal community structure.  We compared these fungal parameters of same crop between long-term crop rotation and continuous cropping systems as the effect of cropping systems on fungal community structure.  The fungal abundance and composition were measured by quantitative real-time PCR and Illumina MiSeq sequencing.  The results revealed that long-term continuous soybean cropping increased the soil fungal abundance compared with soybean rotation, and the fungal abundance was decreased in long-term continuous maize cropping compared with maize rotation.  The long-term continuous soybean cropping also exhibited increased soil fungal diversity.  The variation in the fungal community structure among the three crops was greater than that between long-term continuous cropping and rotation cropping.  Mortierella, Guehomyces and Alternaria were the most important contributors to the dissimilarity of the fungal communities between the continuous cropping and rotation cropping of soybean, maize and wheat.  There were 11 potential pathogen and 11 potential biocontrol fungi identified, and the relative abundance of most of the potential pathogenic fungi increased during the long-term continuous cropping of all three crops.  The relative abundance of most biocontrol fungi increased in long-term continuous soybean cropping but decreased in long-term continuous maize and wheat cropping.  Our results indicate that the response of the soil fungal community structure to long-term continuous cropping varies based upon crop types.

Black soil is one of the most precious soil resources on earth because it has abundant carbon stocks and a relatively high production capacity.  However, decreasing organic matter after land reclamation, and the effects of long-term inputs of organic carbon have made it less fertile black soil in Northeast China.  Straw return could be an effective method for improving soil organic carbon (SOC) sequestration in black soils.  The objective of this study was to evaluate whether straw return effectively increases SOC sequestration.  Long-term field experiments were conducted at three sites in Northeast China with varying latitudes and SOC densities.  Study plots were subjected to three treatments: no fertilization (CK); inorganic fertilization (NPK); and NPK plus straw return (NPKS).  The results showed that the SOC stocks resulting from NPKS treatment were 4.0 and 5.7% higher than those from NPK treatment at two sites, but straw return did not significantly affect the SOC stocks at the third site.  Furthermore, at higher SOC densities, the NPKS treatment resulted in significantly higher soil carbon sequestration rates (CSR) than the NPK treatment.  The equilibrium value of the CSR for the NPKS treatment equated to cultivation times of 17, 11, and 8 years at the different sites.  Straw return did not significantly increase the SOC stocks in regions with low SOC densities, but did enhance the C pool in regions with high SOC densities.  These results show that there is strong regional variation in the effects of straw return on the SOC stocks in black soil in Northeast China.  Additional cultivations and fertilization practices should be used when straw return is considered as an approach for the long-term improvement of the soil organic carbon pool.

Long-term continuous cropping of soybean (Glycine max), spring wheat (Triticum aesativum) and maize (Zea mays) is widely practiced by local farmers in northeast China. A field experiment (started in 1991) was used to investigate the differences in soil carbon dioxide (CO2) emissions under continuous cropping of the three major crops and to evaluate the relationships between CO2 fluxes and soil temperature and moisture for Mollisols in northeast China. Soil CO2 emissions were measured using a closed-chamber method during the growing season in 2011. No remarkable differences in soil organic carbon were found among the cropping systems (P>0.05). However, significant differences in CO2 emissions from soils were observed among the three cropping systems (P<0.05). Over the course of the entire growing season, cumulative soil CO2 emissions under different cropping systems were in the following order: continuous maize ((829±10) g CO2 m-2)>continuous wheat ((629±22) g CO2 m-2)>continuous soybean ((474±30) g CO2 m-2). Soil temperature explained 42-65% of the seasonal variations in soil CO2 flux, with a Q10 between 1.63 and 2.31; water-filled pore space explained 25-47% of the seasonal variations in soil CO2 flux. A multiple regression model including both soil temperature (T, °C) and water-filled pore space (W, %), log(f)=a+bT log(W), was established, accounting for 51-66% of the seasonal variations in soil CO2 flux. The results suggest that soil CO2 emissions and their Q10 values under a continuous cropping system largely depend on crop types in Mollisols of Northeast China.