河套灌区盐碱地秸秆隔层对深层土壤有机碳矿化过程及影响机制的研究

Strengthening the research on the mechanism of deep soil organic carbon mineralization is of great significance for improving the carbon storage of farmland and establishing the target of soil fertilization. Our preliminary study found that placing corn straw interlayer in the depth 40 cm has significant effect on regulating water and salt, increased the microbial diversity and soil respiration rates, also significantly increased the content of soluble organic carbon (DOC) in 40-60 cm soil layer. However, the study on the migration of DOC under different salt conditions and its relationship with deep organic carbon mineralization still need to be further studied. Therefore, based on the field micro-plot experiment in Inner Mongolia, we firstly monitor the changes of content, chemical composition and influence factors of DOC in corn straw interlayer treatment under different salinity gradients, and by field 13C labelled corn straw test the contribution of DOC to total DOC in deep soil was further determined. Secondly, the characteristics of deep CO2 emission in the treatment of corn straw interlayer will be monitored and analyzed. At the same time, the mineralization, transformation of 13C-DOC and the excitation effect on the original organic carbon in the deep layer were also determined with the help of 13C labeled DOC culture. Lastly, we will analyze the relationship among the excitation effect of SOC mineralization, the relative change of microbial community and the exogenous DOC by using phospholipid fatty acid analysis (PLFA) and high throughput sequencing technique, and thus the microbiological mechanism of deep organic carbon mineralization will be revealed. The research results will provide a scientific basis for understanding the mechanism of soil organic carbon fixation and stability of deep saline alkali soil and guiding the rational fertilization in the Hetao Irrigation District.

加强盐碱地深层（﹤30cm）土壤有机碳矿化机制研究对于提高农田碳储量、确立土壤培肥目标意义重大。前期研究发现：盐碱地埋设秸秆隔层后提高了微生物多样性和土壤呼吸，同时对深层可溶性有机碳（DOC）含量有显著影响，但关于该措施在不同盐分条件下DOC迁移及其与深层有机碳矿化关系的研究仍有待深入。为此，拟采用田间微区试验，分析不同盐分梯度下秸秆隔层处理剖面DOC含量、化学组成变化特征及影响因素，结合田间13C标记秸秆试验，明确淋溶DOC对深层DOC的贡献；通过对深层CO2排放特征的监测分析以及结合13C标记DOC培养实验，明确13C-DOC矿化、转化及对深层原有有机碳的激发效应，并运用PLFA和高通量测序方法，探讨深层SOC矿化的激发效应与微生物群落相对变化和外源DOC之间的关系，揭示深层有机碳矿化机制。研究结果将为深入认识河套灌区盐碱地深层有机碳稳定性机制及指导合理培肥提供科学依据。

针对河套灌区盐碱地深层（> 40 cm）土壤有机碳稳定性机制不清的问题，采用田间微区定位试验、室内根箱模拟实验和室内培养试验的方法，结合同位素示踪、高通量测序、酶标仪测定荧光酶活性等技术，分析秸秆隔层条件下深层SOC固存与CO2排放特征，并从物理、化学、生物方面揭示其稳定性机制。结果表明：高量秸秆深还田条件下，耕层土壤和深层土壤都可以作为重要的土壤碳汇，主要是由于秸秆隔层条件下影响有机碳储量的同时，创造了不同养分条件与盐碱环境，且高pH和养分值有利于0-40 cm耕层土壤固碳，低pH和养分值则有利于40-100 cm深层土壤固碳。另外，通过监测作物生育时期CO2排放通量表明高量秸秆隔层促进深层土壤CO2固定，通过结构方程模型分析发现0-80 cm土层CO2排放通量主要受秸秆隔层影响土壤环境因子的间接调控，而底层（80-100 cm）主要受秸秆隔层C投入量的直接影响。从有机碳物理化学保护的研究发现，表层土壤有机碳固存更受大团聚体分布及其有机碳氧化稳定性的影响，而深层土壤有机碳储量变异受物理结构稳定性影响的同时，微团聚体中有机碳的积累可以有效制约团聚体有机碳的氧化活性，提升有机碳稳定性。结合室内根箱与13C-葡萄糖添加培养实验，从生物化学保护的研究发现，秸秆隔层埋设初期提高了0-40 cm土层可溶性碳（DOC）含量，主要是由于增加了亮氨酸胺酞酶（Lue）活性和降低过氧化酶（PEO）活性；降低了60-100 cm土层微生物碳含量（MBC）含量，主要是由于降低了木聚糖酶（Xyl）、酚氧化酶（PhoOx）和PEO活性。秸秆隔层埋设6年后降低了深层SOC的累积矿化量与原有SOC的激发效应，这种激发效应的强度主要取决于较高的养分化学计量比（DOC：Avail-N、DOC：Avail-P和DOC：Avail-K），而不是取决于原土微生物群落特征。本研究可为干旱区盐碱地SOC提升提供理论依据。