东北地区农田杨树防护林对土壤特征影响及深层土壤重要性研究

Three North Shelterbelt, commonly as poplar shelterbelt and neighboring farmland, has significant function of ecological protection, but soil improvement function has not been reported systematically, especially importance of the deep soils. In this proposal, poplar shelterbelt forest in northeast-China plain were used as material, and >75 pairs of poplar vs. corn farmland were sampled from 15 regions and 5 different layers from 1m soil profile. Firstly, content and storage of SOC(soil organic carbon),SIC(soil inorganic carbon) will be used for describing soil C sequestration; soil nutrients of total N, P, K, and their available forms (alkali-hydrolized N, exchangeable P and K) were measured for evaluating nutrient effects; soil physiochemical properties will be evaluated as physics(soil water holding capacity, bulk density, specific surface area) and chemical properties (EC, pH).Thereafter, 5 different soil fractions including coarse soil, fine soil without protection, aggregates protection, silt and clay, acid insoluble was classified. By using FTIR and NMR, 8 functional groups will be measured for finding the carbon stabilization mechanism via chemical compositional stability; Owing to the isotopic discrimination of C and N, isotope 13C and 15N were used to find the carbon turnover rate and proportion separation between farmland and forest origin. Thereafter, carbon distribution into 5 components and mean residence times were calculated for highlighting C sink persistence. Based on above measurement and analysis, the effect size from shelterbelt forests will be clearly defined, and deep soil layer importance owing to the deep roots in tree relative crops will be highlighted. Thereafter, uncertainty analysis will carry out for defining the reason for large regional variations from the viewpoints of soil mineral compositional traits(X-ray diffraction), forest-farmland characteristics(tree size, density, farmland-forest distance, trench or not, road or not, farmland history, etc) and climatic conditions. Anticipated results will update the evaluation methods of shelterbelt improving the degradation soil in farmland, and provide scientific suggestion for Three North Shelterbelt management in the future.

东北地区三北防护林，多为农田杨树防护林，生态防护功能显著，但土壤特征影响及深层土壤重要性未见系统报道。本项目以东北地区农田杨树防护林为研究对象，采集15个地区75对以上杨树-玉米田配对样地0-1m的5层土样，定量研究防护林影响土壤有机和无机碳截获、氮磷钾养分和养分有效态、理化性质及其与土壤深度关系；物理化学法区分粗质、细质未保护、团聚体保护、细沙粘土和酸不溶等5组分，红外光谱、核磁共振及X射线衍射法确认土壤组分内8类官能团组成变化及作用机制；稳定同位素法确定碳氮来源及周转时间，找出受防护林显著影响的土壤指标、发生土壤深度及区域间差异，探索深层土壤对防护林养分、理化性质、碳截获持久性评价的贡献；结合土壤矿物、气候因子、林分及农田特征开展不确定性分析，通过冗余排序及结构方程模型法明确限制因子及作用机制。相关研究结果将更新防护林提升退化农田土壤功能评价方法，并为东北地区三北防护林管理提供建议。

东北地区农田杨树防护林，生态防护功能显著，但其对土壤特征影响尤其是深层土壤未见系统报道。本项目以东北地区农田杨树防护林为研究对象，采集15个区域75对杨树-玉米田配对样地0-1m的5层共750份土样，研究了杨树防护林对土壤理化性质的影响及与土壤深度的关系、不同土壤物理化学组分碳氮含量和官能团组成变化、不同土壤团聚体组分有机和无机碳周转以及原土碳温湿度敏感性等指标。结果表明杨树防护林造林后土壤全磷、电导率以及无机碳显著变化主要发生在0-20cm，土壤硝态氮、容重、孔隙度、含水量以及pH的显著变化可深达80或100cm。防护林建设提高了浅层（0-40cm）团聚体保护碳氮含量并降低了细沙粘土保护组分碳氮含量，在深层（40-100cm）明显提高了粗质未保护组分碳和细沙粘土保护氮。防护林的林分特征对深层土壤组分特征，分组后碳氮特征变化的解释高于表层。杨树防护林提高了表层原土、细沙黏土保护和化学保护、粗质未保护和团聚体保护组分官能团相对含量，但深层变化较小。防护林建设显著提高了表层土壤的无机碳含量（25.27%），主要由细沙黏土组分无机碳含量升高所导致。相比农田土壤，造林降低了原土及各组分有机碳同位素值及其与容重、孔隙度相关性，增加了其与组分占比和NO3-N的关系；无机碳同位素值与MAP显著相关，此外pH与杨树土壤各组分无机碳值显著相关。防护林的营建显著降低了Q10值（15.4%），增强了土壤有机碳稳定性。高通量测序结果表明，杨树防护林改变了土壤微生物的群落结构及功能，显著增加了土壤ECM真菌，降低了硝化与反硝化功能，进而影响了土壤磷与NO3--N含量。结合地理气候因子、林分及农田特征开展不确定性分析，发现不同层次土壤性质变化的影响限制因子不同。表层土壤性质变化主要由MAP、胸径和真菌功能来控制，而深层的土壤性质变化主要由土壤真菌功能解释。本研究将更新防护林提升退化农田土壤功能评价方法，并为东北地区三北防护林管理提供建议。