旱作区核桃/豆科间作系统氮素资源竞争（互补）性利用的过程机理

Walnut is an important oleiferous tree species and ecological tree species. It has high economic and nutritional value. The economic utilization of young walnut trees is the main way to improve its early benefit. The intercropping of walnut-soybean can make full use of land resources, effectively improve the nitrogen utilization rate and reduce the application of nitrogen fertilizer. But, in walnut-soybean intercropping system, the competition and promoting mechanism of nitrogen nutrition in two plants is unclear. It needs to be studied. This project will set the trials of walnut-soybean intercropping and their monoculture as comparison in rain-fed area in Tianshui city of Gansu province. By set as different treatment of experiment, systematic research the trait of the rhizospheric and non-rhizospheric soils physicochemical properties and the changes of enzyme activity and the indexes of walnut trees growth and development. Analyzing the soil organic nitrogen mineralization, nitrogen characteristics and the growth and development of walnut trees. Expound the effects of rhizospheric soil and root exudates on growth and yield quality of soybean. Using the 15N - urea tracer technique, Studies on the property of nitrogen supplying of the soybean and the transfer pathway and the way to the walnut. Discovering the rule of nitrogen absorption, transportation and distribution of the walnut tree different organs in main phenophase. Ascertaining the mechanism of nitrogen resource competition and complementation in walnut- soybean intercropping system in dry farming region. The results will provide a theoretical basis of how to improve nut yield and quality in the dry farming region of loess plateau.

核桃是重要的木本油料和生态树种，具有很高的经济和营养价值。幼龄核桃树林下的经济利用方式是提高其前期效益的主要途径。核桃/大豆间作能充分利用土地资源，有效提高氮素利用率，减少氮肥施用量，但间作体系中两种植物氮素营养的竞争与促进作用机理尚不清楚，需要深入研究。本项目拟在甘肃天水市旱作区设置核桃/大豆间作试验，以其单作分别为对照，测定间作体系不同区域（根际和非根际）土壤理化性状、酶活性变化规律和树体生长发育指标，分析土壤有机氮矿化、氮素特征以及核桃树体生长发育的响应；阐明核桃根域土壤和根系分泌物对大豆生长发育和产量品质的影响。利用15N-尿素示踪技术，研究大豆的供氮特征及向核桃的转移途径和方式，揭示核桃树不同器官主要物候期氮素吸收、运移和分配规律，探明旱作区核桃/大豆间作体系氮素资源竞争（互补）性利用机理。研究成果将为探索提高黄土高原旱作区核桃坚果产量和品质提供理论依据。

核桃（Juglans regia）是兼具经济价值和生态价值的树种。在甘肃省，核桃树大多种植于以低N状态为代表的土壤上，外源N输入量高，加之幼苗定植行距宽，导致土地利用效率低和环境成本高等问题的出现。本研究以甘肃省处于优势地位的核桃/大豆间作栽培模式为研究对象，对间作与单作模式下土壤养分、酶活性、核桃幼树对N素的吸收、利用以及间作模式中N素运转能力等进行了综合分析。主要结果如下，10月间作与单作核桃地上部干物质量每株分别比6月增加了283.35%、282.16%，地下部每株分别增加169.43%、157.63%。间作模式总干物质量显著高于单作。整个生育期，间作与单作核桃中N素来自肥料的比例不断降低，然而间作体系中N素来自肥料比例的加权平均值显著大于单作体系。10月前核桃15N分配率为地上部（叶、枝、主干）高于地下部（根），后期则相反。6~10月，间作体系N肥利用率的加权平均值显著高于单作体系。10月，大豆固N效率、N素转移率及大豆固N转移比例均为最高。间作系统中核桃根系中与碳氮代谢相关的氨基酸代谢、糖代谢和核酸代谢途径被显著富集，发生了与碳氮相关代谢途径的改变。间作各处理土壤微生物量C、N（MBC、MBN）随时间推移逐渐增加，且核桃落叶前，间作各土层土壤C、N、P相关酶活性均显著高于单作。整个生育时期中，核桃单作模式各土层全N含量均显著高于核桃/大豆间作模式，说明间作系统中两物种存在对N素的竞争作用。本研究明确了核桃/大豆间作模式下核桃幼树对N素吸收、运转和分配的特征，提出了适用于减少N素投入的核桃栽培模式，阐明了旱作区核桃/大豆间作体系N素资源竞争（互补）性利用机理，为提高甘肃旱作区核桃生产中间作大豆这一农艺措施的应用提供理论及技术支撑。