玉米/紫花苜蓿间作氮素高效利用的根系-土壤互作机理

Maize and alfalfa, as the important food crop and the excellent leguminous forb, respectively, have been prioritized in the development of the northeast farming and pastoral area, and their intercropping system has promising prospects. However, it is still unclear about the belowground process mechanism of maize/alfalfa intercropping advantages. Nitrogen is one of the most important soil elements affecting crop growth, development and production, and root is a bridge of linking aboveground and underground processes and the important organ of absorbing nitrogen. The variations of root turnover and architecture as well as nitrogen fixation and transfer are strongly correlated with the high nitrogen utilization efficiency. In this study, combining in-situ field and greenhouse experiments, adopting isotope tracer technique, root separation technique and in-situ roots scanning technique, integrated agronomic, ecological and physiological knowledges, we explore the traits of root turnover, root architecture and nitrogen fixation and transfer in different maize/alfalfa intercropping modes, and clarify the relationships between these belowground processes with high nitrogen utilization efficiency. Main aims of the study are to reveal the mechanism of the improved nitrogen utlization efficiency in the maize/alfalfa intercropping system from a root-soil nitrogen interaction perspective. The study will provide theoretical basis for delicately regulating nitrogen fertilizer utilization in maize/alfalfa intercropping system and reducing its input and risks to the environment.

玉米和紫花苜蓿作为东北农牧交错区发展的重要粮食作物和优良豆科牧草，两者间作前景广阔。然而，目前对其间作优势产生的地下过程机理尚不清楚。氮素是影响作物生长发育和产量的最重要营养元素，根系作为联系作物地上与地下过程的桥梁和吸收氮素的重要器官，其周转、构型变化及氮素的固定和转移这三者都与氮素高效利用密切相关。本研究通过田间试验和盆栽试验，采用同位素示踪技术、根系分隔技术和根系原位扫描技术，综合运用农学、生态学及生理学知识，探究玉米/紫花苜蓿间作根系周转、构型及氮素固定和转移特征，阐明这些地下过程与氮素高效利用的关系。本研究从地下根系-土壤养分互作过程的新视角揭示玉米/紫花苜蓿间作提高氮素利用效率的机理。预期成果能为玉米/紫花苜蓿间作体系精细调控氮肥、减少氮肥投入和降低环境风险提供科学理论依据。

豆科/禾本科间作被认为是一种可持续的农业生产体系，可通过提高氮素利用率来减少氮肥的投入。然而，关于间作如何从氮素固定和转移、根系构型等方面提高氮素利用效率的信息很少。通过田间和温室试验定量研究在玉米/苜蓿间作系统中氮素固定、氮素转移和根系构型。我们的研究结果发现，与单作相比，间作增加豆科固氮比例、根瘤数量和豆血红蛋白含量，从而显著提高了氮素利用效率和产量。豆科植物固氮比例的提高不仅与根际硝态氮的消耗有关，而且与苜蓿根际硝铵比的降低和根系分泌物中柠檬酸含量的增加显著相关。在不施氮的情况下，柠檬酸的分泌可酸化根际，活化根际可利用的营养物质，从而促进豆科植物固氮。总的来说，苜蓿固定的15.4%-21.5%N转移到间作玉米，豆科固氮量的增强促进向与玉米进行的氮素转移。AMF和根系分泌物被认为是地下短期氮转移的两种重要的途径。这两种途径的相对重要性取决于土壤氮的有效性。在氮素匮乏土壤中，从苜蓿到玉米的短期氮素转移更依赖于丛枝菌根真菌（AMF）途径，而在氮源充足的条件下，从苜蓿到玉米的短期氮素转移更依赖于根系分泌物途径。此外，玉米/苜蓿间作显著提高了玉米和苜蓿的根表面积和根体积。并且苜蓿的根表面积和根体积的提高与作物产量和氮吸收量呈显著正相关。从根系分布方面，玉米和苜蓿的根系均向水平增殖至间作第一行，苜蓿垂直方向的根长密度在缺氮土壤中显著增加。本研究为根系相互作用如何促进氮素利用效率提供数据支持和理论创新。