种间根系互作对半干旱区豆禾混播草地生物固氮与群体产量的影响

Legume-grass mixture plays an important role in mitigating the grass-livestock conflict in semi-arid region. However, the impact mechanism of interspecific root interaction (IRI) on biological nitrogen fixation (BNF) and population yield of legume-grass mixture located in semi-arid region remains unclear. Based on five years observed data from legume-grass mixture (Medicago sativa L.+ Bromus inermis Leyss.) platform located in semi-arid region, microplot experiment of root barrier techniques, 15N isotope labeling techniques and root exudates ‘feeding’ experiment will be applied to answer (1) What effect has IRI on BNF and population yield? and (2) which process contributes to the BNF of legume, the feedback of grass for nitrogen competition, or the effect of grass exudates, or both? Therefore, this study mainly focus on the effect of IRI on population photosynthesis, root traits, and nodulation and BNF of legume-grass mixture in semi-arid region, the effect of IRI on nitrogen rhizodeposition and transfer between legume and grass, and the impact mechanism of root exudates of grass on nodulation and BNF of legume. This study is expected to reveal the influence mechanism of IRI on BNF and population yield of legume-grass mixture in semi-arid region. It also provides scientific support for guidance of legume-grass mixture construction in semi-arid region.

发展豆禾混播草地对有效缓解半干旱区草畜矛盾具有重要意义。目前关于根系互作对半干旱区豆禾混播草地固氮与群体产量的影响机理，尚不十分清楚。本项目以内蒙古半干旱区豆禾混播草地平台（紫花苜蓿+无芒雀麦）多年观测数据为基础，进一步通过田间根系分隔微区试验、15N同位素标记、根系分泌物“饲喂”等方法，试图回答（1）种间根系互作对豆禾混播草地固氮及牧草群体产量形成有着怎样的影响？（2）在该过程中，混播对豆科牧草固氮的影响是受禾草氮竞争的反馈所致，还是禾草根系分泌物的作用，抑或二者兼而有之？为此，项目着重开展种间根系互作对半干旱区豆禾混播草地群体光合、根系性状和结瘤固氮的影响，研究根系互作对氮素根际沉积与转移的影响及紫花苜蓿结瘤固氮反馈，分析禾草根系分泌物对豆科牧草固氮的作用，通过研究，旨在阐明种间根系互作对豆禾牧草混播生物固氮与产量形成的影响机理，为半干旱区混播草地建设提供一定的理论依据。

植物种间根系互作是决定豆禾混播草地生产力形成与结瘤固氮的关键因子。氮素互惠是豆禾牧草种间互作的关键过程之一，通过氮素转移，豆科植物对邻株禾草生长、营养品质尤其是蛋白质具有改善作用。豆禾牧草之间的氮竞争与禾草根系分泌物可介导豆科植物生物固氮。然而，根系互作对半干旱区豆禾混播草地固氮与群体产量的影响机理还知之甚少。本项目依托已经建立的半干旱区豆禾混播草地原位平台，结合田间根系分隔微区试验、15N同位素标记、室内根系分泌物“饲喂”和植物代谢组学技术，研究种间根系互作对半干旱区豆禾混播草地群体产量和结瘤固氮、氮素根际沉积与转移的影响及禾草根系分泌物在根系互作中的作用。研究表明：1）种间根系互作不仅促进豆禾混播系统中禾草的生长，还促进禾草体内有机物质向地下部的分配；2）种间根系互作有利于提高豆科牧草的氮素转移比例；3）禾草根系分泌物可促进豆禾混播体系中豆科牧草根系类黄酮物质的增加，进而提高固氮能力。综上所述，种间根系互作在维持豆禾牧草混播草地生物固氮与群体产量中产生了重要影响，禾草根系分泌物促进豆科牧草根系结瘤固氮是种间根系互作发挥作用的重要途径。