Root exudates drive interspecific facilitation by enhancing nodulation and N2 fixation
Root exudates drive interspecific facilitation by enhancing nodulation and N2 fixation
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根系分泌物通过增强结瘤和 N-2 固定来促进种间促进
DOI：
10.1073/pnas.1523580113
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发表时间：
2016-06-07
影响因子：
11.1
通讯作者：
Li, Long
中科院分区：
文献类型：
--
作者：
Li, Bai;Li, Yu-Ying;Li, Long
实验系统中的植物多样性通常会提高生态系统的生产力，但人们对导致这种过度屈服的机制只有部分了解。间作蚕豆(Vicia Faba L.)和玉米(Zea Mays L.)这会导致产量过高，还会增强蚕豆的结瘤作用。通过两年田间试验，我们发现蚕豆和玉米之间的根-根相互作用显著增加了间作蚕豆的结瘤和共生固氮。此外，玉米的根分泌物促进蚕豆结瘤，而小麦和大麦的根分泌物不促进。因此，间作谷物引起的土壤硝酸盐浓度下降并不是玉米促进蚕豆结瘤的唯一机制。间作玉米还导致系统中黄酮类物质(根瘤菌的信号化合物)的渗出量增加了两倍。玉米根分泌物处理蚕豆根系后，查尔酮-黄烷酮异构酶(参与类黄酮合成)基因的表达立即增加11倍，同时参与结瘤和生长素反应的基因表达显著增加。35d后，玉米根系分泌物处理后的蚕豆继续表现出早期结瘤蛋白93(ENOD93)等关键结瘤基因的上调，并促进了固氮。我们的结果揭示了间作玉米促进蚕豆固氮的机制，其中玉米根分泌物促进蚕豆类黄酮合成，促进结瘤，并在增强基因表达后刺激固氮。这些结果表明促进了根-根的相互作用，并为物种多样性和生态系统生产力之间的正向关系提供了一种机制。
Plant diversity in experimental systems often enhances ecosystem productivity, but the mechanisms causing this overyielding are only partly understood. Intercropping faba beans (Vicia faba L.) and maize (Zea mays L.) result in overyielding and also, enhanced nodulation by faba beans. By using permeable and impermeable root barriers in a 2-y field experiment, we show that root-root interactions between faba bean and maize significantly increase both nodulation and symbiotic N-2 fixation in intercropped faba bean. Furthermore, root exudates from maize promote faba bean nodulation, whereas root exudates from wheat and barley do not. Thus, a decline of soil nitrate concentrations caused by intercropped cereals is not the sole mechanism for maize promoting faba bean nodulation. Intercropped maize also caused a twofold increase in exudation of flavonoids (signaling compounds for rhizobia) in the systems. Roots of faba bean treated with maize root exudates exhibited an immediate 11-fold increase in the expression of chalcone-flavanone isomerase (involved in flavonoid synthesis) gene together with a significantly increased expression of genes mediating nodulation and auxin response. After 35 d, faba beans treated with maize root exudate continued to show up-regulation of key nodulation genes, such as early nodulin 93 (ENOD93), and promoted nitrogen fixation. Our results reveal a mechanism for how intercropped maize promotes nitrogen fixation of faba bean, where maize root exudates promote flavonoid synthesis in faba bean, increase nodulation, and stimulate nitrogen fixation after enhanced gene expression. These results indicate facilitative root-root interactions and provide a mechanism for a positive relationship between species diversity and ecosystem productivity.