Root Exudates Drive Interspecific Facilitation by Enhancing Nodulation and N2 Fixation. Bai, L.; Yu-Ying, L.; Hua-Mao, W.; Fang-Fang, Z.; Chun-Jie, L.; Xue-Xian, L.; Hans, L.; and Long, L. 113(23):6496–6501.
Root Exudates Drive Interspecific Facilitation by Enhancing Nodulation and N2 Fixation [link]Paper  doi  abstract   bibtex   
[Significance] Plant diversity often leads to an increase in ecosystem productivity, but the underpinning mechanisms remain poorly understood. We found that faba bean/maize intercropping enhances productivity, nodulation, and N2 fixation of faba bean through interspecific root interactions. We provide a mechanism explaining how maize promotes N2 fixation of faba bean, where root exudates from maize increase root hair deformation and nodulation in faba bean, double exudation of flavonoids (signaling compounds for rhizobia), and up-regulate the expression of a chalcone-flavanone isomerase gene involved in flavonoid synthesis, and genes mediating nodulation and auxin responses. Our results provide a mechanism for facilitative root-root interactions explaining how species diversity may enhance ecosystem productivity with important implications for developing sustainable agriculture. [Abstract] 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 N2 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.
@article{baiRootExudatesDrive2016,
  title = {Root Exudates Drive Interspecific Facilitation by Enhancing Nodulation and {{N2}} Fixation},
  author = {Bai, Li and Yu-Ying, Li and Hua-Mao, Wu and Fang-Fang, Zhang and Chun-Jie, Li and Xue-Xian, Li and Hans, Lambers and Long, Li},
  date = {2016-06},
  journaltitle = {Proceedings of the National Academy of Sciences},
  volume = {113},
  pages = {6496--6501},
  issn = {1091-6490},
  doi = {10.1073/pnas.1523580113},
  url = {http://mfkp.org/INRMM/article/14062242},
  abstract = {[Significance]

Plant diversity often leads to an increase in ecosystem productivity, but the underpinning mechanisms remain poorly understood. We found that faba bean/maize intercropping enhances productivity, nodulation, and N2 fixation of faba bean through interspecific root interactions. We provide a mechanism explaining how maize promotes N2 fixation of faba bean, where root exudates from maize increase root hair deformation and nodulation in faba bean, double exudation of flavonoids (signaling compounds for rhizobia), and up-regulate the expression of a chalcone-flavanone isomerase gene involved in flavonoid synthesis, and genes mediating nodulation and auxin responses. Our results provide a mechanism for facilitative root-root interactions explaining how species diversity may enhance ecosystem productivity with important implications for developing sustainable agriculture.

[Abstract]

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 N2 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.},
  keywords = {*imported-from-citeulike-INRMM,~INRMM-MiD:c-14062242,~to-add-doi-URL,agricultural-resources,biodiversity,diversity,ecosystem,nitrogen,soil-resources,species-association,sustainability,vegetation,vicia-faba,zea-mays},
  number = {23}
}
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