Abstract
Flavonoids play a key role in the regulation of plant–plant and plant–microbe interactions, and factors determining their release have been investigated in most of the common forage legumes. However, little is known about the response of flavonoid production and release to co-cultivation with other crop species. This study investigated alterations in the concentration of flavonoids in plant tissues and root exudates in four legumes [alfalfa (Medicago sativa L.), black medic (Medicago polymorpha L.), crimson clover (Trifolium incarnatum L.), and subterranean clover (Trifolium subterraneum L.)] co-cultivated with durum wheat [Triticum turgidum subsp. durum (Desf.) Husn.]. For this purpose, we carried out two experiments in a greenhouse, one with glass beads as growth media for root exudate extraction and one with soil as growth media for flavonoid detection in shoot and root biomass, using LC–MS/MS analysis. This study revealed that interspecific competition with wheat negatively affected legume growth and led to a significant reduction in shoot and root biomass compared with the same legume species grown in monoculture. In contrast, the concentration of flavonoids significantly increased both in legume biomass and in root exudates. Changes in flavonoid concentration involved daidzein, genistein, medicarpin, and formononetin, which have been found to be involved in legume nodulation and regulation of plant–plant interaction. We hypothesize that legumes responded to the co-cultivation with wheat by promoting nodulation and increasing exudation of allelopathic compounds, respectively, to compensate for the lack of nutrients caused by the presence of wheat in the cultivation system and to reduce the competitiveness of neighboring plants. Future studies should elucidate the bioactivity of flavonoid compounds in cereal-legume co-cultivation systems and their specific role in the nodulation process and inter-specific plant interactions such as potential effects on weeds.
Highlights
The need for more sustainable cropping systems has boosted the interest in cropping practices that reduce the reliance on external inputs while maintaining an adequate level of crop productivity.[1]
The impact of legume-cereal intercropping on flavonoid changes in legume tissues and root exudates remains not well studied, elucidating how legumes respond to the co-cultivation with wheat can be of high importance to provide possible mechanistic explanation of the multiple beneficial effects reported at the cropping system level of legume-cereal intercropping.[4]
The concentration of medicarpin was significantly higher in the exudate of all the co-cropped legume species compared to legumes grown alone
Summary
The need for more sustainable cropping systems has boosted the interest in cropping practices that reduce the reliance on external inputs while maintaining an adequate level of crop productivity.[1]. Through exudation of a wide range of compounds, the roots regulate the soil microbial community in the rhizosphere, encourage beneficial and mutualist symbioses, modify the chemical and physical properties of the soil, and inhibit the growth of competing plant species.[5] In particular, flavonoids identified in legume root exudates play a crucial role in regulating inter-plant and plant−microbe interactions,[6,7] and they are pivotal for the activation of nod genes in N-fixing bacteria (node inducer compounds), allowing bacteria to enter plant roots and begin the formation of nodules.[8,9] flavonoids released in the rhizosphere can modify the chemical soil composition and nutrient availability through their activity as reducers or metal chelators. Flavonoids such as kaempferol, nicotiflorin, and rutin have been identified as powerful chelators, and their properties play a key role in nutrient availability, in particular for phosphorus (P) and microelements such as iron (Fe) and manganese (Mn), which are often limited especially under organic farming systems.[6]
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