Chickpea enhances silicon accumulation in neighboring wheat: a role for rhizosheath carboxylates?

Background and aims

Low soil silicon (Si) availability may restrict crop silicification and its associated benefits for resistance to environmental stress. Cereal–legume intercropping offers a potential strategy to enhance soil Si mobility through the release of Si-mobilizing root exudates by legumes, particularly carboxylates. However, direct evidence supporting this mechanism remains limited.

Methods

In a glasshouse pot experiment, wheat (Triticum aestivum) was grown either as two individuals per pot or in combination with one chickpea (Cicer arietinum) individual. To test whether chickpea root exudates could mobilize soil Si and increase wheat Si concentrations ([Si]), 20 chickpea accessions with different patterns of carboxylate release were used. Intraspecific variation in [Si] among the 20 chickpea accessions was also quantified.

Results

Wheat grown together with chickpea showed higher leaf [Si] and Si content than wheat grown either alone or with another wheat plant in the same pot. Rhizosheath carboxylate concentrations were also greater in wheat-chickpea than in wheat-wheat combinations. However, wheat leaf [Si] was only marginally correlated with rhizosheath carboxylates and showed no correlation with chickpea leaf [Mn], used here as a proxy for root carboxylate release. In contrast, wheat leaf [Si] was positively correlated with wheat leaf [Mn]. Chickpea leaf [Si] also varied significantly among accessions.

Conclusion

Our study shows that chickpea promoted Si uptake in wheat. This effect may be partly related to chickpea-induced changes in rhizosphere processes, including carboxylate release, which could enhance the mobilization of poorly-available soil Si; however, further studies are needed to confirm this mechanism and to assess the contribution of other potential mechanisms. The significant variation in chickpea foliar [Si] among accessions also revealed previously overlooked diversity in silicification within this crop. These findings highlight the potential of crop interactions and agricultural management practices to enhance crop silicification, with possible benefits for stress resilience and yield.