Background and aims

While agroecological transition towards sustainable cropping systems has proposed the integration of nitrogen (N)-fixing-legumes to reduce N inputs, current agriculture faces primary limitations of water and N. It is therefore crucial to identify and hierarchize key drivers of legumes water and mineral (hydromineral) acquisition under limiting conditions, especially the underexplored functions provided by root architecture and rhizodeposition.

Methods

We studied the response of spatial exudation patterns in Pisum sativum to contrasted water and N treatments. These patterns were related with structural and functional plant traits involved in carbon (C), N and water uptake, root architecture and root local C and N content. The goal was to i) identify effects of root depth and maturity on local exudation and ii) characterize drivers of C and N allocation during vegetative growth.

Results

We show that younger and shallow roots tend to exude more sugar and amino acids and that root architecture can influence exudation in response to water and N limitations. Water stress (WS) decreased productivity, induced higher C and N allocation towards roots and a root architecture with steeper growth. WS increased the C cost of soil exploration and amino acid exudation. Nitrate shortage had milder effects than WS.

Conclusion

Our results suggest that plant adapt their root system to absorb water in deeper wet soil while optimizing its transport in older C-rich roots in response to water stress. These findings create the opportunity to explore trade-offs between water absorption, transport and exudation within the root system, using distinction between young and mature roots.