Mechanisms of facilitation of water transport in the rhizosphere

Biological activity in soil is very diverse and around plant roots it affects water transport. Root growth displaces soil particles and alters soil porosity, by creating biopores that conduct water. The secretions of plants and microbes modify surface tension, viscosity, absorption and retention of water. Microbial motility may also contribute to water transport, but such effects have not been demonstrated in soil to date. To elucidate how these factors influence root water uptake, we combined dye tracing experiments [1,2], live microscopy and physical characterization of root exudates of winter wheat, along with analyses of cell suspensions and secretions of the bacterium Bacillus subtilis. Using this dataset, we coupled a modified Richards’ equation [3] with the model of Šimůnek and Hopmans [4] to investigate how the combined effects of these processes influence water availability to crops over a complete wet–dry–wet cycle. Results showed that both microbes and plants’ secretions act as facilitators of water infiltration of dry and mildly repellent soil layers. In arid environments, under light and sporadic rainfall events, this effect tends to benefit more deeper-rooted or mature crops. Results also show that microbial motility alone may be inducing an active stress of few Pascals which also contributes to enhance water infiltration. These results have important implications for the management of irrigation in cropping systems. References[1] Liu et al 2025, Biosystems Engineering, https://doi.org/10.1016/j.biosystemseng.2025.02.006[2] Gómez et al 2025, Plant Cell Environment, https://doi.org/10.1111/pce.70240[3] Mair et al 2025, Vadose Zone Journal, https://doi.org/10.1101/2025.03.28.645940[4] Šimůnek and Hopmans 2009, Ecological Modelling, 220(4), 505–521