Coline Deveautour, Jeff R Powell , Margaret M Barbour, Kirk Barnett, Yolima Carrillo

Aims: Soil water availability depends on the capacity of soil pores to hold it via physical forces creating gradient of availability from tightly bound water to highly mobile water. Abiotic factors directly affect the size of these pools and plant access to them. Biotic factors influence plant-soil-water relations and possibly affect soil properties and plant access to different water pools. Thus, our aim was to contrast and assess the effect of biotic and abiotic soil environment on the plant uptake of water from the mobile and bound pool.
Methods: Here, we used an 18O-enriched water approach to trace movement of water from bound and mobile pools into plants with experimentally manipulated soil biotic compositions and soil texture. Comparisons of responses between treatments with intact soil communities and those excluding larger organisms such as mycorrhizal fungi and microfauna allowed us to estimate the extent these organisms influence plant access to water pools. We assessed these responses in an unmodified soil as well as after dilution of soil with sand, to evaluate whether soil texture might influence biotic effects.
Results: We found that removing larger organisms reduced plant access to bound water by 14 % and decreased exchange of water between the bound and mobile pools from 64 % to 41 % in the soil mixed with sand but not in the unmodified soil.
Conclusions: This novel contribution demonstrates that soil biota can influence plant-soil-water relations and we propose further work to identify the specific soil biota and biophysical mechanisms involved.