Quantification of mycorrhizal water uptake via high-resolution on-line water content sensors

Abstract

The benefits of mycorrhizas for host plants are well known for a large number of species. However, experimental evaluations of the hyphal contribution to the total water uptake and the assessment of the bulk flow velocity in the hyphae are so far contradictory. Barley (Hordeum vulgaris L. Scarlet) with the inoculum Glomus intraradices was grown in a split plant-hyphal chamber with a 5 mm air gap. During the preparation of the chambers with a loamy-silt soil, water content sensors were inserted in each of the plant and the hyphal compartments. These sensors allow non-destructive measurements with high resolution. In total, 8 drying periods with a length of several days were applied with repeated watering following each drying period. A clear decline in water content in the hyphal compartment during each drying period supports the ability of hyphae to transfer water into the plant compartment. The difference between the decline in the hyphal compartment with and without arbuscular mycorrhyzal fungi is significant at the p < 0.000001 level. The direct and indirect hyphal contribution to the total water uptake was estimated to be about 20%. The application of capacitance sensors for water content determination with a special geometry adapted to the plant-hyphal chambers allows the evaluation of the hyphal water flow with high accuracy.