Roots to the rescue: how plants harness hydraulic redistribution to survive drought across contrasting soil textures.

Abstract

Hydraulic redistribution (HR) is a critical ecological process whereby plant roots transfer water from wetter to drier soil layers, significantly impacting soil moisture dynamics and plant water and nutrient uptake. Yet a comprehensive understanding of the mechanism triggering HR and its influencing factors remains elusive. Here, we conducted a systematic meta-analysis to discuss the influence of soil conditions and plant species characteristics on HR occurrence. The threshold of HR ranges from -1.80 to -0.05 MPa, with soil hydraulic conductivity between 1.51 × 10^-13 and 6.53 × 10^-5 cm s^-1 when HR occurs. HR is influenced by various factors. Soil texture plays a pivotal role, with loamy soils promoting HR more effectively than sandy and clay soils. Plant root structure and hydraulic conductivity significantly influence HR occurrence, where HR is more prevalent in deep-rooted tree species with larger root canal diameters and dimorphic roots. Additionally, mycorrhizal fungi enhance HR by expanding root uptake area, reducing water transport distances and improving soil structure. However, adverse soil conditions, inadequate plant physiological regulatory capacity, or methodological limitations can hinder HR detection. The findings highlight that HR is more likely to occur where there is a significant water potential gradient, appropriate root-soil contact, and low nocturnal transpiration. Plants can effectively replenish the water in dry root systems under drought conditions by HR by increasing the water potential of root systems to maintain normal physiological functions. Our study identifies key factors influencing HR, offering a comprehensive framework for future research aimed at improving plant drought resistance and refining ecohydrological models.