Depth distribution of soil water sourced by plants at the global scale: A new direct inference approach

Summary

This global meta-analysis synthesised stable isotope data from 65 studies to determine the depth distribution of soil water contributions to plant water uptake across climate zones. Using a novel direct inference method based on isotopic overlap, the authors found that plants in cold and temperate regions predominantly extract water from shallow soil layers (<30 cm), whereas plants in arid and tropical zones access deeper soil water (>30 cm). The findings suggest climate and plant physiology interact to determine rooting strategies and water source utilisation.

Regional applicability

The study's global scope encompasses temperate zones (including United Kingdom conditions), where shallow soil water (<30 cm) was identified as the dominant source for plant water uptake. The methodology and findings on temperate-zone water sourcing are directly applicable to UK agricultural and ecological contexts, though site-specific validation with UK-derived isotope data would strengthen local applicability.

Key measures

Stable isotope signatures (δ2H and δ18O) in xylem water and soil water at multiple depths; median overlap percentages between xylem water and soil water at different soil depths; climate zone classification (cold, temperate, arid, tropical)

Outcomes reported

The study quantified the depth distribution of soil water sources used by plants across different climate zones globally using stable isotope analysis (δ2H and δ18O) from 65 peer-reviewed studies. It found that median xylem-soil water overlap varied between 28% and 100% depending on depth and climate, with shallow water (0–10 cm) dominant in cold/temperate zones and deeper layers exploited in arid/tropical zones.

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