Species-specific roles of ectomycorrhizal fungi in facilitating interplant transfer of hydraulically redistributed water between Pinus halepensis saplings and seedlings

Abstract

Background and aims: Interplant transfer of hydraulically redistributed water (HRW) can take place via mycorrhizal hyphal networks linking the roots of neighboring plants. We conducted a mesocosm experiment to evaluate the influence of reduced extraradical hyphal lengths on interplant HRW transfer. Methods: Ectomycorrhizal Pinus halepensis saplings and seedlings were grown together in two-compartment mesocosms (fungicide-treated or control), and deuterium-labeled water was supplied to the taproot compartment (accessible to sapling taproots) during a 9-day soil drying cycle. Results: Upper soil water contents and seedling water potentials at the end of the drying cycle were lower in fungicide-treated than in control mesocosms. The stem water δD values of seedlings increased (marginally) with increasing soil hyphal length in both treatments separately, suggesting that interplant HRW transfer was at least partly mediated by fungal hyphae. In fungicide-treated mesocosms, the difference in δD values between the stem water of seedlings and upper soil water decreased sharply with increasing soil hyphal length, supporting a key role of ectomycorrhizal fungi (EMF) in interplant HRW transfer at low soil hyphal densities. However, two dominant EMF morphotypes differing in their water repellence properties and hyphal exploration types (Thelephora terrestris and Suillus granulatus) had contrasting impacts on hydraulic redistribution patterns, as only the EMF producing hydrophilic hyphae (T. terrestris) enhanced HRW transfer between pine saplings and seedlings. Conclusions: Changes in the abundance and/or composition of EMF communities in response to anthropogenic disturbance or climate change could affect facilitative plant interactions through alterations of interplant HRW transfer.