Species turnover (β‐diversity) in ectomycorrhizal fungi linked to uptake capacity

<jats:title>Abstract</jats:title><jats:p>Ectomycorrhizal (EcM) fungal communities may be shaped by both deterministic and stochastic processes, potentially influencing ecosystem development and function. We evaluated community assembly processes for EcM fungi of <jats:italic>Pseudotsuga menziesii</jats:italic> among 12 sites up to 400 km apart in southwest British Columbia (Canada) by investigating species turnover (β‐diversity) in relation to soil nitrogen (N) availability and physical distance. We then examined functional traits for an N‐related niche by quantifying net fluxes of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mec13435-math-0003.png" xlink:title="urn:x-wiley:09621083:media:mec13435:mec13435-math-0003" />, <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mec13435-math-0004.png" xlink:title="urn:x-wiley:09621083:media:mec13435:mec13435-math-0004" /> and protons on excised root tips from three contrasting sites using a microelectrode ion flux measurement system. EcM fungal communities were well aligned with soil N availability and <jats:styled-content style="fixed-case">pH</jats:styled-content>, with no effect of site proximity (distance–decay curve) on species assemblages. Species turnover was significant (β<jats:sub>1/2</jats:sub> = 1.48) along soil N gradients, with many more <jats:italic>Tomentella</jats:italic> species on high N than low N soils, in contrast to <jats:italic>Cortinarius</jats:italic> species. Ammonium uptake was greatest in the spring on the medium and rich sites and averaged over 190 nmol/m<jats:sup>2</jats:sup>/s for <jats:italic>Tomentella</jats:italic> species. The lowest uptake rates of <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mec13435-math-0005.png" xlink:title="urn:x-wiley:09621083:media:mec13435:mec13435-math-0005" /> were by nonmycorrhizal roots of axenically grown seedlings (10 nmol/m<jats:sup>2</jats:sup>/s), followed by <jats:italic>Cortinarius</jats:italic> species (60 nmol/m<jats:sup>2</jats:sup>/s). EcM roots from all sites displayed only marginal uptake of nitrate (8.3 nmol/m<jats:sup>2</jats:sup>/s). These results suggest <jats:inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="graphic/mec13435-math-0006.png" xlink:title="urn:x-wiley:09621083:media:mec13435:mec13435-math-0006" /> uptake capacity is an important functional trait influencing the assembly of EcM fungal communities. The diversity of EcM fungal species across the region arguably provides critical belowground adaptations to organic and inorganic N supply that are integral to temperate rainforest ecology.</jats:p>