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

Abstract

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 Pseudotsuga menziesii 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 NH4+, NO3- 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 pH, with no effect of site proximity (distance-decay curve) on species assemblages. Species turnover was significant (β(1/2) = 1.48) along soil N gradients, with many more Tomentella species on high N than low N soils, in contrast to Cortinarius species. Ammonium uptake was greatest in the spring on the medium and rich sites and averaged over 190 nmol/m(2)/s for Tomentella species. The lowest uptake rates of NH4+ were by nonmycorrhizal roots of axenically grown seedlings (10 nmol/m(2)/s), followed by Cortinarius species (60 nmol/m(2)/s). EcM roots from all sites displayed only marginal uptake of nitrate (8.3 nmol/m(2)/s). These results suggest NH4+ 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.

Saprotrophic and ectomycorrhizal fungal sporocarp stoichiometry (C : N : P) across temperate rainforests as evidence of shared nutrient constraints among symbionts

“…Kranabetter et al . () demonstrated this adaptation to site in the enhanced uptake capacity of NH 4 + among EMF species dominating similarly rich coastal ecosystems. An ability to scale up N acquisition with soil N availability likely reflects an appreciable level of competition for N between guilds across a full gradient in soil fertility, which could be of interest in models of soil C storage (Orwin et al ., ; Bödeker et al ., ; Philpott et al ., ) and consumer‐driven nutrient recycling (Zechmeister‐Boltenstern et al ., ).…”

Assembly processes of trophic guilds in the root mycobiome of temperate forests

“…This finding is also in agreement with previous studies that showed that mycorrhizal mycobiomes consist of active symbionts and a cryptic “reserve,” whose members are recruited during temporal turnover of the assemblages (Danielsen et al., , ). This cryptic reserve is probably important for adjusting the functions of the mycorrhizal assemblage under changing environmental conditions, such as drought and soil nitrogen (Courty, Franc, Pierrat, & Garbaye, ; Gallart et al., ; Kranabetter, Durall, & MacKenzie, ; Kranabetter et al., ; Leberecht, Tu, & Polle, ; Pena & Polle, ; Pena, Simon, Rennenberg, & Polle, ). Consequently, many of the potentially symbiotrophic taxa that were detected in RAMs might exist as saprotrophs (Martin, Kohler, Murat, Veneault‐Fourrey, & Hibbett, ) and thus share a habitat with other nonsymbiotic saprotrophic microbes.…”

Quantifying inorganic nitrogen uptake capacity among ectomycorrhizal fungal species using MIFE microelectrode ion flux measurements: theory and applications

“…While ammonium is generally recognized as the most readily utilized source of inorganic N by the majority of ECM fungi (Rygiewicz et al 1984, we hypothesized that sites with inherently high nitrate production would be colonized by ECM species endowed with significant capacity for nitrate uptake. However, when net fluxes of ammonium and nitrate were measured simultaneously on Douglas-fir ECM species, all native fungi tested took up ammonium at higher rates than nitrate, regardless of site N availability (Kranabetter et al 2015). In a continuation of this work on additional sites on the west coast of British Columbia, we tested nitrate uptake from forest stand on a very rich fluvial bench with high rates of insitu production of inorganic N, particularly nitrate (Ubhi 2017 (Wang andQiu 2006, Öpik et al 2014).…”

“…Ectomycorrhizal fungi associated with Douglas-fir roots had average rates of ammonium uptake of 103 nmol m 2 s -1 (ranging from 59.7 nmol m s 1 for Cortinarius hemitrichus to 351 nmol m 2 s 1 for Lactarius hepaticus) (Kranabetter et al 2015). In contrast, the average rate of ammonium uptake for nonmycorrhizal white root tips from some of the same root systems was only 5.8 nmol m 2 s 1 (unpublished data).…”

“…Spring uptake of ammonium by ECM roots of Douglas-fir was greatest on a medium and rich site, compared to a poor site, and averaged over 190 nmol m -2 s -1 for Tomentella species, a ECM group common on high N soils (Kranabetter et al 2015). The lowest uptake rates of ammonium by ECM Douglas-fir roots were by Cortinarius species (60 nmol m -2 s -1 ), a group common to low N soils (Kranabetter et al 2015). Likewise, many Cortinarius species demonstrate significant extracellular enzyme production for the uptake of organic N, particularly under conditions of low N availability .…”