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Contributed Talk

Session: : Biogeochemistry: Aboveground-Belowground Interactions 2

COS 275-3 - Agnostic fungi: herbaceous plant traits explain nitrogen transfer in common arbuscular mycorrhizal networks of Pacific Northwest grasslands

Thursday, August 10, 2023
2:00 PM – 2:15 PM PDT
Location: B115
Abstract: Plants and mycorrhizal fungi form close mutualistic relationships that affect the structure and function of ecosystems. Common mycorrhizal networks (many plants associated with the same fungus) can facilitate preferential transfer of carbon and limiting nutrients. However, the mechanisms behind these networks remain poorly understood. Do common mycorrhizal networks favor fungal growth at the expense of plant resource demands (a fungi-centric view), or are they passive channels through which plants regulate resource fluxes (a plant-centric view)? In an experimental restored prairie and pasture plant systems, replicated at three sites across a 520 km latitudinal gradient in the Pacific Northwest, USA, we used stable isotope tracers, paired with analyses of fungal DNA and plant and fungal community structure and traits, to quantify above- and belowground allocation and transfer of carbon and nitrogen between 18 different plant species. We applied isotopically enriched carbon (13C) and nitrogen (15N) as a pulse of carbon dioxide (CO2) and ammonia (NH3) to the leaves of target “donor” species common across experimental sites. We measured isotopic enrichment of >1,800 leaves and roots, and we found morphological plant traits and tissue stoichiometry were the most important predictors of interspecific resource transfer. Labeled "donor" plants assimilated isotopic tracers at similar highly enriched rates. However, annual receiver plants had four times more enrichment than perennials three weeks post transfer (0.108 ± 0.192 mean percent leaf nitrogen derived from label [% NDFL ± SD] compared to 0.025 ± 0.033 % NDFL). This difference appears to be driven by differences in tissue stoichiometry and structural traits associated with life form and growth strategy, where annuals had a higher carbon-to-nitrogen ratio (50.8 ± 33.9 mean C:N) driven by lower nitrogen content compared to perennials (30.2 ± 15.0 mean C:N). Our findings point to a simple mechanistic answer for long-standing questions regarding mutualism and transfer of resources between plants via mycorrhizal networks.