Agnostic fungi: plant functional types and tissue stoichiometry explain nutrient transfer in common arbuscular mycorrhizal networks of temperate grasslands

Abstract

SummaryPlants and mycorrhizal fungi form close mutualistic relationships that affect how resources flow between organisms and within ecosystems. Common mycorrhizal networks (CMNs) could facilitate preferential transfer of carbon and limiting nutrients but this preference remains difficult to predict. 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)? We used stable isotope tracers (13C and15N), plant traits, and fungal DNA, to quantify above- and belowground allocation and transfer of carbon and nitrogen between 18 plant species in restored prairie and introduced pasture systems in the Pacific Northwest, USA. We found that related plant species and connectivity with fungal communities did not predict resource flow. Instead, plant functional type and tissue stoichiometry were the most important predictors of interspecific resource transfer. Labeled “donor” plants assimilated isotopic tracers at similar rates; however, nitrogen was preferentially transferred to annual and forb “receiver” plants compared to perennial and grass receiver plants. This corresponded tissue stoichiometry differences. Our findings point to a simple mechanistic answer for long-standing questions regarding mutualism and transfer of resources between plants via mycorrhizal networks.