Above‐ and belowground interplay: Canopy CO<sub>2</sub> uptake, carbon and nitrogen allocation and isotope fractionation along the plant‐ectomycorrhiza continuum
Andrea Scartazza, Cristiana Sbrana, Ettore D’Andrea, Gioṙgio Matteucci, Negar Rezaie, Marco Lauteri
Abstract
Abstract In forests, mycorrhizal fungi regulate carbon (C) and nitrogen (N) dynamics. We evaluated the interplay among ectomycorrhizas (ECM), ecosystem C fluxes, tree productivity, C and N exchange and isotopic fractionation along the soil‐ECM‐plant continuum in a Mediterranean beech forest. From bud break to leaf shedding, we monitored: net ecosystem exchange (NEE, a measure of the net exchange of C between an ecosystem and the atmosphere), leaf area index, stem growth, N concentration, δ 13 C and δ 15 N in rhizosphere soil, ectomycorrhizal fine root tips (ERT), ECM‐free fine root portions (NCR) and leaves. Seasonal changes in ERT relative biomass were strictly related to NEE and mimicked those detected in the radial growth. The analysis of δ 13 C in ERT, leaves and NCR highlighted the impact of canopy photosynthesis on ERT development and an asynchronous seasonal C allocation strategy between ERT and NCR at the root tips level. Concerning N, δ 15 N of leaves was negatively related to that of ERT and dependent on seasonal 15 N differences between ERT and NCR. Our results unravel a synchronous C allocation towards ERT and tree stem driven by the increasing NEE in spring‐early summer. Moreover, they highlighted a phenology‐dependent 15 N fractionation during N transfer from ECM to their hosts. This evidence, obtained in mature beech trees under natural conditions, may improve the knowledge of Mediterranean forests functionality.