Interspecific temporal and spatial differences in the acquisition of litter‐derived nitrogen by ectomycorrhizal fungal assemblages

Abstract

Summary The spatiotemporal dynamics of, and interspecific differences in, the acquisition of litter‐derived nitrogen (N) by natural assemblages of ectomycorrhizal root tips are poorly understood. Small cylindrical mesh bags containing 15N‐labelled beech (Fagus sylvatica) leaf litter that permit hyphal but not root ingrowth were inserted vertically into the top soil layer of an old‐growth beech forest. The lateral transfer of 15N into the circumjacent soil, roots, microbes and ectomycorrhizas was measured during an 18‐month exposure period. Ectomycorrhial fungi (EMF) showed large interspecific variation in the temporal pattern and extent of 15N accumulation. Initially, when N was mainly available from the leachate, microbes were more efficient at N immobilization than the majority of EMF, but distinct fungal species also showed significant 15N accumulation. During later phases, the enrichment of 15N in Tomentella badia was higher than in microbes and other EMF species. Roots and soil accumulated 15N with a large delay compared with microbes and EMF. Because approximately half of the studied fungal species had direct access to N from leaf litter and the remainder to N from leached compounds, we suggest that EMF diversity facilitates the N utilization of the host by capturing N originating from early‐released solutes and late degradation products from a recalcitrant source.

Attributing functions to ectomycorrhizal fungal identities in assemblages for nitrogen acquisition under stress

“…However, EMF with emanating hyphae and known saprotrophic capacities, such as Cortinarius sp. and Tomentella viridis, ultimately accumulated more N from degrading leaf litter compared with EMF with short extraradical mycelium, indicating spatiotemporal differentiation for access to a complex organic N source (Pena et al, 2013a). In our study, the aforementioned species were also present but were rare, suggesting that beech trees may foster fungal species without immediate benefits because the supply with NH 4 þ does not require the degradation of organic matter.…”

“…In contrast, studies investigating the utilization of the same resource by distinct taxa in the same environment are scarce, but this information is important for our understanding of the functional redundancy of EMF as contributors to ecosystem resilience. For example, in a forest community, most ectomycorrhizas, regardless of the fungal species, showed early enrichment of litter-derived N, likely from released solutes (Pena et al, 2013a). However, EMF with emanating hyphae and known saprotrophic capacities, such as Cortinarius sp.…”

“…For anatomical analysis, the morphotypes were embedded in styrene-methacrylate (Ducic et al, 2008). Cross-sections with a thickness of 1 mm were cut with an autocut microtome (Ultracut E, Reichert-Jung, Vienna, Austria) and used to measure mantle thickness (Pena et al, 2013a).…”

“…Stable isotope studies have revealed that EMF species differ in their abilities to exploit different N sources (Hobbie and Hö gberg, 2012). Furthermore, in situ ectomycorrhizal communities exhibit strong temporal differences in the capability of different EMF taxa to access litter-derived N (Pena et al, 2013a). The experimental manipulation of EMF diversity has shown context-dependent effects for fungal mixtures on plant biomass production and N nutrition (Chu-Chou and Grace, 1985;Jonsson et al, 2001).…”

Ectomycorrhizal Communities on the Roots of Two Beech (Fagus sylvatica) Populations from Contrasting Climates Differ in Nitrogen Acquisition in a Common Environment

“…The control of N flux by EMF is complex because, on the one hand, a decreased host carbon supply results in decreased N delivery by EMF, whereas high N availability leads to enhanced C transfer to the EMF (8)(9)(10). On the other hand, EMF are instrumental to maintenance of the host N supply under drought stress and for access to organic N from leaf litter (11,12).…”