Access to mycorrhizal networks and roots of trees: importance for seedling survival and resource transfer

Abstract

Mycorrhizal networks (MNs) are fungal hyphae that connect roots of at least two plants. It has been suggested that these networks are ecologically relevant because they may facilitate interplant resource transfer and improve regeneration dynamics. This study investigated the effects of MNs on seedling survival, growth and physiological responses, interplant resource (carbon and nitrogen) transfer, and ectomycorrhizal (EM) fungal colonization of seedlings by trees in dry interior Douglas-fir (Pseudotsuga menziesii var. glauca) forests. On a large, recently harvested site that retained some older trees, we established 160 isolated plots containing pairs of older Douglas-fir "donor" trees and either manually sown seed or planted Douglas-fir "receiver" seedlings. Seed- and greenhouse-grown seedlings were sown and planted into four mesh treatments that served to restrict MN access (i.e., planted into mesh bags with 0.5-, 35-, 250-microm pores, or without mesh). Older trees were pulse labeled with carbon (13CO2) and nitrogen (15NH4(15)NO3) to quantify resource transfer. After two years, seedlings grown from seed in the field had the greatest survival and received the greatest amounts of transferred carbon (0.0063% of donor photo-assimilates) and nitrogen (0.0018%) where they were grown without mesh; however, planted seedlings were not affected by access to tree roots and hyphae. Size of "donor" trees was inversely related to the amount of carbon transferred to seedlings. The potential for MNs to form was high (based on high similarity of EM communities between hosts), and MN-mediated colonization appeared only to be important for seedlings grown from seed in the field. These results demonstrate that MNs and mycorrhizal roots of trees may be ecologically important for natural regeneration in dry forests, but it is still uncertain whether resource transfer is an important mechanism underlying seedling establishment.

Advances in restoration ecology: rising to the challenges of the coming decades

“…Insights from agriculture have long suggested the use of facilitative legumes to ameliorate soil conditions (Bradshaw 1983, Wong 2003. More recent studies have shown mycorrhizal inoculation improves plant survival and growth (e.g., Requena et al 2001, Pineiro et al 2013 although in some systems it may be the presence of a mycorrhizal network (Simard and Durall 2004, Teste et al 2009, Booth and Hoeksema 2010, as opposed to the presence of certain mycorrhizas alone, that facilitates successful restoration.…”

Variation in ectomycorrhizal fungal communities associated with Oreomunnea mexicana (Juglandaceae) in a Neotropical montane forest

“…Ectomycorrhizal networks may increase survival of conspecific seedlings in a spatially structured fashion, disproportionately increasing their abundance near adult trees (Onguene and Kuyper 2002;Henkel 2003;McGuire 2007;Teste et al 2009;Booth and Hoeksema 2010) in a manner consistent with positive plant-soil feedbacks (reviewed by Bever et al 2012). In turn, the presence and strength of plant-soil feedback depends on the functional traits and taxonomic composition of the EM fungal community (e.g., Dickie et al 2002;O'Brien et al 2010;Kennedy et al 2012).…”

Facilitation between woody and herbaceous plants that associate with arbuscular mycorrhizal fungi in temperate European forests

“…The respective (quartile) figures for herbaceous plants were 3%–7% (ECM) and 40%–49% (AM). The mycorrhizal mediation hypothesis has been tested several times with a focus on ECM plants and in most cases the data supported the hypothesis (e.g., Dickie, Guza, Krazewski, & Reich, 2004; Richard, Selosse, & Gardes, 2009; Teste et al., 2009; Moeller, Dickie, Peltzer, & Fukami, 2015) which appears to be due to ECM propagule limitation (Dickie et al., 2004; Dickie, Davis, & Carswell, 2012) . Despite our awareness that AM propagules decline in the forest compared to herbaceous systems (Fisher & Fulé, 2004), we know much less about the possibility that mycorrhizal mediation exists in temperate forests with regard to AM fungi.…”