Relationships Among Fires, Fungi, and Soil Dynamics in Alaskan Boreal Forests

Abstract

Abstract. Fires are critical pathways of carbon loss from boreal forest soils, whereas microbial communities form equally critical controls over carbon accumulation between fires. We used a chronosequence in Alaska to test Read's hypothesis that arbuscular mycorrhizal fungi should dominate ecosystems with low accumulation of surface litter, and ectomycorrhizal fungi should proliferate where organic horizons are well-developed. This pattern is expected because ectomycorrhizal fungi display a greater capacity to mineralize organic compounds than do arbuscular mycorrhizal fungi. The sites were located in upland forests near Delta Junction, Alaska, and represent stages at 3, 15, 45, and 80 years following fire. Soil organic matter accumulated 2.8-fold over time. Fire did not noticeably reduce the abundance of arbuscular mycorrhizal fungi. In contrast, ectomycorrhizal colonization required up to 15 years to return to pre-fire levels. As a result, dominant mycorrhizal groups shifted from arbuscular to ectomycorrhizal fungi as succession progressed. Bacterial functional diversity was greatest in the oldest sites. Altogether, microbes that can mineralize organic compounds (i.e., ectomycorrhizae and bacteria) recovered more slowly than those that cannot (i.e., arbuscular mycorrhizae). Potential net N mineralization and standing pools of ammonium-N were relatively low in the youngest site. In addition, glomalin stocks were positively correlated with arbuscular mycorrhizal hyphal length, peaking early in the chronosequence. Our results indicate that microbial succession may influence soil carbon and nitrogen dynamics in the first several years following fire, by augmenting carbon storage in glomalin while inhibiting mineralization of organic compounds.

Effects of site preparation treatments before afforestation on soil carbon release

“…Second, compared to brush clearing, controlled burning may change the soil microclimate. Treseder et al (2004) found that after burning T S changes temporarily because of the disappearing of the litter mantle and the darkening of ground. In addition, burning can yield hydrophobic hydrocarbons that, together with the layer of ashes, could limit the soil's water infiltration capacity and hence its moisture content (Neary et al, 1999).…”

Nitrogen fertilization reduces diversity and alters community structure of active fungi in boreal ecosystems

“…We collected samples from two sites in east-central Alaska, USA (63155 0 N, 145144 0 W) described in detail by Treseder et al (2004). The first site is a boreal spruce forest that burned in 1999 and is now dominated by shrubs, herbaceous perennials, and small deciduous trees.…”

Ectomycorrhizal fungal spore bank recovery after a severe forest fire: some like it hot

“…Although there is a growing literature on fungal response to wildfire (Dahlberg et al, 2001;Treseder et al, 2004), only one previous set of studies exists in which pre-fire data were available for a wildfire event (Horton et al, 1998;Baar et al, 1999;Grogan et al, 2000), and this was less than a decade after the first application of PCR to the study of fungi (White et al, 1990). All other studies of post-fire ECM fungal recovery have primarily used space-for-time comparison where different aged fires were studied (Buscardo et al, 2010;Kipfer et al, 2011), laboratory heating experiments (Izzo et al, 2006;Peay et al, 2009;Kipfer et al, 2010) or low-intensity prescribed fires where host death was not involved (Stendell et al, 1999;Brown et al, 2013).…”