Post-fire seedlings of Nothofagus alpina in Southern Chile show strong dominance of a single ectomycorrhizal fungus and a vertical shift in root architecture

Abstract

We investigated belowground responses of Nothofagus alpina seedlings to post-fire conditions during natural regeneration after a wildfire in Chile, focusing on mycorrhizal community and root architecture. The complete root systems of 2-year-old N. alpina seedlings were extracted from a post-fire site with natural regeneration and compared to roots of seedlings from undisturbed forest nearby. Mycorrhizal morphotype richness was determined in each seedling. Morphometric parameters of tertiary root structure and dry biomass of whole root systems were determined in 5 cm vertical intervals and in four lateral root classes. With 43.5% of colonized vital mycorrhizal root tips, the Basidiomycete Descolea antarctica was the most abundant fungal symbiont on post-fire seedlings. Tertiary root morphology of these seedlings was distinct from control plants and characterized by a deep-reaching tap root with rather evenly distributed lateral branches whereas seedlings from the undisturbed site had shallower root systems with most lateral roots concentrated in the upper soil layers. Post-fire seedlings had more mycorrhizal rootlets and mycorrhiza-bearing third order lateral roots than control plants which was expressed in a 34% higher total root number but only a 10% higher total root biomass, although both values were not statistically significant. A major part of these fine roots in seedlings from burnt forest was found in deeper soil horizons, compared to the seedlings from undisturbed forest. According to our results, post-fire conditions clearly favour Descolea antarctica as an early ectomycorrhizal colonizer of Nothofagus seedlings at the studied site. As no significant changes in soil chemistry could be observed at the burnt site, the deep-reaching tertiary root architecture of these seedlings may be interpreted as a response to other abiotic factors like reduced moisture in surface soil.

The effects of fire severity on ectomycorrhizal colonization and morphometric features in Pinus pinaster Ait. seedlings

“…For example, seedling root distribution and length varies according to soil depth (Wallander et al, 2004), in this sense postfire seedlings tend to extend their root system vertically as seen in our results by increasing mainly taproot length therefore also changing the distribution and structure of the lateral roots (Palfner et al, 2008). Also the mycelium of ECM fungi which is usually most abundant in the superficial organic soil layers in undisturbed ecosystems (Visser, 1995, Neville et al, 2002, Wallander et al, 2004 may influence root morphology and architecture through the formation of short lateral roots and root tips (Ostonen et al, 2009, Kubisch et al, 2015, therefore affecting seedling growth (Jones et al, 2003).…”

“…Shoot and root dry biomass were determined after drying the plant material at 70ºC for 48 h. in a drying oven (Sousa et al, 2011). Root/shoot ratio was derived from these measurements (Palfner et al, 2008).…”

“…Tap root length and shoot length were measured with a ruler to the nearest millimeter (Palfner et al, 2008). The root 5 Fire effects on mycorrhization and plant parameters…”

Early successional ectomycorrhizal fungi are more likely to naturalize outside their native range than other ectomycorrhizal fungi

“…Similarly, species from the Southern Hemisphere /descolea lineage are also known as common fungal symbionts on postfire sites (Palfner et al, 2008) or on EcM plant seedlings (Kuhar et al, 2017). Also other more likely co-introduced species from / laccaria lineage often occur on early successional sites (Table S2) and they are widespread in nurseries and fruit commonly on disturbed ground (Danielson, 1984).…”

Variación en el contenido de glomalina relacionada a las proteínas del suelo, después de un incendio forestal en un Andisol en bosques de Araucaria araucana del centro-sur de Chile

“…En relación a la densidad y distribución vertical de raí-ces, en plántulas de Nothofagus alpina asociada a ectomicorrizas en áreas quemadas y no quemadas en el mismo sector (Palfner et al 2008), se observó que plántulas germinadas en suelo quemado presentaron una mayor presencia de raíces principales y muy baja o nula formación de raíces secundarias, en comparación a plántulas germinadas en un área no afectada por el fuego, principalmente en los primeros 10 cm de profundidad. Esta adaptación morfológica de las plántulas del área quemada podría estar asociada, a algunos factores abióticos como la baja disponibilidad de agua producto de un aumento en la hidrofobicidad, cambios en las propiedades físico-químico de la materia orgá-nica del suelo y otros efectos importantes del fuego sobre el suelo.…”