Mycorrhizal colonization mediated by species interactions in arctic tundra

Abstract

The Alaskan tussock tundra is a strongly nutrient-limited ecosystem, where almost all vascular plant species are mycorrhizal. We established a long-term removal experiment to document effects of arctic plant species on ecto- and ericoid mycorrhizal fungi and to investigate whether species interactions and/or nutrient availability affect mycorrhizal colonization. The treatments applied were removal of Betula nana ( Betulaceae, dominant deciduous shrub species), removal of Ledum palustre ( Ericaceae, dominant evergreen shrub species), control (no removal), and each of these three treatments with the addition of fertilizer. After 3 years of Ledum removal and fertilization, we found that overall ectomycorrhizal colonization in Betula was significantly reduced. Changes in ectomycorrhizal morphotype composition in removal and fertilized treatments were also observed. These results suggest that the effect of Ledum on Betula's mycorrhizal roots is due to sequestration of nutrients by Ledum, leading to reduced nutrient availability in the soil. In contrast, ericoid mycorrhizal colonization was not affected by fertilization, but the removal of Betula and to a lower degree of Ledum resulted in a reduction of ericoid mycorrhizal colonization suggesting a direct effect of these species on ericoid mycorrhizal colonization. Nutrient availability was only higher in fertilized treatments, but caution should be taken with the interpretation of these data as soil microbes may effectively compete with the ion exchange resins for the nutrients released by plant removal in these nutrient-limited soils.

Two Decades of Experimental Manipulations of Heaths and Forest Understory in the Subarctic

“…Responses to environmental changes in these microbial groups are important, because mycorrhizal fungi supply the host plants with nutrients from the soil in exchange for labile C from the plant, and because fungal composition and diversity influences plant productivity, stability and diversity. In the Subarctic and Low Arctic, most studies of fungal responses to warming and nutrient addition or plant species interactions (Urcelay et al 2003) have focused on ectomycorrhizal fungi, because many of these fungi easily can be distinguished morphologically and because they colonize roots of widespread arctic shrubs species as dwarf birch (Betula nana) and willows (Salix spp). For instance, the ectomycorrhizal community on roots of the prostrate willow (Salix herbacea x polaris) at an arctic-alpine fellfield consists of at least seven fungal species, of which some may also be found in boreal forests.…”

The effect of experimental warming on the root-associated fungal community of Salix arctica

“…Increased soil temperature can influence root growth, phenology and architecture, respiration and ion uptake, water and nutrient availability , but the impacts on soil microbial communities is varied and often unpredictable (Zak et al, 2000). Responses of mycorrhizal fungi to simulated global change factors (CO 2 , warming, shading and fertilization) are also variable, although several studies have found a not unexpected link between increased plant C allocation belowground and increased mycorrhizal colonization (Staddon et al, 2002;Urcelay et al, 2003;Fitter et al, 2004;Heinemeyer and Fitter, 2004;Olsrud et al, 2004;. Some studies have found that experimental treatments alter mycorrhizal community composition (Rygiewicz et al, 2000;Parrent et al, 2006), but these changes are rarely of sufficient magnitude to significantly change the overall richness or diversity of the community.…”

Requerimientos germinativos de enredaderas características del Chaco Serrano de Córdoba, Argentina

“…Los resultados correspondientes a los ensayos de germinación, para el total de especies típicas de cada fisonomía, se analizaron mediante Análisis de la varianza (Anova) con rangos (no paramétrico), puesto que la variable porcentaje de germinación, en cada situación experimental, no cumplió con los supuestos de normalidad ni homogeneidad de varianzas (Conover & Iman 1981, Hora & Conover 1984, Zar 1999, Urcelay et al 2003, aun cuando los porcentajes fueron transformados en √arco-seno. Este Anova con rangos fue tri-factorial, considerando a la fisonomía, la temperatura y la luz/oscuridad como los tres factores principales.…”

“…Se aplicó un LDS de Fischer como test a posteriori. La interpretación de los resultados que arroja este tipo de análisis, se realiza de la misma manera que para un Anova paramétrico (Zar 1999, Urcelay et al 2003.…”