Fungal Community Responses to Past and Future Atmospheric CO ₂ Differ by Soil Type

Abstract

Soils sequester and release substantial atmospheric carbon, but the contribution of fungal communities to soil carbon balance under rising CO 2 is not well understood. Soil properties likely mediate these fungal responses but are rarely explored in CO 2 experiments. We studied soil fungal communities in a grassland ecosystem exposed to a preindustrial-to-future CO 2 gradient (250 to 500 ppm) in a black clay soil and a sandy loam soil. Sanger sequencing and pyrosequencing of the rRNA gene cluster revealed that fungal community composition and its response to CO 2 differed significantly between soils. Fungal species richness and relative abundance of Chytridiomycota (chytrids) increased linearly with CO 2 in the black clay (P < 0.04, R 2 > 0.7), whereas the relative abundance of Glomeromycota (arbuscular mycorrhizal fungi) increased linearly with elevated CO 2 in the sandy loam (P ‫؍‬ 0.02, R 2 ‫؍‬ 0.63). Across both soils, decomposition rate was positively correlated with chytrid relative abundance (r ‫؍‬ 0.57) and, in the black clay soil, fungal species richness. Decomposition rate was more strongly correlated with microbial biomass (r ‫؍‬ 0.88) than with fungal variables. Increased labile carbon availability with elevated CO 2 may explain the greater fungal species richness and Chytridiomycota abundance in the black clay soil, whereas increased phosphorus limitation may explain the increase in Glomeromycota at elevated CO 2 in the sandy loam. Our results demonstrate that soil type plays a key role in soil fungal responses to rising atmospheric CO 2 .

Host plant physiology and mycorrhizal functioning shift across a glacial through future CO2 gradient

“…Plant growth responses to AM fungi increased with rising [CO 2 ], supporting our original hypothesis that these associations will become more beneficial due to reduced plant carbohydrate limitations and increased plant nutrient limitations with rising [CO 2 ] (Johnson, 2010;Mohan et al, 2014 (Treseder et al, 2003;Procter et al, 2014). Unlike what we saw for T. officinale, T. ceratophorum responded positively to AM fungi even at low [CO 2 ].…”

“…Temporal changes in [CO 2 ] since the LGM have likely influenced the functioning of mycorrhizal associations along a continuum from mutualism to parasitism, hereafter referred to as the M-P continuum (Johnson et al, 1997), by altering plant carbohydrate production and nutrient demand. Previous mycorrhizal-CO 2 studies have focused mainly on the effects of modern versus future conditions (Alberton et al, 2005;Mohan et al, 2014), and little is known about mycorrhizal responses to low [CO 2 ] of the past (Treseder et al, 2003;Procter et al, 2014). Assessing mycorrhizal responses to a broad, temporal [CO 2 ] gradient is critical to establish a baseline for how these symbioses functioned prior to anthropogenic forcing, which will provide insight into potential constraints on mycorrhizal responses to future conditions (Ogle et al, 2015).…”

“…One possibility is that AM fungi reduce plant growth at low [CO 2 ] because these symbionts are a major sink for carbohydrates that are expensive to produce when CO 2 is limiting (Gerhart and Ward, 2010;Gerhart et al, 2012). Studies that show reduced AM fungal abundance in soils exposed to preindustrial [CO 2 ] provide tentative support for this hypothesis (Treseder et al, 2003;Procter et al, 2014). Alternatively, some plants may partially compensate for low [CO 2 ] by increasing their investment in the photosynthetic machinery, including the enzyme Rubisco (Sage and Coleman, 2001;Becklin et al, 2014).…”

Relationships between soil fungal and woody plant assemblages differ between ridge and valley habitats in a subtropical mountain forest

“…However, recent studies have detected significant changes in soil fungal communities across substantially larger altitudinal gradients in natural ecosystems in Argentina (400-3000 m asl; Geml et al, 2014), Switzerland (400-3200 m asl; Pellissier et al, 2014) and China (530-2200 m asl; Shen et al, 2014). This is not surprising as large altitudinal gradients are tightly correlated with dramatic changes in climate, soil and vegetation types, resulting in shifts in soil fungal communities (Procter et al, 2014;Tedersoo et al, 2014).…”

“…In contrast, according to plant-soil feedback theory soil fungi may influence plant communities through increasing soil nutrient availability and/or mediating plant coexistence (e.g. van der Putten et al, 2013;Bever et al, 2015;Bennett & Cahill, 2016). For example, mycorrhizal fungi affect plant communities through formation of underground common mycorrhizal networks that redistribute nutrients among plants (e.g.…”