Taking mycocentrism seriously: mycorrhizal fungal and plant responses to elevated CO₂

Abstract

Summary• The aim here was to separately assess mycorrhizal fungal and plant responses under elevated atmospheric CO 2 , and to test a mycocentric model that assumes that increased carbon availability to the fungus will not automatically feed back to enhanced plant growth performance.• Meta-analyses were applied across independent studies. Responses were compared in ectomycorrhizal (ECM) and arbuscular mycorrhizal (AM) fungi, and ECM and AM plants.• Responses of both mycorrhizal fungi and mycorrhizal plants to elevated CO 2 were significantly positive. The response ratio for ECM fungi was 1.34 (an increase of 34%) and for AM fungi 1.21 (21%), indicating a significantly different response. The response ratio for ECM plants was 1.26, similar to that of AM plants (1.25). Fractional colonization proved to be an unsuitable fungal parameter. Evidence was found for the mycocentric view in ECM, but not in AM systems.• Fungal identity and plant identity were important parameters that affected response ratios. The need for better descriptors of fungal and plant responses is emphasized.

Specific root length as an indicator of environmental change

“…The trees with the finest roots 50.5 mm in diameter had performed also increased ectomycorrhizal abundance ) that might influence root architecture. In numerous experiments, CO 2 enrichment elicited an increase in the degree of ectomycorrhizal colonization as well as changes in the morphotype assemblages (Godbold & Berntson, 1997;Treseder, 2004;Alberton et al, 2005). Increased root length and thickening of diameter (Janssens et al, 1998, Pritchard et al, 2001) along with enhanced storage of starch in fine roots (Janssens et al, 1998) has been observed under CO 2 enrichment.…”

Influence of arbuscular mycorrhizal colonization on whole‐plant respiration and thermal acclimation of tropical tree seedlings

“…2003) and roots and associated symbionts can respond differently to environmental change (Alberton et al. 2005; Vega‐Frutis et al. 2014).…”

Arbuscular mycorrhizal mycelial respiration in a moist tropical forest

“…Mycorrhizal fungi have a physiology and chemistry very different to those of plant roots (Smith & Read, 1997) and therefore may respond independently to changes in climate and plant production. A meta-analysis of laboratory and field CO 2 enrichment studies using temperate plants has shown that plants consistently allocate more C to mycorrhizal fungi under elevated CO 2 and nutrient-limiting conditions (Alberton et al, 2005). Therefore, in a world with elevated concentrations of atmospheric CO 2 , there may be significant increases in the allocation of C to AMF in tropical forests, which generally grow on nutrient-poor soils (Vitousek & Sanford, 1986), and which already appear to be increasing in productivity, probably in response to raised concentrations of atmospheric CO 2 (Phillips et al, 2008).…”

“…Soil CO 2 efflux arises from the activity of a wide variety of belowground organisms, but only two sources have been assessed in tropical forests: (1) 'autotrophic respiration', derived from roots, arbuscular mycorrhizal fungi (AMF) and the metabolism of root exudates by microorganisms inhabiting the rhizosphere, and (2) 'heterotrophic respiration', derived from microbial decomposition of plant detritus and soil organic matter (Hanson et al, 2000). Respiration from roots and that from AMF are almost always assessed together as a single source of respiration (Hanson et al, 2000;Subke et al, 2006), yet their assessment as distinct sources is required given that they may respond somewhat independently to environmental change (Alberton et al, 2005).…”