Impacts of long‐term elevated atmospheric CO₂ concentrations on communities of arbuscular mycorrhizal fungi

Abstract

The ecological impacts of long‐term elevated atmospheric CO2 (eCO2) levels on soil microbiota remain largely unknown. This is particularly true for the arbuscular mycorrhizal (AM) fungi, which form mutualistic associations with over two‐thirds of terrestrial plant species and are entirely dependent on their plant hosts for carbon. Here, we use high‐resolution amplicon sequencing (Illumina, HiSeq) to quantify the response of AM fungal communities to the longest running (>15 years) free‐air carbon dioxide enrichment (FACE) experiment in the Northern Hemisphere (GiFACE); providing the first evaluation of these responses from old‐growth (>100 years) semi‐natural grasslands subjected to a 20% increase in atmospheric CO2. eCO2 significantly increased AM fungal richness but had a less‐pronounced impact on the composition of their communities. However, while broader changes in community composition were not observed, more subtle responses of specific AM fungal taxa were with populations both increasing and decreasing in abundance in response to eCO2. Most population‐level responses to eCO2 were not consistent through time, with a significant interaction between sampling time and eCO2 treatment being observed. This suggests that the temporal dynamics of AM fungal populations may be disturbed by anthropogenic stressors. As AM fungi are functionally differentiated, with different taxa providing different benefits to host plants, changes in population densities in response to eCO2 may significantly impact terrestrial plant communities and their productivity. Thus, predictions regarding future terrestrial ecosystems must consider changes both aboveground and belowground, but avoid relying on broad‐scale community‐level responses of soil microbes observed on single occasions.

What drives study‐dependent differences in distance–decay relationships of microbial communities?

“…Aside from resolution, another important variable related to molecular methodology is community coverage. One of the few universal patterns that appears to hold true for most microbial communities is the “long‐tailed” species abundance distribution (Dumbrell et al., 2010; Maček et al., 2019; Shoemaker et al., 2017), which is caused by the majority of microorganisms in a community being rare. The rarer taxa in microbial communities also tend to be the least widespread (Clark et al., 2017; Lindh et al., 2017; Meyer et al., 2018; Shade & Stopnisek, 2019); therefore, detecting only the more abundant, widespread organisms would overestimate compositional similarity across communities and, consequently, weaken distance–decay relationships owing to the lower rate of turnover (Meyer et al., 2018).…”

Effects of Elevated CO2 on Tomato (Lycopersicon esculentum Mill.) Growth and Rhizosphere Soil Microbial Community Structure and Functionality

“…During this later period, the plants used most of the soil N for growth and the soil microbial community tended to shift towards slow-growing taxa (such as fungi) that can obtain N by utilizing recalcitrant C; this is an example of the "priming effect" theory [77,78]. In addition, ectomycorrhizal (EcM) fungi interact with almost 80% of terrestrial plants and supply their host plants with important mineral nutrients (N, P); in return, they receive carbon for their own growth [21,79]. Moreover, eCO 2 increased plant photosynthate allocation to arbuscular mycorrhizal fungi (AMF) and promoted the growth of AMF, which further enhanced plant access to soil minerals due to the powerful external hyphae of the AMF [20,80].…”

Carbon for nutrient exchange between arbuscular mycorrhizal fungi and wheat varies according to cultivar and changes in atmospheric carbon dioxide concentration

“…As illustrated by the present investigation, further factors to consider include the effects of abiotic factors on AMF community structure and diversity. Recent field-scale atmospheric [CO 2 ] manipulation has shown how CO 2 enrichment can affect AMF community composition (Cotton, Fitter, Miller, Dumbrell, & Helgason, 2015;Maček et al, 2019). How these atmospheric [CO 2 ]-driven community changes might influence the stoichiometry of carbon-for-nutrient exchange between symbionts in the field remains to be determined (Cotton, 2018).…”