Does warming by open-top chambers induce change in the root-associated fungal community of the arctic dwarf shrub Cassiope tetragona (Ericaceae)?

Abstract

Climate change may alter mycorrhizal communities, which impact ecosystem characteristics such as carbon sequestration processes. These impacts occur at a greater magnitude in Arctic ecosystems, where the climate is warming faster than in lower latitudes. Cassiope tetragona (L.) D. Don is an Arctic plant species in the Ericaceae family with a circumpolar range. C. tetragona has been reported to form ericoid mycorrhizal (ErM) as well as ectomycorrhizal (ECM) symbioses. In this study, the fungal taxa present within roots of C. tetragona plants collected from Svalbard were investigated using DNA metabarcoding. In light of ongoing climate change in the Arctic, the effects of artificial warming by open-top chambers (OTCs) on the fungal root community of C. tetragona were evaluated. We detected only a weak effect of warming by OTCs on the root-associated fungal communities that was masked by the spatial variation between sampling sites. The root fungal community of C. tetragona was dominated by fungal groups in the Basidiomycota traditionally classified as either saprotrophic or ECM symbionts, including the orders Sebacinales and Agaricales and the genera Clavaria, Cortinarius, and Mycena. Only a minor proportion of the operational taxonomic units (OTUs) could be annotated as ErM-forming fungi. This indicates that C. tetragona may be forming mycorrhizal symbioses with typically ECM-forming fungi, although no characteristic ECM root tips were observed. Previous studies have indicated that some saprophytic fungi may also be involved in biotrophic associations, but whether the saprotrophic fungi in the roots of C. tetragona are involved in biotrophic associations remains unclear. The need for more experimental and microscopy-based studies to reveal the nature of the fungal associations in C. tetragona roots is emphasized.

In vitro evidence of root colonization suggests ecological versatility in the genus Mycena

“…Mycena species may be particularly adapted to exploit different nutritional modes in arctic and alpine areas. Interestingly, Mycena have been recovered in high abundances from plant roots at higher latitudes (Blaalid et al , 2012; Botnen et al , 2014; Lorberau et al , 2017). This could suggest that environmental stress as a result of extreme climatic conditions in cold and nutrient‐limited environments may have provided a selective evolutionary pressure facilitating the ability of fungal partners to invade roots and, furthermore, that these harsh conditions may drive a stronger selection pressure for specialization or niche shifts.…”

Ericoid mycorrhizal symbiosis: theoretical background and methods for its comprehensive investigation

“…Using damaged or moribund hair roots, thicker suberized roots that typically lack rhizodermis (see Fig. 1 in Hamim et al 2017 ) as well as hair root clumps or “fine root threads” (see Lorberau et al 2017 ) favors growth of non-ErM fungi and is therefore discouraged. That said, the distribution of different mycobionts within the ericoid root system as affected by root age/diameter/order is poorly understood (cf.…”

“…Newell andFell 1982 andVohník et al 2016b). For example, Lorberau et al (2017) investigated Cassiope tetragona root samples that were not serially washed or surface-sterilized and reported that the detected mycobiont communities were "dominated by fungal groups in the Basidiomycota traditionally classified as either saprotrophic or EcM symbionts," while only a minor part "could be annotated as ErM-forming fungi". The lack of appropriate root selection and surface treatment casts doubts as to whether C. tetragona might really be "forming mycorrhizal symbioses with typically EcM-forming fungi," as hypothesized by Lorberau et al (2017).…”

Sequence clustering threshold has little effect on the recovery of microbial community structure

“…Consequently, there is also substantial debate over which sequence similarity level gives the biologically most meaningful units (see references above). Typically, clustering thresholds in the range 95%–99% are used in microbial studies (Bonito et al., ; Geml et al., ; Lorberau et al., ; Nemergut et al., ; Vik et al., ). Several studies have addressed the performance of clustering algorithms, including choice of clustering thresholds, in alpha diversity (species richness) estimation (e.g., Koeppel & Wu, ; Tikhonov et al., ; Yamamoto & Bibby, ), while the relationship between OTU similarity thresholds and patterns of beta diversity (compositional turnover) has so far been addressed in few studies (Bik, Halanych, Sharma, & Thomas, ; Frøslev et al., ; Koeppel & Wu, ; Lekberg, Gibbons, & Rosendahl, ).…”