How Does Salinity Shape Bacterial and Fungal Microbiomes of Alnus glutinosa Roots?

Abstract

Black alder (Alnus glutinosa Gaertn.) belongs to dual mycorrhizal trees, forming ectomycorrhizal (EM) and arbuscular (AM) root structures, as well as represents actinorrhizal plants that associate with nitrogen-fixing actinomycete Frankia sp. We hypothesized that the unique ternary structure of symbionts can influence community structure of other plant-associated microorganisms (bacterial and fungal endophytes), particularly under seasonally changing salinity in A. glutinosa roots. In our study we analyzed black alder root bacterial and fungal microbiome present at two forest test sites (saline and non-saline) in two different seasons (spring and fall). The dominant type of root microsymbionts of alder were ectomycorrhizal fungi, whose distribution depended on site (salinity): Tomentella, Lactarius, and Phialocephala were more abundant at the saline site. Mortierella and Naucoria (representatives of saprotrophs or endophytes) displayed the opposite tendency. Arbuscular mycorrhizal fungi belonged to Glomeromycota (orders Paraglomales and Glomales), however, they represented less than 1% of all identified fungi. Bacterial community structure depended on test site but not on season. Sequences affiliated with Rhodanobacter, Granulicella, and Sphingomonas dominated at the saline site, while Bradyrhizobium and Rhizobium were more abundant at the non-saline site. Moreover, genus Frankia was observed only at the saline site. In conclusion, bacterial and fungal community structure of alder root microsymbionts and endophytes depends on five soil chemical parameters: salinity, phosphorus, pH, saturation percentage (SP) as well as total organic carbon (TOC), and seasonality does not appear to be an important factor shaping microbial communities. Ectomycorrhizal fungi are the most abundant symbionts of mature alders growing in saline soils. However, specific distribution of nitrogen-fixing Frankia (forming root nodules) and association of arbuscular fungi at early stages of plant development should be taken into account in further studies.

When Salt Meddles Between Plant, Soil, and Microorganisms

“…They also found that the sampling season was not influencing the biodiversity. Seasonality did not appear to be an essential factor in shaping endophytic microbial communities in saline soils also from other studies (Thiem et al, 2018).…”

“…Kearl et al (2019) isolated bacteria from halophytes (Salicornia and Allenrolfea) and observed that there were different populations in samples collected at different times of the year, with a majority of the genera, however, present independent of when the samples were collected. Thiem et al (2018) analysed the community structure of plant-associated endophytes of Alnus glutinosa, that is a dual mycorrhizal tree that forms ectomycorrhizal (EM) and arbuscular (AM) root structures, and can typically associate also with nitrogen-fixing actinomycetes. The authors sampled the plant's root microbiome present at two forest test sites (saline and non-saline).…”

Contrasted ecological niches shape fungal and prokaryotic community structure in mangroves sediments

“…Investigations conducted in different monospecific forests presenting the same age, the same initial substrate and climatic conditions, showed that the effect of tree species on the composition of soil fungal communities explained up to 47% of the variation observed while the effects of C, N, P and pH were insignificant (Urbanová et al, 2015). However, in New Caledonia mangroves, salinity is also an important factor shaping tree distribution, higher salinity being associated with A. marina (Deborde et al, 2015), and might impact directly or indirectly plant associated fungal communities (Thiem et al, 2018). Moreover, Fungi tended to be tree-specific (Zhou and Hyde, 2001;Buée et al, 2011) even in the case of mangrove ecosystems where the aerial and intertidal parts of A. marina or R. stylosa exhibited different fungal communities (Arfi et al, 2012a).…”

Halo-tolerant plant growth promoting rhizobacteria for improving productivity and remediation of saline soils

“…There are reports claiming that each year around 1–2% of fertile soils are being degraded worldwide due to salinity [6] . It has also been forecasted that in the next 35 years, about 50% of the land on earth will suffer due to various degrees of salinity [7] . Additionally, data indicates that in past few decades the annual cost of salt-induced land degradation in irrigated areas was estimated to be US$ 27.3 billion [8] .…”