TY - JOUR
T1 - Strong regionality and dominance of anaerobic bacterial taxa characterize diazotrophic bacterial communities of the arcto-alpine plant species Oxyria digyna and Saxifraga oppositifolia
AU - Kumar, Manoj
AU - van Elsas, Jan Dirk
AU - Nissinen, Riitta
PY - 2017/10/13
Y1 - 2017/10/13
N2 - Arctic and alpine biomes are most often strongly nitrogen-limited, and hence biological nitrogen fixation is a strong driver of these ecosystems. Both biomes are characterized by low temperatures and short growing seasons, but they differ in seasonality of solar radiation and in soil water balance due to underlying permafrost in the Arctic. Arcto-alpine plant species are well-adapted to the low temperatures that prevail in their habitats, and plant growth is mainly limited by the availability of nutrients, in particular nitrogen, due to slow mineralization. Nitrogen fixing bacteria are likely important for plant growth in these habitats, but very little is known of these bacteria or forces shaping their communities. In this study, we characterized the potential nitrogen fixing bacterial (PNFB) communities associated with two arcto-alpine pioneer plant species, Oxyria digyna (mountain sorrel) and Saxifraga oppositifolia (blue saxifrage), in three climate regions. Both of these plants readily colonize low nutrient mineral soils. Our goal was to investigate how climate (region) and, on the other hand, host plant and plant species shape these communities. To our knowledge, this is the first comprehensive study describing PNFB communities associated with pioneer plants in different arcto-alpine biomes. Replicate samples were taken from two arctic regions, Kilpisjarvi and Ny-angstrom lesund, and one alpine region, Mayrhofen. In these, the PNFB communities in the bulk and rhizosphere soils and the plant endospheres were characterized by nifH-targeted PCR and massive parallel sequencing. The data revealed strong effects of climatic region on the dominating nitrogen fixers. Specifically, nifH sequences related to Geobacter (delta-Proteobacteria) were present in high relative abundances in the nitrogen-fixing communities in the Mayrhofen and Kilpisjarvi regions, while members of the Clostridiales prevailed in the Kilpisjarvi and Ny-angstrom lesund regions. The bulk and rhizosphere soil as well as the endosphere communities in the Mayrhofen region were all characterized by high relative abundances of nifH sequences related to Geobacter. In contrast, the endosphere and soil (bulk or rhizosphere soil) communities in the High Arctic were highly divergent: endosphere communities in the arctic regions were shaped by Clostridium spp., while nifH sequences representing delta-Proteobacteria, beta-Proteobacteria, Cyanobacteria (in Ny-angstrom lesund), and Verrucomicrobia (in Kilpisjarvi) dominated the soil communities. Interestingly, the major PNFB genera identified in this study have been previously identified as members of conserved core microbiomes in the endospheres and seeds of these plants by 16S rRNA gene based analyses combined with bacterial isolation, suggesting a very tight interaction between diazotrophic bacteria and these arctic pioneer plants. Overall, anaerobic bacterial taxa dominated the PNFB communities of the endospheres and rhizospheres of the two plant species in all study sites. This could indicate anoxic conditions in and around plant roots at the time of sampling (early growth season), created by melting snow and underlying permafrost.
AB - Arctic and alpine biomes are most often strongly nitrogen-limited, and hence biological nitrogen fixation is a strong driver of these ecosystems. Both biomes are characterized by low temperatures and short growing seasons, but they differ in seasonality of solar radiation and in soil water balance due to underlying permafrost in the Arctic. Arcto-alpine plant species are well-adapted to the low temperatures that prevail in their habitats, and plant growth is mainly limited by the availability of nutrients, in particular nitrogen, due to slow mineralization. Nitrogen fixing bacteria are likely important for plant growth in these habitats, but very little is known of these bacteria or forces shaping their communities. In this study, we characterized the potential nitrogen fixing bacterial (PNFB) communities associated with two arcto-alpine pioneer plant species, Oxyria digyna (mountain sorrel) and Saxifraga oppositifolia (blue saxifrage), in three climate regions. Both of these plants readily colonize low nutrient mineral soils. Our goal was to investigate how climate (region) and, on the other hand, host plant and plant species shape these communities. To our knowledge, this is the first comprehensive study describing PNFB communities associated with pioneer plants in different arcto-alpine biomes. Replicate samples were taken from two arctic regions, Kilpisjarvi and Ny-angstrom lesund, and one alpine region, Mayrhofen. In these, the PNFB communities in the bulk and rhizosphere soils and the plant endospheres were characterized by nifH-targeted PCR and massive parallel sequencing. The data revealed strong effects of climatic region on the dominating nitrogen fixers. Specifically, nifH sequences related to Geobacter (delta-Proteobacteria) were present in high relative abundances in the nitrogen-fixing communities in the Mayrhofen and Kilpisjarvi regions, while members of the Clostridiales prevailed in the Kilpisjarvi and Ny-angstrom lesund regions. The bulk and rhizosphere soil as well as the endosphere communities in the Mayrhofen region were all characterized by high relative abundances of nifH sequences related to Geobacter. In contrast, the endosphere and soil (bulk or rhizosphere soil) communities in the High Arctic were highly divergent: endosphere communities in the arctic regions were shaped by Clostridium spp., while nifH sequences representing delta-Proteobacteria, beta-Proteobacteria, Cyanobacteria (in Ny-angstrom lesund), and Verrucomicrobia (in Kilpisjarvi) dominated the soil communities. Interestingly, the major PNFB genera identified in this study have been previously identified as members of conserved core microbiomes in the endospheres and seeds of these plants by 16S rRNA gene based analyses combined with bacterial isolation, suggesting a very tight interaction between diazotrophic bacteria and these arctic pioneer plants. Overall, anaerobic bacterial taxa dominated the PNFB communities of the endospheres and rhizospheres of the two plant species in all study sites. This could indicate anoxic conditions in and around plant roots at the time of sampling (early growth season), created by melting snow and underlying permafrost.
KW - nifH
KW - pioneer plants
KW - Geobacter
KW - Clostridium
KW - endophytic bacteria
KW - NITROGEN-FIXING BACTERIA
KW - NIFH GENE
KW - TUSSOCK TUNDRA
KW - HIGH DIVERSITY
KW - SOIL
KW - CARBON
KW - SHRUBS
KW - CHINA
U2 - 10.3389/fmicb.2017.01972
DO - 10.3389/fmicb.2017.01972
M3 - Article
SN - 1664-302X
VL - 8
JO - Frontiers in Microbiology
JF - Frontiers in Microbiology
M1 - 1972
ER -