Project description:Because of severe abiotic limitations, Antarctic soils represent simplified ecosystems, where microorganisms are the principle drivers of nutrient cycling. This relative simplicity makes these ecosystems particularly vulnerable to perturbations, like global warming, and the Antarctic Peninsula is among the most rapidly warming regions on the planet. However, the consequences of the ongoing warming of Antarctica on microorganisms and the processes they mediate are unknown. Here, using 16S rRNA gene pyrosequencing and qPCR, we report a number of highly consistent changes in microbial community structure and abundance across very disparate sub-Antarctic and Antarctic environments following three years of experimental field warming (+ 0.5-2°C). Specifically, we found significant increases in the abundance of fungi and bacteria and in the Alphaproteobacteria-to-Acidobacteria ratio. These alterations were linked to a significant increase in soil respiration. Furthermore, the shifts toward generalist or opportunistic bacterial communities following warming weakened the linkage between bacterial diversity and functional diversity. Warming also increased the abundance of some organisms related to the N-cycle, detected as an increase in the relative abundance of nitrogenase genes via GeoChip microarray analyses. Our results demonstrate that soil microorganisms across a range of sub-Antarctic and Antarctic environments can respond consistently and rapidly to increasing temperatures, thereby potentially disrupting soil functioning.
Project description:Arbuscular mycorrhiza (AM) interactions between plants and Glomeromycota fungi primarily support phosphate aquisition of most terrestrial plant species. To unravel gene expression during early stages of Medicago truncatula root colonization by AM fungi, we used genome-wide transcriptome profiling based on mycorrhizal root fragments enriched for early fungal infection stages. We used Medicago GeneChips to detail the global programme of gene expression in response to early stages of colonization by arbuscular mycorrhizal fungi and identified genes differentially expressed during these early stages.
Project description:Because of severe abiotic limitations, Antarctic soils represent simplified ecosystems, where microorganisms are the principle drivers of nutrient cycling. This relative simplicity makes these ecosystems particularly vulnerable to perturbations, like global warming, and the Antarctic Peninsula is among the most rapidly warming regions on the planet. However, the consequences of the ongoing warming of Antarctica on microorganisms and the processes they mediate are unknown. Here, using 16S rRNA gene pyrosequencing and qPCR, we report a number of highly consistent changes in microbial community structure and abundance across very disparate sub-Antarctic and Antarctic environments following three years of experimental field warming (+ 0.5-2°C). Specifically, we found significant increases in the abundance of fungi and bacteria and in the Alphaproteobacteria-to-Acidobacteria ratio. These alterations were linked to a significant increase in soil respiration. Furthermore, the shifts toward generalist or opportunistic bacterial communities following warming weakened the linkage between bacterial diversity and functional diversity. Warming also increased the abundance of some organisms related to the N-cycle, detected as an increase in the relative abundance of nitrogenase genes via GeoChip microarray analyses. Our results demonstrate that soil microorganisms across a range of sub-Antarctic and Antarctic environments can respond consistently and rapidly to increasing temperatures, thereby potentially disrupting soil functioning. We conducted in situ warming experiments for three years using open-top chambers (OTCs) at one sub-Antarctic (Falkland Islands, 52ºS) and two Antarctic locations (Signy and Anchorage Islands, 60ºS and 67ºS respectively) (see Supplementary Fig. 1 for a map). OTCs increased annual soil temperature by an average of 0.8°C (at a depth of 5 cm), resulting in 8-43% increase in positive-degree days annually and a decrease in freeze-thaw cycle frequency by an average of 15 cycles per year (8). At each location, we included densely vegetated and bare fell-field soils in the experimental design for a total of six environments. Densely vegetated and bare environments represent two contrasting environments for Antarctic soil microorganisms, with large differences in terms of C and N inputs to soils. Massively parallel pyrosequencing (Roche 454 GS FLX Titanium) of 16S rRNA gene amplicons was used to follow bacterial diversity and community composition [GenBank Accession Numbers: HM641909-HM744649], and functional gene microarrays (GeoChip 2.0)(11) were used to assess changes in functional gene distribution. Bacterial and fungal communities were also quantified using real-time PCR.
Project description:Arbuscular mycorrhiza (AM) interactions between plants and Glomeromycota fungi primarily support phosphate aquisition of most terrestrial plant species. To unravel cell-type specific gene expression during early stages of Medicago truncatula root colonization by AM fungi, we used genome-wide transcriptome profiling based on laser-microdissected cells. We used Medicago GeneChips to detail the cell-type specific programme of gene expression in early stages of colonization by arbuscular mycorrhizal fungi and identified genes differentially expressed during these stages. Medicago truncatula Gaertn M-bM-^@M-^XJemalongM-bM-^@M-^Y genotype A17 plantlets were grown in the climate chamber. Plants grown for the collection appressorial root areas (APP) and the corresponding non-appressorial root areas (NAP) were mycorrhized after 3 weeks and roots were harvested at 5-6 dpi.
Project description:Arbuscular mycorrhiza (AM) interactions between plants and Glomeromycota fungi primarily support phosphate aquisition of most terrestrial plant species. To unravel cell-type specific gene expression during late stages of Medicago truncatula root colonization by AM fungi, we used genome-wide transcriptome profiling based on laser-microdissected cells. We used Medicago GeneChips to detail the cell-type specific programme of gene expression in late stages of colonization by arbuscular mycorrhizal fungi and identified genes differentially expressed during these stages. Medicago truncatula Gaertn M-bM-^@M-^XJemalongM-bM-^@M-^Y genotype A17 plantlets were grown in the climate chamber. Plants grown for the collection of root cortical cells containing arbuscules (ARB), root cortical cells from mycorrhizal roots (CMR), and root epidermal cells from mycorrhizal roots (EPI) were mycorrhized after 2 weeks with Glomus intraradices and mycorrhizal roots were harvested at around 21 days post inoculation (dpi).