Presentation_1_Bacterial Response to Permafrost Derived Organic Matter Input in an Arctic Fjord.pdf

<p>The warming of the Arctic causes increased riverine discharge, coastal erosion, and the thawing of permafrost. Together, this is leading to an increased wash out of terrestrial dissolved organic matter (tDOM) into the coastal Arctic ecosystems. This tDOM may be anticipated to affect both carbon and nutrient flow in the microbial food web and microbial community composition, but there are few studies detailing this in Arctic marine ecosystems. We tested the effects of tDOM on the bacterial community composition and net-growth by extracting DOM from the active layer of permafrost soil and adding the aged tDOM concentrate to a natural microbial fjord community (Kongsfjorden, NW Svalbard). This resulted in an increased carbon load of 128 μM DOC in the tDOM treatment relative to the control of 83 μM DOC. We observed changes in community composition and activity in incubations already within 12 h where tDOM was added. Flow cytometry revealed that predominantly large bacteria increased in the tDOM treated incubations. The increase of this group correlated with the increase in relative abundance of the genus Glaciecola (Gammaproteobacteria). Glaciecola were initially not abundant in the bacterial community (0.6%), but their subsequent increase up to 47% after 4 days upon tDOM addition compared to 8% in control incubations indicates that they are likely capable of degrading permafrost derived DOM. Further, according to our experimental results we hypothesize that the tDOM addition increased bacterivorous grazing by small protists and thus tDOM might indirectly also effect higher trophic levels of the microbial food web.</p

Scanning electron microscope images of marine calcium particles with different morphology.

<p>Samples were collected at 5 m depth in Raunefjorden, a coastal sampling station south of Bergen, Norway. A and B) Particles resembling bacteria and microcolonies of bacteria. B and D) Particles similar to the Ca carbonates described to precipitate on the cell surface of cultured marine bacteria. E and F) Particles with one flat surface suggesting that they are formed on a surface or interface. G and H) Particles with rhombohedral shape. I and J) Baton like particles resembling Bahaman ooids. All scale bars are 2 µm except in d) where it is 1 µm and f) where it is 10 µm.</p

The annual variation in CaCO₃ particles and chl <i>a.</i>

<p>Samples were collected at 5 m depth in Raunefjorden, a coastal sampling station south of Bergen, Norway. A) Calcium in the coccolithophore <i>Emiliania huxleyi</i> and in Ca particles estimated from scanning electron microscope counts. B) Total particulate Ca concentration measured by X-ray fluorescence (error bars are SE, n = 3–4) and chl <i>a</i> concentration. Hydrographical data and chl <i>a</i> profiles are shown in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0047887#pone.0047887.s004" target="_blank">Fig. S4</a>.</p

Linear regressions between structural variables and P enrichment.

<p>(A) algae:bacteria ratio (biomass) vs. P enrichment under +UVR and –UVR conditions in the PA and PD periods; (B) Δ-algal P or Δ-bacterial P vs. P enrichment under +UVR and –UVR conditions in the PD period. Dashed and dotted lines indicate 95% interval confidence for each regression. (PA period: phosphorus-availability period; PD period: phosphorus-depletion period).</p

Seasonal and annual variability in the phytoplankton community of the Raunefjord, west coast of Norway from 2001–2006

<p>Changes in phytoplankton community composition potentially affect the entire marine food web. Because of seasonal cycles and inter-annual variations in species composition, long-term monitoring, covering many sequential years, is required to establish a baseline study and to reveal long-term trends. The current study describes the phytoplankton biomass variations and species composition in relation to hydrographic and meteorological conditions in the Raunefjord, western Norway, over a 6-year period from 2001 to 2006. The extent of inflow or upwelling in the fjord varied from year to year and resulted in pronounced differences in water column stability. The annual phytoplankton community succession showed some repeated seasonal patterns, but also high variability between years. Two to four diatom blooms were observed per year, and the spring blooms occurring before water column stratification in March were dominated by <i>Skeletonema marinoi</i> and <i>Chaetoceros socialis</i>, and other <i>Chaetoceros</i> and <i>Thalassiosira</i> spp<i>.</i> Blooms of the haptophytes <i>Phaeocystis pouchetii</i> and <i>Emiliania huxleyi</i> were irregular and in some years totally absent. Although <i>E. huxleyi</i> was present all year round it appeared in bloom concentrations only in 2003, when the summer was warm and the water column characterized by high surface temperatures and pronounced stratification. The annual average abundance of both diatoms and flagellates increased during the six years. Despite the high variation from year to year, our investigation provides valuable knowledge about annual phytoplankton community patterns in the region, and can be used as a reference to detect possible future changes.</p

Non-linear regressions between BP and P enrichment, and bacterial requirements vs. supply of algal carbon.

<p>Dashed and dotted lines indicate 95% interval confidence for each regression, fitted as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0060223#pone-0060223-g002" target="_blank">Figure 2</a> in the PA period (A) and PD period (B). Photosynthetic carbon required by bacteria (CARB) and excretion of organic carbon from algae (EOC) measured in the PA (C) and PD (D) periods. Error bars are standard deviations. Significance of Student’s t-test between CARB and EOC for each experimental treatment: *p<0.05; **p<0.01; ***p<0.001. (PA period: phosphorus-availability period; PD period: phosphorus-depletion period).</p

Biomass variation of each fraction of the planktonic community (<40 µm) over the experiment.

<p>Treatments with full sunlight radiation (+UVR; left panels) and without UV radiation (−UVR; right panels), as well as treatments without (Control) and with nutrient addition (20, 30, 40 and 60 µg P L⁻¹) are displayed. The values are expressed as percentage of carbon. The vertical line divides experimental periods with or without availability of dissolved inorganic P.</p

Physical, chemical, and biological variables measured under initial experimental conditions.

<p>Abbreviations: T, temperature (average water column); UVB_300–318, ultraviolet B radiation measured in the 300–318 nm range (2 nm of interval); UVA_320–398, ultraviolet A radiation measured in the 320–398 nm range (2 nm of interval); TP, total phosphorus; TDP, total dissolved phosphorus.</p>*<p>UV radiation data were measured at noon using a LI-8000 spectroradiometer (LI-COR, Lincoln, NE, USA). Diffuse attenuation coefficients for downward irradiance (K_d) were determined from the slope of the linear regression of the natural logarithm of downwelling irradiance vs. depth for each region of the solar-radiation spectrum.</p

Non-linear regressions between HMFW components and P enrichment in the PA period.

<p>(A) Whole HMFW biomass; (B) bacterial abundance; (C) ciliate abundance; (D) virus abundance. Dashed and dotted lines indicate 95% interval confidence for each regression fitted by peak-Gaussian: or quadratic: functions under +UVR and –UVR conditions. (PA period: phosphorus-availability period).</p

Linear regressions between structural and functional variables.

<p>(A) Virus abundance vs. BP; (B) ciliate abundance vs. total BP estimated for the PA period. Dashed lines indicate 95% interval confidence for each regression. (PA period: phosphorus-availability period).</p