Peatland Diversity and Carbon Dynamics - BES 2011


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Peatlands are carbon cycling hotspots. We characterised plant and microbial diversity, carbon stocks and greenhouse-gas fluxes in a UK blanket peat. We aim to test whether measures of functional diversity (i.e. plant functional types, and microbial molecular diversity) can be used to explain and upscale variance in ecosystem carbon dynamics.

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  • Peatlands are carbon-cycling hotspots. They are important not just in the UK, where they are estimated to contain at least 1300 mega-tonnes of carbon, but on a global scale. Globally, peatlands represent a vast reservoir of carbon, stored over thousands of years. As the climate warms, peatlands begin to release this carbon to the atmosphere, predominantly as the greenhouse gases carbon dioxide and methane. Here in the UK, where our upland peatland ecosystems are threatened by multiple pressures, research by Smith and others has suggested that a loss of 12% of our peatland area would be equivalent to the total annual greenhouse gas emissions from humans in the UK. So being able to accurately quantify the amount of carbon stored in peatlands, and the rates of greenhouse gas emissions, is really important.
  • My work focuses on the following questions, which aim to address some of the ‘whys’ and ‘hows’ behind peatland ecosystem functioning.
  • I’ve been conducting my research at a fieldsite that my be familiar to some of you. The Trout Beck catchment in Moor House National Nature Reserve contains an area of typical UK blanket peatland, is well-researched and heavily-instrumented, with good background data.
  • Our research at Moor House is based around three principal peatland landforms. The rationale for using these is threefold:They have distinctive vegetation assemblages, with different mixtures of the plant functional types: shrubs, graminoids and bryophytes They have distinctive water table regimes, which are linked to the topography. Vegetation and water table are known to be major controlling factors in greenhouse gas exchange As we can see from the aerial background image, they are readily-discernable from remotely sensed data. Focussing on these landforms allows us to sample ecosystem function at an appropriate resolution for upscalingHere’s what they look like up close:
  • Here we can see how the composition of major plant functional types varies between the landforms:Eroding areas have generally less plant cover than the other landformsGullies are dominated by fast-growing sedges and graminoids. Sphagnum mosses thrive in the wet conditions.Open moorland, on the other hand, is dominated by ericoid shrubs such as callunavulgaris and ericatetralixThese vegetation composition data were obtained through a peatland survey, during which we surveyed 419 plots across the Trout Beck for vegetation composition
  • Here we have three graphs, showing carbon and nitrogen in peat beneath each of the three landforms. We see clear differences between the landforms, and gullies in particular have a story to tell. The CN ratio (graph on left) is considerably lower in gullies than it is in eroding areas or open moorland. This implies that the system of feedbacks in gullies operates under less nutrient-limited conditions. Gullies occupy a lower position in the landscape, and the effect of topography makes them a focus for flows of nutrients within the peatland ecosystem. This is also clear from the two graphs on right, which show carbon and nitrogen concentrations – in both cases, gullies are richer. This is reflected in the distinctive vegetation assemblage found in gullies, which (as we saw earlier) are dominated by graminoids, which may in turn deposit greater amounts of C and N through photosynthates and plant litter. Eroding areas are more nutrient-limited.
  • Looking now at some results from the PLFA analyses, starting with total PLFA at the top, we see that eroding areas have much lower total PLFA, while there is no difference between gullies or open moorland. This reflects the lack of plant input on eroding peat and emphasises the importance of plants for the belowground community. It also emphasises the nutrient-limited status of eroding areas. On the right we have depth. There are significant differences in the amount of PLFAs found between all three depths and the declining relationship with depth emphasises the importance of the surface vegetation in providing suitable substrate for the microbial community.The bottom two graphs show the fungal:bacterial ratios for each of the landforms, and the three different depths. There are no significant differences between landforms, but the suggestion of a more bacterial-based microbial community in gullies. Depth-wise, there are significant differences in the fungal:bacterial ratio with depth, but the pattern is less clear.
  • The most recent aspect of this work has focused on measuring the fluxes of the greenhouse gases (carbon dioxide, methane and nitrous oxide) from each of the landforms, between June 2010 and May 2011. Greenhouse gas emissions are one of the most important and globally-relevant elements of peatland ecosystem functioning. We used 36 static chambers, distributed over the three landforms and incorporating a range of peat depths, shown as green dots in the map bottom right. I’m still processing the data, so the following graphs are to present you with a flavour of our findings…
  • Water table depth is a key element in the regulation of greenhouse gas fluxes. This time-series of water table depths, relative to the peat surface, shows clear differences between the landforms once again; gullies have consistently higher water tables, closely-followed by eroding areas. Under open moorland, the water table is generally much lower. These differences are of great relevance to greenhouse gas fluxes, both directly and also indirectly through their influence on the plant communities.
  • Carbon dioxide fluxes show clear differences between landforms throughout the year. Gullies consistently show higher fluxes, perhaps due to plant composition again and possibly due in part to methane oxidation. During the peak of the growing season (start and end of graph), eroding areas have higher fluxes than open moorland, then as the sedges senesce, heather-dominated open moorland overtakes the eroding areas.
  • Methane fluxes also show a pattern linked back to the vegetation – gullies are the greatest emitters due to their high water tables and aerenchymatous vegetation. In the winter (middle-right of the graph), the fluxes are similar to those from eroding areas, suggesting that water table is the primary control on methane flux when vegetation is taken out of the picture. Drier open moorland shows much lower fluxes of methane, and some methane oxidation, throughout the year.
  • To sum up, we see clear differences in plant and microbial community composition between landforms at the ecosystem scale. Gullies are a focus for nutrients, and this is reflected in their microbial ecology: they appear to have a lower fungal:bacterial ratio, and greater fluxes of carbon dioxide and methane. These results emphasise the importance of plant and microbial ecology for peatland ecosystem functioning.
  • Peatland Diversity and Carbon Dynamics - BES 2011

    1. 1. PeatlandDiversity and Carbon Dynamics<br />Mike Whitfield<br />Nick Ostle, Richard Bardgett, Rebekka Artz<br /> |<br />
    2. 2. Background:<br />Peatlands and climate change<br /> Above- below-ground links<br />Research:<br />Landform, plant and soil diversity<br />Peatland C and N<br />Greenhouse gas emissions<br />Conclusions<br />
    3. 3. Peatlands and climate change<br />Introduction: Peatlands and Climate Change<br />To a depth of 1m, UK peatlands contain 1357Mt C, nearly half of which is in Scotland<br />A loss of 12% of the UK peatland area <br />= total annual UK human GHG emissions<br />(Bradley et al. 2005; Smith et al. 2010)<br />
    4. 4. Introduction: Linking Plant and Soil Biodiversity<br />Plant-soil interactions lie at the heart of feedbacks between the biosphere and global biogeochemical cycles.<br />Climate change and land use are powerful drivers of change in plant diversity. <br />Can we use understanding of plant-soil interactions in peatlands to predict biogeochemical functioning?<br />Pendall et al. (2008) Functional Ecology 22 (6)<br />
    5. 5. Main Questions<br />Are there any relationships between plant and microbial community structure at the ecosystem scale?<br />Can these relationships be used to predict ecosystem scale carbon storage and greenhouse gas emissions?<br />How little do we need to know about biodiversity to predict ecosystem C cycling and GHG emissions?<br />Image: R. Bardgett<br />
    6. 6. Field Site: Trout Beck, Moor House, north Pennines<br />Area: 1146 ha<br />Altitudinal range: 535 – 848m<br />90% blanket peat<br />
    7. 7. Peat Bog Landforms<br />Open moorland<br />Gully<br />Eroding area<br />
    8. 8. Above-ground: Vegetation Composition<br />Open moorland<br />Gully<br />Eroding area<br />
    9. 9. Methodology: Peatland survey<br /><ul><li>Large-scale vegetation survey
    10. 10. Composition and height
    11. 11. Topography
    12. 12. Peat depth
    13. 13. Soil C and N
    14. 14. Microbial community composition
    15. 15. By PLFA and M-TRFLP</li></ul>0-5cm: Acrotelm<br /> 15-20cm: Mesotelm<br /> 75-80cm: Catotelm<br />
    16. 16. Below-ground: Peat Carbon and Nitrogen<br />Gullies are less nutrient-limited and a focus for biogeochemical cycling…<br />
    17. 17. Below-ground: Microbial community PLFAs<br />Lower total PLFAs in eroding areas reflects lack of plant inputs<br />Declining trend in total PLFAs with depth<br />Suggestion of a lower fungal-bacterial ratio in gullies<br />(f = 70, p < 0.01)<br />(f = 12, p < 0.01)<br />n.s.<br />(f = 24.7, p < 0.01)<br />
    18. 18. Greenhouse Gas Fluxes: Experimental Design<br />Monthly sampling using static dome chambers, Infra-Red Gas Analysers (IRGAs) and gas chromatography<br />Continuous landform hydrology and temperature<br />June 2010 to May 2011<br />Image: Sue Ward<br />
    19. 19. Water table measurements<br />
    20. 20. Greenhouse Gas Fluxes: CO2 from June 2010 to May 2011<br />Summer<br />Winter<br />
    21. 21. Greenhouse Gas Fluxes: CH4 from June 2010 to May 2011<br />Summer<br />Winter<br />
    22. 22. Conclusions so far…<br /><ul><li>Are there any relationships between plant diversity-abundance and microbial community structure at the landscape scale?
    23. 23. Differences in the composition of Plant Functional Types between landforms are clearly visible
    24. 24. Eroding areas have lower total PLFAs, which may be a reflection of lower vegetation cover on bare peat
    25. 25. Are there differences in below-ground carbon dynamics between landform types?
    26. 26. Gullies have a greater carbon and nitrogen concentration, and a lower CN ratio
    27. 27. Can these relationships be used to predict ecosystem scale greenhouse gas emissions?
    28. 28. Gullies emit larger quantities of methane and carbon dioxide than other landforms</li></li></ul><li>Acknowledgements<br />This talk can be downloaded from<br />Many thanks to:<br />Catherine Turner, Sean Case, Simon Oakley, Susan Ward, Sergio Menendez Villanueva, Harriett Rea, Paula Reimer, David Beilman and Nicola Thompson<br />Mike Whitfield is supported by a Natural Environment Research Council CASE studentship.<br />