Plant litter identity matters in peatlands

A bright, blustery day in England’s north Pennines. Fluffy cotton grass heads bob and bounce on the breeze. On the side of a hill, a strange array of hexagonal, knee-high structures glint and sparkle. Four figures, hunched against the wind, move methodically along jaunty wooden boardwalks, which rest on the blanket bog, crouching at each hexagon in turn. Welcome to Moor House National Nature Reserve, the site of an experiment designed to investigate how a warmer climate will affect the speed with which plant litter is recycled back into the soil, and ultimately the atmosphere.

Passive warming experiment, Moor House NNR

The resulting paper, in ESA Ecology, describes an experiment that uses a combination of open-top, passive warming chambers and plant removal treatments to investigate how the presence of certain plant functional types and warmer temperatures affect rates of litter decomposition. The authors used litter bags, filled with the litter of each plant functional type and buried in plots beneath the plant removal and warming treatments. In all, there were eight treatments (combinations of graminoid, shrub and bryophyte removal, a bare plot and a control with no plants removed), replicated over four blocks, with half the plots warmed by the passive chambers.

The main finding of the paper is that presence or absence of plant functional groups had a stronger effect on peatland litter decomposition than the warming of approximately 1°C achieved by the passive chambers. Removing the shrubs from the peatland resulted in faster decomposition of graminoid and bryophyte litter, after two years. Litter identity was also important – in the first year of the experiment this was the main factor controlling rates of litter decomposition, with bryophyte litter decomposing most slowly, followed by shrubs and graminoids. After two years, the live plants present in the plot (i.e. presence of shrubs) were more important than the litter identity. Warming affected the composition of the bacterial community, while the fungi responded more strongly to the presence of shrubs.

Passive warming experiment, Moor House, summerWhile these results are compelling, they should be taken with caution, as the authors suggest: since the duration of the experiment was two years, further interesting effects resulting from the decomposition of shrub and bryophyte litter, which happens more slowly than in graminoids, might not have been captured. After four or five years, the decomposition of more recalcitrant litter could reveal more interesting effects. The same is true for the warming treatment: given a longer study period, the effect of 1°C warming on plant litter decomposition might become more important. It is, however, easy to write ‘more long-term experiments needed!’ while, in reality, the amount of effort required to maintain the plant removal treatments and warming chambers in the harsh upland environment of the Pennines represents a considerable hurdle. And one has to motivate one’s volunteers to see past the inherent absurdity of weeding a moorland!

Overall then, what’s the message? Dead or alive, whether you’re graminoid, shrub or bryophyte seems to exert much stronger control on litter decomposition rates in peatlands than temperature. While warming doesn’t have much of an effect on plant decomposition, it does affect the bacterial community in the peat, which might have important implications for graminoid decomposition, since bacteria are well-equipped to munch through labile substrates. Fungi respond when you take away the shrubs, which provide the more recalcitrant litter they’re specialised for dealing with, and might therefore moderate the response of the peatland carbon cycle to warming. Given a longer time period, more effects may emerge from this experiment.

I’m interested to know about the responses of decomposition processes in other ecosystems to warming and plant functional group removal. In grasslands, for instance, what happens when you increase the ambient temperature and remove the nitrogen fixers? Of course, these sorts of studies require a sufficiently long period to become stable and start producing results. In a time of apparently perpetually shrinking budgets, what’s next for long-term field experiments in ecology and biogeochemistry?

This is an edited version of a post I contributed to the BES Plants-Soils-Ecosystems journal club.

The power of peat

A wintery sun begins to set in the north pennines

A wintery sun begins to set in the north pennines

Last August I was lucky enough to be one of thirty budding scribes shortlisted for the inaugural Guardian / Wellcome Trust Science Writing Prize. I was invited to spend an afternoon at a science writing workshop at the Guardian HQ, hosted by Alok Jha, where the shortlistees had the opportunity to extract some top tips from established science writers James Randerson, Michael Regnier and Stephen Curry. The evening consisted of a glitzy awards ceremony, hosted by Dara O’Briain at the Wellcome Collection, in which the winners Tess Shellard and Penny Sarchet were announced.

The event was very inspiring and I had a fantastic time; creative juices were in full flow and it was great to have the chance to chat with so many like-minded people. My writing has since had to take a back seat while I finish my PhD, but it’s worth noting that the 2012 Science Writing Prize is to be announced soon!

Below is my original entry to the competition, an edited version of which was published on the Wellcome Trust blog not so long ago.

The power of peat and the climate challenge

When: Sometime after lunch, Tuesday 15th March 2011.

Where: 600 metres up in the north Pennines.

The temperature is supposed to be ten degrees centigrade, but it feels much colder. It’s raining, horizontally – a puddle has actually formed on the page of my notebook. My fingers are frozen, everything is sodden. Every effort is bent on protecting the £5000 box of electronics that I’ve been entrusted with on this important mission, which cannot be allowed to get wet. Why am I here?

My mission, as I chose to accept it nearly three years ago when I started my PhD, is to study an upland peat bog. As a vital part of our planet’s life support system, peat bogs are up there with the rainforests. While the trees in Amazonia are doing the glamorous part, being the lungs of the world and providing us with clean air to breathe each day, peat is sitting there on lonely fell-tops and windy tundra, quietly soaking up the rest of the emissions we produce and swallowing up the occasional sheep. Without peat, we’d be further along the path to a warmer world than we are right now.

Since I began my research, I’ve discovered that working in a landscape that is classified as sub-Arctic, despite its location more than one hundred miles south of Edinburgh, comes with its own set of challenges. Peat is ninety per cent water. Both equipment and field workers can get stuck in the bog all year round, while in the winter blankets of snow cover everything.  In summer, tufts of white cotton grass bob gently on the breeze and sometimes it stops raining, causing swarms of midges to descend upon the unwary scientist. Linnaeus felt the weight of the fieldwork challenge, investigating the mires of Lapland back in 1732:

“The whole of this Lapp country was bog, which is why I call it the Styx. No priest has ever painted Hell so vile that this does not exceed it, no poet described a Styx so foul that this does not eclipse it.”1

He wasn’t keen then. It’s not surprising that peat bogs have a bit of an image problem. But it’s their inhospitable nature that makes them so vital. The cold and wet conditions help peat to lock up CO2 from the atmosphere, storing it as organic carbon. Since the end of the last ice age over ten thousand years ago, our rainy bogs have been soaking up more than a quarter of all the organic carbon stored in soils globally. All that carbon is stored in dark brown, wet deposits many metres deep, with the texture and colour of chocolate sponge cake but none of the charm.

The problem is that, if the sponge cake starts to dry out, thousands of years’ worth of accumulated carbon will start returning to the atmosphere as CO2 faster than the peat can store it, ruining our attempts to slow our changing climate. A loss of less than two per cent of our planet’s peat bogs would be equivalent to the amount of CO2 released by humans annually2. So much for cycling to work and buying organic. Once our peat bogs start losing CO2, it might be difficult to stop them.

There are many threats to peat bogs: drainage for farming, extraction for fuel, wildfires and erosion are four of the more serious. Luckily our attitude towards peat bogs has improved since Linnaeus’ day, and that’s why I find myself crouching in the heather, trying not to sink into the peat while keeping my expensive scientific equipment dry.

My research focuses on the carbon side of the peat bog story. How much do peat bogs store away? How much do they release, and are they storing it away at the same rate? Those are two of the questions I’d like to answer. There is a great variety of research taking place on peat bogs, with topics ranging from erosion to heavy metal pollution, from reconstructing past climates to the importance of peat as a wildlife habitat. They might be under-appreciated, but our peat bogs provide us with a wealth of services: they hold a vast amount of water, provide space for recreation and are a refuge for many rare plant and animal species. Perhaps most importantly for us, they are a crucial tool in our efforts to slow our changing climate. There’s the power of peat.

References:

1 Quoted in Rydin, H. and Jeglum, J.K. 2006: The biology of peatlands. Oxford: Oxford University Press. Page 262.

2 Figures from presentation by Smith, P., given at ‘Investing in Peatlands – the Climate Challenge’ conference, Durham, 28-29th September 2010.

Peatlands are carbon cycling hotspots

Last week I gave a talk at the British Ecological Society’s Annual Meeting in Sheffield – you’ll find it embedded below. If you view the talk on SlideShare, you’ll be able to see notes for each of the slides (under speaker’s notes). The story is similar to the previous talks that I’ve uploaded, but I’ve included a bit more information about the microbial communities in this one, along with some preliminary greenhouse gas emission data.

The quality of the talks and thematic sessions at the BES meeting was generally very high – I’m very much looking forward to attending next year’s.

PhD Introduction: a presentation

Below is a presentation I gave seven months into my PhD project, in a Lancaster University seminar. It provides a basic outline of my project, including an introduction to the fieldsite and methodology. Although a little dated now (highly relevant eight months ago!) I’ve posted it here because it’s still a useful overview and gives a sense of continuity.