Changes in plant functional diversity matter for peatland carbon cycling

Lead Research Organisation: Lancaster University
Department Name: Lancaster Environment Centre

Abstract

The issue of carbon (C) cycling is high on the scientific and political agenda, largely because of concerns over the ability of ecosystems to store C in the face of global change. Much of the research in this area is focussed on moorlands, or peatlands, because they act as vast stores of terrestrial C, currently estimated to be one-third of the global C stock. The main worry here is that changes in climate and land use will destabilise these stores, releasing C back into the atmopshere as carbon dioxide, thereby boosting global warming. To date, most research in this area has looked at how changes in weather, such as climate warming and drought, might affect these important C stores in peat. Very little, however, is known about how land use, and changes in vegetation that result from management, influence these C stores. Land use, for the production of goods and services, is one of the most substantial human influences on Earth, affecting one third to one half of the land surface. While peatlands are thought to be of limited value for farming, they are subject to much land use activity from forestry, peat extraction for fuel and horticulture, rough grazing and game management. All these activities strongly affect the make-up of the vegetation, often increasing the growth of fast growing plants, such as grasses, at the expense of heather, the plant most commonly associated with moorland. In the long-term, this could influence ecosystem C storage by changing the balance between C input to soil, from plant litter and root material, and its loss by decomposition and respiration. In this proposal, we tackle this issue by testing how changes in vegetation resulting from long-term management, namely buring and grazing, influence the cycling of C in peatland ecosystems. To do this, we will use a long-term (50 year) field experiment at the Moor House National Nature Reserve, northern England, with various grazing and burning treatments. We will manipulate vegetation of different management systems to test how this affects C cycling in peatland. To do this, we will use novel pulse labelling approaches which allow us to trace the uptake of C by plants and its transfer to soil, and then back to the atmopshere.
 
Description The aim of this study was to develop understanding of how changes in peatland plant functional composition influences the belowground C cycling. Key findings of our research below:

Objectives 1 & 2: Is the rate of CO2 uptake by photosynthesis and its transfer to soil via roots affected by changes in the functional composition of moorland vegetation, resulting from long-term management change (O1), and is the composition and function of the free-living soil microbial community affected by plant-driven changes in soil C supply via roots (O2)? These objectives were tested on a 50 + year peatland management experiment at Moor House National Nature Reserve. We used a 13CO2 pulse-chase to test the hypothesis that burning and grazing enhance assimilation of new photosynthate by the plant community, its transfer to the soil microbes, and its respiration/release as CO2. We found that burning affected the composition and growth stage of the plant community and the structure of the soil microbial community, measured using phospholipid fatty acid analysis, with less ericoid dwarf-shrubs and fungal biomass. This was linked to increased photosynthetic uptake of CO2 and its transfer to the soil microbial community in burned areas. Grazing had no detectable effects. We found that burning accelerated short-term C cycling and the return of newly fixed CO2 to the atmosphere due to changes in the age and composition of the plant community. In parallel experiments, we found greater assimilation and turnover of photosynthate in peatland graminoids than in shrubs or lower plants, and that vegetation composition had significant impacts on litter decomposition. Overall, our results demonstrate that changes in vegetation and soil microbial communities resulting from land use change can significantly alter short-term C cycling in peatlands, with potential consequences for future C sequestration.

Objective 3: Do changes in peatland plant community composition and functional group identity have consequences for ecosystem CO2 and CH4 effluxes and peat DOC concentrations? This was tested in a field-scale plant functional group removal experiment set-up at Moor House involving removal of all possible combinations of the three dominant plant functional groups (i.e. ericoid dwarf-shrubs, graminoids, and lower plants). We also super-imposed a warming treatment on half of the plots using ITEX design passive warming chambers. We found that vegetation composition affected gross and net CO2 fluxes, with greatest rates of respiration, photosynthesis and net CO2 sink strength when vascular plants (particularly shrubs) were present. The warming treatment (ranging from 0.5 - 2°C) consistently increased rates of respiration across all vegetation types by an average 50%. In contrast, the effects of warming on photosynthesis depended on the identity of the plant functional group, with interactions between vegetation type and warming being observed. Overall, no net effect of warming on net CO2 flux was observed, however, interactions between warming and vegetation type showed that the effect of warming was dependent on the identity of the plant functional group, with the shrub only treatment showing the greatest increase in net CO2 sink with warming. For CH4, strong vegetation effects were found, with the graminoid functional group consisting of the aerenchymous conduit sedge Eriophorum vaginatum. Although no overall warming effect or warming x plant functional group interactions for CH4 flux were detected, we did find that warming increased CH4 emissions in the graminoid only group. For DOC, no warming effect and only weak vegetation effects were detected, with lowest concentrations of DOC where no above-ground vegetation was present. Overall, we conclude that both warming and plant community composition strongly influence ecosystem CO2 and CH4 effluxes. Further, that the degree of interaction with increased temperature and the relative strength of vegetation and temperature effects depends on the identity of the plant functional group and varies with the flux measured.
Exploitation Route The research has continued via two consecutive NERC funded PhD studentships, both using the experiment set up under this grant. Tom Ward will submit his thesis in 2015, whereas Danielle Satterthwaite has just started on a NERC DTP studentship (2014-2018)
Sectors Agriculture, Food and Drink,Environment

 
Description The research outputs have been articulated in a number of policy/general public formats, including: Ward SE, Whitfield M. (2012) From microbe to mountain: How biodiversity affects carbon storage in a moorland ecosystem. ECN biodiversity publication on line January 2012. http://www.ecn.ac.uk/what-we-do/science/ecn-and-research/microbe-to-mountain House J, Clark J, Gallego-Sala A, Orr H (2011) Contributors: Aylen J, Bardgett R, Billett M, Bonn A, Caporn S, Chapman S, Clutterbuck B, Evans C, Evans M, Farewell T, Freeman C, Grayson R, Hall J, Holden J, McMorrow J, Milledge D, Nayak D, Ostle N, Parry L, Prentice C, Stevens C, Smith J, Smith P, Vanguelova E, Ward S, Waldron S, White S, Worrall F, Yallop A. Vulnerability of upland peatland services to climate change. Environment Agency Science Report SC070036/SR. Ward S.E. (2010). Gardening for Greenhouse gases. NERC Planet Earth, Spring 2010, 20-21.
First Year Of Impact 2010
Sector Agriculture, Food and Drink,Environment
Impact Types Policy & public services