WP3: Soil/plant flux measurements (Leader: Dr R Baxter + Ineson, Mencuccini, Williams, Huntley)

We will provide to WP7 high temporal resolution of C exchange of the key tundra-dwarf-shrub and forest understorey communities through diurnal cycles at different times of year, coupled with, where relevant, concomitant measurements of CO₂ exchange of branches of the tree Betula. We propose to employ a series of integrated campaigns of measurements, combining multiplexed automatic clear plastic CO₂ chambers (after Bubier et al, 2002) with an automatic multiplexed branch-bag approach (Rayment et al, 2002). Particular attention will be paid to the key ‘shoulder’ seasons of the winter-spring transition and autumn-winter transition (H3a,b). In addition, the automated chamber approach has been used very successfully previously (Bubier et al, 2002) to measure net ecosystem exchange of C (NEE) during the snow-covered season. Winter fluxes will be measured on a campaign basis of 1-2 weeks in winter, making measurements every 3 hours by sampling changes in headspace concentrations of CO₂. We will pay particular attention to the period of spring thaw when freezing and thawing events can lead to large changes in build-up and release of CO₂ and is an important and often poorly represented period of the annual CO₂ exchange budget.

We will provide suitable fine-scale temporal resolution of C and water exchange across the whole range of dominant vegetation types, and across boundaries between types, at key times of the yearly cycle. This will be achieved by deployment of large 1m x 1m portable chamber systems that are flexible in operation height (Williams et al., in press), linked to a LiCOR 6400 portable IRGA, for use over a range of canopies of dwarf shrub (e.g. Betula nana and Salix species ca. 50 cm and 75-100 cm tall; requiring no permanent collars, and therefore avoiding ‘damage artefacts’). Multiple rapid assessments of light response curves of NEE, over the different vegetation canopies comprising the tundra, and forest, understorey will be made along with light intensity, prevailing air and soil temperature, and soil moisture. We will provide fine-scale spatial and temporal measurements of soil respiration from northern forest and tundra soils. This will be addressed by campaign deployments of a state-of-the-art multiplexed automated soil CO2 flux system, comprising 2 x 12 multiplexed automated chambers (developed by Ineson and Heinemeyer, University of York, in collaboration with LiCOR, inc. USA), and a similar single ‘roving’ unit for obtaining good spatial coverage within and at boundaries of vegetation units.

Deliverables
A. Continuous chamber measurements of NEE over multiple diurnal cycles at intervals throughout the active season in mesic tundra and forest, at Abisko;
B. Repeat of A at Kevo, in mesic and wet tundra. (A paper addressing H7 & H3a in Glob. Ch. Biol.).
C. Light response curves of NEE in all key component vegetation types, and across boundaries between vegetation types, at intervals throughout the active season at Abisko. Also ambient measures of evapotranspiration.
D. Repeat of C at Kevo. (A paper addressing H7 in Glob. Ch. Biol.).
E. Fine-scale temporal and spatial measurements of soil respiration from forest and tundra soils at Abisko throughout the active season (H7).
F. Repeat of E at Kevo. (A paper in Biogeochem. addressing H4a).

Tasks
1. Design and source chamber and branch-bag equipment (May-June 2006).
2. Identify suitable study areas (in collaboration with WP4). July 2006.
3. Initial installation of fixed chambers and branch bags (Abisko) July 2006.
4. Branch bag measurements in forest trees; intervals throughout 2006-8.
5. Continuous measurements of NEE by automatic chambers (Abisko, 2006-7; Kevo, 2008).
6. Measurement of NEE (light response curves) during active season, using roving chambers (Abisko, 2006-7; Kevo 2008).
7. Measurement of winter CO₂ fluxes (early and late winter campaigns, Abisko and Kevo, winters of 2006-7, 07-08 and 08-09).
8. Geo-statistical analysis of soil respiration and NEE from deployment of clear chambers (in collaboration with WP6 (Abisko, intervals throughout 2007; Kevo, 2008).
9. Maintaining and downloading logging equipment associated with automatic chambers (intervals throughout the project).