WP2: Soil processes (Leader: Dr P.A. Wookey + Sommerkorn, Ineson, Garnet, Hopkins, Phoenix)
One of the key uncertainties in the interpretation of landscape scale C flux measurements is the contribution of CO2 released from soils to the observed net ecosystem flux (Shaver et al. 1992; Boone et al. 1998; Liski et al. 1999; Hobbie et al. 2000; Reichstein et al. 2000; Fang & Moncrieff 2001; Fang et al. 2005). More generally, it is vital for our understanding of arctic C dynamics to gain insights into the relative contributions of the series of turnover processes contributing to gaseous losses from the ecosystem, over time-scales ranging from minutes to decades and beyond. In northern forest ecosystems the source of the majority of instantaneous C-losses through respiration is from plant biomass (see e.g. Högberg et al. 2002). However, with respect to the vast amounts of C stored in highly organic arctic soils, and their unknown fate with future climate scenarios, losses from SOM pools could be pivotal in arctic biosphere-atmosphere feedbacks (Dioumaeva et al. 2002). Of particular interest in this respect are the dynamics of, and interaction between, both recent organic matter inputs (above- and below-ground litter, and root exudates) and the more recalcitrant SOM pools (including so-called ‘priming effects’ of recent inputs – Kuzyakov et al. 2000), and the factors controlling their turnover times at contrasting landscape positions. Strong coupling between soil nutrient availability and SOM mineralisation (Mack et al., 2004) likely parallels that between LAI and foliar N content in arctic plant communities (see Fig. 1 and H1). Thus, understanding the controls of, and interactions between, SOM mineralisation and plant production is key to understanding the current and future C balance of arctic systems.
A. Data on fine root biomass, C and N contents at communities identified in WP1 at Abisko.
B. Repeat of A at Kevo. (Joint paper with WP1 in Global Change Biology on H1).
C. SOM survey (including 13C NMR determinations of biochemistry), bulk C and N stocks at Abisko, soil moisture measurements. All data georeferenced for use in WP6 analyses.
D. Repeat of C at Kevo. (Paper on Fennoscandian SOM estimates, in Biogeochemistry).
E. Data on the distribution of ‘bomb’ C in soil profiles at Abisko and Kevo (at contrasting landscape positions, in terms of depth distributions in soil profiles, and partitioned in contrasting SOM fractions) (i) to determine the fate of C assimilated over the last 45-50 years, (ii) to quantify the rates of sequestration of C in these soils during the late Holocene, and (iii) to assess the lability of these ‘intermediate’ age SOM fractions in contrasting environmental scenarios. (Papers in Biogeochem. or Eur. J. of Soil Sci. addressing H3b and H5b).
F. Mean residence time of CO2 emitted from the soil surface as a means of quantifying the contribution of older (decades) SOM pools to current soil metabolism. This approach will enable us to identify and interpret any discrepancies between C age of SOM fractions and turnover times as assessed through gaseous losses. (Joint paper addressing H5b (with WP 5) in Nature or Science).
G. Data on the fate of C and N in double-labelled (13C and 15N-enriched) litter at Abisko (including respiration losses) to quantify short- to medium term (months to years) turn-over of SOM, rhizophere ‘priming’ effects and the strength of coupling between C and N cycling.
H. Repeat of G at Kevo. (Papers in Oecol., Soil Biol. and Biochem. addressing H1, H4b & H5a).
I. Data on net CH4 fluxes and their temporal (thaw season) variability at contrasting landscape positions at Abisko (data geo-referenced for use in WP6).
J. Repeat of I at Kevo. (Joint paper with WPs 3 and 5 in Ecosystems, addressing H6).
1. Preparing and testing soil sampling equipment in the UK; planning survey.
2. Survey at Abisko and Kevo (with WP1) of soil and fine root C and N stocks and soil moisture.
3. Production of double-labelled (13C and 15N) litter in growth-room conditions: summer 2006. Placement of material in the field (both Abisko and Kevo), autumn 2006.
4. Soil profile analysis: bomb-C partitioning in contrasting SOM fractions (including aliphatic hydrocarbons as a form of ‘passive-fraction’ C: see Bol et al. (1999), Huang et al. (1999), Gaudinski et al. (2000), and Trumbore (2000)). Profile sampling 2006; preparation and analysis 2006/07 winter.
5. Solid-state 13C NMR analysis of above samples (information on the distribution of 13C between functional groups representative of the major classes of biochemicals involved in decomposition (Sjögersten et al., 2003; Hopkins & Gregorich, 2005)). Preparation and analysis 2006/07 winter.
6. Preparation of equipment for sampling respired CO2, followed by retrieval and AMS analysis of the 12C:13C:14C atom ratios of the CO2 (Bol & Harkness, 1995; Wookey et al., 2002; Hardie et al., submitted). Winter 2006/07.
7. Sampling respired CO2, with subsequent retrieval for AMS analysis. Spatial and seasonal controls of turnover time of soil fractions to be identified by sampling at key periods (spring melt and peak growing season, see H3) across topographic and hydrologic gradients. Abisko 2007, Kevo 2008.
8. Quantifying the incorporation of the 13C and 15N tracers in double enriched litter into SOM fractions with contrasting turnover times, respired CO2 and microbial biomass, as well as uptake of the 15N tracer into plants. Summers of 2007 and 2008 at both sites.
9. Headspace measurements of CH4 fluxes: weekly, during 2007 in Abisko and 2008 in Kevo.