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Arctic Biosphere Atmosphere Coupling at Multiple Scales

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Hypothesis 5: Litter and soil organic matter

The dynamics of litter and soil C are complicated by the range of ages and reactivities found in their constituents (Schimel & Mikan 2005). Recent additions of plant detritus are rapidly metabolised (Wookey et al. 2002). Given the strong LAI-TFN relations noted above, we expect a strong coupling between rates of litter decomposition, net primary productivity (NPP), and TFN.

H5a. Litter decomposition is strongly coupled to rates of plant nutrient uptake.

The soil also contains humic compounds of great age that turn over only slowly, but these turnover rates may be sensitive to changing climate (Mack et al., 2004). If current SOM stocks are in equilibrium with current climate, then residence times of soil C will be short.

H5b. Mean arctic SOM residence time is short, <5 years.

If H5b is disproved, then older C is being metabolised. WP2 will quantify the distribution of ‘bomb’§ 14C in soil profiles, and the 12C:13C:14C atom ratios of respired CO2 in the field (by Accelerator Mass Spectrometry, AMS dating), to determine the turnover of SOM of contrasting age (H5b). Intermediate rates of SOM turnover (litter inputs), and the implications for N mineralization, will be quantified by following the fate of double-labelled (13C and 15N) litter (H5a). WP7 will test how modelling of litter and SOM turnover, parametrized from measured fluxes, compares with isotopic estimates.

Outcome: Improved modelling of SOM and litter dynamics.

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Last modified: 26 Jan, 2006
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