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Arctic Biosphere Atmosphere Coupling at Multiple Scales

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Hypothesis 1: Plant-soil interactions

Much research has been invested in understanding the activities of individual components of the ecosystem (e.g. incubating soil cores, monitoring individual plants). However, the feedbacks between soil and plant, and interactions among the plant species that comprise the community, are critical to understanding processes. For instance, there is a tight coupling between leaf area index (LAI) and total foliar nitrogen (TFN) in arctic plant communities, though not for individual component species, with similar emergent relationships in both Alaska and Sweden (Van Wijk et al., 2005)(see figure below).

Our models suggest that this allocation pattern maximizes C uptake per unit foliar N (Williams & Rastetter, 1999). If this is the case, we suggest there must be an optimization of plant allocation between components for C sequestration (foliage) and nitrogen (N) uptake (fine roots). We also expect a strong connection between LAI-TFN on the one hand and soil fertility and SOM on the other.

H1: Productive ecosystems in fertile sites (high available N) allocate relatively fewer resources to nutrient uptake, so fine root:foliage ratios are negatively correlated with LAI.

Work-packages (WP) 1 and 2 will test this hypothesis by direct measurements of C and N in foliage, roots and soils at a range of sites, and will determine uptake and turnover through isotopic tracer experiments. Outcome: If confirmed, this hypothesis provides a link between above and below ground C stocks, and so airborne/satellite characterization of LAI can also provide estimates of fine root C. A strength of this analysis is that even a weak relationship will prove valuable, as long as confidence intervals are well characterized. Further quantifying allocation will improve model parametrization.

proposalfig2.jpg

Figure legend: Relationships between total foliar N and LAI for both Alaska and northern Sweden; each point represents the results of a 20 x 20 cm quadrat harvest, (Van Wijk et al., 2005).

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Last modified: 26 Jan, 2006
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