This research will improve understanding of the broad patterns of vegetation function across the Arctic through research on the relationships among arctic vegetation canopy structure, N allocation, and whole-system CO2 fluxes, and ecosystem respiration and its main components, plant and soil respiration. The research is part of a search for the general characteristics of vegetation function, resource allocation, and allometry that can be used to develop large-scale, long-term predictions of vegetation and ecosystem properties and of the role of arctic ecosystems in the arctic system.
Sites planned for research include Toolik Lake and Barrow, Alaska; Cherskii, Siberia; Thule, Greenland; and perhaps sites in northern Canada. Field research at each site will include measurements of the light response of CO2 flux in diverse vegetation (Net Ecosystem Exchange, NEE; Gross Primary Production, GPP; Ecosystem Respiration, RE; Autotrophic Respiration, RA, Heterotrophic Respiration, RH). The vegetation and soil variables to be evaluated--canopy photosynthetic area and its N content, NDVI, soil C and N content, and microclimatic variables like canopy air and soil temperatures--are all key components of regulation of the feedbacks and interactions between the terrestrial landscape and the cycles of energy, water, and elements in the arctic system. The core hypotheses to be tested are:
1. Over the entire arctic region, canopy N content will be a better overall predictor of NEE and GPP than leaf area because leaf N concentrations will increase in higher, colder latitudes, leading to higher GPP per unit leaf area with latitude but similar GPP per unit leaf N.
2. In the long term RE, RA, and RH must all be related to GPP and its controls because GPP determines the total C inputs to the ecosystem. In the short term, RA, and RH will respond differently to environmental variation: RA will be most closely correlated with relatively rapid changes in air temperature while RH will change more slowly and in correlation with more slowly-changing variables like soil temperature and moisture
In addition to empirical analysis of results, modeling of NPP, GPP, and RE will test our ability to extrapolate from one site to another within the Arctic and will help to determine whether a single model parameterization can be developed for the entire Arctic. A key product will be a data base for modeling and extrapolation of vegetation properties and CO2 fluxes across the arctic region.
