Kristian Rost Albert

Seasonal Variation in Gross Ecosystem Production, Plant Biomass, and Carbon and Nitrogen Pools in Five High Arctic Vegetation Types

Abstract The Arctic is extremely vulnerable to projected climate change, and global warming may result in major community reorganizations. The aim of this study was a thorough investigation of plant biomass production throughout an entire growing season in five different high arctic vegetation types: Cassiope, Dryas, and Salix heath, grassland, and fen. The main focus was on the gross ecosystem production (GEP), and the biotic and abiotic factors which may influence GEP. Photosynthesis, aboveground biomass, and carbon, nitrogen, and chlorophyll content were measured weekly during nine weeks. There were large differences in seasonal growth and production within and among vegetation types. Mosses contributed considerably to the total C and N pool in grassland, fen, and Salix heath. Fen, which had the highest pool of leaf N, leaf chlorophyll, and moss N, was the most productive vegetation type in terms of GEP, despite the lowest total biomass. Across vegetation types, leaf biomass, leaf N, and moss N pool size influenced GEP. Within most vegetation types GEP correlated with leaf N, in correspondence with the notion that N may limit plant production in many high arctic ecosystems. The timing of the peaks in C and N pools in leaves did not coincide with that in the mosses and in woody tissues. This emphasizes the importance of sampling throughout the growing season, when using field data from the Arctic to estimate plant biomasses and modeling C and N fluxes and pool sizes.

Ambient UV-B radiation decreases photosynthesis in high arctic Vaccinium uliginosum

An UV-B-exclusion experiment was established in high arctic Zackenberg, Northeast Greenland, to investigate the possible effects of ambient UV-B on plant performance. During almost a whole growing season, canopy gas exchange and Chl fluorescence were measured on Vaccinium uliginosum (bog blueberry). Leaf area, biomass, carbon, nitrogen and UV-B-absorbing compounds were determined from a late season harvest. Compared with the reduced UV-B treatment, the plants in ambient UV-B were found to have a higher content of UV-B-absorbing compounds, and canopy net photosynthesis was as an average 23% lower during the season. By means of the JIP-test, it was found that the potential of processing light energy through the photosynthetic machinery was slightly reduced in ambient UV-B. This indicates that not only the UV-B effects on PSII may be responsible for some of the observed reduction of photosynthesis but also the effects on other parts of the photosynthetic machinery, e.g. the Calvin cycle, might be important. The 60% reduction of the UV-B irradiance used in this study implies a higher relative change in the UV-B load than many of the supplemental experiments do, but the substantial effect on photosynthesis clearly indicates that V. uliginosum is negatively affected by the current level of UV-B.

Is organic farming a mitigation option? – A study on N2O emission from winter wheat

The objective of the study was to evaluate whether N2O emissions from cropping systems are affected by 1) organic versus conventional farming, 2) proportion of N2-fixing crops in the rotation and 3) use of catch crops.

Ecosystem carbon balance under future climate conditions; the CLIMAITE project carbon synthesis

General information State: Published Organisations: Ecosystems, Biosystems Division, Risø National Laboratory for Sustainable Energy, Biosystems Division. Management, Danish Centre for Environment and Energy, University of Copenhagen Contributors: Linden, L., Beier, C., Mikkelsen, T. N., Holmstrup, M., Schmidt, I., Ambus, P., Pilegaard, K., Albert, K. R., Andresen, L. C., Selsted, M. B., Larsen, K. S., Ibrom, A. Pages: 042021 Publication date: 2009