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Notizen: Mass loss, together with nitrogen and carbon loss, from above-ground material and roots of Festuca vivipara were followed for 13 months in a high Arctic polar semi-desert and a low Arctic tree-line dwarf shrub heath. Festuca vivipara for the study was obtained from plants cultivated at two different CO2 concentrations (350 and 500 μL L–1) in controlled environment chambers in the UK. Each of the four resource types (shoots or roots from plants grown in elevated or ambient CO2 concentrations) was subsequently placed in an experiment simulating aspects of environmental change in each Arctic ecosystem. Air, litter and soil temperatures were increased using open-topped polythene tents at both sites, and a 58% increase in summer precipitation was simulated at the high Arctic site.Mass loss was greatest at the low Arctic site, and from the shoot material, rather than the roots. Shoots grown under an elevated CO2 concentration decomposed more slowly at the high Arctic site, and more quickly at the low Arctic one, than shoots grown at ambient CO2. After 13 months, greater amounts of C and N remained in above-ground litter from plants grown under elevated, rather than ambient, CO2 at the polar semi-desert site, although lower amounts of C remained in elevated CO2 litter at the low Arctic ecosystem. In the high Arctic, roots grown in the 500 μL L–1 CO2 concentration decomposed significantly more slowly than below-ground material derived from the ambient CO2 chambers. Elevated CO2 concentrations significantly increased the inital C:N ratio, % soluble carbohydrates and α-cellulose content, and significantly decreased the inital N content, of the above-ground material compared to that derived from the ambient treatment. Initially, the C:N ratio and percentage N were similar in both sets of roots derived from the two different CO2 treatments, but soluble carbohydrate and α-cellulose concentrations were higher, and percentage lignin lower, in the elevated CO2 treatments.The tent treatments significantly retarded shoot decomposition in both ecosystems, probably because of lower litter bag moisture contents, although the additional precipitation treatment had no effect on mass loss from the above-ground material. The results suggest that neither additional summer precipitation (up to 58%), nor soil temperature increase of 1 °C, which may occur by the end of the next century as an effect of a predicted 4 °C rise in air temperature, had an appreciable effect on root decomposition in the short term in a high Arctic soil. However, at the low Arctic site, greater root decomposition, and a lower pool of root N remaining, were observed where soil temperature was increased by 2 °C in response to a 4 °C rise in air temperature. These results suggest that decomposition below-ground in this ecosystem would increase as an effect of predicted climate change. These data also show that there is a difference in the initial results of decomposition processes between the two Arctic ecosystems in response to simulated environmental change.

Notizen: Long-term ecosystem-level experiments, in which the environment is manipulated in a controlled manner, are important tools to predict the responses of ecosystem functioning and composition to future global change. We present the results of a meta-analysis performed on the results of long-term ecosystem-level experiments near Toolik Lake, Alaska, and Abisko, Sweden. We quantified aboveground biomass responses of different arctic and subarctic ecosystems to experimental fertilization, warming and shading. We not only analysed the general patterns but also the differences in responsiveness between sites and regions. Aboveground plant biomass showed a broad similarity of responses in both locations, and also showed some important differences. In both locations, aboveground plant biomass, particularly the biomass of deciduous and graminoid plants, responded most strongly to nutrient addition. The biomass of mosses and lichens decreased in both locations as the biomass of vascular plants increased. An important difference between the two regions was the smaller positive aboveground biomass response of deciduous shrubs in Abisko as compared with Toolik Lake. Whereas in Toolik Lake Betula nana increased its dominance and replaced many of the other plant types, in Abisko all vascular plant types increased in abundance without major shifts in relative abundance. The differences between the responses of the dominant vegetation types of the Toolik Lake region, i.e. tussock tundra systems, and that of the Abisko region, i.e. heath systems, may have important implications for ecosystem development under expected patterns of global change. However, there were also large site-specific differences within each region. Several potential mechanistic explanations for the differences between sites and regions are discussed. The response patterns show the need for analyses of joint data sets from many regions and sites, in order to uncover common responses to changes in climate across large arctic regions from regional or local responses.

Notizen: Summary Growth of the broad-leaved graminoid Milium effusum, occurring in shady deciduous forests, was matched with periods of high light influx through the tree canopy in spring and autumn. Fertile shoots grew faster than sterile shoots. Leaves on flowering shoots were fully developed when the budbreak started on the trees, whereas nonflowering shoots had fully developed leaves when the tree canopy closed. Leaf concentrations of N and P were high (6.1 and 0.74% respectively) in spring but decreased as the leaves expanded. Maximum pool sizes of N and P in whole tillers were reached about one month after the onset of spring growth, whereas maximum spring pools of K, Mg, and Ca were timed with peak biomass about one month later. The leaves lost nutrients during summer when no growth took place. Since leaching losses were negligible, nutrients were probably allocated from the leaves to support root growth. Autumn reallocation to winter stores was low. The pattern of growth and nutrient use suggests that light availability, i.e., the resource in relatively lowest supply, regulates the investment of the resource in highest supply, i.e., nutrients. This is consistent with previously reported observations on Eriophorum vaginatum, a graminoid of low nutrient — high light environments. This species utilizes nutrients efficiently at the expense of less efficient acquisition of carbon. We suggest that selection for efficient utilization of the resource in lowest relative supply has been a strong driving force behind the physiological adaptation of both species to their environments.