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The polar willow (Salix polaris), predominant in the late successional stage in deglaciated areas of Ny-Alesund, Svalbard, is rarely found in the early stage, when purple saxifrage (Saxifraga oppositifolia) dominates. To elucidate the pattern and the mechanism of successional change from the Saxifraga stage to the Salix stage, we examined the distribution pattern, size structure and habitat conditions of a colonizing Salix population in the seral stage where Salix was invading Saxifraga-dominated sites. The present distribution pattern and aerial photographs taken in the past suggest that Salix colonization at this site commenced within the last 70 years. We found 115 Salix individuals (22 male, 13 female and 80 unknown) in a 30 m ¥ 30 m quadrat on the seral stage. Although the largest individual had a size of 2000 cm2 (length ¥ maximum width), the majority (84%) of individuals were smaller than 100 cm2. The seedling size distribution, as inferred from the leaf scar number, indicated that annual recruitment was slight. Of the individuals observed about 75% had colonized bare ground; only four individuals grew within Saxifraga colonies. No significant difference was found in soil characteristics (water content, and carbon and nitrogen concentrations) between the seral stage and the earlier stage prior to colonization by Salix. These results suggest that difficulties in seed production, germination and/or seedling establishment of Salix, rather than soil formation by preceding species (Saxifraga), limits the early-stage colonization by Salix.

Raised beach deposits are widespread on the north-western coast of Spitsbergen, Svalbard. To elucidate the importance of these deposits in an ecosystem carbon cycle, we measured the concentrations of organic carbon and adenosine 5-triphosphate (ATP; an index of living microbial biomass) in a raised beach deposit found under terrestrial vegetation in Ny-Alesund. A shell in the deposit found at a depth of ca. 20 cm below the ground surface had a (not calibrated) 14C age of 11080 _ 140 yr BP, whereas soil organic carbon in the same deposit showed an older 14C age (22380 _ 90 yr BP). Organic carbon concentration in the layer of 20–40 cm belowground was about 1–2%, which was comparable to those in shallower mineral soil layers. Results of ATP analyses suggested that low but non-negligible amounts of microorganisms existed in the deposit. The proportion of biomass carbon to soil organic carbon tended to decrease with increasing depth, suggesting that organic carbon in the deep layer was less available to microorganisms than that in the shallow layers.

The hypotheses that carbon and nitrogen availability limit microbial activity, and that the key factors limiting microbes vary along the successional gradient were tested in a High Arctic glacier foreland. We examined the responses of the respiration rate and the phospholipid fatty acid content to the addition of carbon and/or nitrogen. Soil samples were collected from the early stage and late stage of primary succession in the foreland of a glacier near Ny-Ålesund, Svalbard. The addition of both carbon (glucose) and nitrogen (ammonium nitrate) engendered an increase in the microbial respiration rate in the early stage of succession. In contrast, the addition of either carbon or nitrogen did not increase the microbial respiration rate. In the late stage of succession the addition of carbon alone, as well as the addition of both carbon and nitrogen, increased the microbial respiration rate. However, neither the addition of carbon nor the addition of nitrogen affected the total phospholipid fatty acid content (an index of microbial biomass) for any soil within 15 days of incubation at 10 ° C. An increase in the respiration rate was therefore attributed to changes in the physiological activities of the microbial community, such as enzymatic activity. Our study suggests that microbial respiration was limited by the low availability of both carbon and nitrogen in the early stage of succession. Thereafter, nitrogen limitation is mitigated.

The fruticose lichen Cetrariella delisei is among the dominant lichen species in the deglaciated High Arctic areas of Svalbard. As part of a study of carbon cycling in the High Arctic, we aimed to estimate the primary production of lichen in a deglaciated area in Ny-Alesund, Svalbard (79° N), by examining the effects of abiotic factors on the net photosynthesis (Pn) and dark respiration (R) rates of C. delisei. Experiments were conducted in the snow-free season of 2000 using an open-fl ow gas exchange system with an infrared gas analyser. Positive photosynthetic activities were observed on rainy days or soon after rainfall when the thallus water content was high, whereas photosynthetic activities dropped below the detectable limit on clear days because of the low thallus water content. Under a suffi ciently high thallus water content and close to light saturation, Pn was nearly constant over a wide temperature range of 4 - 20 °C, while R increased with increasing temperature. We constructed a model for estimating the net primary production (NPP) of lichen based on the relationships between abiotic factors and the CO2 exchange rate. The mean, minimum and maximum NPP values in the snow-free season, estimated using meteorological data obtained from 1995–2003, were 5.1, 1.0 and 8.4 g dry wt. m–2 snow-free season–1, respectively. These results suggest that NPP is highly variable and the contribution of lichen to carbon input is small compared with that of vascular plants and mosses in the study site.

As a part of the study on soil carbon flow in a deglaciated area in Ny-Alesund, Svalbard (79°N), we estimated the contribution of the belowground respiration of vascular plants to total soil respiration in August 1996. Four study sites were set up along a primary successional series, ranging from newly deglaciated moraine to older moraine with well-developed vegetation cover. Respiratory activity of the belowground parts (roots + belowground stems) of three dominant species, Salix polaris, Saxifraga oppositifolia and Luzula confusa, was determined under laboratory conditions. The respiratory activity and the Q10 value of the respiration were higher in S. polaris than in the other two species. Total soil respiration rates measured in the field varied widely. The areas with dense vegetation cover tended to show high respiration rates. Belowground respiration of vascular plants was estimated based on the respiratory activity and biomass of the belowground parts at each study site. The contribution to the belowground respiration to total soil respiration was negligible in the early stages of succession. On the other hand, the respiration of the belowground parts contributed to a significant proportion (?29%) of the total soil respiration in the latter stages of succession.