Estimation of the annual primary production of the lichen

The fruticose lichen Cetrariella delisei is among the dominant lichen spe-cies 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 pro-duction of lichen in a deglaciated area in Ny-Ålesund, 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 con-tent was high, whereas photosynthetic activities dropped below the detect-able 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 esti-mating the net primary production (NPP) of lichen based on the relation-ships between abiotic factors and the CO2 exchange rate. The mean, mini-mum 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