Effect of microrelief and vegetation on methane emission from wet polygonal tundra, Lena Delta, Northern Siberia

The effect of microrelief and vegetation on methane (CH₄) emission was investigated in a wet polygonal tundra of the Lena Delta, Northern Siberia (72.37N, 126.47E). Total and plant-mediated CH₄ fluxes were measured by closed-chamber techniques at two typical sites within a low-centred polygon. During the study period, total CH₄ flux averaged 28.0±5.4mgm^–2d^–1 in the depressed polygon centre and only 4.3±0.8mgm^–2d^–1 at the elevated polygon rim. This substantial small-scale spatial variability of CH₄ emission was caused by strong differences of hydrologic conditions within the microrelief of the polygon, which affected aeration status and organic matter content of the soils as well as the vegetation cover. Beside water table position, the vegetation cover was a major factor controlling CH₄ emission from polygonal tundra. It was shown that the dominant vascular plant of the study area, Carex aquatilis, possesses large aerenchyma, which serve as pathways for substantial plant-mediated CH₄ transport. The importance of plant-mediated CH₄ flux was strongly influenced by the position of the water table relative to the main root horizon. Plant-mediated CH₄ transport accounted for about two-thirds of the total flux in the wet polygon centre and for less than one-third of the total flux at the moist polygon rim. A clipping experiment and microscopic-anatomical studies suggested that plant-mediated CH₄ transport via C. aquatilis plants is driven only by diffusion and is limited by the high diffusion resistance of the dense root exodermes.     

Effects of microrelief on species distribution and phytomass variations in a Caricetum curvulae stand

Structure and productivity of a Primulo-Caricetum curvulae on the S slope of the Hohe Tauern range (Austrian Central Alps) were studied in the course of the Austrian MAB-6-Programme. The study site showed no distinct relief, and its vegetational cover, rich in lichens, is characteristic of large areas of the region. The vegetational pattern and the snow melting figures of the site were mapped 1:200. The maps as well as the phytomass yields revealed clear correlations between snow cover and distribution of phanerogamic species. Even a few days's difference in the time of snow melting caused a significant separation of species with different environmental claims. Rosette plants, including some Nardetalia species, prefer snow cover in winter and a humid and relatively favourable microclimate in summer, whereas the bunch grasses dominated on windswept ridges with shallow soils. Carex curvula was distributed very homogeneously all over the study site.A surprising result concerns the phytomass distribution of the lichens: Although the degree of cover of Cetraria and Cladonia species seemed to be higher on ridges with open cover of phanerogams, their phytomass store was positively higher at sites with good snow shelter in winter.Names of phanerogams follow Ehrendorfer (1973), names of archegoniatae follow Gams (1973).This paper is dedicated to Professor Dr. Erich Hübl, Institute of Botany, University of Agriculture, Vienna, for whose broad-minded help and advice I am very grateful. Further, I want to express my gratitude to all those who contributed to the success of this project. It was part of the Austrian MAB-6-Programme and was supported financially by the Fonds zur Förderung der wissenschaftlichen Forschung in Österreich.