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The main objective of the study was to evaluate inter-annual ring-width variation and cumulative growth of aspen (Populus tremula L.) trees growing on the spots of different soil CO2 concentration at natural mofette site. We hypothesized that growth rate of trees is affected by CO2 concentration within their rooting zone. The study site was situated in the flood plain of Plesná stream near Hartoušov (Western Bohemia). Trees growing in a pure aspen stand were selected according to the CO2-gas regime within their rooting zone. Five high [CO2] trees (10-25% CO2 in the soil) and five low [CO2] trees (up to 3% CO2 in the soil) were sampled. Stem growth analysis of each trunk was carried out to study growth pattern in detail. High and low [CO2] trees significantly differed in a growth rate. At the age of 25 years, the basal area of high [CO2] trees exceeded low [CO2] trees by 39 %. The positive effect of CO2 on annual increment was pronounced particularly in the years with optimal growing conditions. Results suggest that trees can be fertilized not only by elevated atmospheric CO2 but also when fed with CO2 via the roots. [ABSTRACT FROM AUTHOR]

A geogenic CO2 emitting site (mofette U1) at the banks of the Laacher See, Eifel Mountains, was chosen to study the relationship between heavy postvolcanic soil degassing and vegetation during spring season. To test any interrelation between soil CO2 degassing and vegetation, soil chemism (pH, water content, conductivity, and humus content) and vegetation studies (number of species, plant-soil coverage) were performed. Geogenic soil degassing patterns of carbon dioxide and oxygen were clearly inhomogeneous, resembling soil porosity and distinct permeation channels within the soil. CO2 concentrations ranged from zero to 100%. Soil CO2 increased, while soil oxygen decreased with increasing soil depth. There was a reasonable correlation between CO2 degassing and soil pH as well as soil conductivity. Soil organic matter (SOM) resembled soil water distribution. The number of plant species (from a total of 69 species) as well as plant coverage strongly followed geogenic CO2 degassing. The total number of growing species was highest in low CO2 soils (max. 17 species per m2) and lowest at high CO2-emitting sites (one species per m2). Plant coverage followed the same pattern. Total plant coverage reached values of up to 84% in slightly degassing soils and only 5-6% on heavy CO2-venting sites. One plant species proved to be highly mofettophilic (marsh sedge, Carex acutiformis) and strictly grew on CO2 degassing sites. Most other species like grove windflower, spring fumewort, fig buttercup, wood bluegrass, addersmeat, and common snowberry showed a mofettophobic behavior and strictly avoided degassing areas. Specific plant species can thus be used to detect and monitor pre- or postvolcanic CO2 degassing. [ABSTRACT FROM AUTHOR]

Mofette fields, i.e. geogenic, cold CO2-exhaling gas vents occurring naturally in regions of tectonic or volcanic disturbances provide an excellent opportunity to investigate long-term responses of the soil biota to increased CO2 concentrations. The upper centimeters of mofette soils present a small-scale mosaic of different CO2 and O2 concentrations: From up to 100% CO2 and 0% O2 around local degassing vents to ambient soil atmosphere (<2% CO2). The present field study investigated the influence of CO2 on the community structure of Collembola as representatives of the air-filled fraction of the pore system and of Nematoda as inhabitants of soil water films. Canonical correspondence analyses revealed strong correlations between soil faunal communities and environmental measures, above all CO2 concentration, organic matter content and plant coverage. An increase in CO2 concentration was followed by a steady decline in collembolan and nematode species richness and collembolan densities, but below a threshold of 62% CO2 had no significant effect on overall nematode densities. Collembolans developed viable populations at up to 20% CO2, where some mofettophilous species had their highest densities and frequencies, but other more general species also occurred (66% of overall collembolan densities). Nematodes, on the other hand, maintained individual-rich populations at up to 62% CO2, but above 20% CO2 nematode communities consisted almost entirely (97.6%) of three mofettophilous species: one feeding on bacteria, one on fungi and one on plant roots. Likely a combination of active and passive life phases together with temporal and micro-scale changes in environmental conditions allows survival of few mofettophilous species under CO2 conditions too extreme for most other species. The finding that mofettophilous species maintained denser populations in high CO2 patches, with species optima between 3% and 40% CO2, indicates that they even profit from CO2 degassing, presumably via changes in food supply or due to the lack of competitors. [ABSTRACT FROM AUTHOR]