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Schönenbuch, Switzerland

Braun S.,Institute for Applied Plant Biology | Schindler C.,Swiss Tropical and Public Health Institute | Rihm B.,Meteotest
Environmental Pollution | Year: 2014

The estimate of growth losses by ozone exposure of forest trees is a significant part in current C sequestration calculations and will also be important in future modeling. It is therefore important to know if the relationship between ozone flux and growth reduction of young trees, used to derive a Critical Level for ozone, is also valid for mature trees. Epidemiological analysis of stem increment data from Fagus sylvatica L. and Picea abies Karst. observed in Swiss forest plots was used to test this hypothesis. The results confirm the validity of the flux-response relationship at least for beech and therefore enable estimating forest growth losses by ozone on a country-wide scale. For Switzerland, these estimates amount to 19.5% growth reduction for deciduous forests, 6.6% for coniferous forests and 11.0% for all forested areas based on annual ozone stomatal uptake during the time period 1991-2011. © 2014 Elsevier Ltd. All rights reserved.

Urban J.,Mendel University in Brno | Bequet R.,University of Antwerp | Mainiero R.,Institute for Applied Plant Biology
Journal of Experimental Botany | Year: 2011

Several electrical methods have been introduced as non-invasive techniques to overcome the limited accessibility to root systems. Among them, the earth impedance method (EIM) represents the most recent development. Applying an electrical field between a cormus and the rooted soil, the EIM measures the absorptive root surface area (ARSA) from grounding resistance patterns. Allometric relationships suggested that this method was a valuable tool. Crucial assumptions for the applicability of the EIM, however, have not been tested experimentally. Focusing on tree root systems, the present study assesses the applicability of the EIM. Six hypotheses, deduced from the EIM approach, were tested in several experiments and the results were compared with conventional methods. None of the hypotheses could be verified and the results allow two major conclusions. First, in terms of an analogue electrical circuit, a tree-root-soil continuum appears as a serial circuit with xylem and soil resistance being the dominant components. Allometric variation in contact resistance, with the latter being the proxy for root surface area, are thus overruled by the spatial and seasonal variation of soil and xylem resistances. Second, in a tree-root-soil continuum, distal roots conduct only a negligible portion of the electric charge. Most of charge carriers leave the root system in the proximal parts of the root-soil interface. © 2010 The Author(s).

Braun S.,Institute for Applied Plant Biology | Schindler C.,Swiss Tropical and Public Health Institute | Leuzinger S.,ETH Zurich
Environmental Pollution | Year: 2010

For a quantitative estimate of the ozone effect on vegetation reliable models for ozone uptake through the stomata are needed. Because of the analogy of ozone uptake and transpiration it is possible to utilize measurements of water loss such as sap flow for quantification of ozone uptake. This technique was applied in three beech (Fagus sylvatica) stands in Switzerland. A canopy conductance was calculated from sap flow velocity and normalized to values between 0 and 1. It represents mainly stomatal conductance as the boundary layer resistance in forests is usually small. Based on this relative conductance, stomatal functions to describe the dependence on light, temperature, vapour pressure deficit and soil moisture were derived using multivariate nonlinear regression. These functions were validated by comparison with conductance values directly estimated from sap flow. The results corroborate the current flux parameterization for beech used in the DO3SE model. © 2010 Elsevier Ltd. All rights reserved.

Mills G.,UK Center for Ecology and Hydrology | Pleijel H.,Gothenburg University | Braun S.,Institute for Applied Plant Biology | Buker P.,University of York | And 11 more authors.
Atmospheric Environment | Year: 2011

The critical levels for ozone effects on vegetation have been reviewed and revised by the LRTAP Convention. Eight new or revised critical levels based on the accumulated stomatal flux of ozone (PODY, the Phytotoxic Ozone Dose above a threshold flux of Y nmol m-2 PLA s-1, where PLA is the projected leaf area) have been agreed. For each receptor, data were combined from experiments conducted under naturally fluctuating environmental conditions in 2-4 countries, resulting in linear dose-response relationships with response variables specific to each receptor (r2 = 0.49-0.87, p < 0.001 for all). For crops, critical levels were derived for effects on wheat (grain yield, grain mass, and protein yield), potato (tuber yield) and tomato (fruit yield). For forest trees, critical levels were derived for effects on changes in annual increment in whole tree biomass for beech and birch, and Norway spruce. For (semi-)natural vegetation, the critical level for effects on productive and high conservation value perennial grasslands was based on effects on important component species of the genus Trifolium (clover species). These critical levels can be used to assess protection against the damaging effects of ozone on food security, important ecosystem services provided by forest trees (roundwood production, C sequestration, soil stability and flood prevention) and the vitality of pasture. © 2011 Elsevier Ltd.

Mainiero R.,Institute for Applied Plant Biology | Kazda M.,University of Ulm | Schmid I.,University of Ulm
European Journal of Forest Research | Year: 2010

Fine root dynamics in mono-specific stands of mature Fagus sylvatica L. and Picea abies Karst. was studied from December 2003 to December 2004 in a stand in Southern Germany. Minirhizotrons were used to draw between species comparisons concerning fine root (≤1 mm) longevity and temporal patterns of fine root dynamics (growth and mortality) as related to seasonal changes in soil water content and soil temperature. In F. sylvatica, median fine root longevity from early seasonal to late-seasonal cohorts was low (77 days). Fine root dynamics scaled positively with seasonal changes in soil water and temperature indicating accelerated fine root turnover during favourable soil conditions. In contrast, fine root longevity in P. abies (273 days) was significantly higher when compared to F. sylvatica and increased from early seasonal to late-seasonal cohorts. Fine root dynamics in P. abies did not correlate with soil environmental conditions. Rather a large proportion of new fine roots occurred during the dry season in superficial soil layers. The data suggest species inherent patterns of fine root longevity and temporal patterns of fine root dynamics. © 2010 Springer-Verlag.

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