Lignification in beech (Fagus sylvatica) grown at elevated CO2 concentrations: interaction with nutrient availability and leaf maturation.

Beech (Fagus sylvatica L.) seedlings were grown in an ambient or elevated CO2 concentration ([CO2]) either in small stands in microcosms for three to four seasons or individually in pots fertilized at different nutrient supply rates. Leaves at different stages of development, as well as stems and roots at the end of the growing season, were used for analysis of structural biomass and lignin. In elevated [CO2], lignification of leaves was slightly retarded compared with structural biomass production and showed a strong correlation with the activities of ionically, cell-wall-bound peroxidases but not with total soluble peroxidases or covalently wall-bound peroxidases. The effect of elevated [CO2] on lignin concentration of mature tissues was dependent on nutrient supply rate. In leaves and roots, elevated [CO2] increased the lignin concentration in dry mass in N-limited plants. In seedlings grown with high nutrient supply, the lignin concentration in dry mass was unaffected or diminished by elevated [CO2]. Because elevated [CO2] enhanced seedling growth in the high nutrient supply treatments, the total amount of lignin produced per seedling was higher in these treatments. We predict that long-term sequestration of carbon will increase as long as biomass production is stimulated by elevated [CO2] and that tissue quality will change depending on developmental stage and nutrient availability.

Stomatal conductance of forest species after long-term exposure to elevated CO2 concentration: a synthesis.

• Data from 13 long-term (> 1 yr), field-based studies of the effects of elevated CO2 concentration ([CO2 ]) on European forest tree species were analysed using meta-analysis and modelling. Meta-analysis was used to determine mean responses across the data sets, and data were fitted to two commonly used models of stomatal conductance in order to explore response to environmental conditions and the relationship with assimilation. • Meta-analysis indicated a significant decrease (21%) in stomatal conductance in response to growth in elevated [CO2 ] across all studies. The response to [CO2 ] was significantly stronger in young trees than old trees, in deciduous compared to coniferous trees, and in water stressed compared to nutrient stressed trees. No evidence of acclimation of stomatal conductance to elevated [CO2 ] was found. • Fits of data to the first model showed that growth in elevated [CO2 ] did not alter the response of stomatal conductance to vapour pressure deficit, soil water content or atmospheric [CO2 ]. Fits of data to the second model indicated that conductance and assimilation responded in parallel to elevated [CO2 ] except when water was limiting. • Data were compared to a previous meta-analysis and it was found that the response of gs to elevated [CO2 ] was much more consistent in long-term (> 1 yr) studies, emphasising the need for long-term elevated [CO2 ] studies. By interpreting data in terms of models, the synthesis will aid future modelling studies of responses of forest trees to elevated [CO2 ].

Evapotranspiration of beech stands and transpiration of beech leaves subject to atmospheric CO(2) enrichment.

Beech trees (Fagus sylvatica L.) show reduced stomatal conductance and increased leaf area index in response to increased atmospheric CO(2) concentration. To determine whether the reduction in stomatal conductance results in lower stand evapotranspiration, we compared transpiration on a leaf-area basis and stand evapotranspiration on a ground-area basis in young European beech trees growing in greenhouses at ambient (360 +/- 34 micro mol mol(-1)) and elevated (698 +/- 10 micro mol mol(-1)) CO(2) concentrations. Trees were grown in homogenized natural soil at constant soil water supply for two growing seasons. At light saturation, leaf transpiration rates were, on average, 18% lower in the elevated CO(2) treatment than in the ambient CO(2) treatment. Mean transpiration coefficients (transpiration/net CO(2) uptake) of leaves were 179 and 110 in the ambient and elevated CO(2) treatments, respectively, indicating improved water use efficiency in trees in the elevated CO(2) treatment. Total leaf conductance was decreased by 32% at light saturation. The elevated CO(2) treatment resulted in a 14% reduction in stand evapotranspiration. In both CO(2) treatments, evapotranspiration increased linearly at a rate of 0.2 kg H(2)O m(-2) day(-1) for each 1 degrees C rise in air temperature between 14 and 25 degrees C. We conclude that, under Central European conditions, water losses from deciduous forest stands will be reduced by a doubling of tropospheric CO(2) concentration.

Dry matter accumulation, CO2 gas exchanges, and water uptake of plants and plant communities under increased CO2 concentration

effect of long term exposure to elevated CO2 levels on biomass production at 18 herbaceous plant species was studied. The grain yield, CO2 gas exchange, and water uptake on plant communities of Trifolium pratense and festucs prstensis were examined at 340 represent ambient conditions, 450, 600 and 800 ppm atmospheric CO2 concentrations in mini - glasshouses under field conditions. Plant species grown at nearly doubling CO2 differed widely in the response to dry weight accumulation, all species together show an average increase of about 30

dry weight. (AU)