Effects of temperature on growth and wood anatomy were studied in young European beech (Fagus sylvatica L.) grown in 7-l pots for 2.5 years in field-phytotron chambers supplied with an ambient (approximately 400 micromol mol-1) or elevated (approximately 700 micromol mol-1) carbon dioxide concentration ([CO2]). Temperatures in the chambers ranged in increments of 2 degrees C from -4 degrees C to +4 degrees C relative to the long-term mean monthly (day and night) air temperature in Berlin-Dahlem. Soil was not fertilized and soil water and air humidity were kept constant. Data were evaluated by regression analysis. At final harvest, stem diameter was significantly greater at increased temperature (Delta1 degrees C: 2.4%), stems were taller (Delta1 degrees C: 8.5%) and stem mass tree-1 (Delta1 degrees C: 10.9%) and leaf area tree-1(Delta1 degrees C: 6.5%) were greater. Allocation pattern was slightly influenced by temperature: leaf mass ratio and leaf area ratio decreased with increasing temperature (Delta1 degrees C: 2.3% and 2.2% respectively), whereas stem mass/total mass increased (Delta1 degrees C: 2.1%). Elevated [CO2] enhanced height growth by 8.8% and decreased coarse root mass/total mass by 10.3% and root/shoot ratio by 11.7%. Additional carbon was mainly invested in aboveground growth. At final harvest a synergistic interaction between elevated [CO2] and temperature yielded trees that were 3.2% taller at -4 degrees C and 12.7% taller at +4 degrees C than trees in ambient [CO2]. After 2.5 seasons, cross-sectional area of the oldest stem part was approximately 32% greater in the +4 degrees C treatment than in the -4 degrees C treatment, and in the last year approximately 67% more leaf area/unit tree ring area was produced in the highest temperature regime compared with the lowest. Elevated [CO2] decreased mean vessel area of the 120 largest vessels per mm2 by 5.8%, causing a decrease in water conducting capacity. There was a positive interaction between temperature and elevated [CO2] for relative vessel area, which was approximately 38% higher at +4 degrees C than at -4 degrees C in elevated [CO2] compared with ambient [CO2]. Overall, temperature had a greater effect on growth than [CO2], but elevated [CO2] caused quantitative changes in wood anatomy.

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Fig. 1. Field mini-greenhouses climatized according to outside conditions for the purpose of C O 2 enrichment studies (with open control plots in front; photo by M. Forstrreuter). AbstractThe CO2 enrichment effects (300-650 #mol mol-1) on mineral concentration (N, P, K, Ca, Mg, Mn, Fe, Zn), absolute total mineral contents per individual and of whole stands of four herbaceous (Trifolium repens L., Trifolium pratense L., Lolium perenne L., Festuca pratensis HUDS.) and two woody species (Acer pseudo-platanus L., Fagus sylvatica L.) were investigated.In general, the mineral concentration of the plant tissues decreased (all six species: N > C a > K > Mg) with the exception of P. Mn and Fe were only determined for the tree species. Both decreased in concentration (Mn > Fe). Zn was only analysed for Trifolium pratense and Festuca pratensis and decreased significantly in the grass.Despite of decreases in concentrations of as much as 20 ~o in some cases there were increases in absolute amounts per individual and, therefore, in the whole vegetation up to 25 ~o because of the enhanced dry matter accumulation at elevated CO2 supply.

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.

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