Four-year growth dynamics of beech-spruce model ecosystems under CO2 enrichment on two different forest soils

Abstract

To elucidate how atmospheric CO 2 enrichment, enhanced nutrient supply and soil quality interact to affect regrowth of temperate forests, young Fagus sylvatica and Picea abies trees were grown together in large model ecosystems. Identical communities were established on a nutrient-poor acidic and on a more fertile calcareous soil and tree growth, leaf area index, fine root density and soil respiration monitored over four complete growing seasons. Biomass responses to CO 2 enrichment and enhanced N supply at the end of the experiment reflected compound interest effects of growth stimulation during the first two to three seasons rather than persistent stimulation over the whole duration of the experiment. Whereas biomass of Picea was enhanced in elevated CO 2 on both soils, Fagus responded negatively to CO 2 on acidic but positively on calcareous soil. Biomass of both species profited from enhanced N supply on the poor acidic soil only. Leaf area index on both soils was greater in high N supply as a consequence of a stimulation early in the experiment, but was unaffected by CO 2 enrichment. Fine root density on acidic soil was increased in high N supply, but this did not stimulate soil respiration rate. In contrast, elevated CO 2 stimulated both fine root density and soil CO 2 efflux on calcareous soil, especially towards the end of the experiment. Our experiment suggests that future species dominance in beech-spruce forests is likely to change in response to CO 2 enrichment, but this response is subject to complex interactions with environmental factors other than CO 2 , particularly soil type.

Potential risks for European beech (Fagus sylvatica L.) in a changing climate

“…the repression of competing species by intense shading-which might result in a loss of dominance of beech at least on acidic soils. Belowground, increased atmospheric CO 2 concentrations stimulated fine-root growth especially under N limiting conditions ( Medlyn et al 2001;Dyckmans and Flessa 2002;Forstreuter 2002;Spinnler et al 2002). This increase in belowground biomass of beech may, in part, compensate for the loss of competitive ability aboveground (Leuschner et al 2001;Schmidt and Kazda 2001) especially at N-limited sites.…”

“…Specifically, soil properties seem to play an important role in modifying CO 2 effects: Growth of beech was increased at elevated atmospheric CO 2 concentrations when growing in competition with spruce on a basic calcareous substrate. However, growth inhibition relative to spruce occurred on acidic substrate (Spinnler et al 2002;Kozovits et al 2005a,b). Constraints on growth proceeded in beech when competing with spruce under exposure to elevated CO 2 for more than 2 years (Kozovits et al 2005a,b).…”

Response of Fagus sylvatica and Picea abies to the interactive effect of neighbor identity and enhanced CO2 levels

“…By contrast, European beech showed a significant reduction in root length density and no effect on average diameter between both treatments. Results of European beech outcompeting Norway spruce have only been shown in nutrient rich calcareous soils (Spinnler et al 2002). Interestingly, the soils of our studied zone are mostly acidic (pH ~ 4) suggesting that other factors may play a major role in determining the direction of this interspecific interaction.…”

“…At the sapling stage, Norway spruce can benefit from high CO 2 levels and outcompete European beech (Kozovits et al 2005). But, the combined effect of CO 2 levels and other environmental factors, especially soil resources, can also mediate interspecific relations leading, for instance, to European beech to benefit from high CO 2 levels and outcompete Norway spruce under certain circumstances (Spinnler et al 2002). Early differences in growth or morphology between both species can determine their performance at the adult stage where differences in crown structure or in the efficiency to occupy space per structural cost can likely affect the resilience of the stand to disturbances (Reiter et al 2005;Pretzsch 2014).…”

Effects of environmental changes on the vitality of forest stands

“…Competition between plants can also play a major role for growth and vitality (e.g. McDonald et al 2002;Spinnler et al 2002;Derner et al 2003). Many direct effects of individual environmental influences on the growth of forests, such as defoliation by insects (Armour et al 2003), plant nutrition and soil acidity (Demchik and Sharpe 2000) or ozone (Barbo et al 2002) have already been described.…”