Net Primary Productivity of a CO 2 -Enriched Deciduous Forest and the Implications for Carbon Storage

Abstract

A central question concerning the response of terrestrial ecosystems to a changing atmosphere is whether increased uptake of carbon in response to increasing atmospheric carbon dioxide concentration results in greater plant biomass and carbon storage or, alternatively, faster cycling of C through the ecosystem. Net primary productivity (NPP) of a closed-canopy Liquidambar styraciflua (sweetgum) forest stand was assessed for three years in a free-air CO 2 -enrichment (FACE) experiment. NPP increased 21% in stands exposed to elevated CO 2 , and there was no loss of response over time. Wood increment increased significantly during the first year of exposure, but subsequently most of the extra C was allocated to production of leaves and fine roots. These pools turn over more rapidly than wood, thereby reducing the potential of the forest stand to sequester additional C in response to atmospheric CO 2 enrichment. Hence, while this experiment provides the first evidence that CO 2 enrichment can increase productivity in a closed-canopy deciduous forest, the implications of this result must be tempered because the increase in productivity resulted in faster cycling of C through the system rather than increased C storage in wood. The fate of the additional C entering the soil system and the environmental interactions that influence allocation need further investigation.

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

“…Processes of down-regulation are often attributed to imbalances between source-sink relationships (Urban et al 2003). However, we did not observe differences in the accumulation of NSC on leaf/needle between CO 2 treatments ( The increase in root biomass in both species at high levels of CO 2 suggests a shift in the allocation of carbon to the root system (Norby et al 2002). This flux could be especially relevant in Norway spruce which showed a significant increase in the concentration of NSC in roots.…”

“…Indeed, we observed a significant correlation between root biomass and NSC concentration for Norway spruce (r = 0.71, P = 0.009), whereas we did not observe this effect in European beech (r = 0.52, P = 0.175). High root NSC concentrations in trees exposed to high levels of CO 2 can be interpreted as an accumulation of substrate available to support the production of fine-roots (Norby et al 2002). However, both species increased their fine root biomass at elevated levels of CO 2 Figure 5 Leaves / needles and roots non-structural carbohydrates concentration (NSC, mg / g) mean values (± S.E) of European beech and Norway spruce per CO 2 treatments, ambient and elevated.…”

Free atmospheric CO<sub>2</sub> enrichment increased above ground biomass but did not affect symbiotic N<sub>2</sub>-fixation and soil carbon dynamics in a mixed deciduous stand in Wales

“…To date, existing experiments have demonstrated that rising atmospheric [CO 2 ] results in increases in net primary production (NPP) and C storage in forest vegetation, e.g. (Calfapietra et al, 2003;DeLucia et al, 1999;Gielen et al, 2005;Hamilton et al, 2002;Handa et al, 2006;Karnosky et al, 2003;Liberloo et al, 2009;Norby et al, 2002). Norby et al (2005) analyzed the response of NPP (g C m −2 y −1 ) to elevated [CO 2 ] in four forest FACE experiments and calculated the following regression NPP elev = 1.18×NPP amb + 55.4 (r 2 = 0.97).…”

Mycorrhizal Hyphal Turnover as a Dominant Process for Carbon Input into Soil Organic Matter

“…Elevated atmospheric CO 2 has been shown to increase rates of photosynthesis and increase productivity (Ceulemans et al, 1999), and in most cases elevated atmospheric CO 2 increases aboveground biomass. However, an increase in belowground biomass greater than the increase in aboveground biomass is often found (Norby et al, 2002;Lukac et al, 2003). To investigate the effects of elevated atmospheric CO 2 on whole ecosystems, Free Air Carbon Dioxide (CO 2 ) Enrichment (FACE) systems have been developed (Hendrey et al, 1999;Miglietta et al, 2001).…”