Foliar physiology of yellow-poplar ( Liriodendron tulipifera L.) exposed to O 3 and elevated CO 2 over five seasons.

Abstract

The chronic effects of ozone (O 3 ) alone or combined with elevated carbon dioxide (CO 2 ) on the foliar physiology of unfertilized field-grown yellowpoplar (Liriodendron tulipifera L.) seedlings were studied from 1992 to 1996. Within open-top chambers, juvenile trees were exposed to the following: charcoal-filtered air (CF); 1 ambient ozone (1XO 3 ); 1.5 ambient ozone (1.5XO 3 ); 1.5 ambient ozone plus 700 ppm carbon dioxide (1.5XO 3 +CO 2 ); or chamberless open-air (OA). Seasonal 24-h mean ambient O 3 concentrations ranged from 32 to 46 ppm over the five seasons. Averaged over 5 years, midseason net photosynthesis at saturating light (A sat ) was reduced by 14% (P=0.029) and stomatal conductance (g s ) was reduced, albeit non-significant, by 13% (P =0.096) in upper canopy foliage exposed to 1.5XO 3 -air relative to CF controls. There were no significant differences over the 5 years in A sat and g s between trees grown in 1XO 3 -and 1.5XO 3 -air. Our results support the hypothesis that the magnitude of O 3 effects on A sat and g s decreases as saplings age. When averaged over the five seasons of exposure, total chlorophyll concentration (chl) was not significantly affected by exposure to elevated O 3 ; however, in 1.5XO 3 +CO 2 -air, foliar chl was reduced by 33% relative to all others (P<0.001). In 1.5XO 3 +CO 2 -air, A sat was 1.4-1.9 times higher (P<0.001) and g s was 0.7 times lower (P=0.022) than all others. O 3 uptake in juvenile trees exposed to elevated O 3 plus elevated CO 2 (1.5XO 3 +CO 2 -air) was most comparable to trees exposed to ambient air (1XO 3 ) throughout the study. These findings suggest that elevated CO 2 may minimize the negative effects of O 3 by reducing O 3 uptake through decreased stomatal conductance.

Importance of changing CO2, temperature, precipitation, and ozone on carbon and water cycles of an upland‐oak forest: incorporating experimental results into model simulations

“…When the O 3 effect is combined with the [CO 2 ] scenario, the O 3 -induced reductions are limited to 2-3% of GPP (calculations not shown). This attenuation of the O 3 response is consistent with experimental observations on a number of hardwood species (Broadmeadow et al, 1999;Karnosky et al, 2003;Rebbeck et al, 2004).…”

Wood properties of two silver birch clones exposed to elevated CO2 and O3

“…In general, increased growth under exposure to elevated CO 2 in most plants is caused by increased photosynthetic rates, individual leaf area, leaf area duration, and water‐use efficiency (Isebrands et al , 2001; Riikonen et al , 2004). O 3 inhibits growth by decreasing stomatal conductance and photosynthesis (Barnes et al , 1995; Kull et al , 1996; Noormets et al , 2001; Rebbeck et al , 2004), the amount and activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) (Oksanen & Saleem, 1999; Noormets et al , 2001), and leaf surface area (Isebrands et al , 2001), and by inducing accelerated senescence of leaves (Kull et al , 1996; Riikonen et al , 2004). Studies of the combined effects of elevated CO 2 and O 3 show variable responses on photosynthesis (Barnes et al , 1995; Kull et al , 1996; Eichelmann et al , 2004; Rebbeck et al , 2004; Riikonen et al , 2005).…”

“…O 3 inhibits growth by decreasing stomatal conductance and photosynthesis (Barnes et al , 1995; Kull et al , 1996; Noormets et al , 2001; Rebbeck et al , 2004), the amount and activity of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) (Oksanen & Saleem, 1999; Noormets et al , 2001), and leaf surface area (Isebrands et al , 2001), and by inducing accelerated senescence of leaves (Kull et al , 1996; Riikonen et al , 2004). Studies of the combined effects of elevated CO 2 and O 3 show variable responses on photosynthesis (Barnes et al , 1995; Kull et al , 1996; Eichelmann et al , 2004; Rebbeck et al , 2004; Riikonen et al , 2005). CO 2 has been reported to ameliorate the adverse effects of O 3 in Betula pendula and Liliodendron tulipifera (Eichelmann et al , 2004; Rebbeck et al , 2004; Riikonen et al , 2004, 2005).…”

Changes in Wood Biomass and Crop Yields in Response to Projected CO2, O3, Nitrogen Deposition, and Climate

“…Conversely, empirical studies using manipulative experiments largely suggest that wood biomass will not increase under the future combination of these forcings. For example, several studies investigating the interactions between elevated O 3 and CO 2 using chambers and FACE technology have found no net change in tree photosynthesis and growth (Karnosky et al, ; Loats & Rebbeck, ; Rebbeck et al, ) and decreases in stem biomass (Karnosky et al, ), results which are supported by a meta‐analysis (Wittig et al, ). While no empirical studies look at the combination of all the forcings considered here, the results of CLM4.5 simulations imply that increases in wood production may not keep pace with increased demand without targeted management strategies.…”