Elevated CO2 increases biomass and tuber yield in potato even at high ozone concentrations.

• Changes in the growth and yield of field-grown potato (Solanum tuberosum cv. Bintje) induced by season-long elevated CO2 and/or ozone concentrations are reported. • Open-top chambers and unchambered field plots were used to examine crop responses to three CO2 (ambient, 550 and 680 µmol mol-1 ) and two ozone (ambient and 65 nmol mol-1 , 8 h d-1 seasonal mean) treatments applied throughout the 105 d growing season. • Elevated CO2 increased both above- and below-ground biomass at intermediate and final harvests. Tuber yield at final harvest was increased by c. 40% due to an increase in mean tuber weight rather than tuber number; tuber yield did not differ significantly between the 550 and 680 µmol mol-1 CO2 treatments. Elevated ozone had no significant effect on growth or yield except for the largest size category of tubers, despite extensive visible foliar injury. Significant CO2  × ozone interactions were detected only for senescent leaf number and green leaf ratio. • Elevated CO2 increases biomass and tuber yield in S. tuberosum cv. Bintje even at high ozone concentrations; these findings are discussed in relation to predicted future atmospheric changes.

Does elevated CO2 ameliorate the impact of O3 on chlorophyll content and photosynthesis in potato (Solanum tuberosum)?

This study examined the impact of season-long exposure to elevated carbon dioxide (CO2) and ozone (O3), individually and in combination, on leaf chlorophyll content and gas exchange characteristics in potato (Solanum tuberosum L. cv. Bintje). Plants grown in open-top chambers were exposed to three CO2 (ambient, 550 and 680 µmol mol-1) and two O3 treatments (ambient and elevated; 25 and 65 nmol mol-1, 8 h day-1 means, respectively) between crop emergence and maturity; plants were also grown in unchambered field plots. Non-destructive measurements of chlorophyll content and visible foliar injury were made for all treatments at 2-week intervals between 43 and 95 days after emergence. Gas exchange measurements were made for all except the intermediate 550 µmol mol-1 CO2 treatment. Season-long exposure to elevated O3 under ambient CO2 reduced chlorophyll content and induced extensive visible foliar damage, but had little effect on net assimilation rate or stomatal conductance. Elevated CO2 had no significant effect on chlorophyll content, but greatly reduced the damaging impact of O3 on chlorophyll content and visible foliar damage. Light-saturated assimilation rates for leaves grown under elevated CO2 were consistently lower when measured under either elevated or ambient CO2 than in equivalent leaves grown under ambient CO2. Analysis of CO2 response curves revealed that CO2-saturated assimilation rate, maximum rates of carboxylation and electron transport and respiration decreased with time. CO2-saturated assimilation rate was reduced by elevated O3 during the early stages of the season, while respiration was significantly greater under elevated CO2 as the crop approached maturity. The physiological origins of these responses and their implications for the performance of potato in a changing climate are discussed.

Impact of elevated CO(2) and O(3) on gas exchange parameters and epidermal characteristics in potato (Solanum tuberosum L.).

Potato plants (Solanum tuberosum L. cv. Bintje) were grown in open-top chambers (OTCs) under three CO(2) levels (ambient and 24 h d(-1) seasonal mean concentrations of 550 and 680 micromol mol(-1)) and two O(3) levels (ambient and a seasonal mean 8 h d(-1) concentration of 50 nmol mol(-1)). The objectives were to determine the effects of season-long exposure to these key climate change gases on gas exchange, leaf thickness and epidermal characteristics. The experimental design also provided an ideal opportunity to examine within-leaf variation in epidermal characteristics at the whole-leaf level. Stomatal and epidermal cell density and stomatal index were measured at specific locations on the youngest fully expanded leaf (centre of lamina, mid-way between tip and base) and representative whole leaves from each treatment. Effects on leaf conductance, assimilation rate and instantaneous transpiration efficiency were determined by infrared gas analysis, while anatomical characteristics were examined using a combination of leaf impressions and thin sections. Exposure to elevated CO(2) or O(3) generally increased leaf thickness, leaf area, stomatal density, and assimilation rate, but reduced leaf conductance. The irregular stomatal distribution within leaves resulted from a combination of uneven differentiation and expansion of the epidermal cells. The results are discussed with reference to sampling protocols and the need to account for within-leaf variation when examining the impact of climate change or other environmental factors on epidermal characteristics.