Influence of carbon dioxide enrichment, ozone and nitrogen fertilization on cotton (Gossypium hirsutum L.) leaf and root composition
The objective of this study was to test whether elevated [CO2], [O3] and nitrogen (N) fertility altered leaf mass per area (LMPA), non-structural carbohydrate (TNC), N, lignin (LTGA) and proanthocyanidin (PA) concentrations in cotton (Gossypium hirsutum L.) leaves and roots. Cotton was grown in 14 dm3 pots with either sufficient (0·8 g N dm−3) or deficient (0·4 and 0·2 g N dm−3) N fertilization, and treated in open-top chambers with either ambient or elevated (+ 175 and + 350 μmol mol−1) [CO2] in combination with either charcoal-filtered air (CF) or non-filtered air plus 1·5 times ambient [O3]. At about 50 d after planting, LMPA, starch and PA concentrations in canopy leaves were as much as 51–72% higher in plants treated with elevated [CO2] compared with plants treated with ambient [CO2], whereas leaf N concentration was 29% lower in elevated [CO2]-treated plants compared with controls. None of the treatments had a major effect on LTGA concentrations on a TNC-free mass basis. LMPA and starch levels were up to 48% lower in plants treated with elevated [O3] and ambient [CO2] compared with CF controls, although the elevated [O3] effect was diminished when plants were treated concurrently with elevated [CO2]. On a total mass basis, leaf N and PA concentrations were higher in samples treated with elevated [O3] in ambient [CO2], but the difference was much reduced by elevated [CO2]. On a TNC-free basis, however, elevated [O3] had little effect on tissue N and PA concentrations. Fertilization treatments resulted in higher PA and lower N concentrations in tissues from the deficient N fertility treatments. The experiment showed that suppression by elevated [O3] of LMPA and starch was largely prevented by elevated [CO2], and that interpretation of [CO2] and [O3] effects should include comparisons on a TNC-free basis. Overall, the experiment indicated that allocation to starch and PA may be related to how environmental factors affect source–sink relationships in plants, although the effects of elevated [O3] on secondary metabolites differed in this respect.