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], [O-3] 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 gown in 14 dm(3) 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 mu mol mol(-1)) [CO2] in combination with either charcoal-filtered air (CF) or non-filtered air plus 1.5 times ambient [O-3], 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 [O-3] and ambient [CO2] compared with CF controls, although the elevated [O-3] 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 [O-3] in ambient [CO2], but the difference was much reduced by elevated [CO2]. On a TNC-free basis, however, elevated [O-3] 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 [O-3] of LMPA and starch was largely prevented by elevated [CO2], and that interpretation of [CO2] and [O-3] 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 [O-3] on secondary metabolites differed in this respect.