Influence of carbon dioxide enrichment, ozone and nitrogen fertilization on cotton (Gossypium hirsutumL.) leaf and root composition

Abstract

ABSTRACTThe 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 hirsutumL.) leaves and roots. Cotton was grown in 14 dm3pots 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+350μmol 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.