Response of soluble sugars and starch in field-grown cotton to ozone, water stress, and their combination

Abstract

Ozone (O 3) stress is known to reduce the growth and yield of a number of crops, and water stress can modify the extent of these effects. Both O 3 and water stress alter the carbohydrate status of plants. Little is known, however, concerning O 3 effects on carbohydrate pools of field-grown plants and whether water stress will modify the carbohydrate response to O 3. Cotton ( Gossypium hirsutum L. “McNair-235”) plants were exposed to five O 3 concentrations in open-top field chambers for 12 hr/day throughout the growing season at two levels of soil water (well-watered or periodically water-stressed). The O 3 concentrations ranged from 0.021 to 0.073 μl/l (seasonal mean 12 hr/day concentration). Plants were sampled from each plot on four occasions encompassing the early- to late-reproductive stages of growth. Soluble sugars (glucose, fructose and sucrose) and starch were measured in leaves, stems and roots at each sampling date. Analysis of variance was performed for main effects and interactions of O 3 and water treatments at each sampling date (O 3 effects were partitioned in linear and quadratic components). Effects of O 3 and water stress on soluble carbohydrates and starch were most common in stems and roots. Ozone suppressed carbohydrate concentrations in all cases where significant O 3 effects were detected in the absence of O 3 × water interactions. On the other hand, soluble carbohydrate concentrations were greater in water-stressed plant tissues when effects were significant and in the absence of interactions. Water-stress effects on starch were variable. Interactions of O 3 and water stress were not consistent but often included interaction with the quadratic O 3 component.