Interactions of CO 2 enrichment and temperature on cotton growth and leaf characteristics

Abstract

Studies on the interactive effects of atmospheric CO 2 and temperature on growth and leaf morphology, particularly on stomatal index and density are limited. Upland cotton was grown in naturally-lit plant growth chambers at 30/22°C day/night temperatures from planting until squaring or the fifth or sixth leaf emerged. Five growth chambers were maintained at ambient (350 μl l −1) CO 2 and another five at twice ambient (700 μl l −1) CO 2 throughout the experiment. Day/night temperature treatments of 20/12, 25/17, 30/22, 35/27 and 40/32°C were imposed at each CO 2 treatment for 42 days after squaring. The plants were irrigated with half-strength Hoagland's nutrient solution three times per day. Growth of plant parts was determined at the end of the experiment. Stomatal characteristics, nonstructural carbohydrates and specific leaf weight were measured on the fully expanded tenth mainstem leaf. Stomatal density and index were not affected by elevated CO 2. Stomata and epidermal cell numbers per leaf increased in high CO 2 and were positively correlated with final leaf sizes irrespective of CO 2 level. Our results suggest that plants do not acclimate to elevated CO 2 by changing stomatal density within a single generation. Leaves had greater area and accumulated more biomass when grown in high CO 2. Growth stimulation expressed as dry weight at 700 μl l −1 over dry weight at 350 μl l −1 CO 2 was uniform across temperatures. Temperature optimum for vegetative and reproductive growth was 30/22°C and was not altered by CO 2 enrichment. Fruit retention was severely curtailed at the two higher temperatures compared to 30/22°C in both CO 2 environments. Increased carbohydrate storage in leaves may be an added advantage for initiation and growth of vegetative structures such as branches at all temperatures. However, it is unlikely that high temperature effects on flower abortion will be ameliorated by high CO 2. Species/cultivars that retain fruits at high temperatures would be more productive both in the present-day cotton producing environments and are even more desirable in the future warmer world.