Changes in Leaf Morphology and Composition with Future Increases in CO2 and Temperature Revisited: Wheat in Field Chambers

Whether leaf morphology is altered by future increases in atmospheric CO2 and temperature has been reexamined over 3 years in wheat grown in field chambers at two levels of nitrogen supply. Flag leaf fresh and dry mass, area, volume, and ratios of these parameters, as well as the contents of water, chlorophyll, nonstructural carbohydrates, and nitrogen compounds have been determined at anthesis and 14 days later. High CO2 decreased rather than increased, as reported in the literature, leaf mass per area and leaf density, and increased water content per area and per volume and water percentage. Warmer temperatures also decreased leaf mass per area, but did not affect density or water per area or per volume, whereas they increased water percentage. Nitrogen supply did not change CO2 and temperature effects on leaf morphology. Nonstructural carbohydrates increased and nitrogen compounds decreased in elevated CO2, and the sum of these compounds decreased with warmer temperatures. These changes in composition did not account for modifications of leaf morphology. We conclude that increases in atmospheric CO2 and temperature after leaf initiation can decrease leaf mass per area, and elevated CO2 can also decrease leaf density, due to decreases in leaf structural compounds. The functional significance of these changes is probably a decrease in photosynthetic capacity per unit leaf area.