Leaves

Burning fossil fuels and land use change have led to a rise in the concentration of carbon dioxide (CO₂) in the atmosphere since the onset of the Industrial Revolution. Carbon dioxide from the atmosphere enters leaves where it is concentrated and transformed into useful organic carbon compounds (food and fiber). In light of the fact that only plant leaves serve this critical function, we provide a brief summary of the effects of rising CO₂ on plant leaves at scales from the molecular to the whole plant community. Within leaves of C₃ plants, photosynthesis is stimulated by elevated CO₂ which generally results in increased biomass. Elevated CO₂ also increases water-use efficiency in both C₃ and C₄ plants by inducing partial closure of stomates which decreases transpiration. Growth in elevated CO₂ can alter leaf morphology, physiology, and chemistry which can affect interactions with pests and diseases. While increases in leaf-level photosynthesis usually translate to increased growth, decreased leaf-level transpiration does not necessarily result in lower whole plant water use; larger plants from exposure to elevated CO₂ can use more water on a whole plant level. Effects of elevated CO₂ scale up to the ecosystem level and gross primary productivity is usually increased. Reduced transpiration under high CO₂ can lead to higher leaf or canopy temperatures. Because not all plants respond in the same manner, growth in elevated CO₂ will benefit some plants to the detriment of others and plant community structure and function can be altered.