Variation in photosynthetic characteristics with growth form in a water-limited scenario: Implications for assimilation rates and water use efficiency in crops

Photosynthesis is a complex process that is intrinsically determined by two main components: the CO2 diffusion from the atmosphere to the chloroplast and the biochemistry. Among CO2 diffusion, mesophyll conductance within the leaf (gm) has been receiving attention in the recent years as a key player determining photosynthesis both across species and in response to the environment; furthermore, gm estimation allows for disentangling the complete set of photosynthesis underlying mechanisms. In a water-limited scenario where crop productivity and efficiency need to be increased, the analysis of available data from photosynthesis among vascular plants and its response to water stress results helpful for a better understanding of crop management and improvement. Here, photosynthesis data are compiled to elucidate if crop and wild species from different growth forms present different photosynthesis limitations under optimum and water stress conditions. From the available data, a double process of apparent photosynthesis selection is revealed: higher values from ferns to woody and herbaceous species and, among angiosperms, a tendency towards greater photosynthesis in crop species (although constrained by growth form). The causes of such photosynthesis variation are discussed. Moreover, crop and herbaceous species present a shift in photosynthesis limitations towards lower mesophyll diffusion constraints, under both well-watered and water-stress conditions. These particular photosynthesis characteristics in crops present several implications for the possible improvement of CO2 assimilation and water use efficiency, providing new guidelines for future engineering and management in agriculture.