Differences in drought sensitivity of photosynthesis between C4 and C3 species in the genus Flaveria (Asteraceae)

Abstract

[eng] At a global scale, drought is considered the most limiting factor for plants, reducing photosynthesis, growth and yield. There is abundant research exploring the effects of water stress on plants and how it affects the photochemistry in C3 plants. However, the responses to water stress in C4 have been much less studied. Due to their carbon concentrating mechanism, C4 plants exhibit grater assimilation rates and water use efficiency. Despite this advantages, when comparing C3 and C4 under water stress conditions, C4 monocots seem to be more sensitive than C3 monocots. Since almost no information is available about dicots, the aim of this study was to compare the effects of drought and rewatering on photosynthesis in two C4 dicot species: Flaveria bidentis and Flaveria trinervia; and one C3 dicot: Flaveria robusta. Water was withheld in the three species until soil water content reached 30%. F. bidentis showed higher rates of assimilation than F. trinervia and F. robusta under both well-watered and water-stress conditions. The decrease in assimilation was, in proportion, lower in F. bidentis than in F. robusta. Rewatring did not translate into a recovery of any parameter measured in any species, indicating metabolic limitations. The two C4 exhibited different degree of tolerance to water stress: F. trinervia was clearly more sensitive, being limited by Rubisco and altering the C3/C4 cycle balance, while in F. bidentis the limitation on Rubisco did not alter the coordination, maybe indicating some degree of general downregulation. This findings suggest different ranges of tolerance within the C4 Flaveria, making it difficult make comparisons with the C3.