Contrasting hydraulic regulation in closely related forage grasses: implications for plant water use

Plant traits that improve crop water use efficiency are highly sought after but difficult to isolate. Here, we examine the integrated function of xylem and stomata in closely related forage grasses to determine whether quantitative differences in water transport properties could be used to predict plant performance under limited water conditions. Cultivars of two forage grass species with different drought tolerance ratings, Lolium multiflorum Lam. and Festuca arundinacea Schreb., were assessed for maximum hydraulic conductivity (Kmax), vulnerability of xylem to hydraulic dysfunction (P50) and stomatal sensitivity to leaf water potential. Species-specific differences were observed in several of these traits, and their effect on whole-plant performance was examined under well-watered and restricted watering conditions. It was shown that although P50 was comparable between species, for F. arundinacea cultivars, there was greater hydraulic risk associated with reduced stomatal sensitivity to leaf hydration. In contrast, L. multiflorum cultivars expressed a higher capacity for water transport, but more conservative stomatal regulation. Despite different susceptibilities to leaf damage observed during acute drought, under the sustained moderate drought treatment, the two strategies were balanced in terms of water conservation and hydraulic utilisation, resulting in similar dry matter production. Characterisation of water use patterns according to the key hydraulic parameters is discussed in terms of implications to yield across different environmental scenarios as well as the applicability of water transport related traits to breeding programs.