Leaf Carbon and Water Isotopes Correlate with Leaf Hydraulic Traits in Three Solanum Species (S. peruvianum, S. lycopersicum and S. chilense)

Abstract

Leaf hydraulic conductance (KLeaf) is a measure of the efficiency of water transport through the leaf, which determines physiological parameters such as stomatal conductance, photosynthesis and transpiration rates. One key anatomical structure that supports KLeaf is leaf venation, which could be subject to evolutionary pressure in dry environments. In this context, it is useful to assess these traits in species from arid climates such as S. peruvianum and S. chilense, in order to determine their hydraulic strategy and potential aptitude for the improvement of domestic tomato (S. lycopersicum). In this work, we measured KLeaf, vein density, together with leaf water isotope composition (δ18O, δ2H) and leaf carbon isotope composition (δ13C), from which we derived proxies for outside-vein hydraulic resistance (Rox) and intrinsic water use efficiency (WUEi), respectively. The two wild species showed contrasting hydraulic strategies, with S. chilense performing as a water-spender, whereas S. peruvianum showed a water-saving strategy. Interestingly, S. lycopersicum was rather conservative, and showed the highest WUEi. The low water transport capacity of S. peruvianum was not explained by vein density traits, but was related with the effective pathlength L, an isotope-derived proxy for Rox. The low WUEi of S. peruvianum suggest strong photosynthetic limitations. Our results show a wide diversity in water-use strategies in the genus, encouraging a detailed characterization of wild relatives. From a methodological point of view, we provide evidence supporting the use of water isotopes to assess changes in mesophyll hydraulic conductance, not attributable to vein density.