The capacity for nitrate regulation of root hydraulic properties correlates with species’ nitrate uptake rates

A mechanism whereby water flow towards root surfaces is stimulated when exposed to nutrient patches may be evolutionarily desirable in environments with heterogeneous soils. Indeed, the presence of nitrate has been shown to increase root hydraulic conductance in a few agricultural species characterized by high nitrate demand. Does a similar stimulation of root conductivity in response to external nitrate addition exist among wild type organisms? To answer this question, we studied and compared the effect of a sudden increase of nitrate concentration on root hydraulic properties in seven species. These included three agricultural species (Cucumis sativus L., Solanum esculentum L., Zea mays L.) and four wild type species (Arabidopsis thaliana L., Festuca arundinacea Schreb., Populus trichocarpa Torr.&Gray, Nephrolepis exaltata L.). The selected species differed in overall nitrate demand and specific nitrate uptake rates. Changes in root hydraulic conductance induced by nitrate varied from non-existent (N. exaltata L.) to more than 50% increases (Z. mays L.). The magnitude of the hydraulic response to nitrate presence was significantly correlated with species nitrate uptake rate. This finding suggests an emergent physiological trait that links together plant nitrate needs, nitrate availability and root hydraulic properties.