Ozone-induced impairment of night-time stomatal closure in O-3-sensitive poplar clone is affected by nitrogen but not by phosphorus enrichment

Nocturnal transpiration may be a key factor influencing water use in plants. Tropospheric ozone (O-3) and availability of nutrients such as nitrogen (N) and phosphorus (P) in the soil can affect daytime water use through stomata, but the combined effects of O-3, N and P on night-time stomatal conductance (g(s)) are not known. We investigated the effects of O-3 and soil availability of N and P on nocturnal g, and the dynamics of stomatal response after leaf severing in an O-3-sensitive poplar clone (Oxford) subjected to combined treatments over a growing season in an O-3 free air controlled exposure (FACE) facility. The treatments were two soil N levels (0 and 80 kg N ha(-1); NO and N80), three soil P levels (0, 40 and 80 kg P ha(-1); P0, P40 and P80) and three O-3 levels ambient concentration, AA ]35.0 ppb as hourly mean]; 1.5 x AA; 2.0 x AA). The analysis of stomatal dynamics after leaf severing suggested that O-3 impaired stomatal closure execution. As a result, nocturnal g(s) was increased by 2.0 x AA O(3 )in August (+39%) and September (+108%). Night-time g s was correlated with POD0 (phytotoxic O-3 dose) and increased exponentially after 40 mmol m(-2) POD0. Such increase of nocturnal g(s) was attributed to the emission of ethylene due to 2.0 x AA O-3 exposure, while foliar abscisic acid (ABA) or indole-3-acetic acid (IAA) did not affect g(s) at night. Interestingly, the O-3-induced stomatal opening at night was limited by N treatments in August, but not limited in September. Phosphorus decreased nocturnal g(s), although P did not modify the O-3-induced stomatal dysfunction. The results suggest that the increased nocturnal g(s) may be associated with a need to improve N acquisition to cope with O-3 stress. (C) 2019 Elsevier B.V. All rights reserved.