Drought stress does not protect Quercus ilex L. from ozone effects: results from a comparative study of two subspecies differing in ozone sensitivity

Abstract

Long-term effects of ozone (O 3 ) exposure and drought stress were assessed on two subspecies of Quercus ilex: ssp. ilex and ssp. ballota. Two-year-old seedlings were continuously exposed for 26 months in open-top chambers to three O 3 treatments: charcoal filtered air, non-filtered air and non-filtered air supplemented with 40 nlÁl À1 O 3 . Additionally, two irrigation regimes were adopted: half of the plants were wellwatered and the others received half of the water supplied to control plants. Growth, shoot water potential and gas exchange rates were assessed seasonally, and biomass accumulation was determined at the end of the experiment. Drought stress caused higher reductions of gas exchange, growth and biomass accumulation than O 3 exposure in both subspecies. The combination of O 3 and drought stress caused further decreases of accumulated aboveground biomass but no additive effects were observed on gas exchange rates or root biomass. Thus, drought stress did not protect Q. ilex from O 3 effects on biomass when the response of the whole plant was considered. Q. ilex ssp. ballota was more sensitive to O 3 and ssp. ilex was more affected by drought stress. The different O 3 sensitivity was not only related to pollutant uptake but also to the ability of plants for resource acquisition and allocation. Based on biomass doseresponse functions, Q. ilex is more resistant to O 3 than other European evergreen tree species, however, O 3 represents an additional stress factor that might be impairing plant ability to withstand current and future climate change.

Chronic drought stress reduced but not protected Shantung maple (Acer truncatum Bunge) from adverse effects of ozone (O3) on growth and physiology in the suburb of Beijing, China

“…Further the defense processes may have been weakened by elevated O 3 concentration to an extent that a greater reduction in growth resulted (Matyssek et al, 2006;Tausz et al, 2007). There were similar reports about drought increases tree sensitivity to O 3 and the overall oxidative risk as well, such as Quercus ilex L. (Alonso et al, 2013), Pinus halepensis (Alonso et al, 2001) and poplar clones (Pollastrini et al, 2014). Although the results indicated that drought didn't protect biomass as well as gas exchange from adverse O 3 injury at the end because the effects of interaction were higher than any individual factor, ozone or drought.…”

“…Drought did not protect trees from O 3 effects but further enhanced O 3 damage. It was reported that drought increase the sensitivity to O 3 (Pollastrini et al, 2014;Alonso et al, 2013) and slowed or even stopped stomata response to abrupt stresses (Paoletti, 2005), which may cause a stronger reduction and may actually increase the overall oxidative risk as well due to limited carbon fixation (Matyssek et al, 2006;Tausz et al, 2007).…”

Cross-Talk between Physiological and Metabolic Adjustments Adopted by Quercus cerris to Mitigate the Effects of Severe Drought and Realistic Future Ozone Concentrations

“…The assumption for which drought-induced stomatal closure would limit O 3 entering the leaf, and the consequent O 3 -triggered damage [10], seems not to be universally acceptable. In some cases, drought does not protect trees from the effects of O 3 but, conversely, further exacerbates O 3 damage [11]. In addition to the physiological status of plants under stress, analyses of cellular and metabolic rearrangements adopted by plants may provide complementing evidence to describe the role(s) of several metabolites (such as compatible solutes, osmoprotectants, low-molecular weight proteins, and antioxidants) in the adaptation/acclimation of plants to harsh environmental conditions, such as the intricate interactions between drought and O 3 [12].…”

Effects of the Antiozonant Ethylenediurea (EDU) on Fraxinus ornus L.: The Role of Drought

“…In our case, we can argue that EDU was able to mitigate the synergic effects of drought and O 3 , possibly by reducing the oxidative pressure caused by the interaction of the two stresses. In fact, although drought is known to protect plants from O 3 by inducing stomatal closure [11,59], recent studies have highlighted that, under certain conditions, drought can instead increase plant sensitivity to O 3 [13], particularly if it occurs later in the season, after O 3 uptake during spring [14]. It has frequently been reported that EDU is able to ameliorate oxidative stress through different mechanisms, involving the inhibition of Reactive Oxygen Species (ROS) production [64] or the enhancement of both enzymatic and non-enzymatic ROS-scavenging mechanisms [17,35,53].…”

“…In fact, under drought conditions, stomatal conductance can be strongly reduced, consequently limiting O 3 uptake and protecting vegetation from potentially harmful O 3 concentrations [8,11,12]. At the same time, however, given that both factors act as oxidative stresses on plants, it may be difficult to establish a cause-effect relationship between O 3 and tree response under natural conditions, where drought may have important confounding effects [13][14][15].…”