Isotopic and Water Relation Responses to Ozone and Water Stress in Seedlings of Three Oak Species with Different Adaptation Strategies

Abstract

The impact of global changes on forest ecosystem processes is based on the species-specific responses of trees to the combined effect of multiple stressors and the capacity of each species to acclimate and cope with the environment modification. Combined environmental constraints can severely affect plant and ecological processes involved in plant functionality. This study provides novel insights into the impact of a simultaneous pairing of abiotic stresses (i.e., water and ozone (O3) stress) on the responses of oak species. Water stress (using 40 and 100% of soil water content at field capacity—WS and WW treatments, respectively) and O3 exposure (1.0, 1.2, and 1.4 times the ambient concentration—AA, 1.2AA, and 1.4AA, respectively) were carried out on Quercus robur L., Quercus ilex L., and Quercus pubescens Willd. seedlings, to study physiological traits (1. isotope signature [δ13C, δ18O and δ15N], 2. water relation [leaf water potential, leaf water content], 3. leaf gas exchange [light-saturated net photosynthesis, Asat, and stomatal conductance, gs]) for adaptation strategies in a Free-Air Controlled Exposure (FACE) experiment. Ozone decreased Asat in Q. robur and Q. pubescens while water stress decreased it in all three oak species. Ozone did not affect δ13C, whereas δ18O was influenced by O3 especially in Q. robur. This may reflect a reduction of gs with the concomitant reduction in photosynthetic capacity. However, the effect of elevated O3 on leaf gas exchange as indicated by the combined analysis of stable isotopes was much lower than that of water stress. Water stress was detectable by δ13C and by δ18O in all three oak species, while δ15N did not define plant response to stress conditions in any species. The δ13C signal was correlated to leaf water content (LWC) in Q. robur and Q. ilex, showing isohydric and anisohydric strategy, respectively, at increasing stress intensity (low value of LWC). No interactive effect of water stress and O3 exposure on the isotopic responses was found, suggesting no cross-protection on seasonal carbon assimilation independently on the species adaptation strategy.

Monitoring drought response and chlorophyll content in Quercus by consumer-grade, near-infrared (NIR) camera: a comparison with reflectance spectroscopy

“…In Q. ilex, this relationship was not significant, suggesting a higher tolerance and different strategy to face drought. Similarly, drought reduced light-saturated rate of photosynthetic carbon uptake and stomatal conductance more in QR and QP than in QI (Cocozza et al 2020). A significant interaction effect between these oak species and drought, as well with other stressors, such as ozone, was observed by Hoshika et al (2018) and Cotrozzi et al (2016), indicating different strategies among the three species.…”

Cumulative growth and stress responses to the 2018–2019 drought in a European floodplain forest

“…The magnitude and timing of drought stress responses were species-specific, which may be related to differences in species hydraulic traits. Oak has a deep reaching root system and may thus be able to maintain water uptake during low precipitation periods 24,29,45 , while its water saving behavior (oak is isohydric 35,36 ) may have helped to avoid xylem cavitation during peak drought periods 21 . In contrast, ash has roots mainly restricted to upper soil layers and is thus more dependent on precipitation than oak 23,24 .…”

“…To this end, we reconstruct the stress exerted by this unprecedented event and compare it to past (single) drought events based on tree-ring records from dominant tree species in the Leipzig floodplain forest, one of the few remaining and thus highly protected floodplain forests in Central Europe 33,34 . The studied species span a gradient in stomatal control and root system architecture, with Quercus robur L. (hereafter oak) having isohydric behavior 35,36 and a deep reaching heart-sinker root system 24,25 , Acer pseudoplatanus L.…”

“…To this end, we reconstruct the stress exerted by this unprecedented event and compare it to past (single) drought events based on tree-ring records from dominant tree species in the Leipzig floodplain forest, one of the few remaining and thus highly protected floodplain forests in Central Europe 33,34 . The studied species span a gradient in stomatal control and root system architecture, with Quercus robur L. (hereafter oak) having isohydric behavior 35,36 and a deep reaching heart-sinker root system 24,25 , Acer pseudoplatanus L. (hereafter maple) having an intermediate (rather isohydric) stomatal control 37,38 and rooting depth 25 and Fraxinus excelsior L. (hereafter ash) having an anisohydric behaviour 37,38 and an allocation of most roots to shallow soil layers 24,25 . This gradient allowed us to explore a broad range of species response strategies to consecutive drought stress.…”

Magnolia grandiflora L. shows better responses to drought than Magnolia × soulangeana in urban environment

“…Furthermore, several studies have evidenced that provenances and species originating from drier climate perform better under drought condition (Pšidová et al 2015, Wang et al 2017. For instance, investigation of the drought tolerance of Quercus ilex L., Q. pubescens Willd., and Q. robur L., showed that the Mediterranean oak species, despite a reduction of light-saturated net photosynthesis (Cocozza et al 2020), maintained higher photosynthetic activity compared to Central-European oak species (Früchtenicht et al 2018).…”