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Different belowground responses to elevated ozone and soil water deficit in three European oak species (Quercus ilex, Q. pubescens and Q. robur)
Tanja Mrak, Ines Štraus, Tine Grebenc, Jožica Gričar, Yasutomo Hoshika, Giulia Carriero, Elena Paoletti, Hojka Kraigher, 2019

Abstract: Effects on roots due to ozone and/or soil water deficit often occur through diminished belowground allocation of carbon. Responses of root biomass, morphology, anatomy and ectomycorrhizal communities were investigated in seedlings of three oak species: Quercus ilex L., Q. pubescens Willd. and Q. robur L., exposed to combined effects of elevated ozone (ambient air and 1.4 x ambient air) and water deficit (100% and 10% irrigation relative to field capacity) for one growing season at a free-air ozone exposure facility. Effects on root biomass were observed as general reduction in coarse root biomass by -26.8 % and in fine root biomass by -13.1 % due to water deficit. Effect on coarse root biomass was the most prominent in Q. robur (-36.3 %). Root morphological changes manifested as changes in proportions of fine root (<2 mm) diameter classes due to ozone and water deficit in Q. pubescens and due to water deficit in Q. robur. In addition, reduced fine root diameter (-8.49 %) in Q. robur was observed under water deficit. Changes in root anatomy were observed as increased vessel density (+18.5 %) due to ozone in all three species, as reduced vessel tangential diameter (-46.7 %) in Q. ilex due to interaction of ozone and water, and as generally increased bark to secondary xylem ratio (+47.0 %) due to interaction of ozone and water. Water deficit influenced occurrence of distinct growth ring boundaries in roots of Q. ilex and Q. robur. It shifted the ectomycorrhizal community towards dominance of stress-resistant species, with reduced relative abundance of Tomentella sp. 2 and increased relative abundances of Sphaerosporella brunnea and Thelephora sp. Our results provide evidence that expression of stress effects varies between root traits; therefore the combined analysis of root traits is necessary to obtain a complete picture of belowground responses.
Keywords: ozone, drought, fine roots, ectomycorrhiza, anatomy, morphology, plants
DiRROS - Published: 20.02.2020; Views: 1208; Downloads: 675
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Isotopic and water relation responses to ozone and water stress in seedlings of three oak species with different adaptation strategies
Claudia Cocozza, Tom Levanič, Saša Zavadlav, Tanja Mrak, Elena Paoletti, Yasutomo Hoshika, Alessio Giovannelli, Hojka Kraigher, 2020

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 [delta 13C, delta 18O and delta 15N], 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 delta 13C, whereas delta 18O 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 delta 13C and by delta 18O in all three oak species, while delta 15N did not define plant response to stress conditions in any species. The delta 13C 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.
Keywords: ozone, gas exchange, English oak, holm oak, downy oak, Quercus ilex L., Quercus robur L., Quercus pubescens Willd
DiRROS - Published: 11.08.2020; Views: 1110; Downloads: 660
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Elevated ozone prevents acquisition of available nitrogen due to smaller root surface area in poplar
Tanja Mrak, Klemen Eler, Ovidiu Badea, Yasutomo Hoshika, Elisa Carrari, Elena Paoletti, Hojka Kraigher, 2020

Abstract: Aims Poplars are ecologically and economically important tree genus, sensitive to ozone (O3). This study aimed to investigate modifying effects of elevated O3 on poplar root response to nutrient addition. Methods In pot experiment, young trees of an O3-sensitive Oxford poplar clone (Populus maximoviczii Henry x berolinensis Dippel) growing in soil with three levels of P (0, 40 and 80 kg ha-1) and two levels of N (0 and 80 kg ha-1) were exposed to three levels of O3 (ambient - AA, 1.5 x AA, 2.0 x AA) at a free air exposure facility. After one growing season, root biomass, fine root (<2 mm) nutrient concentrations and ratios, and fine root morphology were assessed. Results Nitrogen addition resulted in an up to +100.5% increase in coarse and fine root biomass under AA, and only up to +46.3% increase under 2.0 x AA. Elevated O3 and P addition had a positive effect, while N had a negative effect on P concentrations in fine roots. Nitrogen limitation for root growth expressed as a N:P ratio was more pronounced at elevated O3. Nitrogen addition increased root surface area per soil volume by +78.3% at AA and only by +9.9% at 2.0 x AA. Conclusions Smaller root surface area per soil volume at elevated O3 prevented acquisition of available N, rendering N fertilization of young poplar plantations in such conditions economically and environmentally questionable.
Keywords: fine roots, nitrogen, phosphorus, Populusmaximoviczii x berolinensis, ozone, Poplar
DiRROS - Published: 16.06.2020; Views: 1233; Downloads: 547
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