Effect of Long-Term vs. Short-Term Ambient Ozone Exposure on Radial Stem Growth, Sap Flux and Xylem Morphology of O3-Sensitive Poplar Trees

Abstract

High ozone (O3) pollution impairs the carbon and water balance of trees, which is of special interest in planted forests. However, the effect of long-term O3 exposure on tree growth and water use, little remains known. In this study, we analysed the relationships of intra-annual stem growth pattern, seasonal sap flow dynamics and xylem morphology to assess the effect of long term O3 exposure of mature O3-sensitive hybrid poplars (‘Oxford’ clone). Rooted cuttings were planted in autumn 2007 and drip irrigated with 2 liters of water as ambient O3 treatment, or 450 ppm ethylenediurea (N-[2-(2-oxo-1-imidazolidinyl)ethyl]-N0-phenylurea, abbreviated as EDU) solution as O3 protection treatment over all growing seasons. During 2013, point dendrometers and heat pulses were installed to monitor radial growth, stem water relations and sap flow. Ambient O3 did not affect growth rates, even if the seasonal culmination point was 20 days earlier on average than that recorded in the O3 protected trees. Under ambient O3, trees showed reduced seasonal sap flow, however, the lower water use was due to a decrease of Huber value (decrease of leaf area for sapwood unit) rather than to a change in xylem morphology or due to a direct effect of sluggish stomatal responses on transpiration. Under high evaporative demand and ambient O3 concentrations, trees showed a high use of internal stem water resources modulated by stomatal sluggishness, thus predisposing them to be more sensitive water deficit during summer. The results of this study help untangle the compensatory mechanisms involved in the acclimation processes of forest species to long-term O3 exposure in a context of global change.

Ethylenediurea (EDU) effects on Japanese larch: an one growing season experiment with simulated regenerating communities and a four growing season application to individual saplings

“…The finding of successful protection of this coniferous tree over multiple growing seasons is in agreement with the only long-term experiment studying EDU effects on plants (Hoshika et al 2013;Katanić et al 2014;Carriero et al 2015;Giovannelli et al 2019). In that experiment, weekly applications of 450 mg EDU L −1 protected the growth and productivity of a broadleaved hybrid poplar over multiple years, improved its seasonal sap flow by increasing leaf area for sapwood unit, and positively affected the community of mycorrhizal fungi (Katanić et al 2014;Carriero et al 2015;Giovannelli et al 2019). Conversely to experiment I, where EDU200 did not provide as sufficient protection as EDU400, EDU200 offered a similarly sufficient protection with EDU400 in experiment II.…”

“…To this end, individually-grown saplings were exposed to ambient O 3 for 2 years and to elevated O 3 for 2 more years (4 years in total), while treated with EDU (3 concentrations). Nearly all the published studies of EDU effects on plants lasted for only one growing season, while only one experiment with a fast-growing O 3 -susceptible hybrid poplar lasted for several years (Hoshika et al 2013 ; Katanić et al 2014 ; Carriero et al 2015 ; Giovannelli et al 2019 ). Therefore, this experiment with Japanese larch is of high value for potential forestry applications in the future.…”

Early Detection of Decline in Tree Health. Could the Pace of Stem Water Be an Effective Indicator?

“…The long-time delay between the occurrence of onset of stem shrinkage and daily minimum temperature observed in alive and compromised trees can be explained considering the main role of crown transpiration demand in driving water fluxes within the stem. The onset of the stem shrinkage was correlated with the increasing of sap flow and crown transpiration in the early morning in poplar and olive [23,24]. After dawn, the increasing photosynthetic photon flux density induces stomata opening and water is retrieved from storage compartments (i.e.…”

Ethylenediurea (EDU) effects on hybrid larch saplings exposed to ambient or elevated ozone over three growing seasons

“…Although EDU improves various physiological, biochemical, growth, and productivity traits of plants under O 3 stress in the framework of hormesis, there is high intraspecific variation and no universal mechanism explaining its phytoprotective mode of action (Feng et al 2010;Oksanen et al 2013;Singh et al 2015;Agathokleous 2017;Tiwari 2017;Ashrafuzzaman et al 2018;Pandey et al 2019;Surabhi et al 2020). Besides, EDU studies concerning tree species are few (Paoletti et al 2009;Feng et al 2010;Agathokleous 2017;Giovannelli et al 2019) relative to EDU studies concerning non-tree species. Importantly, there have been only two research programs studying the efficacy of EDU in protecting tree species over several years; one with poplars and one with Japanese larch (Giovannelli et al 2019;Agathokleous et al 2021).…”

“…Besides, EDU studies concerning tree species are few (Paoletti et al 2009;Feng et al 2010;Agathokleous 2017;Giovannelli et al 2019) relative to EDU studies concerning non-tree species. Importantly, there have been only two research programs studying the efficacy of EDU in protecting tree species over several years; one with poplars and one with Japanese larch (Giovannelli et al 2019;Agathokleous et al 2021). Therefore, the effects of EDU on plants under O 3 stress over several years remain largely unexplored, yet it is essential to confirm whether EDU can protect various trees against O 3 for multiple years, indicating that long-term responses should be evaluated.…”