Early Responses to Acute Ozone Exposure in Two Fagus Sylvatica Clones Differing in Xeromorphic Adaptations: Photosynthetic and Stomatal Processes, Membrane and Epicuticular Characteristics

Abstract

Two Fagus sylvatica L. clones were used to investigate the early responses to acute O3 exposure (150 nL L(-1), i.e., 1.35x ambient hourly peak in rural Italy) and whether xeromorphic adaptations affect gas exchange, membrane, and epicuticular responses. One clone originated in a wet and temperate climate in Central Italy (Tuscany); the other clone originated in a warmer and drier climate in the southern-most part of the F. sylvatica distribution (Sicily). Because of higher base gas exchange rates, the most negative effects of O3 exposure (gas exchange impairment, uncoupling between net photosynthesis and stomatal conductance, increased membrane lipid peroxidation) were found in the southern clone. Xeromorphic adaptations (higher epicuticular waxes and stomatal density, lower leaf wettability and size) were found in this clone. Our results suggest that xeromorphism may increase O3 sensitivity in species not adapted to face water stress, like the mesophilic F. sylvatica, when experiments are carried out with full irrigation. We present evidence describing the relationship between gas exchange and number and status of stomata. Stomatal density and the structural damage to stomata resulting from O3 exposure did not affect gas exchange: In fact, non-stomatal limitations to photosynthesis prevailed over stomatal limitations.

Differences in histological and physiological traits of ozone sensitive and resistant bean strains

“…Despite the large number of studies confirming that ozone sensitive plants have higher stomatal conductance [7,10,30], our present data did not show significant difference between stomatal conductances of the two genotypes. Ozone sensitive bean strains showed higher photosynthetic intensity (Table 1).…”

Ozone exposure causes a decoupling of conductance and photosynthesis: implications for the Ball-Berry stomatal conductance model

“…In Wittig et al (2007)'s metaanalysis of tree responses to O 3 compared to ambient background air, O 3 caused an average stomatal conductance decrease of 6% compared to an 18% decrease in photosynthesis. Several studies suggest that decreases in conductance are a secondary response to chronic O 3 exposure and only occur following a reduction in carboxylation efficiency (Farage et al 1991;Manes et al 2001;Noormets et al 2001;Paoletti and Grulke 2005;Paoletti et al 2007;Reich 1987).…”

The effects of ozone on Mediterranen forests

“…Per esempio, un ampio studio su cloni di Faggio (Fagus sylvatica L.), esposti a 150 ppb O 3 , corrispondenti a 1.35 x i picchi orari nell'Italia rurale, ha dimostrato il danneggia mento degli scambi gassosi, con disaccoppiamento tra fotosintesi e conduttanza stomatica, l'aumento della perossidazione lipidica delle membrane, e l'al terazione della struttura degli stomi osservata al mi croscopio elettronico a scansione ( Fig. 1 - Paoletti et al 2007f). Comunque, le limitazioni non-stomatiche indotte dall'O 3 alla fotosintesi prevalevano su quelle stomatiche, e le reazioni luminose della fotosintesi (p.e., il tasso di trasporto elettronico) rispondevano all'O 3 più precocemente di quelle della fase oscura (p.e.…”