Photochemical activity and leaf functional traits of Petagnaea gussonei and Sanicula europaea (Apiaceae) as affected by variable environmental conditions

Petagnaea gussonei (Sprengel) Rauschert (=Petagnia saniculifolia Guss.) is a very rare species and is endemic to North Eastern Sicily (Italy). It is confined in a few area of Nebrodi Mountain. Its rarity as well as the general difficulty of sampling make it a very poorly known species up to little time ago (De Castro et al. 2008, 2009). Because no ecophysiological information is available on this rare species, the aim of this work was to assess the photochemical activity and some leaf functional traits as influenced by environmental conditions in order to investigate the strategies that allow plant to adapt successfully to its habitat. For this purpose, measurements of chlorophyll a fluorescence as well as determinations of leaf characteristics such as specific leaf area (SLA), leaf water content (WC), leaf relative water content (RWC) and chlorophylls were performed seasonally on leaves of P. gussonei grown in the field. The same experimental approach was carried out in a parallel fashion on Sanicula europaea L. The two species are morphologically similar but, since S. europaea is very abundant and widespread. In spring and autumn, when no-limiting environmental conditions occur at measuring site, both species showed the highest (P<0.01) quantum yield of PSII electron transport (PSII) and photochemical quenching (qP) as well as higher values (P<0.05) of SLA, WC, RWC and total chlorophyll content compared to summer and winter. In winter both species exhibited the strongest decrease (P<0.001) of SLA, PSII, qP and maximum photochemical efficiency (Fv/Fm) together with the highest non-photochemical quenching (qN) and the greatest amount of carotenoids. No difference was observed among spring, summer and autumn in Fv/Fm between the two species. Data indicate that for both P. gussonei and S. europaea, winter represent the more critical season for photosynthetic apparatus in terms of light harvesting and light conversion to reaction centres and for photoinhibitory damage risks (Huner et al. 1993). However the highest qN and the greatest amount of carotenoids suggest that thermal dissipation is very active in photoprotection at low temperature (Adams et al. 2001). The success of S. europaea in colonizing wide areas seems to be not attributable to a better photochemical performance during the seasons compared to P. gussonei, but rather to other causes that require further investigations. The authors are grateful to Nando Peretti Foundation for funding the study.