Physiological response of eight Mediterranean maquis species to low air temperatures during winter

We analyzed the physiological response of the Mediterranean evergreen species (Arbutus unedo L., Cistus incanus L., Erica arborea L., Erica multiflora L., Phillyrea latifolia L., Pistacia lentiscus L., Quercus ilex L., and Rosmarinus officinalis L.) to winter low air temperatures. In occasion of two cold events, in February 2005 (T _min = 1.8 °C), and January 2006 (T _min = 3.1 °C and minimum T _air = −0.40 °C during the nights preceding the measurements), R. officinalis, C. incanus, and E. multiflora had the highest net photosynthetic rate (P _N) decrease (73 %, mean value) with respect to the winter P _N maximum, followed by A. unedo (62 %), P. latifolia and P. lentiscus (54 %, mean value), E. arborea (49 %), and Q. ilex (44 %). Among the considered species, Q. ilex was able to maintain P _N near the maximum for 150 min during the day, A. unedo, P. lentiscus, E. arborea, P. latifolia, E. multiflora, and R. officinalis for 60 min, and C. incanus for 30 min. The calculated mean winter daily P _N ranged from 7.9±0.6 (Q. ilex) to 2.8±0.5 (R. officinalis) μmol(CO₂) m⁻² s⁻¹. During the study period, chlorophyll (Chl) content decreased by 36 % on an average in the two cold events, and the carotenoid (Car) to Chl ratio increased by 133 % in Q. ilex, having the highest value in January 2006. Principal component analysis underlined the highest cold resistance of Q. ilex by high P _N and high Car/Chl ratio. On the contrary, R. officinalis and C. incanus had the lowest cold resistance by the highest P _N decrease and the lowest Car/Chl (C. incanus). Thus, winter stress could be an additional limitation to Mediterranean evergreen species production, and the capacity of the species to maintain P _N near 90–100 % during winter is determinant for biomass accumulation.