Drought-induced photosynthetic inhibition and autumn recovery in two Mediterranean oak species (Quercus ilex and Quercus suber)

Abstract

Responses of leaf water relations and photosynthesis to summer drought and autumn rewetting were studied in two evergreen Mediterranean oak species, Quercus ilex spp. rotundifolia and Quercus suber. The predawn leaf water potential (Ψ(lPD)), stomatal conductance (gs) and photosynthetic rate (A) at ambient conditions were measured seasonally over a 3-year period. We also measured the photosynthetic response to light and to intercellular CO₂ (A/PPFD and A/C(i) response curves) under water stress (summer) and after recovery due to autumn rainfall. Photosynthetic parameters, Vc(max), J(max) and triose phosphate utilization (TPU) rate, were estimated using the Farquhar model. RuBisCo activity, leaf chlorophyll, leaf nitrogen concentration and leaf carbohydrate concentration were also measured. All measurements were performed in the spring leaves of the current year. In both species, the predawn leaf water potential, stomatal conductance and photosynthetic rate peaked in spring, progressively declined throughout the summer and recovered upon autumn rainfall. During the drought period, Q. ilex maintained a higher predawn leaf water potential and stomatal conductance than Q. suber. During this period, we found that photosynthesis was not only limited by stomatal closure, but was also downregulated as a consequence of a decrease in the maximum carboxylation rate (Vc(max)) and the light-saturated rate of photosynthetic electron transport (J(max)) in both species. The Vc(max) and J(max) increased after the first autumnal rains and this increase was related to RuBisCo activity, leaf nitrogen concentration and chlorophyll concentration. In addition, an increase in the TPU rate and in soluble leaf sugar concentration was observed in this period. The results obtained indicate a high resilience of the photosynthetic apparatus to summer drought as well as good recovery in the following autumn rains of these evergreen oak species.

Effects of fertilization and drought stress on tannin biosynthesis of Casuarina equisetifolia seedlings branchlets

“…Similar with some previous studies (Vaz et al 2010), the soluble sugars increased significantly with drought stress, but the increased starch concentration was different from other studies (Naser et al 2010;Silva et al 2010). Gebauer et al (1998) suggested that strong positive correlations exist between soluble sugar and TP concentrations and between starch and condensed tannins concentrations, respectively.…”

Environmental Drivers of Holocene Forest Development in the Middle Atlas, Morocco

“…However, lack of transpiration blockage can lead to difficulties under prolonged, severe drought (Aussenac, 1984). In contrast, Quercus rotundifolia develops deep rooting structures to access groundwater reserves and maintain high rates of transpiration in combination with stomatal closure under extreme stress (David et al, 2004;Cubera and Moreno, 2007;Vaz et al, 2010). These different strategies leave Cedrus more vulnerable to extended temperature-driven summer drought and low soil moisture.…”

Growth, ectomycorrhization and biochemical parameters of Quercus suber L. seedlings under drought conditions

“…Decrease in chlorophyll contents was due to decrease in chlorophyll biosynthesis rather than its degradation (Jain et al, 2013). Vaz et al (2010) showed no difference in Q. suber tree leaves from summer to autumn.…”