Abstract
In Mediterranean-type ecosystems plants are exposed to several adverse environmental conditions throughout the year, ranging from drought stress during the warm and dry summers to chilling stress due to the typical drop in temperatures during winters. Here we evaluated the ecophysiological response, in terms of photoinhibition and photoprotection, of the dioecious Mediterranean palm, Chamaerops humilis to seasonal variations in environmental conditions. Furthermore, we considered as well the influence of plant size, maturity, and sexual dimorphism. Results showed evidence of winter photoinhibition, with a marked decrease of the Fv/Fm ratio below 0.7 between January and March, which was coincident with the lowest temperatures. During this period, the de-epoxidation state of the xanthophyll cycle and zeaxanthin levels increased, which might serve as a photoprotection mechanism, owing the full recovery from winter photoinhibition during spring. Furthermore, mature plants showed lower chlorophyll levels and higher β-carotene levels per unit of chlorophyll than juvenile plants, and females displayed lower leaf water contents and higher photoinhibition than males during summer, probably due to increased reproductive effort of females. However, neither low temperatures during winter nor reproductive events in females during the summer led to irreversible damage to the photosynthetic apparatus. We conclude that (i) the Mediterranean dwarf palm, C. humilis, suffers from photoinhibition during winter, but this is transient and does not lead to irreversible damage, and (ii) females from this plant species are more sensitive than males to photoinhibition during reproductive events.
Highlights
Different regions of the world are characterized by the so-called Mediterranean-type ecosystems, with generally warm and dry summers, and wet and mild winters, which determines a great diversity in vegetation that is known as “chaparral” in California, “fynbos” in the Cape Province of South Africa, “matorral” in Chile, “malle” in Australia, and “macchia”Photoinhibition and Photoprotection in a Mediterranean Palm in the Mediterranean basin (Cody and Mooney, 1978)
Plant species distribution in Mediterranean macchias appear to be mainly limited by drought stress, that is a combination of water deficit, high temperatures and high solar radiation during the summer, but it has been suggested that low temperatures in winter may play a role in plant adaptation and fitness (Mitrakos, 1982)
Seasonal variations in environmental conditions during the study were typical of the Mediterranean climate with a warm, dry summer and a wet, mild – relatively cold – winter, with most precipitation concentred in autumn, during November (Figure 1)
Summary
Different regions of the world are characterized by the so-called Mediterranean-type ecosystems, with generally warm and dry summers, and wet and mild winters, which determines a great diversity in vegetation that is known as “chaparral” in California, “fynbos” in the Cape Province of South Africa, “matorral” in Chile, “malle” in Australia, and “macchia” (or “maquis”)Photoinhibition and Photoprotection in a Mediterranean Palm in the Mediterranean basin (Cody and Mooney, 1978). Most of the ecophysiological research on this macchia vegetation has been focused on the effects of drought stress during summer, and very few studies have investigated far the response and adaptation of Mediterranean plants to low-temperature winter stress (Martínez-Ferri et al, 2004; Verhoeven, 2014; Esteban et al, 2015; Míguez et al, 2015). Mediterranean ecosystems are generally considered to be characterized by hot and dry summers, and wet, mild winters, previous studies have already shown sustained decreases in the maximum efficiency of photosystem II (PSII) photochemistry (Fv/Fm ratio) during summer drought, and during winter, the so-called “winter photoinhibition”, in some evergreen species (Kyparissis et al, 1995; García-Plazaola et al, 1999b; Oliveira and Peñuelas, 2000; Martínez-Ferri et al, 2004; Valladares et al, 2005). Drought events are becoming more and more unpredictable and are increasingly occurring during winters in Mediterranean-type ecosystems in the frame of global change (Intergovernmental Panel on Climate Change [IPCC], 2014)
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