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Climate change in the Mediterranean region is leading to hotter and drier summers, with an estimated 30% decline in annual precipitation by the end of the XXIst century (Zittis et al., 2021). To cope with drought, trees modulate their leaf chemical and physical traits (Franco-Navarro et al., 2025; Laoué et al., 2022). This study examined if long-term drought (> 10 years) under Mediterranean climate induces a physiological stress level in Quercus pubescens leaves and a modulation of chemical and physical leaf traits to cope with water deficit and associated oxidative stress.
The work was conducted at the O3HP site (Oak Observatory at Observatoire de Haute Provence) – belonging to the AnaEE-France, AnaEE-ERIC, and SEE-life networks – a long-term in natura experimental site in southern France, equipped with a dynamic rain exclusion system above the canopy since April 2012. This system reduces annual precipitation by ~30% in a 300 m2 forest plot (AD: amplified drought) compared to an adjacent plot (ND: natural drought) where trees grown under natural Mediterranean drought. Trees were monitored within each plot (ND and AD) to study their leaf i) physiological functioning (CO2 fixation and transpiration), ii) chemical (central metabolites: carotenoids and chlorophylls; and specialized metabolites: flavonoids) and iii) physical traits.
Results revealed a negative impact of AD on the physiological functioning of Q. pubescens, which induced changes in both chemical and physical leaf defenses. First, the production of central metabolites (chlorophylls and some carotenoids) increased in response to AD – illustrating the acclimation of this species to long-term drought since these metabolites preserve photosynthetic apparatus from extreme oxidative stress (Gallé et al. 2007). Second, trees under AD exhibited a higher non-glandular trichome density limiting water loss (Santos Tozin et al., 2016). Third, leaves featured a reduced leaf size and thickness reducing tissue construction costs when environmental conditions are limiting (Peguero-Pina et al., 2016). While Q. pubescens shows some drought acclimation, two critical results suggest limited long-term resilience. First, CO2 fixation declined over 10 years of AD, showing that Q. pubescens will be increasingly affected by future climate. Second, summer flavonol concentrations declined, potentially increasing herbivore pressure due to their defensive role (Ramaroson et al., 2022).
| Are you participating to the "AnaEE Environmental Rising Star Award "? | Yes |
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