Southeastern Rear Edge Populations of Quercus suber L. Showed Two Alternative Strategies to Cope with Water Stress

Abstract

Climate change models predict an increase in aridity, especially in the regions under Mediterranean-type climates such as the Mediterranean Basin. However, there is a lack of ecophysiological studies supporting the selection of the more drought-adapted ecotypes for reforestation programs. In this study, we analyzed the anatomical and functional adaptations of 18-month-old seedlings to drought on 16 Quercus suber L. populations from the southeastern rear edge of the species distribution in northern Tunisia growing in a common garden, in order to identify the most appropriate material to use in reforestations. The results evidenced that populations from more xeric habitats displayed the highest leaf dry mass per area (LMA) and lowest leaf area (LA) values, together with the largest increase in the bulk modulus of elasticity (Δε) in response to drought (i.e., elastic adjustment). On the other hand, some populations with intermediate values of aridity, LMA and LA displayed the sharpest increase in proline concentration (ΔPro), with a concomitant increase in osmotic potential at full turgor (Δπo) (i.e., osmotic adjustment). Therefore, two different strategies seem to drive the within-species variation of the studied Q. suber populations in response to water scarcity: (i) a water saver strategy for improving water stress tolerance through the maximization of the elastic adjustment; and (ii) a water spender strategy for maintaining water absorption and photosynthetic activity under moderate water stress through the maximization of the osmotic adjustment. We concluded that the higher elastic adjustment, together with reduced LA and increased LMA, implied a better performance under drought stress in the populations of Q. suber from more xeric habitats, which can be considered the most drought-adapted ecotypes and, consequently, the most appropriate for reforestation programs under an eventual increase in aridity.

Adaptation of Mediterranean forest species to climate: Lessons from common garden experiments

“…In Mediterranean oaks, there is ample evidence that drier provenances exhibit lower specific leaf area (SLA), and higher leaf thickness (e.g. Andivia et al., 2012; Ghouil et al., 2020; Gratani et al., 2003; Matías et al., 2019; Ramírez‐Valiente, Lorenzo, et al., 2009; Ramírez‐Valiente et al., 2010, 2011; Ramírez‐Valiente, Valladares & Aranda, 2014), consistent with an adaptive role of sclerophylly to tolerate water deficit (Table 1). Ramírez‐Valiente, Lorenzo, et al.…”

“…However, some studies have failed to find population genetic differences in this trait (e.g. Ghouil et al., 2020; Mead et al., 2019). Turgor loss point is a plastic trait highly influenced by the growing environment and the time of the year (e.g.…”

“…. However, some studies have failed to find population genetic differences in this trait (e.g Ghouil et al, 2020;Mead et al, 2019)…”

Genomic data and common garden experiments reveal climate‐driven selection on ecophysiological traits in two Mediterranean oaks

“…Mediterranean regions are characterized by summers with low precipitation, which creates a period of water stress for plants (Larcher, 2000). Differences in the length and severity of the dry season have been suggested to exert differential selective pressures driving genetic divergence in traits related to drought tolerance and resource‐use strategies (e.g., Gratani et al, 2003; Ramírez‐Valiente et al, 2009; Ramírez‐Valiente, Lorenzo, et al, 2009; Ramírez‐Valiente 2010; Andivia et al, 2012; Ghouil et al, 2020; Solé‐Medina et al, 2022). However, for most Mediterranean species the extent to which nuclear genomic divergence and functional trait divergence may have been influenced by population demographic dynamics is still not well understood.…”

Spatiotemporal Characteristics and Trends of Meteorological Droughts in the Wadi Mina Basin, Northwest Algeria

“…According to Rossi [8] the drought mitigation measures can be divided into three main categories: (1) water-supply oriented, such as using additional sources of low quality water and improvement of existing water system efficiency, (2) water-demand reduction: restriction of municipal uses and irrigation, pricing, dual distribution system, water recycling and (3) minimalization of drought impact by temporal relocation of water resources, tax relief, and development of warning systems. Knowledge about drought phenomena can also help with sustaining reforestation programs under an eventual increase in aridity [9] and with water resources planning and management via reservoirs to overcome scarcity [10].…”