Increased root investment can explain the higher survival of seedlings of ‘mesic’ Quercus suber than ‘xeric’ Quercus ilex in sandy soils during a summer drought

Abstract

In Mediterranean-type ecosystems, drought is considered the main ecological filter for seedling establishment. The evergreen oaks Quercus ilex L. and Quercus suber L. are two of the most abundant tree species in the Mediterranean Basin. Despite their shared evergreen leaf habit and ability to resist low soil water potentials, traditionally it has been suggested that Q. ilex is better suited to resist dry conditions than Q. suber. In this study, we examined how seedlings of Q. ilex and Q. suber grown in sandy soils responded to different levels of water availability using natural dry conditions and supplemental watering. Specifically, we estimated survival and water status of seedlings and explored the role of acorn mass and belowground biomass in seedling performance. To our surprise, Q. suber was better able to survive the summer drought in our experiment than Q. ilex. Nearly 55% of the Q. suber seedlings remained alive after a 2-month period without rain or supplemental water, which represents almost 20% higher survival than Q. ilex over the same period. At the end of the dry period, the surviving seedlings of Q. suber had strikingly higher water potential, potential maximum quantum yield of photosystem II (Fv/Fm) and stomatal conductance (gs) than those of Q. ilex. Acorn mass was associated with the probability of survival under dry conditions; however, it did not explain the differences in survival or water status between the species. In contrast, Q. suber had a higher root ratio and root:shoot ratio than Q. ilex and these traits were positively associated with predawn leaf water potential, Fv/Fm, gs and survival. Taken together, our results suggest that the higher relative investment in roots by Q. suber when growing in a sandy acidic substrate allowed this species to maintain better physiological status and overall condition than Q. ilex, increasing its probability of survival in dry conditions.

Multi‐trait genetic variation in resource‐use strategies and phenotypic plasticity correlates with local climate across the range of a Mediterranean oak (Quercus faginea)

“…2; Table S7). Previous studies have similarly reported higher sclerophylly for both oak populations and species inhabiting drier sites (Wright et al ., 2001; Niinemets, 2015; Ramírez‐Valiente et al ., 2015b; Ghouil et al ., 2020; Sancho‐Knapik et al ., 2021), with precipitation appearing as a major driver of the evolution of SLA and leaf thickness in species from seasonally‐dry ecosystems (Ramírez‐Valiente et al ., 2010, 2019). The functional basis of the association between sclerophylly and water limitation is under ongoing debate (but see Gil‐Pelegrín et al ., 2017; Alonso‐Forn et al ., 2020).…”

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

“…(2013) in a study on P. pinaster populations growing in two common garden experiments found that root biomass was positively associated with T 50 (time at which populations reached 50% of mortality) and with the survival rate in the xeric common garden at the end of the experiment, supporting an adaptive role of root investment under dry conditions. The benefits of higher root investment are usually related to the fact that deep and well‐developed root systems increase access to groundwater and allow plants to maintain a better water status under low soil water potentials (Lloret et al., 1999; Markesteijn & Poorter, 2009; Ramírez‐Valiente et al., 2019). Consistent with these patterns, Matías et al.…”

Responses and Differences in Tolerance to Water Shortage under Climatic Dryness Conditions in Seedlings from Quercus spp. and Andalusian Q. ilex Populations

“…suber and Q. ilex. F v /F m has been employed as a parameter of Quercus performance under drought conditions [60,67], although in some cases different results when comparing species, e.g., Q. ilex and Q. suber, have been reported [68]. This can be due to either the severity of the stress, as well as the genotype, developmental stage, or the climate conditions employed.…”