Cavitation Limits the Recovery of Gas Exchange after Severe Drought Stress in Holm Oak (Quercus ilex L.)

Abstract

Holm oak (Quercus ilex L.) is a Mediterranean species that can withstand intense summer drought through a high resistance to cavitation far beyond the stomatal closure. Besides stomatal limitations, both mesophyll and biochemical limitations to CO2 uptake could increase in holm oak under drought. However, no studies have addressed how hydraulic and non-hydraulic factors may limit the recovery of photosynthesis when re-watering after inducing 50% loss of hydraulic conductivity. We measured photosynthetic traits, xylem embolism, and abscisic acid (ABA) in holm oak with increasing levels of drought stress and seven days after plant re-watering. Drought stress caused a sharp decrease in net CO2 assimilation (AN), stomatal and mesophyll conductance (gs and gm), and maximum velocity of carboxylation (Vcmax). The stomatal closure could be mediated by the rapid increase found in ABA. The high level of xylem embolism explained the strong down-regulation of gs even after re-watering. Therefore, only a partial recovery of AN was observed, in spite of non-hydraulic factors not limiting the recovery of AN, because i/ABA strongly decreased after re-watering, and ii/gm and Vcmax recovered their original values. Therefore, the hydraulic-stomatal limitation model would be involved in the partial recovery of AN, in order to prevent extensive xylem embolism under subsequent drought events that could compromise holm oak survival.

Cell-level anatomy explains leaf age-dependent declines in mesophyll conductance and photosynthetic capacity in the evergreen Mediterranean oak Quercus ilex subsp. rotundifolia

“…This link has been also evidenced for Q. ilex subsp. rotundifolia when describing the within-species variation in g m and A N (Peguero-Pina et al 2017b) and the response of these traits to water stress (Peguero-Pina et al 2018, Alonso-Forn et al 2021. In fact, the results here obtained support the idea that A N was mainly limited by g m and the relative importance of mesophyll limitation (l m ) increased with increasing leaf age (P < 0.05, Figure S3 available as Supplementary data at Tree Physiology Online).…”

“…Studies have also found evidence for increased photosynthetic limitation in older leaves of different plant species due to a reduced mesophyll conductance to CO 2 (g m ) (Loreto et al 1994, Flexas et al 2007a, Zhang et al 2008, Niinemets et al 2009, including Mediterranean evergreen tree species during aging and senescence (Niinemets et al 2005(Niinemets et al , 2006. In fact, g m plays a predominant role in the photosynthetic process of Mediterranean evergreen tree species, being often the most limiting factor for net CO 2 assimilation (Flexas et al 2014, Niinemets and Keenan 2014, Peguero-Pina et al 2016a, Peguero-Pina et al 2017a, Peguero-Pina et al 2018, Alonso-Forn et al 2021.…”

The xylem of anisohydric Quercus alba L. is more vulnerable to embolism than isohydric codominants

“…Thus, Ψ L,min as determined from bagged leaves is likely a close approximation of Ψ x. but may overestimate true extent of embolism propagation if equilibration between Ψ L and Ψ x was not achieved during bagging. Nevertheless, estimating native embolism in this manner yielded similar values to those reported in the literature for L. tulipifera (Johnson et al, 2016), A. saccharum (Wheeler et al, 2013) and Quercus species (Peguero‐Pina et al, 2018; Sperry & Sullivan 1992; Taneda & Sperry, 2008). We assessed differences in estimated native embolisms across species and stands with a two‐way ANOVA, where species and stand age were fixed factors and region was a blocking factor.…”

Widespread Crown Defoliation After a Drought and Heat Wave in the Forests of Tuscany (Central Italy) and Their Recovery—A Case Study From Summer 2017

“…The extreme heat and drought wave that occurred in Tuscany in summer 2017 was an occurrence within the wider context of the fate of the South European forest vegetation under climate change (Bussotti et al, 2014). Cumulative episodes of extreme drought may compromise the resilience of the ecosystems (Lloret et al, 2011) and may damage the long-term performance and survival of Mediterranean evergreen forests (Galiano et al, 2012;Peguero-Pina et al, 2018). Extreme climatic events, rather than trends (Jentsch et al, 2007), drive forest dieback and mortality and can result in dramatic changes at the landscape level.…”