Cork oak physiological responses to manipulated water availability in a Mediterranean woodland

Abstract

This study details the physiological responses of cork oak (Quercus suber L.) to manipulated water inputs. Treatments named as dry, ambient and wet, which received 80, 100 and 120% of the annual precipitation, respectively, were applied to a Mediterranean woodland in southern Portugal. Tree ecophysiology and growth were monitored from 2003 to 2005. The impacts of the water manipulation were primarily observed in tree transpiration, especially during summer drought. Rainfall exclusion reduced the annual stand canopy transpiration by 10% over the 2-year study period, while irrigation increased it by 11%. The accumulated tree transpiration matched precipitation in spring 2004 and 2005 at the stand level, suggesting that cork oak trees rely on precipitation water sources during the peak of the growing season. However, during the summer droughts, groundwater was the main water source for trees. Despite the significant differences in soil water content and tree transpiration, no treatment effects could be detected in leaf water potential and leaf gas exchange, except for a single event after spring irrigations in the very dry year 2005. These irrigations were intentionally delayed to reduce dry spell duration during the peak of tree growing season. They resulted in an acute positive physiological response of trees from the wet treatment one week after the last irrigation event leading to a 32% raise of stem diameter increment the following months. Our results suggest that in a semi-arid environment precipitation changes in spring (amount and timing) have a stronger impact on cork oak physiology and growth than an overall change in the total annual precipitation. The extreme drought of 2005 had a negative impact on tree growth. The annual increment of tree trunk diameter in the ambient and dry treatments was reduced, while it increased for trees from the wet treatment. Water shortage also significantly reduced leaf area. The latter dropped by 10.4% in response to the extreme drought of 2005 in trees from the ambient treatment. The reduction was less pronounced in trees of the wet treatment (−7.6%), and more pronounced in trees of the dry treatment (−14.7%). Cork oak showed high resiliency to inter-annual precipitation variability. The annual accumulated tree transpiration, the minimum midday leaf water potential and the absolute amount of groundwater used Abbreviations: (A), carbon assimilation; (Amax), maximum carbon assimilation; (CV), crown volume; (DBH), diameter at breast height; (DBH inc), trunk diameter increment; (E), sap flux, tree transpiration; (E/DBH), normalized tree transpiration; (ET), potential evapotranspiration; (gs), stomatal conductance; (gsmax), maximum stomatal conductance; (Gt), whole tree specific hydraulic conductance; (LAD), leaf area density; (LAI), leaf area index; (PAR), photosynthetically active radiation; (PCA), projected crown area; (SLA), specific leaf area; (SWC), soil water content; (T), air temperature; (VPD), vapour pressure deficit; («), leaf water potential; (« md), midday leaf wat...

Drought impact on carbon and water cycling in a Mediterranean <i>Quercus suber</i> L. woodland during the extreme drought event in 2012

“…However, the strong reduction in ecosystem evapotranspiration ET o of 26 % in 2012 was vastly exceeded by the reduction in precipitation P of 54 %. This confirms recent results from Besson et al (2014) showing a certain resilience of Q. suber tree transpiration to annual water shortages. This led to ET o /P of 122 % in 2012, which is, to our knowledge, the highest value reported for montado ecosystems so far.…”

Drought-induced oak decline in the western Mediterranean region: an overview on current evidences, mechanisms and management options to improve forest resilience

“…This divergence was interpreted as a compensation mechanism to provide hydraulic conductivity if earlywood vessels experience embolism. Rainfall exclusions performed on Q. suber trees under semi-arid conditions underlined a high resilience of this species to inter-annual precipitation variability, with a remarkable recovery capacity after severe drought events (Besson et al 2014). Moreover, recent observations from NE Spain (Banqué Casanovas et al 2013) indicated that Q. ilex and Q.suber were vulnerable to drought-induced damage, but they were also able to recover rapidly.…”

“…Indeed, latter oaks are often evergreen species whose growth depends more on summer water availability (Corcuera et al 2004a, 2004b, MontserratMartí et al 2009). Within diffuse-porous oak species, Q. ilex and Q. suber show a particular sensitivity to spring precipitation (Corcuera et al 2004a, Gutiérrez et al 2011, Besson et al 2014.…”

Endemic and Emerging Pathogens Threatening Cork Oak Trees: Management Options for Conserving a Unique Forest Ecosystem

“…The changing climate may affect cork oak stands by modifying tree growth and mortality as well as cork production and quality (Besson et al 2014;Carnicer et al 2011;Oliveira et al 2002). In particular, cork growth has been shown to be reduced by drought and high temperatures (Caritat et al 2000).…”