Tree Physiology 00, 1–14 doi:10.1093/treephys/tpaa159 Research paper Intraspecific plasticity in hydraulic and stomatal regulation under drought is linked to aridity at the seed source in a wild pear species Indira Paudel 1,2,5 , Hadas Gerbi 2 , Annat Zisovich 3 , Gal Sapir 4 and Tamir Klein 1 1 Department of Plant and Environmental Sciences, Weizmann Institute of Science, Rehovot 76100, Israel; 2 Department of Forestry and Natural Recourses, Purdue University, West Lafayette, IN 47907, USA; 3 Extension Service, Ministry of Agriculture, Kiryat Shmona 10200, Israel; 4 MIGAL – Galilee Research Institute, PO Box 831, Kiryat Shemona 11016, Israel; 5 Corresponding author (tamir.klein@weizmann.ac.il) Received September 9, 2020; accepted November 11, 2020; handling Editor Roberto Tognetti Adaptations of fruit trees to future climate are a current research priority due to the rapid increase in air temperature and changes in precipitation patterns. This is aimed at securing sustainable food production for our growing populations. Key physiological traits in trees conferring drought tolerance are resistance to embolism and stomatal control over water loss. Recently, we have shown in the field that a native wild pear species performs better under drought than two cultivated pear species. A comparative greenhouse study was conducted to investigate traits associated with drought tolerance in four ecotypes of a wild pear species (Pyrus syriaca Boiss), compared with a wild pear species (Pyrus betulifolia Bunge) commonly used as a pear rootstock. Seed sources were collected from semi-arid, sub-humid and humid sites across northern Israel. Measurements of water relations, leaf physiology, hydraulic conductivity and percent loss of hydraulic conductivity (PLC) were conducted under standard irrigation, drought and recovery from drought. The four P. syriaca ecotypes maintained significantly higher leaf gas exchange values and water-use efficiency and had lower PLC than the rootstock species under prolonged drought as well as during recovery. Across the four ecotypes, stomatal closure occurred at stem water potential () around −3.5 MPa; however,  at 50% PLC ranged from −4.1 MPa in the humid ecotype to −5.2 MPa in one of the semi-arid ecotypes, rendering the latter with a higher hydraulic safety margin (the  difference between stomatal closure and 50% PLC). Divergence of the ecotypes in xylem vulnerability to embolism closely matched the mean annual precipitation at their seed sources. Thus, selection of pear ecotypes from populations in semi-arid sites may be better than the currently used plant material for preparing our cultivated species for hotter and drier future climate. Keywords: fruit trees, local adaptation, phenotypic plasticity, recovery from drought, water stress. Introduction Demand for food is intensifying with an increasing human pop- ulation; at the same time, greenhouse gas emissions and land- use changes are altering our global climate (IPCC 2014). The altered climate trend shows increasing frequency of extreme temperature (Ganguly et al. 2009, Coumou and Robinson 2013, Stéfanon et al. 2014) and drought (Groisman and Knight 2008, Hansen et al. 2012), especially in drier regions. Under these conditions, physiological functions and hydraulic balance in trees could be weakened, which can lead to lower crop yield (Ciais et al. 2005) and increased mortality (Allen et al. 2014, McDowell and Allen 2015), further compromising food pro- duction. However, currently, commonly grown varieties are not suitable (Paudel et al. 2019), as most of the traditional breed- ing has focused on yield and productivity. Therefore, plants’ physiological traits must be adjusted to the changing conditions to ensure agronomical productivity. Studies on mechanisms of growth and survival of relatives of cultivated species and their © The Author(s) 2020. Published by Oxford University Press. All rights reserved. For permissions, please e-mail: journals.permission@oup.com. Downloaded from https://academic.oup.com/treephys/advance-article/doi/10.1093/treephys/tpaa159/5991962 by Weizmann Institute of Science Library user on 25 February 2021