Xylem cavitation caused by drought and freezing stress in four co‐occurring Juniperus species

Abstract

Previous studies indicate that conifers are vulnerable to cavitation induced by drought but in many cases, not by freezing. Rarely have vulnerability to drought and freezing stress been studied together, even though both influence plant physiology and the abundance and distribution of plants in many regions of the world. We studied vulnerability to drought-and freezinginduced cavitation, along with wood density, conduit reinforcement, tracheid diameter, and hydraulic conductivity, in four Juniperus species that typically occupy different habitats, but uniquely co-occur at the same site in Arizona, AZ. We combined drought with a freeze-thaw cycle to create freezing-induced vulnerability curves. All four species demonstrated greater vulnerability to drought þ freezing-than to drought-induced cavitation alone (P < 0.0001). Mean tracheid diameter was correlated with vulnerability to drought þ freezing-induced cavitation (r 5 0.512, P 5 0.01). The vulnerability to cavitation of each species followed expected rankings based on relative moisture within each species' natural distribution. Species with naturally drier distributions showed greater resistance to both drought-and drought þ freezing-induced cavitation. Even conifer species with relatively small tracheid diameters can experience xylem embolism after a single freeze-thaw cycle when under drought stress.

Response of &lt;i&gt;Pinus sylvestris&lt;/i&gt; roots to sheet-erosion exposure: an anatomical approach

“…Under a synergic humidity and temperature stress from drought and freezing, xylem cavitation would make trees highly vulnerable. A narrowing of tracheid sizes protects against embolism and can be seen as an advantageous adaptation (Pitterman and Sperry, 2003;Willson and Jackson, 2006).…”

Investigations Concerning Cavitation and Frost Fatigue in Clonal 84K Poplar Using High-Resolution Cavitron Measurements

“…Unlike methods from other studies (Améglio et al, 2001;Willson and Jackson, 2006;Christensen-Dalsgaard and Tyree, 2013), we froze and thawed the plant material at known tensions in the stems while spinning in a cavitron. We chose tensions of 0.088, 0.5, 1, and 1.5 MPa to continue the frost-fatigue test.…”

“…Larger bubbles may form in conduits with a larger diameter, so species with larger conduits are more vulnerable to frost-induced embolism (Langan et al, 1997;Davis et al, 1999;Pittermann and Sperry, 2006). Furthermore, enhanced loss of hydraulic conductivity (K h ) of trees may occur when stems are subjected to a combination of frost and drought causing low xylem water potential (Mayr et al, 2003;Willson and Jackson, 2006) and repeated freeze-thaw cycles (Sperry and Sullivan, 1992;Cox and Zhu, 2003;Mayr et al, 2003). However, even trees with small conduits are found to suffer severe embolism in winter Améglio et al, 2002) due mostly to freezing-drying of stems.…”

Irreversible diameter change of wood segments correlates with other methods for estimating frost tolerance of living cells in freeze-thaw experiment: a case study with seven urban tree species in Helsinki

“…Gases dissolved in the apoplastic sap form bubbles during freezing, and these bubbles are a risk of expanding and creating an embolism if thawing occurs when sap is under tension (Sperry and Sullivan 1992). Winter embolism causes long-term blockages to water transport and is known to decrease xylem conductivity (Sperry and Sullivan 1992;Sperry et al 1994;Davis et al 1999;Pittermann and Sperry 2003;Wheeler et al 2005;Wilson and Jackson 2006;Charrier et al 2014). The second important aspect of freezing stress experienced by trees is frostinduced cellular damage, i.e., cell membrane rupture caused by ice crystal formation within the living cells or through an extreme water potential difference between the living cells and the apoplast and the consequent extreme shrinking-swelling cycles of living cells upon freeze-thaw events (e.g., Ristic and Ashworth 1993;Thomashow 1998).…”