Phenotypic plasticity and genetic adaptation of functional traits influences intra-specific variation in hydraulic efficiency and safety

Abstract

Understanding which hydraulic traits are under genetic control and/or are phenotypically plastic is essential in understanding how tree species will respond to rapid shifts in climate. We quantified hydraulic traits in Eucalyptus obliqua L'Her. across a precipitation gradient in the field to describe (i) trait variation in relation to long-term climate and (ii) the short-term (seasonal) ability of traits to adjust (i.e., phenotypic plasticity). Seedlings from each field population were raised under controlled conditions to assess (iii) which traits are under strong genetic control. In the field, drier populations had smaller leaves with anatomically thicker xylem vessel walls, a lower leaf hydraulic vulnerability and a lower water potential at turgor loss point, which likely confers higher hydraulic safety. Traits such as the water potential at turgor loss point and ratio of sapwood to leaf area (Huber value) showed significant adjustment from wet to dry conditions in the field, indicating phenotypic plasticity and importantly, the ability to increase hydraulic safety in the short term. In the nursery, seedlings from drier populations had smaller leaves and a lower leaf hydraulic vulnerability, suggesting that key traits associated with hydraulic safety are under strong genetic control. Overall, our study suggests a strong genetic control over traits associated with hydraulic safety, which may compromise the survival of wet-origin populations in drier future climates. However, phenotypic plasticity in physiological and morphological traits may confer sufficient hydraulic safety to facilitate genetic adaptation.

Intra‐specific trait variation remains hidden in the environment

“…Bresson et al ., 2011). Leaf functional traits have also been shown to vary from season to season altering the relationship with climate‐of‐origin (Pritzkow et al ., 2019).…”

Aridity drives coordinated trait shifts but not decreased trait variance across the geographic range of eight Australian trees

“…Even though these morphological traits integrate numerous drought‐related and nondrought‐related anatomical traits, multiple tree species have been found to adjust at least one of these traits depending on water availability (Martinez‐Vilalta et al ., 2009; Anderegg & HilleRisLambers, 2015; Rosas et al ., 2019). Moreover, in recent studies of Eucalyptus species, changes in LMA, HV and WD were associated with more physiologically direct mechanisms of drought tolerance such as changes in xylem anatomy and vulnerability to embolism (Pfautsch et al ., 2012; Zolfaghar et al ., 2015; Pfautsch et al ., 2016; Li et al ., 2018b; Pritzkow et al ., 2019), suggesting that they are relevant markers of drought resistance in eucalypts. These traits are also central to our understanding of plant carbon allocation and carbon stocks.…”

Phenotypic Plasticity of Drought Tolerance Traits in a Widespread Eucalypt (Eucalyptus obliqua)

“…In angiosperms, the hydraulic safety margin can be calculated as the difference between Ψ MD and sapwood P 88 , as P 88 has been identified as a mortality threshold [54]. The leaf P 88 for E. obliqua at this site was −4.72 MPa [25], and the lowest observed Ψ MD was −2.24 MPa (Figure 4a), which indicates a wide safety margin and a low risk of drought-induced mortality. In a drought mortality experiment in two-year-old E. obliqua trees drought mortality occurred at a Ψ PD of −6 MPa (Pritzkow et al, under revision), indicating a large hydraulic safety margin for trees at this site.…”

“…Eucalyptus obliqua L'Hérit, the first described eucalypt, is one of the most widespread and economically important species, ranging from New South Wales in the north to Tasmania in the south and to South Australia in the west [24]. The species shows distinct trait variation among populations, with populations at drier sites being more drought-tolerant with lower Ψ TLP , lower P 50 /P 88 , lower leaf area, and smaller leaves [25]. The expression of many of these traits is strongly genetically controlled, which suggests that individual populations might have different vulnerabilities to seasonal drought and potentially longer-term shifts in climate [25].…”

“…The species shows distinct trait variation among populations, with populations at drier sites being more drought-tolerant with lower Ψ TLP , lower P 50 /P 88 , lower leaf area, and smaller leaves [25]. The expression of many of these traits is strongly genetically controlled, which suggests that individual populations might have different vulnerabilities to seasonal drought and potentially longer-term shifts in climate [25].…”