Abstract
Background and AimsPlant survival under extreme drought events has been associated with xylem vulnerability to embolism (the disruption of water transport due to air bubbles in conduits). Despite the ecological and economic importance of herbaceous species, studies focusing on hydraulic failure in herbs remain scarce. Here, we assess the vulnerability to embolism and anatomical adaptations in stems of seven herbaceous Brassicaceae species occurring in different vegetation zones of the island of Tenerife, Canary Islands, and merged them with a similar hydraulic–anatomical data set for herbaceous Asteraceae from Tenerife.MethodsMeasurements of vulnerability to xylem embolism using the in situ flow centrifuge technique along with light and transmission electron microscope observations were performed in stems of the herbaceous species. We also assessed the link between embolism resistance vs. mean annual precipitation and anatomical stem characters.Key ResultsThe herbaceous species show a 2-fold variation in stem P50 from –2.1 MPa to –4.9 MPa. Within Hirschfeldia incana and Sisymbrium orientale, there is also a significant stem P50 difference between populations growing in contrasting environments. Variation in stem P50 is mainly explained by mean annual precipitation as well as by the variation in the degree of woodiness (calculated as the proportion of lignified area per total stem area) and to a lesser extent by the thickness of intervessel pit membranes. Moreover, mean annual precipitation explains the total variance in embolism resistance and stem anatomical traits.ConclusionsThe degree of woodiness and thickness of intervessel pit membranes are good predictors of embolism resistance in the herbaceous Brassicaceae and Asteraceae species studied. Differences in mean annual precipitation across the sampling sites affect embolism resistance and stem anatomical characters, both being important characters determining survival and distribution of the herbaceous eudicots.
Highlights
Hydraulic failure is one of the main physiological mechanisms associated with reductions in forest productivity and drought-induced tree mortality (Choat et al, 2012; Anderegg et al, 2016; Adams et al, 2017)
The vulnerability to xylem embolism can be measured by vulnerability curves, in which the percentage loss of hydraulic conductivity is plotted against the xylem pressure (Cochard et al, 2010, 2013)
Interspecific and intraspecific stem P50 variation across herbaceous eudicots is strongly linked to precipitation
Summary
Hydraulic failure is one of the main physiological mechanisms associated with reductions in forest productivity and drought-induced tree mortality (Choat et al, 2012; Anderegg et al, 2016; Adams et al, 2017). The P50 value, referring to the negative pressure associated with 50 % loss of hydraulic conductivity, is an oft-cited proxy for plant drought resistance, it does not present a critical threshold value for angiosperms (Urli et al, 2013; Adams et al, 2017). There is considerable interspecific variation in P50 across plant species, from –0.5 MPa up to –19 MPa, and the majority of studies show that species from dry environments are generally more resistant to embolism (more negative P50) than species from wet environments (Choat et al, 2012; Lens et al, 2013, 2016; Larter et al, 2015). Knowledge about intraspecific variation in P50 remains scarce and provides contradictory results: it seems to be species specific, but it can vary either considerably (Kolb and Sperry, 1999; Choat et al, 2007; Corcuera et al, 2011; Nolf et al, 2014, 2016; Volaire et al, 2018; Cardoso et al, 2018) or subtly (Holste et al, 2006; MartínezVilalta et al, 2009; Lamy et al, 2013; Ahmad et al, 2017), or may even be absent (Maherali et al, 2009; Wortemann et al, 2011) for woody as well as for herbaceous species
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