High safety margins to drought‐induced hydraulic failure found in five pasture grasses

Abstract

Determining the relationship between reductions in stomatal conductance (gs) and leaf water transport during dehydration is key to understanding plant drought responses. While numerous studies have analysed the hydraulic function of woody species, minimal research has been conducted on grasses. Here, we sought to characterize hydraulic vulnerability in five widely‐occurring pasture grasses (including both C3 and C4 grasses) and determine whether reductions in gs and leaf hydraulic conductance (Kleaf) during dehydration could be attributed to xylem embolism. Using the optical vulnerability (OV) technique, we found that all species were highly resistant to xylem embolism when compared to other herbaceous angiosperms, with 50% xylem embolism (PX50) occurring at xylem pressures ranging from −4.4 to −6.1 MPa. We observed similar reductions in gs and Kleaf under mild water stress for all species, occurring well before PX50. The onset of xylem embolism (PX12) occurred consistently after stomatal closure and 90% reduction of Kleaf. Our results suggest that factors other than xylem embolism are responsible for the majority of reductions in gs and Kleaf during drought and reductions in the productivity of pasture species under moderate drought may not be driven by embolism.

Belowground carbon allocation, root trait plasticity, and productivity during drought and warming in a pasture grass

“…This finding is at odds with expectations based on the functional equilibrium theory ( Lambers, 1983 ), whereby plants are expected to increase f BNPP ( Hui and Jackson, 2006 ; Franco et al , 2020 ) and RMF ( Poorter et al , 2012 ; Eziz et al , 2017 ) in response to drought since a greater proportional biomass investment belowground can increase the acquisition of water and other soil resources ( Wilcox et al , 2015 ; Zhang et al , 2017 ; Chandregowda et al , 2022a ). The observed reduction in BNPP and f BNPP in our study might be due to the large drought effect size on aboveground physiology, such as a reduction in leaf water potential and associated impacts on overall plant C assimilation (reported in Jacob et al , 2022 ) and the resulting decrease in the availability of carbohydrates to invest in belowground production. A reduction in new C allocation belowground during drought observed in pulse-labelling studies elsewhere ( Hasibeder et al , 2015 ; R.Wang et al , 2021 ) supports our findings.…”

Coordination of hydraulic and morphological traits across dominant grasses in eastern Australia

“…Previous studies have simultaneously tracked declines in K leaf and g s during drought to identify hydraulic safety margins with the assumption that reduced K leaf reflects xylem cavitation (Skelton et al, 2015); however, the rehydration kinetics method used here to quantify P88 Kleaf and P50 Kleaf does not directly measure cavitation events (Brodribb & Holbrook, 2003). Indeed, recent analyses of monocot responses to drought indicated that significant declines in K leaf can occur prior to a visual detection of cavitation events in the leaf (Jacob et al, 2022; Ocheltree et al, 2020). Thus, declines in K leaf during dehydration observed here are likely due to resistance in the extra‐xylary pathway of water transport unrelated to cavitation, such as membrane damage and leakage (Ocheltree et al, 2020).…”

Drought survival and recovery in grasses: Stress intensity and plant–plant interactions impact plant dehydration tolerance

“…has mainly been carried out on detached branches or grass stems (Lens et al, 2013;Urli et al, 2013) and more recently on grass leaves (Jacob et al, 2022;Ocheltree et al, 2016), as a marker of xylem embolism resistance. However, as plant dry-down time was found to be unrelated to embolism resistance, it is now advocated to consider rooting depth that determines plant water availability and survival times .…”

“…The coexistence influence trait expression and phenotypes of associated plants (terHorst et al, 2018; Wang & Callaway, 2021), impacting their adaptation to drought (Zenes et al, 2020). Furthermore, biodiversity is increasingly recognized to buffer plant communities against the negative impacts of climate extremes (Isbell et al, 2017; Loreau et al, 2021) like drought (Wagg et al, 2017; Wright et al, 2021) due to positive plant–plant interactions (e.g., facilitation) and complementarity effects among plants (e.g., niche difference), which together have a potentially positive effect (i) on plant survival during drought and (ii) on plant recovery after the drought (Haberstroh et al, 2021). However, few studies have assessed how positive or negative interactions between neighbouring plants directly affect plant dehydration tolerance, drought survival and drought recovery (Griffin‐Nolan et al, 2021).…”