Coordination and trade‐offs between leaf and stem hydraulic traits and stomatal regulation along a spectrum of isohydry to anisohydry

Abstract

The degree of plant iso/anisohydry, a widely used framework for classifying species‐specific hydraulic strategies, integrates multiple components of the whole‐plant hydraulic pathway. However, little is known about how it associates with coordination of functional and structural traits within and across different organs. We examined stem and leaf hydraulic capacitance and conductivity/conductance, stem xylem anatomical features, stomatal regulation of daily minimum leaf and stem water potential (Ψ), and the kinetics of stomatal responses to vapour pressure deficit (VPD) in six diverse woody species differing markedly in their degree of iso/anisohydry. At the stem level, more anisohydric species had higher wood density and lower native capacitance and conductivity. Like stems, leaves of more anisohydric species had lower hydraulic conductance; however, unlike stems, their leaves had higher native capacitance at their daily minimum values of leaf Ψ. Moreover, rates of VPD‐induced stomatal closure were related to intrinsic rather than native leaf capacitance and were not associated with species' degree of iso/anisohydry. Our results suggest a trade‐off between hydraulic storage and efficiency in the leaf, but a coordination between hydraulic storage and efficiency in the stem along a spectrum of plant iso/anisohydry.

Linking water relations and hydraulics with photosynthesis

“…This same mechanism is described even within a single fern species (Athyrium filixfemina) that displays different fronds with contrasting C leaf (Cardoso et al, 2019). Interestingly, the relationship between T 50 (the time at which g s is at 50%) and C leaf has also been observed in angiosperm tree species differing in their degree of iso-and anisohydry (Fu et al, 2019), although they presented higher overall T 50 values than those reported for ferns and conifers. Figure 4b shows that stomatal closure, even at the fastest rate reported in Martins et al (2016), does not prevent Ψ leaf decrease when C leaf is low.…”

“…Figure 4b shows that stomatal closure, even at the fastest rate reported in Martins et al (2016), does not prevent Ψ leaf decrease when C leaf is low. Hence, the simulation presented here implies that the stomatal response reported in Martins et al (2016) and Fu et al (2019) possibly reflects a passive hydraulic response to a sudden drop in Ψ leaf -driven by the low buffering capacity of species with low C leaf . The active stomatal control in angiosperms in response to water deficits (Brodribb and McAdam, 2011), together with the socalled 'wrong way response' of transient stomatal opening with increased transpiration (Powles et al, 2006;Buckley et al, 2011), lead to a higher sensitivity of angiosperm leaves to sudden Ψ leaf drops (Zhang et al, 2016).…”

“…The modeling described here only shows a C leaf effect on Ψ leaf at a very narrow timescale (0–60 s); however, Fu et al . () reported T 50 as high as 2500 s and still driven by C leaf . Moreover, higher C leaf has been related to the maintenance of higher midday Ψ leaf in savanna tree species (Hao et al ., ) and to the maintenance of transpiration for extended periods of time (~hours) in a mangrove species (Nguyen et al ., ).…”

“…Thus, greater branch capacitance and water storage capacity extends the time before damaging dehydration occurs (Blackman et al ., ). Surprisingly, no clear correlation between C stem and C leaf has been described (Savi et al ., ; Fu et al ., ). Zhang et al .…”

“…() and Fu et al . () possibly reflects a passive hydraulic response to a sudden drop in Ψ leaf –driven by the low buffering capacity of species with low C leaf . The active stomatal control in angiosperms in response to water deficits (Brodribb and McAdam, ), together with the so‐called ‘wrong way response’ of transient stomatal opening with increased transpiration (Powles et al ., ; Buckley et al ., ), lead to a higher sensitivity of angiosperm leaves to sudden Ψ leaf drops (Zhang et al ., ).…”