Data from: Hydraulic traits are coordinated but decoupled from carbon traits in herbaceous species

Plant hydraulic traits primarily define the water regulation strategy,
thus enabling better understanding of vegetation structure, function and
dynamics under varying hydro-environments. Despite being intensively
documented in woody species, variation and correlation of hydraulic traits
across herbaceous species remain largely understudied. Here, we report on
the leaf hydraulics of nine herbs with contrasting growth forms (graminoid
and forb). Traits quantifying drought resistance, including leaf water
potential thresholds triggering xylem embolism (Px), stomatal closure
(Pgs) or leaf turgor loss point (Ptlp), and minimum conductance (gmin),
together with leaf gas exchange, morphological traits and biomass
allocation, were measured on pot grown plants. In addition, an in situ
dry-down was imposed on four representative species, with leaf gas
exchange, water potential and level of xylem embolism, being continuously
monitored during dehydration to determine the dynamics of stomatal closure
and leaf xylem embolism. We found that the studied graminoids tended to be
more drought tolerant than forbs, although the difference in hydraulic
safety margin for stomatal closure (HSMst) did not differ significantly
between these growth forms. Across species, Px was coordinated with Pgs
and Ptlp, but was decoupled from gas exchange traits, including maximum
photosynthetic rate and stomatal conductance. Furthermore, no correlations
were found between hydraulic traits and specific leaf area or the ratio of
aboveground to belowground biomass. For plants that
experienced in situ dehydration, stomatal closure always preceded
the onset of xylem embolism in leaves. Moreover, species exhibited a
distinct stomatal regulation strategy during the dehydration despite
belonging to the same growth form. Our findings contribute to the
understanding of herb hydraulics, which will inform prediction on the
dynamics of grassy ecosystems by providing traits data and guiding the
classification of plant functional types in “grassy” ecosystems.