Grassland plants show no relationship between leaf drought tolerance and soil moisture affinity, but rapidly adjust to changes in soil moisture

Abstract

Assessing drought tolerance and the ability of plants to adjust to changes in available water resources is crucial for understanding current and future distributions of plant species. While turgor loss point (πtlp) has been recognized as a direct determinant of drought tolerance in woody plants, information on it for grassland species is largely missing. We first validated a rapid method to estimate πtlp for grassland species, using osmometry measurements (πtlp‐osm) of osmotic potential at full hydration (πo‐osm), originally proposed for woody species. We confirmed that πo‐osm was tightly positively related to πtlp measured by the classic pressure–volume curve (πtlp‐pv). Cell wall elasticity was not important in the maintenance of turgor and neither specific leaf area nor leaf dry matter content influenced πtlp. We then studied the relationship between πtlp‐osm measured under controlled conditions and species’ soil moisture affinity (Ellenberg indicator values) in 40 diverse grassland species from the full range of soil moisture conditions found in temperate grasslands. On a subset of 12 species, we studied the adjustment in πtlp‐osm to drought stress and recovery from drought. We hypothesized that dry grassland species are better adapted to drier conditions by having comparatively higher leaf drought tolerance (more negative πtlp) and a better ability to adjust to acute drought stress. We found that πtlp‐osm was unrelated to species’ soil moisture affinity. However, all species developed higher leaf drought tolerance by decreasing πtlp‐osm after seven weeks of drought stress. After only one week of recovery, all species reduced the leaf drought tolerance back to the πtlp‐osm level comparable with non‐stressed plants. Our results considerably extend the relationship between πo‐osm and πtlp, originally defined for woody species, and thus propose a yet unexploited direct method for assessing leaf drought tolerance via turgor loss point in herbaceous species. However, the lack of relationship between πtlp and soil moisture affinity suggests that, unlike in woody plants, leaf‐level drought tolerance in grassland plants does not fully translate into whole‐plant drought resistance, suggesting an importance of other drought resistance strategies. A plain language summary is available for this article.

Climatic limits of temperate rainforest tree species are explained by xylem embolism resistance among angiosperms but not among conifers

“…Leaf TLP was estimated from leaf osmotic potential using equation 5 from Bartlett et al (). These estimations have since been validated in other systems (Griffin‐Nolan et al , ; Májeková et al , ).…”

Drought survival is positively associated with high turgor loss points in temperate perennial grassland species

“…Turgor loss point measured with traditional P – V curve methods ( π tlp‐ P – V ) was significantly related to osmotic water potential at full turgor assessed with an osmometer ( π o‐osmo ) across all 14 grassland species, and separately within the forbs and grasses measured in our study. Additionally, relations are shown for C 3 and C 4 grasses, grasses and forbs, and herbaceous and woody species combined from this and previous studies (Bartlett, Scoffoni, Ardy, et al, ; Bartlett, Scoffoni, & Sack, ; Griffin‐Nolan et al, ; Gotsch et al, ; Ocheltree et al, ; Farrell et al, ; Májeková et al, ). Relations were significant within each of the species groups (all p < .05, see legend for r 2 values) and slopes did not differ between grasses versus forbs (this study nor combined), C 3 versus C 4 , nor herbaceous versus woody species (all p > .1).…”

“…We tested the relationships between π tlp and species moisture association based on F value (excluding generalist species with F value x ) and annual rainfall niches (median, 5th and 95th percentile) using Pearson correlation. We additionally tested differences in π tlp between species categorized as associated with dry habitats ( F value 3, 4) and with wet habitats ( F value 6, 7), excluding intermediate species with F value 5 or generalists (compare Májeková et al, ).…”

“…Various morphological or physiological traits are broadly related to habitat moisture gradients in perennial herbaceous species (Belluau & Shipley, ; Craine et al, ; Griffin‐Nolan et al, ; Shipley et al, ; Tucker, Craine, & Nippert, ). However, relations are generally weak and not consistently observed (Májeková, Martínková, & Hájek, ), and insights into the functional role of traits for species drought resistance remain limited. Recent studies have tested relations between physiological traits and leaf mortality under drought (Belluau & Shipley, ; Ocheltree, Nippert, & Prasad, ).…”

“…For example, in C 4 perennial grasses, species with high leaf resistance to hydraulic failure exhibited low π tlp , consistent with woody species (Ocheltree et al, ), but species from drier habitats had higher π tlp than those from wetter habitats, which is opposite to the trend in woody species (re‐analysed from Liu & Osborne, ). In most studies focusing on herbaceous species, π tlp was unrelated to their distributional association with the dryness of habitats (Farrell, Szota, & Arndt, ; Griffin‐Nolan et al, ; Májeková et al, ; Ocheltree et al, ) or biomes (re‐analysed only for herbaceous species from Bartlett, Scoffoni, & Sack, ). In a recent study, π tlp was instead positively correlated with the wet extremes of species distributions (Griffin‐Nolan et al, ), which was attributed to competition from more acquisitive (high‐ π tlp ) species limiting the distribution of low‐ π tlp species into wetter habitats.…”