• Background and Aims More intense droughts under climate change threaten species resilience. Hydraulicstrategies determine drought survival in woody plants but have been hardly studied in... Show more• Background and Aims More intense droughts under climate change threaten species resilience. Hydraulicstrategies determine drought survival in woody plants but have been hardly studied in herbaceous species. Weexplored the intraspecific variability of hydraulic and morphological traits as indicators of dehydration tolerancein a perennial grass, cocksfoot (Dactylis glomerata), which has a large biogeographical distribution in Europe.• Methods Twelve populations of cocksfoot originating from Mediterranean, Temperate and Northern Europeanareas were grown in a controlled environment in pots. Dehydration tolerance, leaf and stem anatomical traits andxylem pressure associated with 88 or 50 % loss of xylem conductance (P88, P50) were measured.• Key Results Across the 12 populations of cocksfoot, P50 ranged from –3.06 to – 6.36 MPa, while P88ranged from –5.06 to –11.6 MPa. This large intraspecific variability of embolism thresholds corresponded withthe biogeographical distribution and some key traits of the populations. In particular, P88 was correlated withdehydration tolerance (r = –0.79). The dehydration-sensitive Temperate populations exhibited the highest P88(–6.1 MPa). The most dehydration-tolerant Mediterranean populations had the greatest leaf dry matter content andleaf fracture toughness, and the lowest P88 (–10.4 MPa). The Northern populations displayed intermediate traitvalues, potentially attributable to frost resistance. The thickness of metaxylem vessel walls in stems was highlycorrelated with P50 (r = –0.92), but no trade-off with stem lignification was observed. The relevance of the linkagebetween hydraulic and stomatal traits is discussed for drought survival in perennial grasses.• Conclusions Compared with woody species, the large intraspecific variability in dehydration tolerance andembolism resistance within cocksfoot has consequences for its sensitivity to climate change. To better understandadaptive strategies of herbaceous species to increasing drought and frost requires further exploration of the role ofhydraulic and mechanical traits using a larger inter- and intraspecific range of species. Show less
More intense droughts under climate change threaten species resilience. Hydraulicstrategies determine drought survival in woody plants but have been hardly studied in herbaceous species. Weexplored... Show moreMore intense droughts under climate change threaten species resilience. Hydraulicstrategies determine drought survival in woody plants but have been hardly studied in herbaceous species. Weexplored the intraspecific variability of hydraulic and morphological traits as indicators of dehydration tolerancein a perennial grass, cocksfoot (Dactylis glomerata), which has a large biogeographical distribution in Europe. Twelve populations of cocksfoot originating from Mediterranean, Temperate and Northern Europeanareas were grown in a controlled environment in pots. Dehydration tolerance, leaf and stem anatomical traits andxylem pressure associated with 88 or 50 % loss of xylem conductance (P88, P50) were measured. Across the 12 populations of cocksfoot, P50 ranged from –3.06 to – 6.36 MPa, while P88ranged from –5.06 to –11.6 MPa. This large intraspecific variability of embolism thresholds corresponded withthe biogeographical distribution and some key traits of the populations. In particular, P88 was correlated withdehydration tolerance (r = –0.79). The dehydration-sensitive Temperate populations exhibited the highest P88(–6.1 MPa). The most dehydration-tolerant Mediterranean populations had the greatest leaf dry matter content andleaf fracture toughness, and the lowest P88 (–10.4 MPa). The Northern populations displayed intermediate traitvalues, potentially attributable to frost resistance. The thickness of metaxylem vessel walls in stems was highlycorrelated with P50 (r = –0.92), but no trade-off with stem lignification was observed. The relevance of the linkagebetween hydraulic and stomatal traits is discussed for drought survival in perennial grasses. Compared with woody species, the large intraspecific variability in dehydration tolerance andembolism resistance within cocksfoot has consequences for its sensitivity to climate change. To better understandadaptive strategies of herbaceous species to increasing drought and frost requires further exploration of the role ofhydraulic and mechanical traits using a larger inter- and intraspecific range of species. Show less
The water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent embolisms (gas bubbles), which could be removed by the... Show moreThe water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent embolisms (gas bubbles), which could be removed by the occurrence of root pressure, especially in grasses. Here, we studied hydraulic failure in herbaceous angiosperms by measuring the pressure inducing 50% loss of hydraulic conductance (P50) in stems of 26 species, mainly European grasses (Poaceae). Our measurements show a large range in P50 from 20.5 to 27.5 MPa, which overlaps with 94% of the woody angiosperm species in a worldwide, published data set and which strongly correlates with an aridity index. Moreover, the P50 values obtained were substantially more negative than the midday water potentials for five grass species monitored throughout the entire growing season, suggesting that embolism formation and repair are not routine and mainly occur under water deficits. These results show that both herbs and trees share the ability to withstand very negative water potentials without considerable embolism formation in their xylem conduits during drought stress. In addition, structure-function trade-offs in grass stems reveal that more resistant species are more lignified, which was confirmed for herbaceous and closely related woody species of the daisy group (Asteraceae). Our findings could imply that herbs with more lignified stems will become more abundant in future grasslands under more frequent and severe droughts, potentially resulting in lower forage digestibility. Show less
The water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent embolisms (gas bubbles), which could be removed by the occurrence of... Show moreThe water transport pipeline in herbs is assumed to be more vulnerable to drought than in trees due to the formation of frequent embolisms (gas bubbles), which could be removed by the occurrence of root pressure, especially in grasses. Here, we studied hydraulic failure in herbaceous angiosperms by measuring the pressure inducing 50% loss of hydraulic conductance (P50)in stems of 26 species, mainly European grasses (Poaceae). Our measurements show a large range in P50 from 20.5 to 27.5 MPa, which overlaps with 94% of the woody angiosperm species in a worldwide, published data set and which strongly correlates with an aridity index. Moreover, the P50 values obtained were substantially more negative than the midday water potentials for five grass species monitored throughout the entire growing season, suggesting that embolism formation and repair are not routine and mainly occur under water deficits. These results show that both herbs and trees share the ability to withstand very negative water potentials without considerable embolism formation in their xylem conduits during drought stress. In addition, structure-function trade-offs in grass stems reveal that more resistant species are more lignified, which was confirmed for herbaceous and closely related woody species of the daisy group (Asteraceae). Our findings could imply that herbs with more lignified stems will become more abundant in future grasslands under more frequent and severe droughts, potentially resulting in lower forage digestibility. Show less
