An official website of the United States government
Abstract Plants differ widely in how soil drying affects stomatal conductance (gs) and leaf water potential (ψleaf), and in the underlying physiological controls. Efforts to breed crops for drought resilience would benefit from a better understanding of these mechanisms and their diversity. We grew 12 diverse genotypes of common bean (Phaseolus vulgarisL.) and four of tepary bean (P. acutifolius;a highly drought resilient species) in the field under irrigation and post‐flowering drought, and quantified responses ofgsandψleaf, and their controls (soil water potential [ψsoil], evaporative demand [Δw] and plant hydraulic conductance [K]). We hypothesised that (i) common beans would be more “isohydric” (i.e., exhibit strong stomatal closure in drought, minimisingψleafdecline) than tepary beans, and that genotypes with largerψleafdecline (more “anisohydric”) would exhibit (ii) smaller increases in Δw, due to less suppression of evaporative cooling by stomatal closure and hence less canopy warming, but (iii) largerKdeclines due toψleafdecline. Contrary to our hypotheses, we found that half of the common bean genotypes were similarly anisohydric to most tepary beans; canopy temperature was cooler in isohydric genotypes leading to smaller increases in Δwin drought; and that stomatal closure andKdecline were similar in isohydric and anisohydric genotypes.gsandψleafwere virtually insensitive to drought in one tepary genotype (G40068). Our results highlight the potential importance of non‐stomatal mechanisms for leaf cooling, and the variability in drought resilience traits among closely related crop legumes.
more »
« less
This content will become publicly available on February 1, 2026
Sensitive Hydraulic and Stomatal Decline in Extreme Drought Tolerant Species of California Ceanothus
ABSTRACT Identifying the physiological mechanisms by which plants are adapted to drought is critical to predict species responses to climate change. We measured the responses of leaf hydraulic and stomatal conductances (Kleafandgs, respectively) to dehydration, and their association with anatomy, in seven species of CaliforniaCeanothusgrown in a common garden, including some of the most drought‐tolerant species in the semi‐arid flora. We tested for matching of maximum hydraulic supply and demand and quantified the role of decline ofKleafin driving stomatal closure. AcrossCeanothusspecies, maximumKleafandgswere negatively correlated, and bothKleafandgsshowed steep declines with decreasing leaf water potential (i.e., a high sensitivity to dehydration). The leaf water potential at 50% decline ingswas linked with a low ratio of maximum hydraulic supply to demand (i.e., maximumKleaf:gs). This sensitivity ofgs, combined with low minimum epidermal conductance and water storage, could contribute to prolonged leaf survival under drought. The specialized anatomy of subg.Cerastesincludes trichomous stomatal crypts and pronounced hypodermis, and was associated with higher water use efficiency and water storage. Combining our data with comparative literature of other California species, species of subg. Cerastesshow traits associated with greater drought tolerance and reliance on leaf water storage relative to other California species. In addition to drought resistance mechanisms such as mechanical protection and resistance to embolism, drought avoidance mechanisms such as sensitive stomatal closure could contribute importantly to drought tolerance in dry‐climate adapted species.
more »
« less
- PAR ID:
- 10595479
- Publisher / Repository:
- Plant, Cell and Environment
- Date Published:
- Journal Name:
- Plant, Cell & Environment
- Volume:
- 48
- Issue:
- 2
- ISSN:
- 0140-7791
- Page Range / eLocation ID:
- 1555 to 1573
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Abstract Stomatal regulation is crucial for forest species performance and survival on drought‐prone sites. We investigated the regulation of root and shoot hydraulics in threePinus radiataclones exposed to drought stress and its coordination with stomatal conductance (gs) and leaf water potential (Ψleaf). All clones experienced a substantial decrease in root‐specific root hydraulic conductance (Kroot‐r) in response to the water stress, but leaf‐specific shoot hydraulic conductance (Kshoot‐l) did not change in any of the clones. The reduction inKroot‐rcaused a decrease in leaf‐specific whole‐plant hydraulic conductance (Kplant‐l). Among clones, the larger the decrease inKplant‐l, the more stomata closed in response to drought. Rewatering resulted in a quick recovery ofKroot‐randgs. Our results demonstrated that the reduction inKplant‐l, attributed to a down regulation of aquaporin activity in roots, was linked to the isohydric stomatal behaviour, resulting in a nearly constant Ψleafas water stress started. We concluded that higherKplant‐lis associated with water stress resistance by sustaining a less negative Ψleafand delaying stomatal closure.more » « less
-
Abstract The ability to transport water through tall stems hydraulically limits stomatal conductance (gs), thereby constraining photosynthesis and growth. However, some plants are able to minimize this height‐related decrease ings, regardless of path length. We hypothesized that kudzu (Pueraria lobata) prevents strong declines ingswith height through appreciable structural and hydraulic compensative alterations. We observed only a 12% decline in maximumgsalong 15‐m‐long stems and were able to model this empirical trend. Increasing resistance with transport distance was not compensated by increasing sapwood‐to‐leaf‐area ratio. Compensating for increasing leaf area by adjusting the driving force would require water potential reaching −1.9 MPa, far below the wilting point (−1.2 MPa). The negative effect of stem length was compensated for by decreasing petiole hydraulic resistance and by increasing stem sapwood area and water storage, with capacitive discharge representing 8–12% of the water flux. In addition, large lateral (petiole, leaves) relative to axial hydraulic resistance helped improve water flow distribution to top leaves. These results indicate thatgsof distal leaves can be similar to that of basal leaves, provided that resistance is highest in petioles, and sufficient amounts of water storage can be used to subsidize the transpiration stream.more » « less
-
Abstract Leaf surface conductance to water vapor and CO2 across the epidermis (gleaf) strongly determines the rates of gas exchange. Thus, clarifying the drivers of gleaf has important implications for resolving the mechanisms of photosynthetic productivity and leaf and plant responses and tolerance to drought. It is well recognized that gleaf is a function of the conductances of the stomata (gs) and of the epidermis + cuticle (gec). Yet, controversies have arisen around the relative roles of stomatal density (d) and size (s), fractional stomatal opening (α; aperture relative to maximum), and gec in determining gleaf. Resolving the importance of these drivers is critical across the range of leaf surface conductances, from strong stomatal closure under drought (gleaf,min), to typical opening for photosynthesis (gleaf,op), to maximum achievable opening (gleaf,max). We derived equations and analyzed a compiled database of published and measured data for approximately 200 species and genotypes. On average, within and across species, higher gleaf,min was determined 10 times more strongly by α and gec than by d and negligibly by s; higher gleaf,op was determined approximately equally by α (47%) and by stomatal anatomy (45% by d and 8% by s), and negligibly by gec; and higher gleaf,max was determined entirely by d. These findings clarify how diversity in stomatal functioning arises from multiple structural and physiological causes with importance shifting with context. The rising importance of d relative to α, from gleaf,min to gleaf,op, enables even species with low gleaf,min, which can retain leaves through drought, to possess high d and thereby achieve rapid gas exchange in periods of high water availability.more » « less
-
Stomatal closure limits transpiration during drought, restricting water potential decline and delaying the onset of embolism. While critical for ensuring survival during drought, the mechanisms driving stomatal closure during drought remain equivocal. The hormone abscisic acid (ABA) will close stomata in seed plants and is synthesized as leaf turgor declines. ABA driven stomatal closure during drought is particularly apparent in species that are more isohydric. In contrast, in species that have a more anisohydric response to drought, like Fagus sylvatica, the importance of ABA in driving stomatal closure during drought is often overlooked or excluded, in place of a hypothesized passive, water potential driven stomatal closure. Here we investigated whether ABA drives stomata closure during a mid-summer drought in field grown F. sylvatica. We found that as leaf water potential declines during a drought, foliage abscisic acid (ABA) levels increase considerably and stomata close. ABA levels in leaves increase as water potentials decline to within 0.3 MPa of turgor loss point, when stomata close. Foliage ABA levels correlate with stomatal conductance throughout a drought and post-drought period. From these results we argue that it is hard to exclude increased ABA levels driving stomatal closure during drought in the anisohydric species F. sylvatica.more » « less
