A comparative study on stomatal control under water deficit was conducted on grapevines of the cultivars Grenache, of Mediterranean origin, and Syrah of mesic origin, grown near Montpellier, France and Geisenheim, Germany. Syrah maintained similar maximum stomatal conductance (gmax) and maximum leaf photosynthesis (Amax) values than Grenache at lower predawn leaf water potentials, Ψleaf, throughout the season. The Ψleaf of Syrah decreased strongly during the day and was lower in stressed than in watered plants, showing anisohydric stomatal behaviour. In contrast, Grenache showed isohydric stomatal behaviour in which Ψleaf did not drop significantly below the minimum Ψleaf of watered plants. When g was plotted versus leaf specific hydraulic conductance, Kl, incorporating leaf transpiration rate and whole-plant water potential gradients, previous differences between varieties disappeared both on a seasonal and diurnal scale. This suggested that isohydric and anisohydric behaviour could be regulated by hydraulic conductance. Pressure-flow measurements on excised organs from plants not previously stressed revealed that Grenache had a two- to three-fold larger hydraulic conductance per unit path length (Kh) and a four- to six-fold larger leaf area specific conductivity (LSC) in leaf petioles than Syrah. Differences between internodes were only apparent for LSC and were much smaller. Cavitation detected as ultrasound acoustic emissions on air-dried shoots showed higher rates for Grenache than Syrah during the early phases of the dry-down. It is hypothesized that the differences in water-conducting capacity of stems and especially petioles may be at the origin of the near-isohydric and anisohydric behaviour of g.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.2003.01064.x

Differences in hydraulic architecture account for near‐isohydric and anisohydric behaviour of two field‐grown Vitis vinifera L. cultivars during drought

Plant hydraulic conductance, namely the rate of water flow inside plants per unit time and unit pressure difference, varies largely from plant to plant and under different environmental conditions. Herein the main factors affecting: (a) the scaling between whole-plant hydraulic conductance and leaf area; (b) the relationship between gas exchange at the leaf level and leaf-specific xylem hydraulic conductance; (c) the short-term physiological regulation of plant hydraulic conductance under conditions of ample soil water, and (d) the long-term structural acclimation of xylem hydraulic conductance to changes in environmental conditions are reviewed. It is shown that plant hydraulic conductance is a highly plastic character that varies as a result of multiple processes acting at several time scales. Across species ranging from coniferous and broad-leaved trees to shrubs, crop and herbaceous species, and desert subshrubs, hydraulic conductance scaled linearly with leaf area, as expected from first principles. Despite considerable convergence in the scaling of hydraulic properties, significant differences were apparent across life forms that underlie their different abilities to conduct gas exchange at the leaf level. A simple model of carbon allocation between leaves and support tissues explained the observed patterns and correctly predicted the inverse relationships with plant height. Therefore, stature appears as a fundamental factor affecting gas exchange across plant life forms. Both short-term physiological regulation and long-term structural acclimation can change the levels of hydraulic conductance significantly. Based on a meta-analysis of the existing literature, any change in environmental parameters that increases the availability of resources (either above- or below-ground) results in the long-term acclimation of a less efficient (per unit leaf area) hydraulic system.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-3040.2003.00991.x

The ecological significance of long-distance water transport: short-term regulation, long-term acclimation and the hydraulic costs of stature across plant life forms

Summary
1Water is a key resource in tropical savannas. Changes in vegetation structure due to land-use change and increased fire frequency may affect the availability of water and the flux of water through these ecosystems.
2We compared the seasonal soil moisture dynamics of two adjacent savanna ecosystems with contrasting tree densities in central Brazil. Our goal was to investigate the influence of tree density on deep water uptake, soil water dynamics and evapotranspiration.
3Soil water was measured using a depth of 7·5 m beneath the tree-dominated cerrado denso ecosystem and to 4 m beneath the grass-dominated campo sujo ecosystem. Plant-available water (PAW) throughout the cerrado denso soil profile ranged from 293 mm at the end of the dry season to 689 mm during the wet season. In the grass-dominated site, PAW in the profile ranged from 155 to 362 mm.
4During the dry season, ≈82% of the water used in cerrado denso and 67% in campo sujo was extracted from the profile below 1 m. The tree-dominated cerrado denso used 137 mm more water than the grass-dominated campo sujo. Significant deep soil water uptake was also observed during the wet season of 1998, when rainfall was below average.
5Evapotranspiration (ET) rates (estimated as change in soil moisture over time) were higher in cerrado denso than in campo sujo during both seasons. Estimated ET ranged from 1·4 mm day−1 during the dry season to 5·8 mm day−1 for the wet season in cerrado denso, and from 0·9 mm day−1 in the dry season to 4·5 mm day−1 in early wet season in campo sujo. The differences in PAW and ET rates between the two ecosystems are associated not only with differences in root distribution, but also with differences in tree densities and the phenology of full-leaf canopies.
6Our results suggest that deep-rooted plants may contribute significantly to the water balance of cerrado ecosystems, and that the hydrological cycle of this biome could change as woody vegetation is replaced by exotic grasses and agricultural crops.

https://besjournals.onlinelibrary.wiley.com/doi/pdf/10.1111/j.1365-2435.2005.01003.x

Deep root function in soil water dynamics in cerrado savannas of central Brazil

https://fs.fed.us/pnw/pubs/journals/meinzer-watertransport.pdf

Water transport in trees: current perspectives, new insights and some controversies

Australia, the flattest, driest, and geologically oldest vegetated continent, has a uniquely high proportion of nutrient-poor soils. We develop a "Nutrient-Poverty/Intense-Fire Theory," which postulates that most anomalous features of organisms and ecosystems of Australia are the evolutionary consequences of adaptations to nutrient poverty, compounded by intense fire that tends to occur as a result of nutrient poverty. The fundamental tenet of the theory is that plants growing in environments with plentiful light and periodic adequate moisture, but on soils poor in phosphorus, zinc, and other indispensible nutrients, can synthesize carbohydrates in excess of the amount that can be combined with, or catalyzed by, these nutrients for metabolism and production of nutrient-rich foliage and reproductive tissues. They use this "expendable energy" to produce well-defended foliage, large quantities of lignified tissues, and readily digestible exudates. Rapid accumulation of nutrient-poor biomass, a result of low rates of herbivory, provides fuel for intense fire. Intense fire exacerbates nutrient poverty by volatilizing certain micronutrients critical for animals. Anomalous features of organisms of Australia that can be explained by this theory, rather than by climate or phylogenetic history alone, include the following: most woody plants have long-lived, durable foliage; plants defend their tissues primarily with carbon-rich but nutrient-poor compounds; an unusually high proportion of plants protects seeds from fire and granivores in sturdy, woody capsules or follicles; plants allocate unusually large amounts of expendable energy to production of carbon-based exudates, such as nectar and gums; an unusually high proportion of plant species is pollinated by vertebrates that average larger size than pollinators on other continents; herbivores are small and have slow metabolism; there are no ruminants, mammals that eat mainly subterranean plant matter, or fungus-culturing termites and ants; vegetation dominated by leaf-spinescent plants is more extensive than vegetation dominated by stem-spinescent plants; nitrogen-fixing plants are major components of most vegetation types; there is a higher proportion of myrmecochorous plant species than on any other continent; there are hardly any stem-succulent and few leaf-succulent, perennial, non-halophytic plant species; and an unusually high proportion of bird species breeds cooperatively. Although the Nutrient-Poverty/Intense-Fire Theory can provide plausible explanations for these anomalous features, some puzzles remain, among them the great success of introduced herbivores, the lack of grazers on extensive grasslands on cracking clays, the apparently low productivity of ants, and the prominence of the parasitic plants of Australia. By examining the ratios of available energy to nutrients, particularly scarce nutrients, ecologists may identify processes not previously recognized as important for life forms or biotic adaptation on other continents.

Ecology of Australia: the effects of nutrient-poor soils and intense fires.

1. Seasonal regulation of transpiration was studied in four evergreen woody species growing in a Brazilian cerrado (savanna) site with a 5 month dry season.



2. Both seasonal and interspecifc variation in leaf water potential (ΨL) were relatively small. Predawn ΨL was about 0·1–0·25 MPa more negative in the dry season than in the wet season.



3. The dependence of maximum whole-plant sap flow rates on sapwood area was similar among all four species during both the wet and dry seasons. When total daily sap flow on a leaf area basis was normalized by the daily average air saturation deficit (ASD), only one of the four species showed significantly greater water use during the wet season.



4. Although seasonal differences in regulation of transpiration were not pronounced, strong stomatal limitation of both maximum daily transpiration rates and total daily transpiration was evident during both the wet and dry seasons. Sap flow typically increased sharply in the morning, briefly attained a maximum value by about 09.30–10.30 h, then decreased sharply, despite steadily increasing solar radiation and atmospheric evaporative demand.



5. The total leaf area-specific apparent hydraulic conductance of the soil/leaf pathway (Gt) varied among plants and diurnally. The identical linear dependence of transpiration and stomatal conductance (gs) on Gt among the four study species suggested that stomatal adjustment to variation in Gt limited transpiration over the entire range of Gt observed.



6. When gs was normalized for daily variation in Gt, about 80% of the remaining variation in gs was associated with variation in ASD. The results suggested that transpiration in these species was not limited by soil water availability per se, but by high atmospheric evaporative demand and hydraulic constraints possibly arising from their deep rooting habit.

Atmospheric and hydraulic limitations on transpiration in Brazilian cerrado woody species

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Atmospheric and hydraulic limitations on transpiration in Brazilian cerrado woody species