Showing papers on "Transpiration published in 2006"
TL;DR: A mechanistic land-surface model and optimal fingerprinting statistical techniques are used to attribute observational runoff changes into contributions due to climate change and variability, and find that the trends are consistent with a suppression of plant transpiration due to CO2-induced stomatal closure.
Abstract: Despite increasing human consumption of water, there was a general upward trend in continental-scale river runoff during the past century. Some researchers claim that this is due to climate change. Gedney et al. have investigated this using a mechanistic land-surface model and a statistical ‘fingerprinting’ method that allows contributions from individual factors to be identified. A climate-change driven component in runoff variation is evident, but is insufficient to account for the whole trend. A more influential factor is reduced plant transpiration due to CO2-induced stomatal closure. To date, this effect has been neglected in projections of future water resources. As CO2 concentrations rise in future, reduced plant water usage is likely to increase both the availability of freshwater and the risk of flooding, and to add to surface warming via reduced energy loss from evaporation. Continental runoff has increased through the twentieth century1,2 despite more intensive human water consumption3. Possible reasons for the increase include: climate change and variability, deforestation, solar dimming4, and direct atmospheric carbon dioxide (CO2) effects on plant transpiration5. All of these mechanisms have the potential to affect precipitation and/or evaporation and thereby modify runoff. Here we use a mechanistic land-surface model6 and optimal fingerprinting statistical techniques7 to attribute observational runoff changes1 into contributions due to these factors. The model successfully captures the climate-driven inter-annual runoff variability, but twentieth-century climate alone is insufficient to explain the runoff trends. Instead we find that the trends are consistent with a suppression of plant transpiration due to CO2-induced stomatal closure. This result will affect projections of freshwater availability, and also represents the detection of a direct CO2 effect on the functioning of the terrestrial biosphere.
808 citations
TL;DR: In this paper, the simultaneous effects of normal transpiration through and tangential movement of a semi-infinite plate on self-similar boundary layer flow beneath a uniform free stream is considered.
661 citations
TL;DR: In this article, the authors proposed a triply green revolution to achieve a green-green revolution, which compared with the first green revolution that lifted large parts of Asia out of an imminent hunger crisis in the 1960s and 1970s, will have to be founded on principles of environmental sustainability.
Abstract: The production of biomass for direct human use—e.g., as food and timber—is by far the largest freshwater-consuming human activity on Earth. However, water policy and development concentrate on a fraction of the water for food challenge, namely, irrigated agriculture, which uses an estimated 25% of the global water used in agriculture, and on the industrial and domestic water supply, which corresponds to less than 10% of direct human water requirements considering only water for food, domestic use, and industry . The reason that biomass production so strongly outclasses other water-dependent processes is that water is one key element involved in plant growth. Simultaneous with the photosynthesis process, when stomata in the foliage open to take in carbon dioxide, large amounts of water are being consumed as transpiration flow and released as vapor from the plant canopy. Furthermore, this productive flow of vapor is accompanied by nonproductive evaporative losses of water from soil, ponded water, and intercepted water from foliage surfaces . Together, vapor fluxes as evaporation and transpiration, here defined as green-water flow, constitute the total consumptive water use in biomass production. Addressing the millennium development goal MDG of halving the proportion of malnourished people in the world by 2015, today amounting to a shocking 800 million people, is thus not only a tremendous agricultural endeavor but is also the world’s largest water-resource challenge. Hunger alleviation will require no less than a new Green revolution during the next 30 years, particularly in sub-Saharan Africa. As stated by Conway 1997 , the challenge is to achieve a green-green revolution, which compared with the first green revolution that lifted large parts of Asia out of an imminent hunger crisis in the 1960s and 1970s, will have to be founded on principles of environmental sustainability. As suggested by Falkenmark and Rockstrom 2004 , there is a third green dimension to a new agricultural revolution, since the focus will have to be on upgrading rain-fed agriculture, which entails increasing the use of the portion of rainfall that infiltrates the soil and is accessible by plants to generate vapor flow in support of biomass growth. This triply green revolution will require huge quantities of freshwater as vapor flow from the soil, through plants to the atmosphere. It raises the question of what eradicating hunger will in fact imply for water-resources planning and management.
636 citations
TL;DR: Methods to impose stable and reproducible soil water deficits are presented and were used to analyse plant responses to water stress and will help identify quantitative trait loci and genes involved in plant tolerance to water deficit.
Abstract: • The high-throughput phenotypic analysis of Arabidopsis thaliana collections requires methodological progress and automation. Methods to impose stable and reproducible soil water deficits are presented and were used to analyse plant responses to water stress. • Several potential complications and methodological difficulties were identified, including the spatial and temporal variability of micrometeorological conditions within a growth chamber, the difference in soil water depletion rates between accessions and the differences in developmental stage of accessions the same time after sowing. Solutions were found. • Nine accessions were grown in four experiments in a rigorously controlled growth-chamber equipped with an automated system to control soil water content and take pictures of individual plants. One accession, An1, was unaffected by water deficit in terms of leaf number, leaf area, root growth and transpiration rate per unit leaf area. • Methods developed here will help identify quantitative trait loci and genes involved in plant tolerance to water deficit.
524 citations
TL;DR: It is suggested that AM colonization improved the osmotic adjustment originating not from proline but from NSC, K(+), Ca(2+) and Mg(2+), resulting in the enhancement of drought tolerance.
460 citations
TL;DR: In this paper, the authors investigated the feasibility of using the normalised difference vegetation index (NDVI) derived from remote sensing data to provide indirect estimates of: (1) the leaf area index (LAI), which is a key-variable of many crop process models; and (2) crop coefficients, which represent the ratio of actual (AET) to reference (ET0) evapotranspiration.
397 citations
TL;DR: In this paper, the authors measured hydrogen isotope compositions (δD) of high-molecular-weight n-alkanes (C27−C33) from grasses grown in greenhouses and collected from the US Great Plains.
347 citations
TL;DR: In this paper, the authors measured soil moisture content at 0.05 and 0.10 m depth intervals between the soil surface and the soil-bedrock boundary on 64 locations across the trenched hillslope in the Panola Mountain Research Watershed, Georgia, USA.
346 citations
TL;DR: Garrigues et al. as mentioned in this paper presented a model describing both soil and plant processes involved in water uptake at the scale of the whole root system with explicit account of individual roots.
Abstract: Soil water uptake by plant roots results from the complex interplay between plant and soil which modulates and determines transport processes at a range of spatial and temporal scales: at small scales, uptake rates are determined by local soil and root hydraulic properties but, at the plant scale, local processes interact within the root system and are integrated through the hydraulic architecture of the root system and plant transpiration. However, because of the inherent complexity of the root system (both structural and functional), plant roots are commonly account for with synthetic but over-simplifying descriptors, valid at a given spatial scale. In this article, we present a model describing both soil and plant processes involved in water uptake at the scale of the whole root system with explicit account of individual roots. This is achieved through the unifying concepts of root system architecture and hydraulic continuity between the soil and plant. The model is based on a combination of architectural, root system hydraulic and soil water transfer modelling. The model can reproduce qualitatively and quantitatively laboratory experimental data obtained from imaging of water uptake by light transmission (cf. Garrigues et al., Water uptake by plant roots: I-Formation and propagation of a water extraction front in mature root systems as evidenced by 2D light transmission imaging. Plant and soil (2006, this issue) or X-ray imaging for two soil types (a sand/clay mix and a sandy clay loam) and different narrow-leaf lupin root systems (taprooted and fibrous), using independently measured soil–plant parameters. Results of the experiments and modelling reported in this paper concur to show that a water extraction front formed on the root system. This uptake front’s spatial extension and propagation were closely related to the local dependence between root and soil hydraulic properties and root axial conductance. Hence, a sharp front formed in the sand/clay mix but was much more attenuated in the sandy loam. Comparison between taprooted and fibrous root systems grown in a sand/clay mix, show that the taprooted architecture induced a more spatially concentrated uptake zone (near the soil surface) with higher flux rates, but with xylem water potential at the base of the root system twice as low than in the fibrous architecture. Modelling provided evidence that hydraulic lift might have occurred when transpiration declined, particularly in soil prone to abrupt variations in soil water potential (sand/clay mix). Finally, such a model, explicitly coupling root system-soil water transfers, can be useful to study water uptake in relation with root architectural traits, distribution of root hydraulic conductance or influence of heterogeneous conditions (localised irrigation, root clumping).
292 citations
TL;DR: In this article, the authors quantify the yield response of corn to deficit irrigation, and determine which of several seasonal water variables correlated best to corn yield in a semi-arid climate.
290 citations
TL;DR: Results suggest that the changes in chloroplast ultrastructure may primarily be a consequence of increased starch accumulation, and the reductions in mineral nutrient concentrations may be a result of dilution by increased concentrations of carbohydrates and also of decreases in stomatal conductance and transpiration rate.
Abstract: Leaves of Arabidopsis thaliana grown under elevated or ambient CO2 (700 or 370 micromol mol(-1), respectively) were examined for physiological, biochemical and structural changes. Stomatal characters, carbohydrate and mineral nutrient concentrations, leaf ultrastructure and plant hormone content were investigated using atomic absorption spectrophotometry, transmission electron microscopy and enzyme-linked immunosorbent assay (ELISA). Elevated CO2 reduced the stomatal density and stomatal index of leaves, and also reduced stomatal conductance and transpiration rate. Elevated CO2 increased chloroplast number, width and profile area, and starch grain size and number, but reduced the number of grana thylakoid membranes. Under elevated CO2, the concentrations of carbohydrates and plant hormones, with the exception of abscisic acid, increased whereas mineral nutrient concentrations declined. These results suggest that the changes in chloroplast ultrastructure may primarily be a consequence of increased starch accumulation. Accelerated A. thaliana growth and development in elevated CO2 could in part be attributed to increased foliar concentrations of plant hormones. The reductions in mineral nutrient concentrations may be a result of dilution by increased concentrations of carbohydrates and also of decreases in stomatal conductance and transpiration rate.
TL;DR: In this paper, the transpiration rate and conductance from both leaves and cuticula of maize plants were measured directly, showing that the role of silicon in decreasing transpiration rates must be largely attributed to the reduction in stomata rather than cuticulas.
Abstract: To characterize the effect of silicon (Si) on decreasing transpiration rate in maize (Zea mays L.) plants, the transpiration rate and conductance from both leaves and cuticula of maize plants were measured directly. Plants were grown in nutrient solutions with and without Si under both normal water conditions and drought stress [20% polyethylene glycol (PEG) concentration in nutrient solution] treatments. Silicon application of 2 mmol L−1 significantly decreased transpiration rate and conductance for both adaxial and abaxial leaf surface, but had no effect on transpiration rate and conductance from the cuticle. These results indicate that the role of Si in decreasing transpiration rate must be largely attributed to the reduction in transpiration rate from stomata rather than cuticula. Stomatal structure, element deposition, and stomatal density on both adaxial and abaxial leaf surfaces were observed with scanning electron microscopy (SEM) and a light microscope. Results showed that changes in nei...
TL;DR: Risking water loss through nighttime transpiration may provide paper birch with an ecological advantage by enabling the species to maximize photosynthesis and support rapid growth, and may also be a mechanism for delivering oxygen to respiring cells in the deep sapwood of paper Birch.
Abstract: Transpiration is generally assumed to be insignificant at night when stomata close in response to the lack of photosynthetically active radiation. However, there is increasing evidence that the stomata of some species remain open at night, which would allow for nighttime transpiration if there were a sufficient environmental driving force. We examined nighttime water use in co-occurring species in a mixed deciduous stand at Harvard Forest, MA, using whole-tree and leaf-level measurements. Diurnal whole-tree water use was monitored continuously with Granier-style sap flux sensors in paper birch (Betula papyrifera Marsh.), red oak (Quercus rubra L.) and red maple (Acer rubrum L.). An analysis was conducted in which nighttime water flux could be partitioned between refilling of internal water stores and transpiration. Substantial nighttime sap flux was observed in all species and much of this flux was attributed to the refilling of depleted water stores. However, in paper birch, nighttime sap flux frequently exceeded recharge estimates. Over 10% of the total daily sap flux during the growing season was due to transpiration at night in paper birch. Nighttime sap flux was over 8% of the total daily flux in red oak and 2% in red maple; however, this flux was mainly associated with recharge. On nights with elevated vapor pressure deficit, sap flux continued through the night in paper birch, whereas it reached zero during the night in red oak and red maple. Measurements of leaf-level gas exchange on a night with elevated vapor pressure deficit showed stomatal conductance dropping by only 25% in paper birch, while approaching zero in red oak and red maple. The study highlighted differences in ecophysiological controls on sap flux exerted by co-occurring species. Paper birch is a fast-growing, shade-intolerant species with an earlier successional status than red oak and red maple. Risking water loss through nighttime transpiration may provide paper birch with an ecological advantage by enabling the species to maximize photosynthesis and support rapid growth. Nighttime transpiration may also be a mechanism for delivering oxygen to respiring cells in the deep sapwood of paper birch.
TL;DR: Pathogenesis of Pseudoperonospora cubensis causing downy mildew of cucumber resulted in changes in the metabolic processes within cucumber leaves including the transpiration rate, which was related to disease severity as described by linear and quadratic regression curves.
Abstract: Pathogenesis of Pseudoperonospora cubensis causing downy mildew of cucumber resulted in changes in the metabolic processes within cucumber leaves including the transpiration rate. Due to the negative correlation between transpiration rate and leaf temperature, digital infrared thermography permitted a non-invasive monitoring and an indirect visualization of downy mildew development. Depending on the stage of pathogenesis and the topology of chloroses and necroses, infection resulted in a typical temperature pattern. Spatial heterogeneity of the leaf temperature could be quantified by the maximum temperature difference (MTD) within a leaf. The MTD increased during pathogenesis with the formation of necrotic tissue and was related to disease severity as described by linear and quadratic regression curves. Under controlled conditions, changes in temperature of infected leaves allowed the discrimination between healthy and infected areas in thermograms, even before visible symptoms of downy mildew appeared. Environmental conditions during thermographic measurement, in particular air temperature and humidity, as well as water content and age of the leaf influenced the temperature of its surface. Conditions enhancing the transpiration rate facilitated the detection of changes in leaf temperature of infected leaves at early stages of infection. As modified by environmental conditions, MTD alone is not suitable for the quantification of downy mildew severity in the field.
TL;DR: In this article, a 14-day period of salinity (0, 50, 100 mM NaCl) was applied to hydroponically grown cucumber plants and the results indicated that NaCl affects photosynthesis through both stomata closure and non-stomatal factors.
Abstract: Hydroponically grown cucumber plants were exposed to 14-d period of salinity (0, 50, 100 mM NaCl). NaCl caused reduction in the relative water content in the leaves. The Na+ content increased and the K+ content decreased. The net photosynthetic rate, stomatal conductance and transpiration rate were markedly decreased by all of the salt treatments. Salinity decreased also the maximum quantum efficiency of photosystem 2 (PS 2) determined as the variable to maximum fluorescence ratio, the photochemical quantum yield of PS 2 and the photochemical fluorescence quenching, while the non-photochemical quenching increased. Above results indicate that NaCl affects photosynthesis through both stomata closure and non-stomatal factors.
TL;DR: It is demonstrated that at common WUE, delta may vary by up to 3 per thousand, which is as large or larger than is commonly reported in many interspecific comparisons of delta, and adds to previous warnings about simplistic interpretations of WUE based on delta.
Abstract: Central paradigms of ecophysiology are that there are recognizable and even explicit and predictable patterns among species, genera, and life forms in the economics of water and nitrogen use in photosynthesis and in carbon isotope discrimination (delta). However most previous examinations have implicitly assumed an infinite internal conductance (gi) and/or that internal conductance scales with the biochemical capacity for photosynthesis. Examination of published data for 54 species and a detailed examination for three well-characterized species--Eucalyptus globulus, Pseudotsuga menziesii and Phaseolus vulgaris--show these assumptions to be incorrect. The reduction in concentration of CO2 between the substomatal cavity (Ci) and the site of carbon fixation (Cc) varies greatly among species. Photosynthesis does not scale perfectly with gi and there is a general trend for plants with low gi to have a larger draw-down from Ci to Cc, further confounding efforts to scale photosynthesis and other attributes with gi. Variation in the gi-photosynthesis relationship contributes to variation in photosynthetic 'use' efficiency of N (PNUE) and water (WUE). Delta is an information-rich signal, but for many species only about two-thirds of this information relates to A/gs with the remaining one-third related to A/gi. Using data for three well-studied species we demonstrate that at common WUE, delta may vary by up to 3 per thousand. This is as large or larger than is commonly reported in many interspecific comparisons of delta, and adds to previous warnings about simplistic interpretations of WUE based on delta. A priority for future research should be elucidation of relationships between gi and gs and how these vary in response to environmental conditions (e.g. soil water, leaf-to-air vapour pressure deficit, temperature) and among species.
TL;DR: The observed stability in leaf-specific apparent hydraulic conductance indicates that the two non-phreatophyte species are able to maintain sufficient water supply to their foliage via, mostly likely, effective morphological adjustment at the scale of the individual plant.
Abstract: Plant water-use strategy is considered to be a function of the complex interactions between species of different functional types and the prevailing environmental conditions. The functional type of a plant’s root system is fundamental in determining the water-use strategy of desert shrubs and the physiological responses of the plant to an occasional rainfall event, or rain pulse. In this current study of Tamarix ramosissima Ledeb. Fl.Alt., Haloxylon ammodendron (C.A.Mey.) Bunge and Reaumuria soongorica (Pall.) Maxim., three dominant shrub species in the Gurbantonggut Desert (Central Asia), plant root systems were excavated in their native habitat to investigate their functional types and water-use strategies. We monitored leaf water potential, photosynthesis and transpiration rate during a 39-day interval between successive precipitation events during which time the upper soil water changed markedly. Plant apparent hydraulic conductance and water-use efficiency were calculated for the varying soil water conditions. Our results show that: 1) The three species of shrub belong to two functional groups: phreatophyte and non-phreatophyte; 2) The photosynthetic capacity and leaf-specific apparent hydraulic conductance of the three species was stable during the time that the water condition in the upper soil changed; 3) Transpiration, leaf water potential and water-use efficiency in Tamarix ramosissima Ledeb. Fl.Alt. were stable during the period of observation, but varied significantly for the other two species. Tamarix ramosissima Ledeb. Fl.Alt., as a phreatophyte, relies mostly on groundwater for survival; its physiological activity is not inhibited in any way by the deficiency in upper soil water. Non-phreatophyte Haloxylon ammodendron (C.A.Mey.) Bunge and Reaumuria soongorica (Pall.) Maxim. use precipitation-derived upper soil water for survival, and thus respond clearly to rain pulse events in terms of leaf water potential and transpiration. The observed similarity in leaf-specific photosynthesis capacity among all three species indicates that the two non-phreatophyte species are able to maintain normal photosynthesis within a wide range of plant water status. The observed stability in leaf-specific apparent hydraulic conductance indicates that the two non-phreatophyte species are able to maintain sufficient water supply to their foliage via, mostly likely, effective morphological adjustment at the scale of the individual plant.
TL;DR: Water and solute flows in the coupled system of xylem and phloem were modeled together with predictions for xyleM and whole stem diameter changes and revealed the existence of Münch “counter flow”, i.e.,xylem water flow in the absence of transpiration resulting from water circulation between the xylems andphloem.
Abstract: Water and solute flows in the coupled system of xylem and phloem were modeled together with predictions for xylem and whole stem diameter changes. With the model we could produce water circulation between xylem and phloem as presented by the Munch hypothesis. Viscosity was modeled as an explicit function of solute concentration and this was found to vary the resistance of the phloem sap flow by many orders of magnitude in the possible physiological range of sap concentrations. Also, the sensitivity of the predicted phloem translocation to changes in the boundary conditions and parameters such as sugar loading, transpiration, and hydraulic conductivity were studied. The system was found to be quite sensitive to the sugar-loading rate, as too high sugar concentration, (approximately 7 MPa) would cause phloem translocation to be irreversibly hindered and soon totally blocked due to accumulation of sugar at the top of the phloem and the consequent rise in the viscosity of the phloem sap. Too low sugar loading rate, on the other hand, would not induce a sufficient axial water pressure gradient. The model also revealed the existence of Munch “counter flow”, i.e., xylem water flow in the absence of transpiration resulting from water circulation between the xylem and phloem. Modeled diameter changes of the stem were found to be compatible with actual stem diameter measurements from earlier studies. The diurnal diameter variation of the whole stem was approximately 0.1 mm of which the xylem constituted approximately one-third.
TL;DR: In this article, the authors measured whole plant transpiration, evapotranspiration, and CO2 fluxes over the course of a growing season at a semiarid Chihuahuan Desert shrubland site in south-eastern Arizona.
Abstract: Key to evaluating the consequences of woody plant encroachment on water and carbon cycling in semiarid ecosystems is a mechanistic understanding of how biological and non-biological processes influence water loss to the atmosphere. To better understand how precipitation is partitioned into the components of evapotranspiration (bare-soil evaporation and plant transpiration) and their relationship to plant uptake of carbon dioxide (CO2) as well as ecosystem respiratory efflux, we measured whole plant transpiration, evapotranspiration, and CO2 fluxes over the course of a growing season at a semiarid Chihuahuan Desert shrubland site in south-eastern Arizona. Whole plant transpiration was measured using the heat balance sap-flow method, while evapotranspiration and net ecosystem exchange (NEE) of CO2 were quantified using the Bowen ratio technique. Before the summer rainy season began, all water and CO2 fluxes were small. At the onset of the rainy season, evapotranspiration was dominated by evaporation and CO2 fluxes were dominated by respiration as it took approximately 10 days for the shrubs to respond to the higher soil moisture content. During the growing season, periods immediately following rain events (<2 days) were dominated by evaporation and respiration while transpiration and CO2 uptake peaked during the interstorm periods. The surface of the coarse, well-drained soils dried quickly, rapidly reducing evaporation. Overall, the ratio of total transpiration to evapotranspiration was 58%, but it was around 70% during the months when the plants were active. Peak respiration responses following rain events generally lagged after the evaporation peak by a couple of days and were better correlated with transpiration. Transpiration and CO2 uptake also decayed rather quickly during interstorm periods, indicating that optimal plant soil moisture conditions were rarely encountered. NEE of CO2 was increasingly more negative as the growing season progressed, indicating a greater net uptake of CO2 and greater water use efficiency due mainly to decreases in respiration. Copyright 2006 John Wiley & Sons, Ltd.
TL;DR: The rise of PvPIP2;1 gene expression and PIP1 protein abundance in the leaves of P. vulgaris plants subjected to drought was correlated with a decline in the transpiration rate, and the increase in the expression of the three PIP genes examined caused by drought and the decline of PIP2 protein abundance were not correlated with any of the parameters measured.
TL;DR: Biophysical and physiological analyses led to three major conclusions; the immediate reduction and sudden recovery in elongation velocity is due to changes in the water potential gradient between leaf xylem and peripheral elongating cells, and significant solute accumulation is detectable from 1 h onwards.
Abstract: Recent results concerning the short-term growth response to salinity of the developing barley leaf are reviewed. Plants were grown hydroponically and the growth response of leaf 3 was studied between 10 min and 5 d following addition of 100 mM NaCl to the root medium. The aim of the experiments was to relate changes in variables that are likely to affect cell elongation to changes in leaf growth. Changes in hormone content (ABA, cytokinins), water and solute relationships (osmolality, turgor, water potential, solute concentrations), gene expression (water channel), cuticle deposition, membrane potential, and transpiration were followed, while leaf elongation velocity was monitored. Leaf elongation decreased close to zero within seconds following addition of NaCl. Between 20 and 30 min after exposure to salt, elongation velocity recovered rather abruptly, to about 46% of the pre-stress level, and remained at the reduced rate for the following 5 d, when it reached about 70% of the level in non-stressed plants. Biophysical and physiological analyses led to three major conclusions. (i) The immediate reduction and sudden recovery in elongation velocity is due to changes in the water potential gradient between leaf xylem and peripheral elongating cells. Changes in transpiration, ABA and cytokinin content, water channel expression, and plasma membrane potential are involved in this response. (ii) Significant solute accumulation, which aids growth recovery, is detectable from 1 h onwards; growing and non-growing leaf regions and mesophyll and epidermis differ in their solute response. (iii) Cuticular wax density is not affected by short-term exposure to salt; transpirational changes are due to stomatal control.
TL;DR: Maximum daily stomatal conductance declined linearly with increasing afternoon loss of root conductivity over the course of the dry season, consistent with a transition from a disequilibrium between plant and soil psi induced by nocturnal transpiration to one induced by hydraulic redistribution of water from deeper soil layers.
Abstract: Vulnerability to water-stress-induced embolism and variation in the degree of native embolism were measured in lateral roots of four co-occurring neotropical savanna tree species. Root embolism varied diurnally and seasonally. Late in the dry season, loss of root xylem conductivity reached 80% in the afternoon when root water potential ( Y root ) was about - 2.6 MPa, and recovered to 25‐40% loss of conductivity in the morning when Y Y Y root was about - 1.0 MPa. Daily variation in Y root decreased, and root xylem vulnerability and capacitance increased with rooting depth. However, all species experienced seasonal minimum Y root close to complete hydraulic failure independent of their rooting depth or resistance to embolism. Predawn Y root was lower than Y Y Y soil when Y soil was relatively high ( > - 0.7 MPa) but became less negative than Y soil later in the dry season, consistent with a transition from a disequilibrium between plant and soil Y induced by nocturnal transpiration to one induced by hydraulic redistribution of water from deeper soil layers. Shallow longitudinal root incisions external to the xylem prevented reversal of embolism overnight, suggesting that root mechanical integrity was necessary for recovery, consistent with the hypothesis that if embolism is a function of tension, refilling may be a function of internal pressure imbalances. All species shared a common relationship in which maximum daily stomatal conductance declined linearly with increasing afternoon loss of root conductivity over the course of the dry season. Daily embolism and refilling in roots is a common occurrence and thus may be an inherent component of a hydraulic signaling mechanism enabling stomata to maintain the integrity of the hydraulic pipeline in long-lived structures such as stems.
TL;DR: In this article, changes in plant growth, photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean [Glycine max (L.) Merr.] plants under drought stress were studied.
Abstract: Changes in plant growth, photosynthetic gas exchange, chlorophyll fluorescence and stem diameter of soybean [Glycine max (L.) Merr.] plants under drought stress were studied. Total plant dry mass was reduced by 30 % compared to well-watered control plants. Leaf water potential was slightly decreased by water stress. Water stress induced daytime shrinkage and reduced night-time expansion of stem. Photosynthetic rate, stomatal conductance and transpiration rate were significantly declined by water stress, while the intercellular CO2 concentration was changed only slightly at the initiation of stress treatment. The maximum photochemical efficiency of photosystem 2 and apparent photosynthetic electron transport rate were not changed by water stress.
TL;DR: The vulnerability of leaves rehydrating after desiccation was compared withulnerability of leaves during steady-state evaporation, and differences between methods suggest that in many cases vein cavitation occurs only as Kleaf approaches zero.
Abstract: The conductance of transpiring leaves to liquid water (K leaf ) was measured across a range of steady-state leaf water potentials ( Y leaf ). Manipulating the transpiration rate in excised leaves enabled us to vary Y leaf in the range - 0.1 MPa to less than - 1.5 MPa while using a flowmeter to monitor the transpiration stream. Employing this technique to measure how desiccation affects K leaf in 19 species, including lycophytes, ferns, gymnosperms and angiosperms, we found two characteristic responses. Three of the six angiosperm species sampled maintained a steady maximum K leaf while Y leaf remained above - 1.2 MPa, although desiccation of leaves beyond this point resulted in a rapid decline in K leaf . In all other species measured, declining Y leaf led to a pro
TL;DR: Conclusively, given the same amount (50% of ETfull) of irrigation, PRD has no advantages compared to DI in terms of biomass production and WUE in potato at tuber initiation stage.
TL;DR: In this article, the relative yield decline that is expected under specific levels of water stress at different moments in the growing period is estimated by integrating the FAO Ky approach, where the relation between water stress in a particular growth stage and the corresponding expected yield is described by a linear function.
TL;DR: In this paper, the authors compared the response of mature Manzanilla olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ETc) was supplied daily by localised irrigation.
Abstract: It is widely believed that partial root drying (PRD) reduces water losses by transpiration without affecting yield. However, experimental work carried out to date does not always support this hypothesis. In many cases a PRD treatment has been compared to a full irrigated treatment, so doubt remains on whether the observed benefits correspond to the switching of irrigation or just to PRD being a deficit irrigation treatment. In addition, not always a PRD treatment has been found advantageous as compared to a companion regulated deficit irrigation (RDI) treatment. In this work we have compared the response of mature ‘Manzanilla‘ olive trees to a PRD and an RDI treatment in which about 50% of the crop evapotranspiration (ETc) was supplied daily by localised irrigation. We alternated irrigation in the PRD treatment every 2 weeks in 2003 and every 3 weeks in 2004. Measurements of stem water potential (Ψstem), stomatal conductance (gs) and net CO2 assimilation rate (A) were made in trees of both treatments, as well as in trees irrigated to 100% of ETc (Control trees) and in Rain-fed trees. Sap flow was also measured in different conductive organs of trees under both PRD and RDI treatments, to evaluate the influence of alternating irrigation on root water uptake and tree water consumption. We found small and random differences in Ψstem, gs and A, which gave no evidence of PRD causing a positive effect on the olive tree performance, as compared to RDI. Stomatal conductance decreased in PRD trees as compared to Control trees, but a similar decrease in gs was also recorded in the RDI trees. Sap flow measurements, which reflected water use throughout the irrigation period, also showed no evidence of gs being more reduced in PRD than in RDI trees. Daily water consumption was also similar in the trees of the deficit irrigation treatments, for most days, throughout the irrigation period. Alternating irrigation in PRD trees did not cause a change in either water taken up by main roots at each side of the trees, or in the sap flow of both trunk locations and main branches of each side. Results from this work, and from previous work conducted in this orchard, suggest that transpiration is restricted in trees under deficit irrigation, in which roots are left in drying soil when water is applied by localised irrigation, and that there is no need to alternate irrigation for achieving this effect.
TL;DR: The hypothesis that teeth enhance rates of carbon uptake at the beginning of the growing season when temperatures are limiting is tested and may provide a proportionally increasing selective advantage to toothed species with decreasing temperature that is reflected in empirical correlations used for paleotemperature estimation.
Abstract: Leaf teeth are conspicuous and often diagnostic features of many plant species. In mesic environments with sufficient nutrient resources, the percentage of toothed species in extant floras generally correlates negatively with temperature; consequently, fossil leaf teeth are widely used to estimate continental paleotemperatures. However, the function of leaf teeth with respect to climate is poorly understood. Here, we test the hypothesis that teeth enhance rates of carbon uptake at the beginning of the growing season when temperatures are limiting. We measure the seasonal patterns of leaf‐margin photosynthesis and transpiration for 60 woody species from two temperate regions with differing climates (Pennsylvania and North Carolina). Three significant results are, first, physiological activity at leaf margins is greatest early in the growing season (first 30 d); second, toothed margins are more active with respect to photosynthesis and transpiration than untoothed margins; finally, leaf margins are more act...
TL;DR: That leaf CK concentration did not decline proportionally with CK delivery suggests that other mechanisms such as CK metabolism influence leaf CK status of PRD plants, and decreased shoot CK status are discussed.
Abstract: Decreased cytokinin (CK) export from roots in drying soil might provide a root-to-shoot signal impacting on shoot physiology. Although several studies show that soil drying decreases the CK concentration of xylem sap collected from the roots, it is not known whether this alters xylem CK concentration ([CK xyl ]) in the leaves and bulk leaf CK concentration. Tomato (Solanum lycopersicum L.) plants were grown with roots split between two soil columns. During experiments, water was applied to both columns (well-watered; WW) or one (partial rootzone drying; PRD) column. Irrigation of WW plants aimed to replace transpirational losses every day, while PRD plants received half this amount. Xylem sap was collected by pressurizing detached leaves using a Scholander pressure chamber, and zeatin-type CKs were immunoassayed using specific antibodies raised against zeatin riboside after separating their different forms (free zeatin, its riboside, and nucleotide) by thin-layer chromatography. PRD decreased the whole plant transpiration rate by 22% and leaf water potential by 0.08 MPa, and increased xylem abscisic acid (ABA) concentration 2.5-fold. Although PRD caused no detectable change in [CK xyl ], it decreased the CK concentration of fully expanded leaves by 46%. That [CKxyi] was maintained and not increased while transpiration decreased suggests that loading of CK into the xylem was also decreased as the soil dried. That leaf CK concentration did not decline proportionally with CK delivery suggests that other mechanisms such as CK metabolism influence leaf CK status of PRD plants. The causes and consequences of decreased shoot CK status are discussed.
TL;DR: In this article, the authors measured sap flux using Granier-type sensors in a northern hardwood-dominated old growth forest in Michigan, upscaled to canopy transpiration, and calculated canopy conductance.
Abstract: [1] Combining sap flux and eddy covariance measurements provides a means to study plant stomatal conductance and the relationship between transpiration and photosynthesis. We measured sap flux using Granier-type sensors in a northern hardwood-dominated old growth forest in Michigan, upscaled to canopy transpiration, and calculated canopy conductance. We also measured carbon and water fluxes with the eddy covariance method and derived daytime gross primary production (GPP). The diurnal patterns of sap flux and canopy transpiration were mainly controlled by vapor pressure deficit (D) and photosynthetically active radiation (PAR). Daily sums of sap flux and canopy transpiration had exponential relationships to D that saturated at higher D and had linear relationships to PAR. Sugar maple (Acer saccharum) and yellow birch (Betula alleghaniesis) had higher sap flux per unit of sapwood area than eastern hemlock (Tsuga canadensis), while sugar maple and hemlock had higher canopy transpiration per unit of leaf area than yellow birch. Sugar maple dominated canopy transpiration per ground area. Canopy transpiration averaged 1.57 mm d−1, accounting for 65% of total evapotranspiration in the growing season. Canopy conductance was controlled by both D and PAR, but the day-to-day variation in canopy conductance mainly followed a negatively logarithmic relationship with D. By removing the influences of PAR, half-hourly canopy conductance was also negatively logarithmically correlated with D. Water use efficiency (WUE) had a strong exponential relationship with D on a daily basis and approached a minimum of 4.4 mg g−1. WUE provides an alternative to estimate GPP from measurements of sap flux.