Showing papers on "Transpiration published in 1994"

Water Relations of Terrestrial Arthropods

Abstract: Introduction. Body Water. Cuticular Transpiration. Respiratory Transpiration. Excretion and Osmoregulation. The Uptake of Water. Water Relations of Eggs. Balancing Salts and Water. Thermoregulation and Relations.

Does Rubisco control the rate of photosynthesis and plant growth? An exercise in molecular ecophysiology

Abstract: Experiments are described in which tobacco (Nicotiana tabacum L.) transformed with antisense rbcS to decrease expression of ribulose-1,5-bisphosphate carboxylase-oxygenase (Rubisco) was used to evaluate the contribution of Rubisco to the control of photosynthetic rate, and the impact of a changed rate of photosynthesis on whole plant composition, allocation and growth. (1) The concept of flux control coefficients is introduced. It is discussed how, with adequate precautions, a set of wild-type and transgenic plants with varying expression of an enzyme can be used to obtain experimental values for its flux control coefficient. (2) The flux control coefficient of Rubisco for photosynthesis depends on the short-term conditions. It increases in high light, or low CO2. (3) When plants are grown under constant irradiance, the flux control coefficient in the growth conditions is low (<0.2) at irradiances of up to 1000μmol quanta m−2 s−1. In a natural irradiance regime exceeding 1500μmol quanta m−2 s−2 over several hours the flux coefficient rose to 0.8–0.9. It is concluded that plants are able to adjust the balance between Rubisco and the remainder of the photosynthetic machinery, and thereby avoid a one-sided limitation of photosynthesis by Rubisco over a wide range of ambient growth irradiance regimes. (4) When the plants were grown on limiting inorganic nitrogen, Rubisco had a higher flux control coefficient (0.5). It is proposed that, in many growth conditions, part of the investment in Rubisco may be viewed as a nitrogen store, albeit bringing additional marginal advantages with respect to photosynthetic rate and water use efficiency. (5) A change in the rate of photosynthesis did not automatically translate into a change in growth rate. Several factors are identified which contribute to this buffering of growth against a changed photosynthetic rate. (6) There is an alteration in whole plant allocation, resulting in an increase in the leaf area ratio. The increase is mainly due to a higher leaf water content, and not to changes in shoot/root allocation. This increased investment in whole plant leaf area partly counteracts the decreased efficiency of photosynthesis at the biochemical level. (7) Plants with decreased Rubisco have a lower intrinsic water use efficiency and contain high levels of inorganic cations and anions. It is proposed that these are a consequence of the increased rate of transpiration, and that the resulting osmotic potential might be a contributory factor to the increased water content and expansion of the leaves. (8) Starch accumulation in source leaves is decreased when unit leaf photosynthesis is reduced, allowing a more efficient use of the fixed carbon. (9) Decreased availability of carbohydrates leads to a down-regulation of nitrate assimilation, acting via a decrease in nitrate reductase activity.

Water-use efficiency and carbon isotope discrimination in peanut under water deficit conditions

Abstract: Because of its relationship with water-use efficiency (W), carbon isotope discrimination in leaves (Δ) was proposed to be useful for identifying genotypes with greater water-use efficiency. In this study we examined the relationship between W and Δ in four peanut (Arachis hypogaea L.) genotypes. The genotypes were grown in and around mini-lysimeters embedded in soil and were subjected to two drought regimes, intermittent and prolonged water deficit conditions, by varying the irrigation timing and amount. Automated rain-out shelters prevented any rain from reaching the experimental plots during the treatment period. The mini-lysimeters allowed accurate measurement of water use and total dry matter (including roots) in a canopy environment. Water-use efficiency, which ranged from 1.81 to 3.15 g kg−1, was negatively correlated with Δ, which ranged from 19.1 to 21.8%. Tifton-8 had the highest W (3.15 g kg−1) and Chico the lowest (1.81 g kg−1, representing a variation in W of 74% among genotypes. Variation in W arose mainly from genotypic differences in total dry matter production rather than from differences in water use. It is concluded that δ is a useful trait for selecting genotypes of peanut with improved W under drought conditions in the field. A strong negative relationship existed between W and specific leaf area (SLA, cm3 g−1) and between Δ and SLA, indicating that genotypes with thicker leaves had greater W. SLA could therefore be used as a rapid and inexpensive selection index for high W in peanut where mass spectrometry facilities are not available.

A model of organic chemical uptake by plants from soil and the atmosphere.

Abstract: A three-compartment mass balance model of a plant is developed to quantify the uptake of organic chemicals from soil and the atmosphere. The compartments are as follows: root, stem, and foliage. The processes involved are diffusion and bulk flow of chemical between soil and root; transport within the plant in the phloem and transpiration streams between root, stem, and foliage; exchange between foliage and air and between soil and air, metabolism and growth. The model is applied to the uptake of Bromacil by the soybean from hydroponic solution, yielding results which compare favorably with experimental data

CO2 alters water use, carbon gain, and yield for the dominant species in a natural grassland.

Abstract: Global atmospheric CO2 is increasing at a rate of 1.5-2 ppm per year and is predicted to double by the end of the next century. Understanding how terrestrial ecosystems will respond in this changing environment is an important goal of current research. Here we present results from a field study of elevated CO2 in a California annual grassland. Elevated CO2 led to lower leaf-level stomatal conductance and transpiration (approximately 50%) and higher mid-day leaf water potentials (30-35%) in the most abundant species of the grassland, Avena barbata Brot. Higher CO2 concentrations also resulted in greater midday photosynthetic rates (70% on average). The effects of CO2 on stomatal conductance and leaf water potential decreased towards the end of the growing season, when Avena began to show signs of senescence. Water-use efficiency was approximately doubled in elevated CO2, as estimated by instantaneous gas-exchange measurements and seasonal carbon isotope discrimination. Increases in CO2 and photosynthesis resulted in more seeds per plant (30%) and taller and heavier plants (27% and 41%, respectively). Elevated CO2 also reduced seed N concentrations (9%).

Evaporation, Evapotranspiration and Climatic Data

Abstract: Definitions of evapotranspiration and transpiration. Measurement of evapotranspiration. Estimating E or ET using climatic data. Atmospheric and Thermodynamic Parameters. Wind profiles and relationships. Thermodynamic parameters. Radiation. Solar radiation Rs. Net radiation_Rn. Soil heat flux. Soil Parameters. Soil water fundamentals. Soil water reference points. Soil water storage. Soil water influences on plant growth. Soil water movement. Soil water supply for evapotranspiration. Estimating Reference Crop ET. Sequence of calculations and flow charts. Potential ET and/or reference crop ET. Crop coefficients. Pemnan methods Penman-Monteith method. Radiation methods. Temperature methods. Radiation and temperature methods flow charts. Estimating reference ET using measured pan evaporation. Estimating ET for Specific Crops. ET using ETr. Botanic and cultural influences. Soil water and ET estimates. Crop curves. Grass-related crop coefficients. Alfalfa-related crop coefficients. Estimation of crop ET without formal Etr. Separate estimation of Es and T. Irrigation water requirements. Components of irrigation water requirements. Sources of water for crop growth. Soil water storage of natural precipitation. Non-growing season precipitation. Production, Vegetation and ET. Uses of production functions. Defining assumptions. Common models. Transferability issues. Sequence of calculations. Flow chart for estimating vegetative production. Evaporation from Water Surfaces. Methods. Comparisons and Example Calculations. Introduction. Example calculations. Chapter 2 examples. Chapter 4 examples. Chapter 5 examples. Chapter 7 examples. Property standards. Sun-earth relationships. Comparisons with standard values.

Testing forest-bgc ecosystem process simulations across a climatic gradient in oregon'

Abstract: Field measurements from the Oregon Transect Ecological Research project (OTTER) were used to validate selected process simulations in the FOREST-BGC eco- system model. Certain hydrologic, carbon, and nitrogen cycle process simulations were tested in this validation, either comparatively across sites, or seasonally at single sites. The range of simulated ecosystem-process rates across the OTTER sites was large; annual evapotranspiration (ET) ranged from 15 to 82 cm, net photosynthesis (as carbon) from 2.2 to 22.8 Mg/ha, and decomposition (as carbon) from 1.0 to 7.2 Mg ha-' Iyr-'. High cor- relations between predicted and measured data were found for: aboveground net primary production, R2 = 0.82; 100-yr stem biomass, R2 = 0.79; and average leaf nitrogen con- centration, R2 = 0.88. However, correlations for pre-dawn leaf water potential and equi- librium leaf area index (LAI) were much lower, because successful simulation of these variables requires accurate data for soil water-holding capacity. Defining the water-holding capacity of the rooting zone and the maximum surface conductance for photosynthesis and transpiration rates proved to be critical system variables that defied routine field mea- surement. Although many other processes are simulated in FOREST-BGC, no other pro- cesses had repeated field data sets for validations. Problems in parameterizing the model from disparate data sets are also evaluated, with suggestions for using ecosystem modeling in future integrated research programs.

Developmental changes in the diurnal water budget of the grape berry exposed to water deficits

Abstract: The diurnal water budget of developing grape (Vitis vinifera L.) berries was evaluated before and after the onset of fruit ripening (veraison). The diameter of individual berries of potted ‘Zinfandel’ and ‘Cabernet Sauvignon’ grapevines was measured continuously with electronic displacement transducers over 24 h periods under controlled environmental conditions, and leaf water status was determined by the pressure chamber technique. For well-watered vines, daytime contraction was much less during ripening (after veraison) than before ripening. Daytime contraction was reduced by restricting berry or shoot transpiration, with the larger effect being shoot transpiration pre-veraison and berry transpiration post-veraison. The contributions of the pedicel xylem and phloem as well as berry transpiration to the net diurnal water budget of the fruit were estimated by eliminating phloem or phloem and xylem pathways. Berry transpiration was significant and comprised the bulk of water outflow for the berry both before and after veraison. A nearly exclusive role for the xylem in water transport into the berry was evident during pre-veraison development, but the phloem was clearly dominant in the post-veraison water budget. Daytime contraction was very sensitive to plant water status before veraison but was remarkably insensitive to changes in plant water status after veraison. This transition is attributed to an increased phloem inflow and a partial discontinuity in berry xylem during ripening.

An analytical solution for coupled leaf photosynthesis and stomatal conductance models.

Abstract: Iterative solutions of coupled leaf photosynthesis and stomatal conductance equations sometimes yield bifurcated or chaotic solutions. An analytical solution for coupled leaf photosynthesis-stomatal conductance equations is preferred because an analytical model has specific and known roots, and partial derivatives can be taken to perform sensitivity analyses. I present an analytical solution for coupled leaf photosynthesis and stomatal conductance equations that are based on established biochemical and physiological theory.

Water flux in a hybrid poplar stand.

Abstract: We studied water flux in a four-year-old stand of hybrid Populus during midsummer 1992. Study trees ranged in height from 11.0 to 15.1 m and in diameter from 8.3 to 15.1 cm. The large-leafed Populus hybrid was relatively poorly coupled to the atmosphere. The average value of the stomatal decoupling coefficient, Omega, was 0.66, indicating that, on average, a 10% change in stomatal conductance would result in only a 3 to 4% change in transpiration. During the middle of the summer, the smallest study tree used between 20 and 26 kg of water per day, whereas the largest tree used between 39 and 51 kg day(-1). The maximum observed rate of stand water loss was 4.8 mm day(-1) in this Populus clone. Maximum rates of sap velocity within the xylem were as high as 12.5 m h(-1); measured rates for exposed sunlit branches approached 90% of this maximum. Within-canopy patterns of stomatal conductance generally reflected patterns of incident radiation. Stomatal conductance of foliage grown in shade, even when exposed to non-limiting light and water source conditions, did not increase appreciably. Patterns of stomatal conductance under limiting and non-limiting conditions suggested that both stomatal conductance and leaf specific hydraulic conductivity (LSHC) were linked with the ability to exploit the light resource.

Applications of fertilizer cations affect cadmium and zinc concentrations in soil solutions and uptake by plants

Abstract: Summary A pot experiment was conducted to study changes over time of Cd and Zn in soil solution and in plants. Radish was grown in a soil which had been contaminated with heavy metals prior to 1961. Constant amounts of a fertilizer solution (NH4NO3, KNO3) were added daily. Soil solution was obtained at intervals by displacement with water. The cumulative additions of small amounts of fertilizers were made equal to the plants' requirements at the final harvest but were found to exceed them during most of the experiment. Excess fertilizers caused substantial increases of major (K, Ca, Mg) and heavy-metal (Cd, Zn) ions in soil solutions and a decrease in soil pH, probably due to ion-exchange mechanisms and the dissolution of carbonates. Uptake of Cd and Zn into leaves was correlated with the mass flow of Cd (adjusted r2= 0.798) and Zn (adjusted r2= 0.859). Uptake of K, Ca and Mg by the plants was independent of their concentrations in solution. It is concluded that, in order to study effects of plants on heavy-metal availability and obtain soil solution that has not been altered by fertilizer ions, nutrients must be added according to the needs and growth of the plants. This could be achieved by linking fertilizer additions to the rate of transpiration, as nutrient uptake and transpiration were closely correlated in this experiment.

Direct impact of atmospheric CO2 enrichment on regional transpiration

Abstract: Plant physiological research has revealed that stomatal aperture of many plant species is reduced by CO 2 . Therefore, the question has been raised as to how transpiration will be affected if the ambient C0 2 concentration increases. This study focuses on the prediction of changes in transpiration at the regional scale (10-100 km horizontal, 1-5 km vertical). A rather detailed, coupled vegetation- Planetary Boundary Layer (PBL) model has been constructed in order to identify important processes that control such changes.The coupled model uses the well-known "big-leaf' model for the vegetation part. Surface resistance (r s ) is described by means of an up-scaled ''A-g s '' model, where stomatal conductance is related to photosynthetic rate. The background of this model for (r s ) is outlined. A new parameterization to mimic stomatal humidity responses is proposed. The parameterization prescribes a linear relation between the specific humidity deficit at the leaf surface and the ratio of the internal C0 2 concentration to the external C0 2 concentration. The resulting ''A-g s '' model simulates stomatal responses to CO 2 , light, temperature, humidity as well as their synergistic interactions. The model is tested using data for grapevines ( VitisVinifera L., cv. Airen). The model is able to simulate the photosynthetic rate and the stomatal conductance of this species satisfactorily.The PBL part of the coupled model is a 1D, first-order closure model, which takes into account nonlocal turbulent transport by means of a countergradient correction. The PBL model also simulates C0 2 fluxes and concentrations. The surface flux of C0 2 is driven by photosynthetic rate from the up-scaled ''A-g s '' model. The complete coupled model realistically simulates the state of the PBL, (r s ) transpiration, and the most important aspects of the biosphere-atmosphere interaction for extensive, homogeneous, well-watered canopies with dry leaves.Systematic sensitivity studies using the coupled model reveal that the interaction between vegetation and the PBL has a significant effect on transpiration and on (r s ) On the one hand, the PBL provides a strong negative feedback on transpiration which reduces the change in the transpiration at given change in (r s ) The influence of the PBL depends strongly on surface roughness. On the other hand, the simultaneous change of (r s ) and of the specific humidity deficit inside the canopy provides a positive feedback, thereby increasing the initial perturbation of (r s ) and transpiration. A second positive feedback mechanism is present if the optimum temperature for photosynthesis is exceeded.The main conclusion is that the interaction between the PBL and vegetation has to be taken into account if transpiration and its changes due to changing surface characteristics are to be predicted at the regional scale.

Water relations of a tropical vine-like bamboo (Rhipidocladum racemiflorum): root pressures, vulnerability to cavitation and seasonal changes in embolism

Abstract: The occurrence of root pressure, the vulnerability of xylem vessels to drought-induced cavitation, and the seasonal changes in hydraulic conductivity due to embolism were studied in the culms of Rhipidocladum racemiflorum (Steud.) McClure, a tropical vine-like bamboo from central Panama. Positive hydrostatic potentials up to 120 kPa occurred only during the wet season when the transpiration rate of the plant was low, i.e. at night or during rain events. Although the xylem vessels were large and efficient for conducting water, they were highly resistant to cavitation. Xylem water potentials lower than -4.5 MPa were required to induce 50% loss of hydraulic conductivity in culms

Variation in foliar delta(13)C values within the crowns of Pinus radiata trees.

Abstract: Although herbaceous species generally show little within plant variation in delta(13)C, trees show large spatial and temporal differences. We found that the aspect of exposure and branch length accounted for up to 6 per thousand delta(13)C difference within the foliage of individual trees of Pinus radiata D. Don. The foliage on branches 0.5 m in length was as much as 4 per thousand more depleted in (13)C than foliage on 10-m long branches, and an additional 2 per thousand more depleted on the shaded side than on the exposed side. We confirmed that on clear days, relative branch hydraulic conductivity, defined as the ratio of transpiration to the water potential gradient, was much higher in short branches than in long branches. Stomatal conductance remained high in foliage on short branches during the day, whereas it declined progressively in long-branch foliage under similar conditions. These differences were sufficient to explain the observed variation in delta(13)C in foliage on long and short branches.

Interactive effects of elevated CO2 and soil drought on growth and transpiration efficiency and its determinants in two European forest tree species

Abstract: The responses of growth and transpiration efficiency (W = biomass accumulation/water consumption) to ambient and elevated atmospheric CO(2) concentrations (350 and 700 micro mol mol(-1), respectively) were investigated under optimal nutrient supply in well-watered and in drought conditions in two temperate-forest tree species: Quercus petraea Liebl. and Pinus pinaster Ait. Under well-watered conditions, doubling the CO(2) concentration for one growing season increased biomass growth by 138% in Q. petraea and by 63% in P. pinaster. In contrast, under drought conditions, elevated CO(2) increased biomass growth by only 47% in Q. petraea and had no significant effect on biomass growth in P. pinaster. Transpiration efficiency was higher in Q. petraea than in P. pinaster in all treatments. This difference was linked (i) to lower carbon isotope discrimination (Delta), and thus lower values of the intercellular/ambient CO(2) concentration (c(i)/c(a)) ratio, in Q. petraea, (ii) to lower values of leaf mass ratio (LMR, leaf mass/whole plant mass), which we suggest was positively related to the proportion of daytime carbon fixation lost by respiration (Phi), in Q. petraea, and (iii) to slightly lower C concentrations in Q. petraea than in P. pinaster. The CO(2)-promoted increase in W was higher in Q. petraea (+80%) than in P. pinaster (+50%), and the difference was associated with a more pronounced decrease in Phi in response to elevated CO(2) in Q. petraea than in P. pinaster, which could be linked with the N dilution effect observed in Q. petraea. Because Phi also directly affects growth, the CO(2)-induced enhancement of Phi in Q. petraea is a crucial determinant of the growth stimulation observed in this species. Leaf gas exchange regulation was not the only factor involved in the responses of growth and W to elevated CO(2) and drought, other physiological processes that have crucial roles include carbon and N allocation and respiration.

Patterns of hydraulic architecture and water relations of two tropical canopy trees with contrasting leaf phenologies: Ochroma pyramidale and Pseudobombax septenatum.

Abstract: Summary Many authors have attempted to explain the adaptive response of tropical plants to drought based on studies of water relations at the leaf level. Little attention has been given to the role of the xylem system in the control of plant water requirements. To evaluate this role, we studied the hydraulic architecture and water relations parameters of two tropical canopy trees with contrasting leaf phenologies: deciduous Pseudobombax septenatum (Jacq.) Dug and evergreen Ochromapyramidale (Cav. ex lamb) Urban, both in the family Bombacaceae. The hydraulic architecture parameters studied include hydraulic conductivity, specific conductivity, leaf specific conductivity, and Huber value. Water relations parameters include leaf water potential, stem and leaf water storage capacitance, transpiration, stomatal conductance, and vulnerability of stems to cavitation and loss of hydraulic conductivity by embolisms. Compared to temperate trees, both species showed a pattern of highly vulnerable stems (50% loss of conductivity due to embolism at water potentials less than 1 MPa) with high leaf specific conductivities. The vulnerability of xylem to water-stress-induced embolism was remarkably similar for the two species but the leaf specific conductivity of petioles and leaf-bearing stems of the evergreen species, Ochroma (e.g., 9.08 and 11.4 x 10m4 kg s-’ m-’ MPa-‘, respectively), were 3.4 and 2.3 times higher, respectively, than those of the deciduous species, Pseudobombax (e.g., 2.64 and 5.15 x 1O-4 kg s-t mm’ MPa-‘, respectively). A runaway embolism model was used to test the ability of Ochroma and Pseudobombax stems to maintain elevated transpiration rates during the higher evaporative demand of the dry season. The percent loss of leaf area predicted by the runaway embolism model for stems of Pseudobombax ranged from 5 to 30%, not enough to explain the deciduous phenology of this tree species without analysis of root resistance or leaf and petiole vulnerability to embolism.

Groundwater discharge by phreatophyte shrubs in the Great Basin as related to depth to groundwater

Abstract: An equation describing the mean daily discharge of groundwater by transpiration from phreatophyte shrubs as a function of plant density, leaf area index, and depth to groundwater was developed using an energy combination model calibrated with energy fluxes calculated from micrometeorological data. The energy combination model partitions the energy budget between the soil and canopy permitting plant transpiration to be separated from evaporation from the soil. The shrubs include greasewood, rabbitbrush, shadscale, and sagebrush. Converting a daily groundwater discharge rate calculated by the equation to an annual rate requires an estimate of the number of days the plants used only groundwater. Rates used during previous studies in the Great Basin range from 0.030 to 0.152 m yr -1 ; rates calculated with the equation developed during this study range from 0.024 to 0.308 m yr -1 for the reported field conditions. Annual rates estimated in this study differ from the estimated annual rates used in previous studies by factors ranging from 0.8 to 5.0.

Three methods for monitoring the gas exchange of individual tree canopies: ventilated-chamber, sap-flow and Penman-Monteith measurements on evergreen oaks

Abstract: Functional Ecology 1994 TECHNICAL REPO RT Three methods for monitoring the gas exchange of individual tree canopies: ventilated-chamber, sap-flow and Penman-Monteith measurements on evergreen oaks M. L. GOULDEN*H and C . B. FIELDt *Department of Biological Sciences, Stanford University and tcarnegie Institution of Washington, Department of Plant Biology, Stanford, California 94305, USA Summary I. Physiological methods applicable to scales between individual leaves and whole forests have the potential to improve substantially our understanding of ecosystem gas exchange. 2. We compared three approaches for determining the canopy gas exchange of individuals representing a pair of mediterranean-climate oak species. 3. We estimated transpiration from the Penman-Monteith equation, measured sap flow with heat-balance sensors, and also measured net C0 2 assimilation, transpir- ation and conductance with a whole-canopy gas-exchange system. 4. Simultaneously measured sap flow and chamber transpiration were qualitatively similar, provided that the sensors were designed to compensate for thermal gradients along the tree trunk. Both in situ and bench-top measurements indicated that the quantitative relationship beween transpiration and the signal from the sap-flow sensor varied among stems. The sap flow of individual trees measured on consecutive days with the tree in the chamber 1 day, and out the next, was similar, indicating that enclosure had only a small impact on transpiration. Total daily sap flow, which was similar during atmospherically moist period to the Penman- Monteith transpiration calculated assuming a fixed stomata! conductance, became almost insensitive to further increases in evaporative demand during hot and dry intervals. S. While the application of each approach is limited by experimental considerations, these shortcomings may be overcome by using the techniques in combination. Key-words: Conductance, evaporation, Quercus agrifolia , Quercus durata, transpiration Fu11ctio11al Ecology (1994) 8, 125-135 Introduction Researchers need a better understanding of the role plants play in controlling the flux of water vapour and carbon dioxide between forests and the atmosphere (Jarvis & McNaughton 1986; Committee on Global Change 1990). Achieving this understanding will require an interdisciplinary effort to link leaf-level physiology with canopy measurements based on micrometerological techniques. One possible strategy is to scale gas exchange directly from the leaf to the canopy, bypassing explicit consideration of :j: Present address: Dr M. L. Goulden, Division of Applied Sciences, Harvard University, Cambridge, Massachusetts 02138, USA. processes that occur at the whole-plant level (Baldoc- chi, Luxmoore & Hatfield 1991; Baldocchi 1993). While this approach holds promise, it precludes the possibility of drawing upon a body of theory, derived from community (Tilman 1988) and evolutionary (Bloom, Chapin & Mooney 1985) studies, that is based on the response of the individual to the environment. In contrast, approaches that explicitly consider whole-plant processes have the potential to explore the consequences of plant-to-plant variation in physiological characteristics and access to resources, as well as capitalize on possible simplifi- cations resulting from physiological integration at the level of the individual. Unfortunately, past progress in this direction has been limited by the unavailability

Effect of NaCl salinity on growth, pigment and mineral element contents, and gas exchange of broad bean and pea plants

Abstract: Increasing salinity of growth medium induced a reduction in growth and transpiration rate. The concentrations of chlorophylls and carotenoids were increased in most cases in broad bean leaves while in pea plants they remained more or less unchanged with the rise of salinization up to 80mM NaCl. Thereabove a significant decrease in these contents was observed. A stimulation of the net photosynthetic rate of pea was observed at the lowest levels of NaCl but at the highest levels inhibitory effect was recorded. In broad bean all salinization levels inhibited photosynthetic activity, but dark respiration of both plant species was stimulated. The content of Na+ in the roots and shoots of both species increased at increasing salinity. In broad bean, Ca2+ concentration in shoots and K+ and Ca2+ contents of roots increased at increasing salinization, while in pea plants, the content of K+ and Ca2+ was almost unaffected by salinity. Salinity induced an increase in the content of these ions in pea roots. Mg2+ content in shoots and roots of both broad bean and pea decreased at increasing salinity except in roots of pea, where it was generally increased.

Scaling sun and shade photosynthetic acclimation of Alocasia macrorrhiza to whole-plant performance – I. Carbon balance and allocation at different daily photon flux densities

Abstract: We determined the carbon allocation patterns and construction costs of Alocasia macrorrhiza plants grown at different photon flux densities (PFD) as well as the whole-plant carbon gain of these plants at different daily PFDs. Growth at high PFD resulted in thicker leaves with a higher leaf mass per unit area, and increased biomass allocation to petioles and roots, as compared to growth at low PFD. Increased allocation to petioles may have been necessary to support the heavier leaves, whereas increased allocation to roots may have been necessary to supply sufficient water for the higher transpiration rates in high PFD. Root biomass was highly correlated with the daily, whole-plant transpiration rate. Tissue construction costs per unit dry mass were unchanged by acclimation, but, since the mass per unit areas of leaves, roots and petioles all increased, construction costs per unit leaf area were much higher for plants grown at high PFD. On a per unit leaf area basis, daily whole-plant carbon gain measured at high daily PFD was higher in high- than in low-PFD-grown plants. However, on a per unit leaf mass basis, low-PFD-grown plants had a daily carbon gain at least as high as that of high-PFD-grown plants at high daily PFD. At low daily PFD, low-PFD-grown plants maintained an advantage over high-PFD-grown plants in terms of carbon gain because of their larger leaf area ratios. Thus, in terms of carbon gain, low-PFD-grown plants performed better than sun plants at low PFD and as well as high-PFD-grown plants at high PFD, despite their lower photosynthetic capacities per unit area. For high-PFD-grown plants, the higher construction costs per unit leaf area resulted in lower leaf area ratios, which counteracted the advantage of higher photosynthetic rates per unit leaf area.

Novel Methods of Measuring Hydraulic Conductivity of Tree Root Systems and Interpretation Using AMAIZED (A Maize-Root Dynamic Model for Water and Solute Transport)

Abstract: Steady-state and dynamic methods were used to measure the conductivity to water flow in large woody root systems. The methods were destructive in that the root must be excised from the shoot but do not require removal of the root from the soil. The methods involve pushing water from the excised base of the root to the apex, causing flow in a direction opposite to that during normal transpiration. Sample data are given for two tropical (Cecropia obtusifolia and Lacistema aggregatum) and two temperate species (Acer saccharum and Juglans regia cv Lara). A hysteresis was observed in the relationship between applied pressure and resulting flow during dynamic measurements. A mathematical model (AMAIZED) was derived for the dynamics of solute and water flow in roots. The model was used to interpret results obtained from steady-state and dynamic measurements. AMAIZED is mathematically identical with the equations that describe Munch pressure flow of solute and water in the phloem of leaves. Results are discussed in terms of the predictions of AMAIZED, and suggestions for the improvement of methods are made.

Isotopic heterogeneity of water in transpiring leaves: identification of the component that controls the δ18O of atmospheric O2 and CO2

Abstract: Two direct but independent approaches were developed to identify the average δ18O value of the water fraction in the chloroplasts of transpiring leaves. In the first approach, we used the δ18O value of CO2 in isotopic equilibrium with leaf water to reconstruct the δ18O value of water in the chloroplasts. This method was based on the idea that the enzyme carbonic anhydrase facilitates isotopic equilibrium between CO2 and H2O predominantly in the chloroplasts, at a rate that is several orders of magnitude faster than the non-catalysed exchange in other leaf water fractions. In the second approach, we measured the δ18O value of O2 from photosynthetic water oxidation in the chloroplasts of intact leaves. Since O2 is produced from chloroplast water irreversibly and without discrimination, the δ18O value of the O2 should be identical to that of chloroplast water. In intact, transpiring leaves of sunflower (Helianthus annuus cv. giant mammoth) under the experimental conditions used, the average δ18O value of chloroplasts water was displaced by 3—10 % (depending on relative humidity and atmospheric composition) below the value predicted by the conventional Craig & Gordon model. Furthermore, this δ18O value was always lower than the δ18O value that was measured for bulk leaf water. Our results have implications for a variety of environmental studies since it is the δ18O value of water in the chloroplasts that is the relevant quantity in considering terrestrial plants influence on the δ18O values of atmospheric CO2 and O2, as well as in influencing the δ18O of plant organic matter.

Consequences of growth at two carbon dioxide concentrations and two temperatures for leaf gas exchange in Pascopyrum smithii (C3) and Bouteloua gracilis (C4)

Abstract: Continually rising atmospheric CO2 concentrations and possible climatic change may cause significant changes in plant communities. This study was undertaken to investigate gas exchange in two important grass species of the short-grass steppe, Pascopyrum smithii (western wheat-grass), C3, and Bouteloua gracilis (blue grama), C4, grown at different CO2 concentrations and temperatures. Intact soil cores containing each species were extracted from grasslands in north-eastern Colorado, USA, placed in growth chambers, and grown at combinations of two CO2 concentrations (350 and 700 μmol mol−1) and two temperature regimes (field average and elevated by 4°C). Leaf gas exchange was measured during the second, third and fourth growth seasons. All plants exhibited higher leaf CO2 assimilation rates (A) with increasing measurement CO2 concentration, with greater responses being observed in the cool-season C3 species P. smithii. Changes in the shape of intercellular CO2 response curves of A for both species indicated photosynthetic acclimation to the different growth environments. The photosynthetic capacity of P. smithii leaves tended to be reduced in plants grown at high CO2 concentrations, although A for plants grown and measured at 700μmol mol−1 CO2 was 41% greater than that in plants grown and measured at 350 μmol mol−1 CO2. Low leaf N concentration may have contributed to photosynthetic acclimation to CO2. A severe reduction in photosynthetic capacity was exhibited in P. smithii plants grown long-term at elevated temperatures. As a result, the potential response of photosynthesis to CO2 enrichment was reduced in P. smithii plants grown long-term at the higher temperature.