bluuebunny/crossref_metadata_2025_split huggingface dataset:
Sap flow in wheat under free‐air CO2 enrichment
Authors: SENOCK R. S. , HAM J. M. , LOUGHIN T. M. , KIMBALL B. A. , HUNSAKER D. J. , PINTER P. J. , WALL G. W. , GARCIA R. L. , LaMORTE R. L. 
Published: April 2006

ABSTRACTThe effects of elevated carbon dioxide (CO2) concentration on plant water use are best evaluated on plants grown under field conditions and with measurement techniques that do not disturb the natural function of the plant. Heat balance sap flow gauges were used on individual main stems of wheat (Triticum aestivum L. cv Yecora rojo) grown under normal ambient conditions (control) and in a free‐air CO2 enrichment (FACE) system in Arizona with either high (control + high H2O = CW; FACE + high H2O = FW) or low (control + low H2O = CD; FACE + low H2O = FD) irrigation regimens. Over a 30d period (stem elongation to anthesis), combinations of treatments were monitored with,10–40 gauges per treatment. The effects of increased CO2 on tiller water use were inconsistent in both the diurnal patterns of sap flow and the statistical analyses of daily sap flow (Ftot). Initial results suggested that the reductions in Ftot, from CO2 enrichment were small (,0–10%) in relation to the H2O treatment effect (,20–30%). For a 3d period, Ftot of FW was,19–26% less than that of CW (P = 0.10). Examination of the different sources of variation in the study revealed that the location of gauges within the experimental plots influenced the variance of the sap flow measurements. This variation was probably related to positional variation in subsurface drip lines used to irrigate plots. A sampling design was proposed for use of sap flow gauges in FACE systems with subsurface irrigation that takes into account the main treatment effects of CO2 enrichment and the other sources of variation identified in this study. Despite the small and often statistically non‐significant differences in Ftot between the CW and FW treatments, cumulative water use of the FW treatment at the end of the first three test periods ranged from 7 to 23% lower than that of the CW treatment. Differences in sap flow between FW and CW compared well with treatment differences in evapotranspiration. The results of the study, based on the first reported sap flow measurements of wheat, suggest that irrigation requirements for wheat production, in the present climatic regimen of the south‐western US, may be predicted to decrease slightly because of increasing atmospheric CO2.
Contribution of intercellular reflectance to photosynthesis in shade leaves
Authors: DeLUCIA E. H. , NELSON K. , VOGELMANN T. C. , SMITH W. K. 
Published: April 2006

ABSTRACTThe potential contribution of intercellular light reflectance to photosynthesis was investigated by infiltrating shade leaves with mineral oil. Infiltration of leaves of Hydrophyllum canadense and Asarum canadense with mineral oil decreased adaxial leaf reflectance but increased transmittance. As a result of the large increase in transmittance, infiltration caused a decrease in absorptance of 25% and 30% at 550 and 750 nm, respectively. Thus, intercellular reflectance increased absorptance in these species by this amount. In a comparison of sun and shade leaves of Acer saccharum and Parthenocissus quinquefolia, oil infiltration decreased absorptance more in shade than in sun leaves. This difference suggests that the higher proportion of spongy mesophyll in shade leaves may increase internal light scattering and thus absorptance. The importance of the spongy mesophyll in increasing internal reflectance was also evident in comparisons of the optics of Populus leaves and in the fluorescence yield of oil‐infiltrated leaves of several sun and shade species. Oil infiltration decreased the quantum yield of fluorescence (Fo) by 39–52% for shade leaves but only 21–25% for sun leaves. We conclude that the greater proportion of spongy parenchyma in shade leaves increased intercellular light scattering and thus absorptance. Direct measurements with fibre‐optic light probes of the distribution of light inside leaves of Hydrophyllum canadense confirmed that oil infiltration decreased the amount of back‐scattered light and that most of the light scattering for this species occurred from the middle of the palisade layer to the middle of the spongy mesophyll. We were not, however, able to assess the potential contribution of reflectance from the internal abaxial epidermis to total internal light scattering in these experiments. Using a mathematical model to compare the response of net photosynthesis (O2, flux) to incident irradiance for control leaves of H. canadense and theoretical leaves with no intercellular reflectance, we calculated that intercellular reflectance caused a 1.97‐fold increase in photosynthesis at 20 μmol m−2s−1 (incident photon flux density). This enhancement of absorption and photosynthesis by inter‐cellular reflectance, without additional production and maintenance of photosynthetic pigments, may maintain shade leaves above the photosynthetic light compensation point between sunflecks and maintain the light induction state during protracted periods of low diffuse light.
The water relations of the root–soil interface
Authors: STIRZAKER R. J. , PASSIOURA J. B. 
Published: April 2006

ABSTRACTThe difference in hydrostatic pressure between the xylem of the leaf and the soil depends, for a given transpiration rate, on the series of hydraulic resistances encountered along this pathway. Many studies have shown that the sum of the resistances in the plant and the soil is too small to account for the fall in water pressure between the leaf xylem and the soil, especially when plants are growing in sandy soils, which are prone to dry rapidly. A resistance at the root–soil interface, caused possibly by poor contact between the roots and the soil, has been proposed to account for the discrepancy. We explored the resistance in the pathway from soil to leaf using a technique that allows precise and continuous non‐destructive measurement of the hydrostatic pressure in the leaf xylem. When the soil was leached with water, the fall in leaf water status as the soil dried was reasonably well described by a simple physical model without the need to invoke an interfacial resistance. However, when the soil was flushed with a nutrient solution with an osmotic pressure of 70kPa, the hydrostatic pressure in the leaf xylem fell several times faster than that in the soil. We suggest that solutes accumulated either in the root or just outside it, creating large osmotic pressures, which gave the appearance of an interfacial resistance.
Effect of environment on the early steps of ear initiation in maize (Zea mays L.)
Authors: LEJEUNE P. , BERNIER G. 
Published: April 2006

ABSTRACTThe effects of environmental conditions on ear‐shoot initiation have been investigated in three inbred genotypes of Zea mays L. which are used for seed production. Scanning electron microscopy (SEM) and binocular examination during the vegetative phase showed that axillary meristems are initiated at the same rate as the leaf primordia on the apical meristem, but with a delay of 5.6–7.0 plastochrons, depending on the genotype. Furthermore, the topmost axillary meristem is initiated on the same day as the tassel, whatever the genotype. One of the inbreds (B22) used in this study has been reported to exhibit, in field conditions, a reproductive failure affecting car initiation, causing the topmost car to be replaced at maturity by a sterile, leaf‐like, structure. Scanning electron microscopic study of the formation of the abnormal axillary buds indicated that ear failure resulted from the early collapse of the axillary meristem followed by elongation of the prophyll or of the meristem itself. Using controlled environments, ear abortion was mimicked by a chilling treatment (10°C), given just before tassel initiation. Other factors, such as high irradiance and flooding, enhanced the abortive response. The critical stage for the main car was just before the initiation of the topmost axillary meristem which also corresponded to tassel initiation. Chilling the plants before or after tassel initiation either induced an acclimation response or had no effect. The three inbreds showed differential responses to the stress treatment, indicating that a genetic factor is implicated as well. It is suggested that chilling causes a perturbation of apical dominance which, in the responsive genotypes, represses axillary meristem development. The use of a stress‐sensitive inbred such as B22 as a model system could yield some interesting clues to the mechanism of endogenous control of ear initiation in maize.
Measurement of short‐term nutrient uptake rates in cranberry by aeroponics
Authors: BARAK P. , SMITH J. D. , KRUEGER A. R. , PETERSON L. A. 
Published: April 2006

ABSTRACTAeroponics, a soil‐less plant culture system in which fresh nutrient solutions are intermittently or continuously misted on to plant roots, is capable of sustaining plant growth for extended periods of time while maintaining a constantly refreshed nutrient solution. Although used relatively extensively in commercial installations and in root physiology research, use of aeroponics in nutrient studies is rare. The object of this study was to examine whether nutrient uptake rates could be calculated for aeroponic systems by difference using measurements of concentrations and volumes of input and efflux solutions. Data were collected from an experiment with cranberry plants (Vaccinium macrocarpon Ait. cv. Stevens) cultured aeroponically with nutrient solutions containing various concentrations of ammonium‐N and isotopically labelled nitrate‐N. Validation of the calculated uptake rates was sought by: (1) evaluating charge balance of the solutions and total ion uptake (including proton efflux) and (2) comparison with N‐isotope measurements. Charge balance and proton efflux calculations required use of chemical modelling of the solutions to determine speciation of dissolved phosphate and acid‐neutralizing capacity (ANC). The results show that charge balance requirements were acceptably satisfied for individual solution analyses and for total ion uptake when proton efflux was included. Relative rates of nitrate/ammonium uptake determined by difference were in agreement with those determined by isotopic techniques. Additional information was easily obtained from this experimental technique, including evidence of diurnal variation in nutrient uptake, correlation between ammonium uptake and proton efflux, and the relationship between ion concentration and uptake. Use of aeroponic systems for non‐destructive measurement of water and ion uptake rates for numerous other species and nutrients appears promising.
Expression of cold‐inducible genes and frost hardiness in the crown meristem of young barley (Hordeum vulgare L. cv. Igri) plants grown in different environments
Authors: PEARCE R. S. , DUNN M. A. , RIXON J. E. , HARRISON P. , HUGHES M. A. 
Published: April 2006

ABSTRACTThe purpose of this work was to examine environmental control of expression, at the mRNA level, of cold‐inducible genes and to test the relationship of the expression of the genes to cold acclimation. Barley plants (Hordeum vulgare L. cv. Igri) at the three‐ to four‐leaf stage were (a) grown in different temperature environments between 20/15°C and +4/‐4°C or (b) transferred between 20/15°C and 6/2°C or (c) grown under drought or nutrient stress conditions. Frost hardiness (using a regrowth method) and mRNA levels for three cold‐induced genes, blt4‐9, blt14 and blt101, from meristematic crown tissue (vegetative shoot meristem plus subtending stem and associated root initials) were measured. Hardiness and levels of blt4‐9, blt14 and blt101 mRNAs increased with lower growth temperatures, below a maximum inductive temperature. Prior temperature environment and plant age affected the rate of change in mRNA levels of these genes in response to a change of temperature environment. Hardiness was strongly correlated with mRNA levels of these genes in plants grown in different temperature environments. This correlation did not extend to plants exposed to drought or nutrient stresses. Implications are drawn for plant responses to a warmer climate.
Antioxidants in the apoplast and symplast of beech (Fagus sylvatica L.) leaves: seasonal variations and responses to changing ozone concentrations in air
Authors: LUWE M. 
Published: April 2006

ABSTRACTConcentrations of the antioxidants ascorbate and glutathione were measured in the apoplast of beech (Fagus sylvatica L.) leaves and in leaf tissue. During early leaf development, reduced ascorbate (ASC) was almost absent from the apoplast, whereas levels of oxidized ascorbate (DHA) were high. Less than 20% of the apoplastic ascorbate was reduced. ASC increased towards midsummer, reaching top levels of about 4molm−3 apoplast volume in July and August. Reduction increased to 60–75% in summer. Neither DHA reductase nor glutathione was detected in the apoplast of beech leaves. Levels of apoplastic ascorbate were compared with ambient concentrations of ozone in air. Statistical analysis indicated a significant interrelation between atmospheric ozone and apoplastic ascorbate. In midsummer of 1993, contents of DHA were increased in the apoplast when ozone concentrations were high. Apoplastic ASC was also positively correlated with ambient ozone concentrations, but with a delay of 3 to 7d. In leaf tissue, levels of ascorbate were between 17 and 21 μmolg−1 FW in summer. Except for late April and November, more than 95% of the intracellular ascorbate was reduced. Glutathione contents were lowest during the summer. Oxidation was increased in spring and autumn, when apoplastic ascorbate was also largely oxidized. Usually, 80 to 90% of the glutathione was reduced. During the summer, intracellular concentrations of oxidized glutathione (GSSG) were increased, with a delay of about 1d following periods of high ambient ozone concentrations. The transitory accumulation of GSSG may be explained by slow enzymatic regeneration of glutathione.
Interaction between atmospheric and pedospheric nitrogen nutrition in spruce (Picea abies L. Karst) seedlings
Authors: MULLER B. , TOURAINE B. , RENNENBERG H. 
Published: April 2006

ABSTRACTThe effect of NO2 fumigation on root N uptake and metabolism was investigated in 3‐month‐old spruce (Picea abics L. Karst) seedlings. In a first experiment, the contribution of NO2 to the plant N budget was measured during a 48 h fumigation with 100mm3m−3 NO2. Plants were pre‐treated with various nutrient solutions containing NO2 and NH4+, NO3− only or no nitrogen source for 1 week prior to the beginning of fumigation. Absence of NH4+ in the solution for 6d led to an increased capacity for NO3− uptake, whereas the absence of both ions caused a decrease in the plant N concentration, with no change in NO3− uptake. In fumigated plants, NO2 uptake accounted for 20–40% of NO3− uptake. Root NO3− uptake in plants supplied with NH4+plus NO3− solutions was decreased by NO2 fumigation, whereas it was not significantly altered in the other treatments. In a second experiment, spruce seedlings were grown on a solution containing both NO2 and NH4+ and were fumigated or not with 100mm3m−3 NO2 for 7 weeks. Fumigated plants accumulated less dry matter, especially in the roots. Fluxes of the two N species were estimated from their accumulations in shoots and roots, xylem exudate analysis and 15N labelling. Root NH4+ uptake was approximately three times higher than NO3− uptake. Nitrogen dioxide uptake represented 10–15% of the total N budget of the plants. In control plants, N assimilation occurred mainly in the roots and organic nitrogen was the main form of N transported to the shoot. Phloem transport of organic nitrogen accounted for 17% of its xylem transport. In fumigated plants, neither NO3− nor NH4+ accumulated in the shoot, showing that all the absorbed NO2 was assimilated. Root NO3− reduction was reduced whereas organic nitrogen transport in the phloem increased by a factor of 3 in NO2‐fimugated as compared with control plants. The significance of the results for the regulation of whole‐plant N utilization is discussed.
Carbon isotope composition of C4 grasses is influenced by light and water supply
Authors: BUCHMANN N. , BROOKS J. R. , RAPP K. D. , EHLERINGER J. R. 
Published: April 2006

ABSTRACTThe carbon isotope composition of C4 grasses has the potential to be used as an indicator of changes in the isotopic composition and concentration of atmospheric CO2, especially for climate reconstruction. The usefulness of C4 grasses for this purpose hinges on the assumption that their photosynthetic discrimination against 13C remains constant in a wide range of environmental conditions. We tested this assumption by examining the effects of light and water stress on the carbon isotope composition of C4 grasses using different biochemical subtypes (NADP‐ME, NAD‐ME, PCK) in glasshouse experiments. We grew 14 different C4 grass species in four treatments: sun‐watered, sun‐drought, shade‐watered and shade‐drought. Carbon isotope discrimination (Δ) rarely remained constant. In general, Δ values were lowest in sun‐watered grasses, greater for sun‐drought plants and even higher for plants of the shade‐watered treatment. The highest Δ values were generally found in the most stressed grasses, the shade‐drought plants. Grasses of the NADP‐ME subtype were the least influenced by a change in environmental variables, followed by PCK and NAD‐ME subtypes. Water availability affected the carbon isotope discrimination less than light limitation in PCK and NAD‐ME subtypes, but similarly in NADP‐ME subtypes.In another experiment, we studied the effect of increasing light levels (150 to 1500 μmol photons m−2 s−1) on the Δ values of 18 well‐watered C4 grass species. Carbon isotope discrimination remained constant until photon flux density (PFD) was less than 700 μmol photons m−2 s−1. Below this light level, Δ values increased with decreasing irradiance for all biochemical subtypes. The change in A was less pronounced in NADP‐ME and PCK than in NAD‐ME grasses. Grasses grown in the field and in the glasshouse showed a similar pattern. Thus, caution should be exercised when using C4 plants under varying environmental conditions to monitor the concentration or carbon isotopic composition of atmospheric CO2 in field/glasshouse studies or climate reconstruction.
Microclimate and fluxes of water vapour, sensible heat and carbon dioxide in structurally differing subalpine plant communities in the Central Caucasus
Authors: Tappeiner U. , Cernusca A. 
Published: April 2006

ABSTRACTEffects of canopy structure on microclimate, energy budget and CO2 exchange were analysed in a pasture, two hay meadows, a tall herb community and a dwarf shrub community in the subalpine belt of the Central Caucasus. The results show that canopy structure exerts a marked influence on the distribution of photon flux density, temperature and canopy photosynthesis Ac. Three canopy types were distinguished. Type 1 (pasture) has a small LAI (leaf area index) and more than two‐thirds of the phytomass is concentrated in the lowest few cm of the canopy, mainly as planophile leaves. This results in (1) a low degree of utilization of photosynthetic photon flux density (PPFD) by assimilatory plant components, (2) high leaf temperatures and a high soil heat flux during the phase of incoming radiation, and (3) a relatively low Ac/ LAI ratio. Type 2 (meadows), in spite of its erect leaves, which at high solar elevations permit light to penetrate to the lower canopy layers, is characterized by (1) marked effects of mutual shading in the lower canopy layers for most of the day, and thus (2) only slight variations in air and leaf temperatures and (3) a comparatively low Ac/LAI ratio. In canopies of type 3 (tall herb and dwarf shrub communities), there is a concentration of flat leaves in the upper layers. This results in (1) very good utilization of PPFD; (2) no strong fluctuations in canopy temperature as the flat leaves act as a buffer, reducing the amounts of incoming and outgoing radiation in lower canopy layers, and (3) high values of the Ac/LAI ratio. The energy budgets of the canopies investigated are governed not so much by their spatial structure, but rather indirectly by LAI and the degree of coupling of the canopy with the atmosphere.
Spatial variation in carbon isotope discrimination across the thalli of several lichen species
Authors: MÁGUAS C. , BRUGNOLI E. 
Published: April 2006

ABSTRACTVariations in stable carbon isotope discrimination (δ) were investigated across the thalli of several lichen species possessing different photobiont associations. Lichens containing (i) green algae (phycobiont), (ii) green algae in association with cyanobacteria confined in cephalodia, or (iii) cyanobacteria (cyanobiont) as the photobiont partner were studied. Carbon isotope discrimination was analysed in different thallus sections, which varied in distance from the margin and in age. The marginal thallus region is considered to be youngest, while the central region is thought to be oldest. This analysis showed a clear variation in δ across the thallus related to distance from the growing margin. In most of the species examined, the highest δ values were found in marginal regions (younger), while the central and basal regions (older) showed significantly lower δ. To investigate the effects of the historical increase in atmospheric CO2 concentration and the concurrent decrease in the 13C content of atmospheric CO2 on the δ of lichens, experiments were carried out on herbarium samples of Lobaria pulmonaria collected from the mid 19th Century to 1953. The results obtained showed a pattern of variation of δ consistent with that of freshly collected samples; δ decreased substantially with increasing distance from the thallus margin, irrespective of the collection date. Moreover, no consistent variation of discrimination was found among different collection dates. These results demonstrate that the observed variation in δ is caused by age‐related changes in the physiological behaviour of different thallus sections, and that the past 150 years of increasing CO2 concentration have not had significant effects on A in L. pulmonaria. Photosynthesis measurements, chlorophyll analysis and observations using optical microscopy, performed on freshly collected lichens, showed significant changes in morphological and physiological characteristics across the thallus. Particularly, remarkable variations in thickness were found across the thallus. These anatomical changes may be responsible for the variation in δ, through variations in CO2 transfer resistance and, consequently, in CO2 availability across the thallus. The lack of age‐dependent variation in δ in cyanobiont lichens is possibly attributable to the operation of a CO2‐coneentrating mechanism and, therefore, to a more constant CO2 environment across the thallus in this lichen group.