bluuebunny/crossref_metadata_2025 huggingface dataset:
Estimation of growth parameters in salt‐stressed maize: comparison of the pressure‐block and applied‐tension techniques
Authors: CRAMER G. R. , SCHMIDT C.
Published: April 2006

A custom‐built pressure block was used to estimate the effective turgor (turgor pressure minus the yield threshold) and the cell wall extensibility of the growing zone of the third leaves of 8‐d‐old maize (Zea mays L.) seedlings. In response to cell wall loosening, pressure in the chamber increased rapidly and reached a maximum after approximately 60 min. Plants treated with 80 mol m−3 NaCl for 4 h were compared to control plants. Pressure‐block analysis revealed that salinity reduced effective turgor, but had no effect on cell wall extensibility. These results are qualitatively and quantitatively similar to those obtained with an applied‐tension technique used previously in our laboratory. This study indicates that the pressure‐block and applied‐tension techniques, which use very different methodologies, estimate similar growth parameters.
Differential effects of elevated ultraviolet‐B radiation on the photochemical and reproductive performances of dicotyledonous and monocotyledonous arid‐environment ephemerals
Authors: MUSIL C. F.
Published: April 2006

Four dicotyledonous Astcraceac and four monocotyledonous Iridaceac species were grown from seed under three different effective ultraviolet‐B (UV‐B, 280–320 nm) fluenccs, which approximated those received daily over the natural growing periods of these species at their southerly and northerly distribution limits under ambient stratospheric ozone, and at the northerly limit assuming a 20% ozone depletion. Diminished photochemical efficiencies, delayed flowering, decreased flower production, pollen germination and tube growth, and reduced numbers of seeds set, accompanied by corresponding increases in mass per seed, were observed mainly in dicotyledons under elevated UV‐B radiation, despite their higher foliar and pollen polyphenolic contents, their possession of trinucleatc pollen and their natural occurrence at lower latitudes than monocotyledons with binucleate pollen. The results demonstrate the difficulties in determining plant sensitivity to UV‐B radiation from polyphenolic content, pollen type and natural geographic distribution, and suggest that monocotyledons possess other attributes that confer greater resilience to UV‐B radiation.
Effects of free‐air CO2 enrichment on the development of the photosynthetic apparatus in wheat, as indicated by changes in leaf proteins
Authors: NIE G. Y , LONG S. P. , GARCIA R. L. , KIMBALL B. A. , LAMORTE R. L. , PINTER P. J. , WALL G. W. , WEBBER A. N.
Published: April 2006

A spring wheat crop was grown at ambient and elevated (550 μmol mol−1) CO2 concentrations under free‐air CO2 enrichment (FACE) in the field. Four experimental blocks, each comprising 21‐m‐diameter FACE and control experimental areas, were used. CO2 elevation was maintained day and night from crop emergence to final grain harvest. This experiment provided a unique opportunity to examine the hypothesis that CO2 elevation in the field would lead to acclimatory changes within the photosynthetic apparatus under open field conditions and lo assess whether acclimation was affected by crop developmental stage, leaf ontogeny and leaf age. Change in the photosynthetic apparatus was assessed by measuring changes in the composition of total leaf and thylakoid polypeptides separated by SDS‐PAGE. For leaves at completion of emergence of the blade, growth at the elevated CO2 concentration had no apparent effect on the amount of any of the major proteins of the photosynthetic apparatus regardless of the leaf examined. Leaf 5 on the main stem was in full sunlight at emergence, but then became shaded progressively as 3–4 further leaves formed above with continued development of the crop. By 35 d following completion of blade emergence, leaf 5 was in shade. At this point, the chlorophyll alb ratio had declined by 26% both in plants grown at the control CO2 concentration and in those grown at the elevated CO2 concentration, which is indicative of shade acclimation. The ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) content declined by 45% in the control leaves, but by 60% in the leaves grown at the elevated CO2 concentration. The light‐ harvesting complex of photosystcm II (LHCII) and the chlorophyll content showed no decrease and no difference between treatments, indicating that the decrease in Rubisco was not an effect of earlier senescence in the leaves at the elevated CO2 concentration. Following completion of the emergence of the flag‐leaf blade, the elevated‐CO2 treatment inhibited the further accumulation of Rubisco which was apparent in control leaves over the subsequent 14 d. From this point onwards, the flag leaves from both treatments showed a loss of Rubisco, which was far more pronounced in the elevated‐CO2 treatment, so that by 36 d the Rubisco content of these leaves was just 70% of that of the controls and by 52 d it was only 20%. At 36 d, there was no decline in chlorophyll, LHCII or the chloroplast ATPase coupling factor (CFI) in the elevated CO2 concentration treatment relative to the control. By 52 d, all of these proteins showed a significant decline relative to the control. This indicates that the decreased concentration of Rubisco at this final stage probably reflected earlier senescence in the elevated‐CO2 treatment, but that this was preceded by a CO2‐concentration‐dependent decline in Rubisco.
Acclimation of photosynthesis in relation to Rubisco and non‐structural carbohydrate contents and in situ carboxylase activity in Scirpus olneyi grown at elevated CO2 in the field
Authors: JACOB J. , GREITNER C. , DRAKE B. G.
Published: April 2006

Stands of Scirpus olneyi, a native saltmarsh sedge with C3 photosynthesis, had been exposed to normal ambient and elevated atmospheric CO2 concentrations (Ca) in their native habitat since 1987. The objective of this investigation was to characterize the acclimation of photosynthesis of Scirpus olneyi stems, the photosynthesizing organs of this species, to long‐term elevated Ca treatment in relation to the concentrations of Rubisco and non‐structural carbohydrates. Measurements were made on intact stems in the Held under existing natural conditions and in the laboratory under controlled conditions on stems excised in the field early in the morning. Plants grown at elevated Ca had a significantly higher (30–59%) net CO2 assimilation rate (A) than those grown at ambient Ca when measurements were performed on excised stems at the respective growth Ca. However, when measurements were made at normal ambient Ca, A was smaller (45–53%) in plants grown at elevated Ca than in those grown at ambient Ca. The reductions in A at normal ambient Ca, carboxylation efficiency and in situ carboxylase activity were caused by a decreased Rubisco concentration (30–58%) in plants grown at elevated Ca; these plants also contained less soluble protein (39–52%). The Rubisco content was 43 to 58% of soluble protein, and this relationship was not significantly altered by the growth CO2 concentrations. The Rubisco activation state increased slightly, but the in situ carboxylase activity decreased substantially in plants grown at elevated Ca. When measurements were made on intact stems in the field, the elevated Ca treatment caused a greater stimulation of,A (100%) and a smaller reduction in carboxylation efficiency (which was not statistically significant) than when measurements were made on excised stems in the laboratory. The possible reasons for this arc discussed.

Plants grown at elevated Ca contained more non‐structural carbohydrates (25–53%) than those grown at ambient Ca. Plants grown at elevated Ca appear to have sufficient sink capacity to utilize the additional carbohydrates formed during photosynthesis.

Overall, our results are in agreement with the hypothesis that elevated Ca leads to an increased carbohydrate concentration and the ensuing acclimation of the photo‐synthetic apparatus in C3 plants results in a reduction in the protein complement, especially Rubisco, which reduces the photosynthetic capacity in plants grown at elevated Ca, relative to plants grown at normal ambient Ca. Nevertheless, when compared at their respective growth Ca, Scirpus olneyi plants grown at elevated Ca in their native habitat maintained a substantially higher rate of photosynthesis than those grown at normal ambient Ca even after 8 years of growth at elevated Ca.
Interaction of ozone pollution and light effects on photosynthesis in a forest canopy experiment
Authors: TJOELKER M. G. , VOLIN J. C. , OLEKSYN J. , REICH P. B.
Published: April 2006

Ozone pollution may reduce net carbon gain in forests, yet data from mature trees are rare and the effects of irradiance on the response of photosynthesis to ozone remain untested. We used an open‐air system to expose 10 branches within the upper canopy of an 18‐m‐tall stand of sugar maple (Acer saccharumMarsh.) to twice‐ambient concentrations of ozone (95nmol mol−1, 0900 to 1700, 1 h mean) relative to 10 paired, untreated controls (45nmol mol−1) over 3 months. The branch pairs were selected along a gradient from relatively high irradiance (PPFD 14.5 mol m−2d−1) to deep shade (0.7mol m−2d−1). Ozone reduced light‐saturated rates of net photosynthesis (Asat) and increased dark respiration by as much as 56 and 40%, respectively. Compared to sun leaves, shade leaves exhibited greater proportional reductions in Asatand had lower chlorophyll concentrations, quantum efficiencies, and leaf absorptances when treated with ozone relative to controls. With increasing ozone dose over time, Asatbecame uncoupled from stomatal conductance as ratios of internal to external concentrations of carbon dioxide increased, reducing water‐use efficiency. Ozone reduced net photosynthesis and impaired stomatal function, with these effects depending on the irradiance environment of the canopy leaves. Increased ozone sensitivity of shade leaves compared to sun leaves has consequences for net carbon gain in canopies.
Rapid recycling of triose phosphates in oak stem tissue
Authors: HILL S. A. , WATERHOUSE J. S. , FIELD E. M. , SWITSUR V. R. , AP REES T.
Published: April 2006

We report the carbon‐13 and oxygen‐18 isotope ratios in cellulose from the early and late wood of pedunculate oak (Quercus robur L.). The δ13 C value of the early wood correlates best with that of the late wood of the previous year. The δ18O value of the early wood correlates best with that of the late wood of the same year. We suggest that a biochemical explanation of these data is that there is a rapid cycle between hexose monophosphates and triose phosphates in oak stem tissue during cellulose synthesis. Evidence in support of this explanation is provided by the intramolecular distribution of 14C in labelled fructose extracted from cores of wood that had been supplied with [1−14C]‐ and [6‐14C]glucose.
Environmental and hormonal regulation of barley late‐embryogenesis‐abundant (Lea) mRNAs is via different signal transduction pathways
Authors: ESPELUND M. , DE BEDOUT J.A. , JR OUTLAW W.H. , JAKOBSEN K.S.
Published: April 2006

Late‐embryogenesis‐abundant (Lea) genes are induced in immature embryos by ABA and osmotic stress. Using the ABA‐biosynthesis inhibitor norflurazon in combination with ionic and non‐ionic stress, the expression of three distinct groups of Lea transcripts in immature barley embryos was investigated, these groups being embryoand aleurone‐specific B15C mRNAs, embryo‐specific B19 inRNAs, and rab/dehydrin mRNAs, which encode stress‐related proteins that are also expressed in vegetative tissues. The expression of B15C and rab/dehydrins in response to mannitol was not affected by the addition of norflurazon, which decreased the endogenous ABA levels by 89%; this observation is consistent with an ABA‐independent pathway. The expression of B19 was only slightly dependent on ABA. In contrast, induction of the Lea genes by salt (NaCI) required at least 25ümol m−3 endogenous ABA. Together, these results are evidence for different signal transduction pathways linking ionic and non‐ionic osmotic stress to Lea mRNA accumulation in barley embryos.
The effects of elevated temperature and atmospheric carbon dioxide concentration on the quality of grain lipids in wheat (Triticum aestivum L.) grown at two levels of nitrogen application
Authors: WILLIAMS M. , SHEWRY P. R. , LAWLOR D.W. , HARWOOD J. L.
Published: April 2006

Wheat plants were cultivated under growth regimes combining two temperatures (ambient and 4°C above ambient temperature) with two concentrations or carbon dioxide (350 and 700 μmol mol) and two nitrogen fertilizer applications (high and low). The aim of this study was to define any changes in the acyl lipid composition of wheat grains which could result from alterations in the growth conditions. Qualitative and quantitative changes were observed in both non‐starch and starch lipid fractions. Temperature was by far the most influential growth factor, although interactions between all three growth conditions occurred, as confirmed by analysis of variance. Growth at elevated temperatures had the general effect of reducing the amounts of accumulated lipids, particularly non‐polar lipids (1322 nig fatty acids per 100 g fresh weight at ambient temperatures as opposed to 777 mg fatty acids per lOOg fresh weight at 4°C above ambient temperatures). There were changes in the proportions of the major non‐starch as well as the starch lipids. In the former category, non‐polar lipids (principally triacylglyc‐erols), the membrane glycosylglyccridcs and phos‐phatidylcholinc were the main constituents, whereas in the starch lipids, lysophosphatidylcholine and lysophos‐phatidylethanolamine represented over 70% of the total. Depending on the growth conditions, the percentages of lipids such as monogalactosyldiacylglycerol, digalactosyl‐diacylglycerol and phosphatidyleholine (non‐starch) or the starch lysophosphatidylethanolamine varied 2‐fold or more. Significant changes in the acyl composition of individual lipids were also observed, most often in the proportions of palmitate, oleate and linoleate. The observed alterations in wheat lipids arc likely to affect the properties of any flours derived from grain grown under climate change conditions.
Biosynthesis of halomethanes and methanethiol by higher plants via a novel methyltransferase reaction
Authors: SAINI H. S. , ATTIEH J. M. , HANSON A. D.
Published: April 2006

Biogenic emissions of halomethanes (CH3CI, CH3Br and CH3I) and methanethiol (CH3SH) are of major significance to atmospheric chemistry, but there is little information on such emissions from higher plants. We present evidence that plants can produce all these gases through an identical methyltransferase reaction. A survey of 118 herbaceous species, based on CH3I production by leaf discs supplied with Kl, detected the presence of in vivo halide methyltransferase activity in 87 species. The activities ranged over nearly 4 orders of magnitude. Plants generally considered salt tolerant had relatively low activities, and salinization of three such species did not increase the activity. The highest activities were found in the family Brassicaceae. Leaf extracts of Brassica oleracea catalysed the S‐adenosyl‐L‐methioninc‐dependenl niethylalion of the halides I−, Br− and CI− to the respective halomethanes. In addition, the extract similarly methylated HS− (bisulphide) to CH3SH. These two types of enzyme activity (halide and bisulphide methyltransferase) were also present in all of the 20 species comprising a subsample that represented the range of CH3I emissions observed in the initial survey of in vivo CH3I production ability, and in a marine red alga Endocladia muricata. Moreover, the two activities occurred in approximately the same ratio in all the higher plants tested. These findings highlight the potential of higher plants to contribute to the atmosphericbudget of halomethanes and melhanethiol. The halide and bisulphide methyltransferase activities may also provide a mechanism for the elimination of halide and HS− ions, both of which are known to be phytotoxic.
Salt tolerance of maize (Zea mays L.): the role of sodium exclusion
Authors: FORTMEIER R. , SCHUBERT S.
Published: April 2006

The influence of NaCl and Na2SO4 on growth of two maize cultivars (Zea mays cv. Pioneer 3906 and cv. Across 8023) differing in Na+ uptake was investigated in two green‐house experiments. Na+ treatment with different accompanying anions (Cl−/SO42−) showed that ion toxicity was caused by Na+. While shoot growth of the two cultivars was markedly affected by salt in comparison to the control during the first 2–3 weeks, there were only slight differences between the cultivars. The shoot Ca2+ concentration was reduced in both cultivars, and the youngest leaves contained an even lower concentration compared with the rest of the shoot. During this first phase, Across 8023 tended to have higher concentrations of Ca2+ than Pioneer 3906. The Na+‐excluding cultivar Pioneer 3906 showed continuous, although reduced, growth compared with the control, while the Na+ concentration in the shoot decreased until flowering. Cultivar Across 8023 accumulated Na+ until flowering: the reduction in the growth of stressed plants was greater than that for Pioneer 3906. Leaves of cultivar Across 8023 showed clear toxic symptoms, while those of the more salt‐tolerant cultivar Pioneer 3906 did not. It is concluded that Na+ exclusion contributes to the salt tolerance of maize.
Temperature gradient chambers for research on global environment change. I. Portable chambers for research on short‐stature vegetation
Authors: RAWSON H. M. , GIFFORD R. M. , CONDON B. N.
Published: April 2006

Field temperature gradient chambers designed for experiments on short‐stature plants such as wheat are deseribed. The chambers are portable, easily erected and dismantled, and are self‐contained for control and measuring equipment. The design is modular, the modules being bolted together longitudinally although separated by slotted transparent septa which divide the chamber into zones of different temperature. Fresh air, which is blown in horizontally into one end of the chamber by two fans and extracted by a fan mounted vertically at the other end, passes sequentially through the modules. The air stream progressively heats when the sun is shining. Fans are automatically speed‐controlled in 100 steps between 20 and 100% of full output to keep the end‐to‐end temperature difference to within 5°C. During darkness, when the fans are running at minimum speed, heaters mounted in the outlet module are turned on. The chambers in the configuration described enclose 6 × 8m rows of crop, are l‐25m high and have side walls which are entirely composed of rigid, vertically sliding doors for crop access.
Comparative ecophysiology of leaf and canopy photosynthesis
Authors: TERASHIMA I. , HIKOSAKA K.
Published: April 2006

Leaves and herbaceous leaf canopies photosynthesize efficiently although the distribution of light, the ultimate resource of photosynthesis, is very biased in these systems. As has been suggested in theoretical studies, if a photosynthetic system is organized such that every photosynthetic apparatus photosynthesizes in concert, the system as a whole has the sharpest light response curve and is most adaptive. This condition can be approached by (i) homogenization of the light environment and (ii) acclimation of the photosynthetic properties of leaves or chloroplasts to their local light environments. This review examines these two factors in the herbaceous leaf canopy and in the leaf. Changes in the inclination of leaves in the canopy and differentiation of mesophyll into palisade and spongy tissue contribute to the moderation of the light gradient. Leaf and chloroplast movements in the upper parts of these systems under high irradiances also moderate light gradients. Moreover, acclimation of leaves and chloroplasts to the local light environment is substantial. These factors increase the efficiency of photosynthesis considerably. However, the systems appear to be less efficient than the theoretical optimum. When the systems are optically dense, the light gradients may be too great for leaves or chloroplasts to acclimate. The loss of photosynthetic production attributed to the imperfect adjustment of photosynthetic apparatus to the local light environment is most apparent when the photosynthesis of the system is in the transition between the light‐limited and light‐saturated phases. Although acclimation of the photosynthetic apparatus and moderation of light gradients are imperfect, these markedly raise the efficiency of photosynthesis. Thus more mechanistic studies on these adaptive attributes are needed. The causes and consequences of imperfect adjustment should also be investigated.
A simple calibrated model of Amazon rainforest productivity based on leaf biochemical properties
Authors: LLOYD J. , GRACE J. , MIRANDA A. C. , MEIR P. , WONG S. C. , MIRANDA H. S. , WRIGHT I. R. , GASH J. H. C. , McINTYRE J.
Published: April 2006

A simple ‘big leaf’ ecosystem gas exchange model was developed, using eddy covariance data collected at an undisturbed tropical rainforest in south‐western Amazonia (Brazil). The model used mechanistic equations of canopy biochemistry combined with an empirical stomatal model describing responses to light, temperature and humidity. After calibration, the model was driven using hourly data from a weather station at the top of the tower at the measurement site, yielding an estimate of gross primary productivity (annual photosynthesis) in 1992/1993 of about 200 mol C m−2 year −. Although incoming photon flux density emerged as the major control on photosynthesis in this forest, at a given PAR CO2 assimilation rates were higher in the mornings than in the afternoons. This was attributable to stomatal closure in the afternoon in response to increasing canopy‐to‐air vapour pressure differences. Although most morning gas exchange was clearly limited by the rate of electron transport, afternoon gas exchange was generally observed to be very nearly co‐limited by both Rubisco activity (Vmax) and electron transport rate. The sensitivity of the model to changes in nitrogen allocation showed that the modelled ratio of Vmax to electron transport (Jmax) served nearly to maximize the annual carbon gain, and indeed, would have resulted in almost maximum annual carbon gain at the pre‐industrial revolution atmospheric CO2 concentration of 27 Pa. Modelled gross primary productivity (GPP) was somewhat lower at 27 Pa, being about 160 mol C m−2 year−1. The model suggests that, in the absence of any negative feedbacks on GPP, future higher concentrations of atmospheric CO2 will continue to increase the GPP of this rainforest, up to about 230 mol C m−2 year−1 at 70 Pa.
Scaling carbon dioxide and water vapour exchange from leaf to canopy in a deciduous forest. I. Leaf model parametrization
Authors: HARLEY P. C. , BALDOCCHI D. D.
Published: April 2006

In order to parametrize a leaf submodel of a canopy level gas‐exchange model, a series of photosynthesis and stomatal conductance measurements were made on leaves of white oak (Quercus alba L.) and red maple (Acer rubrum L.) in a mature deciduous forest near Oak Ridge, TN. Gas‐exchange characteristics of sun leaves growing at the top of a 30 m canopy and of shade leaves growing at a depth of 3–4 m from the top of the canopy were determined. Measured rates of net photosynthesis at a leaf temperature of 30°C and saturating photosynthetic photon flux density, expressed on a leaf area basis, were significantly lower (P = 0.01; n = 8) in shade leaves (7.9μmol m−2 s−1) than in sun leaves (11–5μmol m−2 s−1). Specific leaf area increased significantly with depth in the canopy, and when photosynthesis rates were expressed on a dry mass basis, they were not significantly different for shade and sun leaves. The percentage leaf nitrogen did not vary significantly with height in the canopy; thus, rates expressed on a per unit nitrogen basis were also not significantly different in shade and sun leaves. A widely used model integrating photosynthesis and stomatal conductance was parametrized independently for sun and shade leaves, enabling us to model successfully diurnal variations in photosynthesis and evapotranspiration of both classes of leaves. Key photosynthesis model parameters were found to scale with leaf nitrogen levels. The leaf model parametrizations were then incorporated into a canopy‐scale gas‐exchange model that is discussed and tested in a companion paper (Baldocchi & Harley 1995, Plant, Cell and Environment 18, 1157–1173).
Scaling carbon dioxide and water vapour exchange from leaf to canopy in a deciduous forest. II. Model testing and application
Authors: BALDOCCHI D. D. , HARLEY P. C.
Published: April 2006

The scaling of CO2 and water vapour transfer from leaf to canopy dimensions was achieved by integrating mechanistic models for physiological (photosynthesis, stomatal conductance and soil/root and bole respiration) and micrometeorological (radiative transfer, turbulent transfer and surface energy exchanges) processes. The main objectives of this paper are to describe a canopy photosynthesis and evaporation model for a temperate broadleaf forest and to test it against field measurements. The other goal of this paper is to use the validated model to address some contemporary ecological and physiological questions concerning the transfer of carbon and water between forest canopies and the atmosphere. In particular, we examine the role of simple versus complex radiative transfer models and the effect of environmental (solar radiation and CO2) and ecophysiological (photo‐synthetic capacity) variables on canopy‐scale carbon and water vapour fluxes.
Leaf nitrogen, photosynthesis, conductance and transpiration: scaling from leaves to canopies
Authors: LEUNING R. , KELLIHER F. M. , DE PURY D. G. G. , SCHULZE E.‐D.
Published: April 2006

A model is presented which solves simultaneously for leaf‐scale stomatal conductance, CO2 assimilation and the energy balance as a function of leaf position within canopies of well‐watered vegetation. Fluxes and conductances were calculated separately for sunlit and shaded leaves. A linear dependence of photosynthetic capacity on leaf nitrogen content was assumed, while leaf nitrogen content and light intensity were assumed to decrease exponentially within canopies. Separate extinction coefficients were used for diffuse and direct beam radiation. An efficient Gaussian integration technique was used to compute fluxes and mean conductances for the canopy. The multilayer model synthesizes current knowledge of radiation penetration, leaf physiology and the physics of evaporation and provides insights into the response of whole canopies to multiple, interacting factors. The model was also used to explore sources of variation in the slopes of two simple parametric models (nitrogen‐ and light‐use efficiency), and to set bounds on the magnitudes of the parameters.

For canopies low in total N, daily assimilation rates are ∼10% lower when leaf N is distributed uniformly than when the same total N is distributed according to the exponentially decreasing profile of absorbed radiation. However, gains are negligible for plants with high N concentrations. Canopy conductance, Gc should be calculated as Gc=Aσ(fslgsl+fshgsh), where Δ is leaf area index, fsi and fsh are the fractions of sunlit and shaded leaves at each level, and gsi and gsh are the corresponding stomatal conductances. Simple addition of conductances without this weighting causes errors in transpiration calculated using the ‘big‐leaf’ version of the Penman‐Monteith equation. Partitioning of available energy between sensible and latent heat is very responsive to the parameter describing the sensitivity of stomata to the atmospheric humidity deficit. This parameter also affects canopy conductance, but has a relatively small impact on canopy assimilation.

Simple parametric models are useful for extrapolating understanding from small to large scales, but the complexity of real ecosystems is thus subsumed in unexplained variations in parameter values. Simulations with the multilayer model show that both nitrogen‐ and radiation‐use efficiencies depend on plant nutritional status and the diffuse component of incident radiation, causing a 2‐ to 3‐fold variation in these efficiencies.
Stomatal responses to increased CO2: implications from the plant to the global scale
Authors: FIELD C. B. , JACKSON R. B. , MOONEY H. A.
Published: April 2006

Increased atmospheric CO2 often but not always leads to large decreases in leaf conductance. Decreased leaf conductance has important implications for a number of components of CO2 responses, from the plant to the global scale. All of the factors that are sensitive to a change in soil moisture, either amount or timing, may be affected by increased CO2. The list of potentially sensitive processes includes soil evaporation, run‐off, decomposition, and physiological adjustments of plants, as well as factors such as canopy development and the composition of the plant and microbial communities. Experimental evidence concerning ecosystem‐scale consequences of the effects of CO2 on water use is only beginning to accumulate, but the initial indication is that, in water‐limited areas, the effects of CO2‐induced changes in leaf conductance are comparable in importance to those of CO,2‐induced changes in photosynthesis.

Above the leaf scale, a number of processes interact to modulate the response of canopy or regional evapotran‐spiration to increased CO2. While some components of these processes tend to amplify the sensitivity of evapo‐transpiration to altered leaf conductance, the most likely overall pattern is one in which the responses of canopy and regional evapotranspiration are substantially smaller than the responses of canopy conductance. The effects of increased CO2 on canopy evapotranspiration are likely to be smallest in aerodynamically smooth canopies with high leaf conductances. Under these circumstances, which are largely restricted to agriculture, decreases in evapotranspiration may be only one‐fourth as large as decreases in canopy conductance.

Decreased canopy conductances over large regions may lead to altered climate, including increased temperature and decreased precipitation. The simulation experiments to date predict small effects globally, but these could be important regionally, especially in combination with radiative (greenhouse) effects of increased CO2.
High‐light effects on CO2 fixation gradients across leaves
Authors: SUN J. , NISHIO J. N. , VOGELMANN T. C.
Published: April 2006

Chlorophyll fluorescence and internal patterns of 14CO2 fixation were measured in sun and shade leaves of spinach after treatment with various light intensities. When sun leaves were irradiated with 2000μmol m−2 s−1 for 2h, FV/FM decreased by about 15%, but 14CO2 fixation was unaffected, whereas shade leaves exhibited a 21% decrease in Fv/FM and a 25% decrease in 14CO2 fixation. Irradiation of sun and shade leaves with 4000μmol m−1 for 4 h decreased FV/FM by 30% in sun leaves and 40% in shade leaves, while total 14CO2 fixation decreased by 41% in sun leaves and 55% in shade leaves. After light treatment, gradients of CO2 fixation across leaves were determined by measuring 14CO2 fixed in paradermal leaf sections after a 10s pulse of 14CO2. Gradients of 14CO2 fixation in control sun and shade leaves were identified when expressed on a relative basis and normalized for leaf depth. Treatment of leaves with 2000 μmol PAR m−2 s−1 for 2h did not after patterns of carbon fixation across sun leaves, but slightly altered the pattern in shade leaves. In contrast, treatment of sun and shade leaves with 4000μmol m−2 s−1 for 4h decreased carbon fixation more in the palisade mesophyll cells than in the spongy mesophyll cells of sun and shade leaves, and fixation in medial tissue of shade leaves was dramatically decreased compared to the adaxial and abaxial tissue. The interaction between leaf anatomy and biochemical parameters involved in tolerance to photoinhibition in spinach is discussed.
Ammonia compensation points in two cultivars of Hordeum vulgare L. during vegetative and generative growth
Authors: HUSTED S. , MATTSSON M. , SCHJOERRING J.K.
Published: April 2006

The NH3 compensation point (χNH3) in Hordeum vulgare cvs Golf and Laevigatum was determined at different growth stages under controlled environmental conditions. The plants were grown to maturity in hydroponics under N limitation. When plants were exposed to NH3 at realistic ambient levels ranging from 0 to 25 nmol NH3 mol−1 air at an air temperature of 20°C, a significant (P < 0.001) linear correlation between the NH3 flux and the atmospheric NH3 mole fraction was observed, showing a constant conductivity to NH3 exchange irrespective of the NH3 level. For both cultivars a marked decrease in χNH3 was observed in the period from tillering to anthesis. In cv. Golf, χNH3 decreased from 6.4 ± 1.1 to 3.0 ± 0.4 nmol NH3 mol−1 air, while χNH3 in cv. Laevigatum dropped from 4.2 ± 0.3 nmol NH3 mol−1 air to below the detection limit (< 0.9 nmol NH3 mol−1 air). The NH3 compensation points increased again during senescence, peaking at 5.3 ± 0.8 nmol NH3 mol−1 air for cv. Laevigatum. The modern and high‐yielding cv. Golf had significantly higher (P < 0.01) NH3 compensation points than the old and primitive cv. Laevigatum. Golf also had higher shoot NH4+ and total nitrogen concentrations than Laevigatum. During generative growth the ratio between NH3 and water vapour conductivities increased 10‐fold, suggesting a shortening of the diffusive path length for NH3 compared to H2O during leaf senescence.
Nitrogen isotope composition of tomato (Lycopersicon esculentumMill. cv. T‐5) grown under ammonium or nitrate nutrition
Authors: EVANS R. D. , BLOOM A. J. , SUKRAPANNA S. S. , EHLERINGER J. R.
Published: April 2006

Studies that quantify plant δ15N often assume that fractionation during nitrogen uptake and intra‐plant variation in δ15N are minimal. We tested both assumptions by growing tomato (Lycopersicon esculetumMill. cv. T‐5) at NH4+or NO−3concentrations typical of those found in the soil. Fractionation did not occur with uptake; whole‐plant δ15N was not significantly different from source δ15N for plants grown on either nitrogen form. No intra‐plant variation in δ15N was observed for plants grown with NH+4. In contrast. δ15N of leaves was as much as 5.8% greater than that of roots for plants grown with NO−3. The contrasting patterns of intra‐plant variation are probably caused by different assimilation patterns. NH+4is assimilated immediately in the root, so organic nitrogen in the shoot and root is the product of a single assimilation event. NO−3assimilation can occur in shoots and roots. Fractionation during assimilation caused the δ15N of NO−3to become enriched relative to organic nitrogen; the δ15N of NO−3was 11.1 and 12.9% greater than the δ15N of organic nitrogen in leaves and roots, respectively. Leaf δ15N may therefore be greater than that of roots because the NO−3available for assimilation in leaves originates from a NO−3pool that was previously exposed to nitrate assimilation in the root.
Temperate forest responses to carbon dioxide, temperature and nitrogen: a model analysis
Authors: THORNLEY J. H. M. , CANNELL M. G. R.
Published: April 2006

The ITE Edinburgh Forest Model, which describes diurnal and seasonal changes in the pools and fluxes of C, N and water in a fully coupled forest–soil system, was parametrized to simulate a managed conifer plantation in upland Britain. The model was used to examine (i) the transient effects on forest growth of an IS92a scenario of increasing [CO2] and temperature over two future rotations, and (ii) the equilibrium (sustainable) effects of all combinations of increases in [CO2] from 350 to 550 and 750 μmol mol−1, mean annual temperature from 7.5 to 8.5 and 9.5°C and annual inputs of 20 or 40 kg N ha−1. Changes in underlying processes represented in the model were then used to explain the responses. Eight conclusions were supported by the model for this forest type and climate.

Increasing temperatures above 3°C alone may cause forest decline owing to water stress.

Elevated [CO2] can protect trees from water stress that they may otherwise suffer in response to increased temperature.

In N‐limiting conditions, elevated [CO2] can increase allocation to roots with little increase in leaf area, whereas in N‐rich conditions elevated [CO2] may not increase allocation to roots and generally increases leaf area.

Elevated [CO2] can decrease water use by forests in N‐limited conditions and increase water use in N‐rich conditions.

Elevated [CO2] can increase forest productivity even in N‐limiting conditions owing to increased N acquisition and use efficiency.

Rising temperatures (along with rising [CO2]) may increase or decrease forest productivity depending on the supply of N and changes in water stress.

Gaseous losses of N from the soil can increase or decrease in response to elevated [CO2] and temperature.

Projected increases in [CO2] and temperature (IS92a) are likely to increase net ecosystem productivity and hence C sequestration in temperate forests.
Heterogeneity of leaf CO2 assimilation during photosynthetic induction
Authors: BRO E. , MEYER S. , GENTY B.
Published: April 2006

Spatial mid temporal variations in the distribution of photosynthesis over the leaf area were investigated during induction upon illumination of Rosa rubiginosa L. leaves. Gas exchange and maps of relative photosynthetie electron transport activity computed from chlorophyll fluorescence images were simultaneously monitored. In air, after 15 h of dark adaptation, linear electron transport was heterogeneously distributed over the leaf area during the induction. This patchy induction was explained by asynchronous metabolism activation for the first 10 min of illumination, concomitant asynchronous limitation by intrinsic metabolism and stomatal apertures (10–30 min) and finally by only stomatal limitation beyond 30 min. A brief transition to non‐photorespiratory conditions after 20 min of illumination under subsaturating irradiance revealed a marked heterogeneity of CO2 assimilation, presumably as a result of heterogeneous stomatal apertures. The frequency distribution of CO2 assimilation was unimodal. During the induction, heterogeneity gradually decreased and photosynthesis was uniform at steady‐state. After 10 min of dark adaptation, heterogeneity of linear electron transport activity occurred during the first 15 min of a second induction and mainly resulted from metabolic limitation.
Thylakoid membrane stability to heat stress studied by flash spectroscopic measurements of the electrochromic shift in intact potato leaves: influence of the xanthophyll content
Authors: HAVAUX M. , TARDY F. , RAVENEL J. , CHANU D. , PAROT P.
Published: April 2006

A flash‐induced transthylakoid electric field was measured at 515 nm as an electrochromic absorbance shift in intact potato leaves using a double flash differential spectrophotometer. The decay rate of the electrochromic shift in dark‐adapted samples was used to examine the conductance to ions of thylakoid membranes. Heat stress (39.5 °C for 15 min) was found to accelerate drastically the electric field decay, with the half decay time falling from more than 200 ms to less than 45 ms. Heat‐induced acceleration of the electric field breakdown was insensitive to the PSII electron donor Hydroxylamine and to the ATPase inhibitor dicyclohexylcarbodiimide (DCCD), thus indicating that it reflects an increase in thylakoid membrane permeability after heat stress. This phenomenon did not involve peroxidative damage of membrane lipids. Acceleration of the electric field relaxation exhibited the same temperature dependence as that of PSII deactivation, suggesting that the ionic permeability of thylakoid membranes is one of the most heat‐sensitive components of the photosynthetic apparatus. When potato leaves were infiltrated with 100 mol m−3 ascorbate (in a buffer of pH 5), there was massive conversion of the carotenoid violaxanthin to zeaxanthin. This change in carotenoid composition protected thylakoid membranes against heat‐induced changes in permeability, as revealed by the maintenance of a slow decay of the 515 nm absorbance change after heat stress. No such effect was observed after treatments which did not induce the vio‐laxanthin‐to‐zeaxanthin conversion: leaf infiltration with 0 mol m−3 ascorbate (at pH 5 or 8), 100 mol m−3 ascorbate at pH 8 or 100 mol m−3 ascorbate +5 mol m−3 dithiothreitol at pH 5. Increased stability of the permeability properties of thylakoid membranes was also observed after a mild heat treatment (2 h at 35 °C). The data presented suggest that de‐epoxidized xanthophylls in vivo stabilize thylakoid membranes and protect thylakoids against heat‐induced disorganization.
Effects of pH on ammonium uptake byTypha latifoliaL.
Authors: DYHR‐JENSEN K. , BRIX H.
Published: April 2006

The effects of solution pH on NH4+uptake kinetics and net H+extrusion byTypha latifoliaL. were studied during short‐term (days) and long‐term (weeks) exposure to pH in the range of pH 3.5–8.0. The NH4+uptake kinetics were estimated from depletion curves using a modified Michaelis‐Menten model.T. latifoliawas able to grow in solution culture with NH4+as the sole N source and to withstand a low medium pH for short periods (days). With prolonged exposure (weeks) to pH 3.5, however, the plants showed severe symptoms of stress and stopped growing. The solution pH affected NH4+uptake kinetics. The affinity for NH4+, as quantified by the half saturation constant (K1/2) andCmin(the NH4+concentration at which uptake ceases), decreased with pH.K1/2was increased from 7.1 to 19.2 mmol m−3andCminfrom 2.0 to 5.7 mmol m−3by lowering the pH in steps from 8.0 to 3.5.Vmaxwas, however, largely unaffected by pH (∼22 μmol h−1g−1root dry weight). Under prolonged exposure to constant pH, growth rates were highest at PH 5.0 and 6.5. At pH 8.0 growth was slightly depressed and at pH 3.5 growth completely stopped. NH4+uptake kinetics were similar at pH 5.0, 6.5 and 8.0 whereas at pH 3.5 NH4+uptake almost completely stopped. The ratio between net H+extrusion and NH4+uptake decreased significantly at low pH. The adverse effects of low pH on NH4+uptake kinetics are probably a consequence of a reduced H+‐ATPase activity and/or an increased re‐entry of H+at low pH, and the associated decrease in the electrochemical gradient across the plasma membranes of the root cells.
Salinity‐induced enhancement of L‐myo‐inositol 1‐phosphate synthase in rice (Oryza sativa L.)
Authors: RAYCHAUDHURI A. , MAJUMDER A. LAHIRI
Published: April 2006

The salt‐tolerant varieties of rice (Oryza sativa L.) exhibit enhanced activity of the chloroplast form of L‐myo‐inositol 1‐phosphate synthase (EC 5.5.4.1) under NaCl treatment either during the seedling stage or in fully grown plants during field growth. The salt‐induced enhancement was noticeable only in chloroplasts from light‐grown plants. The effects of these treatments on the cytosolic inositol synthase activity were less pronounced. While the effect of salt on the activity of the two forms was marginal in the salt‐sensitive varieties during seedling growth, salinity affected the chloroplast inositol synthase activity adversely in these varieties during growth of the plants under field conditions. The salt‐enhanced activities of inositol synthase(s) in the highly salt‐tolerant varieties studied were found to be comparable to that observed in Porteresia coarctata, a halophytic wild rice species. The implications of these findings, which suggest a role of the inositol pathway in osmoregulation, are discussed.
1H‐NMR spin‐spin relaxation time assessment of the reflection coefficient of the Triticale seed cell wall–plasmalemma barrier to mannitol
Authors: MIEDZIEJKO E. M. , PLENZLER G. B. , NAPIERAŁA D. M. , NAROŻNA A. T.
Published: April 2006

The 1H‐NMR spin‐spin relaxation time (T2) in Triticale seeds swelling in external osmotica, polyethylene glycol 8000 or mannitol can identify both bound and free water. At the same water content, the free water spin‐spin relaxation time increases for seeds imbibed with the mannitol solution, demonstrating inadequate water potential adjustment. The exchange rate of free/bound water molecules is apparently influenced by the driving force for water flow. The reciprocal lifetime of free water molecules, as a measure of water flow through the main cell barrier, was obtained. From a model of the seed as a resistance–capacitor network for water flow, a method was derived for calculating the reflection coefficient σ as a lifetime ratio of the free water molecules in seeds imbibed with two different osmotica (one penetrating across the main cell barrier and one not penetrating) at the same water potential. The 1H‐NMR method and the classical method based on volume rate changes yielded reflection coefficients for mannitol for the cell wall–plasmalemma barrier of 0.78 ± 0.08 and 0.68 ± 0.06, respectively.
Thermal acclimation and photoacclimation of photosynthesis in the brown alga Laminaria saccharina
Authors: MACHALEK K. M. , DAVISON I. R. , FALKOWSKI P. G.
Published: April 2006

Thermal acclimation and photoacclimation of photosynthesis were compared in Laminaria saccharina sporophytes grown at temperatures of 5 and 17 °C and irradiances of 15 and 150μmol photons m−2 s−1. When measured at a standard temperature (17°C), rates of light‐saturated photosynthesis (Pmax) were higher in 5 °C‐grown algae (c. 3.0 μmol O2 m−2 s−1) than in 17 °C‐grown algae (c. 0.9 μmol O2 m‐2 s‐1). Concentrations of Rubisco were also 3‐fold higher (per unit protein) in 5 °C‐grown algae than in algae grown at 17 °C. Light‐limited photosynthesis responded similarly to high temperature and low light Photon yields (α) were higher in algae grown at high temperature (regardless of light), and at 5 °C in low light, than in algae grown at 5 °C in high light Differences in a were correlated with light absorption; both groups of 17 °C algae and 5 °C low‐light algae absorbed c. 75% of incident light, whereas 5 °C high‐light algae absorbed c. 55%. Increased absorption was correlated with increases in pigment content PSII reaction centre densities and the fucoxanthin‐Chl ale protein complex (FCP). Changes in a were also attributed, in part, to changes in the maximum photon yield of photosynthesis (0max). PSI reaction centre densities were unaffected by growth temperature, but the areal concentration of PSI in low‐light‐grown algae was twice that of high‐light‐grown algae (c. 160.0 versus 80.0 nmol m−2). We suggest that complex metabolic regulation allows L, saccharina to optimize photosynthesis over the wide range of temperatures and light levels encountered in nature.
Accumulated effect of elevated ultraviolet‐B radiation over multiple generations of the arid‐environment annualDimorphotheca sinuataDC. (Asteraceae)
Authors: MUSIL C. F.
Published: April 2006

TwoD. sinuatapopulations, established from the same seed batch, were cultured concurrently under ambient (2.5–8.9 kj m−2d−1) and enhanced (4.7–11.4 kj m−2d−1) ultraviolet‐B radiation for two consecutive generations. The two populations, designated low‐ and high‐UV‐B cultivars, were each grown for an additional generation under both UV‐B fluences at different alignments. Differences in plant performance were examined between UV‐B treatments (immediate UV‐B effects), cultivars (accumulated UV‐B effects), alignments and their interactions. Accumulated UV‐B had a greater effect on plant performance than immediate UV‐B. The former induced earlier reproductive effort, substantial (up to 35%) reductions in dry mass (stems, leaves and reproductive organs), decreased stem and inflorescence production, and diminished steady‐state fluorescence yields, chlorophyllaconcentrations, pollen tube growth and germination of seeds set. The latter caused only diminished non‐photochemical quenching, reduced chlorophylla, soluble sugar and starch concentrations, decreased pollen germination, and increased carotenoid contents. Interactions between UV‐B fluence level and alignment occurred for all measured dry mass parameters, leaf area, photosynthetic pigment and soluble sugar concentrations, and germination success of seeds set. These results indicate altered DNA integrity rather than an indirect UV‐B effect of photomorphogenic origin.