bluuebunny/crossref_metadata_2025_split huggingface dataset:
Effects of elevated [CO2] on photosynthesis in European forest species: a meta‐analysis of model parameters
Authors: Medlyn B. E. , Badeck F. ‐W. , De Pury D. G. G. , Barton C. V. M. , Broadmeadow M. , Ceulemans R. , De Angelis P. , Forstreuter M. , Jach M. E. , Kellomäki S. , Laitat E. , Marek M. , Philippot S. , Rey A. , Strassemeyer J. , Laitinen K. , Liozon R. , Portier B. , Roberntz P. , Wang K. , Jstbid P. G. 
Published: March 2003

ABSTRACTThe effects of elevated atmospheric CO2 concentration on growth of forest tree species are difficult to predict because practical limitations restrict experiments to much shorter than the average life‐span of a tree. Long‐term, process‐based computer models must be used to extrapolate from shorter‐term experiments. A key problem is to ensure a strong flow of information between experiments and models. In this study, meta‐analysis techniques were used to summarize a suite of photosynthetic model parameters obtained from 15 field‐based elevated [CO2] experiments on European forest tree species. The parameters studied are commonly used in modelling photosynthesis, and include observed light‐saturated photosynthetic rates (Amax), the potential electron transport rate (Jmax), the maximum Rubisco activity (Vcmax) and leaf nitrogen concentration on mass (Nm) and area (Na) bases. Across all experiments, light‐saturated photosynthesis was strongly stimulated by growth in elevated [CO2]. However, significant down‐regulation of photosynthesis was also observed; when measured at the same CO2 concentration, photosynthesis was reduced by 10–20%. The underlying biochemistry of photosynthesis was affected, as shown by a down‐regulation of the parameters Jmax and Vcmax of the order of 10%. This reduction in Jmax and Vcmax was linked to the effects of elevated [CO2] on leaf nitrogen concentration. It was concluded that the current model is adequate to model photosynthesis in elevated [CO2]. Tables of model parameter values for different European forest species are given.
Xylem cavitation and hydraulic control of stomatal conductance in Laurel (Laurus nobilis L.)
Authors: Salleo Sebastiano , Nardini Andrea , Pitt Franco , Gullo Maria A. Lo 
Published: March 2003

ABSTRACTThe possible link between stomatal conductance (gL), leaf water potential (ΨL) and xylem cavitation was studied in leaves and shoots of detached branches as well as of whole plants of Laurus nobilis L. (Laurel). Shoot cavitation induced complete stomatal closure in air‐dehydrated detached branches in less than 10 min. By contrast, a fine regulation of gL in whole plants was the consequence of ΨL reaching the cavitation threshold (ΨCAV) for shoots. A pulse of xylem cavitation in the shoots was paralleled by a decrease in gL of about 50%, while ΨL stabilized at values preventing further xylem cavitation. In these experiments, no root signals were likely to be sent to the leaves from the roots in response to soil dryness because branches were either detached or whole plants were growing in constantly wet soil. The stomatal response to increasing evaporative demand appeared therefore to be the result of hydraulic signals generated during shoot cavitation. A negative feedback link is proposed between gL and ΨCAV rather than with ΨL itself.
Control of transpiration in an irrigated Eucalyptus globulus Labill. plantation
Authors: White D. A. , Beadle C. L. , Worledge D. 
Published: March 2003

ABSTRACTStomatal conductance and transpiration were measured concurrently in an irrigated Eucalyptus globulus Labill. plantation. Canopy stomatal conductance, canopy boundary layer conductance and the dimensionless decoupling coefficient (Ω) were calculated (a) summing the conductance of three canopy layers (gc) and (b) weighting the contribution of foliage according to the amount of radiation received (gc′). Canopy transpiration was then calculated from gc and gc′ for Ω = 1 (Eeq), Ω = 0 (Eimp) and by weighting Eeq and Eimp using Ω (EΩ). Eeq, Eimp and EΩ were compared to transpiration estimated from measurements of heat pulse velocity. The mean value of Ω was 0·63. Transpiration calculated using gc and assuming perfect coupling (12·5 ± 0·9 mmol m−2 s−1) significantly overestimated measured values (8·7 ± 0·8 mmol m−2 s−1). Good estimates of canopy transpiration were obtained either (a) calculating EΩ separately for the individual canopy layers or (b) treating the canopy as a single layer and using gc′ in a calculation of Eimp (Ω = 0). The latter approach only required measurement of stomatal conductance at a single canopy position but would be unsuitable for use in combined models of canopy transpiration and assimilation. It should however, be suitable for estimating transpiration in forests regardless of the degree of coupling.
The effect of tree height on crown level stomatal conductance
Authors: Schäfer K. V. R. , Oren R. , Tenhunen J. D. 
Published: March 2003

ABSTRACTVariation in stomatal conductance is typically explained in relation to environmental conditions. However, tree height may also contribute to the variability in mean stomatal conductance. Mean canopy stomatal conductance of individual tree crowns (GSi) was estimated using sap flux measurements in Fagus sylvatica L., and the hypothesis that GSi decreases with tree height was tested. Over 13 d of the growing season during which soil moisture was not limiting, GSi decreased linearly with the natural logarithm of vapour pressure deficit (D), and increased exponentially to saturation with photosynthetic photon flux density (Qo). Under conditions of D= 1 kPa and saturating Qo, GSi decreased by approximately 60% with 30 m increase in tree height. Over the same range in height, sapwood‐to‐leaf area ratio (AS:AL) doubled. A simple hydraulic model explained the variation in GSi based on an inverse relationship with height, and a linear relationship with AS:AL. Thus, in F. sylvatica, adjustments in AS:AL partially compensate for the negative effect of increased flow‐path length on leaf conductance. Furthermore, because stomata with low conductance are less sensitive to D, gas exchange of tall trees is reduced less by high D. Despite these compensations, decreasing hydraulic conductance with tree height in F. sylvatica reduces carbon uptake through a corresponding decrease in stomatal conductance.
The ultrastructure of chilling stress
Authors: Kratsch H. A. , Wise R. R. 
Published: March 2003

ABSTRACTChilling injury to crop plants was first described 70 years ago and has been systematically investigated with electron microscopy since the late 1960s. Chloroplasts are the first and most severely impacted organelle. Thylakoids swell and distort, starch granules disappear, and a peripheral reticulum (vesicles arising from inner membrane of chloroplast envelope) appears. Chloroplast disintegration follows prolonged chilling. Mitochondria, nuclei and other organelles are less susceptible to chilling injury. Organellar development and ontogeny may also be disrupted. The inherent chilling sensitivity of a plant, as well as the ability of some species to acclimate to chilling, influence the timing and appearance of ultrastructural injury with the resulting outcome being mild, moderate, or severe. Other environmental factors that exacerbate injury are irradiance, chilling duration, and water status. The physiological basis for chloroplast swelling may be linked to chilling‐stable starch‐degrading enzymes that produce soluble sugars thus lowering stromal water potential at a time when chloroplast photosynthate export is reduced. Thylakoid dilation appears to be related to photo‐oxidative conditions produced during chilling in the light. The peripheral reticulum is proposed to increase surface area of the transport‐limiting membrane (chloroplast inner membrane) in response to the chilling‐induced reduction in metabolite transport. Many of the ultrastructural symptoms appearing during moderate stress resemble those seen in programmed cell death. Future research directions are discussed.
Responses of CAM species to increasing atmospheric CO2 concentrations
Authors: Drennan P. M. , Nobel P. S. 
Published: March 2003

ABSTRACTCrassulacean acid metabolism (CAM) species show an average increase in biomass productivity of 35% in response to a doubled atmospheric CO2 concentration. Daily net CO2 uptake is similarly enhanced, reflecting in part an increase in chlorenchyma thickness and accompanied by an even greater increase in water‐use efficiency. The responses of net CO2 uptake in CAM species to increasing atmospheric CO2 concentrations are similar to those for C3 species and much greater than those for C4 species. Increases in net daily CO2 uptake by CAM plants under elevated atmospheric CO2 concentrations reflect increases in both Rubisco‐mediated daytime CO2 uptake and phosphoenolpyruvate carboxylase (PEPCase)‐mediated night‐time CO2 uptake, the latter resulting in increased nocturnal malate accumulation. Chlorophyll contents and the activities of Rubisco and PEPCase decrease under elevated atmospheric CO2, but the activated percentage for Rubisco increases and the KM(HCO3−) for PEPCase decreases, resulting in more efficient photosynthesis. Increases in root:shoot ratios and the formation of additional photosynthetic organs, together with increases in sucrose‐Pi synthase and starch synthase activity in these organs under elevated atmospheric CO2 concentrations, decrease the potential feedback inhibition of photosynthesis. Longer‐term studies for several CAM species show no downward acclimatization of photosynthesis in response to elevated atmospheric CO2 concentrations. With increasing temperature and drought duration, the percentage enhancement of daily net CO2 uptake caused by elevated atmospheric CO2 concentrations increases. Thus net CO2 uptake, productivity, and the potential area for cultivation of CAM species will be enhanced by the increasing atmospheric CO2 concentrations and the increasing temperatures associated with global climate change.
Nitrate uptake and reduction in higher and lower plants
Authors: Tischner R. 
Published: March 2003

ABSTRACTThe nitrogen compounds nitrate and ammonium are the minerals that plants need in large quantities and which limit their growth in temperate zones. The nitrate assimilation pathway starts with nitrate uptake followed by nitrate reduction resulting in ammonium which is fixed into the amino acids glutamine and glutamate in most plants. This review concentrates on nitrate uptake and nitrate reduction with respect to higher and lower plants. The physiology and the progress in molecular approaches of both processes are considered. For nitrate uptake the well‐established uptake systems are discussed and special attention is drawn to nitrate sensing and the nitrate carrier. Knowledge, particularly on nitrate sensing is rare, but it seems to be the first step in a signal transduction chain triggered by nitrate. Therefore further work should consider this topic more frequently. For nitrate reductase the focus is on the post‐translational modification as a regulatory tool for nitrate assimilation, on the intersections of carbon and nitrogen metabolism and on the molecular approaches. A few remarks on how environmental conditions affect nitrate assimilation are also included. Further progress is needed to understand the transduction of positive and negative signals from the environment affecting the expression of genes coding for the nitrate assimilating pathway.
Cold comfort farm: the acclimation of plants to freezing temperatures
Authors: Xin Z. , Browse J. 
Published: March 2003

ABSTRACTPlant acclimation to freezing temperatures is very complex. Many temperate plants increase in freezing tolerance upon exposure to a period of low but non‐freezing temperatures, an adaptive process known as cold acclimation. This acclimation phenomenon has encouraged investigations of physiological, biochemical, and molecular changes that are associated with the development of freezing tolerance. Although many biochemical and gene‐expression changes occur during cold acclimation, few have been unequivocally demonstrated to contribute to the development of freezing tolerance. However, in the last few years, exciting new progress has been made through the use of mutational analysis and molecular genetic approaches. We now recognize that several interacting signal pathways are activated to bring about cold acclimation and ensure the winter survival of plants. The challenge for the future is to understand these pathways at a mechanistic level. Facile map‐based cloning in Arabidopsis and techniques (such as DNA micro‐arrays) for transcript profiling will provide the tools needed for this task.
Evaluation of instant light‐response curves of chlorophyll fluorescence parameters obtained with a portable chlorophyll fluorometer on site in the field
Authors: Rascher U. , Liebig M. , Lüttge U. 
Published: March 2003

ABSTRACTMiniaturized pulse‐amplitude modulated photosynthesis yield analysers are primarily designed for measuring effective quantum yield (ΔF/Fm′) of photosystem II under momentary ambient light conditions in the field. Although this provides important ecophysiological information, it is often necessary to learn more about the potential intrinsic capacities of leaves by measuring light‐response curves. Thus, instruments provide light‐curve programmes, where light intensities are increased in short intervals and instant light‐response curves are recorded within a few minutes. This method can be criticized because photosynthesis will most likely not be in steady state. This technical report shows that with the appropriate precautions instant light curves can nevertheless provide reliable information about cardinal points of photosynthesis. First, the geometry of the light source of the instrument in relation to the quantum sensor must be considered and quantum sensor readings must be corrected. Second, the measurements of the light‐response curves must be compared with readings of effective quantum yield of photosystem II under ambient light conditions where photosynthesis is in steady state. This may show that in the critical range of the light curves either both measurements perfectly coincide or are offset against each other by a constant value (examples are given here). In the first case results of light curves can be taken at face values, and in the second case a simple correction can be applied. With these precautions and careful interpretations instant light‐response curves can be an enormous advantage in ecophysiological field work.
Stomatal and non‐stomatal limitation to photosynthesis in two trembling aspen (Populus tremuloides Michx.) clones exposed to elevated CO2 and/or O3
Authors: Noormets A. , Sôber A. , Pell E. J. , Dickson R. E. , Podila G. K. , Sôber J. , Isebrands J. G. , Karnosky D. F. 
Published: March 2003

ABSTRACTLeaf gas exchange parameters and the content of ribulose‐1,5‐bisphosphate carboxylase/oxygenase (Rubisco) in the leaves of two 2‐year‐old aspen (Populus tremuloides Michx.) clones (no. 216, ozone tolerant and no. 259, ozone sensitive) were determined to estimate the relative stomatal and mesophyll limitations to photosynthesis and to determine how these limitations were altered by exposure to elevated CO2 and/or O3. The plants were exposed either to ambient air (control), elevated CO2 (560 p.p.m.) elevated O3 (55 p.p.b.) or a mixture of elevated CO2 and O3 in a free air CO2 enrichment (FACE) facility located near Rhinelander, Wisconsin, USA. Light‐saturated photosynthesis and stomatal conductance were measured in all leaves of the current terminal and of two lateral branches (one from the upper and one from the lower canopy) to detect possible age‐related variation in relative stomatal limitation (leaf age is described as a function of leaf plastochron index). Photosynthesis was increased by elevated CO2 and decreased by O3 at both control and elevated CO2. The relative stomatal limitation to photosynthesis (ls) was in both clones about 10% under control and elevated O3. Exposure to elevated CO2 + O3 in both clones and to elevated CO2 in clone 259, decreased ls even further – to about 5%. The corresponding changes in Rubisco content and the stability of Ci/Ca ratio suggest that the changes in photosynthesis in response to elevated CO2 and O3 were primarily triggered by altered mesophyll processes in the two aspen clones of contrasting O3 tolerance. The changes in stomatal conductance seem to be a secondary response, maintaining stable Ci under the given treatment, that indicates close coupling between stomatal and mesophyll processes.
δ13C of CO2 respired in the dark in relation to δ13C of leaf metabolites: comparison between Nicotiana sylvestris and Helianthus annuus under drought
Authors: Ghashghaie J. , Duranceau M. , Badeck F.‐W. , Cornic G. , Adeline M.‐T. , Deleens E. 
Published: March 2003

ABSTRACTThe variations of δ13C in leaf metabolites (lipids, organic acids, starch and soluble sugars), leaf organic matter and CO2 respired in the dark from leaves of Nicotiana sylvestris and Helianthus annuus were investigated during a progressive drought. Under well‐watered conditions, CO2 respired in the dark was 13C‐enriched compared to sucrose by about 4‰ in N. sylvestris and by about 3‰ and 6‰ in two different sets of experiments in H. annuus plants. In a previous work on cotyledonary leaves of Phaseolus vulgaris, we observed a constant 13C‐enrichment by about 6‰ in respired CO2 compared to sucrose, suggesting a constant fractionation during dark respiration, whatever the leaf age and relative water content. In contrast, the 13C‐enrichment in respired CO2 increased in dehydrated N. sylvestris and decreased in dehydrated H. annuus in comparison with control plants. We conclude that (i) carbon isotope fractionation during dark respiration is a widespread phenomenon occurring in C3 plants, but that (ii) this fractionation is not constant and varies among species and (iii) it also varies with environmental conditions (water deficit in the present work) but differently among species. We also conclude that (iv) a discrimination during dark respiration processes occurred, releasing CO2 enriched in 13C compared to several major leaf reserves (carbohydrates, lipids and organic acids) and whole leaf organic matter.
Establishment of far‐red high irradiance responses in wheat through transgenic expression of an oat phytochrome A gene
Authors: Shlumukov L. R. , Barro F. , Barcelo P. , Lazzeri P. , Smith H. 
Published: March 2003

AbstractA transgenic wheat line over‐expressing an oat phytochrome A gene under the control of the constitutive maize ubiquitin promoter was generated using a biolistic particle delivery system from immature wheat embryos. The resulting line showed increased levels of total phytochrome A protein in both dark‐grown and light‐grown plants. When grown under continuous far‐red light, seedlings of this line showed additional inhibition of the coleoptile extension in comparison with wild‐type seedlings. Unlike the response of wild‐type seedlings to continuous far‐red, this additional inhibition was dependent on fluence rate and was not observed under half‐hourly pulses of far‐red delivering the same total fluence as the continuous irradiation treatment. These observations suggest that increase in phytochrome A levels in wheat leads to the establishment of a far‐red high irradiation reaction in this monocotyledonous plant. Exposure to continuous red light caused a similar inhibition of coleoptile extension in both the wild types and the transgenic seedlings. When wild‐type seedlings were grown under continuous far‐red, their coleoptiles remained completely colourless and first leaves remained tightly rolled. In contrast, transgenic seedlings grown in the same conditions produced significant levels of anthocyanins in their coleoptiles and their first leaves became unrolled. Taken together, our data suggest that the increased levels of phytochrome A in wheat can change the type of response of some developmental processes to light signals, leading to the generation of a high irradiance reaction which is otherwise absent in the wild types under the conditions used.
Altered physiological and growth responses to elevated [CO2] in offspring from holm oak (Quercus ilex L.) mother trees with lifetime exposure to naturally elevated [CO2]
Authors: Polle A. , McKee I. , Blaschke L. 
Published: March 2003

AbstractAn important question with respect to plant performance in future climatic scenarios is whether the offspring of mature trees that have experienced lifelong exposure to elevated [CO2] show altered physiological responses to elevated [CO2] compared with those originating from current ambient CO2 concentrations. To investigate this question, acorns were collected from two seed sources, denoted as ‘control’ and ‘spring’, from Quercus ilex mother trees grown at ambient (36 Pa) and at about twice ambient CO2 concentrations, respectively, close to a natural CO2 spring, Laiatico, central Italy. The seedlings were raised for 8 months under controlled conditions at ambient and elevated [CO2] in a reciprocal experimental design and were used for the determination of biomass, photosynthesis and foliar carbohydrate concentrations, as well as the accumulation of structural biomass and lignin during leaf maturation. Under ambient [CO2], biomass and foliar carbon acquisition in control progeny were not significantly different from spring progeny. However, under elevated [CO2], spring seedlings showed less CO2 acclimation than control seedlings but no significant differences in non‐structural carbohydrate concentrations and structural biomass per unit leaf dry mass. Developmental lignin accumulation in leaves was delayed under elevated [CO2] compared with ambient [CO2], but only in control progeny. Under elevated [CO2], whole‐plant biomass, leaf area and stem diameter were significantly increased in Quercus ilex seedlings from both seed sources but with a higher stimulation of above‐ground biomass in spring than in control seedlings and a higher stimulation of below‐ground biomass in control seedlings. These results indicate that life history and/or progeny may determine the species‐specific CO2 response and suggest that positive CO2 acclimation is possible.
Cation‐induced superoxide generation in tobacco cell suspension culture is dependent on ion valence
Authors: Kawano T. , Kawano N. , Muto S. , Lapeyrie F. 
Published: March 2003

AbstractThere have been many reports suggesting the involvement of reactive oxygen species (ROS), including superoxide anion (O2.–), in salt stress. Herein, direct evidence that treatments of cell suspension culture of tobacco (Nicotiana tabacum L.; cell line, BY‐2) with various salts of trivalent, divalent and monovalent metals stimulate the immediate production of O2.– is reported. Among the salts tested, LaCl3 and GdCl3 induced the greatest responses in O2.– production, whereas CaCl2 and MgCl2 showed only moderate effects; salts of monovalent metals such as KCl and NaCl induced much lower responses, indicating that there is a strong relationship between the valence of metals and the level of O2.– production. As the valence of the added metals increased from monovalent to divalent and trivalent, the concentrations required for maximal responses were lowered. Although O2.– production by NaCl and KCl required high concentrations associated with hyperosmolarity, the O2.– generation induced by NaCl and KCl was significantly greater than that induced simply by hyperosmolarity. Since an NADPH oxidase inhibitor, diphenyleneiodonium chloride, showed a strong inhibitory effect on the trivalent and divalent cation‐induced generation of O2.–, it is likely that cation treatments activate the O2.–‐generating activity of NADPH oxidase.