bluuebunny/crossref_metadata_2025 huggingface dataset:
Effects of temperature on the establishment potential in the U.K. of the non‐native glasshouse biocontrol agent Macrolophus caliginosus
Authors: Hart Andrew J. , Tullett Andrew G. , Bale Jeffrey S. , Walters Keith F. A.
Published: March 2003

Abstract This study investigated the effect of temperature on the development and winter survival of the predatory mirid Macrolophus caliginosus Wagner, recently introduced into the U.K. as a biocontrol agent for glasshouse whitefly Trialeurodes vaporariorum. The developmental threshold for M. caliginosus calculated by three methods was between 7.3 and 8.4 °C, with a day‐degree requirement per generation varying between 472 and 524 day‐degrees. It was estimated that under outdoor conditions M. caliginosus could complete two generations per year in the U.K. All life stages of M. caliginosus had supercooling points around −20 °C, with some pre‐freeze mortality evident in both acute and chronic low temperature exposures. Acclimation increased survival of nymphal M. caliginosus from approximately 24–52 days when exposed to a constant 0 °C. Provision of prey extended survival of nymphs in the laboratory at a constant 5 °C from 39 to 64 days and in the field by c. 150 days. The results are discussed in the context of the occurrence and establishment of M. caliginosus in the U.K. and the need to develop a reliable risk assessment system for non‐native species used in glasshouse biocontrol.
Short‐term nutrient deprivation affects immune function
Authors: Siva‐Jothy Michael T. , Thompson John J. W.
Published: March 2003

Abstract Measurement of insect immune effector system function aimed at identifying costs has largely been stimulated by the ideas of Hamilton & Zuk (1982), who proposed that choosy females may derive some genetic benefit from selecting parasite‐resistant males. Field studies of such systems assume that most variation in measured immune traits is affected strongly by genes and pay little attention subsequently to the role of nutritional status in determining the magnitude of assayed immune effector systems. In this paper the effects of nutrient deprivation on immune function are measured in the mealworm beetle (Tenebrio molitor L.) reared in otherwise ideal conditions. The results suggest that immune effector system function is down‐regulated during short‐term nutritional deprivation, but is rapidly up‐regulated to pre‐deprivation levels after animals are allowed access to food. This rapid modulation of immune function in the context of nutritional status has important implications for measuring immune function in the field, as well as the interpretation of those measures.
Diurnal variation of Δ13CO2, ΔC18O16O and evaporative site enrichment of δH218O in Piper aduncum under field conditions in Trinidad
Authors: Harwood K. G. , Gillon J. S. , Griffiths H. , Broadmeadow M. S. J.
Published: March 2003

Concurrent measurements of gas exchange, instantaneous isotope discrimination (Δ) against 13CO2 and C18O16O, and extent of 18O enrichment in H2O at the evaporative sites, were followed in a tropical forest pioneer, Piper aduncum, on two different days in Trinidad during February 1995. Δ13CO2 differed from that predicted from measurements of internal:external CO2 concentration (Ci/Ca) and showed a wide range of values which decreased throughout the course of the day. Derivation of Cc (the CO2 concentration at the carboxylation site) was not possible using carbon isotope discrimination under field conditions in situ and was derived assuming a constant value of internal transfer conductance (gw). Under low rates of assimilation the derived Cc/Ca, like Ci/Ca, remained relatively stable over the course of both days and ΔC18O16O followed evaporative demand. Lower values of ΔC18O16O on day 2 occurred in response to the indirect effect of increased leaf‐to‐air vapour pressure deficits (VPD) and reduced stomatal conductance. For the first time, direct determination of the δH218O of transpired water vapour (δt) allowed derivation of evaporative site enrichment without the prerequisite of isotopic steady state (ISS) defined in the Craig and Gordon model. Generally, δt was less enriched than the source water (δs) in the morning and more enriched in the afternoon, which would be predicted from an increase and decrease in ambient VPD, respectively. On both days, leaves of P. aduncum approached ISS (indicated where δt≈δs) between 1300 and 1500 h. Evaporative site enrichment was maintained into the late afternoon, despite a decrease in ambient VPD. The data presented provide a greater insight into the natural variation in isotopic discrimination under field conditions, which may help to refine models of terrestrial biome discrimination.
The flavonoid naringenin stimulates the intercellular colonization of wheat roots by Azorhizobium caulinodans
Authors: Webster G. , Jain V. , Davey M. R. , Gough C. , Vasse J. , Dénarié J. , Cocking E. C.
Published: March 2003

We have studied intercellular colonization of wheat roots by Azorhizobium caulinodans and other diazotrophic bacteria, using strains marked with the lacZ reporter gene to facilitate their detection and identification. A. caulinodans was observed by light and electron microscopy to enter the roots of wheat at high frequency at the points of emergence of lateral roots (lateral root cracks). After lateral root crack colonization, bacteria moved into intercellular spaces within the cortical cell layer of roots. The flavonoid naringenin at 10 and 100 mmol m–3 significantly stimulated root colonization. The roles of the structural nodABC genes and the regulatory nodD gene were also studied; lateral root crack colonization of wheat was shown to be Nod factor‐ and NodD‐independent. Similar frequencies of lateral root crack colonization were observed following inoculation of wheat with Azospirillum brasilense. Colonization by A. brasilense was stimulated by naringenin and also by other flavonoid molecules.
Steady‐state nutrition and growth responses of Betula pendula to different relative supply rates of copper
Authors: Göransson
Published: March 2003

In a series of experiments on the growth and nutrition of copper‐limited birch (Betula pendula Roth) plants, growth was controlled by the relative addition rate of copper, RCu (d–1). This was 0·05, 0·10, 0·15 or 0·20 d–1 with free access to all other nutrients. An additional treatment provided free access to all nutrients. The pH in the nutrient solution was ≈ 4·5 and conductivity was 100 μS cm–1. At steady‐state growth, there was a linear relationship between the relative growth rate, RG, and RCu. The [Cu] of the plants ranged from 2·4 to 2·7 μg g–1 dry mass (DM) in all treatments with limiting RCu and was ≈ 28 μg g–1 in the free access treatment. The plants showed specific copper deficiency symptoms at limitation. Total non‐structural carbohydrate concentrations and the fraction of plant DM partitioned to roots was much less at copper limitation than at free access. The uptake rate of copper per unit root growth rate, dCu/dWr (μmol g–1 root DM) was unaffected by the copper supply. Low rates of plant growth at copper limitation were associated with high values of specific leaf area (SLA; 47 m2 kg–1) and leaf area ratio (LAR; 28 m2 kg–1 plant DM) but lower values of net assimilation rate (NAR; 2·5 kg m–2 leaf DM d–1) than were found at free access, 28 m2 kg–1 (SLA), 17 m2 kg–1 DM (LAR) and 14 kg m–2 leaf DM d–1 (NAR), respectively. It is not obvious from the present data how the growth response can help alleviate copper limitation in the field.
The stomatal response to CO2 is linked to changes in guard cell zeaxanthin*
Authors: Zhu J. , Talbott L. D. , Jin X. , Zeiger E.
Published: March 2003

The mechanisms mediating CO2 sensing and light–CO2 interactions in guard cells are unknown. In growth chamber‐grown Vicia faba leaves kept under constant light (500 μmol m–2 s–1) and temperature, guard cell zeaxanthin content tracked ambient [CO2] and stomatal apertures. Increases in [CO2] from 400 to 1200 cm3 m–3 decreased zeaxanthin content from 180 to 80 mmol mol–1 Chl and decreased stomatal apertures by 7·0 μm. Changes in zeaxanthin and aperture were reversed when [CO2] was lowered. Guard cell zeaxanthin content was linearly correlated with stomatal apertures. In the dark, the CO2‐induced changes in stomatal aperture were much smaller, and guard cell zeaxanthin content did not change with chamber [CO2]. Guard cell zeaxanthin also tracked [CO2] and stomatal aperture in illuminated stomata from epidermal peels. Dithiothreitol (DTT), an inhibitor of zeaxanthin formation, eliminated CO2‐induced zeaxanthin changes in guard cells from illuminated epidermal peels and reduced the stomatal CO2 response to the level observed in the dark. These data suggest that CO2‐dependent changes in the zeaxanthin content of guard cells could modulate CO2‐dependent changes of stomatal apertures in the light while a zeaxanthin‐independent CO2 sensing mechanism would modulate the CO2 response in the dark.
Effect of increased concentration of soil CO2 on intermittent flushes of seed germination in Echinochloa crus‐galli var. crus‐galli
Authors: Yoshioka T. , Satoh S. , Yamasue Y.
Published: March 2003

Soil‐buried seeds of barnyardgrass (Echinochloa crus‐galli var. crus‐galli) germinated from April to June in three intermittent flushes. The later two flushes of germination occurred after heavy rainfall. Carbon dioxide concentration in soil air transiently increased to 30 dm3 m–3 after the rainfall, probably due to the increase in soil temperature and water potential. Germination of exhumed seeds was stimulated by exposure to CO2 at 30 dm3 m–3. Fluctuating temperature, light, water, ethylene, and nitrate are known to promote seed germination in many species. However, of these environmental factors, within ranges found in the field, only CO2 was effective in enhancing the germination of barnyardgrass seeds. We conclude that soil CO2 is responsible for causing intermittent flushes of germination. Detection of vegetation gaps may be explained by the responsiveness of buried seeds to CO2.
Photosynthetic down‐regulation in Larrea tridentata exposed to elevated atmospheric CO2: interaction with drought under glasshouse and field (FACE) exposure
Authors: Huxman T. E. , Hamerlynck E. P. , Moore B. D. , Smith S. D. , Jordan D. N. , Zitzer S. F. , Nowak R. S. , Coleman J. S. , Seemann J. R.
Published: March 2003

The photosynthetic response of Larrea tridentata Cav., an evergreen Mojave Desert shrub, to elevated atmospheric CO2 and drought was examined to assist in the understanding of how plants from water‐limited ecosystems will respond to rising CO2. We hypothesized that photosynthetic down‐regulation would disappear during periods of water limitation, and would, therefore, likely be a seasonally transient event. To test this we measured photosynthetic, water relations and fluorescence responses during periods of increased and decreased water availability in two different treatment implementations: (1) from seedlings exposed to 360, 550, and 700 μmol mol–1 CO2 in a glasshouse; and (2) from intact adults exposed to 360 and 550 μmol mol–1 CO2 at the Nevada Desert FACE (Free Air CO2 Enrichment) Facility. FACE and glasshouse well‐watered Larrea significantly down‐regulated photosynthesis at elevated CO2, reducing maximum photosynthetic rate (Amax), carboxylation efficiency (CE), and Rubisco catalytic sites, whereas droughted Larrea showed a differing response depending on treatment technique. Amax and CE were lower in droughted Larrea compared with well‐watered plants, and CO2 had no effect on these reduced photosynthetic parameters. However, Rubisco catalytic sites decreased in droughted Larrea at elevated CO2. Operating Ci increased at elevated CO2 in droughted plants, resulting in greater photosynthetic rates at elevated CO2 as compared with ambient CO2. In well‐watered plants, the changes in operating Ci, CE and Amax resulted in similar photosynthetic rates across CO2 treatments. Our results suggest that drought can diminish photosynthetic down‐regulation to elevated CO2 in Larrea, resulting in seasonally transient patterns of enhanced carbon gain. These results suggest that water status may ultimately control the photosynthetic response of desert systems to rising CO2.
Regulation of growth: the meristem network approach
Authors: AMZALLAG G. N.
Published: March 2003

Gibberellin (GA) and/or cytokinin (CK) supplied to the root medium modified the rate of growth of the shoot, the adventitious and seminal roots in young seedlings of Sorghum bicolor (L.) Moench. For each population submitted to a hormonal treatment, the link between the weight of these three organs was analysed. All these links build a network of relationships, also termed a meristem network. Treatments with 1–100 μM CK modified the relative growth of these three organs, as well as the meristem network. Treatments with 1–100 μM GA slightly modified the growth, but the meristem network was considerably changed. When GA and CK were applied simultaneously, the growth was similar to that of CK‐treated plants, and the meristem network was similar to that of GA‐treated plants. Similar experiments were performed on plants exposed to 150 mM NaCl. They showed that both growth and meristem networks are modified by salinity. Growth was unrelated to the network variations in non‐salinized plants, while an optimal level of relationship for growth was observed in salinized plants. It is concluded that stress generates an imbalance between the self‐stimulation of meristem activity and its regulation by the other organs. A definition of stress, independent from the rate of growth, is proposed.
Changes in leaf nitrogen and carbohydrates underlie temperature and CO2 acclimation of dark respiration in five boreal tree species
Authors: Tjoelker M. G. , Reich P. B. , Oleksyn J.
Published: March 2003

We tested the hypothesis that acclimation of foliar dark respiration to CO2 concentration and temperature is associated with adjustments in leaf structure and chemistry. Populus tremuloides Michx., Betula papyrifera Marsh., Larix laricina (Du Roi) K. Koch, Pinus banksiana Lamb., and Picea mariana (Mill.) B.S.P. were grown from seed in combined CO2 (370 or 580 μmol mol–1) and temperature treatments (18/12, 24/18, or 30/24 °C). Temperature and CO2 effects were predominately independent. Specific respiration rates partially acclimated to warmer thermal environments through downward adjustment in the intercept, but not Q10 of the temperature–response functions. Temperature acclimation of respiration was larger for conifers than broad‐leaved species and was associated with pronounced reductions in leaf nitrogen concentrations in conifers at higher growth temperatures. Short‐term increases in CO2 concentration did not inhibit respiration. Growth in the elevated CO2 concentration reduced leaf nitrogen and increased non‐structural carbohydrate concentrations. However, for a given nitrogen concentration, respiration was higher in leaves grown in the elevated CO2 concentration, as rates increased with increasing carbohydrates. Across species and treatments, respiration rates were a function of both leaf nitrogen and carbohydrate concentrations (R2 = 0·71, P < 0·0001). Long‐term acclimation of foliar dark respiration to temperature and CO2 concentration is largely associated with changes in nitrogen and carbohydrate concentrations.
The carbon balance of tropical, temperate and boreal forests
Authors: MALHI Y. , BALDOCCHI D. D. , JARVIS P. G.
Published: March 2003

Forest biomes are major reserves for terrestrial carbon, and major components of global primary productivity. The carbon balance of forests is determined by a number of component processes of carbon acquisition and carbon loss, and a small shift in the magnitude of these processes would have a large impact on the global carbon cycle. In this paper, we discuss the climatic influences on the carbon dynamics of boreal, temperate and tropical forests by presenting a new synthesis of micrometeorological, ecophysiological and forestry data, concentrating on three case‐study sites. Historical changes in the carbon balance of each biome are also reviewed, and the evidence for a carbon sink in each forest biome and its likely behaviour under future global change are discussed. We conclude that there have been significant advances in determining the carbon balance of forests, but there are still critical uncertainties remaining, particularly in the behaviour of soil carbon stocks.
The nitrate and ammonium nitrate supply have a major influence on the response of photosynthesis, carbon metabolism, nitrogen metabolism and growth to elevated carbon dioxide in tobacco
Authors: Geiger M. , Haake V. , Ludewig F. , Sonnewald U. , Stitt M.
Published: March 2003

The effect of elevated [CO2] on biomass, nitrate, ammonium, amino acids, protein, nitrate reductase activity, carbohydrates, photosynthesis, the activities of Rubisco and six other Calvin cycle enzymes, and transcripts for Rubisco small subunit, Rubisco activase, chlorophyll a binding protein, NADP‐glyceraldehyde‐3‐phosphate dehydrogenase, aldolase, transketolase, plastid fructose‐1,6‐bisphosphatase and ADP‐glucose pyrophosphorylase was investigated in tobacco growing on 2, 6 and 20 m
M nitrate and 1, 3 and 10 m
M ammonium nitate. (i) The growth stimulation in elevated [CO2] was attenuated in intermediate and abolished in low nitrogen. (ii) Elevated [CO2] led to a decline of nitrate, ammonium, amino acids especially glutamine, and protein in low nitrogen and a dramatic decrease in intermediate nitrogen, but not in high nitrogen. (iii) Elevated [CO2] led to a decrease of nitrate reductase activity in low, intermediate and high ammonium nitrate and in intermediate nitrate, but not in high nitrate. (iii) At low nitrogen, starch increased relative to sugars. Elevated [CO2] exaggerated this shift. ADP‐glucose pyrophosphorylase transcript increased in low nitrogen, and in elevated [CO2]. (iv) In high nitrogen, sugars rose in elevated [CO2], but there was no acclimation of photosynthetic rate, only a small decrease of Rubisco and no decrease of other Calvin cycle enzymes, and no decrease of the corresponding transcripts. In lower nitrogen, there was a marked acclimation of photosynthetic rate and a general decrease of Calvin cycle enzymes, even though sugar levels did not increase. The decreased activities were due to a general decrease of leaf protein. The corresponding transcripts did not decrease except at very low nitrogen. (v) It is concluded that many of the effects of elevated [CO2] on nitrate metabolism, photosynthate allocation, photosynthetic acclimation and growth are due to a shift in nitrogen status.
Chloroplast movements in fern leaves: correlation of movement dynamics and environmental flexibility of the species
Authors: Augustynowicz J , Gabry`s H.
Published: March 2003

The movements of chloroplasts in response to varying levels and wavelengths of incident light were investigated in leaves of four fern species: Adiantum capillus‐veneris, Adiantum caudatum, Adiantum diaphanum and Pteris cretica. In all of the species studied blue light induced chloroplast redistribution resulting in face and profile patterns that were typical of low and high fluence rates, respectively. Fluence rate response characteristics and the kinetics of transmission changes accompanying these blue‐light‐induced movements were similar to those observed in the leaves of higher plants. Only in A. capillus‐veneris was the distribution of chloroplasts affected by red light. The response was of the weak‐light type, irrespective of the light intensity. The most effective fluence rate for red light was found to be below 7·2 μmol m–2 s–1 (1 W m–2). The effect of red light was far‐red reversible, indicating phytochrome involvement. Chloroplast responses were more dynamic in A. capillus‐veneris and P. cretica, the two species that exhibited higher environmental flexibility.
Expression of a cassava granule‐bound starch synthase gene in the amylose‐free potato only partially restores amylose content
Authors: Salehuzzaman Shah N. I. M. , Vincken Jean‐Paul , De Wal Marion Van , Jacobsen Evert , Visser Richard G. F.
Published: March 2003

Granule‐bound starch synthase I (GBSS I) is responsible for the synthesis of amylose in starch granules. A heterologous cassava GBSS I gene was tested for its ability to restore amylose synthesis in amylose‐free (amf) potato mutants. For this purpose, the cassava GBSS I was equipped with different transit peptides. In addition, a hybrid containing the potato transit peptide, the N‐terminal 89 amino acids of the mature potato GBSS I, and the C‐terminal part of cassava GBSS I was prepared. The transgenic starches were first analysed by iodine staining. Only with the hybrid could full phenotypic complementation of the amf mutation be achieved in 13% of the plants. Most transformants showed partial complementation, but interestingly the size of the blue core was similar in all granules derived from one tuber of a given plant. The amylose content was only partially restored, up to 60% of wild‐type values or potato GBSS I‐complemented plants; however, the GBSS activity in these granules was similar to that found in wild‐type ones. From this, and the observation that the hybrid protein (a partial potato GBSS I look‐alike) performs best, it was concluded that potato and cassava GBSS I have different intrinsic properties and that the cassava enzyme is not fully adapted to the potato situation.
Shape of leaf photosynthetic electron transport versus temperature response curve is not constant along canopy light gradients in temperate deciduous trees
Authors: Niinemets Ü. , Oja V. , Kull O.
Published: March 2003

Responses of foliar light‐saturated net assimilation rate (Amax), capacity for photosynthetic electron transport (Jmax) and mitochondrial respiration rate (Rd) to long‐term canopy light and temperature environment were investigated in a temperate deciduous canopy composed of Populus tremula L. in the upper (17–28 m) and of Tilia cordata Mill. in the lower canopy layer (4–17 m). Climatic measurements indicated that seasonal average daily maximum air temperature (Tmax) was 5·5 °C (range 0·7–10·5 °C) higher in the top than in the bottom of the canopy, and strong positive correlations were observed between Tmax and seasonal average integrated quantum flux density (Qint), as well as between seasonal average daily mean temperature and Qint. Because of changes in leaf dry mass and nitrogen per unit area, Amax, Jmax, and Rd scaled positively with Qint in both species at a common leaf temperature (T). According to Jmax versus T response curves and dark chlorophyll fluorescence transients, photosynthetic electron transport was less heat resistant in P. tremula with optimum temperature of Jmax, Topt, of 33·5 ± 0·6 °C than in T. cordata with Topt of 40·7 ± 0·6 °C. This difference was suggested to manifest evolutionary adaptation of photosynthetic electron transport to cooler environments in P. tremula, the range of which extends farther north than that in T. cordata. Possibly because of acclimation to long‐term canopy temperature environment, Topt was positively related to Qint in P. tremula, foliage of which was also exposed to higher irradiances and temperatures, but not in T. cordata, in the canopy of which quantum flux densities and temperatures were lower, and gradients in the environmental factors less pronounced. Parallel to changes in Topt, the activation energy for photosynthetic electron transport decreased with increasing Qint in P. tremula, indicating that Jmax of leaves acclimated to colder environment was more responsive to T in lower temperatures than that of high T acclimated leaves. Similar alterations in the activation energy for mitochondrial respiration rate were also observed, indicating that acclimation to temperature of mitochondrial and chloroplastic electron transport proceeds in a co‐ordinated manner, and possibly involves long‐term changes in membrane fluidity properties. We conclude that, because of correlations between temperature and light, the shapes of Jmax versus T, and Rd versus T response curves vary within tree canopies, and this needs to be taken account in modelling whole canopy photosynthesis.
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

The 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

The 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

Stomatal 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

Variation 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

Chilling 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

Crassulacean 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

The 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

Plant 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

Miniaturized 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

Leaf 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

The 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

A 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

An 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

There 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.