bluuebunny/crossref_metadata_2025_split huggingface dataset:
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

ABSTRACTField 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

ABSTRACTLeaves 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

ABSTRACTA 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

ABSTRACTIn 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

ABSTRACTThe 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

ABSTRACTA 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

ABSTRACTIncreased 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

ABSTRACTChlorophyll 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

ABSTRACTThe 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

ABSTRACTStudies 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

ABSTRACTThe 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

ABSTRACTSpatial 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

ABSTRACTA 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.