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Examines the temperature dependence of the photosynthetic stimulation of ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) by elevated carbon dioxide in wheat and barley. Kinetic characteristics of the Rubisco enzyme; Response of the global vegetation to the increasing concentration of carbon dioxide in the atmosphere; Reasons for the low relative stimulation of photosynthesis at high photon flux.

Introduction: Patients undergoing emergency abdominal surgery for inflammatory bowel disease (IBD) are a complex cohort who are relatively poorly represented in published literature. This is partly due to the lack of consensus of the definition of the term emergency in IBD surgery. There is ongoing and recent work defining clinical urgency for unplanned surgical procedures and categorizing the high-risk surgical patient. This paper aims to report the difference in patient metrics and risks as recorded by the National Emergency Laparotomy Audit (NELA)., Methods: Complete patient data, including histology, were available in the NELA database between 2013 and 2016. Urgency categories recorded by NELA are <2 h, 2-6 h, 6-18 h, and >18 h. Patient characteristics, physiology, biochemistry, and outcomes are reported according to these urgency categories with regression analysis used to compare differences between them., Results: Mortality in Crohn's disease (CD) ranged from 1.4% in the >18 h urgency to 14.6% in the most urgent. In ulcerative colitis (UC), this range was from 3.1% to 14.8%. In both CD and UC, there were significant trends in hemodynamic instability, serum white cell count, serum electrolytes and creatinine, and outcome measures length of stay and unplanned return to theater., Conclusions: Patients having emergency surgery for IBD are not a single cohort when considering physiology, blood biochemistry, or most importantly, outcomes. Risk counseling and management should reflect this. Hemodynamic changes are subtle and may be missed in this cohort., (© 2024 The Author(s). World Journal of Surgery published by John Wiley & Sons Ltd on behalf of International Society of Surgery/Société Internationale de Chirurgie (ISS/SIC).)

Aim: The medical management of inflammatory bowel disease (IBD) is rapidly progressing; however, many patients with the disease still require surgery. Often this is done as an emergency. Initiatives such as the National Emergency Laparotomy Audit have shown how evidence-based emergency surgery improves outcomes for the patient. The aim of this scoping review is to describe the current evidence base on risk stratification in emergency abdominal surgery for IBD., Methods: A literature search, abstract and full paper screening resulted in 17 articles representing 63 472 patients from seven countries., Results: It is likely that age, the American Society of Anesthesiologists grade, comorbidity and organ dysfunction play a similar role in risk stratification in IBD patients as in other emergency abdominal surgery cohorts. However, the reporting of what is considered an IBD emergency is variable. Six studies include clear definitions of emergency in our study. The range of what is considered an emergency is within 12 h of admission to any time within an unplanned admission., Conclusion: To have data driven, evidence-based emergency surgical practice in IBD we need consistency of reporting, including the definitions of emergency and urgency. Core descriptor sets in IBD would be valuable., (© 2023 The Authors. Colorectal Disease published by John Wiley & Sons Ltd on behalf of Association of Coloproctology of Great Britain and Ireland.)

Introduction: Emergency laparotomy may be required in patients with inflammatory bowel disease (IBD). NELA is the largest prospectively maintained database of adult emergency laparotomies in England and Wales and includes clinical urgency of the cases. The impact of surgeon subspeciality on outcomes after emergency laparotomy for IBD is unclear. We have investigated this association, according to the degree of urgency in IBD emergency laparotomy, including the effect of minimally invasive surgery (MIS)., Methods: Adults with IBD in the NELA database between 2013 and 2016 were included. Surgeon subspeciality was colorectal or non-colorectal. Urgencies are 'Immediate', '2-6 h', '6-18 h' and '18-24 h'. Logistic regression was used to investigate in-patient mortality and post-operative length of stay (LOS)., Results: There was significantly reduced mortality and LOS in IBD patients who were operated on by a colorectal surgeon in the least urgent category of emergency laparotomies; Mortality adjusted OR 2.99 (CI 1.2-7.8) P = 0.025, LOS IRR 1.18 (CI 1.02-1.4) P = 0.025. This association was not seen in more urgent categories. Colorectal surgeons were more likely to use MIS, P < 0.001, and MIS was associated with decreased LOS in the least urgent cohort, P < 0.001, but not in the other urgencies., Conclusions: We found improved outcomes in the least urgent cohort of IBD emergency laparotomies when operated on by a colorectal surgeon in comparison to a non-colorectal general surgeon. In the most urgent cases, there was no benefit in the operation being performed by a colorectal surgeon. Further work on characterising IBD emergencies by urgency would be of value., (© 2023. The Author(s).)

Short-term responses of plant dark respiration to carbon dioxide concentration ([CO 2 ]) in the range anticipated in the atmosphere with global change remain controversial, primarily because it is difficult to convincingly eliminate the many possible sources of experimental error in measurements of carbon dioxide or oxygen exchange rates. Plant dark respiration is a major component of the carbon balance of many ecosystems. In seedlings without senescent tissue, the rate of loss of dry mass during darkness indicates the rate of respiration. This method of measuring respiration was used to test for [CO 2 ] effects on respiration in seedlings of three species with relatively large seeds. The time it took respiration to exhaust substrates and cause seedling death in darkness was used as an indicator of respiration rate in four other species with smaller seeds. The third method was measuring rates of CO 2 exchange in excised petioles sealed in a cuvette submerged in water to prevent leaks. Petioles were utilized as the plant tissue type with the most reliable rates of respiration, for excised tissue. The rate of loss of dry mass in the dark decreased with increasing [CO 2 ] in the range of 200-800 μmol mol -1 in all three large-seeded species. The seedling survival time in the dark increased with [CO 2 ] in the same concentration range in all four of the smaller-seeded species. Respiration rates of excised petioles of several species also decreased over this [CO 2 ] range. The data provide new evidence that the rate of dark respiration in plant tissue often decreases with increasing [CO 2 ] in the 200-800 μmol mol -1 range., (Published by Oxford University Press on behalf of the Annals of Botany Company 2021.)

The intensifying pace of research based on cross-cultural studies in the social sciences necessitates a discussion of the unique challenges of multi-sited research. Given an increasing demand for social scientists to expand their data collection beyond WEIRD (Western, educated, industrialized, rich and democratic) populations, there is an urgent need for transdisciplinary conversations on the logistical, scientific and ethical considerations inherent to this type of scholarship. As a group of social scientists engaged in cross-cultural research in psychology and anthropology, we hope to guide prospective cross-cultural researchers through some of the complex scientific and ethical challenges involved in such work: (a) study site selection, (b) community involvement and (c) culturally appropriate research methods. We aim to shed light on some of the difficult ethical quandaries of this type of research. Our recommendation emphasizes a community-centred approach, in which the desires of the community regarding research approach and methodology, community involvement, results communication and distribution, and data sharing are held in the highest regard by the researchers. We argue that such considerations are central to scientific rigour and the foundation of the study of human behaviour.

Interaction between members of culturally distinct (ethnic) groups is an important driver of the evolutionary dynamics of human culture, yet relevant mechanisms remain underexplored. For example, cultural loss resulting from integration with culturally distinct immigrants or colonial majority populations remains a topic whose political salience exceeds our understanding of mechanisms that may drive or impede it. For such dynamics, one mediating factor is the ability to interact successfully across cultural boundaries (cross-cultural competence). However, measurement difficulties often hinder its investigation. Here, simple field methods in a uniquely suited Amazonian population and Bayesian item-response theory models are used to derive the first experience-level measure of cross-cultural competence, as well as evidence for two developmental paths: cross-cultural competence may emerge as a side effect of adopting out-group cultural norms, or it may be acquired while maintaining in-group norms. Ethnographic evidence suggests that the path taken is a likely consequence of power differences in inter- vs intra-group interaction. The former path, paralleling language extinction, may lead to cultural loss; the latter to cultural sustainability. Recognition of such path-dependent effects is vital to theory of cultural dynamics in humans and perhaps other species, and to effective policy promoting cultural diversity and constructive inter-ethnic interaction., Competing Interests: J.A.B. declares no conflict of interest., (© The Author(s) 2020.)

Plants would experience more complex environments, such as sudden heat shock (SHS) stress combined with elevated CO 2 in the future, and might adapt to this stressful condition by optimizing photosynthetic carbon metabolism (PCM). It is interesting to understand whether this acclimation process would be altered in different genotypes of maize under elevated CO 2 , and which metabolites represent key indicators reflecting the photosynthetic rates (P N ) following SHS. Although B76 had greater reduction in P N during SHS treatment, our results indicated that P N in genotype B76, displayed faster recovery after SHS treatment under elevated CO 2 than in genotype B106. Furthermore, we employed a stepwise feature extraction approach by partial linear regression model. Our findings demonstrated that 9 key metabolites over the total (35 metabolites) can largely explain the variance of P N during recovery from SHS across two maize genotypes and two CO 2 grown conditions. Of these key metabolites, malate, valine, isoleucine, glucose and starch are positively correlated with recovery pattern of P N . Malate metabolites responses to SHS were further discussed by incorporating with the activities and gene expression of three C 4 photosynthesis-related key enzymes. We highlighted the importance of malate metabolism during photosynthesis recovery from short-term SHS, and data integration analysis to better comprehend the regulatory framework of PCM in response to abiotic stress.

Detached leaves at top canopy structures always experience higher solar irradiance and leaf temperature under natural conditions. The ability of tolerance to high temperature represents thermotolerance potential of whole-plants, but was less of concern. In this study, we used a heat-tolerant (B76) and a heat-susceptible (B106) maize inbred line to assess the possible mitigation of sudden heat shock (SHS) effects on photosynthesis (PN) and C4 assimilation pathway by elevated [CO2]. Two maize lines were grown in field-based open top chambers (OTCs) at ambient and elevated (+180 ppm) [CO2]. Top-expanded leaves for 30 days after emergence were suddenly exposed to a 45°C SHS for 2 hours in midday during measurements. Analysis on thermostability of cellular membrane showed there was 20% greater electrolyte leakage in response to the SHS in B106 compared to B76, in agreement with prior studies. Elevated [CO2] protected PN from SHS in B76 but not B106. The responses of PN to SHS among the two lines and grown CO2 treatments were closely correlated with measured decreases of NADP-ME enzyme activity and also to its reduced transcript abundance. The SHS treatments induced starch depletion, the accumulation of hexoses and also disrupted the TCA cycle as well as the C4 assimilation pathway in the both lines. Elevated [CO2] reversed SHS effects on citrate and related TCA cycle metabolites in B106 but the effects of elevated [CO2] were small in B76. These findings suggested that heat stress tolerance is a complex trait, and it is difficult to identify biochemical, physiological or molecular markers that accurately and consistently predict heat stress tolerance.

Ethnic groups are universal and unique to human societies. Such groups sometimes have norms of behavior that are adaptively linked to their social and ecological circumstances, and ethnic boundaries may function to protect that variation from erosion by interethnic interaction. However, such interaction is often frequent and voluntary, suggesting that individuals may be able to strategically reduce its costs, allowing adaptive cultural variation to persist in spite of interaction with out-groups with different norms. We examine five mechanisms influencing the dynamics of ethnically distinct cultural norms, each focused on strategic individual-level choices in interethnic interaction: bargaining, interaction-frequency-biased norm adoption, assortment on norms, success-biased interethnic social learning, and childhood socialization. We use Bayesian item response models to analyze patterns of norm variation and interethnic interaction in an ethnically structured Amazonian population. We show that, among indigenous Matsigenka, interethnic education with colonial Mestizos is more strongly associated with Mestizo-typical norms than even extensive interethnic experience in commerce and wage labor is. Using ethnographic observations, we show that all five of the proposed mechanisms of norm adoption may contribute to this effect. However, of these mechanisms, we argue that changes in relative bargaining power are particularly important for ethnic minorities wishing to preserve distinctive norms while engaging in interethnic interaction in domains such as education. If this mechanism proves applicable in a range of other ethnographic contexts, it would constitute one cogent explanation for when and why ethnically structured cultural variation can either persist or erode given frequent, and often mutually beneficial, interethnic interaction.

Intraspecific variation in crop responses to global climate change conditions would provide opportunities to adapt crops to future climates. These experiments explored intraspecific variation in response to elevated CO₂ and to high temperature during anthesis in Chenopodium quinoa Wild. Three cultivars of quinoa were grown to maturity at 400 ("ambient") and 600 ("elevated") μmol·mol -1 CO₂ concentrations at 20/14 °C day/night ("control") temperatures, with or without exposure to day/night temperatures of 35/29 °C ("high" temperatures) for seven days during anthesis. At control temperatures, the elevated CO₂ concentration increased the total aboveground dry mass at maturity similarly in all cultivars, but by only about 10%. A large down-regulation of photosynthesis at elevated CO₂ occurred during grain filling. In contrast to shoot mass, the increase in seed dry mass at elevated CO₂ ranged from 12% to 44% among cultivars at the control temperature. At ambient CO₂, the week-long high temperature treatment greatly decreased (0.30 × control) or increased (1.70 × control) seed yield, depending on the cultivar. At elevated CO₂, the high temperature treatment increased seed yield moderately in all cultivars. These quinoa cultivars had a wide range of responses to both elevated CO₂ and to high temperatures during anthesis, and much more variation in harvest index responses to elevated CO₂ than other crops that have been examined., Competing Interests: The author declares no conflict of interest.

High CO2 and high temperature have an antagonistic interaction effect on rice yield potential and present a unique challenge to adapting rice to projected future climates. Understanding how the differences in response to these two abiotic variables are partitioned across rice germplasm accessions may be key to identifying potentially useful sources of resilient alleles for adapting rice to climate change. In this study, we evaluated eleven globally diverse rice accessions under controlled conditions at two carbon dioxide concentrations (400 and 600 ppm) and four temperature environments (29 °C day/21 °C night; 29 °C day/21 °C night with additional heat stress at anthesis; 34 °C day/26 °C night; and 34 °C day/26 °C night with additional heat stress at anthesis) for a suite of traits including five yield components, five growth characteristics, one phenological trait, and four photosynthesis-related measurements. Multivariate analyses of mean trait data from these eight treatments divide our rice panel into two primary groups consistent with the genetic classification of INDICA/INDICA-like and JAPONICA populations. Overall, we find that the productivity of plants grown under elevated [CO2 ] was more sensitive (negative response) to high temperature stress compared with that of plants grown under ambient [CO2 ] across this diversity panel. We report differential response to CO2 × temperature interaction for INDICA/INDICA-like and JAPONICA rice accessions and find preliminary evidence for the beneficial introduction of exotic alleles into cultivated rice genomic background. Overall, these results support the idea of using wild or currently unadapted gene pools in rice to enhance breeding efforts to secure future climate change adaptation., (Published 2016. This article is a US Government work and is in the public domain in the USA.)

The X-linked gene polymorphism responsible for the variable color vision of most Neotropical monkeys and some lemurs is thought to be maintained by balancing selection, such that trichromats have an advantage over dichromats for some ecologically important task(s). However, evidence for such an advantage in wild primate populations is equivocal. The purpose of this study is to refine a hypothesis for a trichromat advantage by tailoring it to the ecology of territorial primates with female natal dispersal, such that dispersing trichromatic females have a foraging and, by extension, survival advantage over dichromats. I then examine the most practical way to test this hypothesis using field data. Indirect evidence in support of the hypothesis may take the form of differences in genotype frequencies among life stages and differences in disperser food item encounter rates. A deterministic evolutionary matrix population model and a stochastic model of food patch encounter rates are constructed to investigate the magnitude of such differences and the likelihood of statistical detection using field data. Results suggest that, although the sampling effort required to detect the hypothesized genotype frequency differences is impractical, a field study of reasonable scope may be able to detect differences in disperser foraging rates. This study demonstrates the utility of incorporating socioecological details into formal hypotheses during the planning stages of field studies of primate color vision., (© 2015 Wiley Periodicals, Inc.)

It has been suggested that the stimulation of soybean photosynthesis by elevated CO2 was less in free-air carbon dioxide enrichment (FACE) systems than in open top chambers (OTC), which might explain smaller yield increases at elevated CO2 in FACE systems. However, this has not been tested using the same cultivars grown in the same location. I tested whether soybean photosynthesis at high light and elevated CO2 (ambient+180 μmol mol(-1)) was limited by electron transport (J) in FACE systems but by ribulose-bisphosphate carboxylation capacity (VCmax) in OTC. FACE systems with daytime and continuous CO2 enrichment were also compared. The results indicated that in both cultivars examined, midday photosynthesis at high light was always limited by VCmax, both in the FACE and in the OTC systems. Daytime only CO2 enrichment did not affect photosynthetic parameters or limitations, but did result in significantly smaller yields in both cultivars than continuous elevation. Photosynthesis measured at low photosynthetic photon flux density (PPFD) was not higher at elevated than at ambient CO2, because of an acclimation to elevated CO2 which was only evident at low measurement PPFDs., (Published by Elsevier Ireland Ltd.)

Systems for exposing plants to elevated concentrations of CO₂ may expose plants to pulses of CO₂ concentrations considerably above the control set point. The importance of such pulses to plant function is unknown. Single leaves of wheat (Triticum aestivum cv Choptank) and rice (Oryza sativa cv Akitakomachi) were exposed for 30 minutes to pulses of elevated CO₂ similar to the frequency, duration and magnitude of pulses observed in free-air CO₂ enrichment systems. Stomatal conductance decreased within a few minutes of exposure to once per minute pulses of high CO₂ of all the durations tested, in both species. Both species had 20-35% lower stomatal conductance for at least 30 min after the termination of the pulses. After the pulses had stopped, in all cases photosynthesis was below the values expected for the observed substomatal CO₂ concentration, which suggests that either patchy stomatal closure occurred or that photosynthesis was directly inhibited. It was also found that a single, 2 s pulse of elevated CO₂ concentration reaching a maximum of 1000 µmol mol⁻¹ decreased stomatal conductance in both species. On the basis of these results, it is probable that plants in many CO₂ enrichment systems have lower photosynthesis and stomatal conductance than would plants exposed to the same mean CO₂ concentration but without pulses of higher concentration., (© 2013 Scandinavian Plant Physiology Society.)

Nutrients such as phosphorus may exert a major control over plant response to rising atmospheric carbon dioxide concentration (CO2), which is projected to double by the end of the 21st century. Elevated CO2 may overcome the diffusional limitations to photosynthesis posed by stomata and mesophyll and alter the photo-biochemical limitations resulting from phosphorus deficiency. To evaluate these ideas, cotton (Gossypium hirsutum) was grown in controlled environment growth chambers with three levels of phosphate (Pi) supply (0.2, 0.05 and 0.01mM) and two levels of CO2 concentration (ambient 400 and elevated 800μmolmol(-1)) under optimum temperature and irrigation. Phosphate deficiency drastically inhibited photosynthetic characteristics and decreased cotton growth for both CO2 treatments. Under Pi stress, an apparent limitation to the photosynthetic potential was evident by CO2 diffusion through stomata and mesophyll, impairment of photosystem functioning and inhibition of biochemical process including the carboxylation efficiency of ribulose-1,5-bisphosphate carboxylase/oxyganase and the rate of ribulose-1,5-bisphosphate regeneration. The diffusional limitation posed by mesophyll was up to 58% greater than the limitation due to stomatal conductance (gs) under Pi stress. As expected, elevated CO2 reduced these diffusional limitations to photosynthesis across Pi levels; however, it failed to reduce the photo-biochemical limitations to photosynthesis in phosphorus deficient plants. Acclimation/down regulation of photosynthetic capacity was evident under elevated CO2 across Pi treatments. Despite a decrease in phosphorus, nitrogen and chlorophyll concentrations in leaf tissue and reduced stomatal conductance at elevated CO2, the rate of photosynthesis per unit leaf area when measured at the growth CO2 concentration tended to be higher for all except the lowest Pi treatment. Nevertheless, plant biomass increased at elevated CO2 across Pi nutrition with taller plants, increased leaf number and larger leaf area., (Copyright © 2013 Elsevier GmbH. All rights reserved.)

Agricultural production is under increasing pressure by global anthropogenic changes, including rising population, diversion of cereals to biofuels, increased protein demands and climatic extremes. Because of the immediate and dynamic nature of these changes, adaptation measures are urgently needed to ensure both the stability and continued increase of the global food supply. Although potential adaption options often consider regional or sectoral variations of existing risk management (e.g. earlier planting dates, choice of crop), there may be a global-centric strategy for increasing productivity. In spite of the recognition that atmospheric carbon dioxide (CO(2)) is an essential plant resource that has increased globally by approximately 25 per cent since 1959, efforts to increase the biological conversion of atmospheric CO(2) to stimulate seed yield through crop selection is not generally recognized as an effective adaptation measure. In this review, we challenge that viewpoint through an assessment of existing studies on CO(2) and intraspecific variability to illustrate the potential biological basis for differential plant response among crop lines and demonstrate that while technical hurdles remain, active selection and breeding for CO(2) responsiveness among cereal varieties may provide one of the simplest and direct strategies for increasing global yields and maintaining food security with anthropogenic change.

The color vision of most platyrrhine primates is determined by alleles at the polymorphic X-linked locus coding for the opsin responsible for the middle- to long-wavelength (M/L) cone photopigment. Females who are heterozygous at the locus have trichromatic vision, whereas homozygous females and all males are dichromatic. This study characterized the opsin alleles in a wild population of the socially monogamous platyrrhine monkey Callicebus brunneus (the brown titi monkey), a primate that an earlier study suggests may possess an unusual number of alleles at this locus and thus may be a subject of special interest in the study of primate color vision. Direct sequencing of regions of the M/L opsin gene using feces-, blood-, and saliva-derived DNA obtained from 14 individuals yielded evidence for the presence of three functionally distinct alleles, corresponding to the most common M/L photopigment variants inferred from a physiological study of cone spectral sensitivity in captive Callicebus., (© 2010 Wiley-Liss, Inc.)

Methods of estimating the mesophyll conductance (g(m)) to the movement of CO(2) from the substomatal airspace to the site of fixation are expensive or rely upon numerous assumptions. It is proposed that, for C(3) species, measurement of the response of photosynthesis to [O(2)] at limiting [CO(2)], combined with a standard biochemical model of photosynthesis, can provide an estimate of g(m). This method was used to determine whether g(m) changed with [CO(2)] and with water stress in soybean leaves. The value of g(m) estimated using the O(2) response method agreed with values obtained using other methods. The g(m) was unchanged over the tested range of substomatal [CO(2)]. Water stress, which decreased stomatal conductance (g(s)) by about 80%, did not affect g(m), while the model parameter V(Cmax) was reduced by about 25%. Leaves with g(s) reduced by about 90% had g(m) values reduced by about 50%, while V(Cmax) was reduced by about 64%. It is concluded that g(m) in C(3) species can be conveniently estimated using the response of photosynthesis to [O(2)] at limiting [CO(2)], and that g(m) in soybean was much less sensitive to water stress than g(s), and was somewhat less sensitive to water stress than V(Cmax).

To examine the impact of projected climate changes on secondary succession, we exposed the same fallow soil with a common seed bank to an in situ gradient of urban to rural macroenvironments that differed in temperature and CO2 concentration ([CO2]). This gradient was established at three locations: Baltimore city center (urban), a city park on the outskirts of Baltimore (suburban), and an organic farm 87 km from the Baltimore city center site (rural). Over a five-year period, the urban site averaged 2.1 degrees C warmer and had a [CO2] that was ~20% higher than at the rural location, indicating that this gradient was a reasonable surrogate for projected changes in those variables for this century. Previous work had demonstrated that other abiotic variables measured across the transect, including tropospheric ozone and nitrogen deposition, did not differ consistently. The first year of exposure resulted in (two- to threefold) greater aboveground biomass in the urban relative to the rural site, but with uniform species composition across sites. Simple regression of abiotic variables indicated that temperature and vapor pressure deficit (VPD) were the best predictors of plant biomass among locations. Stepwise multiple regressions were also performed to analyze the effect of more than one macroenvironmental variable on total plant biomass. The combination of daily CO2 concentration and nighttime temperature explained 87% (P < 0.01) of the variability in total biomass between sites. After five years, the species demography of the plant communities had changed significantly, with a greater ratio of perennials to annuals for the urban relative to the rural location. Greater first-year biomass and litter accumulation at the urban site may have suppressed the subsequent seed germination of annual species, accelerating changes in species composition. If urban macroenvironments reflect future global change conditions, these data suggest a faster rate of secondary succession in a warmer, higher [CO2] world.

Background and Aims: Nitrogen (N) is a major factor affecting yield gain of crops under elevated atmospheric carbon dioxide concentrations [CO(2)]. It is well established that elevated [CO(2)] increases root mass, but there are inconsistent reports on the effects on N uptake capacity per root mass. In the present study, it was hypothesized that the responses of N uptake capacity would change with the duration of exposure to elevated [CO(2)]., Methods: The hypothesis was tested by measuring N uptake capacity in rice plants exposed to long-term and short-term [CO(2)] treatments at different growth stages in plants grown under non-limiting N conditions in hydroponic culture. Seasonal changes in photosynthesis rate and transpiration rate were also measured., Key Results: In the long-term [CO(2)] study, leaf photosynthetic responses to intercellular CO(2) concentration (Ci) were not affected by elevated [CO(2)] before the heading stage, but the initial slope in this response was decreased by elevated [CO(2)] at the grain-filling stage. Nitrate and ammonium uptake capacities per root dry weight were not affected by elevated [CO(2)] at panicle initiation, but thereafter they were reduced by elevated [CO(2)] by 31-41 % at the full heading and mid-ripening growth stages. In the short-term study (24 h exposures), elevated [CO(2)] enhanced nitrate and ammonium uptake capacities at the early vegetative growth stage, but elevated [CO(2)] decreased the uptake capacities at the mid-reproductive stage., Conclusions: This study showed that N uptake capacity was downregulated under long-term exposure to elevated [CO(2)] and its response to elevated [CO(2)] varied greatly with growth stage.

Plant growth, photosynthesis and leaf constituents were examined in the wild-type (WT) and mutant nar1 of barley (Hordeum vulgare L. cv. Steptoe) that contains a defective structural gene encoding NADH-dependent nitrate reductase (NADH-NAR). In controlled environment experiments, total biomass, rates of photosynthesis, stomatal conductance, intercellular CO(2) concentrations and foliar non-structural carbohydrate levels were unchanged or differed slightly in the mutant compared with the WT. Both genotypes displayed accelerated plant growth rates when the CO(2) partial pressure was increased from 36 to 98 Pa. Total NADH-NAR activity was 90% lower in the mutant than in the WT, and this was further decreased by CO(2) enrichment in both genotypes. Inorganic nitrate was greater in the mutant than in the WT, whereas in situ nitrate assimilation by excised leaves was two-fold greater for the WT than for the mutant. Foliar ammonia was 50% lower in the mutant than in the WT under ambient CO(2). Ammonia levels in the WT were decreased by about one-half by CO(2) enrichment, whereas ammonia was unaffected by elevated CO(2) in mutant leaves. Total soluble amino acid concentrations in WT and mutant plants grown in the ambient CO(2) treatment were 30.1 and 28.4 micromol g(-1) FW, respectively, when measured at the onset of the light period. Seven of the twelve individual amino acids reported here increased during the first 12 h of light in the ambient CO(2) treatment, leading to a doubling of total soluble amino acids in the WT. The most striking effect of the mutation was to eliminate increases of glutamine, aspartate and alanine during the latter half of the photoperiod in the ambient CO(2) treatment. Growth in elevated CO(2) decreased levels of total soluble amino acids on a diurnal basis in the WT but not in mutant barley leaves. The above results indicated that a defect in NADH-NAR primarily affected nitrogenous leaf constituents in barley. Also, we did not observe synergistic effects of CO(2) enrichment and decreased foliar NADH-NAR activity on most N-containing compounds.

Background and Aims: Accounting for the acclimation of respiration of plants to temperature remains a major problem in analysis of carbon balances of plants and ecosystems. Translocation of carbohydrates out of leaves in the dark requires energy from respiration. In this study relationships between the responses of leaf respiration and translocation to temperature are examined., Methods: Direct and acclimatory responses to temperature of respiration and translocation in the dark were investigated in mature leaves of soybean and amaranth. In some cases translocation from leaves was prevented by heat-girdling the phloem in the leaf petiole, or photosynthesis during the previous day was altered., Key Results: In both species short-term increases in temperature early in the dark period led to exponential increases in rates of respiration. However, respiration rates decreased toward the end of the dark period at higher temperatures. Stopping translocation largely prevented this decrease in respiration, suggesting that the decrease in respiration was due to low availability of substrates. In soybean, translocation also increased with temperature, and both respiration and translocation fully acclimated to temperature. In amaranth, translocation in the dark was independent of temperature, and respiration did not acclimate to temperature. Respiration and translocation rates both decreased with lower photosynthesis during the previous day in the two species., Conclusions: Substrate supply limited total night-time respiration in both species at high temperatures and following days with low photosynthesis. This resulted in an apparent acclimation of respiration to high temperatures within one night in both species. However, after long-term exposure to different temperatures there was no evidence that lack of substrates limited respiration in either species. In amaranth, respiration did not limit translocation rates over the temperature range of 20-35 degrees C.

Recent breakthroughs in CO(2) fumigation methods using free-air CO(2) enrichment (FACE) technology have prompted comparisons between FACE experiments and enclosure studies with respect to quantification of the effects of projected atmospheric CO(2) concentrations on crop yields. On the basis of one such comparison, it was argued that model projections of future food supply (some of which are based on older enclosure data) may have significantly overestimated the positive effect of elevated CO(2) concentration on crop yields and, by extension, food security. However, in the comparison, no effort was made to differentiate enclosure study methodologies with respect to maintaining projected CO(2) concentration or to consider other climatic changes (e.g. warming) that could impact crop yields. In this review, we demonstrate that relative yield stimulations in response to future CO(2) concentrations obtained using a number of enclosure methodologies are quantitatively consistent with FACE results for three crops of global importance: rice (Oryza sativa), soybean (Glycine max) and wheat (Triticum aestivum). We suggest, that instead of focusing on methodological disparities per se, improved projections of future food supply could be achieved by better characterization of the biotic/abiotic uncertainties associated with projected changes in CO(2) and climate and incorporation of these uncertainties into current crop models.

A reduction in leaf stomatal conductance (g) with increasing leaf-to-air difference in water vapour pressure (D) is nearly ubiquitous. Ecological comparisons of sensitivity have led to the hypothesis that the reduction in g with increasing D serves to maintain leaf water potentials above those that would cause loss of hydraulic conductance. A reduction in leaf water potential is commonly hypothesized to cause stomatal closure at high D. The importance of these particular hydraulic factors was tested by exposing Abutilon theophrasti, Glycine max, Gossypium hirsutum and Xanthium strumarium to D high enough to reduce g and then decreasing ambient carbon dioxide concentration ([CO2]), and observing the resulting changes in g, transpiration rate and leaf water potential, and their reversibility. Reducing the [CO2] at high D increased g and transpiration rate and lowered leaf water potential. The abnormally high transpiration rates did not result in reductions in hydraulic conductance. Results indicate that low water potential effects on g at high D could be overcome by low [CO2], and that even lower leaf water potentials did not cause a reduction in hydraulic conductance in these well-watered plants. Reduced g at high D in these species resulted primarily from increased stomatal sensitivity to [CO2] at high D, and this increased sensitivity may mediate stomatal responses to leaf hydraulics at high D.

Background and Aims: Respiration is an important component of plant carbon balance, but it remains uncertain how respiration will respond to increases in atmospheric carbon dioxide concentration, and there are few measurements of respiration for crop plants grown at elevated [CO(2)] under field conditions. The hypothesis that respiration of leaves of soybeans grown at elevated [CO(2)] is increased is tested; and the effects of photosynthesis and acclimation to temperature examined., Methods: Net rates of carbon dioxide exchange were recorded every 10 min, 24 h per day for mature upper canopy leaves of soybeans grown in field plots at the current ambient [CO(2)] and at ambient plus 350 micromol mol(-1) [CO(2)] in open top chambers. Measurements were made on pairs of leaves from both [CO(2)] treatments on a total of 16 d during the middle of the growing seasons of two years., Key Results: Elevated [CO(2)] increased daytime net carbon dioxide fixation rates per unit of leaf area by an average of 48 %, but had no effect on night-time respiration expressed per unit of area, which averaged 53 mmol m(-2) d(-1) (1.4 micromol m(-2) s(-1)) for both the ambient and elevated [CO(2)] treatments. Leaf dry mass per unit of area was increased on average by 23 % by elevated [CO(2)], and respiration per unit of mass was significantly lower at elevated [CO(2)]. Respiration increased by a factor of 2.5 between 18 and 26 degrees C average night temperature, for both [CO(2)] treatments., Conclusions: These results do not support predictions that elevated [CO(2)] would increase respiration per unit of area by increasing photosynthesis or by increasing leaf mass per unit of area, nor the idea that acclimation of respiration to temperature would be rapid enough to make dark respiration insensitive to variation in temperature between nights.

Background and Aims: Respiration of autotrophs is an important component of their carbon balance as well as the global carbon dioxide budget. How autotrophic respiration may respond to increasing carbon dioxide concentrations, [CO(2)], in the atmosphere remains uncertain. The existence of short-term responses of respiration rates of plant leaves to [CO(2)] is controversial. Short-term responses of respiration to temperature are not disputed. This work compared responses of dark respiration and two processes dependent on the energy and reductant supplied by dark respiration, translocation and nitrate reduction, to changes in [CO(2)] and temperature., Methods: Mature soybean leaves were exposed for a single 8-h dark period to one of five combinations of air temperature and [CO(2)], and rates of respiration, translocation and nitrate reduction were determined for each treatment., Key Results: Low temperature and elevated [CO(2)] reduced rates of respiration, translocation and nitrate reduction, while increased temperature and low [CO(2)] increased rates of all three processes. A given change in the rate of respiration was accompanied by the same change in the rate of translocation or nitrate reduction, regardless of whether the altered respiration was caused by a change in temperature or by a change in [CO(2)]., Conclusions: These results make it highly unlikely that the observed responses of respiration rate to [CO(2)] were artefacts due to errors in the measurement of carbon dioxide exchange rates in this case, and indicate that elevated [CO(2)] at night can affect translocation and nitrate reduction through its effect on respiration.

Reductions in leaf stomatal conductance with rising atmospheric carbon dioxide concentration ([CO2]) could reduce water use by vegetation and potentially alter climate. Crop plants have among the largest reductions in stomatal conductance at elevated [CO2]. The relative reduction in stomatal conductance caused by a given increase in [CO2] is often not constant within a day nor between days, but may vary considerably with light, temperature and humidity. Species also differ in response, with a doubling of [CO2] reducing mean midday conductances by <15% in some crop species to >50% in others. Elevated [CO2] increases leaf area index throughout the growing season in some species. Simulations, and measurements in free air carbon dioxide enrichment systems both indicate that the relatively large reductions in stomatal conductance in crops would translate into reductions of <10% in evapotranspiration, partly because of increases in temperature and decreases in humidity in the air around crop leaves. The reduction in evapotranspiration in crops is similar to that in other types of vegetation which have smaller relative reductions in stomatal conductance, because of the poorer aerodynamic coupling of the canopy to the atmosphere in crops. The small decreases in evapotranspiration at elevated [CO2] may themselves be important to crop production in dry environments, but changes in climate and microclimate caused by reduced stomatal conductance could also be important to crop production.

To examine the impact of climate change on vegetative productivity, we exposed fallow agricultural soil to an in situ temperature and CO2 gradient between urban, suburban and rural areas in 2002. Along the gradient, average daytime CO2 concentration increased by 21% and maximum (daytime) and minimum (nighttime) daily temperatures increased by 1.6 and 3.3 degrees C, respectively in an urban relative to a rural location. Consistent location differences in soil temperature were also ascertained. No other consistent differences in meteorological variables (e.g. wind speed, humidity, PAR, tropospheric ozone) as a function of urbanization were documented. The urban-induced environmental changes that were observed were consistent with most short-term (approximately 50 year) global change scenarios regarding CO2 concentration and air temperature. Productivity, determined as final above-ground biomass, and maximum plant height were positively affected by daytime and soil temperatures as well as enhanced [CO2], increasing 60 and 115% for the suburban and urban sites, respectively, relative to the rural site. While long-term data are needed, these initial results suggest that urban environments may act as a reasonable surrogate for investigating future climatic change in vegetative communities.

The effects of elevated CO2 concentrations on the antioxidant capacity and flavonoid content in strawberry fruit (Fragaria x ananassa Duch.) were studied under field conditions. Increased CO(2) (300 and 600 micromol mol(-1) above ambient) concentrations resulted in increases in ascorbic acid (AsA), glutathione (GSH), and ratios of AsA to dehydroascorbic acid (DHAsA) and GSH to oxidized glutathione (GSSG), and a decrease in DHAsA in strawberry fruit. High anthocyanin and phenolic content were also found in fruit of CO(2) treated plants. Growing strawberry plants under CO(2) enrichment conditions significantly enhanced fruit p-coumaroylglucose, dihydroflavonol, quercetin 3-glucoside, quercetin 3-glucuronide, and kaempferol 3-glucoside contents, as well as cyanidin 3-glucoside, pelargonidin 3-glucoside, and pelargonidin 3-glucoside-succinate content. Fruit of strawberry plants grown in the CO(2) enrichment conditions also had high oxygen radical absorbance activity against ROO(*), O(2)(*-), H(2)O(2), OH(*), and (1)O(2) radicals.

Studies have indicated that the concentration of carbon dioxide [CO2] during the dark period may influence plant dry matter accumulation. It is often suggested that these effects on growth result from effects of [CO2] on rates of respiration, but responses of respiration to [CO2] remain controversial, and connections between changes in respiration rate and altered growth rate have not always been clear. The present experiments tested whether translocation, a major consumer of energy from respiration in exporting leaves, was sensitive to [CO2]. Nineteen-day-old soybean plants grown initially at a constant [CO2] of 350 micromol mol(-1) were exposed to three consecutive nights with a [CO2] of 220-1400 micromol mol(-1), with a daytime [CO2] of 350 micromol mol(-1). Change in dry mass of the individual second, third and fourth trifoliate leaves over the 3-d period was determined, along with rates of respiration and photosynthesis of second leaves, measured by net CO2 exchange. Translocation was determined from mass balance for second leaves. Additional experiments were conducted where the [CO2] around individual leaves was controlled separately from that of the rest of the plant. Results indicated that low [CO2] at night increased both respiration and translocation and elevated [CO2] decreased both processes, to similar relative extents. The effect of [CO2] during the dark on the change in leaf mass over 3 d was largest in second leaves, where the change in mass was about 50% greater at 1400 micromol mol(-1) CO2 than at 220 micromol mol(-1) CO2. The response of translocation to [CO2] was localized in individual leaves. Results indicated that effects of [CO2] on net carbon dioxide exchange rate in the dark either caused or reflected a change in a physiologically important process which is known to depend on energy supplied by respiration. Thus, it is unlikely that the observed effects of [CO2] on respiration were artefacts of the measurement process in this case.

Use of infrared analyzers to measure water vapor concentrations in photosynthesis systems is becoming common. It is known that sensitivity of infrared carbon dioxide and water vapor analyzers is affected by the oxygen concentration in the background gas, particularly for absolute analyzers, but the potential for large errors in estimates of stomatal conductance due to effects of oxygen concentration on the sensitivity of infrared water vapor analyzers is not widely recognized. This work tested three types of infrared water vapor analyzers for changes in sensitivity of infrared water vapor analyzers depending on the oxygen content of the background gas. It was found that changing from either 0 or 2% to 21% oxygen in nitrogen decreased the sensitivity to water vapor for all three types of infrared water vapor analyzers by about 4%. The change in sensitivity was linear with oxygen mole fraction. The resulting error in calculated stomatal conductance would depend strongly on the leaf to air vapor pressure difference and leaf temperature, and also on whether leaf temperature was directly measured or calculated from energy balance. Examples of measurements of gas exchange on soybean leaves under glasshouse conditions indicated that changing from 21% to 2% oxygen produced an artifactual apparent increase in stomatal conductance which averaged about 30%. Similar errors occurred for 'conductances' of wet filter paper. Such errors could affect inferences about the carbon dioxide dependence of the sensitivity of photosynthesis to oxygen.

Single leaf photosynthetic rates and various leaf components of potato (Solanum tuberosum L.) were studied 1-3 days after reciprocally transferring plants between the ambient and elevated growth CO2 treatments. Plants were raised from individual tuber sections in controlled environment chambers at either ambient (36 Pa) or elevated (72 Pa) CO2. One half of the plants in each growth CO2 treatment were transferred to the opposite CO2 treatment 34 days after sowing (DAS). Net photosynthesis (Pn) rates and various leaf components were then measured 34, 35 and 37 DAS at both 36 and 72 Pa CO2. Three-day means of single leaf Pn rates, leaf starch, glucose, initial and total Rubisco activity, Rubisco protein, chlorophyll (a+b), chlorophyll (a/b), alpha-amino N, and nitrate levels differed significantly in the continuous ambient and elevated CO2 treatments. Acclimation of single leaf Pn rates was partially to completely reversed 3 days after elevated CO2-grown plants were shifted to ambient CO2, whereas there was little evidence of photosynthetic acclimation 3 days after ambient CO2-grown plants were shifted to elevated CO2. In a four-way comparison of the 36, 72, 36 to 72 (shifted up) and 72 to 36 (shifted down) Pa CO2 treatments 37 DAS, leaf starch, soluble carbohydrates, Rubisco protein and nitrate were the only photosynthetic factors that differed significantly. Simple and multiple regression analyses suggested that negative changes of Pn in response to growth CO2 treatment were most closely correlated with increased leaf starch levels.

Strawberry (Fragaria x ananassa) plants were grown in field plots at the current ambient [CO(2)], and at ambient + 300 and ambient + 600 mumol mol(-1) [CO(2)]. Approximately weekly measurements were made of single leaf gas exchange of upper canopy leaves from early spring through fall of two years, in order to determine the temperature dependence of the stimulation of photosynthesis by elevated [CO(2)], whether growth at elevated [CO(2)] resulted in acclimation of photosynthesis, and whether any photosynthetic acclimation was reduced when fruiting created additional demand for the products of photosynthesis. Stimulation of photosynthetic CO(2) assimilation by short-term increases in [CO(2)] increased strongly with measurement temperature. The stimulation exceeded that predicted from the kinetic characteristics of ribulose-1,5-bisphosphate carboxylase at all temperatures. Acclimation of photosynthesis to growth at elevated [CO(2)] was evident from early spring through summer, including the fruiting period in early summer, with lower rates under standard measurement conditions in plants grown at elevated [CO(2)]. The degree of acclimation increased with growth [CO(2)]. However, there were no significant differences between [CO(2)] treatments in total nitrogen per leaf area, and photosynthetic acclimation was reversed one day after switching the [CO(2)] treatments. Tests showed that acclimation did not result from a limitation of photosynthesis by triose phosphate utilization rate at elevated [CO(2)]. Photosynthetic acclimation was not evident during dry periods in midsummer, when the elevated [CO(2)] treatments conserved soil water and photosynthesis declined more at ambient than at elevated [CO(2)]. Acclimation was also not evident during the fall, when plants were vegetative, despite wet conditions and continued higher leaf starch content at elevated [CO(2)]. Stomatal conductance responded little to short-term changes in [CO(2)] except during drought, and changed in parallel with photosynthetic acclimation through the seasons in response to the long-term [CO(2)] treatments. The data do not support the hypothesis that source-sink balance controls the seasonal occurrence of photosynthetic acclimation to elevated [CO(2)] in this species.

We examined the influence of water stress (water deficit) induced by drought on the steady state levels of ascorbic acid (ASC), dehydroascorbate (DHA), and the ASC&rcolon;DHA redox status in leaflets of Glycine max (soybean) and leaves of Spinacia oleracea (spinach). Two soybean cultivars (cv. Essex and cv. Forrest) and one spinach cultivar (cv. Nordic) were grown in high-light growth chambers ( approximately 1000-1200 µmol m-2 s-1) or in the greenhouse during May, June, and July 1999. The cultivars were supplied with water until approximately 25-29 d postemergence, at which time one-half of the plants were not watered for a period of from 4.5 to 7.5 d; the other half of the plants were provided water daily and served as controls. On designated days, leaf water potential (PsiLeaf) was measured, and leaf disks of constant area were excised in the period between approximately 1230 and 1330 hours. Leaf disk samples were immediately frozen in liquid N2, samples were extracted, and ASC and DHA levels were measured and expressed as µmol per gram dry mass per time point. For the soybean cultivars, low PsiLeaf values ( approximately -3.00 to -3.95 MPa) were accompanied by slight decreases in ASC levels and slight increases in DHA levels per gram dry mass. In some cases, leaflet ASC levels of water-stressed soybeans were similar to controls or were even increased by as much as 1.2 times. In soybeans, the mole fraction of ASC remained at 93-99 mol% of the total ascorbate (ASC+DHA), indicating that most of the total ascorbate remained in the reduced form even at low water potential. In spinach plants subjected to water stress (-1.8 to -2.6 MPa), leaf ASC decreased as much as 38%, but the ASC remained at 96-99 mol% of the total ascorbate. It is concluded that during water stress, enzymes of the ascorbate-glutathione cycle in leaf mesophyll cells, as well as in the system that generates reductant to support DHA to ASC recycling, e.g., photosynthetic electron transport in chloroplasts, is able to remain active enough to maintain reduction of DHA to ASC.

The relative stimulation of photosynthesis by elevated carbon dioxide in C(3) species normally increases strongly with increasing temperature. This results from the kinetic characteristics of Rubisco, and has potentially important implications for responses of vegetation to increasing atmospheric carbon dioxide. It is often assumed that because Rubisco characteristics are conservative, all C(3) species have the same temperature dependence of the response of photosynthesis to elevated carbon dioxide. However, in this field study of Taraxacum officinale, there were no significant differences in the relative stimulation of photosynthesis by elevated carbon dioxide among days with temperatures ranging from 15 to 34 degrees C. Nevertheless, short-term measurements indicated a strong temperature dependence of the stimulation. This suggested that acclimation to temperature caused the lack of variation in the seasonal data. Experiments in controlled environments indicated that complete acclimation of the relative stimulation of photosynthesis by elevated carbon dioxide occurred for growth temperatures of 10 - 25 degrees C. The apparent specificity of Rubisco for carbon dioxide relative to oxygen at 15 degrees C, as assayed in vivo by measurements of the carbon dioxide concentration at which carboxylation equalled oxygenation, also varied with growth temperature. Changes in the apparent specificity of Rubisco accounted for the acclimation of the temperature dependence of the relative stimulation of photosynthesis by elevated carbon dioxide. It is premature to conclude that low temperatures will necessarily reduce the relative stimulation of photosynthesis caused by rising atmospheric carbon dioxide.

To determine how parameters of a Farquhar-type photosynthesis model varied with measurement temperature and with growth temperature, eight cool and warm climate herbaceous crop and weed species were grown at 15 and 25 degrees C and single leaf carbon dioxide and water vapor exchange rates were measured over the range of 15 - 35 degrees C. Photosynthetic parameters examined were the initial slope of the response of assimilation rate (A) to substomatal carbon dioxide concentration (C(i)), A at high C(i), and stomatal conductance. The first two measurements allow calculation of V(Cmax), the maximum rate of carboxylation of ribulose bisphosphate carboxylase and J(max), the maximum rate of photosynthetic electron transport, of Farquhar-type photosynthesis models. In all species, stomatal conductance increased exponentially with temperature over the whole range of 15 - 35 degrees C, even when A decreased at high measurement temperature. There were larger increases in conductance over this temperature range in the warm climate species (4.3 x) than in the cool climate species (2.5 x). The initial slope of A vs. C(i) exhibited an optimum temperature which ranged from 20 to 30 degrees C. There was a larger increase in the optimum temperature of the initial slope at the warmer growth temperature in the cool climate species than in the warm climate species. The optimum temperature for A at high C(i) ranged from 25 to 30 degrees C among species, but changed little with growth temperature. The absolute values of both the initial slope of A vs. C(i) and A at high C(i) were increased about 10% by growth at the warmer temperature in the warm climate species, and decreased about 20% in the cool climate species. The ratio of J(max) - V(Cmax) normalized to 20 degrees C varied by more than a factor of 2 across species and growth temperatures, but differences in the temperature response of photosynthesis were more related to variation in the temperature dependencies of J(max) and V(Cmax) than to the ratio of their normalized values.

Photosynthetic rates and photosynthate partitioning were studied in three-week-old soybean [Glycine max (L.) Merr. cv. Williams] plants exposed to either ambient (35 Pa) or elevated (70 Pa) CO2 in controlled environment chambers. Ambient CO2-grown plants also were given a single 24 h treatment with 70 Pa CO2 1 d prior to sampling. Photosynthetic rates of ambient CO2-grown plants initially increased 36% when the measurement CO2 was doubled from 35 to 70 Pa. Photosynthetic rates of the third trifoliolate leaf, both after 1 and 21 d of elevated CO2 treatment, were 30 to 45% below those of ambient CO2-grown plants when measured at 35 Pa CO2. These reduced photosynthetic rates were not due to increased stomatal resistance and were observed for 2 to 8 h after plants given 1 d of CO2 enrichment were returned to ambient CO2. Initial and total ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) activities, percent activation, Rubisco protein, soluble protein and leaf chlorophyll content were similar in all CO2 treatments. Quantum yields of photosynthesis, determined at limiting irradiances and at 35 Pa CO2, were 0.049±0.003 and 0.038±0.005 mol CO2 fixed per mol quanta for ambient and elevated CO2-grown plants, respectively (p<0.05). Leaf starch and sucrose levels were greater in plants grown at 70 than at 35 Pa CO2. Starch accumulation rates during the day were greater in ambient CO2-grown plants than in plants exposed to elevated CO2 for either 1 or 21 d. However, the percentage of C partitioned to starch relative to total C fixed was unaffected by 1 d of CO2 enrichment. The above results showed that both photosynthetic and starch accumulation rates of soybean leaflets measured at 35 Pa CO2 were temporarily reduced after 1 and 21 d of CO2 enrichment. The biochemical mechanism affecting these responses was not identified.

This study investigated the basis of the negative relationship between leaf size and photosynthetic rate per unit of area among five cultivars of soybeans. Exposure of developing mainstem leaves to light, and sizes and light saturated photosynthesis rates of those leaves at maturity were compared in cultivars grown in field plots for two years at Beltsville, Maryland, USA. Plants were grown both in stands at 2.5 cm by 1 m spacing and as isolated plants. While cultivar differences in leaf size were large and consistent in both planting arrangements, significant cultivar differences in light saturated photosynthetic rates were found only in plants grown in stands. Similarly, leaf size was significantly correlated with specific leaf weight only for plants grown in stands. The mainstem apex and developing mainstem leaves experienced more severe shading in large-leaved cultivars than in small-leaved cultivars when plants were grown in stands. Thus, cultivar differences in photosynthetic capacity were probably a consequence of differences in the exposure of developing leaves to light.

Water vapor was added differentially to the gas streams entering the cells of three makes of differential infrared carbon dioxide analysers. Analyser deflections were compared with those expected from dilution of the carbon dioxide by the additional gas. Tests were made at 0, 365, and 730 cm(3) m(-3) concentrations of carbon dioxide, and with the dewpoint in one cell of the analysers held constant at 15, 20, or 25°C. None of the analysers always responded in the ways predicted from dilution. The results showed that errors of a few cm(3) m(-3) could occur in estimates of carbon dioxide differentials using the theoretical correction for dilution. Furthermore the amount of error varied with the carbon dioxide range, the difference in water content, and in some cases the dewpoint range.

Net photosynthetic rates and mesophyll conductances were measured under standardized conditions for leaves of two C3 and one C4 annual species grown at temperatures of 20 to 32°C. Plants were grown with varying day and night temperatures, and also at constant temperatures equal to all the day and night temperatures used. Plants were grown with 8, 12, and 16 hours of light per day. This design allowed determination of whether photosynthetic characteristics were best correlated with day, night, mean, or time-weighted mean temperatures, The results showed that for Glycine max (L.) Merr. (C3) night temperature was most important in determining photosynthetic characteristics, while in Helianthus annuus L. (C3) and Amaranthus hypochondriacus L. (C4) the time-weighted mean temperature was most important. The results for all species were consistent with the hypothesis that development of photosynthetic characteristics is related to a balance between the rate of leaf expansion and the rate of photosynthesis under the growth conditions.

Large underestimates of the limitation to photosynthesis imposed by stomata can occur because of an error in the standard method of calculating average substomatal pressures of carbon dioxide when heterogeneity of those pressures occurs across a leaf surface. Most gas exchange data supposedly indicating nonstomatal inhibition of photosynthesis by water stress could have this error. However, if no stomatal closure occurs, any reduction in photosynthesis must be due to nonstomatal inhibition of photosynthesis. Net carbon dioxide exchange rates and conductances to water vapor were measured under field conditions in upper canopy leaves of tomato plants during two summers in Beltsville, Maryland, USA. Comparisons were made near midday at high irradiance between leaflets in air with the ambient water vapor content and in air with a higher water content. The higher water content, which lowered the leaf to air water vapor pressure difference (VPD), was imposed either one half hour or several hours before measurements of gas exchange. In both seasons, and irrespective of the timing of the imposition of different VPDs, net photosynthesis increased 60% after decreasing the VPD from 3 to 1 kPa. There were no differences in leaf conductance between leaves at different VPDs, thus transpiration rates were threefold higher at 3 than at 1 kPa VPD. It is concluded that nonstomatal inhibition of photosynthesis did occur in these leaves at high transpiration rate.

Net photosynthetic rates and mesophyll conductances at 25 °C at light saturation and air levels of carbon dioxide and oxygen were measured on recently fully expanded leaflets of second trifoliolate leaves of soybeans (Glycine max cv. Kent). Plants were grown outdoors in pots at Beltsville, Maryland with 14 planting times from May through August, 1983. Air temperature and humidity, and photosynthetically active radiation (PAR) were measured for the expansion periods of the second trifoliolate leaves. Rates of net photosynthesis ranged from 24 to 33 μmol m(-2) s(-1), and mesophyll conductances from 0.24 to 0.35 cm s(-1) for the different planting dates. Mean 24-h air temperatures ranged from 20.6 to 29.0 °C, and mean daily PAR ranged from 29.4 to 58.4 mol m(-2) d(-1) for the leaf expansion periods. There was a positive relationship between photosynthetic characteristics and PAR during leaf expansion, and a negative relationship between photosynthetic characteristics and leaf expansion rates, with 96% of the variation in photosynthetic characteristics accounted for by these two variables. Leaf expansion rates were highly correlated with air temperature.

Daytime rates of net photosynthesis of upper canopy leaflets of soybeans were compared on 17 days for leaflets exposed to air at the ambient humidity and at a higher humidity. Leaflets at the higher humidity had higher rates of net photosynthesis on 16 of the 17 days. The daily total of net photosynthesis of leaflets at the higher humidity was on average 1.32 times that for leaflets at ambient humidity. A strong limitation of net photosynthesis by ambient humidity was found throughout the growing season.

Photosynthetic characteristics at high measurement irradiance were analyzed for single leaves of two C3 and one C4 species grown under twenty one combinations of irradiance level, irradiance duration, and air temperature in order to test the idea that photosynthetic characteristies developed by leaves in different environments are controlled by the daily amount of photosynthesis. Photosynthetic rates per unit area and mesophyll conductances at 25°C and air levels of CO2 and O2, and parameters for two photosynthesis models were used to characterize the photosynthetic properties of the leaves. Leaves with highest values of the photosynthetic parameters for each species were often developed in environments with irradiance levels below saturation for photosynthesis, and with only 12 hours of irradiance per day. Lower air temperature during growth increased the photosynthetic characteristics for a given irradiance regime. Photosynthetic characteristics had higher correlation coefficients with daily photosynthesis of mature leaves divided by 24-hour leaf elongation rates of young leaves, than with daily photosynthesis alone, indicating that photosynthetic characteristics may be related to a balance between photosynthesis and leaf expansion.

Soybean plants (Glycine max var. Ransom) were grown at light intensities of 850 and 250 mueinsteins m(-2) sec(-1) of photosynthetically active radiation. A group of plants was shifted from each environment into the other environment 24 hours before the beginning of the experiment. Net photosynthetic rates and stomatal conductances were measured at 2,000 and 100 mueinsteins m(-2) sec(-1) photosynthetically active radiation on the 1st, 2nd, and 5th days of the experiment to determine the time course of photosynthetic light adaptation. The following factors were also measured: dark respiration, leaf water potential, leaf thickness, internal surface area per external surface area, chlorophyll content, photosynthetic unit size and number, specific leaf weight, and activities of malate dehydrogenase, and glycolate oxidase. Comparisons were made with plants maintained in either 850 or 250 mueinsteins m(-2) sec(-1) environments. Changes in photosynthesis, stomatal conductance, leaf anatomy, leaf water potential, photosynthetic unit size, and glycolate oxidase activity occurred upon altering the light environment, and were complete within 1 day, whereas chlorophyll content, numbers of photosynthetic units, specific leaf weight, and malate dehydrogenase activity showed slower changes. Differences in photosynthetic rates at high light were largely accounted for by internal surface area differences with low environmental light associated with low internal area and low photosynthetic rate. An exception to this was the fact that plants grown at 250 mueinsteins m(-2) sec(-1) then switched to 850 mueinsteins m(-2) sec(-1) showed lower photosynthesis at high light than any other treatment. This was associated with higher glycolate oxidase and malate dehydrogenase activity. Photosynthesis at low light was higher in plants kept at or switched to the lower light environment. This increased rate was associated with larger photosynthetic unit size, and lower dark respiration and malate dehydrogenase activity. Both anatomical and physiological changes with environmental light occurred even after leaf expansion was complete and both were important in determining photosynthetic response to light.

Light-saturated photosynthetic rates at air levels of carbon dioxide were measured about weekly in upper canopy leaves of two soybean cultivars grown at stand densities of 40 and 100 plants per square meter. Early in the season, when leaf area indices differed between stand densities, plants of both cultivars grown at high stand density had photosynthetic rates which averaged 23% lower than plants at low stand density. Later in the season, when there were no differences in leaf area index between stand densities, there were no differences in photosynthetic rates in the cultivar Kent, but rate differences of about 14% persisted in the cultivar Williams. In Williams mainstem leaves emerged into full sunlight later in their development at high than at low stand density. In both cultivars the oldest fully exposed leaves were photosynthetically immature for much of the season, as higher rates could be achieved by lower leaves which were shaded in situ. The results identify shading of young developing leaves and photosynthetic immaturity of fully exposed leaves as factors limiting canopy photosynthesis in soybeans, and indicate cultivar differences in how much high stand density reduces photosynthetic capacity.

It was hypothesized that since sub-stomatal carbon dioxide concentrations are often saturating to photosynthesis at ambient external concentrations in C 4 plants at high light, photosynthesis might be insensitive to partial stomatal closure caused by large leaf-air water vapor pressure difference. The response of stomatal conductance and photosynthesis at high irradiance to vapor pressure difference was determined under uniform conditions in C 4 plants grown under controlled conditions, and outdoors. In several cases, photosynthesis was less sensitive to stomatal closure than it would have been if photosynthesis had a linear response to sub-stomatal carbon dioxide concentration. No change in photosynthesis at up to 25 mbar vapor pressure difference was demonstrated in the C 4 species Portulaca oleracea and Amaranthus hypochondriacus, despite reductions in stomatal conductance of 32 and 17%, respectively. Sensitivity of photosynthesis to leaf-air vapor pressure difference was found to depend on the species and on the growth conditions.