Urgency adjusted outcomes of emergency abdominal surgery for inflammatory bowel disease.

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.

A call for clarity: a scoping review of predictors of poor outcome after emergency abdominal surgery for inflammatory bowel disease.

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.

The Impact of Surgeon Speciality Interest on Outcomes of Emergency Laparotomy in IBD.

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.

Establishment of local wastewater-based surveillance programmes in response to the spread and infection of COVID-19 - case studies from South Africa, the Netherlands, Turkey and England.

The COVID-19 pandemic has resulted in over 340 million infection cases (as of 21 January 2022) and more than 5.57 million deaths globally. In reaction, science, technology and innovation communities across the globe have organised themselves to contribute to national responses to COVID-19 disease. A significant contribution has been from the establishment of wastewater-based epidemiological (WBE) surveillance interventions and programmes for monitoring the spread of COVID-19 in at least 55 countries. Here, we examine and share experiences and lessons learnt in establishing such surveillance programmes. We use case studies to highlight testing methods and logistics considerations associated in scaling the implementing of such programmes in South Africa, the Netherlands, Turkey and England. The four countries were selected to represent different regions of the world and the perspective based on the considerable progress made in establishing and implementing their national WBE programmes. The selected countries also represent different climatic zones, economies, and development stages, which influence the implementation of national programmes of this nature and magnitude. In addition, the four countries' programmes offer good experiences and lessons learnt since they are systematic, and cover extensive areas, disseminate knowledge locally and internationally and partnered with authorities (government). The programmes also strengthened working relations and partnerships between and among local and global organisations. This paper shares these experiences and lessons to encourage others in the water and public health sectors on the benefits and value of WBE in tackling SARS-CoV-2 and related future circumstances.

Quantitative FIT stratification is superior to NICE referral criteria NG12 in a high-risk colorectal cancer population.

BACKGROUND: Guidelines for urgent investigation of colorectal cancer (CRC) are based on age and symptom-based criteria. This study aims to compare the diagnostic value of clinical features and faecal immunochemical test (FIT) results to identify those at a higher risk of CRC, thereby facilitating effective triage of patients. METHODS: We undertook a review of all patients referred for investigation of CRC at our centre between September 2016 and June 2018. Patients were identified using a prospectively recorded local database. We performed a logistic regression analysis of factors associated with a diagnosis of CRC. RESULTS: One-thousand-and-seven-hundred-eighty-four patients with FIT results were included in the study. Change in bowel habit (CIBH) was the most common referring clinical feature (38.3%). Patients diagnosed with CRC were significantly older than those without malignancy (74.0 years vs 68.9 years, p = 0.0007). Male patients were more likely to be diagnosed with CRC than females (6.5% vs 2.5%, Chi-squared 16.93, p < 0.0001). CRC was diagnosed in 3.5% (24/684) with CIBH compared to 8.1% (6/74) with both CIBH and iron deficiency anaemia. No individual or combination of referring clinical features was associated with an increased diagnosis of CRC (Chi-squared, 8.03, p = 0.155). Three patients with negative FIT results (< 4 µg Hb/g faeces) were diagnosed with CRC (3/1027, 0.3%). The highest proportion of cancers detected was in the ≥ 100 µg Hb/g faeces group (55/181, 30.4%). CONCLUSION: In a multivariate model, FIT outperforms age, sex and all symptoms prompting referral. FIT has greater stratification value than any referral symptoms. FIT does have value in patients with iron deficiency anaemia.

Thrombocytosis helps to stratify risk of colorectal cancer in patients referred on a 2-week-wait pathway.

PURPOSE: Primary care studies suggest that thrombocytosis (platelet counts > 400 × 109/L) is associated with an increased risk of colorectal cancer (CRC). We aimed to establish whether this marker has significant stratification value in patients seen in secondary care. METHODS: A retrospective review of 2991 patients referred to our colorectal 2-week-wait (2WW) pathway between August 2014 and August 2017. Patient demographics were recorded prospectively, and local electronic records systems were used to retrieve full blood counts (FBC) and cancer diagnoses. Patients with no recent platelet count at the time of referral or incomplete records were excluded. RESULTS: 2236 patients were included in this evaluation. There was no significant difference in the age distribution of those with thrombocytosis and those without. There were significantly more females in the thrombocytosis group (72.1% vs 53.9%, chi-squared 24.63, p < 0.0001). 130 CRCs were detected (5.8%) and patients with thrombocytosis were more likely to have CRC (OR 2.62, 95% CI 1.60-4.30). The CRC diagnosis rate was significantly higher in females with thrombocytosis (10.3% vs 2.9%, chi-squared 19.41, p < 0.0001) and males with thrombocytosis (16.1% vs 7.9%, chi-squared 4.62, p = 0.032). CONCLUSION: Thrombocytosis appears to have stratification value in the 2WW population. Further evaluation of its value alone or in combination with other stratification tests is required.

Macroclimate associated with urbanization increases the rate of secondary succession from fallow soil.

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.

Service evaluation of faecal immunochemical testing and anaemia for risk stratification in the 2-week-wait pathway for colorectal cancer.

Background: New national guidance on urgent referral for investigation of colorectal cancer included faecal occult blood testing in 2015. A service evaluation of faecal immunochemical testing (FIT) and anaemia as risk stratification tools in symptomatic patients suspected of having CRC was undertaken. Methods: Postal FIT was incorporated into the colorectal cancer 2-week wait (2WW) pathway for all patients without rectal bleeding in 2016. Patients were investigated in the 2WW pathway as normal, and outcomes of investigations were recorded prospectively. Anaemia was defined as a haemoglobin level below 120 g/l in women and 130 g/l in men. Results: FIT kits were sent to 1106 patients, with an 80·9 per cent return rate; 810 patients completed investigations and 40 colorectal cancers were diagnosed (4·9 per cent). FIT results were significantly higher in patients with anaemia (median (i.q.r.) 4·8 (0·8-34·1) versus 1·2 (0-6·4) µg Hb/g faeces in those without anaemia; P < 0·001). Some 60·4 per cent of patients (538 of 891) had a result lower than 4 µg haemoglobin (Hb) per g faeces (limit of detectability), and 69·7 per cent (621 of 891) had less than 10 µg Hb/g faeces. Some 60 per cent of patients with colorectal cancer had a FIT reading of 150 µg Hb/g faeces or more. For five colorectal cancers diagnosed in patients with a FIT value below 10 µg Hb/g faeces, there was either a palpable rectal mass or the patient was anaemic. A FIT result of more than 4 µg Hb/g faeces had 97·5 per cent sensitivity and 64·5 per cent specificity for a diagnosis of colorectal cancer. A FIT result above 4 µg Hb/g faeces and/or anaemia had a 100 per cent sensitivity and 45·3 per cent specificity for colorectal cancer diagnosis. Conclusion: FIT is most useful at the extremes of detectability; strongly positive readings predict high rates of colorectal cancer and other significant pathology, whereas very low readings in the absence of anaemia or a palpable rectal mass identify a group with very low risk. High return rates for FIT within this 2WW pathway indicate its acceptability.

Forebrain circuitry involved in effort-related choice: Injections of the GABAA agonist muscimol into ventral pallidum alter response allocation in food-seeking behavior.

Organisms often make effort-related choices based upon assessments of motivational value and work requirements. Nucleus accumbens dopamine is a critical component of the brain circuitry regulating work output in reinforcement-seeking behavior. Rats with accumbens dopamine depletions reallocate their instrumental behavior away from food-reinforced tasks that have high response requirements, and instead they select a less-effortful type of food-seeking behavior. The ventral pallidum is a brain area that receives substantial GABAergic input from nucleus accumbens. It was hypothesized that stimulation of GABA(A) receptors in the ventral pallidum would result in behavioral effects that resemble those produced by interference with accumbens dopamine transmission. The present studies employed a concurrent choice lever pressing/chow intake procedure; with this task, interference with accumbens dopamine transmission shifts choice behavior such that lever pressing for food is decreased but chow intake is increased. In the present experiments, infusions of the GABA(A) agonist muscimol (5.0-10.0 ng) into the ventral pallidum decreased lever pressing for preferred food, but increased consumption of the less preferred chow. In contrast, ventral pallidal infusions of muscimol (10.0 ng) had no significant effect on preference for the palatable food in free-feeding choice tests. Furthermore, injections of muscimol into a control site dorsal to the ventral pallidum produced no significant effects on lever pressing and chow intake. These data indicate that stimulation of GABA receptors in ventral pallidum produces behavioral effects similar to those produced by accumbens dopamine depletions. Ventral pallidum appears to be a component of the brain circuitry regulating response allocation and effort-related choice behavior, and may act to convey information from nucleus accumbens to other parts of this circuitry. This research may have implications for understanding the brain mechanisms involved in energy-related psychiatric dysfunctions such as psychomotor retardation in depression, anergia, and apathy.

Antibiotic resistance and antibiotic prescribing by dentists in England 2007-2016.

The early prescribers of penicillin realised that antibiotics should be used wisely and as an adjunct to traditional surgical provision. They predicted that inappropriate use would increase sensitisation to the drug. National Health Service dentists prescribed almost 10% of antibiotics issued in NHS general practice in 2016 and an audit shows that many of these may have been prescribed inappropriately. One of the causes of antimicrobial resistance is over prescription of the drugs. This paper recalls the recommendations of some early users of penicillin, reports on the current prescription patterns of dentists in England, describes the mechanism of acquisition of anti-microbial resistance and discusses dentists' role in attempting to reduce the problem.

Population density controls on microbial pollution across the Ganga catchment.

For millions of people worldwide, sewage-polluted surface waters threaten water security, food security and human health. Yet the extent of the problem and its causes are poorly understood. Given rapid widespread global urbanisation, the impact of urban versus rural populations is particularly important but unknown. Exploiting previously unpublished archival data for the Ganga (Ganges) catchment, we find a strong non-linear relationship between upstream population density and microbial pollution, and predict that these river systems would fail faecal coliform standards for irrigation waters available to 79% of the catchment's 500 million inhabitants. Overall, this work shows that microbial pollution is conditioned by the continental-scale network structure of rivers, compounded by the location of cities whose growing populations contribute c. 100 times more microbial pollutants per capita than their rural counterparts.

Homoallylic amines related to zimeldine. A comparative study on neuronal serotonin and norepinephrine reuptake based on conformational analysis.

A number of tertiary and secondary homoallylic amines, i.e. (Z)- and (E)-4-(4-bromophenyl)-4-(3-pyridyl)-3-buten-1-ylamines, were synthesized in diastereomerically pure forms. The compounds were evaluated as neuronal norepinephrine (NE) and serotonin (5-HT) uptake inhibitors under in vitro and ex vivo conditions and compared with the tricyclics amitriptyline and nortriptyline having homoallylic side chains and with the corresponding diastereomers in the zimeldine series having allylic side chains. The Z isomers of the new homoallylic derivatives (3Z, 4Z) were specific 5-HT uptake inhibitors in analogy with the corresponding allylic derivatives zimeldine (1Z) and norzimeldine (2Z). Likewise, the selectivity profile of the homoallylic (3E, 4E) and the allylic (1E, 2E) derivatives was comparable. In general, the homoallylic compounds were less potent inhibitors than their allylic counterparts. The similarities and discrepancies were evaluated in terms of conformational preferences determined by CAMSEQ molecular mechanics calculations. Homonorzimeldine (4Z) can accommodate energetically favored, but less populated, conformations having amino nitrogen atom to aromatic ring center distances comparable to those in norzimeldine. These facts correlate to retained 5-HT selectivity but diminished potency of 4Z compared to 2Z.

Timing of administration mediates the memory effects of intraseptal carbachol infusion.

Medial septal neurons innervate the entire hippocampal formation. This input provides a potent regulation of hippocampal formation physiology (e.g. theta) and memory function. Medial septal neurons are rich in cholinergic receptors and thus are potential targets for the development of cognitive enhancers. Direct intraseptal infusion of cholinomimetics alters hippocampal physiology and can produce either promnestic or amnestic effects. Several variables (e.g. age of animal, integrity of septohippocampal circuits, task difficulty) may influence treatment outcome. We have previously demonstrated that intraseptal carbachol (12.5-125 ng) infusion immediately after the sample session of a delayed-non-match-to-sample radial maze paradigm produces a dose-dependent amnesia. The present study examined whether manipulating the timing of intraseptal carbachol infusion with respect to the sample session would alter the amnestic effect. A within-subjects design was used to examine the effect of intraseptal carbachol (125 ng/0.5 microl) in a delayed-non-match to sample radial maze task. During a sample session, rats retrieved rewards from six of 12 maze arms. At the test session (3 h later), only the alternate set contained reward and entries into the sample set arms constituted errors. Intraseptal carbachol was administered: 1) 30 min prior; 2) immediately prior; 3) immediately after and 4) 90 min after the sample session. Intraseptal carbachol prior to the sample had no effect on any index of accuracy. Infusion immediately after the sample, or delayed 90 min into the retention interval, produced an acute amnesia. These findings demonstrate that the timing of treatment is a critical variable in determining the memory effects of septohippocampal manipulations and that dynamic changes in cholinergic tone are important for memory.

Intraseptal infusion of oxotremorine impairs memory in a delayed-non-match-to-sample radial maze task.

The medial septal nucleus is part of the forebrain circuitry that supports memory. This nucleus is rich in cholinergic receptors and is a putative target for the development of cholinomimetic cognitive-enhancing drugs. Septal neurons, primarily cholinergic and GABAergic, innervate the entire hippocampal formation and regulate hippocampal formation physiology and emergent function. Direct intraseptal drug infusions can produce amnestic or promnestic effects depending upon the type of drug administered. However, intraseptal infusion of the cholinomimetic oxotremorine has been reported to produce both promnestic and amnestic effects when administered prior to task performance. The present study examined whether post-acquisition intraseptal infusion of oxotremorine would be promnestic or amnestic in a delayed-non-match-to-sample radial maze task. In this task rats must remember information about spatial locations visited during a daily sample session and maintain that information over extended retention intervals (hours) in order to perform accurately on the daily test session. Treatments may then be administered during the retention interval. Alterations in maze performance during the test session an hour or more after treatment evidences effects on memory. In the present study, intraseptal infusion of oxotremorine (1.0-10.0 microg) produced a linear dose-related impairment of memory performance. Importantly, we also observed disrupted performance on the day after treatment. This persistent deficit was related only to memory over the retention interval and did not affect indices of short-term memory (ability to avoid repetitive or proactive errors during both the pre- and post-delay sessions). The persistent deficit contrasts with the acute amnestic effects of other intraseptally administered drugs including the cholinomimetics carbachol and tacrine. Thus, intraseptal oxotremorine produced a preferential disruption of memory consolidation as well as a persistent alteration of medial septal circuits. These findings are discussed with regards to multi-stage models of hippocampal-dependent memory formation and the further development of therapeutic strategies in the treatment of mild cognitive impairment as well as age-related decline and Alzheimer's dementia.

Seasonal patterns of photosynthetic response and acclimation to elevated carbon dioxide in field-grown strawberry.

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.

Acclimation to temperature of the response of photosynthesis to increased carbon dioxide concentration in Taraxacum officinale.

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.

Acclimation of photosynthesis to temperature in eight cool and warm climate herbaceous C(3) species: Temperature dependence of parameters of a biochemical photosynthesis model.

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.

Responses of gas exchange to humidity in populations of three herbs from environments differing in atmospheric water.

Responses to humidity of net photosynthesis and leaf conductance of single attached leaves were examined in populations of herbs from wet soil sites in Beltsville, Maryland and Davis, California, USA. Plants were grown in controlled environments under three conditions which differed in the magnitude of the day-night temperature difference and in daytime air saturation deficit. No population differences in response were found in Abutilon theophrasti. In Amaranthus hybridus stomatal conductance and net photosynthesis were more reduced by increasing leaf to air water vapor pressure difference (VPD) in the population from Beltsville, but only for the growth condition with a constant 25°C temperature. In Chenopodium album, stomatal conductance was more sensitive to VPD in the population from Davis, but only for the growth condition with 28/22°C day/night temperatures. Population differences in the sensitivity to VPD of leaf conductance were associated with differences in leaf area to root weight ratio. The relative reduction of net photosynthesis as VPD increased was greater than, equal to, or less than the relative decrease in substomatal carbon dioxide partial pressure. The pattern depended on species, and on growth condition. From these results one can not conclude that environmental humidity has been a strong selective force in determining sensitivity to humidity of stomatal conductance.

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis.

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.

Photosynthetic characteristics of leaves developed at different irradiances and temperatures: an extension of the current hypothesis.

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 characteristics 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 iradiance 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.