Interactive effects of changes in UV radiation and climate on terrestrial ecosystems, biogeochemical cycles, and feedbacks to the climate system.

Terrestrial organisms and ecosystems are being exposed to new and rapidly changing combinations of solar UV radiation and other environmental factors because of ongoing changes in stratospheric ozone and climate. In this Quadrennial Assessment, we examine the interactive effects of changes in stratospheric ozone, UV radiation and climate on terrestrial ecosystems and biogeochemical cycles in the context of the Montreal Protocol. We specifically assess effects on terrestrial organisms, agriculture and food supply, biodiversity, ecosystem services and feedbacks to the climate system. Emphasis is placed on the role of extreme climate events in altering the exposure to UV radiation of organisms and ecosystems and the potential effects on biodiversity. We also address the responses of plants to increased temporal variability in solar UV radiation, the interactive effects of UV radiation and other climate change factors (e.g. drought, temperature) on crops, and the role of UV radiation in driving the breakdown of organic matter from dead plant material (i.e. litter) and biocides (pesticides and herbicides). Our assessment indicates that UV radiation and climate interact in various ways to affect the structure and function of terrestrial ecosystems, and that by protecting the ozone layer, the Montreal Protocol continues to play a vital role in maintaining healthy, diverse ecosystems on land that sustain life on Earth. Furthermore, the Montreal Protocol and its Kigali Amendment are mitigating some of the negative environmental consequences of climate change by limiting the emissions of greenhouse gases and protecting the carbon sequestration potential of vegetation and the terrestrial carbon pool.

The Montreal Protocol and the fate of environmental plastic debris.

Microplastics (MPs) are an emerging class of pollutants in air, soil and especially in all aquatic environments. Secondary MPs are generated in the environment during fragmentation of especially photo-oxidised plastic litter. Photo-oxidation is mediated primarily by solar UV radiation. The implementation of the Montreal Protocol and its Amendments, which have resulted in controlling the tropospheric UV-B (280-315 nm) radiation load, is therefore pertinent to the fate of environmental plastic debris. Due to the Montreal Protocol high amounts of solar UV-B radiation at the Earth's surface have been avoided, retarding the oxidative fragmentation of plastic debris, leading to a slower generation and accumulation of MPs in the environment. Quantifying the impact of the Montreal Protocol in reducing the abundance of MPs in the environment, however, is complicated as the role of potential mechanical fragmentation of plastics under environmental mechanical stresses is poorly understood.

Oxidation and fragmentation of plastics in a changing environment; from UV-radiation to biological degradation.

Understanding the fate of plastics in the environment is of critical importance for the quantitative assessment of the biological impacts of plastic waste. Specially, there is a need to analyze in more detail the reputed longevity of plastics in the context of plastic degradation through oxidation and fragmentation reactions. Photo-oxidation of plastic debris by solar UV radiation (UVR) makes material prone to subsequent fragmentation. The fragments generated following oxidation and subsequent exposure to mechanical stresses include secondary micro- or nanoparticles, an emerging class of pollutants. The paper discusses the UV-driven photo-oxidation process, identifying relevant knowledge gaps and uncertainties. Serious gaps in knowledge exist concerning the wavelength sensitivity and the dose-response of the photo-fragmentation process. Given the heterogeneity of natural UV irradiance varying from no exposure in sediments to full UV exposure of floating, beach litter or air-borne plastics, it is argued that the rates of UV-driven degradation/fragmentation will also vary dramatically between different locations and environmental niches. Biological phenomena such as biofouling will further modulate the exposure of plastics to UV radiation, while potentially also contributing to degradation and/or fragmentation of plastics independent of solar UVR. Reductions in solar UVR in many regions, consequent to the implementation of the Montreal Protocol and its Amendments for protecting stratospheric ozone, will have consequences for global UV-driven plastic degradation in a heterogeneous manner across different geographic and environmental zones. The interacting effects of global warming, stratospheric ozone and UV radiation are projected to increase UV irradiance at the surface in localized areas, mainly because of decreased cloud cover. Given the complexity and uncertainty of future environmental conditions, this currently precludes reliable quantitative predictions of plastic persistence on a global scale.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2021.

The Environmental Effects Assessment Panel of the Montreal Protocol under the United Nations Environment Programme evaluates effects on the environment and human health that arise from changes in the stratospheric ozone layer and concomitant variations in ultraviolet (UV) radiation at the Earth's surface. The current update is based on scientific advances that have accumulated since our last assessment (Photochem and Photobiol Sci 20(1):1-67, 2021). We also discuss how climate change affects stratospheric ozone depletion and ultraviolet radiation, and how stratospheric ozone depletion affects climate change. The resulting interlinking effects of stratospheric ozone depletion, UV radiation, and climate change are assessed in terms of air quality, carbon sinks, ecosystems, human health, and natural and synthetic materials. We further highlight potential impacts on the biosphere from extreme climate events that are occurring with increasing frequency as a consequence of climate change. These and other interactive effects are examined with respect to the benefits that the Montreal Protocol and its Amendments are providing to life on Earth by controlling the production of various substances that contribute to both stratospheric ozone depletion and climate change.

Environmental effects of stratospheric ozone depletion, UV radiation, and interactions with climate change: UNEP Environmental Effects Assessment Panel, Update 2020.

This assessment by the Environmental Effects Assessment Panel (EEAP) of the United Nations Environment Programme (UNEP) provides the latest scientific update since our most recent comprehensive assessment (Photochemical and Photobiological Sciences, 2019, 18, 595-828). The interactive effects between the stratospheric ozone layer, solar ultraviolet (UV) radiation, and climate change are presented within the framework of the Montreal Protocol and the United Nations Sustainable Development Goals. We address how these global environmental changes affect the atmosphere and air quality; human health; terrestrial and aquatic ecosystems; biogeochemical cycles; and materials used in outdoor construction, solar energy technologies, and fabrics. In many cases, there is a growing influence from changes in seasonality and extreme events due to climate change. Additionally, we assess the transmission and environmental effects of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), which is responsible for the COVID-19 pandemic, in the context of linkages with solar UV radiation and the Montreal Protocol.

Environmental effects of stratospheric ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2019.

This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.

Environmental effects of ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2017.

The Environmental Effects Assessment Panel (EEAP) is one of three Panels of experts that inform the Parties to the Montreal Protocol. The EEAP focuses on the effects of UV radiation on human health, terrestrial and aquatic ecosystems, air quality, and materials, as well as on the interactive effects of UV radiation and global climate change. When considering the effects of climate change, it has become clear that processes resulting in changes in stratospheric ozone are more complex than previously held. Because of the Montreal Protocol, there are now indications of the beginnings of a recovery of stratospheric ozone, although the time required to reach levels like those before the 1960s is still uncertain, particularly as the effects of stratospheric ozone on climate change and vice versa, are not yet fully understood. Some regions will likely receive enhanced levels of UV radiation, while other areas will likely experience a reduction in UV radiation as ozone- and climate-driven changes affect the amounts of UV radiation reaching the Earth's surface. Like the other Panels, the EEAP produces detailed Quadrennial Reports every four years; the most recent was published as a series of seven papers in 2015 (Photochem. Photobiol. Sci., 2015, 14, 1-184). In the years in between, the EEAP produces less detailed and shorter Update Reports of recent and relevant scientific findings. The most recent of these was for 2016 (Photochem. Photobiol. Sci., 2017, 16, 107-145). The present 2017 Update Report assesses some of the highlights and new insights about the interactive nature of the direct and indirect effects of UV radiation, atmospheric processes, and climate change. A full 2018 Quadrennial Assessment, will be made available in 2018/2019.

Solar ultraviolet radiation and ozone depletion-driven climate change: effects on terrestrial ecosystems.

In this assessment we summarise advances in our knowledge of how UV-B radiation (280-315 nm), together with other climate change factors, influence terrestrial organisms and ecosystems. We identify key uncertainties and knowledge gaps that limit our ability to fully evaluate the interactive effects of ozone depletion and climate change on these systems. We also evaluate the biological consequences of the way in which stratospheric ozone depletion has contributed to climate change in the Southern Hemisphere. Since the last assessment, several new findings or insights have emerged or been strengthened. These include: (1) the increasing recognition that UV-B radiation has specific regulatory roles in plant growth and development that in turn can have beneficial consequences for plant productivity via effects on plant hardiness, enhanced plant resistance to herbivores and pathogens, and improved quality of agricultural products with subsequent implications for food security; (2) UV-B radiation together with UV-A (315-400 nm) and visible (400-700 nm) radiation are significant drivers of decomposition of plant litter in globally important arid and semi-arid ecosystems, such as grasslands and deserts. This occurs through the process of photodegradation, which has implications for nutrient cycling and carbon storage, although considerable uncertainty exists in quantifying its regional and global biogeochemical significance; (3) UV radiation can contribute to climate change via its stimulation of volatile organic compounds from plants, plant litter and soils, although the magnitude, rates and spatial patterns of these emissions remain highly uncertain at present. UV-induced release of carbon from plant litter and soils may also contribute to global warming; and (4) depletion of ozone in the Southern Hemisphere modifies climate directly via effects on seasonal weather patterns (precipitation and wind) and these in turn have been linked to changes in the growth of plants across the Southern Hemisphere. Such research has broadened our understanding of the linkages that exist between the effects of ozone depletion, UV-B radiation and climate change on terrestrial ecosystems.

Acclimation to UV-B radiation and visible light in Lactuca sativa involves up-regulation of photosynthetic performance and orchestration of metabolome-wide responses.

UV-B radiation is often viewed as a source of stress for higher plants. In particular, photosynthetic function has been described as a common target for UV-B impairment; yet as our understanding of UV-B photomorphogenesis increases, there are opportunities to expand the emerging paradigm of regulatory UV response. Lactuca sativa is an important dietary crop species and is often subjected to rapid sunlight exposure at field transfer. Acclimation to UV-B and visible light conditions in L. sativa was dissected using gas exchange and chlorophyll fluorescence measurements, in addition to non-destructive assessments of UV epidermal shielding (SUV ). After UV-B treatment, seedlings were subjected to wide-range metabolomic analysis using liquid chromatography hybrid quadrupole time-of-flight high-resolution mass spectrometry (LC-QTOF-HRMS). During the acclimation period, net photosynthetic rate increased in UV-treated plants, epidermal UV shielding increased in both subsets of plants transferred to the acclimatory conditions (UV+/UV- plants) and Fv /Fm declined slightly in UV+/UV- plants. Metabolomic analysis revealed that a key group of secondary compounds was up-regulated by higher light conditions, yet several of these compounds were elevated further by UV-B radiation. In conclusion, acclimation to UV-B radiation involves co-protection from the effects of visible light, and responses to UV-B radiation at a photosynthetic level may not be consistently viewed as damaging to plant development.

Blast flagging with the UniCel DxH 800 Coulter Cellular Analysis System.

We recently conducted a series of evaluations of the new UniCel DxH 800 Coulter Cellular Analysis System at Barnes-Jewish Hospital in St. Louis, Missouri. This report addresses issues relating to the flagging performance of the DxH 800, especially as it relates to the detection of blast cells. The DxH 800 was designed with major performance and hardware enhancements over the previous LH series analyzer. Capturing 29 individual measurements per cell analyzed, the system provides improved sensitivity and specificity, which means more reliable assessment of abnormal cell populations. We undertook these particular studies to assess these enhancements and to evaluate the analytical performance of the DxH 800's automated white blood cell differential and flagging of abnormal blood samples. Our studies placed specific emphases on the detection of blast cells. The Initial evaluation of the ability of the DxH 800 to flag blast cells was remarkable. We ran 95 samples containing > or =1% blasts on both the Beckman Coulter LH 750 and DxH 800 instruments. Whereas the LH 750 had a 6.4% false-negative rate, the DxH 800 had a 0.0% false-negative rate. We then conducted an extensive study of 435 blast-positive samples on the LH 750, 302 of which were analyzed on the DxH 800 and 94 of which were analyzed on Siemens' ADVIA 2120 Hematology System. With a 0.3% false-negative rate, the DxH 800 outperformed the LH 750, which had a 9.6% false-negative rate. In a previous study of 311 random patient samples, the overall success rate of the DxH 800 in detecting abnormal samples in a mixed population of samples resulted in fewer false negatives (3 versus 6) and significantly fewer false positives (60 versus 152) than the LH 750. The lower rate of false positives for the DxH 800 dramatically reduced the number of unnecessary smear reviews that otherwise would have to be run on the LH 750. The DxH 800 has demonstrated that it is capable of reducing the number of unnecessary differentials performed, while performing better at detecting samples with abnormalities, particularly when blast cells are present.

The international consensus group for hematology review: suggested criteria for action following automated CBC and WBC differential analysis.

In the half century since the first use of automated analyzers, manual techniques, especially microscopic examination of a stained blood film, have complemented analyzer results to provide a comprehensive hematology report on a patient's blood sample. Over the years, as the capabilities and performance of automated analyzers have improved, the respective roles of the automated analyzer and the complementary procedures have changed. Manual action (most commonly smear review) following automated analyzer results is usually triggered by determining whether the results trigger one of a series of criteria for review of results. There is little uniformity among different laboratories on criteria for action. Recognizing the long-standing need for generally accepted guidelines ("rules") which could be applied to criteria for review of CBC and differential results from automated hematology analyzers, Dr. Berend Houwen invited 20 experts to a meeting in the Spring of 2002 to discuss the issues and determine the most appropriate criteria. At this meeting, 83 rules were developed by consensus agreement. These rules were then tested in 15 laboratories on a total of 13,298 blood samples. After a detailed analysis of the data, the rules were refined and consolidated to produce 41 rules that are presented here. They include rules for first-time samples as well as delta rules for repeat samples within 72 hours from a patient. It is hoped that these rules will be useful to a large number of hematology laboratories worldwide. To facilitate validating these rules in individual laboratories before implementation in routine operation for patient samples, a suggested protocol is attached to this paper.

Soil moisture redistribution as a mechanism of facilitation in savanna tree-shrub clusters.

Plant-soil water relations were examined in the context of a selective removal study conducted in tree-shrub communities occupying different but contiguous soil types (small discrete clusters on shallow, duplex soils versus larger, extensive groves on deep, sandy soils) in a subtropical savanna parkland. We (1) tested for the occurrence of soil moisture redistribution by hydraulic lift (HL), (2) determined the influence of edaphic factors on HL, and (3) evaluated the significance of HL for overstory tree-understory shrub interactions. Diel cycling and nocturnal increases in soil water potential (Psisoil), characteristic signatures of HL, occurred intermittently throughout an annual growth cycle in both communities over a range of moisture levels (Psisoil=-0.5 to -6.0 MPa) but only when soils were distinctly stratified with depth (dry surface/wet deep soil layers). The magnitude of mean (+/-SE) diel fluctuations in Psisoil (0.19+/-0.01 MPa) did not differ on the two community types, though HL occurred more frequently in groves (deep soils) than clusters (shallow soils). Selective removal of either Prosopis glandulosa overstory or mixed-species shrub understory reduced the frequency of HL, indicating that Prosopis and at least one other woody species was conducting HL. For Zanthoxylum fagara, a shallow-rooted understory shrub, Prosopis removal from clusters decreased leaf water potential (Psileaf) and net CO2 exchange (A) during periods of HL. In contrast, overstory removal had neutral to positive effects on more deeply-rooted shrub species (Berberis trifoliolata and Condalia hookeri). Removal of the shrub understory in groves increased A in the overstory Prosopis. Results indicate the following: (a) HL is common but temporally dynamic in these savanna tree-shrub communities; (b) edaphic factors influencing the degree of overstory/understory development, rooting patterns and soil moisture distribution influence HL; (c) net interactions between overstory and understory elements in these woody patches can be positive, negative and neutral over an annual cycle, and (d) Prosopis-mediated HL is an important mechanism of faciliation for some, but not all, understory shrubs.

Comparison of performance characteristics between first- and third-generation hematology systems.

In 1996, Barnes-Jewish Hospital introduced the first fully robotic hematology system in North America. This first-generation Coulter/IDS robotic automated system consisted of a series of transport lanes, inlet and outlet stations, 2 robotic arms, and an on-line slide maker/strainer. The success of the system and its exceptional performance was detailed in an article published in 1998. In 2004, our laboratory replaced this system with a new third-generation robotics system, the LH 1502 from Beckman Coulter, Inc. The new system consists of 2 LH 755 workcells (LH 750 plus slide maker/stainer), an inlet/outlet unit, and a stock-yard. The system has been interfaced to our laboratory computer system (Cerner Millieum) by customized software that allows auto-verification and testing rules to be applied to individual samples. Since its implementation in January 2005, we have monitored its performance characteristics relative to the previous first generation system. We report here on our findings through June 2005. We compared and contrasted the two systems with respects to the following parameters: (1) sample handling; (2) reduction in staff exposure to hazardous materials; (3) stat and routine turnaround times; (4) productivity; (5) reduction in backup testing; (6) operating costs; (7) payback; and (8) reduction in FTEs. We found that manual sample handling was virtually identical between the two systems. The LH 1502 holds a slight edge over our older system with respect to staff exposure mainly due to further reduction in manual backup testing. Stat TAT after introduction of the LH 1502 showed an additional 44% drop from 50 to 28 minutes, while the routine TAT was reduced by 23%, down from 61 to 47 minutes. Gains achieved in productivity after installation of the first-generation system were maintained with the LH 1502, with significant extra volume capacity yet to be utilized. The space required for operating the system was also reduced by nearly 49%. There was a 20.3% reduction in backup blood smears that required manual review (due primarily to the lower flagging rates for the LH versus STKS). The improvements in overall operating costs (> dollar 195,000) were also maintained. Payback was not considered since this was a replacement of our previous system, which had already eliminated more than 6 FTEs.

An evaluation of the utility of performing body fluid counts on the coulter LH 750.

Performing a manual body fluid count is a tedious, time-consuming, and frequently imprecise process for any clinical laboratory. The ability to perform many of these counts with an automated hematology analyzer has the real potential of making a major impact on laboratory precision and productivity. The manual chamber count is fraught with many variables and is often very technologist/technique dependent, often leading to inaccuracies in test results. Our laboratory undertook a series of studies designed to evaluate the capability of the Coulter LH 750 hematology analyzer to supplement our current manual method in the performance of body fluid analysis. First, we established the performance of our current manual counting method, the gold standard against which LH 750 performance would be judged. We looked at the precision of manual cell counting by having 4 technologists perform manual counts on each of 35 spinal, synovial, peritoneal, and other fluids with white blood cell (WBC) and/or red blood cell (RBC) counts of greater than 0.3 x 10(9) /L and 0.03 x 10(12) /L, respectively. Our results support earlier reports that the variability in counts among technologists using the manual chamber cell count methods is often very significant. After each sample was manually counted, it was analyzed on the Coulter LH 750, and the results were compared with those of our current manual method. Results showed good correlation between the manual and LH 750 methods. Next, we conducted a series of separate tests to evaluate the stability of different cellular elements (WBCs and RBCs) in each of these body fluid types. The study consisted of 2 sets of 4--3-mL samples of each fluid type--which were analyzed on the LH 750 immediately on receipt and after 1 hour, 4 hours, 8 hours, 16 hours, and 24 hours. The findings suggested varying degrees of stability that were dependent on fluid type and initial cell concentration. Finally, we looked at whether it is necessary to perform background counts before analyzing each body fluid sample and the impact of automating body fluid counts on our workload.

Effect of heparin on whole blood activated partial thromboplastin time using a portable, whole blood coagulation monitor.

OBJECTIVES: To evaluate the responsiveness of whole blood activated partial thromboplastin time (aPTT) to varying heparin doses in vitro and to examine the ex vivo relationship of whole blood aPTT to plasma heparin concentration. DESIGN: Prospective, controlled laboratory study. SETTING: Surgical suites and laboratory at a tertiary center. PATIENTS: Surgical patients and volunteers at a tertiary center were eligible for inclusion in this study. In vitro evaluation was performed using specimens obtained from each of five, healthy volunteers. Ex vivo evaluation was performed using specimens obtained from 30 cardiac surgical patients before and after systemic administration of heparin for extracorporeal circulation. INTERVENTIONS: Blood specimens were obtained from volunteers and added to syringes containing varying amounts of unfractionated porcine heparin for in vitro evaluation. For ex vivo evaluation, blood specimens were obtained from patients before and after systemic administration of 20 U/kg of heparin. MEASUREMENTS AND MAIN RESULTS: For the in vitro evaluation, specimens were divided into two aliquots after mixing with varying amounts of unfractionated porcine heparin. One aliquot was used to measure whole blood aPTT using a whole blood coagulation monitor immediately after blood collection and 3 mins later, and a second aliquot was used to determine plasma aPTT with a conventional, laboratory-based assay. Linear regression analysis demonstrated a high correlation (r = .94; r2 = .88) between aPTT assay systems and bias analysis demonstrated a mean aPTT measurement difference of 1.6 secs with +/- 2 SD limits of -15 to +18.2 secs. As indicated by comparable regression slopes, the in vitro aPTT responsiveness to increasing heparin concentration was similar with the two assay systems among individual subjects. Whole blood aPTT measurements after 3 mins of blood specimen storage were similar to immediate measurements. For ex vivo evaluation, blood specimens obtained from patients before and after systemic administration of heparin were divided into two aliquots. One aliquot was used to measure whole blood aPTT in duplicate and a second aliquot was used to measure plasma heparin concentration with an antifactor X active chromogenic assay. A high correlation (r = .89; r2 = .79) between whole blood aPTT and plasma heparin concentration was observed. CONCLUSIONS: Heparin responsiveness of whole blood aPTT, measured with a portable whole blood coagulation monitor, is similar to that of conventional laboratory aPTT over a clinically relevant range of heparin concentrations in vitro and ex vivo. On-site whole blood aPTT measurements should be useful in clinical situations requiring rapid aPTT results.

Standards of care in reproductive health services.

Standards of care for all medical services are designed by and for professionals and generally follow medical professional society guidelines. Most managed care organizations rely on professional medical standards of practice, which provide broad guidelines to providers. Family planning agencies, on the other hand, generally follow Title X program guidelines, which provide specific standards of care. The Title X guidelines include detailed instructions about service delivery and program content. The differences between these two sets of standards result in a wide variation in practice guidelines across the spectrum of health care providers. From the patient perspective, evaluation of care is generally not related to professional standards, but instead focuses on quality measures related to access and interpersonal aspects of care. The member satisfaction surveys developed by some managed care organizations now have a large enough sample size to provide meaningful measures of patient satisfaction at the individual provider level. A uniform set of practice guidelines is needed for family planning services that incorporates the strengths of all three approaches and that link performance to generally accepted practice guidelines.

PIP: There are three standards of care generally being applied to medical professionals in the US. First, there are standards of care for all medical services designed by and for professionals, which generally follow medical professional society guidelines. Most managed care organizations rely upon these professional medical standards of practice, which provide broad guidelines to providers. Family planning agencies, however, tend to follow Title X program guidelines providing specific standards of care. These latter guidelines include detailed instructions about service delivery and program content. Differences between these two sets of standards result in a wide variation in practice guidelines across the spectrum of health care providers. The third standard of care derives from the patient's perspective. Patients tend to evaluate care not with regard to professional standards, but instead to access and the interpersonal aspects of care. Member satisfaction surveys developed by some managed care organizations now have a large enough sample size to provide meaningful measures of patient satisfaction at the individual provider level. A uniform set of practice guidelines is therefore needed for family planning services which incorporates the strengths of these three approaches and which links performance to generally accepted practice guidelines.

Forging partnerships that work: a strategy for near-patient testing.

Near-patient testing systems, which bring innovative technologies to the site of patient care, also offer management challenges to effectively integrate clinical and laboratory services. A two-tiered committee structure--composed of an umbrella "advisory" organization supported by several subcommittees operating as the "working arms" of the program--offers a viable strategy to address issues involved in implementing and monitoring near-patient testing systems.

Plant competition for light analyzed with a multispecies canopy model : III. Influence of canopy structure in mixtures and monocultures of wheat and wild oat.

A multispecies canopy photosynthesis simulation model was used to examine the importance of canopy structure in influencing light interception and carbon gain in mixed and pure stands of wheat (Triticum aestivum L.) and wild oat (Avena fatua L.), a common weedy competitor of wheat. In the mixtures, the fraction of the simulated canopy photosynthesis contributed by wheat was found to decline during the growing season and this decline was closely related to reductions in the amount of leaf area in upper canopy layers. For both species in mixture and in monoculture, simulated photosynthesis was greatest in the middle or upper-middle canopy layers and sensitivity analyses revealed that canopy photosynthesis was most sensitive to changes in leaf area and leaf inclination in these layers. Changes in LAI and leaf inclination affected canopy carbon gain differently for mixtures and monocultures, but the responses were not the same for the two species. Results from simulations where the structural characteristics of the two species were substituted indicated that species differences in leaf inclination, sheath area and the fraction of leaf area alive were of minor consequence compared with the differences in total leaf area in influencing relative canopy carbon gain in mixtures. Competition for light in these species mixtures appears to be influenced most by differences in the positioning of leaf area in upper canopy layers which determines, to a great extent, the amount of light intercepted.

Plant competition for light analyzed with a multispecies canopy model : I. Model development and influence of enhanced UV-B conditions on photosynthesis in mixed wheat and wild oat canopies.

Competition for light among species in a mixed canopy can be assessed quantitatively by a simulation model which evaluates the importance of different morphological and photosynthetic characteristics of each species. A model was developed that simulates how the foliage of all species attenuate radiation in the canopy and how much radiation is received by foliage of each species. The model can account for different kinds of foliage (leaf blades, stems, etc.) for each species. The photosynthesis and transpiration for sunlit and shaded foliage of each species is also computed for different layers in the canopy. The model is an extension of previously described single-species canopy photosynthesis simulation models. Model predictions of the fraction of foliage sunlit and interception of light by sunlit and shaded foliage for monoculture and mixed canopies of wheat (Triticum aestivum) and wild oat (Avena fatua) in the field compared very well with measured values. The model was used to calculate light interception and canopy photosynthesis for both species of wheat/wild oat mixtures grown under normal solar and enhanced ultraviolet-B (290-320 nm) radiation (UV-B) in a glasshouse experiment with no root competition. In these experiments, measurements showed that the mixtures receiving enhanced UV-B radiation had a greater proportion of the total foliage area composed of wheat compared to mixtures in the control treatments. The difference in species foliage area and its position in the canopy resulted in a calculated increase in the portion of total canopy radiation interception and photosynthesis by wheat. This, in turn, is consistent with greater canopy biomass of wheat reported in canopies irradiated with supplemental UV-B.

Plant competition for light analyzed with a multispecies canopy model : II. Influence of photosynthetic characteristics on mixtures of wheat and wild oat.

The importance of photosynthetic characteristics such as quantum efficiency or carboxylation efficiency for carbon gain of plants competing for light in dense stands is dependent on several environmental factors and structural features of the canopy. A quantitative analysis of photosynthesis of competing plants in mixed stands of wheat and wild oat (Avena fatua L.), a common weed of wheat, involved measuring photosynthetic parameters of individual leaves at different heights in the canopy throughout the growing season. This information combined with detailed assessments of canopy structure was used with a multispecies canopy model to evaluate the importance of different photosynthetic characteristics for carbon gain in this canopy environment. Independent photosynthesis data sets were used to validate predictions of the model. Carboxylation efficiency (CE) and CO2-and light-saturated photosynthetic capacity (AML) were highly correlated and decreased with depth in the canopy for both species. Quantum efficiency (α) did not tend to decrease with depth in the canopy. Sensitivity analyses with the model for whole-plant carbon gain of each species over entire day periods were conducted. These showed that changes in CE and AML had an influence similar to that of changes in α on carbon gain for both species. This was not necessarily expected from single-leaf photosynthetic behavior in response to changes in CE, AML and α. The influence of α is more pronounced in the lower, more shaded portions of the canopy than are changes in CE and AML. Appreciable differences between the species were apparent for carbon gain under different weather conditions. The differences between the species in carbon gain when in competition for light were associated more with structural features rather than with photosynthetic characteristics.