Towards a global-scale soil climate mitigation strategy.

Sustainable soil carbon sequestration practices need to be rapidly scaled up and implemented to contribute to climate change mitigation. We highlight that the major potential for carbon sequestration is in cropland soils, especially those with large yield gaps and/or large historic soil organic carbon losses. The implementation of soil carbon sequestration measures requires a diverse set of options, each adapted to local soil conditions and management opportunities, and accounting for site-specific trade-offs. We propose the establishment of a soil information system containing localised information on soil group, degradation status, crop yield gap, and the associated carbon-sequestration potentials, as well as the provision of incentives and policies to translate management options into region- and soil-specific practices.

Leaf age as a risk factor in contamination of lettuce with Escherichia coli O157:H7 and Salmonella enterica.

Outbreaks of Escherichia coli O157:H7 infections have been linked increasingly to leafy greens, particularly to lettuce. We present here the first evidence that this enteric pathogen can multiply on the leaves of romaine lettuce plants. The increases in population size of E. coli O157:H7 in the phyllosphere of young lettuce plants ranged from 16- to 100-fold under conditions of warm temperature and the presence of free water on the leaves and varied significantly with leaf age. The population size was consistently ca. 10-fold higher on the young (inner) leaves than on the middle leaves. The growth rates of Salmonella enterica and of the natural bacterial microflora were similarly leaf age dependent. Both enteric pathogens also achieved higher population sizes on young leaves than on middle leaves harvested from mature lettuce heads, suggesting that leaf age affects preharvest as well as postharvest colonization. Elemental analysis of the exudates collected from the surfaces of leaves of different ages revealed that young-leaf exudates were 2.9 and 1.5 times richer in total nitrogen and carbon, respectively, than middle-leaf exudates. This trend mirrored the nitrogen and carbon content of the leaf tissue. Application of ammonium nitrate, but not glucose, to middle leaves enhanced the growth of E. coli O157:H7 significantly, suggesting that low nitrogen limits its growth on these leaves. Our results indicate that leaf age and nitrogen content contribute to shaping the bacterial communities of preharvest and postharvest lettuce and that young lettuce leaves may be associated with a greater risk of contamination with E. coli O157:H7.

Embryology and evolution 1920-1960: worlds apart?

During the early part of the 20th century most embryologists were skeptical about the significance of Mendelian genetics to embryological development. A few embryologists began to study the developmental effects of Mendelian genes around 1940. Such work was a necessary step on the path to modern developmental biology. It occurred during the time when the Evolutionary Synthesis was integrating Mendelian and population genetics into a unified evolutionary theory. Why did the first embryological geneticists begin their study at that particular time? One possible explanation is that developmental genetics was a potential avenue of alliance between embryology and evolutionary biology, two fields that had been separated since the 1890s. To assess this possible motive it is necessary to explore the methodological contrasts that obtained between embryology and both Mendelian-chromosomal genetics and neo-Darwinian evolutionary theory. Some of these contrasts persist to the present day.

Boxelder water sources and physiology at perennial and ephemeral stream sites in Arizona.

To assess the influence of stream water on leaf gas exchange and water potential in different sized boxelder trees (Acer negundo L.), we compared these characteristics in trees growing beside a perennial stream and a nearby ephemeral stream in a montane-riparian forest in northern Arizona. Patterns of tree water use were quantified by stable isotope analysis (delta(18)O). Physiological characteristics were similar for large and small trees. Similarity between sites in predawn and daytime water potentials and xylem delta(18)O indicated that stream water was not a physiologically important water source. Seasonal and site variations in light-saturated net photosynthetic rate were significantly related to leaf-to-air vapor pressure deficit (r = -0.691) and foliar nitrogen concentration (r = 0.388). Although deep water was the dominant water source, surface soil water was utilized following precipitation, especially by small trees. We conclude that net carbon gain and severity of water stress are only weakly coupled to stream water availability.

ECT after cerebral aneurysm repair.

Cerebral aneurysms or recent surgical repair of aneurysms are relative contraindications for electroconvulsive therapy (ECT), yet the literature contains at least three cases in which ECT resulted in no known CNS complications. The following case describes a course of ECT in a patient 4 months after he had undergone surgical repair of a posterior cerebral artery aneurysm. Blood pressure control in patients with CNS aneurysms and repaired aneurysms can be achieved through choice of anesthetic agent, and intravenous antihypertensives, thus reducing the risk of cerebrovascular complications.

Response of sugar maple to multiple year exposures to ozone and simulated acidic precipitation.

Potted sugar maple seedlings were exposed to ozone and acidic precipitation in open-top chambers for three consecutive growing seasons. Periodic measurements of photosynthesis, dark respiration, through-fall and soil solution chemistry, and annual measurements of the weight of plant parts were made. Experimental treatments caused few and minor effects on above- or below-ground growth of the seedlings, even after three growing seasons. There were trends for reduced photosynthesis in trees exposed to elevated concentrations of ozone and increased photosynthesis in those exposed to the lowest pH simulated rain treatment. The chemistries of soil-solutions and through-fall were not altered significantly by treatment. Although major effects were not observed, sugar maple may respond to exposures that take place over a significant part of its life cycle.

Influence of foliar N on foliar soluble sugars and starch of red spruce saplings exposed to ambient and elevated ozone.

Red spruce (Picea rubens Sarg.) trees growing at high elevation in the northeastern United States have experienced decline in recent years but seedlings have proved to be relatively tolerant of a wide range of environmental stresses in controlled studies. One possible reason for the wide tolerance to stress in seedlings is their inherently large pool of carbohydrate reserves, which is available for maintenance during and regrowth after periods of stress. We tested for the effects of foliar N and exposure to ozone on foliar carbohydrate reserves of 20-year-old naturally regenerated saplings. The trees were maintained in native soil in 360-l containers for 5 years before the experiment. The year before the experiment, trees were fertilized with N,P,K to provide a population of trees from N deficient to N sufficient. As foliar N decreased below 0.9%, length of current-year shoots and specific needle area of current-year needles declined. Foliar N concentration was correlated with foliar sugar and starch concentrations, but relationships varied with time of year. Before bud break, foliar carbohydrates and N, in general, were positively correlated, and date of bud break was delayed in N-deficient trees. During active growth, foliar soluble sugars and N were positively correlated, but starch concentrations were negatively correlated with N. By late September, neither starch nor sugar concentration was correlated with N concentration. Ozone and foliar N concentrations did not interact to change foliar carbohydrate concentrations or shoot and needle growth in this relatively short-term study.

Arabidopsis Flavonoid Mutants Are Hypersensitive to UV-B Irradiation.

Increases in the terrestrial levels of ultraviolet-B (UV-B) radiation (280 to 320 nm) due to diminished stratospheric ozone have prompted an investigation of the protective mechanisms that contribute to UV-B tolerance in plants. In response to UV-B stress, flowering plants produce a variety of UV-absorptive secondary products derived from phenylalanine. Arabidopsis mutants with defects in the synthesis of these compounds were tested for UV-B sensitivity. The transparent testa-4 (tt4) mutant, which has reduced flavonoids and normal levels of sinapate esters, is more sensitive to UV-B than the wild type when grown under high UV-B irradiance. The tt5 and tt6 mutants, which have reduced levels of UV-absorptive leaf flavonoids and the monocyclic sinapic acid ester phenolic compounds, are highly sensitive to the damaging effects of UV-B radiation. These results demonstrate that both flavonoids and other phenolic compounds play important roles in vivo in plant UV-B protection.

Effects of radiational heating at low air temperature on water balance, cold tolerance, and visible injury of red spruce foliage.

Recent studies have shown that winter needle mortality in red spruce (Picea rubens Sarg.) is increased by exposure to direct solar radiation, possibly as a result of photo-oxidative damage, accelerated winter desiccation, or reduced cold tolerance due to heating of sun-exposed needles. In an experiment at controlled subfreezing air temperatures of -10 to -20 degrees C, visible radiation was less effective than infrared radiation in producing needle desiccation and visible injury during freeze-thaw cycles. However, visible radiation produced a red-brown color in injured needles, similar to natural winter injury, whereas injured needles exposed to infrared radiation were yellow and injured needles kept in darkness were dark brown. Thus, visible radiation was necessary to produce the red-brown color of damaged needles, but not the injury itself. Needle desiccation was not strongly correlated with visible injury, but the pattern of variation in visible injury among trees and the positive correlation between electrolyte leakage and visible injury suggested that freezing damage following freeze-thaw cycles might cause the visible injury. This was confirmed by a second experiment that showed loss of cold hardiness in needles thawed by radiational heating for six consecutive days. Even with a constant nighttime temperature of -10 degrees C, six days of radiational heating of needles to above freezing caused a small (2.8 degrees C) mean decrease in needle cold tolerance, as measured by electrolyte leakage. Continuous darkness at -10 degrees C for six days resulted in an estimated 5.6 degrees C mean increase in needle cold tolerance. Freezing injury stimulated desiccation: cooling at 4 degrees C h(-1) to -43 or -48 degrees C increased the dehydration rate of isolated shoots by a factor of two to three during the first day after thawing. Within three days at 15 to 22 degrees C and 50% relative humidity, the mean water content of these shoots fell to 60% or lower, compared to 90% or greater for unfrozen controls or shoots subject to less severe freezing stress. In some but not all severely freeze-stressed shoots, accelerated needle desiccation and abscission were accompanied by a red-brown color typical of red spruce winter needle injury. We conclude that severe winter desiccation in red spruce may often be due to prior freezing injury, increased as a result of exposure to direct solar radiation. Furthermore, freezing injury in red spruce may sometimes cause desiccation and abscission of green needles.

Uptake of [3H]serotonin and [3H]glutamate by primary astrocyte cultures. II. Differences in cultures prepared from different brain regions.

Regional astrocyte cultures were derived by dissecting six regions; brain stem, cerebellum, mesencephalon, basal ganglia plus diencephalon, cerebral cortex, and hippocampus, from 3 to 4-day-old neonatal rat brains. Glial fibrillary acidic protein (GFAP) immunocytochemistry was used to confirm the astrocyte composition of the cultures. The percentage of GFAP (+) cells between regions varied from 75% to 100%. Once confluent these cultures were incubated with radiolabeled serotonin or glutamate for uptake and autoradiographic studies. For the different brain regions Na(+)-dependent, [3H] L-glutamate, and fluoxetine-sensitive [3H] 5-HT uptake varied markedly. The relative order of uptake for [3H] 5-HT was MS (mesencephalon) greater than CC (cerebral cortex) greater than BG + DI (basal ganglia + diencephalon) greater than HP (hippocampus) greater than BS (brain stem) greater than CB (cerebellum). For [3H] L-glutamate the order was HP greater than CC greater than BG + DI greater than MS = BS greater than CB. For [3H] 5-HT this essentially corresponds to the reported order of binding in situ of the [3H] 5-HT-specific uptake ligand [3H] citalopram. For [3H] L-glutamate regional variation of the uptake for the different cultures corresponds to the regional uptake reported for different regions of rat brain. Double-label studies with GFAP and radiolabeled neurotransmitters were also used to study uptake into GFAP(+) astrocytes by autoradiography. Flat GFAP cells with or without processes comprised 65-98% of the cultures and represented most of the uptake. The percentage of all GFAP(+) cells that were positive for uptake of ARG varied from 50% to 90% and also showed differences in grain density both intra- and inter-regionally. These differences in transmitter uptake by GFAP(+) astrocytes in primary culture, which are dependent on the region of origin and correspond to regional differences in situ, suggest that such uptake in vitro may reflect uptake by astrocytes in vivo. Implied in this is that uptake by astrocytes represents a significant component of serotonin uptake in vivo.

Uptake of [3H]serotonin and [3H]glutamate by primary astrocyte cultures. I. Effects of different sera and time in culture.

Na(+)-dependent, fluoxetine-sensitive high-affinity uptake of serotonin and Na(+)-dependent uptake of glutamate were studied in primary astrocyte cultures from 1-day-old rat neocortex. This uptake was independent of time in culture from 1 to 6 weeks. High-affinity serotonin uptake was decreased when cells were grown in horse serum as compared to fetal bovine serum and was almost absent when cells were grown in chemically defined medium. In contrast, glutamate uptake was unaffected by the composition of the medium in which the cultures were grown. The serum effect on serotonin uptake was not due to the greater level of serotonin in the fetal bovine serum and was only reversed by a change of serum over a time period of days.

Seasonal changes in antioxidants in red spruce (Picea rubens Sarg.) from three field sites in the northeastern United States.

Changes in antioxidant levels were investigated in red spruce (Picea rubens Sarg.) from three field sites in the northeastern United States. Whiteface Mountain, NY at an elevation of 1090 m, represents a red spruce population in decline, while Millinocket and Howland, Maine are at 518 and 105 m above sea level, respectively, and have red spruce stands that show no symptoms of decline. The Millinocket site with saplings that are 15-20 yr old was compared with the Howland site with 60-yr-old trees to test the effect of age on antioxidant levels. The Howland site was compared with the Whiteface Mountain site, which has trees more than 100 yr old, to test the effects of air quality and elevation. Foliage developed in 1987 (87 needles) and in 1988 (88 needles) was sampled from May to November and from July to November, 1988, respectively. Quadratic polynomial and linear regressions were used to model the relationships through time of each variable measured. Regression coefficients were obtained by one-way analysis of variance. The means for total glutathione and oxidized glutathione were higher at Whiteface Mountain in 87 needles, and needles of both age classes sampled in November had significantly higher oxidized glutathione at Whiteface Mountain compared to those at Howland. No significant difference was observed in the mean ascorbate content of either needle class at all the three sites. The activity of superoxide dismutase declined with time in 87 needles at Whiteface Mountain and the mean activity was lower at Whiteface Mountain than at Howland. The effects of ozone concentration, site elevation and other environmental factors on seasonal changes in antioxidant levels and superoxide dismutase activity are discussed.

Perineuronal glial responses after axotomy of central and peripheral axons. A comparison.

In each of 6 mature rats, unilateral rubrospinal tractotomy and hypoglossal neurectomy were done at one operative sitting. Paired operated animals were killed by formaldehyde and ethanol-acetic acid perfusion 3, 14 and 28 days later. One pair of unoperated control rats was perfused also. All rats were injected i.p. with [3H]thymidine 24 h before death. Immunohistochemical methods were applied to paraffin sections to visualize glial fibrillary acidic protein (GFAP) and transferrin in astrocytes and oligodendroglia, respectively. Microglia were demonstrated by both lectin-binding and histoautoradiographic methods. Neuroglia and nerve cells were counted in hematoxylin-eosin and azure B stains. Cell areas and the RNA concentration of hypoglossal neurons were determined by the Zeiss Image Scan System. Three days after hypoglossal neurectomy, increased astroglial staining (GFAP) and microglial hyperplasia (radiolabeled nuclei) were evident in the ipsilateral hypoglossal nucleus (HN). Microglial hyperplasia waned rapidly after 3 days and microglial numbers decreased. However, astroglial hypertrophy, demonstrable by GFAP staining, persisted 4 weeks postoperatively when astroglial processes were concentrated in a perineuronal position. Oligodendroglia were unaltered. In contrast to the HN, the axotomized red nucleus (RN) contained few radiolabeled microglia while a slight increase in GFAP-positive astroglial processes was seen only in animals killed 28 days postoperatively. Again, oligodendroglia were unchanged. In neither HN nor RN did axotomy cause nerve cell death. Although axotomized rubral neurons atrophy and become depleted of RNA, no statistically significant changes in somal size and RNA content of axotomized hypoglossal neurons occurred. The apparent absence of a neuroglial response of putatively supportive nature in the environs of axotomized rubral neurons may relate to their failure to regenerate. The neuroglial response likely is originated by the axotomized neuron and its absence may be an innate defect in the reaction of intrinsic neurons to axonic severance. Somas of axotomized peripherally projecting nerve cells appear to have the capacity to summon a neuroglial response.

Seasonal changes in antioxidants in red spruce as affected by ozone.

Two-year-old red spruce (Picea rubens Sarg.) seedlings were exposed to various levels of ozone, from 0.4 to 3 times ambient levels, in open-top chambers in Ithaca, NY, USA. Exposures, which varied with changes in day length, were from 30 May to 16 December 1987 and 1 June to 1 December, 1988. During the second exposure period, ascorbic acid, total and oxidized glutathione, α-tocopherol, and superoxide dismutase were measured in current and previous year's needles at monthly intervals from May to July, and at bi-weekly intervals from September to December. Orthogonalized polynomials were used to model the response through time of each variable measured. A one-way analysis of variance model was fitted to every regression coefficient in each polynomial model to test for ozone effects on seasonal patterns of antioxidant levels. Ozone influenced seasonal changes in total glutathione, the oxidized/total glutathione ratio, and α-tocopherol in previous years's needles and α-tocopherol and superoxide dismutase in current year's needles. Averaged over the whole growing season, the oxidized/total glutathione ratio and superoxide dismutase showed an ozone treatment effect in both age classes. Mean total glutathione content increased in previous year's needles, but was not influenced by ozone in current year's needles. Mean oxidized glutathione content was higher with ozone exposure in current year's needles, but not in previous year's needles. The role of antioxidants in cold hardiness and ozone detoxification is discussed.

Evaluation of the effects of ozone and acidic precipitation, alone and in combination, on the photosynthesis, nutrition, and growth of red spruce and sugar maple.

Substantial and widespread morbidity and mortality of red spruce have been observed in high elevation forests of the northeast under circumstances indicative of a stress-related disease. Whether red spruce at lower elevations are experiencing a more subtle loss of growth and vigor is uncertain. In addition, sugar maple has exhibited decline of varying extent and intensity for several decades. Forests in the northeast are exposed to two air pollutants, ozone (O3) and acidic precipitation, that are widespread in occurrence and have the potential, both individually and collectively, to produce impacts to forest trees. the roles, if any, of these two stress agents in the tree declines found in the northeast are not known.In 1986, a five-year study was initiated to evaluate the effects of O3 and acidic precipitation on red spruce and sugar maple. The trees will be exposed to controlled levels of O3 and acidic precipitation in the field using open-top chambers. The experiment is a 4×3 factorial conducted in split plots with O3 treatments as whole plots and simulated rain treatments comprising the split plots. Broadly stated, the research will evaluate the effects of the pollutants on the processes, fluxes, and pools associated with carbon, water, and nutrients in the soil/tree/atmosphere system. These evaluations will be conducted on a systems level and will be integrated through the development of mechanistic simulation models.Assessment of the effects of the treatments on carbon fixation by photosynthesis, the loss of carbon through respiration, and the allocation of carbon in growth will be a central focus of the study. Whole-tree cuvettes will be used to assess net photosynthesis, respiration, transpiration, and stomatal conductance.Considerable emphasis will be placed on determining the influences of the treatments on the biogeochemistry of the system. These studies will focus on the leaching of nutrients from the tree canopy, the mobilization and loss of nutrients from the soil, soil solution chemistry, and the alteration of tree nutrition by the input of additional nitrogen in precipitation.Statistical and simulation modeling will be used to assess and describe the effects of the treatments. The modeling approaches are different in technique, but complementary. Statistical models will be used to describe the responses of growth and physiological variables to the ozone and acidic precipitation treatments. Simulation models will be built to describe the relationships between photosynthesis, respiration, nutrition, and water use, how these processes are affected by the treatments, and how these effects ultimately result in altered growth. The simulation models will initially provide a framework for the formulation of hypotheses regarding the interrelationships of plant components and processes and how they are affected by the treatments.

A comparison of soil climate and biological activity along an elevation gradient in the eastern Mojave Desert.

Soil temperature, moisture, and CO2 were monitored at four sites along an elevation transect in the eastern Mojave Desert from January to October, 1987. Climate appeared to be the major factor controlling CO2 partial pressures, primarily through its influence of rates of biological reactions, vegetation densities, and organic matter production. With increasing elevation, and increasing actual evapotranspiration, the organic C, plant density, and the CO2 content of the soils increased. Between January and May, soil CO2 concentrations at a given site were closely related to variations in soil temperature. In July and October, temperatures had little effect on CO2, presumably due to low soil moisture levels. Up to 75% of litter placed in the field in March was lost by October whereas, for the 3 lower elevations, less than 10% of the litter placed in the field in April was lost through decomposition processes.

Ambient levels of ozone reduce net photosynthesis in tree and crop species.

Experiments were conducted to measure the photosynthetic response of three crop and four tree species to realistic concentrations of ozone and (for tree species only) simulated acidic rain. The ozone concentrations were representative of those found in clean ambient air, in mildly to moderately polluted air such as occurs in much of the United States during the summer, and in more heavily polluted air. However, the highest concentrations of ozone used were lower than those found regularly in the Los Angeles area. The mean pH of the simulated acid rain treatments ranged from more alkaline to much more acidic than the mean pH of precipitation in the United States. Exposure to any increase in ozone reduced net photosynthesis in all species tested. In contrast, acidic rain had no negative effect on photosynthesis in tree species, and no interaction between ozone and acidic rain was observed. Ozone-induced reductions in photosynthesis were related to declines in growth or yield. Species with higher stomatal conductances and thus higher potential for pollutant uptake exhibited greater negative responses to similar ozone treatments. Since exposure to ozone concentrations typical of levels of the pollutant observed in the eastern half of the United States reduced the rates of net photosynthesis of all species tested, reductions in net photosynthesis may be occurring over much of the eastern United States.

Effects of SO(2) on Stomatal Metabolism in Pisum sativum L.

Pea (Pisum sativum L. cv ;Little Marvel') plants were exposed to SO(2) for short term (3 hours) and long term (2 days) at 0.2 and at 0.5 microliter per liter (ppm) levels. The effect of this treatment on the activity of phosphoenolpyruvate carboxylase, NAD- and NADP-malate dehydrogenases, and alanine aminotransferase from epidermis and whole leaves was investigated. Short-term exposure to SO(2) at 0.2 or 0.5 ppm decreased the activity of the carboxylase and the dehydrogenases in the epidermis. In contrast, the activity of the same three enzymes increased in whole leaves with either short- or long-term exposure to SO(2). Alanine aminotransferase in epidermis or whole leaves was not much affected by short-term exposure, but the epidermal activity was decreased and whole leaf activity was increased with long-term exposure. SO(2) exposure which was initiated prior to illumination decreased the free thiol content of both epidermis and of whole leaf. Net photosynthesis was reversibly inhibited by long-term exposure to SO(2) at 0.5 ppm. No effect of 0.5 ppm SO(2) on stomatal conductance was detectable after 3 hours. Stomatal conductance appeared to decrease after longer exposure times (2 days) at 0.5 ppm.