Higher Atmospheric CO2 Levels Research Articles

The past is a guide to the future? Comparing Middle Pliocene vegetation with predicted biome distributions for the twenty-first century

During the Middle Pliocene, the Earth experienced greater global warmth compared with today, coupled with higher atmospheric CO2 concentrations. To determine the extent to which the Middle Pliocene can be used as a 'test bed' for future warming, we compare data and model-based Middle Pliocene vegetation with simulated global biome distributions for the mid- and late twenty-first century. The best agreement is found when a Middle Pliocene biome reconstruction is compared with a future scenario using 560 ppmv atmospheric CO2. In accordance with palaeobotanical data, all model simulations indicate a generally warmer and wetter climate, resulting in a northward shift of the taiga-tundra boundary and a spread of tropical savannah and woodland in Africa and Australia at the expense of deserts. Our data-model comparison reveals differences in the distribution of polar vegetation, which indicate that the high latitudes during the Middle Pliocene were still warmer than its predicted modern analogue by several degrees. However, our future scenarios do not consider multipliers associated with 'long-term' climate sensitivity. Changes in global temperature, and thus biome distributions, at higher atmospheric CO2 levels will not have reached an equilibrium state (as is the case for the Middle Pliocene) by the end of this century.

Effect of elevated CO2 and nitrogen levels on lentil growth and nodulation

Global carbon dioxide levels are rising, and could reach levels of 815 μmol mol−1 by the year 2100. Since photosynthetic rate in C3 species under the current levels of ambient CO2 is still below physiological saturation levels, it is anticipated that photosynthesis and consequently productivity for most crops should be stimulated by the higher levels of atmospheric CO2. A stronger response is expected in legumes as nitrogen is not considered as a limiting factor for growth. This study investigates the effect of elevated CO2 and different nitrogen fertilizer levels on the growth and nodulation of lentils. Syrian lentil was grown under ambient CO2 concentration of 400 μmol mol−1, and under elevated CO2 concentration of 700 μmol mol−1, at five nitrogen levels equivalent to 5, 25, 50, 75 and 100 kg N ha−1. Five harvests were conducted over the growth period and measurements of leaf area index (LAI), biomass dry weight, nodule number, and seed yield at the final harvest were recorded. The results showed that, compared to the ambient control, elevated CO2 led to a significant increase in LAI after flowering (+20–30%), biomass dry weight (+35%) and seed yield (+60%) from 1292.74 kg ha−1 to 2639.55 kg ha−1 at the lowest and highest N levels respectively. Moreover these values increased with increasing levels of nitrogen. Nodule number also increased under elevated CO2 and the highest nodule number was observed at the nitrogen level equivalent to 50 kg N ha−1 under ambient and 75 kg N ha−1 under elevated CO2. The average increase of nodule number for all treatments under elevated CO2 was +52%. Examination of total nitrogen and phosphorus concentrations in the dry matter showed that the total uptake was higher under elevated CO2 but due to the increases in biomass concentration levels were slightly lower. For all parameters, no significant interaction between CO2 and nitrogen treatment was recorded.

The Ordovician Biodiversification: revolution in the oceanic trophic chain

The Early Palaeozoic phytoplankton (acritarch) radiation paralleled a long-term increase in sea level between the Early Cambrian and the Late Ordovician. In the Late Cambrian, after the SPICE delta C-13(carb) excursion, acritarchs underwent a major change in morphological disparity and their taxonomical diversity increased to reach highest values during the Middle Ordovician (Darriwilian). This highest phytoplankton diversity of the Palaeozoic was possibly the result of palaeogeography (greatest continental dispersal) and major orogenic and volcanic activity, which provided maximum ecospace and large amounts of nutrients. With its warm climate and high atmospheric CO2 levels, the Ordovician was similar to the Cretaceous: a period when phytoplankton diversity was at its maximum during the Mesozoic. With increased phytoplankton availability in the Late Cambrian and Ordovician a radiation of zooplanktonic organisms took place at the same time as a major diversification of suspension feeders. In addition, planktotrophy originated in invertebrate larvae during the Late Cambrian-Early Ordovician. These important changes in the trophic chain can be considered as a major palaeoecological revolution (part of the rise of the Palaeozoic Evolutionary Fauna of Sepkoski). There is now sufficient evidence that this trophic chain revolution was related to the diversification of the phytoplankton, of which the organic-walled fraction is partly preserved.

炭素循環から考える新生代のグローバル気候変動

The global carbon cycle controls the climate change in the Earth's environment on a geological timescale and is mainly associated with greenhouse effects produced by atmospheric carbon dioxide (CO2) and methane (CH4). This paper reviews the relationship between the global carbon cycle and presumed climate events during the Cenozoic. The global carbon cycle is primarily regulated by the balance between weathering and metamorphism-volcanism. Moreover, the organic carbon subcycle involving oxidative weathering and burial is of secondary importance. The balance of these geochemical processes results in variations of atmospheric CO2. The past climate on a geological time scale is reconstructed by several geochemical and paleontological methods or proxies. For example, sea-surface and deep-water temperature are deduced from oxygen isotope ratio and Mg/Ca ratio of foraminiferal tests. Terrestrial atmospheric temperature is estimated from leaf fossil and paleovegetation. Atmospheric CO2 level is calculated from carbon isotope ratios of phytoplankton and soil carbonate, stomatal density of leaf fossil, boron isotope ratio of foraminiferal test, Ce anomaly, and global carbon cycle modeling. It is important to consider their advantages and disadvantages in order to evaluate the paleoclimate adequately. Next, we discuss climate change based on these proxies. As a general trend, the Cenozoic climate change is characterized by a transition from ice-free to ice-covered conditions across the Eocene/Oligocene boundary. The Earth's surface environment was significantly warmed from the Paleocene to the Eocene by high levels of atmospheric CO2. Thereafter, it gradually cooled towards the present, which is possibly attributed to changes in ocean currents and other marine environments accompanying continental drift. This trend has been punctuated by several short-term climate events. The Paleocene-Eocene Thermal Maximum (PETM) was a remarkable warming event at the Paleocene/Eocene boundary, possibly attributed to the release of methane from hydrates into the atmosphere. Rapid cooling occurred at the Eocene/Oligocene boundary to form extensive continental ice sheets including the Antarctica, which seems to have been caused by atmospheric CO2 and change of oceanographic circulation and marine environment. After a moderate period from the late Oligocene to the early Miocene, there was a transient but significant warming in the middle Miocene. Since then, the Earth's environment has gradually cooled towards the present accompanied by the evolution of glaciations and marine environmental changes but a causal link between cooling and global carbon cycle has recently been pointed out. Although the carbon cycle including atmospheric CO2 and CH4 cannot explain all of the global climate changes in Cenozoic, it has undoubtedly played a dominant role on the Earth's climate.

Long term fate of anthropogenic carbon

Two earth‐system models of intermediate complexity are used to study the long term response to an input of 5000 Pg of carbon into the atmosphere. About 75% of CO2 emissions have an average perturbation lifetime of 1800 years and 25% have lifetimes much longer than 5000 years. In the simulations, higher levels of atmospheric CO2 remain in the atmosphere than predicted by previous experiments and the average perturbation lifetime of atmospheric CO2 for this level of emissions is much longer than the 300–400 years proposed by other studies. At year 6800, CO2 concentrations between about 960 to 1440 ppmv result in global surface temperature increases between 6 and 8°C. There is also significant surface ocean acidification, with pH decreasing from 8.16 to 7.46 units between years 2000 and 2300.

Space-based ecological observations: the NASA decadal survey

In the coming decade, accelerating climate change and human modification of both landscapes and oceans will cause tremendous changes in ecosystem distribution and function. These changes will affect the capacity of ecosystems to provide food, water, healthy living environments, and a range of other services, and they will also affect the rate at which global warming continues to increase. Changes are already occurring in many parts of the world, notably in coastal zones where much of the world's population lives, at high latitudes where climate change is lengthening the snow-free season, and in tropical forests undergoing massive conversions for agricultural expansion and timber extraction. The vast, remote open ocean is experiencing increasing acidity as a result of higher levels of atmospheric CO2 while over-harvesting of fish is leading to global changes in marine ecosystems. Global ecosystem management is a growing challenge for the future. In order to understand and manage ecosystem changes and their feedback to the Earth's climate system, continuous global observations are critical. Space-based observations of ecosystems now span decades and capture variability and trends in ecosystems by studying large areas repeatedly. Observations of the physical environment provide the context for understanding ecosystems' sensitivity to climate change. Measurements such as soil moisture, ocean topography, ocean vector winds, earth radiation, and precipitation are among those needed. The Space Studies Board of the National Research Council has organized a decadal survey study, “Earth observations from space: a community assessment and strategy for the future” (http://qp.nas.edu/decadalsurvey). NASA has used decadal surveys in other disciplines to establish a framework for science priorities and missions, but this is the first attempt to use the process for the Earth sciences, including ecology. Satellite observations and the analyses they provide have an important and growing role in environmental science and management, so the decadal survey will have a major impact in ecology and environmental management. Within this process, the Earth Science and Applications Panel on Ecosystems was appointed to address terrestrial, aquatic, and marine environments. (Although the authors are members of this panel, the views in this editorial are based on personal observations of the process.) The survey will generate recommendations regarding science and applications priorities, identify opportunities afforded by new measurement types and new vantage points, and take a systems approach to observations that encompass the research programs of NASA and the related operational programs of NOAA and the USGS. This study will recommend priority measurements to support research, monitoring, and management during the decade 2005–2015 and beyond. In addition to elucidating fundamental Earth system processes and those underlying environmental change, applications needs also include weather and hydrological forecasting, climate prediction, aviation safety, earthquake prediction, natural resources management, agricultural assessment, homeland security, and infrastructure planning. The ecosystems panel evaluated ecological, technical, and management challenges, identified the contribution of remote observations to research and applications, and reviewed existing plans for ongoing ecologically relevant measurements. The panel strongly supports continuity of critical time series begun with LANDSAT, MODIS, and other sensors, and has tentatively identified four high-priority satellite missions. These research missions will employ new technologies to add new observations. The first new mission focuses on the detection and diagnosis of changes in ecosystem function (productivity, nutrient and water status, invasive species distributions, and coral reef status). The second focuses on terrestrial ecosystem structure and biomass, providing information on woody biomass, horizontal and vertical heterogeneity of forest habitat, and the effects of land use and deforestation on carbon stocks. A third mission will detail changes in CO2 concentration profiles above land and oceans, to quantify the global carbon budget. The fourth will view the coastal zone diurnally from a geostationary orbit to measure coastal ecosystem dynamics, including instances of harmful algal blooms, transport of organic matter, productivity, fisheries, and impacts of pollution episodes. The panel will also make recommendations about the need for new in situ and airborne capability. Remote sensing is used to address global-change ecology, conservation biology and planning, invasive species management, fisheries, wildfire management, precision agriculture, water resource planning, and a host of other ecological problems. The outcome of the decadal survey will influence the ecological satellite data resources available for the future. Interested scientists are strongly encouraged to contact the authors of this editorial or the NRC directly with their views. Bringing the next decade's ecological remote sensing program to fruition will require input, involvement, and support for spaced-based science and funding by ecologists and managers in an environment where many needs compete for limited opportunities. David Schimel, Senior Scientist, National Center for Atmospheric Research, Boulder, CO Inez Fung, Co-Director, Berkeley Institute of the Environment, CA Ruth Defries, Associate Professor, University of Maryland, MD

Contrasting seasonal patterns of carbon gain in evergreen and deciduous trees of ancient polar forests

Abstract Polar deciduous forests were an important biome during much of the Mesozoic and Paleogene, occupying upwards of 40% of the total land surface. Little is known about their physiological ecology, however, because these types of forests do not exist for study today. Furthermore, the role of high atmospheric CO2 levels in modulating the physiological response of ancient polar forests is poorly known. Here we report detailed measurements of whole-tree net carbon uptake over a full annual cycle for five tree species whose close ancestors were components of Cretaceous and Paleogene polar forests. Measurements were made on both evergreen and deciduous species after two years growth in a simulated Mesozoic polar (69°N) environment at either ambient (400 ppmv) or elevated (800 ppmv) levels of CO2. The deciduous species exhibited a significant pulse in carbon uptake during the late summer and early autumn (August to mid-October) that enabled them to achieve annual carbon budgets similar to those of evergree...

Ice and Its Consequences: Glaciation in the Late Ordovician, Late Devonian, Pennsylvanian‐Permian, and Cenozoic Compared

Abstract Comparison of the duration, onset conditions, and biotic response to the four Phanerozoic glaciations suggests that there are two Phanerozoic glacial modes. Late Ordovician glaciation typifies short‐duration, high atmospheric CO2 events, characterized by cosmopolitan faunal distributions and two episodes of catastrophic extinction. Pennsylvanian‐Permian and Cenozoic glaciation typify long‐duration, low atmospheric CO2 events, characterized by abundant biogeographic differentiation and stable or rising biotic diversity. Late Devonian glaciation appears most similar to Late Ordovician glaciation: it had a short duration; Late Devonian biotas were cosmopolitan; and Late Devonian glaciation was associated with increased extinction at the Devonian‐Carboniferous boundary. On the basis of biotic response, we would predict high atmospheric CO2 levels at the time of Devonian glaciation. However, the Berner GeoCarb curve suggests relatively low atmospheric CO2 levels in the Late Devonian.

Biophysical constraints on the origin of leaves inferred from the fossil record.

The molecular tool kit for producing flat-bladed photosynthetic structures evolved in marine and terrestrial plants during the middle Paleozoic, but it took a further 20 million years before leaves suddenly spread throughout land floras. This delay has long been difficult to explain, given the apparent advantage of leaves for photosynthetic primary production. Theory and experiments predict that exceptionally high atmospheric CO2 levels in the middle Paleozoic delayed the origin of leaves by restricting stomatal development. This would have limited evaporative cooling, leading to lethal overheating of leaves absorbing large quantities of solar energy. Here we test the central prediction of this argument with a morphometric analysis of 300 plant fossils from major European collections. We show a 25-fold enlargement of leaf blades in two phylogenetically independent clades as atmospheric CO2 levels fell during the late Paleozoic. Furthermore, preliminary data suggest that the first abrupt increase in leaf size was accompanied by an 8-fold rise in stomatal density. These evolutionary patterns support the relaxation of biophysical constraints on leaf area predicted by theory and point to a significant role for CO2 in plant evolution.

Longleaf Pine: A Sustainable Approach for Increasing Terrestrial Carbon in the Southern United Stat es

Natural communities dominated by longleaf pine (Pinus palustris Mill.) once covered an estimated two thirds of the forested area in the southeastern United States. Today, less than 1.2 million ha remain. However, over the past 10–15 years, public land managers have begun to restore many longleaf pine forests. More recently incentive programs have prompted reforestation and afforestation programs on nonindustrial private lands. These activities have been facilitated by improved longleaf regeneration technology and by expanded educational and outreach efforts. In the South, there is also a growing trend towards longer rotations due to changes in wood/fiber markets and prices. These trends suggest a new strategy to increase terrestrial carbon storage in the southeastern United States in a way that provides many simultaneous ecological and economic benefits. For example, longleaf pine is a long-lived species with a low mortality rate. Among the southern pine species, it has a high specific gravity and can tolerate a very wide variety of habitats. Longleaf pine is better able to sustain growth at older ages (over 150 years) and is tolerant to fire and many insects and diseases. Recent research also indicates that longleaf pine managed for longer rotations outperforms other commercial southern pine species on most sites and might better adapt to future climate scenarios with higher temperatures and higher atmospheric CO2 levels. Moreover, the higher-value, longer-lasting wood products derived from longleaf pine forests will continue to store carbon over long time periods.

Late Cretaceous ocean: Coupled simulations with the National Center for Atmospheric Research Climate System Model

Deep‐ocean circulation may be a significant factor in determining climate. Here, we describe two long, fully coupled atmosphere‐ocean simulations with the National Center for Atmospheric Research Climate System Model for the Late Cretaceous (80 Ma). Our results suggest that higher levels of atmospheric CO2 and the altered paleogeography of the Late Cretaceous resulted in a surface ocean state, temperature, salinity, and circulation, significantly different than at present. This, in turn, resulted in deepwater features that, although formed by mechanisms similar to the present, were quite different from the present. The simulations exhibit large overturning cells in both hemispheres extending from the surface to the ocean bottom and with intensity comparable to the present‐day North Atlantic simulated overturning. In the Northern Hemisphere the sinking takes place in the Pacific due to cooling of the much warmer and saltier waters compared to the present day. In the Southern Hemisphere the sinking occurs primarily in the southern Atlantic and Indian Oceans. For a simulation with atmospheric CO2reduced from 6 times to 4 times preindustrial concentrations, the southern branch is reduced by 35%percnt; due to less poleward transport of salty waters in the South Atlantic Ocean. Warm waters inferred from proxy data in deep‐sea cores can be explained by the high‐latitude sites of overturning. These results contradict the traditional hypothesis that warm Cretaceous ocean bottom waters must have formed by sinking in shallow low‐latitude seas.

The potential impacts of climate change on the mid-Atlantic coastal region

CR Climate Research Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials CR 14:219-233 (2000) - doi:10.3354/cr014219 The potential impacts of climate change on the mid-Atlantic coastal region Raymond G. Najjar1,*, Henry A. Walker2, Patti J. Anderson3, Eric J. Barron4, Richard J. Bord5, Jody R. Gibson6, Victor S. Kennedy7, C. Gregory Knight8, J. Patrick Megonigal9, Robert E. O¹Connor10, Colin D. Polsky8, Norbert P. Psuty11, Bruce A. Richards12, Lisa G. Sorenson13, Eric M. Steele8, Robert S. Swanson1 1Department of Meteorology, 3Environmental Resources Research Institute, 4The Environment Institute, 5Department of Sociology, 6Department of Geosciences, 8Department of Geography, and 10Department of Political Science, The Pennsylvania State University, University Park, Pennsylvania 16802, USA 2Atlantic Ecology Division, National Health and Environmental Effects Research Laboratory, US Environmental Protection Agency, 27 Tarzwell Drive, Narragansett, Rhode Island 02882, USA 7Horn Point Laboratory, University of Maryland Center for Environmental Science, 2020 HornsPoint Rd, Cambridge, Maryland 21613, USA 9Department of Biology, George Mason University, Fairfax, Virginia 22030-4444, USA 11Institute of Marine and Coastal Sciences, 71 Dudley Road, Rutgers University, Cook Campus, New Brunswick, New Jersey 08901, USA 12Delaware Center for the Inland Bays, 467 Highway One, Lewes, Delaware 19969, USA 13Department of Biology, Boston University, 5 Cummington Street, Boston, Massachusetts 02215, USA *E-mail: najjar@essc.psu.edu ABSTRACT: This paper assesses the potential impacts of climate change on the mid-Atlantic coastal (MAC) region of the United States. In order of increasing uncertainty, it is projected that sea level, temperature and streamflow will increase in the MAC region in response to higher levels of atmospheric CO2. A case study for Delaware based on digital elevation models suggests that, by the end of the 21st century, 1.6% of its land area and 21% of its wetlands will be lost to an encroaching sea. Sea-level rise will also result in higher storm surges, causing 100 yr floods to occur 3 or 4 times more frequently by the end of the 21st century. Increased accretion in coastal wetlands, however, which may occur in response to increases in CO2, temperature, and streamflow, could mitigate some of the flooding effect of sea-level rise. Warming alone will result in northward displacements of some mobile estuarine species and will exacerbate the already low summer oxygen levels in mid-Atlantic estuaries because of increased oxygen demand and decreased oxygen solubility. Streamflow increases could substantially degrade water quality, with significant negative consequences for submerged aquatic vegetation and birds. Though climate change may have some positive impacts on the MAC region, such as increased coastal tourism due to warming and some ecological benefits from less-frequent harsh winters, most impacts are expected to be negative. Policies designed to minimize adverse ecological impacts of human activities on coastal ecosystems in the mid-Atlantic, such as decreases in nutrient loading of watersheds, could help mitigate some of the risks associated with future climate variability and change in this region. KEY WORDS: Climate change impacts · Coastal regions · Sea-level rise Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in CR Vol. 14, No. 3. Online publication date: May 02, 2000 Print ISSN: 0936-577X; Online ISSN: 1616-1572 Copyright © 2000 Inter-Research.

Variation in Stomatal Density in the Late Carboniferous Gymnosperm Frond Neuropteris Ovata

Fossil foliage cuticles of the Late Carboniferous medullosalean pteridosperm Neuropteris ovata show a marked drop in stomatal density and index in the very early Stephanian, and a return to higher values at the end of the Stephanian. This probably reflects a rise in CO2 partial pressure in the atmosphere during the Stephanian, due to a drastic contraction of the tropical forests. This interval of high atmospheric CO2 levels appears to coincide with a warming interval in both the Gondwanan and Angaran areas.

Free Air CO2 Enrichment of potato (Solanum tuberosum L.): development, growth and yield

AbstractA FACE (Free Air CO2 Enrichment) experiment was carried out on Potato (Solanum tuberosum L., cv. Primura) in 1995 in Italy. Three FACE rings were used to fumigate circular field plots of 8 m diameter while two rings were used as controls at ambient CO2 concentrations. Four CO2 exposure levels were used in the rings (ambient, 460, 560 and 660 μmol mol–1). Phenology and crop development, canopy surface temperature, above‐ and below‐ground biomass were monitored during the growing season. Crop phenology was affected by elevated CO2, as the date of flowering was progressively anticipated in the 660, 560, 460 μmol mol–1 treatments. Crop development was not affected significantly as plant height, leaf area and the number of leaves per plant were the same in the four treatments. Elevated atmospheric CO2 levels had, instead, a significant effect on the accumulation of total nonstructural carbohydrates (TNC = soluble sugars + starch) in the leaves during a sunny day. Specific leaf area was decreased under elevated CO2 with a response that paralleled that of TNC concentrations. This reflected the occurrence of a progressive increase of photosynthetic rates and carbon assimilation in plants exposed to increasingly higher levels of atmospheric CO2. Tuber growth and final tuber yield were also stimulated by rising CO2 levels. When calculated by regression of tuber yield vs. the imposed levels of CO2concentration, yield stimulation was as large as 10% every 100 μmol mol–1 increase, which translated into over 40% enhancement in yield under 660 μmol mol–1. This was related to a higher number of tubers rather than greater mean tuber mass or size. Leaf senescence was accelerated under elevated CO2 and a linear relationship was found between atmospheric CO2 levels and leaf reflectance measured at 0.55 μm wavelength. We conclude that significant CO2 stimulation of yield has to be expected for potato under future climate scenarios, and that crop phenology will be affected as well.

Root to shoot ratio of crops as influenced by CO2

Crops of tomorrow are likely to grow under higher levels of atmospheric CO2. Fundamental crop growth processes will be affected and chief among these is carbon allocation. The root to shoot ratio (R:S, defined as dry weight of root biomass divided by dry weight of shoot biomass) depends upon the partitioning of photosynthate which may be influenced by environmental stimuli. Exposure of plant canopies to high CO2 concentration often stimulates the growth of both shoot and root, but the question remains whether elevated atmospheric CO2 concentration will affect roots and shoots of crop plants proportionally. Since elevated CO2 can induce changes in plant structure and function, there may be differences in allocation between root and shoot, at least under some conditions. The effect of elevated atmospheric CO2 on carbon allocation has yet to be fully elucidated, especially in the context of changing resource availability. Herein we review root to shoot allocation as affected by increased concentrations of atmospheric CO2 and provide recommendations for further research. Review of the available literature shows substantial variation in R:S response for crop plants. In many cases (59.5%) R:S increased, in a very few (3.0%) remained unchanged, and in others (37.5%) decreased. The explanation for these differences probably resides in crop type, resource supply, and other experimental factors. Efforts to understand allocation under CO2 enrichment will add substantially to the global change response data base.

Limiting future atmospheric carbon dioxide

We estimate anthropogenic carbon emissions required to stabilize future atmospheric CO2 at various levels ranging from 350 ppm to 750 ppm. Over the next three centuries, uptake by the ocean and terrestrial biosphere would permit emissions to be 3 to 6 times greater than the total atmospheric increase, with each of them contributing approximately equal amounts. Owing to the nonlinear dependence of oceanic and terrestrial biospheric uptake on CO2 concentration, the uptake by these two sinks decreases substantially at higher atmospheric CO2 levels. The uptake also decreases with increased atmospheric CO2 growth rate. All the stabilization scenarios require a substantial future reduction in emissions.

Apical Development and Growth of Barley under Different CO2 and Nitrogen Regimes

AbstractIncreases in atmospheric carbon dioxide (CO2) concentration have stimulated interest in the response of agricultural crops to elevated levels of CO2. Several studies have addressed the response of C3 cereals to CO2, but the interactive effect of nutrient supply and CO2 on apical development and spikelet set and survival has not been investigated thoroughly. Hence, an experiment was conducted in the greenhouse to evaluate the effect of high (700 μmol CO2mol−1 air) and low (400 μmol mol−1) levels of atmospheric CO2 on apical development, spikelet set and abortion, and pre‐ and post‐anthesis growth in spring barley (Hordeum vulgare L.) grown under high N (0.3 g N pot−1 before sowing −1–0.11 g N pot−1 week−1) and low N (0.3 g N pot−1) regimes. The plants were grown in 5 L pots. Development of spike was hastened due to CO2 enrichment, and the C+ plants pollinated few days earlier than the C— plants. Carbon dioxide enrichment had no effect on date of ripening. Development of spike slowed following application of extra N, and plants pollinated 10 days later and matured 2 weeks later when compared with plants under low N. Carbon dioxide enrichment did not affect the number of spikelets at anthesis. Excess N decreased spikelet abortion and the increased maximum number of spikelets under both [CO2]. Barley plants did not tiller when grown in low [CO2] and low N. Increased endogenous IAA concentration in those plants, recorded three days before tillers appeared in other treatments, may have contributed to this. Carbon dioxide enrichment increased the C concentration of plants, but decreased the N concentration under high N regime. Both the C and N concentration of plants were increased under high N regime. Carbon dioxide enrichment increased the total dry matter of mature plants by 9 % under high N regime and by 21 % under low N regime. Under high [CO2] increased kernel number on tiller spikes, and increased kernel weight both on main stem and on tiller spikes resulted in a 23 % increase in kernel yield under low N regime and 76 % increase in kernel yield under high N regime. The rate of N application influenced growth and yield components to a greater extent than CO2 enrichment. At maturity, plant dry matter, kernel weight, the number of kernels per spike, and the number of spikes per plant were higher under high N regime than under low N regime.Long days (16 h), low light intensity (280 μmol m−2s−1), and at constant temperature of 20 °C high [CO2] increased kernel weight and the number of kernels on tiller spikes under high and low N application rate, but did not increase the number of kernels on main stem spike, or the number of tillers or tiller spikes per plant.

Possibility of chemical weathering before the advent of vascular land plants

CHEMICAL weathering today is generally assumed to occur primarily in soils1,2. The rise of vascular plants during the Silurian and Devonian periods about 400 Myr ago brought about an increase in soil microbial activity and thus in soil CO2 generation, and it has therefore been widely believed that, as a result of these changes, soil CO2 replaced atmospheric CO2 as the primary agent of chemical weathering3–6. Here we show that the aerated region above the water table (the vadose zone) exerts a strong influence on the CO2 concentration to which runoff is exposed as it percolates beneath the soil, and we argue that this could have been the case before the Silurian. We present calculations which show that, for present-day atmospheric CO2 concentrations, a low level of microbial respiration may be sufficient to support appreciable CO2 concentrations in the vadose zone because of the slow rate of CO2 loss to the surface. Despite the small amount of microbial respiration in pre-Silurian soils, CO2 concentrations in subsoil vadose zones might therefore have been sufficient to account for the apparent constancy of chemical weathering since the mid-Proterozoic7, obviating the need to invoke high levels of atmospheric CO2 to explain the weathering record.

Secular variation in microfossil preservation: causes and consequences of the biogeochemical evolution of the oceans

Because of their abundance, composition, and widespread occurrence throughout the Phanerozoic, microfossils are ideal subjects for teasing apart the ecological, evolutionary, geochemical, and taphonomic controls on the fossil record, and for testing hypotheses of evolutionary paleoecology against secular change in ocean chemistry as evidenced by patterns of fossil preservation. The history of calcareous plankton is one of interaction between the evolutionary innovation of regulatory pathways in hardpart construction and the paleochemistry of the seas. Diversification of ancestral shelfal calcareous plankton lineages in the Mesozoic was related to sea level transgression, water column stratification, and habitat diversity, as evidenced by major expansions of these groups in association with Oceanic Anoxic Events. In the case of coccolithophorids (calcareous Haptophyceae), the origination of calcified lineages also appears to have been related to nutrient resuspension from bottom sediments and anoxic waters (which may have promoted calcification) advected into the photic zone over shallow shelves during transgressions. Invasion of pelagic habitats by Foraminifera was facilitated by the evolution of test secretory mechanisms (beginning in the Late Paleozoic) that conferred greater cellular control over shell microstructure and density. The beginnings of calcareous nannoplankton, however, are traceable to microfossil “Lagerstätten” that hint at the first attempts at calcification by naked haptophycean lineages much earlier in the Paleozoic. During the Early-Mid Paleozoic greenhouse phase, calcareous nannoplankton assemblages were unlikely to be preserved because high levels of atmospheric (and therefore oceanic) CO2 and extraction of CaCO3 in epeiric seas by calcareous biota resulted in a very shallow CCD. With the advent of the Late Paleozoic icehouse phase (and associated sea level fall), the locus of biogenic limestone deposition shifted seaward and the CCD deepened. Significant accumulations of calcareous pelagic sediments followed in the Late Jurassic in response to diversification of calcareous plankton. As deep pelagic oozes began to accumulate, a new component was added to the global carbon cycle: the metamorphic decarbonation of pelagic limestones that controls long-term (i.e., tens to hundreds-of-millions of years) global warming.

TRANSPORT OF CARBON AMONG CONNECTED RAMETS OF EICHHORNIA CRASSIPES (PONTEDERIACEAE) AT NORMAL AND HIGH LEVELS OF CO2

The floating, stoloniferous plant, Eichhornia crassipes, has high rates of productivity and rapidly invades new sites. Because the transport of carbon among connected ramets is known to increase the growth of clonal plants, we asked whether there is intraclonal carbon transport in E. crassipes. Because net photosynthesis of E. crassipes is significantly higher at high levels of atmospheric CO2, we also asked if high CO2 can change patterns of carbon transport in ways that might modify clonal growth. We exposed individual ramets within groups of connected ramets to 14CO2 for 15–45 min and measured the distribution of 14C in the group after 4 days of growth at 350, 700, 1,400, or 2,800 μ1 1−‐1 CO2. At 350 μ1 1−‐1 CO2, a parent ramet exported approximately 10% of the 14C that it assimilated to its first rooted offspring ramet. The offspring exported a similar percentage of the l4C it assimilated toward the parent; two‐thirds of this 14C was retained by the parent, and one‐third moved into new offspring of the parent. In all ramets, imported carbon moved into leaves as well as roots. At the higher levels of CO2, the percentage of assimilated carbon exported from a parent ramet to the leaf blades of its first offspring was lower by half. High CO2 had little other effect on carbon transport. E. crassipes maintains bidirectional transport of carbon between ramets even under uniform and favorable environmental conditions and when external CO2 levels are very high.