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  • 1
    ISSN: 1432-1939
    Keywords: Carbon cycle ; Ecosystem ; Global change ; Respiration
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract This study was designed to identify potential effects of elevated CO2 on belowground respiration (the sum of root and heterotrophic respiration) in field and microcosm ecosystems and on the annual carbon budget. We made three sets of respiration measurements in two CO2 treatments, i.e., (1) monthly in the sandstone grassland and in microcosms from November 1993 to June 1994; (2) at the annual peak of live biomass (March and April) in the serpentine and sandstone grasslands in 1993 and 1994; and (3) at peak biomass in the microcosms with monocultures of seven species in 1993. To help understand ecosystem carbon cycling, we also made supplementary measurements of belowground respiration monthly in sandstone and serpentine grasslands located within 500 m of the CO2 experiment site. The seasonal average respiration rate in the sandstone grassland was 2.12 μmol m-2 s-1 in elevated CO2, which was 42% higher than the 1.49 μmol m-2 s-1 measured in ambient CO2 (P=0.007). Studies of seven individual species in the microcosms indicated that respiration was positively correlated with plant biomass and increased, on average, by 70% with CO2. Monthly measurements revealed a strong seasonality in belowground respiration, being low (0–0.5 μmol CO2 m-2 s-1 in the two grasslands adjacent to the CO2 site) in the summer dry season and high (2–4 μmol CO2 m-2 s-1 in the sandstone grassland and 2–7 μmol CO2 m-2 s-1 in the microcosms) during the growing season from the onset of fall rains in November to early spring in April and May. Estimated annual carbon effluxes from the soil were 323 and 440 g C m-2 year-1 for the sandstone grasslands in ambient and elevated CO2. That CO2-stimulated increase in annual soil carbon efflux is more than twice as big as the increase in aboveground net primary productivity (NPPa) and approximately 60% of NPPa in this grassland in the current CO2 environment. The results of this study suggest that below-ground respiration can dissipate most of the increase in photosynthesis stimulated by elevated CO2.
    Type of Medium: Electronic Resource
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  • 2
    Publication Date: 2019-06-28
    Description: How humans, interacting within social systems, affect and are affected by global change is explored. Recognizing the impact human activities have on the environment and responding to the need to document the interactions among human activities, the Consortium for International Earth Science Information Network (CIESIN) commissioned a group of 12 scientists to develop a framework illustrating the key human systems that contribute to global change. This framework, called the Social Process Diagram, will help natural and social scientists, educators, resource managers and policy makers envision and analyze how human systems interact among themselves and with the natural system. The Social Process Diagram consists of the following blocks that constitute the Diagram's structural framework: (1) fund of knowledge and experience; (2) preferences and expectations; (3) factors of production and technology; (4) population and social structure; (5) economic systems; (6) political systems and institutions; and (7) global scale environmental processes. To demonstrate potential ways the Diagram can be used, this document includes 3 hypothetical scenarios of global change issues: global warming and sea level rise; the environmental impact of human population migration; and energy and the environment. These scenarios demonstrate the Diagram's usefulness for visualizing specific processes that might be studied to evaluate a particular global change issues. The scenario also shows that interesting and unanticipated questions may emerge as links are explored between categories on the Diagram.
    Keywords: ENVIRONMENT POLLUTION
    Type: NASA-CR-190678 , NAS 1.26:190678
    Format: application/pdf
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  • 3
    Publication Date: 2019-07-12
    Description: This symposium was organized to study the unusual convergence of a number of observations, both short and long term that defy an integrated explanation. Of particular importance are surface temperature observations and observations of upper atmospheric temperatures, which have declined significantly in parts of the stratosphere. There has also been a dramatic decline in ozone concentration over Antarctica that was not predicted. Significant changes in precipitation that seem to be latitude dependent have occurred. There has been a threefold increase in methane in the last 100 years; this is a problem because a source does not appear to exist for methane of the right isotopic composition to explain the increase. These and other meteorological global climate changes are examined in detail.
    Keywords: ENVIRONMENT POLLUTION
    Type: NASA-CR-185323 , NAS 1.26:185323 , LC-88-31544
    Format: application/pdf
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