Summary of Scientific Studies
in the Week:
May, 27th, 2005

  • Effects of Elevated CO2 on the Isoflavone Content of Soybean Seeds

  • Thickness Trends of the Antarctic Ice Sheet

  • The Roman Warm Period and Dark Ages Cold Period in China

    Effects of Elevated CO2 on the Isoflavone
    Content of Soybean Seeds

    Caldwell, C.R., Britz, S.J. and Mirecki, R.M.  2005.  Effect of temperature, elevated carbon dioxide, and drought during seed development on the isoflavone content of dwarf soybean [Glycine max (L.) Merrill] grown in controlled environments.  Journal of Agricultural and Food Chemistry 53: 1125-1129.
    The authors write that "the beneficial effects of isoflavone-rich foods have been the subject of numerous studies (Birt et al., 2001; Messina, 1999)," and that "foods derived from soybeans are generally considered to provide both specific and general health benefits," presumably via these substances.  Hence, it is only natural they should wonder how the isoflavone content of soybean seeds might be affected by the ongoing rise in the air's CO2 content, and that they would conduct a set of experiments to find the answer.

    What was done
    Well-watered and fertilized soybean plants were grown from seed to maturity in pots within two controlled-environment chambers, one maintained at an atmospheric CO2 concentration of 400 ppm and one at 700 ppm.  The chambers were initially kept at a constant air temperature of 25°C.  At the onset of seed fill, however, air temperature was reduced to 18°C until seed development was complete, in order to simulate average outdoor temperatures at this stage of plant development.  In a second experiment, this protocol was repeated, except that the temperature during seed fill was maintained at 23°C, with and without drought (a third treatment), while in a third experiment, seed-fill temperature was maintained at 28°C, with or without drought.

    What was learned
    In the first experiment, where air temperature during seed fill was 18°C, the elevated CO2 treatment increased the total isoflavone content of the soybean seeds by 8%.  In the second experiment, where air temperature during seed fill was 23°C, the extra CO2 increased total seed isoflavone content by 104%, while in the third experiment, where air temperature during seed fill was 28°C, the CO2-induced isoflavone increase was 101%.  Finally, when drought-stress was added as a third environmental variable, the extra CO2 boosted total seed isoflavone content by 186% when seed-fill air temperature was 23°C, while at a seed-fill temperature of 28°C, it increased isoflavone content by 38%.

    What it means
    Under all environmental circumstances studied, enriching the air with an extra 300 ppm of CO2 increased the total isoflavone content of soybean seeds.  In addition, the percent increases measured under the stress situations investigated were always greater than the percent increase measured under optimal growing conditions.  Consequently, the direct effects of atmospheric CO2 enrichment on the health-promoting properties of soybean seeds are likely universally beneficial and a boon to the entire human race, especially in light of the fact that Bernacchi et al. (2005) characterize the soybean as "the world's most important seed legume."

    • Bernacchi, C.J., Morgan, P.B., Ort, D.R. and Long, S.P.  2005.  The growth of soybean under free air [CO2] enrichment (FACE) stimulates photosynthesis while decreasing in vivo Rubisco capacity.  Planta 220: 434-446.
    • Birt, D.F., Hendrich, W. and Wang, W.  2001.  Dietary agents in cancer prevention: flavonoids and isoflavonoids.  Pharmacology & Therapeutics 90: 157-177.
    • Messina, M.J.  1999.  Legumes and soybeans: overview of their nutritional profiles and health effects.  American Journal of Clinical Nutrition 70(S): 439s-450s.


    Thickness Trends of the Antarctic Ice Sheet

    Davis, C.H. and Ferguson, A.C.  2004.  Elevation change of the Antarctic ice sheet, 1995-2000, from ERS-2 satellite radar altimetry.  IEEE Transactions on Geoscience and Remote Sensing 42: 2437-2445.

    What was done
    The authors evaluated elevation changes of the Antarctic ice sheet throughout the five-year period June 1995 to April 2000 based on more than 123 million elevation change measurements made by the European Space Agency's (ESA) European Remote Sensing 2 (ERS-2) satellite radar altimeter.

    What was learned
    It was determined that the east Antarctic ice sheet had a five-year trend of 1.0 ± 0.6 cm/year, that the west Antarctic ice sheet had a five-year trend of -3.6 ± 1.0 cm/year, and that the entire Antarctic continent (north of 81.6°S) had a five-year trend of 0.4 ± 0.4 cm/year.  In addition, the Pine Island, Thwaites, DeVicq and Land glaciers of west Antarctica exhibited five-year trends ranging from - 26 to - 135 cm/year.

    What it means
    Davis and Ferguson note that the strongly negative trends of the coastal glacier outlets "suggest that the basin results are due to dynamic changes in glacier flow," and that recent observations "indicate strong basal melting, caused by ocean temperature increases, is occurring at the grounding lines of these outlet glaciers."  Hence, they conclude "there is good evidence that the strongly negative trends at these outlet glaciers, the mass balance of the corresponding drainage basins, and the overall mass balance of the west Antarctic ice sheet may be related to increased basal melting caused by ocean temperature increases."  Nevertheless, driven by the significantly positive trend of the much larger east Antarctic ice sheet, the ice volume of the entire continent grew ever larger over the last five years of the 20th century, the majority of which increase, according to Davis and Ferguson, was due to increased snowfall.


    The Roman Warm Period and Dark Ages Cold Period in China

    Yu, K.-F., Zhao, J.-X, Wei, G.-J., Cheng, X.-R., Chen, T.-G., Felis, T., Wang, P.-X. and Liu, T-.S.  2005.  18O, Sr/Ca and Mg/Ca records of Porites lutea corals from Leizhou Peninsula, northern South China Sea, and their applicability as paleoclimatic indicators.  Palaeogeography, Palaeoclimatology, Palaeoecology 218: 57-73.

    What was done
    As in the study of Wei et al. (2004), the authors derived high-resolution Sr/Ca ratios for two Porites lutea coral samples taken from the coast of the Leizhou Peninsula (20°12'N, 109°55'E) in the northern South China Sea, while determining their ages by means of U-Th dating.  The transfer function relating the Sr/Ca ratio to temperature was established on a modern Porites lutea coral in the same location by calibrating against sea surface temperatures (SSTs) measured from 1960 to 2000 at the nearby Haikou Ocean Observatory.

    What was learned
    Yu et al. first determined that the coral Sr/Ca ratio is "an ideal and reliable thermometer," after which they employed it to learn that the coral sample dated to ~541 BC "yields a mean of Sr/Ca-SST maxima of 29.3°C and a mean of Sr/Ca-SST minima of 19.5°C, similar to those of the 1990s (the warmest period of the last century)."  Likewise, they determined that "the ~487 AD coral yields a mean of Sr/Ca-SST maxima of 28.7°C and a mean of Sr/Ca-SST minima of 16.5°C, which are 0.7 and 3.8°C lower than those of the 1990s."

    What it means
    The two dates that correspond to these relatively warm and cool temperatures occur within the Roman Warm Period and Dark Ages Cold Period, respectively. In harmony with this conclusion, Yu et al. say "historic records show that it was relatively warm and wet in China during 800-300 BC (Eastern Zhou Dynasty), but was significantly colder and drier in east China during the period of 386-589 AD (several degrees Celsius colder than today; Chu, 1973; Ge et al., 2003; Mann et al., 2000)."  As two graphic corroborating examples of these facts, they report "it was so warm during the early Eastern Zhou Dynasty (770-256 BC) that rivers in today's Shangdong province (35-38°N) never froze for the whole winter season in 698, 590, and 545 BC," but that "the period of Southern-Northern Dynasties (42-550 AD) was so dry and cold ... that Beiwei Dynasty (386-534 AD) was forced to move its capital from Pingcheng (40.10°N) to Luoyang (34.67°N) in 493 AD after a series of severe droughts."

    These observations add to the voluminous evidence for the reality and global extent of the millennial-scale oscillation of climate that has alternately produced, not only the Roman Warm Period and Dark Ages Cold Period, but the subsequent Medieval Warm Period, Little Ice Age and Modern Warm Period, all without any help from changes in the air's CO2 content.

    • Wei, G., Yu, K. and Zhao, J.  2004.  Sea surface temperature variations recorded on coralline Sr/Ca ratios during Mid-Late Holocene in Leizhou Peninsula.  Chinese Science Bulletin 49: 1876-1881.
    • Chu, K.  1973.  A preliminary study on the climatic fluctuations during the last 5000 years in China.  Science in China, Series B, Chemistry, Life Sciences & Earth Sciences 16: 226-256.
    • Ge, Q.S., Zheng, J.Y., Fang, X.Q., Man, Z.M., Zhang, X.Q., Zhang, P.Y. and Wang, W.C.  2003.  Winter half-year temperature reconstruction for the middle and lower reaches of the Yellow River and Yangtze River, China, during the past 2000 years.  The Holocene 13: 933-940.
    • Man, Z.M., Ge, Q.S. and Zhang, P.Y.  2000.  Case studies on the impact of climatic changes on the farming-pastoral transitional zone in historical period.  Geographical Research 19: 141-147.
      Reviewed 25 May 2005

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