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  • 1
    ISSN: 1432-1793
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Description / Table of Contents: Zusammenfassung 1. An zwei im Brackwasser lebenden Crustaceen, Gammarus salinus Spooner und Idotea balthica Pallas, wird die Abhängigkeit der Hitzeresistenz von konstanten (8°, 14° und 20 °C) und tagesperiodisch schwankenden Vorbehandlungstemperaturen (8°↔20 °C) untersucht. 2. Geschlecht und Größe der Versuchstiere beeinflussen das Resistenzverhalten. Beide Arten zeigen neben einer sinnvollen Hitzeadaptation nach einem langfristigen Aufenthalt bei konstanten Temperaturen (mit der Adaptationstemperatur [AT] ansteigende Hitzeresistenz) eine schnell verlaufende Resistenzänderung nach einem AT-Wechsel (8°→20 °C bzw. 20°→8 °C). Dies führt bei inkonstanter Temperaturvorbehandlung zu tagesrhythmischen mit der Temperatur schwankenden Resistenzwerten. Bei I. balthica kommt eine endogene Tagesperiodizität der Hitzeresistenz hinzu. 3. Nach einem langfristigen Aufenthalt (2 bis 4 Wochen) bei inkonstanten Temperaturen (Dauer des Temperaturwechsels: 2 Std [ΔT/2 h]) zeigt G. salinus während des Tages einen mittleren Wert für die Hitzeresistenz (der mit dem Wert für die AT=14 °C-Kontrollen übereinstimmt); dieser läßt sich auf eine nachgewiesene Temperaturunabhängigkeit der Adaptationsprozesse (gleiche Änderungsgeschwindigkeit der Resistenz nach Senkung wie Erhöhung der AT) zurückführen. Ein schneller Temperaturwechsel (ΔT/1 h) während der inkonstanten Vorbehandlung führt dagegen zu einer signifikanten Steigerung der Hitzeresistenz wahrscheinlich auf Grund hinzukommender Stresseffekte und wird von G. salinus schlechter vertragen als ein langsamer Wechsel von ΔT/2 h. 4. Bei I. balthica sind niedrige ATs weniger wirksam für das Ausmaß der Hitzeresistenz als hohe (großer Resistenzunterschied zwischen AT=14° und 20°, ein geringer zwischen AT=8° und 14 °C). Eine Senkung der AT (20°→8 °C) führt in den ersten 12 Std bei ♂♂ zu einem schnelleren Verlust an Hitzeresistenz als im umgekehrten Falle zu einem Gewinn (nach längerem Aufenthalt in neuen ATs erweist sich das Ende der Umadaptation hingegen als im üblichen Sinn temperaturabhängig). Bei inkonstanter Vorbehandlung (ΔT/2 h) steigt die Resistenz über den mittleren Wert (AT=14 °C) hinaus an. Ein weiterer Anstieg der Resistenz läßt sich durch einen schnellen Temperaturwechsel (ΔT/1 h) erzielen. Daß eine Verdoppelung des Temperaturwechsels eine signifikante Erhöhung der Hitzeresistenz zur Folge hat, macht ebenfalls die Beteiligung von Stresseffekten wahrscheinlich, die von der Resistenzadaptation zu trennen sind. 5. Bei G. salinus, der in Biotopen mit größeren Temperaturschwankungen lebt als I. balthica, sind die Reaktionen weniger stark ausgeprägt.
    Notes: Abstract The crustaceans Gammarus salinus Spooner and Idotea balthica Pallas live in brackish waters and are capable of tolerating a variety of temperature and salinity conditions. Thus far, the capacity for non-genetic adaptation of such euryplastic animals has only been tested at different levels of constant temperatures. If exposed to both constant (8°, 14° or 20°C) and fluctuating (daily fluctuation: 8°↔20°C) temperatures, the tested individuals reveal significant differences in heat resistance which become apparent within 12 h. G. salinus and I. balthica exhibit reasonable (meaningful) heat resistance, i.e., a positive correlation between the degree of heat resistance and the level of adaptation temperature (AT). Following a shift in AT (8° → 20°C or 20° → 8°C) the degree of resistance changes rather fast. This leads, under fluctuating temperature conditions, to diurnal changes in the degree of heat resistance. I. balthica also shows an endogenous diurnal periodicity of its heat resistance. In G. salinus, long-term exposure (2 to 4 weeks) to fluctuating temperatures [duration of temperature change: 2 h (Δ/2 h)] produces, during the day, a mean resistance value which coincides with the value obtained for AT 14°C-controls. This fact results from temperature-independent adaptation speeds (same after decrease and increase of AT). However, fast temperature change (ΔT/1 h) during exposure to fluctuating temperatures leads to a significant augmentation of heat resistance, presumably due to additional stress; such fast temperature changes are less well tolerated than slow fluctuations (ΔT/2 h). In I. balthica, low ATs are less efficient in terms of heat resistance than high ATs (great difference between AT=14° and 20 °C; small difference between AT=8° and 14 °C). In males, lowering of AT from 20° to 8 °C results, within the first 12 h, to faster loss of heat resistance than is the case for gain in heat resistance after AT increase from 8° to 20 °C. However, after prolonged exposure to the new ATs, completion of readaptation is temperature-independent. Under conditions of fluctuating temperatures (ΔT/2 h) resistance increases beyond the mean value (AT=14 °C). Further increase in resistance can be obtained through fast temperature changes (ΔT/1 h). In G. salinus, which occupies habitats with more extensive temperature fluctuations, the responses studied are less pronounced than in I. balthica.
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  • 2
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract Denitrification processes were measured by the acetylene-blockage technique under changing flood conditions along the aquatic/terrestrial transition zone on the Amazon floodplain at Lago Camaleão, near Manaus, Brazil. In flooded sediments, denitrification was recorded after the amendment with NO 3 − (100 μmol liter−1) throughout the whole study period from August 1992 to February 1993. It ranged from 192.3 to 640.7 μmol N m−2 h−1 in the 0- to 5-cm sediment layer. Without substrate amendment, denitrification was detected only during low water in November and December 1992, when it occurred at a rate of up to 12.2 μmol N m−2 h−1 Higher rates of denitrification at an average rate of 73.3 μmol N m−2 h−1 were measured in sediments from the shallow lake basin that were exposed to air at low water. N2O evolution was never detected in flooded sediments, but in exposed sediments, it was detected at an average rate of 28.3 μmol N m−2 h−1 during the low-water period. The results indicate that under natural conditions there is denitrification and hence a loss in nitrogen from the Amazon floodplain to the atmosphere. Rates of denitrification in flooded sediments were one to two orders of magnitude smaller than in temperate regions. However, the nitrogen removal of exposed sediments exceeded that of undisturbed wetland soils of temperate regions, indicating a considerable impact of the flood pulse on the gaseous turnover of nitrogen in the Amazon floodplain.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1432-184X
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract. Denitrification processes were measured by the acetylene-blockage technique under changing flood conditions along the aquatic/terrestrial transition zone on the Amazon floodplain at Lago Camaleão, near Manaus, Brazil. In flooded sediments, denitrification was recorded after the amendment with NO3 − (100 μmol liter−1) throughout the whole study period from August 1992 to February 1993. It ranged from 192.3 to 640.7 μmol N m−2 h−1 in the 0- to 5-cm sediment layer. Without substrate amendment, denitrification was detected only during low water in November and December 1992, when it occurred at a rate of up to 12.2 μmol N m−2 h−1. Higher rates of denitrification at an average rate of 73.3 μmol N m−2 h−1 were measured in sediments from the shallow lake basin that were exposed to air at low water. N2O evolution was never detected in flooded sediments, but in exposed sediments, it was detected at an average rate of 28.3 μmol N m−2 h−1 during the low-water period. The results indicate that under natural conditions there is denitrification and hence a loss in nitrogen from the Amazon floodplain to the atmosphere. Rates of denitrification in flooded sediments were one to two orders of magnitude smaller than in temperate regions. However, the nitrogen removal of exposed sediments exceeded that of undisturbed wetland soils of temperate regions, indicating a considerable impact of the flood pulse on the gaseous turnover of nitrogen in the Amazon floodplain.
    Type of Medium: Electronic Resource
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