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Reduced mycorrhizae on Juniperus monosperma with mistletoe: the influence of environmental stress and tree gender on a plant parasite and a plant-fungal mutualism (1992)

Gehring, Catherine A. ; Whitham, Thomas G.

Springer

Oecologia 89 (1992), S. 298-303

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ISSN: 1432-1939

Keywords: Dioecy ; Environmental stress ; Parasitic mistletoe ; Mutualist ; Mycorrhizal fungi

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Summary We examined how an important plant mutualist (fungal mycorrhizae) interacted with a common tree parasite, a xylem-tapping mistletoe (Phoradendron juniperium Engelm.) growing on one-seeded juniper (Juniperus monosperma Engelm.). We also examined how host tree gender and environmental stress might be involved in this interaction. Four major patterns were observed. First, the mycorrhizal levels of trees of both sexes were negatively correlated with mistletoe density. In comparisons of heavily and lightly infested trees at the stressful site, high mistletoe levels were associated with 27% less mycorrhizae on male trees and 38% less mycorrhizae on the roots of female trees. Second, the reduction of mycorrhizae on trees with high mistletoe levels was slightly but significantly greater for female trees than male trees. These results are consistent with the hypothesis that severe mistletoe infestation suppresses mycoresis and that this suppression is more severe in female trees because of their greater energetic investment in reproduction. Third, female junipers growing in the stressful ash and cinder fields averaged three-fold higher levels of mistletoe infestation than male trees. Fourth, no differences in mistletoe infestation were observed between male and female trees growing in the more favorable soils. Comparisons with other systems suggest that both mistletoes and herbivores have similar interactions with mycorrhizae.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00317231

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Determination of the Enthalpies of Formation of DyI2 and DyI3 and estimation of the Dy3+/Dy2+ standard aqueous electrode potentialDedicated to Professor Rudolf Hoppe on his 70th Birthday (1992)

Morss, Lester R. ; Spence, Thomas G.

Weinheim : Wiley-Blackwell

Zeitschrift für anorganische Chemie 616 (1992), S. 162-168

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ISSN: 0044-2313

Keywords: Dysprosiumdiiodide ; dysprosium triiodide ; enthalpy ; electrode potential ; Chemistry ; Inorganic Chemistry

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Chemistry and Pharmacology

Description / Table of Contents: Bestimmung der Bildungsenthalpien von DyI2 und DyI3 sowie Abschätzung des Dy3+/Dy2+-Standardelektrodenpotentials in wäßrigem MediumDyI2 and DyI3 wurden nach Literaturmethoden hergestellt. Ihre Lösungsenthalpien wurden bestimmt und die Bildungsenthalpien zu ΔfH°(DyI3, s, 298 K) = -(394 ± 16) kJ · mol-1 und ΔfH°(DyI2, s, 298 K) = -(616 ± 10) kJ· mol-1 berechnet. Entsprechenden Literaturangaben sowie geschätzten Lösungsenthalpien und Standardentropien wurde E°(Dy3+/Dy2+, aq.) zu -(2.6 ± 0.2) V berechnet. Ein Vergleich der Enthalpien für die Reduktion von DyI3 zu DyI2 bzw. DyI zu DyI2 wird vorgenommen.

Notes: DyI2 and Dy3I were synthesized by literature techniques. Their enthalpies of solution were determined and their enthalpies of formation calculated to be ΔfH°(DyI2, s, 298 K) = -(394 ± 16) kJ· mol-1 and ΔfH°(DyI3, s, 298 K) = -(616 ± 10) kJ· mol-1. With appropriate literature and estimated enthalpies of solution and standard entropies, the E°(Dy3+/Dy2+, aq) was calculated to be -(2.6 ± 0.2) V. A comparison is made of the enthalpies of reduction of DyI3 to DyI2 and of DyCl3 to DyCl2.

Additional Material: 2 Tab.