Microbial utilization of dissolved organic carbon leached from riparian litterfall

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Abstract:

Dissolved organic carbon (DOC) in aquatic systems is abundant and used within stream food webs, but DOC quality is rarely studied. DOC in the leachates from the litter of five tree species (red alder, Alnus rubra; vine maple, Acer circinatum; western red cedar, Thuja plicata; western hemlock, Tsuga hetrophylla; and Douglas-fir, Pseudotsuga menziesii) were assessed for their chemistry and relative ability to support growth of heterotrophic, stream bacteria. Bacterial growth was measured using [3H]leucine incorporated into protein over 24 h of exposure to nutrient-amended leachates. Bacterial growth was greatest in deciduous and western red cedar leachates, controlling for DOC concentration. Bacterial growth rates on most leachates were greatest after 1 h and then declined in a negative exponential pattern. The DOC less than 10 kDa supported lower bacterial growth rates than DOC from whole leachates on a per milligram DOC basis. The DOC C:N atomic ratio was the best predictor of bacterial growth (r2 = 0.84). DOC release from western hemlock needles increased linearly during 7 days of leaching, whereas most red alder and western red cedar DOC was released after 1 and 2 days, respectively. Successional changes in composition of riparian forest trees may influence the stream microbial productivity based on the changes in dissolved organic carbon.

Le carbone organique dissous (DOC) est abondant dans les systèmes aquatiques et il est incorporé dans les réseaux alimentaires des cours d'eau; cependant, la qualité du DOC est rarement prise en compte. Nous avons analysé chimiquement les DOC des lixiviats de litière de cinq espèces d'arbres, l'aulne de l'Oregon (Alnus rubra), l'érable circiné (Acer circinatum), le thuya géant (Thuja plicata), la pruche de l'Ouest (Tsuga hetrophylla) et le sapin de Douglas (Pseudotsuga menziesii), et déterminé leurs capacités relatives à supporter la croissance de bactéries lotiques hétérotrophes. La croissance bactérienne a été évaluée par l'incorporation de [3H]leucine dans les protéines en 24 h d'exposition aux lixiviats additionnés de nutriments. À concentrations de DOC égales, la croissance bactérienne est maximale dans les lixiviats d'arbres décidus et du thuya géant. Dans la plupart des lixiviats, les taux de croissance bactérienne atteignent un sommet au bout de 1 h, pour ensuite diminuer selon une courbe exponentielle négative. Le DOC de moins de 10 kDa supporte une croissance bactérienne par mg de DOC plus faible que les lixiviats entiers. Le rapport atomique C:N du DOC est la variable prédictive la plus efficace de la croissance bactérienne (r2 = 0,84). La libération de DOC des aiguilles de la pruche de l'Ouest augmente de façon linéaire pendant 7 jours de lessivage, alors que le DOC provenant de l'aulne de l'Oregon et celui du thuya géant sont libérés, respectivement, après 1 et 2 jours. Les changements dans la composition des arbres de la rive au cours de la succession écologique peut donc influencer la productivité microbienne du cours d'eau à cause des variations du carbone organique dissous.[Traduit par la Rédaction]

Document Type: Research Article

Publication date: October 1, 2002

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  • Published continuously since 1901 (under various titles), this monthly journal is the primary publishing vehicle for the multidisciplinary field of aquatic sciences. It publishes perspectives (syntheses, critiques, and re-evaluations), discussions (comments and replies), articles, and rapid communications, relating to current research on cells, organisms, populations, ecosystems, or processes that affect aquatic systems. The journal seeks to amplify, modify, question, or redirect accumulated knowledge in the field of fisheries and aquatic science. Occasional supplements are dedicated to single topics or to proceedings of international symposia.
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