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AME 29:253-266 (2002)
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Abstract
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Microbial plankton response to contrasting climatic conditions: insights from community structure, productivity and fraction stoichiometry
Manuel Villar-Argaiz1,*, Juan M. Medina-Sánchez1, Presentación Carrillo2
1Departamento de Biología Animal y Ecología, Facultad de Ciencias, Universidad de Granada, 18071 Granada, Spain
2Instituto del Agua, Universidad de Granada, 18071 Granada, Spain
*E-mail: mvillar@ugr.es
ABSTRACT: Climatic events are among the most important forces governing natural processes in ecosystems. Over a 3 yr period, we monitored changes in the hydrological, chemical and biological regimes of a high mountain lake severely affected by a drought
that peaked in 1995. During the drought, the decrease in lake volume enhanced the contribution of the sediment to the lake nutrient budget. The community became more complex, with the appearance of ciliates and heterotrophic nanoflagellates, organisms
rarely found prior to the drought. The impaired post-drought recovery of the zooplankton, which did not reach normal densities for this lake until 1997, resulted in a microbial-dominated food web in 1996 and a classical grazing food web in 1997. Besides
the species composition or abundance and the autotrophic to heterotrophic ratio, food web changes associated with the drought and atmospheric nutrient inputs were reflected in the stoichiometry and contribution of both bacteria and phytoplankton fractions
to the planktonic particulate matter. Specific productivity measurements showed that cellular N:P ratios could be used to evaluate the growth conditions of phytoplankton but not of bacteria, indicating that an element other than P may limit bacteria
growth. Assessments of phytoplankton and bacteria productivity and of the photosynthetic carbon release relative to bacteria demand in microcosms revealed that after a phosphorus pulse, the phytoplankton N:P ratio determines the nature of the interaction
between phytoplankton and bacteria as either commensalistic or competitive for inorganic P. If phytoplankton N:P is initially high (P-deficient algae), a P pulse can reduce photosynthetic extracellular release (PER) and bacteria can experience C
limitation, whereas if phytoplankton N:P is initially low (P-sufficient algae) and bacteria N:P is high, increased PER is observed and competition for inorganic P may occur.
KEY WORDS: Drought · Atmospheric depositions · Food web · Phytoplankton vs bacteria interaction · Productivity · Stoichiometry
Full text in pdf format
Published in AME Vol.
29, No. 3
(2002) on October 23
Print ISSN: 0948-3055; Online ISSN: 1616-1564.
Copyright © Inter-Research, Oldendorf/Luhe, 2002
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