Contribution of microbial and invertebrate communities to leaf litter colonization in a Mediterranean stream
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Leaf litter inputs and retention play an important role in ecosystem functioning in forested
streams. We examined colonization of leaves by microbes (bacteria, fungi, and protozoa) and fauna in
Fuirosos, an intermittent forested Mediterranean stream. Black poplar (Populus nigra) and plane (Platanus
acerifolia) leaf packs were placed in the stream for 4 mo. We measured the biomasses and calculated the
densities of bacteria, fungi, protozoa, meiofauna, and macroinvertebrates to determine their dynamics and
potential interactions throughout the colonization process. Colonization was strongly correlated with
hydrological variability (defined mainly by water temperature and discharge). The 1st week of colonization
was characterized by hydrological stability and warm water temperatures, and allocation of C from
microbial to invertebrate compartments on the leaf packs was rapid. Clumps of fine particulate organic
matter (FPOM) were retained by the leaf packs, and enhanced rapid colonization by microfauna and
meiofaunal collector-gatherers (ostracods and copepods). After 2 wk, an autumnal flood caused a 20-fold
increase in water flow. Higher discharge and lower water temperature caused FPOM-related fauna to drift
away from the packs and modified the subsequent colonization sequence. Fungi showed the highest
biomass, with similar values to those recorded at the beginning of the experiment. After 70 d of postflood
colonization, fungi decreased to nearly 40% of the total C in the leaf packs, whereas invertebrates became
more abundant and accounted for 60% of the C. Natural flood occurrence in Mediterranean streams could
be a key factor in the colonization and processing of organic matter
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