Towards a better understanding of phagotrophic protists in leaf processing of freshwaters: Studies on micro-environment and food web structure
Zusammenfassung der Projektergebnisse
Leaf litter tends to accumulate in retention zones of aquatic systems. Here, leaf associated microbial activity and negligible advective transport can lead to low oxic and hypoxic conditions which are hostile for shredding invertebrates. However, phagotrophic protists that can tolerate low oxygen concentrations are suggested to promote leaf litter processing. The project focused on the importance of phagotrophic protists in leaf litter processing at contrasting oxic conditions. The following key hypotheses were tested: (1) Leaf-associated phagotrophic protists accelerate carbon flow during leaf litter processing irrespective of oxic conditions; and (2) micro-currents generated by the mobility of phagotrophic protists enhance nutrient and oxygen transfer towards leaf-associated microbial communities and consequently microbial activity. Microcosm and field experiments demonstrated that oxygen concentration marginally affected microbial mediated leaf litter processing, leaf quality and microbial colonization dynamics. At normoxic conditions, the microbial mediated leaf litter processing was accelerated in the presence of phagotrophic protists by stimulating the leaf-associated microbial community respiration. However at low oxic conditions, phagotrophic protists accelerated the microbial mediated leaf litter processing but not the leaf-associated community respiration. The data suggests that other microbial processes, such as fermentation, result in similar rates of leaf litter processing at low oxic. Besides, phagotrophic protists seemed to have a higher energy demand of cell specific processes and in turn lower growth efficiency at low oxic and hypoxic conditions compared to normoxic conditions. By inducing micro-currents and recycling of nutrients phagotrophic protists, both, promoted the performance of leaf associated aquatic hyphomycetes and in turn leaf litter processing. Burying leaf litter in shifting sandy sediments resulted in a polished leaf’s cuticle which seemed to act as barrier for oxygen transport. However, shifting sandy sediments are colonized by a diverse and abundant community of phagotrophic protists that may positively modulate leaf associated microbial communities. Taken together, results of the project clearly indicate that phagotrophic protists should be taken into consideration when studying leaf litter processing. The leaf litter acts as substrate and surface for a great diversity of phagotrophic protists. In presence of phagotrophic protists at abundances typically found at decaying leaf litter, performance of leaf associated microbial communities and, in turn, carbon flow within the ecosystem is modulated irrespective of oxygen concentration.
Projektbezogene Publikationen (Auswahl)
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2012. Aquatic protists modulate the microbial activity associated with mineral surfaces and leaf litter. Aquatic Microbial Ecology 66: 133–147
Risse-Buhl, U., Karsubke, M., Schlief, J., Baschien, C., Weitere, M. & Mutz, M.
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2012. Tracking the authochthonous carbon flow in stream biofilm food webs. FEMS Microbiology Ecology 79: 118-131
Risse-Buhl, U., Trefzger, N. M., Seifert, A.-G., Schönborn, W., Gleixner, G. & Küsel, K.
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2013. Dynamics, chemical properties and bioavailability of DOC in an early successional catchment. Biogeosciences 10: 1011–1049
Risse-Buhl, U., Hagedorn, F., Dümig, A., Gessner, M. O., Schaaf, W., Nii-Annang, S., Gerull, L. & Mutz, M.
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2013. Lehrbuch der Limnologie. 2nd Edition. Schweitzerbartsche Verlagsbuchhandlung. Stuttgart
Schönborn, W. & Risse-Buhl, U.
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2013. Phagotrophic protist diversity in the groundwater of a karstified aquifer - morphological and molecular analysis. Journal of Eukaryotic Microbiology 60: 467– 479
Risse-Buhl, U., Herrmann, M., Lange, P., Akob, D. M., Pizani, N., Schönborn, W., Totsche, K. U. & Küsel, K.
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2014. Colonization dynamics of ciliate morphotypes modified by shifting sandy sediments. European Journal of Protistology 50: 345-355
Risse-Buhl, U., Felsmann, K. & Mutz, M.
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2015. Molecular and morphological snapshot characterization of the protist communities in contrasting alpine glacier forefields. Acta Protozoologica, Vol 54, No 2 (2015)
Lazzaro, A., Risse-Buhl, U. & Brankatschk, R.
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Phagotrophic protists are a key component of microbial communities processing leaf litter under contrasting oxic conditions. Freshwater Biology Volume 60, Issue 11, November 2015, Pages 2310-2322
Risse-Buhl, U., Schlief, J. & Mutz, M.
