Importance of Rhizosphere Bacteria-Grazing Protozoa for Diversity and Structure of Bacterial Communitites, Carbon Turnover and Plant Growth in Grassland Ecosystems

• Research unit: COST
• Project number: C01.0015

Research programs (English)

COST-Action 627 - Carbon Storage in European grasslands

Short description (English)

See abstract

Partners and International Organizations (English)

A, B, CZ, DK, FIN, F, D, H, IS, IRL, I, LT, N, SI, E, CH, GB

Abstract (English)

During the first months of year 2004, we learned methods to cultivate and identified the main soil bacterivorous protozoa in the rhizosphere. These experiments were realized in the collaboration with Dr Flemming Ekelund (department of Terrestrial Ecology, Zoological Institute, University of Copenhagen, Denmark). We attached this learning with a small experiment in which we evaluated the response of rhizobacteria and their predators (Protozoa and nematodes) to aboveground herbivory on barley growth, under two nitrogen fertilization levels (29 and 144mg N per Kg soil). To simulate herbivory attack, one semi-circle (3mm in diameter) of barley leaves was randomly cut every day from each plant, starting one week before sampling. Barley showed a response to both, N-fertilization and to simulated herbivory attack, probably by changing the relative allocation between below and aboveground biomass. The densities of bacteria, protozoa and to a lesser extend nematodes, increased during the experimental period in the rhizosphere of barley. High N-fertilization led to increase the bacterial density (highly significant after 42 days). Simulated herbivory attack did not affected bacterial density. Slight responses of predators were found. The length of the experiment should be shorter to display significant effects on bacterial predators. The effect of N-fertilization and simulated herbivory attack on the structure of bacterial communities associated with barley is actually in progress (DGGE analysis). During the second half of year 2004, we set up microcosms to assess the impact of one protozoan species on soil bacterial communities associated with Lolium perenne. To extend to functional groups, we choose 6 different species of protozoa: 2 flagellates (Neocercomonas, Bodo) 2 Ciliates (Colpoda), 2 amoebas (Acanthamoeba and Naegleria). These experiments were realized in the collaboration with Dr Michael Bonkowski (Institut für Zoologie, TU darmstadt, Germany). We extracted DNA and RNA from the different soil fraction (Bulk soil, rhizospheric soil and rhizoplan-endorhizospher) of each microcosm. For each sample we amplified the 16SrDNA by PCR (Reverse Transcriptase PCR for RNA samples) and compared the DGGE fingerprints. The analyses are in progress.

References in databases (English)

Swiss Database: COST-DB of the State Secretariat for Education and Research Hallwylstrasse 4 CH-3003 Berne, Switzerland Tel. [phone] Swiss Project-Number: C01.0015