Microbial catabolic diversity in and beyond the rhizosphere of plant species and plant genotypes
Brolsma, Karst M. ; Vonk, J.A. ; Mommer, Liesje ; Ruijven, Jasper van; Hoffland, Ellis ; Goede, Ron G.M. de - \ 2017
Pedobiologia 61 (2017). - ISSN 0031-4056 - p. 43 - 49.
Brassica juncea - Forbs - Genotypes - Grasses - Grassland species - MicroResp - Solanum tuberosum - Species - Substrate-induced respiration
Microorganisms in the rhizosphere drive important ecosystem processes such as nutrient cycling and organic matter decomposition. Microbial activity in the rhizosphere is a function of both rhizodeposition and the soil's inherent microbial community. In this study, we investigated plant species and genotype effects on microbial functioning in the rhizosphere and compared it to the corresponding bulk soil. We investigated the rhizospheres and bulk soils from eight natural grassland species (four grasses and four forbs) in a long-term biodiversity experiment and genotypes of two crop species (Solanum tuberosum and Brassica juncea) in a short term experiment. Soil microbial functioning was assessed by determining microbial catabolic diversity, which is the microbial response to addition of several carbon-rich substrates. Substrate-induced respiration was higher in the rhizosphere than in the bulk soil for all plant species and genotypes, except for the grasses Agrostis capillaris, Anthoxanthum odoratum and Holcus lanatus, which yielded similar microbial activities in the two soil zones. Microbial catabolic profiles in the rhizospheres of Rumex acetosa, Leucanthemum vulgare and Plantago lanceolata were most distinct from each other and from the other grassland species. The bulk soil's microbial community catabolic profile was also species dependent. For S. tuberosum we found a genotype effect on the microbial catabolic profile in the rhizsophere but not in the bulk soil. For Brassica juncea no such genotype effects were found in the rhizosphere or bulk soil. This is a first step to link microbial rhizosphere activities to soil functioning in natural and agricultural ecosystems.
The stretched exponential as one of the alternatives for the power law to fit ranked species abundance data
Straatsma, G. ; Egli, S. - \ 2017
Matters (2017). - ISSN 2297-8240
Species - Abundance - Distribution - Stretched - Exponential
A central object in community ecology is the species abundance distribution, SAD. We are interested in the power law and its allies for ranked species abundance data. We collected 12 large data sets consisting of many samples. The preliminary fitting result makes a robust impression (12 systems at three scales of integration) that the stretched exponential is an interesting alternative for the power law. For further work advanced statistics are required. Not only ‘our’ data but, quite often, other data as well, consist of sample × species cross tables. With cross tables, also 'within species over samples' characteristics can be studied. An integrated view on data-patterns in multi-sample sets may help to identify generative processes for and the formulation of a relatively simple model for species abundance data.