Zum Einfluss von fungivoren Bodenorganismen und Fungiziden auf die Demografie von Samen-Populationen im Boden
|Other Titles:||Influence of fungivorous soil organisms and fungicides on the demography of seed-populations in the soil||Authors:||Mitschunas, Nadine||Supervisor:||Filser, Juliane||1. Expert:||Filser, Juliane||2. Expert:||Diekmann, Martin||Abstract:||
The seeds of many plant species form seed banks in the soil to synchronise seedling emergence with the occurrence of favourable conditions for plant establishment. This adaptation to reduce seedling mortality does however come at a cost, as it increases the probability of mortality at the seed stage, for example through decomposition by micro-organisms, among which saprophytic fungi deserve special mention.Within this PhD project, two literature reviews were carried out to document the current state of research regarding the influence of these fungi on the demography of buried seeds, and regarding the interactions between soil fungi and the soil mesofauna. Based on these literature reviews, hypotheses were derived to be tested in the experimental part of my PhD project.Seed burial studies carried out across a range of ecosystems to compare the demographic fates of fungicide-treated seeds and of untreated seeds have demonstrated a negative effect of such fungi on the longevity of buried seeds. Soil fungi themselves are consumed by a wide range of soil-dwelling animals. It seems possible that the fungivorous soil mesofauna, through its feeding activity, may be able to reduce fungal attack of seeds buried in the soil, and thus to increase seed survival.In two experiments I investigated whether this can indeed be the case. The first experiment was carried out under constant environmental conditions conducive to both the growth of soil fungi and the reproduction of collembolans, and at the same time inhibitive to seed germination. This experiment was conducted in Petri dish Ã ¯Ã ¿Ã ½microcosmsÃ ¯Ã ¿Ã ½ containing soil and the seeds of four different grassland plant species. At the beginning of a five-week incubation period, individuals of the collembolan Protaphorura fimata were added to a subset of Petri dishes. This resulted in an increase in the number of viable ungerminated seeds at the end of the experiment in three of the species, Centaurea nigra, Dactylis glomerata and Origanum vulgare. In a subsequent field experiment I used perforated steel cylinders lined with gauze and filled with defaunated soil and seeds of 3 grassland plant species as experimental mesocosms, which were buried in autumn. I tested whether similar results to those observed in the first experiment under lab conditions would be found with respect to seedling emergence under field conditions. Again, P. fimata was added to a subset of these mesocosms. Both in C. nigra and in O. vulgare seedling emergence was significantly higher in the presence of added P. fimata. The results of these two experiments allow the conclusion that the fungivorous soil mesofauna may potentially affect plant species composition by promoting some species via a reduction in fungal-induced seed mortality, but not others. In a third experiment I investigated whether methodological variations with respect to use and combination of different fungicides would be able to affect levels of seed mortality attributed to fungal-induced seed decomposition, and also whether dormancy levels, and thus the readiness of seeds to germinate, would be affected by fungicide treatments. For this purpose, in autumn the seeds of three grassland plant species were treated with up to three different fungicides (captan, iprodione and mancozeb) alone and in combination - an untreated control treatment was also included - and buried in the field using seed bags made of nylon stockings. In the following spring, after retrieval of the seed bags, I used germination tests and tetrazolium viability testing to determine levels of seed mortality during the burial period. In two species, Daucus carota and Anthriscus sylvestris, the combination of two fungicides generally resulted in a lower mortality than use of a single fungicide. However, in Daucus the use of all three fungicides in combination generally resulted in a slightly higher mortality than the use of just two fungicides in combination. The use of mancozeb resulted in a longer-lasting increase in dormancy levels in Daucus, whereas a similar effect on seed dormancy in Centaurea nigra was more short-lived. As these effects on seed mortality and dormancy were both species-specific and fungicide-specific, I recommend to conduct pilot studies to investigate such fungicide effects before an actual seed burial study is carried out, and to do so particularly when a study is designed with the aim to measure in situ seedling emergence.
|Keywords:||Collembola, fungal attack, seed bank persistence, seed longevity, grassland species, saprophytic fungi, soil mesocosms, Protaphorura fimata, fungicide treatment, seed mortality, dormancy, seed burial experiments||Issue Date:||6-May-2008||URN:||urn:nbn:de:gbv:46-diss000110695||Institution:||Universität Bremen||Faculty:||FB2 Biologie/Chemie|
|Appears in Collections:||Dissertationen|
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