Evidence for a positive influence of fungivorous soil invertebrates on the seed bank persistence of grassland species

1 Seeds in soil seed banks are exposed to a number of mortality factors, including fungal attack. The composition of the soil fungal community is affected by fungus-feeding soil invertebrates, suggesting that fungus-feeding soil animals may affect losses of seeds caused by fungal attack. We tested this assumption with a full factorial experiment that examined the effects of fungivorous Collembola and of seed coating with a fungicide on seed longevity of four grassland plant species. 2 Seeds of Centaurea nigra, Dactylis glomerata, Origanum vulgare and Taraxacum officinale were kept in Petri dishes filled with soil under conditions that stimulate fungal growth but not seed germination. Treatment factors were (i) addition of the collembolan Protaphorura fimata, a soil-dwelling fungus feeder; and (ii) seed treatment with the fungicide chitosan. After 5 weeks, germination was recorded and viability of the remaining ungerminated seeds was determined. 3 In three species, the addition of P. fimata resulted in an increase in the number of remaining ungerminated viable seeds. This was due to reduced seed mortality (C. nigra, O. vulgare) or to reduced germination (D. glomerata). Seeds of T. officinale remained unaffected. 4 For the fungicide treatment, no significant main effect was found in any species, although in two species there was a significant interaction between the addition of Collembola and seed coating with chitosan. There is circumstantial evidence that this interaction may have resulted from a negative effect of chitosan on adult survival of P. fimata. 5 These results show that fungus-feeding soil invertebrates affect not only the performance of live plants, as shown in previous studies, but also the persistence of seeds in the soil, and that this effect varies between different plant species. 6 Our results suggest that by reducing the mortality of seeds due to fungal decay, fungal grazers may influence the dynamics of plant populations and the assembly of plant communities. Further experimentation under more realistic conditions is, however, required to investigate the importance of this process under field conditions.