Small-scale shifting mosaics of two dominant grassland species: the possible role of soil-borne pathogens

Abstract

We analyzed the dynamics of dominant plant species in a grazed grassland over 17 years, and investigated whether local shifts in these dominant species, leading to vegetation mosaics, could be attributed to interactions between plants and soil-borne pathogens. We found that Festuca rubra and Carex arenaria locally alternated in abundance, with different sites close together behaving out of phase, resulting in a shifting mosaic. The net effect of killing all soil biota on the growth of these two species was investigated in a greenhouse experiment using gamma radiation, controlling for possible effects of sterilization on soil chemistry. Both plant species showed a strong net positive response to soil sterilization, indicating that pathogens (e.g., nematodes, pathogenic fungi) outweighed the effect of mutualists (e.g., mycorrhizae). This positive growth response towards soil sterilization appeared not be due to effects of sterilization on soil chemistry. Growth of Carex was strongly reduced by soil-borne pathogens (86% reduction relative to its growth on sterilized soil) on soil from a site where this species decreased during the last decade (and Festuca increased), while it was reduced much less (50%) on soil from a nearby site where it increased in abundance during the last decade. Similarly, Festuca was reduced more (67%) on soil from the site where it decreased (and Carex increased) than on soil from the site where it increased (55%, the site where Carex decreased). Plant-feeding nematodes showed high small-scale variation in densities, and we related this variation to the observed growth reductions in both plant species. Carex growth on unsterilized soil was significantly more reduced at higher densities of plant-feeding nematodes, while the growth reduction in Festuca was independent of plant-feeding nematode densities. At high plant-feeding nematode densities, growth of Carex was reduced more than Festuca, while at low nematode densities the opposite was found. Each plant species thus seems to be affected by different (groups of) soil-borne pathogens. The resulting interaction web of plants and soil-borne pathogens is discussed. We hypothesize that soil disturbances by digging ants and rabbits may explain the small-scale variation in nematode densities, by locally providing "fresh" sand. We conclude that soil-borne pathogens may contribute to plant diversity and spatial mosaics of plants in grasslands.

Aboveground environment type, soil nutrient content and arbuscular mycorrhizal fungi explain establishment success of Centaurea jacea on ex-arable land and in late-successional grasslands

“…(Klironomos 2002;De Deyn et al 2003;Kardol et al 2006;Bezemer et al 2006;Macel et al 2007). However, various other groups of soil organisms can also affect seedling survival, including root feeding insects and nematodes (Brown and Gange 1989;Olff et al 2000;De Deyn et al 2003). Further studies are required to assess the relative effect of soil fungi and other groups of soil organisms on seedling survival of C. jacea.…”

“…Hence, the results suggest that plants are more likely to encounter circumstances that promote AM fungal colonization at sites with such abiotic soil conditions and have higher establishment rates. Our investigations largely focused on AM fungi, which generally have a positive influence on plant growth, but other groups of soil organism can either positively or negatively impact plant performance (Brown and Gange 1989;Olff et al 2000;Klironomos 2002;De Deyn et al 2003;Kardol et al 2006). The overall effect of the belowground environment clearly depends on the combined impact of the various groups of organisms (Bever et al 1997).…”

Negative Plant–Soil Feedback and Positive Species Interaction in a Herbaceous Plant Community

“…Several studies showed how negative feedback affects the spatial distribution of clonal modules , thus indicating that the foraging of plant rhizomes depends on that local environmental heterogeneity (Hutchings and de Kroon 1994). Negative feedback involves effects on the same species, while effects on other species are strongly species-specific ( Van der Putten et al 1993;Bever 1994;Olff et al 2000;, suggesting an important role in the competitive relation between coexisting species (Bever et al 1997;Bever 2003;.…”

Disease in Natural Plant Populations, Communities, and Ecosystems: Insights into Ecological and Evolutionary Processes

“…For example, in grassland communities in the Netherlands, spatial variation in pathogenic nematode activity is important in determining fine-scale patterns in plant community composition. Variation in nematode numbers, however, depends on soil disturbance due to ant nest construction, and the numbers of ant nests are in turn dependent on rabbit and cattle grazing patterns (26,92).…”