Small-scale shifting mosaics of two dominant grassland species: the possible role of soil-borne pathogens |
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Authors: | H Olff B Hoorens R G M de Goede W H van der Putten J M Gleichman |
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Institution: | (1) Nature Conservation and Plant Ecology Group, Wageningen Agricultural University, Bornsesteeg 69, 6708 PD Wageningen, The Netherlands, NL;(2) Soil Biology Group, Wageningen Agricultural University, P.O. Box 8005, 6700 EC Wageningen, The Netherlands, NL;(3) Netherlands Institute of Ecology, P.O. Box 40, 6666 ZG Heteren, The Netherlands, NL |
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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.
Received: 19 January 2000 / Accepted: 11 April 2000 |
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Keywords: | Soil-borne pathogens Nematodes Carex arenaria Festuca rubra Interaction web |
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