Could plant-feeding nematodes affect the competition between grass species during succession in grasslands under restoration management?

Summary

1 We examined the effects of plant-feeding nematodes on competition between Holcus lanatus and Anthoxanthum odoratum. In the Drentse A nature reserve, the Netherlands, a relatively productive grassland, represented by H. lanatus, has gradually been replaced by a less-productive community, represented by A. odoratum, after the application of fertiliser was stopped. Stressed plants are generally considered to be more sensitive to herbivory. 2 We hypothesized that plant-feeding nematodes would exacerbate the competitive disadvantage of H. lanatus resulting from nutrient limitation. We compared performance in an adjusted De Wit replacement series with monocultures, grown in soil that was either treated or untreated with nematicides at both low and high nutrient supply. 3 The biomass production of both plant species was negatively affected by intra- and interspecific competition. Although H. lanatus was a stronger competitor than A. odoratum in mixed cultures, it was more sensitive to plant-feeding nematodes and nutrient limitation. Nematodes and nutrient stress therefore reduced the competitive suppression of A. odoratum by H. lanatus. Low nutrient availability did not enhance the effect of plant-feeding nematodes on plant growth and competition, indicating additive rather than synergistic effects on plant performance. 4 We conclude that plant-feeding nematodes may contribute to species replacements in grasslands after fertilization has been stopped, albeit to a lesser extent than reduced nutrient availability. Plant species-specific differences in tolerance to plant-feeding nematodes in general, rather than host specificity of nematodes, are responsible for any effects