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Puccinellia distans is a non-agricultural halophytic grass that has become another host plant for Epichloe typhina, hitherto not reported from Poland. In 1992 we noticed the first symptoms of choke disease in a single population of P. distans in central Poland. Since then we have observed choke disease in 5 populations of P. distans only in man-made habitats. These habitats are strongly anthropogenically salinated but they exhibit the pattern of species composition characteristic of natural salines. In this paper we test the hypothesis that the level of salinity affects the infection of P. distans by the fungus E. typhina. Seven plots were established in the field and each plot was divided into 25 subplots. Within each plot the level of infection in a spring generation of shoots was negatively correlated with salinity (common regression within the plots, beta = -0.674, df = 117, p < 0.001). Negative correlation was also found in an autumn generation within the plots (beta = -0.682, df = 94, p < 0.001) after excluding plot P in which the frequency of infected individuals was the lowest and equal only to 0.05. The proportion of individuals infected by the endophytic stage of the fungus in the populations was assessed using diagnostic polymerase chain reaction. The greatest percentage (98.3%) of infected individuals was found in the population growing in the habitat of the lowest salinity. The high salinity reduces the chance of P. distans to become infected, but may promote the stroma formation of E. typhina twice in the season. Disease expression in autumn clearly represents a misadaptation which could be explained by the fact that the species interactions described here appeared relatively recently as a result of human activity. This hypothesis requires further experimental verification.
The mechanisms of vegetation zonation were determined in order to provide an advice for restoration of natural saline habitats. Field experiments were conducted to examine the response of mature plants to different edaphic conditions. Three dominant species Salicornia europaea L., Puccinellia distans (L.) Parl. and Elymus repens (L.) Golud, characteristic of distinct zones along the salinity gradient (ECe 28.5–2.3 m Scm⁻¹) were studied. Results from a 2-year reciprocal transplant experiment demonstrated that species were restricted to every zone mostly by a salinity level. The obligatory halophyte S. europaea had optimal growth conditions at its home site. This is an opposite result to the one known from inland salt marshes of North America. A distinct growth limitation of transplants was observed in the P. distans and E. repens zones of lower salinity. Fewer individuals and lower aboveground biomass were recorded in the P. distans zone, whereas in the E. repens zone all seedlings died in the second year of observations. The glycophyte E. repens from the less saline site (ca 2.3 mS cm⁻¹) was strongly inhibited in the most saline S. europaea zone (15.8–28.5 mS cm⁻¹). Compared to the control transplants in the S. europaea zone it had shorter new shoots, fewer and shorter shoots, lower above-ground biomass and biomass of rhizomes. The P. distans transplants were markedly limited in the E. repens zone of lower salinity. Fewer and shorter new shoots, flowering shoots, lower above-ground biomass and biomass of grasses’ roots were noted in the transplants of this zone. Since P. distans was found in non-saline areas outside the investigated meadow this effect could not result from the salinity level but from E. repens interaction. The obtained results suggest that for restoration of natural saline habitats the most important is to keep or rebuild the original salinity level of soils. As the second point the control of strong competitors by cutting or grazing should be considered.
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