The tolerance to salinity and nutrient supply in four European Bolboschoenus species (B-maritimus, B-laticarpus, B-planiculmis and B-yagara) affects their vulnerability or expansiveness

The effects of increasing salinity and nutrient levels on the fitness of four European Bolboschoenus species (Bolboschoenus maritimus, B. laticarpus, B. planiculmis and B. yagara) were studied in cultivation experiments. The study aimed to find whether increases in the salinity or nutrient supply act as key factors in ecological differentiation among the species and whether the responses of species to experimental conditions correspond to their habitat preferences in nature. The plants were cultivated in a salinity gradient with a maximum concentration of 1.5% NaCl and in a nutrient gradient with the following maximum concentrations of nutrients: N 1249.8 mg/l, P 466.8 mg/l, K 585 mg/l, Ca 586.2 mg/l and Mg 585 mg/l. Performance traits indicating plant fitness and proportional traits indicating the characteristics of biomass allocation were compared among species; a general linear model, planned comparisons and plasticity indices were used for data evaluation. The crucial role of salinity tolerance in ecological differentiation among the species was confirmed: the halophyte B. maritimus differed from other species in its salinity tolerance (the lowest plasticity index) in accordance with its habitat specialisation. An important role of nutrient availability in ecological differentiation was also demonstrated: B. laticarpus differed significantly from other species in that it was the most tolerant to high nutrient levels. This species was best able to utilise available nutrients along the entire factor gradient, in accordance with its broad habitat range. In contrast, B. maritimus was least able to utilise available nutrients. This result may be attributed to evolutionary adaptation to a stressed environment - stress resistance syndrome. A broader extent of phenotypic plasticity was found in the other two species. This characteristic enabled B. planiculmis to inhabit various secondary habitats and also to extend its range to saline habitats. B. yagara was highly plastic relative to salinity and nutrient levels, indicating its sensitivity to both factors. B. maritimus and B. yagara may be considered threatened in natural conditions, whereas the expansion of B. laticarpus is possible. (C) 2013 Elsevier B.V. All rights reserved.