Nutrient limitation along eutrophic rivers? Roles of N, P and K input in a species-rich floodplain hay meadow

Question: Is the growth of biodiverse floodplain plant communities along nutrient-rich lowland rivers still limited by nutrients? Location: Floodplains of the river Overijsselse Vecht, the Netherlands. Methods: Soil characteristics and potential nutrient limitation of the vegetation types were studied in two hay meadows, both belonging to the Fritillario-Alopecuretum, in the floodplain of the eutrophic river Overijsselse Vecht (the Netherlands). The meadows had different fertilization histories: one was a species-rich hay meadow managed as a nature reserve, the other a newly created nature reserve that had been used as an agricultural pasture before. Sods collected from both locations were transferred to a glass-house, fertilized weekly with NP, NK, PK, NPK or control solutions and harvested three times a year during two successive growing seasons. Results: Biomass production of sods from both locations of this floodplain still appeared to be limited by N. Interestingly, the sods from the existing nature reserve were also limited by K, but only in the second year. Fertilization caused a shift in the relative abundance of the different plant families. Tissue nutrient concentrations were increased by fertilization with the nutrient in question, but decreased if biomass production was stimulated. Conclusions: Even in eutrophic river areas, the nutrient concentrations of the surface water may still determine the development of potentially biodiverse floodplain vegetation.