Effects of nitrogen addition on nitrogen mineralization and nutrient content of expanding Calamagrostis epigejos in the Podyjí National Park, Czech Republic

Effects of extra nitrogen (N) input on biomass production, the concentration of N and phosphorus (P) in plant material, and net N mineralization were studied during three growing seasons in a dry acidophilous grassland dominated by Festuca ovina and in a grassland where the tall grass Calamagrostis epigejos was aggressively expanding. In contrast to dry grassland, the Calamagrostis stand utilized more N due to higher plant and microbial demands for soil mineral N, which could prevent the N losses. Additional N supply resulted in the increased net N mineralization mainly in expanding Calamagrostis. There was no effect of N addition on biomass production of Calamagrostis , while a significant increase of total biomass was observed in Festuca in the dry grassland. This higher production was entirely accounted for by the increase in root dry weight. Concentrations of N in the aboveground biomass increased in both Calamagrostis and Festuca dry grassland as a result of N addition. However, P concentrations in Festuca were reduced, while being enhanced in Calamagrostis. The N : P ratio in aboveground biomass significantly increased in both vegetation types studied following N addition, although reaching higher values in dry grassland than in Calamagrostis. This species compensated enhanced N availability with a higher P uptake as compared to Festuca.