Effekter av kvävegödsling och förna på artrikedom och artsammansättning av strandväxter

Sammanfattning

Due to today’s fossil fuel combustion and agricultural fertilization, nitrogen input into terrestrial ecosystems has increased, which is considered the limiting nutrient in most terrestrial plant communities. Increased nitrogen availability often leads to greater biomass and therefore more competition for light, while more biomass also results in increased litter accumulation. Litter can in turn affect plant communities through shading, by acting as a physical barrier for establishment, and by altering the soil microclimate and nutrient dynamics. The purpose of this study was to investigate how nitrogen fertilization affects the species richness and species composition of the plant community, as well as to analyze the effects of litter on species richness. The interactive effects of nitrogen fertilization and litter on species richness will also be analyzed. The study was based on a previous field experiment conducted between 1995 and 1999 on an alluvial meadow near Strycksele along the Vindel River in northern Sweden. The vegetation was examined in plots exposed to three levels of nitrogen fertilization (0, 12 och 48 g N/ m2), both with and without added litter. The effects on the species richness were analyzed using analysis of variance (ANOVA), while changes in species composition were examined through changes in species cover between 1995 and 1999. The results showed that nitrogen fertilization had a significantly negative effect on total species richness, with the largest decrease observed between the control and 12 g N/ m2. The effect was particularly evident among forb species, while the species richness of graminoid species was not significantly affected. The added litter had no significant effect on species richness, and neither did the interaction between nitrogen fertilization and litter, although the result was close to the level of significance. However, species’ composition distinctly changed over the years. Several forb species decreased in cover, particularly in the fertilized plots, while a few graminoid species strongly increased. In addition, year had a significant effect on species richness, which may partly be linked to natural variation, but mainly to the effects of nitrogen fertilization that gradually decreased richness from year to year.