Nutrient and Organic Matter Dynamics in Beech Forest Floors, in Relation to the Presence of Ground Flora

Abstract: The objective of this thesis was to quantify differences between adjacent patches with and without ground flora of Deschampsia flexuosa L. Trin or Anemone nemorosa L. in two acid European beech (Fagus sylvatica L.) forest floors in south-west of Sweden. The studies included soil properties and chemistry, N mineralisation and bioavailability of dissolved organic carbon (DOC), in soil leachates (SL), soil matrix solution (SMS) and soil water extractions (SWE). The studies showed that soil properties and chemistry and N mineralisation differ between plots with and without ground flora. Whereas there were no differences in bioavailability of DOC in soil solutions from plots with and without ground flora. I found higher pH in plots with D. flexuosa and lower soil organic matter (SOM) content, water content, cation exchange capacity, base saturation and N concentration, than in plots without grass. At the A. nemorosa site, pH, and base saturation were higher in plots with ground flora than without. N mineralisation rate was lower in plots with D. flexuosa than without. Contrary, the amount of mineralised N was higher in plots with A. nemorosa than without. In June at the A. nemorosa site, the nitrogen concentrations in SL were higher in plots with A. nemorosa than without. This may be due to plant uptake or microbial immobilisation. At the D. flexuosa site mean NO3-N concentration in SL and SMS was lower in plots with grass than without. The amount of mineralised N in the soil from the A. nemorosa site was twice as high as in the soil from the D. flexuosa site, with domination of NO3-N and NH4-N respectively. These differences were probably caused by lower pH (KCl) and higher SOM content in the D. flexuosa soil than in the A. nemorosa soil. Mixing the nitrifying soil from the A. nemorosa site with the low nitrifying soil from the D. flexuosa site, induced nitrification and ammonification rate in the D. flexuosa soil, in plots with grass. These results indicate that the microorganisms are limited by C at the A. nemorosa site and N at the D. flexuosa site. SMS was more acid than the SL at both sites. Probably due to the more rapid passage of incoming rain water and hence a lower contact time and ion exchange rate with the acidic soil matrix in SL. At the D. flexuosa site, NO3-N, NH4-N, DON and PO4-P concentrations were lower in SMS than in SL, indicating plant uptake, microbial immobilisation and/or adsorption in the soil. A higher concentration of NO3-N was found in SMS than in SL at the A. nemorosa site, probably due to a higher nitrification rate in the smaller pores and/or longer contact time between soil and water and a larger population of nitrifiers. The bioavailability of DOC differed between soil solution types. DOC in SWE was the most bioavailable and DOC in SMS was the least bioavailable. These results are probably reflecting different origin of DOC in soil solutions in larger and smaller pores of the forest floor, which will influence the quality of DOC.