Replacement of nutrient losses caused by acidification of a beech forest soil and its effects on transplanted field-layer species

Acidification of south Swedish forest soils has caused considerable decreases in pH and exchangeable cations during recent decades. The lowered abundance of several field-layer species is probably related to the altered soil chemistry. The present study focuses on the importance for the vegetation of reduced amounts of Ca, Mg and K. These elements were applied separately or mixed as C1+SO₄, six times the current exchangeable amount of the topsoil of an acid beech forest soil (pH H₂O 4.1). Soil pH was raised to 7 by Na₂CO₃ application and Na was also given as C1+SO₄. Survival and growth of the seven transplanted species were measured during three years (Dentaria bulbifera, Gagea spathacea, Galium odoratum, Lamium galeobdolon, Melica uniflora, Mercurialis perennis and Viola reichenbachiana.Half a year after the treatment the exchangeable amounts of K, Ca and Mg had increased by ca. 2.5 times when applied separately. Howerver, the retention of Mg was strongly disfavoured by the application of all other elements. Exchangeable K and Na thereafter decreased while the effects on Ca and Mg were persistent during the study. D. bulbifera, G. odoratum and M. perennis hardly survived any treatment, possibly due to the low soil pH, while 40–70% of the other species survived. Growth to normal size was only attained by G. spathacea, M. uniflora and V. reichenbachiana. The application of Ca+Mg+K was positive for G. spathacea, L. galeobdolon and M. perennis and Na (as C1+SO₄) for D. bulbifera, L. galeobdolon, M. uniflora and M. perennis. The effects of the Na treatment may partly be caused by the increased pH (5.3). Application of Mg favoured M. uniflora and Na₂CO₃ V. reichenbachiana. Addition of K gave no positive effects.It can be concluded that addition of Ca, Mg and K without raising pH was insufficient for a normal growth for all studied species but M. uniflora and V. reichenbachiana. These two species also had a relatively high survival in the control plots but performance was enhanced by Mg or Na₂CO₃ application.