POOLS AND FLUXES OF CARBON AND NITROGEN IN 40-YEAR-OLD FOREST LIMING EXPERIMENTS IN SOUTHERN SWEDEN

Soil samples were collected from litter, humus and mineral soil layers to a depth of 50 cm in 37-42 year-old limed and unlimed plots in one beech and three spruce stands in S Sweden for determination of carbon (C) and nitrogen (N) pools, C and N mineralization rates and nitrifica tion rates. The samples were sifted while still fresh and incubated at a constant temperature (15 degrees C) and soil moisture (50% WHC) for 110-180 days with periodic subsamplings. The C and N pools in the upp ermost soil layers were significantly lower in plots limed with 9-10 t CaCO3 ha(-1) than in unlimed plots, whereas the pools in the deeper m ineral soil did not differ markedly between the treatments. In the who le soil profile, the C and N pools had, on average, decreased by 16% ( P<0.05) and 11% (P>0.05), respectively, after 40 yrs. The smaller redu ction in N pools resulted in significantly lower C:N ratios and increa sed N immobilization in the limed spruce plots but not in the limed be ech plot. C and net N mineralization rates were increased in some of t he limed plots and decreased in others. This indicates that liming can still have a stimulatory effect after 40 yrs in some soils. The nitri fication potential was increased in the limed plots. Liming did not in crease tree growth in the stands investigated. We conclude that liming with high doses of CaCO3 is likely to reduce pools of soil C and poss ibly even soil N in relation to unlimed areas in spruce and beech fore sts in S Sweden. If trees in limed stands do not respond with better g rowth, the treatment will thus result in a net ecosystem loss of C and N in relation to unlimed areas. It was not possible to conclude wheth er the effects of low doses of lime would be similar to those of high doses.