BIOGEOCHEMICAL CYCLING FOLLOWING PLANTING TO RED PINE ON A SANDY PRAIRIE SOIL

Native prairies in the Lower Wisconsin River Valley provide a means of comparing nutrient cycling patterns across undisturbed and managed ec osystems. Bulk precipitation, throughfall, and soil solutions at three depths were collected from August 1991 to December 1993 at three stud y sites (native prairie and native prairie planted to 30 and 40-year-o ld red pine, Pinus resinosa Ait.). Elemental input-output balances wer e calculated from water chemistry data and from water balances using c hloride as a tracer. Concentrations of cations and dissolved organic c arbon (DOC) in soil solution were greater in the conifer plantations t han in the prairie ecosystem. Inorganic acid concentrations were only slightly higher under pine than under prairie, suggesting that the gre ater cation leaching under pine vegetation was dependent on DOC contri buted by throughfall and leaching from the forest floor. There was a s mall net gain in Mg and losses in Ca, K, and S in the prairie ecosyste m. There was a net loss in all elements from the pine ecosystem, and l osses were greater than from the prairie. The greater losses in Mg, K, and S from the pine ecosystem are attributed to interception of dry d eposition by the tree canopy. Sulfur contributed by dry deposition to the pine ecosystem was mainly returned to the forest floor as organic S and oxidized to SO42- as solutions passed through the soil profile. In contrast, greater Ca losses under pine than under prairie are attri buted to increased weathering due to afforestation.