fae Paces Pergamon Press 1965. Vol. 11, pp. 1363-1369. Printed in Northern Ircland MINERAL CYCLING IN A DOUGLAS FIR FOREST STAND* HANS RIEKERK and STANLEY P. GESSEL College of Forestry, University of Washington, Seattle, Washington (Presented by H, RiEkerx) Abstract—Thisstudy of the movementof mineral clements through the forest soil confirmed several observations made by other investigators. The early fall rains cause a flushing of decay products accumulated during the summer. Movementof the various mineral elements depends very much on their chemical! characteristics, and on the fixation properties of the soil system, =Prelease from the forest floor ranged from 2 to 14 per cent, ®*Rb release was 0.01-1.88 per cent and “4Ca release was 0.06-0.86 per cent for similar periods of leaching. “5Ca release over periods of leaching two to three times longer amounted to 0.1-4.1 per cent. Release of =P from the surface soil was about 2800 times less than that from theforest floor. ®*Rb was 2200 times fess and “4Ca was about 160 times less than the release from the forest floor. Release patterns of Ca indicated a slow movementas compared to **P and ®*Rb. Uptake of2? by the trees was evident within a week after application, 92P uptake was about ten times more during spring than duringfall, Uptake of ®®Rb was evidentafter about a mouth during the spring season, but was not observed during fall. Uptake of #°Ca was not significant. INTRODUCTION Antarch in forest productivity and fertil- sation has indicated the importanceof nutrient érnamics."-2) The entry of radioactive fallout wrducts into the cycling processes of biological mportance has received considerable attention, Cote®reported on a study ofmineral cycling = western Washington. He found marked aterences in the mineral! retention of the major tirient elements by the forest floor. The nual release of potassium was 56 per cent of ~¢ total capital present in the forest floor. ':'cum release was 7 per cent, nitrogen 2 per “ot and phosphorus } per cent of the total. “mparisen of these releases to the input by <erfall indicated an accumulation process. ~erhing prior to usual collection of litterfall visdeduced to be 80 per cent ofthe potassium ied 40 per cent of the magnesium involved with ** uansfer. Maximum rates of release were ‘This study is based on work performed partly v-h support from a National Science Foundation Faint to S. P, Gessei, and partly with support from * Radiation Biology Laboratory (AEC Contract '5-1)1385), University of Washington, Seattle, “ashiagton. reported for fall. Abrupt changes in the eccsystem byclearcutting andfertilization modified these general release patterns.“ Except for calcium these treatments had no effects on the movement of mineral elements decper in the soil. Nearly all the elements were retained within the rooting zone. Studies conducted at the Oak Ridge National Laboratory, Tennessee, with radio-cesium tracers in White Oak and Tulip Poplar indicated a high mobility. In particular, freshly fallen litter released relatively large amounts of cesium in a short time.6-6 It is the purpose of the present study to investigate in more detail the cycling processes as reported by Core and Gesset. The use of radioactive tracers makes it possible to measure velocities, and more important, to distinguish newly arrived nutrient elements from the amounts already present in the various components ofthe ecosystem. For example, the calcium contentofthe soil solution is a mixture ofcalcium released by the soil and calcium passing through directly from the forest floor. For this study three contrasting mineral elements in carrier solutions were tagged and applied to the forest floor or surface soil. 1363