Uptake of cations under two different water regimes in a boreal Scots pineforest

There is still much to find out about how trees react to changing nutrient conditions. In this cation uptake study, Cs-134 and Na-22 were injected bet ween the humus and the mineral soil, and into a 20-cm depth in the mineral soil, respectively. Half of the experimental site was subjected to desiccat ion in 1995 and 1996, while the other half was subjected to irrigation in 1 995, and desiccation in 1996. One month after the injections, the concentra tion of Cs-134 , the xylem sap was higher in the irrigated plots (ID) than in the desiccated plots (DD). In August 1995, the difference in the Cs-134 concentration in the xylem sap was even higher between the treatments. In 1 995, Na-22 was also higher in the xylem sap on the ID plots than on the DD plots, but not significantly. Exponential relationships were found between the amount of Cs-134 and Na-22 in the xylem sap; the relative water uptake from humus and 0-10-cm mineral soil (Cs-134); and 10-25-cm mineral soil (22 Na) in Jury 1995, when the tracers had not yet reached the top of the boles . The relative uptake of injected 22Na was larger than that of injected Cs- 134, probably due to low exchangeability of Cs in the soil. One year after the injection (1996), more Cs-134 was found in the wood, bark, needles and cones on the plots irrigated in 1995 than on the desiccated plots. The cont ent of Cs-134 in the stem wood and stump amounted to nearly 80% of the tota l uptake in the trees. The Cs distribution 1 year after the Chernobyl accid ent was dominated by Cs on/in needles and bark. After 10 years of redistrib ution, the Chernobyl Cs content of the different parts of the trees approac hed that of K. (C) 2000 Elsevier Science B.V. All rights reserved.