Seasonal changes of bioelements in the litter and their potential return to green leaves in four species of the Argentine subtropical forest

The aim of this work was to analyse the nutrient concentrations of N, P, Ca , Mg, K and Na in mature leaves, branches and fruits and to investigate rel ationships between the contents of these bioelements in senescent and fresh leaves in four forest species: Gleditsia amorphoides (Espina Corona), Pata gonula americana (Guayaibi), Chlorophora tinctoria (Mora) and Astronium bal ansae (Urunday). The study site was located in the Colonia Benitez Estricta Nature Research (Chaco, Argentina). In this subtropical forest, total litt er was collected monthly and was sorted into three groups: (1) leaves; (2) branches and fruit; (3) unidentified. Total dry matter was recorded and ana lysed for N, P, Ca, Mg, K and Na. Espina Corona had the highest leaf concen trations of N, while Mora had the highest concentrations of Ca and Mg. The highest leaf concentrations of P were found in Espina Corona, Mora and Urun day. No significant differences in K were found among the different species . Na concentrations were higher in Espina Corona and Guayaibi than Mora and Urunday. A marked seasonal variability was observed in the concentrations of N, P and K, with no important differences for Ca and Mg, except in Espin a Corona. These variations in nutrient concentrations were greater in leave s than in branches and fruits. N and P were translocated to other tree orga ns and Ca, Mg and Na were accumulated in mature leaves. The bioelement K is the only one that undergoes leaching and mobilization in all species. Reso rbed N and P can be used for the production of new leaf organs in the follo wing annual cycle. This resorption supports a portion of the production of new foliage, diminishing the demand from soil. (C) 2000 Annals of Botany Co mpany.