Nutrient concentrations and fluxes in the throughfall and stemflow of Fraxinus angustifolia Vahl

Abstract

The effect of the ash-tree (Fraxinus angustifolia Vahl) crown on characteristics of throughfall and stemflowsolutions was assessed in wet pastures located in north eastern Portugal. The amounts de gross rainfall, throughfall and stemflow were measured continuously and samples were periodically collected to determine pH, dissolved organic C (DOC) and N (DON), and nutrients. The annual fluxes of DOC, DON, Cl, K, Na, Ca, Mg and P in gross rainfall were, respectively, 3.93, 0.92, 0.20, 0.06, 1.81, 2.40, 1.11, 1.16, 0.29 and 0.06 g m^-2, while those regarding throughfall were 4.42, 0.20, 1.82, 1.82, 0.31, 0.54, 0.62 and 0.20 g m^-2; the flux of N-NH₄⁺ was nil and that of N-NO^-₃ was negative (-0.03 g m^-2). The fluxes in relation with stemflow were small if expressed on a tree crown projection area basis, but can be much greater if the actual area affected is considered. The amounts and distribution of nutrients turned to the soil by throughfall and stemflow may lead to soil chemical characteristics differentiation beneath tree crowns.