Autumn nutrient resorption and losses in four deciduous forest tree species

Nutrient resorption prior to leaf senescence is an important mechanism of nutrient conservation in forest tree species. However, despite the abundance of literature on the subject, inter-specific comparison of common temperate tree species is complicated by both the variability of resorption efficiency, which is affected by many environmental factors, and methodological differences between the studies, especially in relation to measurements of nutrient losses. This study compares the autumn nutrient resorption and nutrient losses via throughfall and litterfall of N, P, K, S, Mg, Ca, Cu, Fe and Mn in adjacent 40-year-old stands of Quercus robur L., Tilia cordata Mill., Fraxinus excelsior L. and Betula pendula Roth. In addition, the relative susceptibility of leaves to leaching was studied in the laboratory. For all species and elements, except K in ash stands, nutrient losses via throughfall were considerably lower than the losses via litterfall during the sampling period (from the end of August to the middle of October). Nutrient amounts in the throughfall were mostly governed by the susceptibility of the respective species to foliar leaching, which was highest in ash trees, but also depended on nutrient amounts in the pre-senescent leaves. K showed the highest losses via throughfall among the studied elements, 30% of the green leaf content being lost in the ash stand and 8–11% in the other stands. Ash also showed considerable throughfall losses (9–19% of green leaf content) of S, Mn, Mg, Ca and P, while the corresponding losses of these elements in other species were lower in relation to the nutrient content of their foliage. Species with higher amounts of nutrients in the green leaves tended to have higher amounts of nutrients in their litter, but this tendency was not observed for all species and elements. Nutrient resorption efficiency, calculated on leaf area basis, differed among species and was highest for N (ranging from 36% in ash to 69% in birch), P (from 37 in ash to 59% in lime), K (from 38% in ash to 51% in lime) and S (from 31% in ash to 48% in birch). Fe and Cu were the most efficiently withdrawn micronutrients (the amounts resorbed ranging from 7–10% in lime to 20–37% in the other species).