© 2005 Heron Publishing—Victoria, Canada
Species differences in timing of leaf fall and foliage chemistry modify nutrient resorption efficiency in deciduous temperate
forest stands
Ülo Niinemets (1, 2, 3) and Ülo Tamm (4)
1. Department of Plant Physiology, University of Tartu, Riia 23, Tartu 51011, Estonia / 2. Centro di Ecologia Alpina, I-38040 Viote del Monte Bondone (TN), Italy / 3. Corresponding author (ylon@ut.ee) / 4. Institute of Forest Research, Estonian Agricultural University, Kreutzwaldi 5, Tartu 51014, Estonia / Received October 15, 2004; accepted December 14, 2004; published online June 1, 2005
Summary
Extensive variation in fractional resorption of mineral elements from plant leaves is still not fully understood. In multi-species
forest stands, species leaf fall phenology and leaf constitution may significantly modify the timing of nutrient return to
the soil and overall plant nutrient loss. We studied leaf fall and nutrient loss kinetics, and leaf composition in three natural,
temperate, deciduous broadleaf forest stands to determine the role of timing of leaf abscission and nutrient immobilization
in cell walls on nutrient resorption efficiency of senescing leaves. Nitrogen (N), phosphorus and potassium contents decreased
continuously in attached leaves after peak physiological activity during mid-season. Changes in nutrient contents of attached
leaves were paralleled by decreases in nutrient contents in freshly fallen leaf litter. In different species and for different
nutrients, resorption of nutrients from senescing leaves proceeded with different kinetics. The maximum nutrient resorption
efficiency (the fraction of specific nutrient resorbed from the leaves at the end of leaf fall) did not depend on the mid-seasonal
nutrient concentration. Species with earlier leaf fall resorbed leaf nutrients at a faster rate, partly compensating for the
earlier leaf fall. Nevertheless, the litter-mass weighted mean nutrient contents in leaf litter were still larger in species
with earlier leaf fall, demonstrating an inherent trade-off between early leaf fall and efficient nutrient resorption. This
trade-off was most important for N. Losses of the non-mobile nutrients calcium and magnesium were unaffected by the timing
of leaf fall. There was large variation in the maximum N resorption efficiency among species. Correlations among leaf chemical
variables suggested that the maximum N resorption efficiency decreased with the increasing fraction of cell walls in the leaves,
possibly due to a greater fraction of N occluded in cell wall matrix. We conclude that species leaf fall phenology and leaf
chemistry modify the timing and quantities of plant nutrient losses, and that more diverse forest stands supporting a spectrum
of species with different phenologies and leaf types produce litter with more variable chemical characteristics than monotypic
stands.
Keywords:
calcium, cell wall content, litter quality, nitrogen, phosphorus, potassium, species diversity, temporal variation.
