Seasonal variation of macronutrients in leaves, stems and roots of Salix dasyclados Wimm. grown at two nutrient levels

In order to obtain a more compete understanding of the macronutrient dynamics in coppiced willow plantations, a pot experiment with Salix dasyclados was performed. In this study, the seasonal variation in concentration and amounts of N, P, K, Mg, Ca and S in roots, cutting, stem and leaves were determined. Plants were grown in pots containing 1 l of washed sand under outdoor conditions. Nutrients were given during the first 3–4 weeks at two relative addition rates, 0.08 (−Nutr) and 0.12 (+Nutr) day−1, respectively. Nine harvests were performed and covered a whole seasonal cycle. At each harvest, leaf area (growing season only), dry weight and macronutrient concentrations in roots, cutting, stem and leaves (growing season only) were determined. Plants in the +Nutr treatment continued to grow 2 weeks longer in the autumn than −Nutr plants and started to grow 1 week earlier the following spring. The leaf area and the weight of the different plant parts were significantly higher in the +Nutr plants. Between 40% and 50% of N and about 60% of P was withdrawn from the leaves prior to abscission and stored mainly in the above-ground perennial organs. Retranslocation of K and S from senescing leaves was only observed in −Nutr plants. No seasonal trends and no retranslocation from senescing leaves were observed for Ca and Mg. At bud break, N stored in all perennial organs was used for growth of new shoots.