Seasonal dynamics and effects of nitrogen supply rate on nitrogen and carbohydrate reserves in cutting-derived Salix viminalis plants

Nutrient storage is an important aspect of resprouting potential and production of Salix viminalis L., a pioneer species used for biomass production in Sweden. Seasonal dynamics of nitrogen (N), protein, soluble carbohydrates, starch, and lipids were studied in roots, cuttings, stems, and leaves during a full growth cycle induced by varying photoperiod and temperature in a growth chamber. Nitrogen was supplied at two rates. Both season and N availability significantly affected storage of N and carbohydrates. Reserves peaked in dormancy, and plants grown at a higher N availability were able to build up larger N reserves, whereas carbohydrate reserves were similar in the two N treatments. All perennial plant organs functioned as storage sites for N. Roots were prominent in carbohydrate storage, in good agreement with the notion of a pioneer species adapted to recurring disturbance by a pronounced resprouting capacity. Roots differed from aboveground plant parts in their exceptionally high starch levels, and in that N storage in roots to a greater extent involved nonprotein compounds. Triglycerides contributed to carbon storage in aerial plant parts but not in roots. Our results suggest that an increased N supply enhance both the accumulation of nutrient reserves and early season growth.