Der Stickstoffhaushalt von Pappelrinden und seine Beziehungen zur Temperatur

Abstract

Seasonal changes in nitrogen compounds were investigated in the bark of Populus balsamifera L. The behaviour of these compounds seems to be strongly correlated to the growing activities of the plants. During wintertime we find 95 % of nitrogen in the protein fraction. In the early spring the proteins are mobilized and soluble nitrogen compounds, including free amino acids, increase. Reserve proteins have been found to decrease until the phloem takes up its full function. During the main growth period the bark is mostly used for the transport of the nitrogen compounds. A 25 °C-treatment of twigs during wintertime always causes a decrease of protein-N, and an increase of soluble N-compounds. A 4 °C-treatment of twigs in summer never leads to an increase of proteins. Therefore, a correlation of protein accumulation and frost resistance does not seem to exist. However, when cooling the twigs in June, a strong increase of free N-compounds is found; it might be caused by a stress situation on the growing twigs. Daily changes of N-compounds are correlated to growing intensity and probably to photosynthesis. At night an accumulation of proteins is found. Free proline occurs during water stress on twigs held at 25 °C. Free amino acids are often a small portion of the soluble N-fraction.