Seasonal trends in energy contents of storage substances in evergreen gymnosperms growing under mild climatic conditions in Central Europe

Abstract

From the contents of the soluble sugars, starch, and total lipide measured at monthly intervals during the course of a year in leaves and barks of Taxus baccata, Juniperus communis, Thuja occidentaliis, Picea excelsa and Sequoiadendron giganteum the energy contents of storage substances were calculated and their seasonal trends established. From Taxus and Juniperus the wood was investigated in the same manner. Furtheron, the seasonal trends in total N-contents of leaves and barks of Taxus, Juniperus and Thuja were measured. As energy storing substances the N-compounds are not important. From the seasonal trends of the N-contents a function of the old leaves as an important N-storage pool for the budding may by concluded. In the one year old needles of Picea and Taxus the carbonic acid contents were measured, from an energetic point of view the acids are not important as reserve-substances. From the seasonal trends of the energy contents in the different species a general pattern of storage in gymnosperms growing under mild climatic conditions in Central Europe was deduced. Remarkably, according to this pattern the highest amounts of starch are found in the spring or early summer, the maximum contents of total lipide are reached during autumn or early winter and the highest contents of soluble sugars are found in the winter. This pattern confirms earlier assumptions regarding the functions of different storage substances. The total energy contents decline during the growth period and reach their lowest values in the late spring and early summer. In the winter none of the species showed an extensive diminution of storage energy, but rather sometimes a rise was seen which points to a net production during the winter months. Thus, the highest energy contents in the leaves are often found in the winter. The old needles have an important function as storage sites in the evergreen gymnosperms.