© 1998 Heron Publishing—Victoria, Canada
Seasonal fluctuations of starch in root and stem tissues of coppiced Salix viminalis plants grown under two nitrogen regimes
Yuehua Von Fircks (1) and Lisa Sennerby-Forsse (2)
1. Department of Short Rotation Forestry, Swedish University of Agricultural Sciences, P.O. Box 7016, S-750 07 Uppsala, Sweden / 2. The Forestry Research Institute of Sweden, Glunten, S-751 83 Uppsala, Sweden / Received April 28, 1997
Summary
Seasonal changes in starch were studied at the tissue and cellular levels in roots and stems of Salix viminalis L. cuttings. Cuttings were planted in pots containing sand and grown in a controlled environment chamber in which seasons
were artificially induced by changes in temperature and photoperiod. Nitrogen was supplied at optimum and low rates, and during
dormancy, one-half of the plants were decapitated. Starch concentrations in root and stem tissues were determined regularly
during shoot extension growth, dormancy and resprouting after dormancy. We used light microscopy (LM) combined with image
analysis (IA) to determine the cellular localization and amount of starch in different cell types of stem and root tissues.
Chemical analysis confirmed that starch concentrations were lower in plants receiving a high-N supply rate than in plants
receiving a low-N supply rate. In all plants, the highest concentration of starch was in the roots. Light microscopy and IA
showed that starch accumulated mainly in the phloem and cortical cells of both root and stem tissues. Starch grains were also
regularly found in ray parenchyma cells. The amount of starch as well as the size of the grains showed strong seasonal fluctuations.
In both roots and stems, starch concentrations were highest during predormancy and lowest during periods of shoot extension
growth. At the time of resprouting, root cells of decapitated plants were more depleted of starch than root cells of intact
plants, supporting the hypothesis that starch reserves in roots are important during the early phase of resprouting in coppice
systems.
Keywords:
accumulation, decapitation, energy forestry, mobilization, nutritional status, resprouting, storage compounds.
