© 1986 Heron Publishing—Victoria, Canada
Site fertility affects seasonal carbon reserves in loblolly pine
Elaine M. Birk (1) and Pamela A. Matson (2)
1. Ecosystems Research Center, Cornell University, Ithaca, New York 14853, USA / 2. Ecosystem Science and Technology Branch, NASA-Ames Research Center, Moffett Field, California 94035, USA /
Summary
Concentrations of nitrogen, phosphorus and total non-structural carbohydrates were examined in loblolly pine foliage from
control stands and stands fertilized with sludge containing 450 kg N ha–1. Needles from the fertilized sites had higher N concentrations regardless of needle age. Fertilization increased P concentration
in needles relative to the control sites. Seasonal patterns of change in sugar concentrations were similar among sites for
both current-year and one-year-old needles, the highest concentration (126 mg g–1) occurring in February. Sugar concentrations were lowest in June and were generally lower in current needles than year-old
needles. Starch concentrations and the amount of starch per fascicle varied both seasonally and among sites. Fertilization
increased starch reserves in current needles at the end of the growing season (7 mg g–1 and 14 mg g–1 for the control and fertilized sites, respectively), and increased the rate of starch mobilization during the initiation
of needle growth. In the growing season, starch concentrations were lower in current foliage from high fertility sites than
low fertility sites. Carbon reserves accumulated during the growing season in mature one-year-old needles from control sites
indicating a lower sink strength for carbon under low nutrient conditions. There was a positive relationship between starch
and nitrogen concentrations during the dormant season whereas the relationship was negative during the growing season. The
magnitude and direction of change in starch reserves with the onset of growth following the dormant season may indicate nutrient
limitation and potential growth response to fertilization.
