© 1992 Heron Publishing—Victoria, Canada
Growth and phenology of seedlings of four contrasting slash pine families in ten nitrogen regimes
L. Dewald (1), T. L. White (2) and M. L. Duryea (2)
1. Department of Biology, Warren Wilson College, Swannanoa, NC 28778, USA / 2. Department of Forestry, University of Florida, Gainesville, FL 32611, USA / Received May 21, 1991
Summary
Seedlings of two fast- and two slow-growing families of slash pine, Pinus elliottii Englm. var. elliottii, were grown in a greenhouse for one growing season in one of 10 nitrogen (N) regimes. Increasing the N concentration in the
nutrient solution resulted in both increased growth rates during the exponential growth phase and extended duration of the
growing season. The two components of total height, free growth (epicotyl length to the first bud) and summer growth (height
growth after the first bud), both increased significantly with increasing N concentrations up to 40–60 mg l–1 but decreased at N concentrations above 180 mg l–1. Compared to seedlings grown in the presence of an optimum N concentration, seedlings grown in the presence of trace amounts
of N were smaller and had less summer growth as a percentage of total growth, earlier cessation of height growth, fewer flushes,
lower shoot/root ratio, higher root fibrosity, and lower N concentrations in all seedling tissues. Compared to slow-growing
families, fast-growing families had more summer height growth, more flushes and later growth cessation, higher shoot/root
ratios and higher root fibrosity at all N concentrations. In the presence of an optimum or higher concentration of N, the
fast-growing families also had higher needle and total N concentrations than the slow-growing families. Strong family by N-treatment
interactions occurred for height, phenology and biomass traits because of the extra responsiveness of one family to increasing
N concentration. Several seedling traits were identified that appear promising for predicting field performance in slash pine.
The results indicated that the nutrient environment greatly influences genetic expression (e.g., family patterns of summer
growth were most closely related to field rankings for seedlings in the trace-N treatment).
