© 2004 Heron Publishing—Victoria, Canada
Fine root dynamics in a developing Populus deltoides plantation
Christel C. Kern (1, 2), Alexander L. Friend (3), Jane M.-F. Johnson (4) and Mark D. Coleman (5)
1. USDA Forest Service, North Central Research Station, 1831 Hwy 169 E, Grand Rapids, MN 55744, USA / 2. Corresponding author (cckern@fs.fed.us) / 3. USDA Forest Service, North Central Research Station, 410 MacInnes Drive, Houghton, MI 49931, USA / 4. USDA Agricultural Research Service, North Central Soil Conservation Research Laboratory, 803 Iowa Avenue, Morris, MN 56267,
USA / 5. USDA Forest Service, Southern Research Station, P.O. Box 700, New Ellenton, SC 29801, USA / Received July 14, 2003; accepted November 21, 2003; published online April 1, 2004
Summary
A closely spaced (1 × 1 m) cottonwood (Populus deltoides Bartr.) plantation was established to evaluate the effects of nutrient availability on fine root dynamics. Slow-release fertilizer
(17:6:12 N,P,K plus micronutrients) was applied to 225-m2 plots at 0, 50, 100 and 200 kg N ha–1, and plots were monitored for two growing seasons. Fine root production, mortality, live root standing crop and life span
were analyzed based on monthly minirhizotron observations. Fine root biomass was measured in soil cores. Fine root dynamics
were controlled more by temporal, depth and root diameter factors than by fertilization. Cumulative fine root production and
mortality showed strong seasonal patterns; production was greatest in the middle of the growing season and mortality was greatest
after the growing season. Small diameter roots at shallow soil depths cycled more rapidly than larger or deeper roots. The
strongest treatment effects were found in the most rapidly cycling roots. The standing crop of live roots increased with fertilizer
treatment according to both minirhizotron and soil coring methods. However, production and mortality had unique treatment
response patterns. Although cumulative mortality decreased in response to increased fertilization, cumulative production was
intermediate at 0 kg N ha–1, lowest with 50 kg N ha –1, and highest with 200 kg N ha–1. Aboveground growth responded positively to fertilization up to an application rate of 50 kg N ha–1, but no further increases in growth were observed despite a threefold increase in application rate. Median fine root life
span varied from 307 to over 700 days and increased with depth, diameter and nutrient availability.
Keywords:
cottonwood, fine root production, nitrogen fertilizer, root longevity, short rotation woody crops, stand development.
