© 2004 Heron Publishing—Victoria, Canada
Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants grown in different N regimes
and sprayed with urea in autumn
Shufu Dong (1, 2), Lailiang Cheng (3), Carolyn F. Scagel (4) and Leslie H. Fuchigami (4, 5)
1. Pacific Agri-Food Research Center, Agriculture and Agri-Food Canada, Summerland, BC V0H 1Z0, Canada / 2. Corresponding author (dongs@agr.gc.ca) / 3. Department of Horticulture, Cornell University, Ithaca, NY 14853, USA / 4. USDA-ARS, Horticultural Crops Research Laboratory, Corvallis, OR 97330, USA / 5. Department of Horticulture, Oregon State University, Corvallis, OR 97331, USA / Received February 24, 2003; accepted August 10, 2003; published online January 2, 2004
Summary
Nitrogen mobilization, nitrogen uptake and growth of cuttings obtained from poplar stock plants fertigated with different
nitrogen (N) treatments and sprayed with urea in autumn were studied. Stock plants propagated from poplar cuttings were trained
to a single shoot and fertigated with 0, 5, 10, 15 or 20 mmol l–1 N during the first growing season. In October, a subset of stock plants from each N fertigation treatment was sprayed twice
with either 3% urea or water, and overwintered outside. In March, total tree biomass and total N concentration and content
of stems were estimated for stock plants in each treatment, and cuttings were taken from the middle of each stock plant and
stored in plastic bags at 2 °C. In mid-April, cuttings were planted in 7.5-l pots containing N-free medium and grown outdoors
with a weekly fertigation with nutrient solution containing 0 or 10 mmol l–1 15NH415NO3. In mid-July, cuttings were harvested, and new shoot (new stems and leaves), shank (old cutting stem) and roots were analyzed
for new biomass growth and total N and 15N content. Growth of stock plants was positively related to N supply in the previous growing season. Foliar urea application
in autumn had no effect on subsequent stock plant growth even though urea sprays increased both N concentration and content
in stem tissues. Biomass growth of cuttings obtained from stock plants was closely related to their N content when the cuttings
were grown in an N-free medium regardless of previous treatments applied to the stock plants. When N was supplied in the growth
medium, the strength of the relationship between regrowth and N content of cuttings was significantly reduced. Cuttings from
stock plants treated with foliar urea and grown in a N-free medium remobilized between 75 and 82% of their total N for new
growth, whereas cuttings from plants receiving no urea spray remobilized only between 60 and 69% of their total N for new
growth. Current N fertilization of the cuttings reduced the percentage of N remobilized. We conclude that new growth of poplar
cuttings in spring was more dependent on currently applied N than on reserve N, and urea N applied as a spray in autumn was
more easily remobilized than N taken up by roots during the previous season.
Keywords:
biomass, fertigation, 15N, Populus trichocarpa × P. deltoides
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