© 1991 Heron Publishing—Victoria, Canada
Quantification of two-year-old hybrid poplar root systems: morphology, biomass, and 14C distribution
Alexander L. Friend (1), Giuseppe Scarascia-Mugnozza (2), J. G. Isebrands (3) and Paul E. Heilman (4)
1. Department of Forestry , Mississippi State University, Mississippi State, MS 39762, USA / 2. Department of Forest Environment and Resources, University of Tuscia, 01100 Viterbo, Italy / 3. USDA Forest Service, North Central Forest Experiment Station, Rhinelander, WI 54501, USA / 4. Western Washington Research and Extension Center, Puyallup, WA 98371, USA / Received June 3, 1990
Summary
Root morphology, biomass, and 14C distribution were studied in two 2-year-old Populus trichocarpa × P. deltoides hybrids, which originated from hardwood cuttings, to determine the pattern of root distribution in a plantation and to refine
methods for root recovery. The trees were labeled with 14CO2 and harvested after a 72-hour chase period. Roots attached to each labeled tree were analyzed for morphological traits at
the time of harvest. Detached roots from within a 1-m3 volume of soil surrounding each tree were separated from the soil and sorted on the basis of rooting depth and root diameter.
Lateral roots > 2 mm in diameter had a largely horizontal orientation at their point of origin from the cutting and extended
horizontally up to 4 m from the cutting. This resulted in considerable overlap of root systems in the plantation. Results
from 14C labeling indicated that 24 ± 4% (± SD) of the carbon exported from branches—labeled within two weeks after branch budset—was
translocated to the root system. Dilution of the root 14C label indicated that from 0 (> 5 mm diameter roots) to 75% (< 2 mm diameter roots) of the roots recovered from within the
1-m3 volume of soil surrounding a harvested tree originated from other trees. Total root biomass was 6 ± 1 Mg ha–1 for both hybrids. Sixty percent of the root biomass was recovered directly from excavation, 16% from coarse-sieving excavated
soil, and 24% from re-sorting sieved soil. The study indicated that root growth of hybrid poplars may be rapid and extensive
and that detailed sorting of soil subsamples substantially improves the recovery of fine roots < 2 mm in diameter.
