Document: MAR-3-58-6

Fine-root production, turnover and soil CO₂ efflux in pine and poplar plantations.

COLEMAN, M.D.* ¹, R.E.DICKSON ² and J.G.ISEBRANDS ²

USDA Forest Service, New Ellenton, SC 29809 USA ¹
USDA Forest Service, Rhinelander, WI USA ²

Abstract:
A three-year study in red pine (Pinus resinosa Ait.) and hybrid poplar (Populus tristis X P. balsamifera cv 'Tristis no. 1') plantations was undertaken to compare belowground root dynamics. We measured fine-root production, turnover and standing crop, as well as soil CO₂ efflux. During the course of the experiment, pine fine-root production was 2.9% that of poplar; 85 pine roots were observed in minirhizotron tubes compared to 4088 for poplar. Live-root density oscillated seasonally for both species with late winter minimum and autumnal maximum. Poplar produced a constant maximum amount of live-root length on minirhizotron surfaces within the first growing season, but pine fine roots continued to reach higher maximum length on the minirhizotron surface for the next three growing seasons. Median fine-root longevity was 291 days for pine roots compared with 149 for poplar roots. Fine-root longevity increased with depth in the soil and was greater for roots with initial diameter >0.5 mm. Within the first 100 days following initial appearance, 22% of the pine roots disappeared and 38% of the poplar roots disappeared. The probability of poplar root death from late February to May was more than three times that of any other season, regardless of root age. Soil CO₂ efflux was greater in pine despite greater poplar root production and live-root length. Pine and poplar appear to have very different strategies of root deployment, which may impact soil resource accumulation.

Keywords: minirhizotrons, survival analysis, root activity, hybrid poplar, short rotation woody crops

This abstract is being presented at: 2:15 PM in session:
Oral Session #12: Roots.