Data from: Contrasting fine-root production, survival and soil CO2 efflux in pine and poplar plantations

Tree root activity, including fine-root production, turnover and metabolic
activity are significant components of forest productivity and nutrient
cycling. Differences in root activity among forest types are not well
known. A 3-year study was undertaken in red pine (Pinus resinosa Ait.) and
hybrid poplar (Populus tristis X P. balsamifera cv `Tristis no. 1')
plantations to compare belowground root dynamics. We measured fine-root
production, mortality and standing crop, as well as soil CO2 efflux. Pine
fine-root production was only 2.9% of that of poplar during three years;
85 pine roots were observed in minirhizotron tubes compared with 4088
poplar roots. Live-root density oscillated seasonally for both species
with late winter minimum and autumn maximum. Poplar reached constant
maximum live-root length within the first growing season, but pine
continued to increase observed fine-root length for three growing seasons.
Within the first 100 days following initial appearance, 22% of the pine
roots disappeared and 38% of the poplar roots disappeared. Median
fine-root longevity of pine was 291 days compared with 149 days for poplar
roots. Fine-root longevity increased with depth in the soil, and was
greater for roots with initial diameter >0.5 mm. The probability of
poplar root death from late February to May was more than three times that
in any other season, regardless of root age. Despite the greater poplar
root production and live-root length, fine-root biomass and soil CO2
efflux was greater in pine. Greater metabolic activity in the pine stand
may be due to greater fine-root biomass or greater heterotrophic
respiration.