ROOT MASS, NET PRIMARY PRODUCTION AND TURNOVER IN ASPEN, JACK PINE AND BLACK SPRUCE FORESTS IN SASKATCHEWAN AND MANITOBA, CANADA

Root biomass, net primary production and turnover were studied in aspe n, jack pine and black spruce forests in two contrasting climates. The climate of the Southern Study Area (SSA) near Prince Albert, Saskatch ewan is warmer and drier in the summer and milder in the winter than t he Northern Study Area (NSA) near Thompson, Manitoba, Canada. Ingrowth soil cores and minirhizotrons were used to quantify fine root net pri mary production (NPPFR) Average daily fine root growth (m m(-2) day(-1 )) was positively correlated with soil temperature at 10-cm depth (r(2 ) = 0.83-0.93) for all three species, with black spruce showing the st rongest temperature effect. At both study areas, fine root biomass (me asured from soil cores) and fine root length (measured from minirhizot rons) were less for jack pine than for the other two species. Except f or the aspen stands, estimates of NPPFR from minirhizotrons were signi ficantly greater than estimates from ingrowth cores. The core method u nderestimated NPPFR because it does not account for simultaneous fine root growth and mortality. Minirhizotron NPPFR estimates ranged from 5 9 g m(-2) year(-1) for aspen stands at SSA to 235 g m(-2) year(-1) for black spruce at NSA. The ratio of NPPFR to total detritus production (aboveground litterfall + NPPFR) was greater for evergreen forests tha n for deciduous forests, suggesting that carbon allocation patterns di ffer between boreal evergreen and deciduous forests. In all stands, NP PFR consistently exceeded annual fine root turnover and the difference s were larger for stands in the NSA than for stands in the SSA, wherea s the difference between study areas was only significant for black sp ruce. The imbalance between NPPFR and fine root turnover is sufficient to explain the net accumulation of carbon in boreal forest soils.