Biology and ecology of Sphaeronema sasseri, Pratylenchus macrostylus, and associated nematodes on Fraser fir and red spruce

The temporal and spatial dynamics of Sphaeronema sasseri, Pratylenchus macrostylus, other associated nematodes, and spruce-fir feeder root-biomass were compared between stands with different health characteristics or elevations in the Black Mountains, North Carolina. Numbers of Sphaeronema sasseri were highest in soil in the spring and then tapered off. Sphaeronema sasseri-root densities increased as root biomass decreased in stands with slight to moderate canopy deterioration. Highest P. macrostylus numbers were in regenerating fir stands. Population densities of P. macrostylus and S. sasseri did not vary between healthy stands at different elevations. Numbers of S. sasseri were correlated to root biomass (r = {dollar}-{dollar}0.45 to {dollar}-{dollar}0.97 P {dollar}<{dollar} 0.01) in high-elevation healthy or declining sites. Population levels of P. macrostylus per g-roots were correlated with feeder roots in high elevation healthy spruce (r = {dollar}-{dollar}0.40, P = 0.01) and fir (r = {dollar}-{dollar}0.94, P {dollar}<{dollar} 0.01), and regenerating fir (r = {dollar}-{dollar}0.81, P {dollar}<{dollar} 0.0001).; Fir feeder-roots had regular to random dispersal patterns. Morisita's indices indicated that the primary nematodes under study were aggregated. Sphaeronema sasseri was detected in 96% of quadrats and related to fir root biomass, r = {dollar}-{dollar}0.61 and r = {dollar}-{dollar}0.50, P {dollar}<{dollar} 0.0001, in intact and deteriorating stands, respectively. In deteriorating stands, numbers of P. macrostylus and fir feeder-root biomass were related, r = {dollar}-{dollar}0.73, P {dollar}<{dollar} 0.001.; Fir seedlings in west-slope microplots amended with S. sasseri and P. macrostylus infected root pieces had restricted tree height, terminal length, and basal diameter (P {dollar}<{dollar} 0.0001) compared to controls after 3 years. Numbers of S. sasseri per g-feeder roots were related to feeder roots, r = {dollar}-{dollar}0.90, P {dollar}<{dollar} 0.02, length of feeder roots {dollar}<{dollar}1-mm diameter, r = {dollar}-{dollar}0.88, P {dollar}<{dollar} 0.03, and plant height, r = {dollar}-{dollar}0.82, P {dollar}<{dollar} 0.05.; Based on observations from temporal and spatial studies, S. sasseri and P. macrostylus were associated with declining spruce-fir stands and exhibited a temporal-spatial-quantitative relationship with feeder-root dynamics.; The description of Pratylenchus macrostylus Wu was amended, using specimens from the Black Mountains. Nematode measurements overlapped the type series, but stylet length (21.8{dollar}-{dollar}24.7 {dollar}pm{dollar} 1.1 {dollar}mu{dollar}m), body length, and the C ratio were greater in North Carolina specimens.