Fine root diversity, density, and phenology among native hybridizing riparian trees at multiple elevations

We studied minirhizotron fine root (<2mm) diversity, density, and phenology in  natural riparian forest stands in Northern Utah. We examine numbers of standing roots in four classes (newly produced cottonwood, suberized cottonwood, mycorrhizal cottonwood, and herbaceous) throughout an entire growing season at three elevations. Using genetically diverse stands and data from a nearby common garden we were also able to examine genetic influences on root partitioning among the four classes in the soil through time. We find that our high elevation site exhibited high production and high turnover, and was dominated by short-lived young roots. Lower elevation sites where dominated by more persistent suberized roots and mycorrhizal roots. Additionally, while root presence in the soil showed a bimodal distribution at lower elevations where root densisty (number of roots per area of soil) was highest during spring and fall, root density more typically showed a single peak at higher elevations near the middle of summer. We also found in a common garden that high elevation genotypes had a higher fractal dimension in the soil, and were also dominated by greater numbers of shorter lived roots. These data demonstrate interesting diversity in root types and phenology within forest stands dominated by closely related riparian trees of the same genus.