Forested regions represent a major area of uncertainty for landscape- and ecosystem- level carbon models. Little is known about how carbon fluxes in and out of root systems vary within forests due to the influence of different landscape elements and their effects on abiotic conditions. In particular, soil water conditions are known to be spatially structured across topographically diverse landscapes. It is largely unknown whether fine root dynamics that affect carbon flux are influenced by topography within a landscape. We hypothesized that tree fine root dynamics would vary nonlinearly across a mesic, forested catchment due to temporal variability in soil water content associated with hillslope position. Specifically, we hypothesized that fine root production and lifespan would be highest in areas of optimal soil water content, which is somewhere in the middle of the soil water content spectrum, and that decreasing or increasing soil water content beyond this optimal point would result in declining fine root lifespan and production. We hypothesized the converse with root turnover, such that root turnover would be lowest in optimally wet locations and highest in excessively wet or dry locations.
Results/Conclusions
Preliminary results indicated that fine root production was opposite of that hypothesized. In 2016 and 2017, midslope and swale locations, areas of the landscape with middle range soil water content, had the least fine root production. In 2018, there was no significant difference among topographic locations. Root turnover was largely similar among topographic regions within each of the three years. Root lifespan flipped from having the shortest root lifespan in 2017 to having the longest in 2018 for the driest locations. Annual precipitation levels may have differentially impacted fine root dynamics at different topographic locations. Preliminary results indicated that fine root lifespans tended to decrease across all four topographic elements over the three years. Conversely, midslope planar and swale locations increased in net annual production and turnover rates across the three years. Valley floor locations increased in turnover and production between the first two years, but returned to first year rates in the third year. Ridge top showed similar turnover patterns. Overall, the topographical impact on fine root dynamics varied annually and with shifts in precipitation. This study underscores the challenge of using simple relationships of soil moisture with fine root dynamics in modeling forested landscapes.