Fluctuations in soil moisture caused by climate change could profoundly impact belowground carbon dynamics. However, most studies investigating the impact of soil moisture fluctuations on belowground carbon processes are plot-level experiments, with minimal topographic variation. Scaling these experiments to the landscape level is challenging because complex topographic variation drives spatial and temporal patterns of soil water content. We examined how variation in soil moisture along with other factors such as temperature, soil thickness, soil nutrients and aboveground species distribution influenced fine root distribution across a topographically diverse first-order catchment (Shale Hills CZO).
During the 2014 field season, 250 soil cores were taken at 4 slope positions (ridge top, midslope planar, midslope swale, and valley floor) to a maximum depth of 165cm. Soil cores were divided into depth increments of 20 to 40 cm, homogenized then split so that each half contained roughly equal soil and root constituents. One half of the sample was analyzed for root distribution, and the other half was analyzed for soil properties. Root samples were separated into absorptive roots (1st to 3rd order roots) and transport roots (>3rd order roots). Root length and average diameter were determined using WinRHIZO software. Soil samples were analyzed for NO3-, NH4+, soil organic matter, rock content, exchangeable acidity, C:N and CEC. Other measures including LAI, leaf litter mass and tree diameter were also determined within each plot to compare aboveground patterns with root distribution.
Initial results show complex spatial variation in root distribution, where soil water content may play a critical role in the top 20cm of the soil while ammonium concentration and exchangeable acidity contribute deeper within the soil profile. These results suggest simple metrics such as slope position or soil moisture may not be adequate to predict fine root distribution.