Digging deeper into above and belowground relationships: linking canopy and root structure with soil respiration

Soil respiration (Rs) is the largest flux of carbon (C) to the atmosphere, and is closely related to abiotic factors such as temperature and moisture. Variation in soil respiration among ecosystems cannot be fully explained by abiotic factors, however, suggesting biotic factors also play a critical regulatory role. One known biotic influence on soil respiration is the quantity of root biomass, which is a measure of respiring plant tissue and organic substrate available to heterotrophs. While biomass provides a measure of quantity useful to the prediction of Rs and other fluxes, its arrangement may serve as an even more integrative indicator of root C cycling processes, similar to aboveground measures. For example, aboveground, LiDAR-derived forest structural features including height, leaf area, and complexity are mechanistically associated with primary production through resource use and acquisition. In addition, the quantity of aboveground biomass is separately shown to correlate with root biomass, suggesting coupled above-belowground structure-function relationships may link aboveground structure to belowground Rs. In forests spanning a range of aboveground structures shaped by age and disturbance history, we assessed linkages between analogous measures of above- and belowground structure to determine whether canopy structure predicts Rs rates through its ties to root structure. Preliminary analysis reveals canopy rugosity, a complexity measure, is a stronger predictor of mean stand soil respiration than vegetation area. Based on data collection that is underway, we will assess relationships between canopy structure and root biomass and expect that above and belowground stand-scale structural properties will be positively correlated. We also expect that at stand scale, complex canopies with high biomass will have cooler soil surfaces as more light is absorbed, resulting in lower rates of soil respiration, and theorize that this indirect effect of canopy structure on microclimate may override the direct influence of root quantity. We will conclude by discussing how established relationships between canopy structure and Rs could aid in the prediction of C fluxes via remote sensing of aboveground properties, improving the certainty of net C balance estimates.