Fine root productivity and dynamics across a topographical sequence in Congaree National Park, SC

Background/Question/Methods

Floodplain forests are one of the most important ecosystems in the world, providing many benefits including sediment retention, excess nutrient retention, erosion control, flood control, and habitat for many organisms. Increased sedimentation rates from anthropogenic disturbances have been shown to decrease net primary production (NPP) in floodplain forests. Since aboveground portions of plants do not always reflect belowground response to environmental stress, roots can be used to indicate environmental stresses. The goal of this study was to determine how sedimentation affects fine root dynamics, particularly in relation to carbon and nitrogen. Fine roots were studied across an elevational gradient in the Congaree National Park, SC. Elevation decreased across the following microsite types—natural levee> upper hardwood flat > lower hardwood flat> backswamp. The sequential coring method was used to collect roots to a depth of 11 cm. Cores went through a manual low pressure rinse to extract roots. Roots were separated between type classes of live and dead as well as size classes including 0-1.0 mm, 1.1-2.0 mm, and 2.1-3.0 mm. Samples were oven-dried and ground by hand or in a Wiley mill to pass a 0.40 mm sieve. Root contents of carbon and nitrogen were quantified using thermal combustion. 

Results/Conclusions

Preliminary data suggest that differences exist along the elevational gradient. Fine root biomass tended to decrease with decreasing elevation with the highest biomass in the natural levee and the lowest biomass in the backswamp. Current data suggests that BNPP along the natural levee was 42.67 g/m². While on the upper hardwood flat, BNPP decreased to 29.78 g/m²to a depth of 11 cm. The lower hardwood flat BNPP measured 16.24 g/m². The backswamp had the smallest BNPP with 7.23 g/m². Root biomass C and N content tended to be larger in live roots rather than dead roots and declined with decreasing elevation. Live roots also had a higher C:N ratio than dead roots.This study suggests that significant differences in root growth patterns and nutrient dynamics occur along an elevational gradients in riparian forests, providing information that is key to understanding the carbon storage on forested floodplain systems.