Effects of Longleaf Pine (LLP) Restoration on Key Soil Chemical Processes.

We propose to examine the effects of longleaf pine (LLP) groundcover restoration on key soil chemical processes by using stable isotope ratios of carbon (C) and nitrogen (N) to determine the relative inputs of C and N to soil pools. Research will primarily focus on C and N cycling and variations in their pools related to LLP thinning/planting and native legume and warm-season grass ground cover restoration.

We hypothesize that C and N changes will be driven primarily by influences from grass and legume organic matter inputs associated with ground cover restoration and secondarily organic matter from pine root turnover. Planted stands will be driven initially by residual old field nutrients, shifting to ground cover restoration, with introduction of organic matter from C₄ grasses and legumes. It has been demonstrated that isotopic ratios may be used to evaluate nutrient replacement in forest surface soil horizons. Grass inputs, prescribed fire generated black carbon, root turnover and decomposition will be detectable with shifts in land use as illustrated.

Former agricultural soils in old field and young plantation management are significantly depleted in C and N  and elevated in  phosphorous for several years following pine establishment. Clear relationships have been seen between soil C concentration and land use history at Ichauway with significant differences and increasing values of C concentration from abandoned ag<young plantation<old field LLP<reference LLP. Due to differences in C isotope values between C₃ and C₄ plants shown and N isotope values in N fixing versus non N fixing plants, we will be able to track and quantify relative changes in soil C and N attributable to C₄ grasses and legumes using stable isotopes. These shifts will be identifiable through differences in isotope values with time and depth due to root inputs and organic matter incorporation as illustrated with work on similar LLP plantations and LLP woodlands.