Relative Contribution of Trees and Warm-Season Grasses to Soil Carbon Sequestration in Silvopastoral Systems.

Silvopastoral systems integrate trees in pasture production systems. The contribution of these trees to enhance soil carbon (C) storage is in these land-use systems is not known. To quantify the relative soil C contribution from woody vegetation (C3) vs. warm-season grass vegetation (C4) in silvopastoral systems, soil samples were collected from silvopastures of slash pine (Pinus elliottii) + bahiagrass (Paspalum notatum), and adjacent open pasture at six depths up to 125 cm, at two sites, representing Spodosols and Ultisols. The plant sources of C in whole soil and three soil fraction-sizes (250 – 2000, 53 – 250 and <53 µm) of each soil layer were traced using stable C isotope signatures. In both soil orders, the C3 plant (slash pine) contributed more C than the C4 plant (bahiagrass) at all soil depths, particularly at the lower depth. In the relatively stable size fraction (<53µm), higher proportion of C was derived from tree components (C3 plants) in both pasture systems. The results suggest that the tree based-pasture system has greater potential for C sequestration compared with the treeless system.