Sweetgum and broomsedge response to competition across a range of soil organic matter during the first year of plant establishment

Sweetgum (Liquidambar styraciflua L.) seedlings and broomsedge (Andropogon virginicus L.) rooted tillers were planted in a factorial combination of de nsities (additive series) in east central Alabama on a formerly cultivated field which varied in soil organic matter (soil OM). Mean plant aboveground biomass of sweetgum one growing season after planting declined in a hyperb olic fashion as a function of increasing density of either itself or brooms edge. Broomsedge biomass over the same time period also declined in a hyper bolic fashion as a function of increasing density of itself and sweetgum, e xcept for sweetgum densities from 0 to 1 m(-2), where biomass did not chang e, Sweetgum response was positively correlated with soil OM across all spec ies-density combinations, whereas broomsedge response was correlated with s oil OM only at higher densities of broomsedge. Nonlinear models including b oth species density and soil OM explained a nearly equal amount of variatio n in response of each species: 74 to 75% for sweetgum and 70% for broomsedg e. Relative effects of intraspecific versus interspecific competition on th e response of each species was dependent on the density of one or both spec ies. Effect of sweetgum on broomsedge response was two to three times that of broomsedge on itself, with the effect decreasing slightly as soil OM dec reased. Over a common range of densities of each species, effects of brooms edge on sweetgum were slightly greater than or nearly equal to effects of s weetgum on itself. The greater interspecific effects on the response of eac h species suggests no niche differentiation between broomsedge and sweetgum through one growing season.