Ecosystem function differs between Old World bluestem invaded and native coastal prairie in South Texas

Exotic Old World bluestem grasses (OWBG) are invading prairie and savanna ecosystems of the southern Great Plains USA, yet little is known about whether or how this invasion alters ecosystem processes. We conducted a study in a south Texas coastal prairie to address the following questions: (1) Does litter production, quality, decomposition rates, and soil nutrient dynamics differ significantly between areas dominated by OWBG versus native prairie?; and, (2) Does soil texture influence the effects of OWBG dominance on ecosystem processes? Ecosystem parameters were measured in adjacent patches of native and OWBG invaded coastal prairie on two soil textures, sandy loam and clay. Our findings indicate that ecosystem function differed between OWBG and native prairie dominated areas, but these results were not consistent across soil textures. On sandy loam soil, the soil microclimate differed substantially between OWBG and native prairie, and areas dominated by OWBG had higher aboveground plant production, soil organic C and total N pools, soil inorganic N concentrations and mineralization rates, and litter decomposition rates than native prairie. In contrast, on clay soils, these ecosystem properties often varied little between OWBG and native prairie. Dominance of OWBG appears to have altered native ecosystem function; yet, in this study the directionality and extent of these OWBG effects were strongly soil texture dependent, suggesting that local edaphic factors will likely interact with OWBG dominance in determining ecosystem properties. Consideration of these results may be valuable for managing OWBG such that control or restoration efforts on coarse-textured soils may be given priority over finer-textured soils.