Technical Abstract: Vegetative buffers have been shown to reduce nutrient loss associated with the transport of detached soil particles and may through plant uptake offer a means to capture dissolved nutrients moving to surface waters through the soil solution. The objective of this 4-year study was to evaluate changes in the biomass and phorphorus (P) content of the roots and shoots of plants growing in a multi-species vs. a single species riparian buffer as an index of P capture potential. Periodic harvests of above ground vegetation were combined with root cores to estimate the total standing biomass and the pool of P in plant tissue in three vegetative cover types. The mixed-buffer species included switchgrass (Panicum virgatum L.), an alfalfa (Medicago sativa L.)-smooth bromegrass (Bromis inermis Leyss) mixture, and a fast growing superior cottonwood (Populus deltoids Bartr., clone 42-7). An existing smooth bromegrass served as the single species control. Standing biomass increased in all three cover types during the 4-year study, with the greatest increases in the cottonwood (2345 g m-2) and switchgrass (1818 g m-2). Biomass production in the smooth brome control did not change during the study period. Based on the fourth year samples, standing pools of P closely paralleled total plant biomass and root surface area with cottonwood accumulating the greatest amount of P at 19.4 g m-2 compared to 4.3 g m-2 for the smooth brome control. Estimates of potential P removal via biomass harvest from a mixed buffer over a 4-year interval were 101 kg ha-1 compared to 62 kg ha-1 for the smooth brome control; a 63% increase in export capacity due largely to the inclusion of cottonwood. Addition of a fast growing woody species combined with periodic biomass harvests has the potential to reduce P movement to surface waters.