Effects of fire, mowing and nitrogen addition on root characteristics in tall‐grass prairie

Root harvests and root windows were used to study the influence of fire, mowing and nitrogen additions on root lengths, biomass, and nitrogen content in tall‐grass prairie. Four years of nitrogen additions (10 g m2 yr−1) increased below‐ground mass by 15 % and nitrogen concentration in that mass by 77 %. In general, live roots and rhizomes exhibited greater increases in nitrogen concentrations than detrital roots and rhizomes. After four years of treatment, live roots and rhizomes immobilized an additional 1.5 to 5 g/m2 of nitrogen, depending upon specific treatment, while dead roots and rhizomes immobilized an additional 3 to 3.5 g/m2. Average root growth parameters, as measured with root windows, were positively correlated with above‐ground peak foliage biomass; however, the only significant correlation was between average new root growth and above‐ground peak foliage biomass (r = 0.73, p ≤ 0.04). Root growth and decay, as measured by annual mean values for eight root windows over a four year interval, were insensitive to climatic and treatment effects.