title: Nitrogen mineralization dynamics in grass monocultures.
abstract: Although Wedin and Tilman (1990) observed large differences in in situ N mineralization among monocultures of five grass species, the mechanisms responsible were unclear. In this study, we found that the species did not change total soil C or N, and soil C: N ratio (range 12.9-14.1) was only slightly, but significantly, changed after four years. Nor did the species significantly affect the total amount of N mineralized (per g soil N) in year-long aerobic laboratory incubations. However, short-term N mineralization rates in the incubations (day 1-day 17) differed significantly among species and were significantly correlated with annual in situ mineralization. When pool sizes and turnover rates of potentially mineralizable N (No) were estimated, the best model treated Noas two pools: a labile pool, which differed among species in size (Nl, range 2-3% of total N) and rate constant (h, range 0.04-0.26 wk-1), and a larger recalcitrant pool with a constant mineralization rate across species. The rate constant of the labile pool (h) was highly correlated with annual in situ N mineralization (+0.96). Therefore, plant species need only change the dynamics of a small fraction of soil organic matter, in this case estimated to be less than 3%, to have large effects on overall system N dynamics.
authors.affiliation: Natural Resources Research Institute, University of Minnesota, 55811, Duluth, MN, USA.
authors.forename: David A
authors.initials: DA
authors.lastname: Wedin
authors.affiliation: Natural Resources Research Institute, University of Minnesota, 55811, Duluth, MN, USA.
authors.forename: John
authors.initials: J
authors.lastname: Pastor
keywords: Grasses; Monocultures; N mineralization; Soil organic matter