The properties of root systems of grassland species and their relationships to ecosystem properties.

摘要

I examined a suite of ecophysiological, whole-plant, and plant-associated ecosystem traits for 33 species common in the grassland flora of central Minnesota, USA that were grown for five years in monoculture on low-N soils. A major finding of this study is that nonlegumes appear to be best arrayed along one continuous axis that encompasses ecophysiological, whole-plant, and associated ecosystem traits as well as the production and maintenance of biomass on low-N soils. Legumes vary greatly with cool-season legumes having not only earlier biological activity, but also greater rates of N fixation and total production than warm-season legumes.; In another experiment, I examined more in detail the construction, production, and placement of fine and coarse belowground biomass in the soil profile of eleven grassland species after having been grown in the field for two and a half growing seasons. There was little support for functional dichotomies between C3 and C4 species or between grasses and forbs. Among the findings, legumes depleted water evenly throughout the soil profile, with little capacity for acquisition of inorganic nitrogen throughout the lm soil profile. The three rhizomatous species had shallow fine root distributions, a large relative investment in shallow rhizomes, and moisture and NO 3- levels were low in shallow soils, but high at depth. Tallgrass species maintained a large standing root biomass of high-density, low-nitrogen fine roots, and acquire nitrogen and water from a large, deep volume of soil, in which inorganic nitrogen is present in low concentrations.; I tested the effects of plant species and plant size on root properties, soil NO3- concentrations, soil moisture, and soil CO2 flux by harvesting plants in their second and third years of growth. As plants increased in size, root tissue density increased and diameter decreased, consistent with cortical loss associated with the aging of roots. For non-legumes, increases in fine root C:N with increasing biomass reflected greater plant-induced lowering of nitrogen availability as soil NO3- concentrations decreased with increasing root biomass. For legumes, nitrogen fixation provided sufficient nitrogen to maintain constant C:N ratios in fine roots as plants increased in size. Neither the relative amounts of biomass in coarse and fine roots nor the depth placement of fine roots in the soil profile changed as plants increased in size.