Document: HOR-3-33-23

Species-specific responses of tall-grass prairie legumes to nitrogen addition.

BASSIRIRAD, H.* and D.NYBERG

University of Illinois at Chicago ¹

Abstract:
Many prairie ecosystems in the tall-grass region of the U. S. A. have experienced recent elevations in atmospheric nitrogen (N) deposition. We tested the hypothesis that increased N deposition decreases growth and the competitive ability of five native legume species: Amorpha canescens, Baptisia leucophaea, Cassia fasciculata, Cassia hebecarpa, and Desmodium canadense. Individuals of each legume species were planted together with an individual of a C4 prairie grass species, Andropogon scoparius, in a 4-L pot containing river-washed sand. Plants were grown for 10 weeks under field conditions. Twice a week, each pot received 200 mL of nutrient solution that contained 0.1 mM N supplied as ammonium chloride plus potassium nitrate at one of the following concentrations: 0.0, 0.2, 1.0, 2.0, 5.0, or 10 mM. Nitrogen addition significantly affected growth of all species tested and much of the effect was species specific. In the range of 0.0 to 2.0 mM, nitrate addition increased total biomass in B. leucophaea, D. canadense and A. canescens to a greater extent than the competing grass, so in this N addition range, these legumes out-competed the grass. At 5 and 10 mM, nitrogen addition decreased growth of B. leucophaea and A. canescens while growth in the grass species was either increased or uninhibited. Therefore, N addition at the two highest concentrations reduced the competitive ability of these legumes relative to the grass. D. canadense outperformed the grass at all N concentrations, but its biomass response to N addition reached a maximum at the 2 mM treatment. A. canescens and C. fasciculata produced less biomass than the grass at all N treatments except at the highest concentration. The pattern of nodule dry weight responses to increased N was similar to total plant biomass. The interspecies differences of legumes to N loading may have significant implications for N cycling and biodiversity in tall-grass prairies.

Keywords: legumes, atmospheric N deposition, competition, tall-grass prairies

This abstract is being presented at: 9:00 AM in session:
Oral Session #61: Plant Responses to Nutrients.