Role of N2-fixation in Constructed Old-field Communities Under Different Regimes of [CO2], Temperature, and Water Availability
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Nitrogen fixation was measured in constructed old-field ecosystems that were exposed for 3 years to different combinations of elevated atmospheric [CO2] and temperature (300 ppm and 3°C above ambient, respectively), and ambient or reduced soil moisture (corresponding to 25 or 2 mm rainfall per week). The old-fields included seven planted herbaceous annual and perennial species, including two legumes (Trifolium pratense and Lespedeza cuneata). Potential asymbiotic N2-fixation by soils, measured in laboratory incubations, was significantly less under the “dry” treatment but was estimated to contribute little overall to annual ecosystem N budgets. Foliar N concentrations declined significantly under elevated [CO2]. Effects of the three environmental factors on the mean (±SE) fraction of legume N derived from atmospheric N2 (FN dfa) varied from year-to-year, and FN dfa ranged from 0.64 ± 0.05 to 0.94 ± 0.03 depending on species and growing season. High rates of symbiotic N2-fixation (4.6–12 g N m−2 y−1) that annually contributed from 44% to 51% to the aboveground N stock in the old-field community was an important process driving changes in species composition over the 3-year experiment. Lespedeza biomass increased over time at the expense of several other species, including the other N-fixer, Trifolium. The dominance of Lespedeza in our ecosystem was due to high symbiotic N2-fixation rates, as well as shading effects on other species. The high symbiotic N2-fixation rates were largely independent of manipulations of [CO2], temperature, and water. The relatively high percentage of the aboveground N stock in this ecosystem contributed by symbiotic N2-fixation suggests that non-legume species may have benefited indirectly via reduced community demands on soil N supplies. Species-specific traits were important in the constructed ecosystems, indicating that multi-species studies are required for understanding complex interactions among environmental factors and dynamic changes in community composition.
KeywordsLespedeza legumes 15N natural abundance method multi-factor experiments climate change constructed ecosystems
This research was sponsored by the U.S. Department of Energy, Office of Science, Biological and Environmental Research/Program for Ecosystem Research under contract DE-AC05-00OR22725 with Oak Ridge National Laboratory (ORNL), managed by UT-Battelle, LLC. We wish to thank B. Lu, E.C. Engel, P. Allen, C. Reilly Sheehan, S. Wan, S. Freyaldenhoven, and K. Cox for their valuable assistance in the laboratory and/or field. We would also like to thank the ORNL/UT Ecosystem Ecology lab group (C. Iversen, H. Castro, O. Dermody, C. Campany, D. Weston, K. Sides, E. Austin, E. Felker-Quinn) for insightful comments on the draft manuscript.
- Athar M, Johnson DA. 1996. Nodulation, biomass production, and nitrogen fixation in alfalfa under drought. J Plant Nutr 19:185–99.Google Scholar
- Dear BS, Cocks PS, Peoples MB, Swan AD, Smith AB. 1999. Nitrogen fixation by subterranean clover (Trifolium subterraneum L.) growing in pure culture and in mixtures with varying densities of lucerne (Medicago sativa L.) or phalaris (Phalaris aquatica L.). Aust J Agr Res 50:1047–58.CrossRefGoogle Scholar
- Eddy TA, Moore CM. 1998. Effects of sericea lespedeza (Lespedeza cuneata (Dumont) G. Don) invasion on oak savannas in Kansas. Trans Wisconsin Acad Sci Arts Lett 86:57–62.Google Scholar
- Garten CT. 1990. Multispecies methods of testing for toxicity: use of the Rhizobium-legume symbiosis in nitrogen fixation and correlations between responses by algae and terrestrial plants. In: Wang W, Gorsuch JW, Lower WR, Eds. Plants for toxicity assessment, ASTM STP 1091. Philadelphia: American Society for Testing and Materials. pp 69–84.Google Scholar
- Høgh-Jensen H, Schjoerring JK. 1997. Effects of drought and inorganic N form on nitrogen fixation and carbon isotope discrimination in Trifolium repens. Plant Physiol Bioch 35:55–62.Google Scholar
- Kalburtji KL, Mosjidis JA, Mamolos AP. 2001. Allelopathic plants. 2. Lespedeza cuneata. Allelopathy J 8:41–9.Google Scholar
- McWilliam JR. 1978. Response of pasture plants to temperature. In: Wilson JR Ed. Plant relations in Pastures. Australia: Commonwealth Scientific and Industrial Research Organization, East Melbourne. pp 17–34.Google Scholar
- Ohashi Y, Saneoka H, Matsumoto K, Ogata S, Premachandra GS, Fujita K. 1999. Comparison of water stress effects on growth, leaf water status, and nitrogen fixation activity in tropical pasture legumes Siratro and Desmodium with soybean. Soil Sci Plant Nutr 45:795–802.Google Scholar
- Shearer G, Kohl DH. 1986. N2-fixation in field settings: estimations based on natural 15N abundance. Aust J Plant Physiol 13:699–756.Google Scholar