Nitrogen preferences and plant-soil feedbacks as influenced by neighbors in the alpine tundra

• Published in: Oecologia 2008-06, Vol.156 (3), p.625-636
• Main Authors: Ashton, I. W, Miller, A. E, Bowman, W. D, Suding, K. N
• Format: Article
• Language: English
• Subjects: Acid soils; Agricultural soils; Ammonium; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; Biomedical and Life Sciences; Coexistence; Community Ecology - Original Paper; Ecology; Ecosystem; Enzymatic activity; Enzymes - metabolism; Feedback, Physiological; Foliar nitrogen concentrations; Fundamental and applied biological sciences. Psychology; General aspects; Hydrology/Water Resources; Interspecific interactions; Life Sciences; Neighbor effect; Neighborhoods; Niches; Nitrogen; Nitrogen - metabolism; Nitrogen uptake patterns; Organic soils; Plant resource partitioning; Plant resources; Plant roots; Plant Sciences; Plant species; Plant-soil feedback; Planting density; Plants; Poaceae - chemistry; Poaceae - enzymology; Poaceae - metabolism; Resource partitioning; Rhizosphere; Rosaceae - chemistry; Rosaceae - enzymology; Rosaceae - metabolism; Soil - analysis; Soil ecology; Soil microorganisms; Soils; Tundra
• ISSN: 0029-8549; 1432-1939
• DOI: 10.1007/s00442-008-1006-1

Plant resource partitioning of chemical forms of nitrogen (N) may be an important factor promoting species coexistence in N-limited ecosystems. Since the microbial community regulates N-form transformations, plant partitioning of N may be related to plant-soil feedbacks. We conducted a ¹⁵N tracer addition experiment to study the ability of two alpine plant species, Acomastylis rossii and Deschampsia caespitosa, to partition organic and inorganic forms of N. The species are codominant and associated with strong plant-soil feedbacks that affect N cycling. We manipulated interspecific interactions by removing Acomastylis or Deschampsia from areas where the species were codominant to test if N uptake patterns varied in the presence of the other species. We found that Deschampsia acquired organic and inorganic N more rapidly than Acomastylis, regardless of neighbor treatment. Plant N uptake--specifically ammonium uptake--increased with plant density and the presence of an interspecific neighbor. Interestingly, this change in N uptake was not in the expected direction to reduce niche overlap and instead suggested facilitation of ammonium use. To test if N acquisition patterns were consistent with plant-soil feedbacks, we also compared microbial rhizosphere extracellular enzyme activity in patches dominated by one or the other species and in areas where they grew together. The presence of both species was generally associated with increased rhizosphere extracellular enzyme activity (five of ten enzymes) and a trend towards increased foliar N concentrations. Taken together, these results suggest that feedbacks through the microbial community, either in response to increased plant density or specific plant neighbors, could facilitate coexistence. However, coexistence is promoted via enhanced resource uptake rather than reduced niche overlap. The importance of resource partitioning to reduce the intensity of competitive interactions might vary across systems, particularly as a function of plant-soil feedbacks.