Sampling spatial and temporal variation in soil nitrogen availability |
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Authors: | Michael L Cain Scott Subler Jonathan P Evans Marie-Josée Fortin |
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Institution: | (1) Department of Biology, New Mexico State University, Las Cruces, NM 88003, USA e-mail: mcain@nmsu.edu; Fax: +1-505-6465665, MX;(2) The Ohio State University Soil Ecology Laboratory, Columbus, OH 43210, USA, US;(3) Department of Biology, The University of the South, Sewanee, TN 37383, USA, US;(4) Département de biologie, Université de Sherbrooke, Sherbrooke, Québec, J1K 2R1, Canada, CA |
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Abstract: | There are few studies in natural ecosystems on how spatial maps of soil attributes change within a growing season. In part,
this is due to methodological difficulties associated with sampling the same spatial locations repeatedly over time. We describe
the use of ion exchange membrane spikes, a relatively nondestructive way to measure how soil resources at a given point in
space fluctuate over time. We used this method to examine spatial patterns of soil ammonium (NH+
4) and nitrate (NO−
3) availability in a mid-successional coastal dune for four periods of time during the growing season. For a single point in
time, we also measured soil NH+
4 and NO−
3 concentrations from soil cores collected from the mid-successional dune and from an early and a late successional dune. Soil
nitrogen concentrations were low and highly variable in dunes of all ages. Mean NH+
4 and NO−
3 concentrations increased with the age of the dune, whereas coefficients of variation for NH+
4 and NO−
3 concentrations decreased with the age of the dune. Soil NO−
3 concentration showed strong spatial structure, but soil NH+
4 concentration was not spatially structured. Plant-available NH+
4 and NO−
3 showed relatively little spatial structure: only NO−
3 availability in the second sampling period had significant patch structure. Spatial maps of NH+
4 and NO−
3 availability changed greatly over time, and there were few significant correlations among soil nitrogen availability at different
points in time. NO−
3 availability in the second sampling period was highly correlated (r = 0.90) with the initial soil NO−
3 concentrations, providing some evidence that patches of plant-available NO−
3 may reappear at the same spatial locations at irregular points in time.
Received: 20 February 1998 / Accepted: 23 November 1998 |
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Keywords: | Coastal dune ecosystems Ion exchange membrane spikes Soil nitrogen availability Soil resource heterogeneity Spatial statistics |
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