| Abstract: | Woody vegetation is distributed patchily in many arid and semi-arid ecosystems, where it is often associated with elevated nitrogen (N) pools and availability in islands of fertility. We measured N availability and ??15N in paired blue-oak versus annual grass dominated patches to characterize the causes and consequences of spatial variation in N dynamics of grassland-savanna in Sequoia-Kings Canyon National Park. We found significantly greater surface soil N pools (0-20 cm) in oak patches compared to adjacent grass areas across a 700 m elevation gradient from foothills to the savanna-forest boundary. N accumulation under oaks was associated with a 0.6??? depletion in soil ??15N relative to grass patches. Results from a simple ??15N mass balance simulation model, constrained by surface soil N and ??15N measured in the field, suggest that the development of islands of N fertility under oaks can be traced primarily to enhanced N inputs. Net N mineralization and percent nitrification in laboratory incubations were consistently higher under oaks across a range of experimental soil moisture regimes, suggesting a scenario whereby greater N inputs to oak patches result in net N accumulation and enhanced N cycling, with a potential for greater nitrate loss as well. N concentrations of three common herbaceous annual plants were nearly 50% greater under oak than in adjacent grass patches, with community composition shifted towards more N-demanding species under oaks. We find that oaks imprint distinct N-rich islands of fertility that foster local feedback between soil N cycling, plant N uptake, and herbaceous community composition. Such patch-scale differences in N inputs and plant-soil interactions increase biogeochemical heterogeneity in grassland-savanna ecosystems and may shape watershed-level responses to chronic N deposition. ?? 2006 Springer Science+Business Media, Inc. |
| Genre: | Article |
| ProdID: | 70030901 |
| Citation Author: | Perakis, S. S.; Kellogg, C. H. |
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| Citation End Page: | 220 |
| Citation Issue: | 2 |
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| Citation Language: | English |
| Citation Larger Work Title: | Plant Ecology |
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| Citation Number Of Pages: | 12 |
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| Citation Search Results Text: | Imprint of oaks on nitrogen availability and ??15N in California grassland-savanna: A case of enhanced N inputs?; 2007; Article; Journal; Plant Ecology; Perakis, S. S.; Kellogg, C. H. |
| Citation Start Page: | 209 |
| Citation Volume: | 191 |
| Citation Year: | 2007 |
| Type: | citation/reference |
| Text: | Imprint of oaks on nitrogen availability and ??15N in California grassland-savanna: A case of enhanced N inputs?; 2007; Article; Journal; Plant Ecology; Perakis, S. S.; Kellogg, C. H. |
| URL (THUMBNAIL): | http://pubs.er.usgs.gov/thumbnails/outside_thumb.jpg |
| URL (DIGITAL OBJECT IDENTIFIER): | http://dx.doi.org/10.1007/s11258-006-9238-9 |
| Date Other: | Mon, 1 Jan 2007 00:00 -0600 |
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