title: Controls of nitrogen cycling evaluated along a well-characterized climate gradient.
abstract: The supply of nitrogen (N) constrains primary productivity in many ecosystems, raising the question "what controls the availability and cycling of N"? As a step toward answering this question, we evaluated N cycling processes and aspects of their regulation on a climate gradient on Kohala Volcano, Hawaii, USA. The gradient extends from sites receiving <300 mm/yr of rain to those receiving >3,000 mm/yr, and the pedology and dynamics of rock-derived nutrients in soils on the gradient are well understood. In particular, there is a soil process domain at intermediate rainfall within which ongoing weathering and biological uplift have enriched total and available pools of rock-derived nutrients substantially; sites at higher rainfall than this domain are acid and infertile as a consequence of depletion of rock-derived nutrients, while sites at lower rainfall are unproductive and subject to wind erosion. We found elevated rates of potential net N mineralization in the domain where rock-derived nutrients are enriched. Higher-rainfall sites have low rates of potential net N mineralization and high rates of microbial N immobilization, despite relatively high rates of gross N mineralization. Lower-rainfall sites have moderately low potential net N mineralization, relatively low rates of gross N mineralization, and rates of microbial N immobilization sufficient to sequester almost all the mineral N produced. Bulk soil δ15N also varied along the gradient, from +4‰ at high rainfall sites to +14‰ at low rainfall sites, indicating differences in the sources and dynamics of soil N. Our analysis shows that there is a strong association between N cycling and soil process domains that are defined using soil characteristics independent of N along this gradient, and that short-term controls of N cycling can be understood in terms of the supply of and demand for N.
authors.affiliation: Department of Biology, Stanford University, Stanford, California, 94305, USA.
authors.forename: Christian
authors.initials: C
authors.lastname: von Sperber
authors.affiliation: Department of Geography, University of California, Santa Barbara, California, 93106, USA.
authors.forename: Oliver A
authors.initials: OA
authors.lastname: Chadwick
authors.affiliation: Department of Earth System Science, Stanford University, Stanford, California, 94305, USA.
authors.forename: Karen L
authors.initials: KL
authors.lastname: Casciotti
authors.affiliation: Department of Biology, Stanford University, Stanford, California, 94305, USA.
authors.forename: Kabir G
authors.initials: KG
authors.lastname: Peay
authors.affiliation: Department of Earth System Science, Stanford University, Stanford, California, 94305, USA.
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Francis
authors.affiliation: Earth Systems Program, Stanford University, Stanford, California, 94305, USA.
authors.forename: Amy E
authors.initials: AE
authors.lastname: Kim
authors.affiliation: Department of Biology, Stanford University, Stanford, California, 94305, USA.
authors.forename: Peter M
authors.initials: PM
authors.lastname: Vitousek
mesh_terms: D002980:Climate; D006254:Hawaii; D009584:Nitrogen; D058458:Nitrogen Cycle; D012987:Soil
chemical_list: D012987:Soil; D009584:Nitrogen
keywords: Hawaii; climate gradient; isotope dilution; nitrogen availability; nitrogen cycling; nitrogen mineralization; soil fertility; δ15N