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Soil N and 15N variation with time in a California annual grassland ecosystem

January 1, 2001

The %N and ??15N values of soils and plants were measured along a chronosequence spanning 3 to 3000 Ky in a California annual grassland. Total soil N decreased with increasing soil age (1.1 to 0.4 kg N m-2) while the mean ?? 15N values of the soil N increased by several ??? from the youngest to oldest sites (+3.5 to +6.2 ???). The ?? 15N values of plants varied along the gradient, reflecting changing soil N pools and differences in the form of N uptake. The decline in total N storage with time is hypothesized to be due to a shift from N to P limitation with increasing soil age. The general increase in ?? 15N values with time is interpreted using a N mass balance model, and appears to reflect a shift toward an increasing proportional losses of inorganic mineral forms of N (vs. organic forms) with increasing soil age. We develop a quantitative index of this trend (mineral vs. organic forms of N loss) using mass balance considerations and parameters. The %N and ?? 15N values along the California age gradient were compared to the published data for a comparably aged chronosequence in Hawaii. Most striking in this comparison is the observation that the California soil and plant ?? 15N values are several ??? greater than those on comparably aged Hawaiian sites. Multiple explanations are plausible, but assuming the sites have a similar range in ?? 15N values of atmospheric inputs, the isotopic differences suggest that N may be, at least seasonally, in greater excess in the strongly seasonal, semi-arid, California grassland. Copyright ?? 2001 Elsevier Science Ltd.

Citation Information

Publication Year 2001
Title Soil N and 15N variation with time in a California annual grassland ecosystem
DOI 10.1016/S0016-7037(01)00699-8
Authors D.L. Brenner, Ronald Amundson, W. Troy Baisden, C. Kendall, J. Harden
Publication Type Article
Publication Subtype Journal Article
Series Title Geochimica et Cosmochimica Acta
Index ID 70022807
Record Source USGS Publications Warehouse
USGS Organization California Water Science Center

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