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

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

Nov 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001gecoa..65.4171b&link_type=abstract

Geochimica et Cosmochimica Acta, vol. 65, Issue 22, pp.4171-4186

Computer Science

14

Scientific paper

The %N and 15 N 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 15 N values of the soil N increased by several from the youngest to oldest sites (+3.5 to +6.2 ). The 15 N 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 15 N 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 15 N 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 15 N values are several greater than those on comparably aged Hawaiian sites. Multiple explanations are plausible, but assuming the sites have a similar range in 15 N 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.

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