[1] We compiled new and published data on the natural abundance N isotope composition (d 15 N values) of soil and plant organic matter from around the world. Across a broad range of climate and ecosystem types, we found that soil and plant d ) with climate. Nitrogen isotopes reflect time integrated measures of the controls on N storage that are critical for predictions of how these ecosystems will respond to humanmediated disturbances of the global N cycle.

[1] We measured 14 C/ 12 C in density fractions from soils collected before and after atmospheric thermonuclear weapons testing to examine soil organic matter (SOM) dynamics along a 3 million year California soil chronosequence. The mineral-free particulate organic matter (FPOM; <1.6 g cm À3 ) mainly contains recognizable plant material, fungal hyphae, and charcoal. Mineral-associated light fractions (1.6-2.2 g cm À3 ) display partially or completely humified fine POM, while the dense fraction (>2.2 g cm À3 ) consists of relatively OM-free sand and OM-rich clays. Three indicators of decomposition (C:N, d 13 C, and d 15 N) all suggest increasing SOM decomposition with increasing fraction density. The D 14 C-derived SOM turnover rates suggest that !90% of FPOM turns over in <10 years. The four mineral-associated fractions contain 69-86%

[1] We examine soil organic matter (SOM) turnover and transport using C and N isotopes in soil profiles sampled circa 1949, 1978, and 1998 (a period spanning pulse thermonuclear 14 C enrichment of the atmosphere) along a 3-million-year annual grassland soil chronosequence. Temporal differences in soil D

Predictive understanding of precipitation δ(2)H and δ(18)O in New Zealand faces unique challenges, including high spatial variability in precipitation amounts, alternation between subtropical and sub-Antarctic precipitation sources, and a compressed latitudinal range of 34 to 47 °S. To map the precipitation isotope ratios across New Zealand, three years of integrated monthly precipitation samples were acquired from >50 stations. Conventional mean-annual precipitation δ(2)H and δ(18)O maps were produced by regressions using geographic and annual climate variables. Incomplete data and short-term variation in climate and precipitation sources limited the utility of this approach. We overcome these difficulties by calculating precipitation-weighted monthly climate parameters using national 5-km-gridded daily climate data. This data plus geographic variables were regressed to predict δ(2)H, δ(18)O, and d-excess at all sites. The procedure yields statistically-valid predictions of the isotope composition of precipitation (long-term average root mean square error (RMSE) for δ(18)O = 0.6 ‰; δ(2)H = 5.5 ‰); and monthly RMSE δ(18)O = 1.9 ‰, δ(2)H = 16 ‰. This approach has substantial benefits for studies that require the isotope composition of precipitation during specific time intervals, and may be further improved by comparison to daily and event-based precipitation samples as well as the use of back-trajectory calculations.