Saturday, October 6, 2012

Landscape level patterns of soil N flux and N isotopes

This might be of interest to just a few, but I've been working hard to understand the degree to which global patterns of soil del15N represent differences in the proportion of gaseous N loss (fractionating loss hypothesis) vs. difference in the degree of decomposition of soil organic matter (microbial processing hypothesis).

There are few papers that try to contextualize losses of N via gaseous pathways vs. leaching, for example.

There also are few papers that look at spatial patterns of gaseous N flux, local or global.

Velthof 2000 did a great gradient study involving 162 flux chambers along 400 m of slope in a grassland.

This is probably the best study that asks whether spatial variation in gaseous N flux patterns soil del15N.

At least over 4 days of measurements, they found a good correlation between the two.

Best correlations were with shallow soils (0-5 cm). r2 was about 0.4. But correlations for del 15N of soils even just 10-15cm deep were non-significant (r2 = 0.03, P > 0.3)

For what it's worth, they said that "Both the del15N values and N2O fluxes were highest at the steepest part of the slope."

Would steep slopes also have more processed OM?

Velthof, G. L., J. W. van Groenigen, G. Gebauer, S. Pietrzak, S. C. Jarvis, M. Pinto, W. Corre, and O. Oenema. 2000. Temporal stability of spatial patterns of nitrous oxide fluxes from sloping grassland. Journal of Environmental Quality 29:1397-1407.

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