Friday, March 22, 2013

Changes in nitrogen cycling over the past 15 thousand years

Figure 2 | Changes in lacustrine sedimentary d15N during the late Pleistocene and Holocene. a, A smoothing spline curve (0.05 smoothing parameter) fitted to the means of sites in 100-yr bins is shown (red) with 95% bootstrapped confidence intervals (grey). Declines in sedimentary d15N from 15,000 cal. yr BP  to the breakpoint at 7,0566597 cal. yr BP correspond with periods of global net terrestrial carbon gain (shaded green)4. Dotted black line is the breakpoint regression. b, A different set of high-resolution sedimentary d15N records shows no net change over the past 500 yr.

Just a quick note to say that Kendra's paper on reconstructing N availability was just published.

It's an amazing synthesis.

What makes it amazing is the ability to look back in time at an index of terrestrial N availability and see that for thousands of years during the Pleistocene-Holocene transition.

As interesting, there just wasn't any evidence of N availability increasing over the past 500 years.

Whether N availability--the supply of N relative to biotic demand--is increasing at the global scale is one of the most fascinating debates that isn't occurring.

McLauchlan, K. K., J. J. Williams, J. M. Craine, and E. S. Jeffers. 2013. Global nitrogen cycling changed during the Holocene as terrestrial ecosystems accumulated carbon. Nature 495:352-355.