In 2009, I led a paper on foliar N isotopes. In it, we synthesized >10,000 samples to come up with some global patterns, but also looked at individual studies that related foliar del15N to indices of N availability. In general, we said, N availability and plant del15N scale positively, but there were exceptions.
In my mind at least, I remember thinking it doesn't always work, but looking at it again, it didn't work sometimes when potential N mineralized was measured. It always seemed to work with actual measurements.
I replotted all the actual measurements of Nmineralization on to a common scale (0-1) and centered the foliar del15N across sites (gave them the same mean of zero).
When you do that, it looks like this:
That's a pretty good summary of almost 4‰ increase in del15N across N availability gradients within sites.
Actually, my first attempt at showing the N availability data was a 1-panel summary rather than 16 panels.
Looking back, reviewers didn't like the 16 symbols and I thought 16 panels were necessary. Reviewers always seem to ask for more data, more panels, more analyses. They rarely tell me (at least) to simplify.
The 16 panel graph is pretty good. It's clear I should just not have shown the potential N mineralization data in the same graph. 2 out of 3 times they didn't work and should have been shifted out.
Either way, the 1-panel graph is still a pretty good summary of the data....