I am conducting a large scale herbivory experiment across many sites and would like to examine if nutrient concentrations/availability (namely N and P) may also vary between mangrove sites. My primary hypothesis is herbivory will vary, but I'd like to test alternative hyp's as well (including if nutrient levels or availability varies).

Because a nutrient study is not the primary focus, I was hoping to receive some advice for ways to measure nutrient levels/availability between sites that is relatively straight forward. Does anyone have any advice or references to recommend?

I realize nutrient manipulations would be ideal (c/o Feller, Lovelock) but I just do not have time for it. A colleague dissuaded me from examining the soil chemistry because it may not inform whats available to the plant. Perhaps examining the leaf chemistry would be informative?