Global-Scale Patterns Of Soil Carbon And Nitrogen Content With Depth: What Are The Underlying Mechanisms?

Abstract:

Organic matter composition and shifts that occur with depth have been evaluated biochemically and isotopically in surface (0-30cm) mineral soils extensively. However, to date, our understanding of broad-scale (e.g. global) patterns of OM composition and soil minerals at depth has been limited. Here, I examine global scale patterns of C and N with depth up to 100 cm using prior published studies and a global-scale pedon C and N content data set made available through the International Soil Carbon Network (ISCN). Questions addressed include: (1) How do C and N soil profile depth trends vary by soil type and biogeoclimatically, and (2) What might this tell us about underlying mechanisms controlling C and N abundance and OM composition in soil ? I draw heavily on prior studies in evaluating the current state of knowledge and uncertainty in terms of these trends. Underlying possible mechanisms of declining C to N ratio are evaluated based on a range of soil litter, laboratory incubation and mineral sorption experiments. The extent to which microorganisms may influence soil C and N depth patterns is further evaluated. The study is part of broader effort through the North American Carbon Program to better understand global-scale mechanisms for soil carbon accumulation and stabilization in the subsoil.