Using DRIFTS to Determine the Relative Contribution of Inputs to SOM.

The relative significance of aboveground and belowground inputs to soil carbon (quantity and quality) is important in determining management strategies for the maintenance and sequestration of soil carbon in forested systems. Using 18 individual species-plots within a 35 years-old tropical arboretum we asked: How does the spectral fingerprint of soil organic matter under a single species compare to those of foliage, litter or roots of the same species? Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) was used to characterize foliage, fresh litter, fine roots and soil. A graphical comparison of the sum of squared differences between the various inputs and soil spectra showed greater similarity between the spectra of soil and roots than between soil and litter spectra. This indicated a greater contribution of belowground inputs to soil organic matter than aboveground inputs. Isotopic ratio analysis confirmed greater similarity between soil organic matter and root tissue, as compared to litter. The use of DRIFTS offers a faster and more cost effective technique for assessing the relative dominance of soil inputs to SOM that does not require long term root exclusion experiments or the excessive handling and pretreatment of sample materials.