Can litter decomposability be predicted by near infrared reflectance spectroscopy?

Several decomposition experiments were used to explore the potential of nea r infrared reflectance spectroscopy (NIRS) for predicting litter decomposab ility. A first experiment was conducted on a calibration set, and predictiv e equations were established between the NIR spectral data of the initial l itters and the decay descriptors. These equations were then applied to two validation sets. The 34 litters of the calibration set were incubated for e ight weeks in microcosms in the laboratory. The values of litter mass remai ning (LMR) in relation to incubation time were fitted to the single-exponen tial decay model (LMR = e(-kt)). The litter mass loss (LML) values at diffe rent sampling dates and the rate constant k were strongly correlated with t he initial litter characteristics. The calibrations carried out between mea surements of the NIR spectra on the initial litters and the different descr iptors of the decomposition patterns of the 34 litters showed that the LML values at the different sampling dates and the rate constant k were correla ted with the spectra of the initial litters more closely than with their in itial characteristics. The descriptors of litter decomposition patterns cou ld therefore be predicted by NIRS. Among these descriptors, which were all correlated with one another, the easiest to measure (LML after one week inc ubation in the microcosm) was tested as a litter decomposability index (LDI ). LDI was predicted by NIRS on the initial litters in two validation sets, the first consisting of 12 litters incubated under the same conditions in microcosms over a longer period (14 mo), the second consisting of four litt ers incubated in the field for one year at three stations situated along a climatic gradient. The results showed that the values of LDI predicted by N IRS were significantly correlated with the decay rate constant k in the two validation sets. The values of LDI predicted by NIRS therefore expressed a decomposability scale that was valid for litters decomposing over a longer period under the same incubation conditions and for litters subjected to d ifferent incubation conditions. The possibility of predicting litter decomp osability by NIRS provides many opportunities, firstly for studying spatial and temporal variability in the rate of recycling of organic matter, and s econdly for characterizing the gradual changes in litter quality during dec omposition.