Variability in litter quality and its relationship to litter decay in Canadian forests

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Abstract
Predicting the effects of climate change on litter decomposition requires an improved understanding of the link between organic composition and the parameters used to define litter quality. Carbon-13 nuclear magnetic resonance spectroscopy with cross-polarization and magic-angle spinning (CPMAS NMR) was used to characterize 36 foliar litters, including the species used in the Canadian Intersite Decomposition Experiment (CIDET), a Canada-wide long-term litter decomposition study. The litters showed a wide range of organic composition, qualitatively interpreted as the sum of component biopolymers (mainly carbohydrates, cutin, tannins, and lignin). Only weak correlations were found between NMR parameters and Klason lignin (KLIG); however, cluster analysis based on elemental, NMR, and proximate analysis gave good separation of botanical classes. NMR also had little predictive value for 3-year CIDET mass losses, which were negatively correlated with both KLIG and KLIG/N. Mass loss generally decreased in the following order: grass > pioneer broad-leafed deciduous > conifer (deciduous and evergreen) > American beech (a fagaceae) > wood. Predictive models for 3-year CIDET mass loss derived from linear regression with elemental, proximate, and NMR analyses were superior to those using only NMR parameters, with the best model based on KLIG, N, and Ca. Although providing no molecular-level understanding, KLIG integrates the most insoluble lignin, cutin, and tannin components. Limitations and possible improvements for NMR evaluation of litter quality are discussed.Key words: Klason lignin, 13C CPMAS NMR, proximate analysis, litter decomposition, tannin, cutin, CIDET.

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