Macroclimate and lignin control of litter decomposition rates

In order to develop a general model of litter decomposition rates suitable for theprediction of regional variations in decay rates, and to determine the relative control by macroclimateand litter quality on decomposition rates, data were selected from 5 locations ranging in climate fromsubpolar to warm temperate. Actual evapotranspiration (AET) was selected as an index of the climatic(energy and moisture) forcing function of the specialized decomposers which is superior to temper-ature and precipitation. Lignin concentration was selected as an index of litter quality and may betreated as a mediator of climatically (AET) regulated decay rates. In a stepwise, multiple linearcorrelation—regression, using AET, lignin concentration (%) and AET/lignin concentration (interac-tion), AET alone accounted for 51% of the variance in observed decay rates, AET/lignin concentration(interaction) added 19% and lignin concentration added 2% of the total (72%) variance accounted.Simple correlation of the five locations between lignin concentration and decomposition rate rangedfrom r = .32 to r = .95, however, the regression lines for each of the 5 locations indicated that theseslopes progressively declined with AET. Moreover, the slope decline was not parallel, indicating aclimatically variable control by lignin concentration on decay rates. In low-AET (not arid) climates,litter with high and low lignin, will decay at more nearly similar rates, but as the AET environmentincreases, the difference in decay rates becomes progressively greater than the increase in AET alonewould seem to warrant. A general model of the interaction control by AET and lignin concentrationon decomposition rates was formulated which overcomes the restraints of the multiple regressionmodel. At the scale of subpolar to warm-temperate climates, the climate as indicated by AET isseveral orders of magnitude more important as a predictor of decay rate than is litter quality. Thisimportance is evident in spite of the fact that the data on lignin concentration used in this analysishad a 12-fold range while the AET values had a 2.3-fold range.
Key words: actual evapotranspiration; climatic control; curve-fitting; decomposition rates; ge-ography of decomposition; lignin; litter; macroclimate; North Carolina; Norway; Oregon; regionalanalysis, substrate quality; Tennessee; United Kingdom.