Does the correlation of chemical traits between leaves and roots drive coordinated variation of decomposition rates?

Background/Question/Methods

Recent evidence indicates that chemical composition is correlated between leaf litter and absorptive roots (lowest two branch orders on a stream-based branch ordering system) across species. But whether this correlation in litter chemistry will translate into correlation in litter decomposition rates is unclear. Here, we investigated this question with a one year laboratory incubation experiment in which leaf litter and absorptive roots collected from 18 temperate and subtropical tree species were used. We assessed carbon and nutrient quality (i.e., organic soluble fraction, acid insoluble fraction, C concentration, N concentration, P concentration and Ca concentration) of initial litter of all these species and measured CO₂ release rates every month as a proxy for litter decomposition rates.

Results/Conclusions

The decomposition rates of leaf litter were positively correlated with those of absorptive roots for the first three months, but the correlation between leaf and root litter decomposition decreased progressively through time (first month r = 0.81, second month r = 0.66, third month r = 0.60, all P values < 0.01). These correlations could be a direct consequence of the correlation of potential chemical drivers (i.e., N concentration r = 0.82, Ca concentration r = 0.60 and P concentration r = 0.48, all P values < 0.05) among species. After three months, leaf and root litter decomposition were no longer correlated. This may be due to carbon compounds (i.e., C concentration and acid insoluble fraction), which were not correlated or less well-correlated, being more important during the later stages of decomposition. Our results imply that while initial rates of decomposition of leaves and roots may be correlated, the longer-term decomposition rates of leaves and roots was inconsistent and uncoordinated. This suggests that a holistic study of effects of plant chemical traits on decomposition should take both leaf and root chemical traits into consideration.