Scots pine needle litter – can it offer a mechanism for carbon sequestration? Presentation of a theory

Abstract

Aim. The aim behind this work is: (i) to review the work on Scots pine needle litter in order to construct a model for the decomposition process, from litterfall until a stable fraction is left, (ii) suggest a simple regulating mechanism for its sequestration of carbon. Focus will be on foliar litter of Scots pine and the genus Pinus. Discussion. The chemical composition of newly shed pine litter is in part determined by climate, e.g. mean annual temperature (MAT). Thus concentrations of nitrogen (N) are higher – and those of manganese (Mn) lower – with higher MAT. This may also influence the decomposition process. Mass loss of newly shed pine needle litter is positively influenced by climate (e.g. MAT), as well as by N and phosphorus (P) concentrations. In the late stage (above c. 30% accumulated mass loss) the influence of climate fades and those of lignin (Acid Unhydrolyzable Residue – AUR), N, and Mn are regulating the decomposition process. As the degradation of AUR dominates the decomposition process important parameters are those that influence the degradation of AUR, thus N and Mn. In the humus-near organic matter limit values have been related to litter Mn concentration over a wide climate gradient. Thus, the higher the Mn concentration, the further the process goes and the smaller the stable fraction. Conclusions. It appears that factors regulating the size of the stable litter fraction may be used as a tool on a larger geographical scale to predict carbon sequestration rates in pine forests.