Forest soil organic carbon dynamics as affected by plant species and their corresponding litters: a fluorescence spectroscopy approach

The effect of forest cover distribution and plant litter input on soil organic carbon were analyzed to better understand the dynamics of carbon cycling across ecosystems on the Natural Oriented Reserve Bosco delle Pianelle. Fluorescence spectroscopy represents a very useful tool to characterize soil organic matter properties, since it allows to directly monitor the molecular status of a fluorophore depending on its chemical environment, as well as on its structure, substituents of the aromatic moieties, and molecular weight. Here, fluorescence analysis was performed on humic acids isolated from four litters (HALs) and their underlying soils (HAs) at three depths. All samples were collected from a protected forest area, Southern Italy, under different plant covering: Quercus ilex L. (Q), mixed Carpinus betulus L. and Carpinus orientalis Mill. (CC), Pinus halepensis L. (P), and mixed Quercus trojana Webb. and Quercus ilex L. (QQ). Data obtained showed a fast decomposition process for P and QQ litters, with HAs in the underlying soils characterized by the presence of simple, highly fluorescent structural components also in the deepest layers. On the contrary, a slow decomposition process was observed for Q and CC litters, whose underlying soil HAs were characterized by an increasing aromatic polycondensation and humification degree from the surface to the deepest layers, as supported by low values of fluorescence intensity and high wavelength maxima. Results obtained indicate that P and QQ species promote C accumulation and stock in the underlying soils, thanks to a greater decomposition of their litter, and fluorescence spectroscopy is a very simple and suitable method to evaluate the influence of three species distribution on soil organic carbon pools.