Root seasonal pattern, spatial distribution, and C:N ratio of matgrasspasture (Nardus stricta L.) in the Lombardy Prealps

The aim of the present study was to investigate carbon and nutrient cycling and the role of root dynamics in terrestrial ecosystems such as large abandoned pastures and natural grasslands present in the Prealps, for which below-ground processes are currently enigmatic. In particular, we quantified root/leaf biomass and C:N ratio throughout two growing seasons. Additionally, root traits such as root length density (RLD), root mass density (RMD), and root diameter classes (RDC) were also investigated with the aim of understanding the spatial distribution of roots in the soil. In our samples, we found that the roots could be divided into three main diameter classes and hence quantified the presence of each class along the soil profile. With regard to total root biomass, we found the occurrence of two peaks of biomass accumulation during the growth season, and when biomass accumulation was compared with climatic data, it was impossible to obtain a clear indication of the root turnover rate. In fact, the strong influence of grazing on the above-ground biomass could have affected, in turn, root biomass. In future, this possible complication will be avoided by repeating the measurements within enclosures to avoid grazing interference. We found that C:N ratio remained constant, with a single peak, suggesting a lower root decomposition during the warmest period (August 2006). The concentration of nitrogen in roots decreased with depth as a result of a decrease in roots with smaller diameters. The reverse was found for carbon content, which increased with depth, probably due to an increase in roots with larger diameters. This study represents the first attempt to estimate root turnover rates in this prealpine ecosystem, which have been analysed to date only for the above-ground biomass.