Floristic gradients of herbaceous vegetation and P/N ratio in soil in a Mediterranean area

A broad range of herbaceous plant comunities in a Mediterranean Landscape in central Italy, running from heavily urbanized areas to semi-natural pastures, has been studied. These communities can be easily arranged along a gradient of ruderality. We inspected which of a series of soil parameters could better explain this gradient (pH, CaCO3, granulometry, N, P, C/N, P/N). We show that (1) the single most important explanatory variable is P/N ratio of soil; (2) nitrogen and carbon pools in soil are related, in the set of communities studied, with another gradient of decreasingly frequent, predictable, moderate disturbance such as trampling. We discuss the meaning of these results.