Different seasons and vegetation cover more than fire control nutrient stoichiometry and biological activities in Mediterranean soils

Mediterranean soils are affected by degradation phenomena, exacerbated by anthropic disturbance. These ecosystems are affected by peculiar climatic conditions, characteristic vegetation and frequent fire that with the anthropic activities can compromise soil nutrient status. Studies concerning the nutrients stoichiometry in Mediterranean area are scarce, therefore the present research aim to fill the gap about the effect of seasonal variations, vegetation cover and fire occurrences on soil nutrient balance and microbial biomass and activity. The sampling was performed inside the Vesuvius National Park across 24 sites during two seasons (Fall and Spring), under trees and shrubs and in burned and unburned areas. Soils were characterized for carbon (C), nitrogen (N), phosphorous (P) and potassium (K) concentrations, for bacterial and fungal biomass (Eub and Fungi) and for microbial activities (respiration, hydrolase: HA, dehydrogenase: DHA, β-glucosidase: β-glu and urease: U). The results showed that, both in Fall and Spring, high C:N (18.7), C:P (130) and N:P (6.74) ratios were observed in soils under trees. Both in soils under trees and shrubs, low eubacterial biomass (trees: 90.2 ng g− 1 w.w.; shrubs: 44.4 ng g− 1 w.w.), respiration (trees: 0.24 mg CO2 g− 1 d.w. min− 1 ; shrubs: 0.14 mg CO2 g− 1 d.w. min− 1 ) and hydrolase (trees: 37.0 mmol FDA g− 1 d.w. min− 1 ; shrubs: 11.9 mmol FDA g− 1 d.w. min− 1 ) activities were observed in Spring. Fire effect was evident only in Fall where low values of eubacterial biomass (667 ng g− 1 w. w.) and respiration activity (0.60 mg CO2 g− 1 d.w. min− 1 ) were observed in burnt soils. In conclusion, the seasonal variations and the vegetation cover appeared the main environmental factors that affect nutrient stoichiometry and microbial biomass and activity in Mediterranean soils. It is necessary to monitor Mediterra nean soils during different seasons and encourage the growth of native vegetation to enhance nutrient cycling and maintain soil health.