Changes of topsoil under Fagus sylvatica along a small latitudinal-altitudinal gradient

This study evaluated soil properties along a small transect in the Apennines chain (central Italy). Using latitude and altitude as surrogates for temperature differences, three locations at different latitudes were selected for the study. At each location, two altitudes were selected (800 and 1000 m). The study was conducted by contrasting chemical and biochemical parameters [microbial biomass-C content, amount of CO 2 evolved during basal respiration (ΣCO 2 –C), and potential enzyme activities] of topsoils (O and A horizons) supporting European beech (Fagus sylvatica L.) forests at different scales of investigation: horizons, altitude, and latitude. Along the topsoil, the trend of all investigated properties was unique to each O and A horizon according to its level of organic matter degradation, availability of substrates, and nutrients. Contrasting the altitudes, the difference of 1 °C of temperature between 800 and 1000 m significantly affected some of the chemical parameters and both microbial and enzyme activities mainly in the mineral horizons, although glucuronidase and phosphodiesterase activities appeared to be mainly controlled by TOC content. Generally, the different enzyme activities were more clearly highlighted when they were expressed per organic C unit, rather than on a soil mass basis. Latitudinal sensitivity was recorded for total N, ΣCO 2 –C, and some enzyme activities, although no difference in mean annual air temperature occurred along the latitudinal transect. In this case, it is plausible that the summer-winter thermal excursion, which was lower for the southernmost location and increased going north, might have indirectly affected these parameters through changes in the plant-soil relationships, composition of the macro- and mesofauna population, and microbial activity. Considering all the investigated aspects, an increase of 1 °C in mean annual air temperature (in the range 9–10 °C) and/or the alteration of summer-winter thermal excursion might affect the actual soil-plant balance in temperate beech forests, with possible greater mineralization of the topsoil organic matter and a major release of CO 2 in the atmosphere