Rosa Francaviglia and Anna Benedetti Soil organic carbon and biological fertility in a Mediterranean forest area (Italy)  Rosa Francaviglia and Anna Benedetti Centro di Ricerca per lo studio delle Relazioni tra Pianta e Suolo, Rome, Italy rosa.francaviglia@entecra.it

Study area Castelporziano Estate is a natural ecosystem with high environmental value which lies in Central Italy at the western outskirts of Rome, about 20 km from the city centre and in front of the Tyrrhenian Sea.

Study area

Study area Soil morphology is mainly plain (30 m mean elevation) with sandy materials of alluvial nature, and only the inner part is formed of volcanic and alluvial materials with a slight elevation above the sea level (85 m). The total area is about 6000 ha, the climate is Mediterranean, total rainfall is 700 mm, and mean temperatures range from 4 °C in winter and 30 °C in summer. The vegetation is typically Mediterranean, mainly oaks, mixed broadleaf groves, and Mediterranean maquis along the seacoast. Areas with reforestation of pines, as well as corkwoods, pastures, and small agricultural fields are also present.

Soil sampling Soils were sampled at five different sites QI, forest of Quercus ilex L. MM, Mediterranean maquis AR, arable land MF, mixed hygrophilous back-dune forest QI, forest of Quercus ilex L.; Xeropsamments mixed thermic aquic MM, Mediterranean maquis (Myrtus communis L., Erica arborea L., Pistacia lentiscus L., Arbutus unedo L., Juniperus spp., Phyllirea spp., Smilax aspera L., Cistus spp., etc.); soils on sandy coastal dunes; sulle dune costiere. Complesso di Xeropsamments mixed thermic PP, Pinus pinea L. reforestation (60 years old); Haploxeralfs typic, loam coarse, mixed, thermic MF, mixed hygrophilous back-dune forest (Populus alba L., Quercus cerris L., Fraxinus oxycarpa L.); Xeropsamments aquic mixed thermic AR, arable land, Haploxeralfs typic, loamy, fine, mixed, thermic. PP, Pinus pinea L. reforestation 11/11/2018

Main soil parameters 11/11/2018 Microbial biomass carbon (Cmic): Chloroform Fumigation Extraction method (Vance et al., 1987). Soil samples were incubated for 10 days at -33 kPa water tension and 30 °C. Soil respiration was measured in a closed system with the method of Isermeyer (1952). Soils were rewetted to -33 kPa of water tension, and incubated at 30 °C. CO2 evolution was measured after 1, 2, 4, 7, 10, 14, 17, 21, 28 days. 11/11/2018

Soil sampling and analyses Five soil samples from each site were collected (0-20 cm of depth), about 2 m far from each other. SOC: Springer-Klee method (1954) SOM=SOCx1.724 Total N (Kjeldahl) Microbial biomass carbon (Cmic): Chloroform Fumigation Extraction method (Vance et al., 1987) Soil respiration: in closed glass jars (Isermeyer, 1952) The basal respiration (Cbas) is the average at the 28th day, cumulative respiration (Ccum) is the cumulated value after 28 days. Microbial biomass carbon (Cmic): Chloroform Fumigation Extraction method (Vance et al., 1987). Soil samples were incubated for 10 days at -33 kPa water tension and 30 °C. Soil respiration was measured in a closed system with the method of Isermeyer (1952). Soils were rewetted to -33 kPa of water tension, and incubated at 30 °C. CO2 evolution was measured after 1, 2, 4, 7, 10, 14, 17, 21, 28 days. 11/11/2018

Soil sampling and analyses The metabolic quotient (qCO2): ratio between Cbas and Cmic (Anderson and Domsch, 1990; 1993). The mineralisation quotient (qM): ratio between Ccum and SOC (Dommergues, 1960). The index of biological fertility (IBF), a comprehensive indicator considering SOM, Cbas, Ccum, Cmic, qCO2 and qM was also calculated for the different land uses (Benedetti and Mocali, 2008). Five intervals of values have been set for each parameter, and a score increasing from 1 to 5 has been assigned to each interval. The metabolic quotient (qCO2): expresses the relation between the activity (basal respiration) and the carbon content of the microbial biomass. The unit is (mg C-CO2/mg Cmic)/24*100, where 24 are the hours in a day (Anderson and Domsch, 1990; 1993). The mineralisation quotient (qM) is the ratio between the cumulated respiration and the soil organic carbon, and is expressed in %. The quotient indicates the efficiency of micro-flora in metabolising soil organic carbon (Dommergues, 1960) . 11/11/2018

The Index of Biological Fertility (IBF) Scores of the intervals of values of the different parameters 11/11/2018

The Index of Biological Fertility (IBF) The algebraic sum of the scores for each parameter gives the classes of biological fertility Fertility class I II III IV V Stress Pre-stress Medium Good High IBF scores sum 6 7-12 13-18 19-24 25-30 11/11/2018

IBF parameters and corresponding scores for IBF evaluation. IBF results IBF parameters and corresponding scores for IBF evaluation. 11/11/2018

Conclusions The IBF indicator has proved effective to discriminate the biological fertility in the different land uses The order is MM>MF>PP>QI>AR The fertility classes are HIGH (MM), GOOD (MF, PP, QI), MEDIUM (AR) The methodology presented in this research has been widely used in Italy, and might be easily applied to other agro-forestry systems with available information on soil and land use 11/11/2018

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