Factors influencing the stability of organic carbon pool in some Mediterranean soils.

Soils from pine, fir and chestnut woods, Mediterranean maquis at different successional stages, mixed area of maquis with pines introduced by foresters, Pteridium grasslands, garigue and clearing area in southern Italy were compared for microbial biomass and activity as well as for the stability of carbon reserve. Cluster analysis and principal component analysis showed that carbon turnover was influenced in decreasing order by soil age and both soil origin (volcanic or non-volcanic) and anthropic activity, with mature volcanic undisturbed soil being characterised by a low rate of carbon mineralization and the highest content of organic and microbial carbon. A long history of grazing, cutting and burning of vegetation, resulting in a garigue, as well as frequent fires or the introduction of pine to the maquis had a higher impact on the soil than the management of the chestnut orchards or coppice

Post-fire stimulation of soil biogenic emission of CO2 in a sandy soil of a Mediterranean shrubland

Fire is a frequent perturbation in Mediterranean-type ecosystems, altering soil organic matter turnover. In a Mediterranean shrubland subjected to experimental fire, soil CO2 emissions were measured over an annual cycle in burned and unburned sites using static chambers. Some chemical-physical parameters affecting soil C turnover (soil nitrogen and organic carbon content, pH, soil temperature and water content) and some microbial indicators of soil C turnover, i.e. soil potential respiration, microbial carbon, metabolic quotient and coefficient of endogenous mineralisation, were also measured. A high spatial variability of CO2 effluxes was detected in control as well as in burned plots, with 8.9 and 16.6% respectively of -hot spots' of gas emission; the -hot spots' contributed 33% to the whole annual soil CO 2 emission in control plots and 54.1% in the burned plots. No relationship between temperature and CO2 effluxes was found. In contrast, the data showed that soil water availability is the main climatic factor affecting field CO2 effluxes in the burned plots. Laboratory measurements under 55% of water-holding capacity showed a stimulating action of fire on soil organic matter mineralisation as indicated by coefficient of endogenous mineralisation, microbial carbon and metabolic quotient values. We concluded that fire could decrease the efficiency of soil microflora at conserving C. © IAWF 2007

Litter decomposition in Mediterranean ecosystems: Modelling the controlling role of climatic conditions and litter quality

A new process-based model of litter decomposition, characterized by detailed climatic data input and simple litter quality parameters, is proposed. Compared to existing litter carbon models, speci\ufb01c imple- mentations for temperature and moisture limiting effects have been adopted. The model is capable to represent decomposition processes in Mediterranean ecosystems, with summer drought slowing down, even at optimal temperatures, the litter decay rates of sclerophyll plants whose leaf masses are rich in structural compounds and low in N content. The model was calibrated by a best \ufb01tting procedure of two different datasets. First, unpublished results of litterbag experiments on leaf litter of 9 Mediterranean species, decomposing under controlled and not limiting temperature and water conditions, have been used to estimate the decay rate dependency from litter quality that was de\ufb01ned by only three initial C pools (labile, stable and recalcitrant compounds) instead of traditional N-based indices. Second, a set of published data from three medium-term \ufb01eld experiments on a single species, Phillyrea angustifolia, decomposing under different climatic conditions, have been used to estimate the limiting effects of tem- perature and moisture. The model was then validated against published data on seven other species and showed a correct reproduction of the major patterns of litter mass loss during decomposition processes of other seven different Mediterranean species. The model simulations, satisfactory for different litter types under a wide range of climatic conditions, suggest that factors which were not taken into account, such as initial litter N contents, microclimatic variations related to stand structure, soil chemistry and texture, and microbial communities, are not very signi\ufb01cant for assessing decomposition dynamics in Mediter- ranean ecosystems. The minimal requirements of input data, the simple structure, and the easiness of parameterisation make our model, among the many other available litter carbon models, an attractive alternative for different research purposes, at least for Mediterranean ecosystems

Litter decomposition in Mediterranean ecosystems: Modelling the controlling role of climatic conditions and litter quality

A new process-based model of litter decomposition, characterized by detailed climatic data input and simple litter quality parameters, is proposed. Compared to existing litter carbon models, specific implementations for temperature and moisture limiting effects have been adopted. The model is capable to represent decomposition processes in Mediterranean ecosystems, with summer drought slowing down, even at optimal temperatures, the litter decay rates of sclerophyll plants whose leaf masses are rich in structural compounds and low in N content. The model was calibrated by a best fitting procedure of two different datasets. First, unpublished results of litterbag experiments on leaf litter of 9 Mediterranean species, decomposing under controlled and not limiting temperature and water conditions, have been used to estimate the decay rate dependency from litter quality that was defined by only three initial C pools (labile, stable and recalcitrant compounds) instead of traditional N-based indices. Second, a set of published data from three medium-term field experiments on a single species, Phillyrea angustifolia, decomposing under different climatic conditions, have been used to estimate the limiting effects of temperature and moisture. The model was then validated against published data on seven other species and showed a correct reproduction of the major patterns of litter mass loss during decomposition processes of other seven different Mediterranean species. The model simulations, satisfactory for different litter types under a wide range of climatic conditions, suggest that factors which were not taken into account, such as initial litter N contents, microclimatic variations related to stand structure, soil chemistry and texture, and microbial communities, are not very significant for assessing decomposition dynamics in Mediterranean ecosystems. The minimal requirements of input data, the simple structure, and the easiness of parameterisation make our model, among the many other available litter carbon models, an attractive alternative for different research purposes, at least for Mediterranean ecosystems. © 2011 Elsevier B.V