Mediterranean natural forest living at elevated carbon dioxide: soil biological properties and plant biomass growth.

Biomass productivity and soil microbial responses to long-term CO2 enrichment have been investigated in a Mediterranean natural forest ecosystem. Several biochemical parameters have been measured on soil samples taken from six open top chambers (OTCs), enclosing clumps of natural Mediterranean woody vegetation including: Quercus ilex L., Phillyrea angustifolia L, Pistacia lentiscus L. and Myrtus communis L. The CO2 concentration of the air inside the OTCs was either ambient or ambient plus 350 mu mol mol(-1) (c. 710 ppm as mean daily value), Microbial C biomass, microbial respiration, dehydrogenase, beta -glucosidase, acid phosphatase and protease activities, inorganic N and soluble P, were tested in order to evaluate soil microbial size and activity. Statistically correlated seasonal patterns have been identified in some biochemical parameters in response to climatic conditions, soil nutritional status and the physiology of the vegetative cover. In situ soil respiration and above- and below-ground productivity were also measured. Microbial responses to CO2 enrichment were observed only at the beginning of the study and a general progressive reduction of the CO2 effect was recorded as monitoring continued. These results are in agreement with data from literature regarding similar studies on natural complex communities.