Soil Microbial Activity Under Sclerophyll Vegetation with Different Degrees of Anthropogenic Perturbations in Central Chile.

Schlerophyll ecosystems is the predominant vegetation type in Central Chile where, the greatest proportion of the population lives, emphasizing the need for its conservation. The development of rural settlements has had a negative effect on these type of ecosystems, as a result of wildfires, firewood extraction, indequate implementation of annual crops, and overgrazing practices. These degradative processes have resulted in soil erosion and soil degradation. Current protection of previously over-exploited areas has permitted, to some extent, the recovery of  vegetation and the re-activation of some soil forming processes. The aim of this study was to evaluate soil biological properties that can be used as indicators of the recovery of these ecosystems. Soil biological indicators were evaluated under four types of sclerophyll vegetation, each one affected by different degrees of long-term anthropogenic disturbances. Vegetation types considered peumo (Cryptocarya alba (Mol.) Looser) (PEU) forests, peumo–litre (Lithrea caustica (Mol.) Hook et Arn.)–quillay (Quillaja saponaria Mol.) (PLQ) forests, quillay–tevo (Retamilla trinervia (Gillies et Hook.) Hook. et. Arn.)–colliguay (Colliguaya odorifera Mol.) (QTC) shrub-type formations, and savannah-type formations composed of espino (Acacia caven (Mol.) Mol.) and annual grasses. Soil samples were extracted at depth intervals of 0-6 cm and 6-12 cm below the canopy cover of the different tree and shrub species as well as from the open spaces between plants. Soil organic C (SOC), microbial biomass-C by the fumigation-incubation method (C-SMB) and soil basal respiration (BR) were determined under laboratory conditions. The derived metabolic quotient qCO₂, as well as the microbial and mineralization quotients (qMic and qM, respectively) were also evaluated. The largest SOC was found under the less disturbed formation (PEU, 8.04%, p≤0.05 as compared to ESP). However, largest values of C-SMB, BR, qMic and qM were found under the savannah-type formation (ESP). No clear trend in qCO₂ was observed. A positive and significant linear correlation was found between SOC and C-SMB (r values between 0.91 and 0.98; p≤0.001 for all formations), particularly when contrasting SOC and C-SMB under the same vegetal formation, suggesting that the amount and origin of soil organic matter (i.e. plant species source) play a fundamental role in microbial development. Plant species composition which is related to the degree of anthropogenic disturbance, seem to be a key factor for microbial development in these Chilean sclerophyllous ecosystems.