Impact of grazing on soil microbial communities along a chronosequence of Acacia tortilis subsp. raddiana in arid soils in Tunisia

Acacia tortilis (Forssk.) subsp. raddiana (Savi) Brenan is a woody legume recommended for adoption in arid lands of Tunisia, but their grazing is recognized as one of the main causes of soil degradation and desertification in these areas. The aim of this research was to explore the effects of grazing intensity on soil properties under A. tortilis subsp. raddiana along a chronosequence of young, mid-aged and old trees. Soil chemical, microbial and biochemical properties were evaluated. The results showed that tree growth increased soil pH, electrical conductivity, soil organic carbon (Corg), microbial biomass carbon (Cmic), Cmic:Corg ratio and enzyme activities (dehydrogenase, phosphatase and β-glucosidase). In contrast, C:N ratio and metabolic quotient (qCO2) decreased with increasing tree age. For the impact of grazing intensity, the amount of organic matter, microbial biomass and enzyme activities were reduced in intensively grazed site, while C:N ratio and metabolic quotient were higher.The findings demonstrated significant impacts of Acacia age-classes and grazing intensity on soil properties. It is concluded that A. tortilis subsp. raddiana establishment and development enhanced the development and the activity of microbial communities in soil; however, intensive grazing was detrimental to soil quality. This indicates that A. tortilis subsp. raddiana improved soil quality and play an important role in soil protection of degraded lands in Tunisia.

► Acacia raddiana growth increased soil organic carbon, microbial biomass carbon and enzyme activities.
► A. raddiana establishment enhanced the activity of microbial communities in soil.
► Significant impacts of Acacia age succession on soil properties.
► Soil properties were highly sensitive to grazing intensity in the arid ecosystem.
► A. raddiana improved soil quality and play an important role in soil protection of in Tunisia.