Plant-soil interactions in response to grazing intensity in a semi-arid ecosystem from NE Spain

Livestock grazing is an important element in ecosystem regulation since it may affect essential ecosystem functions, such as nutrient acquisition, organic matter decomposition, or litter accumulation in the soil. Overgrazing can threaten the conservation of ecosystems through excessive defoliation of plants or trampling. On the contrary, moderate grazing can have benefits on ecosystem dynamics by favoring nutrient cycling or the soil microbial activity. The aim of this study was to analyze these effects in a semi-arid Mediterranean shrubland located in NE Spain. We established six study sites including three grazing intensities, where we sampled vegetation biomass and soil properties: nitrogen content, microbial biomass, water infiltration capacity, porosity, and gypsum content. These parameters were included in a plant-soil interaction model tested through Structural Equation Modeling. Grazing had a direct negative effect on plant biomass (p < 0.01) and water infiltration capacity (p < 0.05) affecting soil nitrogen content (p < 0.001) and microbial biomass (p < 0.5), respectively. Infiltration capacity and porosity were primary drivers of plant biomass (p < 0.05, both cases), and plant biomass was the main contributor to the soil nitrogen pool. Microbial biomass was dependent on infiltration capacity (p < 0.05), porosity (p < 0.01), and nitrogen (p < 0.01). Grazing directly or indirectly affected the functioning of the ecosystem through effects on plant and soil attributes, which may result in changes in plant growth, litter decomposition, or plant nutrient acquisition. This study revealed that moderate grazing can maintain optimal ecosystem features and prevent ecosystem degradation.