The impact of land management and abandonment on soil enzymatic activity, glomalin content and aggregate stability

Selected environments ranging from cultivated soils under vines and olive groves to sequential abandonment with forest, meadow and scrub cover were investigated for their impact on relevant physical and chemical properties in the shallow soils of the Cap de Creus Peninsula (NE Spain). Both insufficient agricultural practices and periodical wildfire occurrence in abandoned areas were focused as components triggering degradation processes. Despite that, less fire affected soils under Erica scrubs or meadows were found to be more active in carbon preservation potential. Soil properties like moisture, bulk density, water holding capacity, pH, organic carbon (SOC), carbon dioxide emission (CO2) and total nitrogen (TN) showed significant seasonal patterns within and between the investigated soil environments, but total phosphorus (TP) did not show a clear trending. Carbon loss (C–CO2) was extremely variable along the seasons in soil under vines, ranging from 3% to 10% of SOC stocks on annual basis. Assessment of C–CO2 losses allowed establishing soils and associated management or stage of abandonment more susceptible to organic compound depletion. Glomalin and organic carbon were found to be significantly more active in favoring structural stability in the 2.00–5.60mm aggregate class with respect to the 0.25–2.00mm aggregate class, indicating that stable organic compounds may enhance the formation of larger aggregates and a better organized soil crumb. Seasonally, β-glucosidase, protease and phosphatase activities were much lower in soils under vines in agreement with the lowest organic carbon content. Enzyme activity increased from soils under vines to soil under pasture and showed significant patterns within soil environments and between seasons. A three component factor structure showed component 1 to be positively and significantly related with variables favoring better soil conditions except the ratio C–CO2/SOC and the bulk density. Soils under pasture and Erica scrub were scored as being more relevant to the first component–variable association especially in winter, spring and autumn, as opposed to the soils under vines (V) at each season. In the summer season the structural stability of 0.25–2.00mm aggregate class of all the soil environments but vines was loaded in the component 2 and resulted in opposition to CO2 emission and soil moisture only at soils under pasture and Cistus scrub, suggesting that CO2 emission increases at higher moisture content and both may cause disruption of smaller aggregates. Total phosphorus dynamics was found to depend by pH variation. The work showed the current trends of the soils under study underlying both susceptibility to degradation and potential for carbon storage and data should stimulate management plans for abandoned land aimed at recovering the landscape heterogeneity.