Soil microbial activity in relation with stages of plant colonization in mine tailings soils of a Mediterranean area

Resumen

Mine tailings show high metal levels, extreme pHs, limited organic matter anddeficient physical properties. As a consequence soil biota activity andbiogeochemical cycling might be hindered, affecting soil functioning. Mosttailings are abandoned without any restoration and might be spontaneouslycolonized by plants. This colonization occurs along with changes in functional soilproperties. Identifying these changes helps to understand those processesunderlying natural ecosystems recovery, and might be used to design moreeffective management for reducing tailings environmental risks. This study aimsto assess soil microbial activity in mine tailings soils related to different stages ofspontaneous colonization by native vegetation under Mediterranean climate. Sixenvironments were studied in an abandoned mining area (SE Spain, n=4): A)Within mine tailings: 1. Bare soils (S); 2. Small groups of Pinus halepensis trees(2-5) ≤≈2.5 m high growing scattered (P); 3. Isolated P. halepensis trees >≈4 mhigh with shrubs and herbs under the canopy (P+MS); 4. Dense patches withseveral P. halepensis trees (>5) >≈4 m high and shrubs and herbs under thecanopy (DP+MS). B) Outside mine tailings: 5. Contaminated forest with P.halepensis trees >5 m high and shrubs and herbs under the canopy (PF); 6. Noncontaminated control forest with P. halepensis trees >5 m high and shrubs andherbs under the canopy (CF). Soil microbial activity (upper 15 cm) was assessedby quantifying microbial biomass carbon (MBC), dehydrogenase/β-glucosidaseactivities and soil respiration. CF showed the highest MBC, β-glucosidase activityand soil respiration (1523 mg C kg -1, 3.76 µmol p-NP g-1 h-1 and 0.74 g m-2 h-1,respectively) which could be related to less stressful conditions in noncontaminated forest soils. However, inside mine tailings, resources scarcity could have led to lower microbial activity (e.g., 170 mg C kg -1, 1.09 µmol p-NP g-1 h-1and 0.34 g m-2 h-1 in DP+MS). P showed the highest dehydrogenase activity (4.75µg INTF g-1 h-1) which could be related to the presence of some adapted functionalgroups. CF also showed high dehydrogenase activity (3.28 µg INTF g-1 h-1), whileit was lower in the other stressed environments (0.02 – 2.66 µg INTF g-1 h-1). Thecharacteristics observed in the different environments showed that it could existfunctional differences among them. Soil microbial activity was closer to CF inthose tailing environments with higher plant colonization.