Functional and structural soil-vegetation indicators of ecosystem functioningin metal-contaminated environments: a case study in SE Spain

Resumen

Functional and structural soil parameters of six environments defined by stages ofvegetation colonization were studied in abandoned mine tailings area. Theenvironments were: A) Within the mine tailings: 1. Bare soils (S); 2. Small groupsof Pinus halepensis trees (2-5) ≤≈2.5 m high, growing scattered (P); 3. Isolated P.halepensis trees >≈4 m high with shrubs and herbs under the canopy (P+MS); 4.Dense patches with several P. halepensis trees (>5) >≈4 m high and shrubs andherbs under the canopy (DP+MS). B) Outside the mine tailings: 5. Polluted forestwith P. halepensis trees > 5 m high and shrubs and herbs under the canopy (PF); 6.Control mature forest not contaminated with P. halepensis trees > 5 m high andshrubs and herbs under the canopy (CF). Ecological indexes of vegetation wereevaluated and soils analyzed for physical, chemical, and biological parameters. Soiltemperature, feeding activity of invertebrates and decomposition were measured insitu. P+MS, DP+MS and PF showed the highest diversity of plant species and P thelowest. The organic C/N ratio was ≈20 in P+MS, DP+MS, PF and CF and ≈13 in Sand P, which was in accordance with larger accumulation of litter in the first fourenvironments. Cation exchange capacity (CEC), an indicator of the buffer capacityof the soil and the stability of the organic matter, was largely higher in CF (≈32)followed by PF (≈20), P+MS and DP+MS (≈12) and finally P and S (≈5). Watersoluble organic carbon (the most labile fraction of soil organic C) and C frommicrobial biomass (indicator of micro-organisms population) followed the samepattern than CEC. Total metal(oid)s concentrations (mg kg-1) widely varied withinthe tailings, without a clear pattern related with plant colonization (e.g. Pb:5400-14600; Zn: 8600-18000; As 200-1200). Water soluble metal(-oid)s (µg kg-1),the most toxic fraction, were largely higher in S (e.g. Pb≈4600; Zn≈210000). Teabags decomposition showed two different tendencies: DP+MS, P+MS and S had ahigher weight loss than PF, CF and P. Feeding activity was (% of holes fed upon):CF =42%, P =39%, S= 31%, P+MS =21%, AF =8%, DP+MS =7%. Total andsoluble/available metals concentrations cannot to be considered the only factorsrelated with the activity of biota in polluted sites. Field studies including physical,chemical, and biological parameters must be considered together to obtain realisticinformation for understanding soil ecosystem functioning and recovering.