Rhizosphere interactions and functional adaptive mechanisms of plants during spontaneous restoration of pyrite-waste degraded soil

Miroslav Nikolić, Project Leader

Nina Nikolić

Vuk Maksimović (Life Science Department)

Acid mine drainage is recognized as the single greatest environmental challenge in the European mining sector (FP5-ERMITE; Wolkersdofer et al ., 2005). The high level of pollution and the associated transboundary environmental risks make the Bor copper mine complex (Figure1) one of the four environmental hotspots in Serbia (EPR UN , 2003).

For more than 50 years the flotation waste from this mine (pyrite tailings with very high acidifying potential, metals and As) had been discharged into the local river system. Concomitantly, about 10,000 ha of the highly productive alluvial land has been destroyed, and far more degraded by layers of pyrite-containing sludge deposited on the fields by spring and autumn floods of the rivers Timok and Borska reka (Figure 2).

The distinctiveness of this area (no literature data on comparable environmental setup, extent of degradation, combination of stress factors, lack of anthropogenic influence, and only a very recent onset of spontaneous revegetation), together with the growing importance of “ecological” (i.e. reliance on spontaneous restoration) vs. purely technical reclamation strategies, make this post-mining landscape a very interesting model locality to study the mechanisms of plant adaptations to marginal conditions.

Under the imposed multiple stress, the establishment and survival of a plant is principally determined by the processes in the rhizosphere as a primary interaction zone between the plant and the environment. The major aim of the proposed project is to study the complex interactions in the rhizosphere and to clarify the mechanisms of functional adaptations of different plant species to differently degraded soils. Besides the fundamental character of the results, the gained understanding of key processes and mechanisms of restoration already operating in the nature should provide a necessary base to design a sustainable and economically efficient reclamation strategy for this area. Our preliminary field investigations indicate that the prevailing abiotic stress is caused by low pH, deficiency of soil organic matter, and severe deficiency of the available mineral nutrients. In addition, due to the terrain configuration, flooding regime and land use history, toxic concentration of metals (Cu , Zn , Fe , Pb ) and Аs, as well as periodic droughts, are assumed as stress factors at certain localities (Figure 3).

The process of spontaneous restoration comprises the succession of phases dominated by different functional types (life forms, life strategies, propagation strategies, etc.) of plants adapted to the specific environmental conditions. The proposed study sets out from the hypothesis that the prevailing tolerance mechanisms of plants (root exudates as organic acids, polysaccharides, phenolic compounds; activity of rhizosphere bacteria and establishment of mycorrhiza; nutrient use efficiency; Si accumulation; increase of the antioxidative capacity) would also successively change in the process of revegetation.

The research is based on the complementarity of the field work (a search for patterns of vegetation-soil interactions), and laboratory experiments under the controlled conditions (tests to clarify the underlying physiological mechanisms at the plant level). Field work includes terrain reconnaissance (selection of appropriate transects, i.e. land cover gradients, principle of false chronosequence), vegetation survey, soil sampling and plant tissue sampling along the selected transects (Figure 4). Upon the multivariate gradient analyses, the a) plant nutritional status; b) Si distribution in spontaneous vegetation (depending on soil pH/soil organic matter and plant biomass production; c) the role of mycorrhiza (dominance of mycorrhizal plant species, type and intensity of mycorrhiza); d) soil biological activity (activity of rhizosphere bacteria; ratio of heterotrophes to pyrite-oxidizing hemotrophes) will also be investigated for the established phases of revegetation.

The model experiments will be designed to simulate the relevant abiotic stress in order to study the response mechanisms of the selected adapted plant species (including some crops). Specifically, the a) influence of the pyrite tailings on inducing the adaptive reactions in roots (root exudates and rhizosphere pH regulation) of plants from the spontaneous flora and crop species (barley, ray, lupine, clover); b) influence of soil conditioners and fertilizers on the process of pyrite oxidation, rhizosphere pH, microbial activity and functional diversity of rhizosphere microbes, and on the nutrient use efficiency of plants; c) effect of Si nutrition on the plant growth on pyrite tailings; d) mechanisms of acquisition and mobilization of nutrients in the root apoplast, the role of mycorrhiza and rhizosphere bacteria; and e) the role of mineral nutrition in modulating plant response to oxidative stress caused by the multiple abiotic stress will be investigated.

Report 2008 (in Serbian) (0.8 MB)