Effects of Calamagrostis epigejos, Chamaenerion palustre and Tussilago farfara on nutrient availability and microbial activity in the surface layer of spoil heaps after hard coal mining

• Effects of C. epigejos, C. palustre and T. farfara on coal mine spoils are tested.
• The plants increase C, P, K and Ca and microbial activity in the spoil material.
• Effects of studied plants on spoil’s properties are species-dependent.
• The studied plants can play a key role in soil formation on heaps after coal mining.

This study examined three herbaceous plant species, namely Calamagrostis epigejos, Chamaenerion palustre and Tussilago farfara spontaneously colonizing spoil heaps after hard (bituminous) coal mining for their effects on selected physico-chemical and microbial parameters of the spoil material. The parameters were measured for plots of C. epigejos, C. palustre, T. farfara and controls (bare ground) established on heaps belonging to two age categories: 5–10 and 15–20 years from the end of spoil heaping. The spoil material was characterized by varying pH values (from 4.0 to 9.1), high content of total C (10.3 ± 3.8%), deficiency of other nutrients (1.04 ± 0.76 mg N–NO3 kg−1, 2.16 ± 1.07 mg Olsen P kg−1, 572 ± 163 mg exchangeable Ca kg−1) and low respiration rate (0.64 ± 0.34 μM CO2 gdwt−1 24 h−1). The spoils under the plants had less N–NO3 and more exchangeable Ca and K, available (Olsen) P and total C than the spoils from non-vegetated plots. The effect for the latter three variables was species-dependent. Electrical conductivity and N–NO3 concentrations were lower in the spoils from the older heaps than those from the younger ones, while the opposite effect was found for N–NH4 and Ca concentrations. The spoils from the vegetated plots supported more active and richer microbial communities than the bare spoils. This effect was strong, especially for the older heaps. Microbial respiration was the highest under C. palustre; it averaged 0.92 ± 0.31 μM CO2 gdwt−1 24 h−1, i.e., 2.6 times more than in the bare spoils. Microbial communities studied with Biolog plates were more active and utilized a higher number of carbon substrates under the plants than in the bare spoils. T. farfara differed considerably from the two other species in the structure of microbial communities (the metabolic fingerprint) it supported. Overall, the results show that the three plant species significantly affected nutrient availability and enhanced microbial performance in the coal mine spoil material. Since these plants effectively colonize industrial waste sites, they can be recommended for use in reclamation programs.