Effects of organic enrichment of mine spoil on growth and nutrient uptake in oak seedlings inoculated with selected ectomycorrhizal fungi

  • Published source details Lunt P.H. & Hedger J.N. (2003) Effects of organic enrichment of mine spoil on growth and nutrient uptake in oak seedlings inoculated with selected ectomycorrhizal fungi. Restoration Ecology, 11, 125-130.


In the UK, attempts are being made to restore vegetation after surface mine extraction of coal. Some sites are located in partially wooded areas in which pedunculate oak Quercus robur and sessile oak Q.petraea are the dominant tree species. However, practices such as soil stripping, storage and reinstatement (replacement of surface layers) result in the loss or deterioration of topsoil quality. Stunted growth of peduculate oak has been reported on such sites where overburden and subsoil have been spread, attributed to a lack of macronutrients (NPK) and an adverse soil environment for root growth and mycorrhizal development. In this study, growth, mineral nutrition and ectomycorrhizal colonization of oak seedlings were investigated in an experiment in which mine spoil was enriched with a leaf litter mulch.

The study was undertaken in a nursery glass house. Pedunculate oak acorns were surface sterilized in a 1% aqueous solution of sodium hypochlorite and germinated in a 2:1 mixture of sterilized peat and perlite. Mycorrhizal inoculation took place after 11 weeks growth (seedlings around 15 cm tall and sufficient fine roots for mycorrhizal infection). Controls were established without inoculation. Seedlings were transplanted into 2 litre pots in overburden material (weathered shale) from Garnant surface mine (south Wales). Seedlings were potted with or without organic matter and grown in a glasshouse over spring and summer.

Three ectomycorrhizal fungi were used for inoculation: Hebeloma crustuliniforme, Laccaria laccata and Cortinarius anomalus. Organic matter consisted of a 2:1 mix of heat sterilized oak leaves and fresh grass clippings, added to the upper half of each pot (3:2 mixture of litter and overburden).

Dry weight, mycorrhizal formation and foliar macronutrient concentrations were determined 17 weeks after inoculation. Seedlings were divided into roots, shoots and leaves and dried and weighed. Before drying, root samples were removed and counts of infected and uninfected roots were made and colonization by the inoculum species assessed.

Dried leaf samples and organic matter were analyzed for macronutrient concentrations most likely to limit tree growth (i.e. N, P, K and Mg). Amended and unamended overburden samples, and reference soils were also analyzed. Further analysis was carried out at the end of the experiment on organic matter within the enriched pots to assess nutrient mineralization.

Organic matter addition of produced a two- to threefold increase in seedling dry weight (14-21 g) and seedlings appeared healthy, whilst seedlings in unamended spoil had poor growth and severe chlorosis.

Organic enrichment enhanced biomass of seedlings inoculated with L.laccata (21 g) and H.crustuliniforme (18 g), whilst those inoculated with C.anomalus (15 g) were about the same as controls (14 g). L.laccata proved the most successful of these ectomycorrhizal species, with much higher levels of infection (c.31%) than H.crustuliniforme (c.18%). Organic matter addition caused a nine-fold increase in H.crustuliniforme mycorrhizal infection and enhanced L.laccata colonization to a lesser extent. C.anomalus showed very limited colonization (<1%) whether with and without organic matter addition. Organic matter addition also stimulated contaminant mycorrhizal infection. Uninoculated control seedlings with organic matter had on average a 200% increase in mycorrhization than controls with no organic matter.

Addition of organic matter produced a significant increase in concentrations of leaf N (average 2.7%) compared with no organic matter (average 1.2%), but there was no consistent effect on leaf P, K or Mg. There was an effect of inoculation with L.laccata on total accumulated leaf N in the organically enriched treatment, with inoculated seedlings having almost a 50% greater accumulated N than controls. There was no effect of inoculation treatment on accumulated leaf P either with or without organic matter addition.

Percentage concentrations of combined N (0.21 to 0.34) and extractable P (3.33 to 6.67) and K (106.3 to 143.3) were enhanced by organic matter addition, whilst significant decreases were observed in pH (7.4 to 6.6) and extractable Mg (1,300 to 1,100). Increases in leaf nutrient concentrations in the enriched spoil were mirrored by reduced concentrations due to mineralization of 56% (N), 36% (P) and 9% (K).

Conclusions: The results indicate that organic matter addition can enhance pedunculate oak seedling growth in surface mine spoil as compared to application of inorganic fertilizers alone. The combined treatment produced significant increases in growth and foliar N concentrations of seedlings. Inoculation with Laccaria laccata and Hebeloma crustuliniforme clearly stimulated oak seedling growth in the leaf litter amended spoil, but not in unamended spoil. Organic matter addition significantly stimulated mycorrhizal infection of inoculum and other species.

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