Canadian Forest Service Publications
Coppice growth responses of two North American willows (Salix spp.) in acidic clay deposits on coal mine overburden. 2014. Mosseler, A.; Major, J.E. Canadian Journal of Plant Science 94(7) : 1269-1279.
Issued by: Atlantic Forestry Centre
Catalog ID: 39592
Availability: PDF (download)
Acid-generating mine spoils with low pH are a major problem for revegetation and site reclamation. We compared growth responses of 15 genotypes from two widespread willow species, Salix discolor Muhl. (DIS) and S. eriocephala Michx. (ERI), native to eastern and central North America on two adjacent coal mine spoil sites that differed strongly in both pH (3.6 vs. 6.8) and soil texture. Despite significantly poorer growth responses for several coppice biomass traits on a highly acidic clay deposit compared with adjacent shale overburden, these willow clones demonstrated a surprising tolerance for extremely acidic soil conditions. Analysis of survival and growth uncovered genotype x environment interactions, indicating that both species and genotypic differences within species could be used to select better-adapted genotypes for extreme conditions. Most ERI and DIS clones grew comparatively better on the shale overburden site, but two of eight ERI clones and one of seven DIS clones grew significantly better on the acidic clay site, indicating the possibility for clonal selection for specific site adaptations within a species. Allometric relationships between coppice height and basal stem diameter were constant at both the species and site levels. However, there was a divergence of height and diameter in their relationship with green mass yields on the two different site types.
Plain Language Summary
Plants regularly experience suboptimal environments, but this can be particularly acute on highly disturbed mine sites such as the extensive coal mine spoils in central New Brunswick. Willows have proven to be very effective invaders and colonizers of such highly disturbed areas. Two North American willows—Salix discolor Muhl. (DIS) and S. eriocephala Michx. (ERI)—were artificially established in common-garden field tests on two adjacent coal mine spoil sites: one with high clay content and a low pH (3.6), the other consisting of shale overburden that dominates this former coal mine with a neutral pH (6.8). Both willows showed large variation among genotypes within each species in foliar concentrations of various nutrients and heavy metals, and some clones of DIS and ERI had up to 16× the Fe and Al uptake in foliage on the acidic site versus the adjacent shale overburden. Genetic selection among species and genotypes may be useful for reclamation activities aimed at reducing specific metal concentrations on abandoned mine sites. Results showed that the greater acidity of the clay site resulted in greater metal mobility and availability for uptake by plants. Despite the high metal uptake and content in these plants, willow plants showed no foliar symptoms of metal toxicity. Phytoremediation efforts aimed at reclaiming potentially toxic mine sites require plants that can tolerate such harsh and toxic conditions. Strong clonal variation among the 15 clones tested from these two willows suggests that selection and breeding for willow clones with special capacities for uptake of heavy metals from moderately contaminated sites looks promising; especially in the case of ERI which can take up high concentrations of metals without showing adverse effects on growth.