Abstract
The objective of this study was to investigate the impact of different soil covers used to reclaim decommissioned oil sands mining sites on the genetic diversity of aspen and their associated belowground microbiota. Aspen genotyping showed that trees mostly originated from sexual reproduction on sites reclaimed with soil covers made of upland forest floor-mineral mix (FFMM) and lowland peat-mineral mix (PMM). In contrast, most individuals in mature and burned stands sampled as benchmarks for natural disturbances originated from vegetative reproduction. Nonetheless, aspen populations in the FFMM and PMM sites were not genetically different from those in mature and burned stands. DNA metabarcoding of bacteria and fungi in root and soil samples revealed that the diversity of the belowground microbiota associated with aspen and the relative abundance of putative symbiotic taxa in PMM were significantly lower than for FFMM and naturally disturbed sites. Despite similar aspen genetic diversity between FFMM and PMM sites, trees were not associated with the same belowground microbiota. Because the soil microbiome and more specifically the mycorrhizal communities are variable both in space and time, long-term monitoring is particularly important to better understand the ecological trajectory of these novel ecosystems.
Highlights
Oil sands surface mining in the Athabasca region of northern Alberta (Canada) is a significant anthropogenic disturbance that resets boreal forest development and succession to early stages
A very high degree of clonality was detected among sampled P. tremuloides trees from the Mature and Fire sites, while fewer clones were observed in the forest floor-mineral mix (FFMM) and peat-mineral mix (PMM) sites (Fisher’s exact test: p = 2.2 × 10−16 between natural and reclaimed sites) (Table 1)
Results showed that (i) aspen colonised the reclaimed sites via seed recruitment rather than from vegetative propagation as in naturally disturbed sites, (ii) aspen in reclaimed sites were genetically similar to those in the surrounding natural sites, (iii) and despite the fact that aspen genetic diversity was very similar between FFMM and PMM sites, trees were not associated with the same belowground microbiota
Summary
Oil sands surface mining in the Athabasca region of northern Alberta (Canada) is a significant anthropogenic disturbance that resets boreal forest development and succession to early stages. Horton et al.[13] showed in Californian pine forests that seedlings were colonised with the resident inoculum within the first days following establishment and the entire root system was colonised after six months, mostly by ectomycorrhizal fungi, and to a lesser extent, by root fungal associates This quick connection to the soil network of fungal symbionts and its associated bacterial communities[14,15,16] is key for nutrient acquisition and plant productivity[17]. To better understand the ability of the different reclamation strategies to return heavily disturbed industrial sites in a state of functional ecosystems, the aboveground host genetic and belowground bacterial and fungal diversity in sites reclaimed with FFMM and PMM soil covers were characterized and compared to ancient (mature aspen stands) and recent (three-year-old burned aspen stands) naturally disturbed sites (hereafter Mature and Fire sites). We addressed the following hypotheses: (i) Aspen in reclaimed sites are genetically different from those in the surrounding naturally disturbed stands, (ii) Different types of soil cover result in differences in taxonomic and putative functional diversities of aspen root and soil microbiomes, and (iii) Aspen root and soil microbiomes from the different types of soil cover are different from those in naturally disturbed stands
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