Impact of stockpiling on soil microbial communities and their functions
Creators: Cabrera Hernandez, Julian Ariel
Publisher: name: University of Alberta Library
Year: 2024

<p>Abstract<br>
Soil stockpiling before mining activities is a by-law-mandated procedure that has adverse effects on soil health, which raises concerns about the suitability of stockpiled soils as a reclamation substrate. Relatively few studies have addressed the effects of stockpiling on soil biology, and particularly the impact of this disturbance on soil microbial communities is not clear. Since microbes have a fundamental role in nutrient cycling and can respond rapidly to changing soil conditions, the impact of soil stockpiling on microbial communities can be used as an indicator of soil quality, to shed light on the usefulness of the stored topsoil in the restoration of disturbed ecosystems. Using marker gene sequencing, I analyzed the structure and composition of microbial communities in a chronosequence of 0.5-28-year-old stockpiled soils at increasing depths (0-300 cm), in two oil-extraction locations in northern Alberta, Canada.<br>
In Chapter 2, I analyze the effect of stockpiling on soil prokaryotic communities. My results indicate that stockpiling shifts the microbial community composition outside the range of natural variability. Furthermore, while microbial communities in younger and older stockpiles were dissimilar to the reference soils, the communities of intermediate-age stockpiles were more similar to those in the reference soils, which may indicate that initial disturbance leads to a shift in the microbial community, which then recovers following several years of storage, but eventually, long-term storage leads to a secondary divergence from the range of natural variability. Additionally, the bacterial diversity decreased significantly with increasing stockpile depth, which could be attributed to the harsh conditions of the deeper stockpile layers and the scarcity of nutrients. <br>
In Chapter 3, I examine the impact of soil stockpiling on fungal communities and their functions. I found that fungal communities of the stockpiles differ from the communities in the nearby undisturbed reference soils. Also, similar to previous studies, there was a decrease in fungal richness and overall diversity with increasing stockpile depth. Furthermore, soil stockpiling generated a shift in the inferred function in the form of putative fungal guilds and trophic modes. Ectomycorrhizal fungi decreased and saprotrophic fungi increased in the stockpiles relative to the reference soils. These findings indicate that stockpiling may have important implications for ecosystem functions and services associated with fungal communities, such as litter decomposition and plant growth promotion when these stockpiles are used to reclaim ecosystems. <br>
In Chapter 4, I assess the predictors associated with the variability in microbial communities of stockpiled soils. I apply the null model operational framework proposed by Stegen et al. (2013), to shed light on the assembly processes influencing the β-diversity in the microbial communities of stockpiled soils. There was a significant correlation between specific microbial taxa and the conditions found in the disturbed soils. However, less than 20% of the variability in the microbial communities was explained by the predictors assessed by the study. Regarding the assembly processes shaping the communities, stochastic factors like drift and dispersal exerted the most important influence in all microbial groups (Bacteria, Archaea, and fungi). Therefore, the disturbance generated by the soil mechanized handling and management seems to be more important in the assembly of microbial communities of the stockpiles than the commonly attributed harsh physicochemical conditions created by stockpile depth and storage time.<br>
Taken together, the results of my thesis provide important insights into the impact of soil stockpiling on microbial communities and their functions and shed light on the effects of stockpile depth and storage time on soil microbial diversity and community composition. Similarly, the results reveal that selective pressures promoted by environmental filters or legacy effects, may not be as important as usually described in the literature for the structuring and variability of the microbial communities in the stockpiled soils. These findings are useful for reclamation specialists/agencies to determine optimal conditions for the storage of topsoil and for stockpiled topsoil to be used effectively in post-mining reclamation operations.</p>