COS 127-1 - Biological soil crusts as ecosystem engineers on mining-disturbed substrates in the low Arctic

Background/Question/Methods

Biological soil crusts (BSCs; soil surface communities of bryophytes, lichens, bacteria, and fungi) are initial colonizers in disturbed terrestrial systems that can promote colonization of vascular species and soil development by modifying their surroundings (e.g., soil stabilization, moisture retention). In Canada’s low Arctic, resource exploration and extraction are major disturbances and understanding BSC development post-disturbance is crucial to inform restoration efforts and promote ecosystem resilience and function. Thus, we aimed to determine: i) short-term changes in BSC cover and microclimatic conditions on mining-disturbed substrates (i.e., drilling waste); ii) changes in BSC cover and function along a 20-year chronosequence of mining disturbance. Over 3 years, we monitored microclimatic conditions (e.g., photosynthetically active radiation (PAR), soil temperature and moisture, relative humidity, and air temperature) and BSC and vascular plant cover on crusted and bare drilling wastes. In addition, 24 chronosequence sites (disturbed between 1992-2013) were assessed for BSC cover and in-situ gas flux (CO₂, CH₄ and N₂O). BSC samples were collected to determine: i) optimal nitrogen fixation rates and gas fluxes; ii) nutrient concentrations of BSCs and underlying substrates; and iii) BSC bacterial (16S), fungal (ITS), and cyanobacterial (nifH) communities via Illumina amplicon sequencing.

Results/Conclusions

Compared to crusted drilling wastes, bare wastes had higher soil temperature and PAR, and lower water content during peak growing season. Additionally, there was a clear progression from greater cover of drilling waste to moss crust, then increasing lichen crust and vascular species cover with time in both studies. Across the chronosequence, there were no differences in in-situ or optimal gas fluxes despite BSC development. Interestingly, optimal nitrogen fixation increased with site age and had a significant, albeit weak, relationship with lichen crust cover. Nutrient concentrations of BSCs also increased with site age but remained relatively stable in underlying substrates, suggesting that BSCs were not modifying soil nutrients in the first 20 years of establishment. These results demonstrate that: i) BSCs naturally colonize and develop on mining-disturbed substrates; ii) BSCs alter microclimatic conditions at the soil surface; iii) BSC function (as nitrogen fixation and elevated nutrient concentrations) changes with community development. Overall, our results suggest that BSCs are niche constructors in these early soil surface environments and likely play an important role in recovery of Arctic plant-soil systems. A better understanding of colonization and function of BSCs post-disturbance can inform restoration efforts of mining-impacted sites in the low Arctic.