Justine Lejoly

Non-native earthworms have been invading North America since European settlement. Compared to temperate forests, their presence in the boreal forest is much more recent and thus remains understudied, despite the potential threat they represent for soil carbon (C) stocks. Here we compared earthworm-invaded and earthworm- free zones in soil types representative of the boreal forest, including Luvisols, Podzols, and Brunisols (Cambisols). We observed that the forest floor (surface organic layer, or LFH) decreased in thickness after invasion in most cases and developed into a Vermimull, with the loss of the most humified layer (humic or H horizon). Simul- taneously, the surface mineral horizon was reworked by earthworms into a novel Ahu horizon, characterized by higher organic matter and enriched in earthworm casts. Forest floor C stocks decreased by 94% and 59% for Luvisols and Brunisols respectively, while those of Podzols remained apparently unaffected. Mineral soil C stocks in Brunisols increased after invasion, while no changes were observed in Luvisols and Podzols. Our results demonstrated the substantial impact that invading earthworms are having on soil morphological features and C stocks in boreal forests. Effects were similar to what has been reported for temperate forests, although the degree of impact depended on soil type. While C stocks were less affected in the mineral soil compared to the forest floor, the development of a novel surface horizon reworked by earthworms could alter microbial dynamics and impact mineral C persistence. Further research is needed to quantify long-term implications of earthworm presence for boreal soil C stocks.

Soil organic matter (SOM) dynamics and termite activity have now been widely accepted as key players for improving soil properties in tropical agro-ecosystems. Numerous studies have described environmental impacts of aboveground termite mounds, while few data are available on temporary structures built for food foraging, called termite sheetings. The effects of termite activity on soil properties resulting from organic matter (OM) amendment under two contrasting management practices were studied in similar pedological and climatic conditions in Southern India (Auroville). Our results showed an increase in bio-available nutrients (K, Mg and P), organic carbon (OC) content, cationic exchange capacity (CEC), exchangeable base cations and water pH in the termite sheetings compared to the underlying and reference soils, in the organic tilled field. On the other hand, only bio-available K increased in the permanent raised beds. Aggregation processes were improved in termite sheetings for the organic tilled field, as the amounts of macroaggregates (250 μm– 2 mm) and protected mi- croaggregates increased, whereas the amount of free microaggregates (50–250 μm) decreased. Moreover, termite activity favoured SOM storage in termite sheetings by increasing OC content in each aggregate fraction, while no differences were observed in the permanent raised beds. Our study demonstrates that termite activity can im- prove nutrient availability, carbon storage and pH conditions in agro-ecosystems but that the magnitude of the effect likely depends on the agronomic practices in use.

With respect to the pedosphere, human activities in the last 100 years have been the major driver of soil change. Despite human activities being one of the main soil forming factors recognized by soil scientists (in addition to climate, organisms, parent material, relief, groundwater, and time), the Canadian System of Soil Classification (CSSC) emphasizes soil as a natural body. We argue human agricultural activities are direct and indirect drivers of significant changes to the carbon balance and cycling in A horizons of Gray Luvisolic soils in western Canada, resulting in changes to A horizon carbon stocks, structure, and micromorphology. Evidence from scientific literature, in-field soil profile observations, and the National Pedon Database are presented in support of our argument. We propose a polygenetic, two-stage model of Gray Luvisol soil formation. The first stage is dominated by the climate forcing of the Holocene, resulting in a relatively stable boreal forest ecosystem including perturbations from natural and human-induced wildfire and other disturbances. The second stage is dominated by direct, human-driven disturbances such as cultivation, release of exotic fauna (earthworms), and indirect human-driven disturbances associated with anthropogenic climate change. Further, we propose modest amendments to the CSSC to reflect a polygenetic model of soil genesis in Gray Luvisolic soils that preserve the balance between observation and interpretation inherent in the system.