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Northern forest soils represent globally important stores of carbon (C), yet there is no consensus about how they are altered by the widespread practice of harvesting that dominates many forested landscapes. Here we present the first study to systematically investigate the utility of δ13C and C content depth profiles to infer temporal changes in belowground carbon cycling processes following disturbance in a pure C3 ecosystem. We document carbon concentration and δ13C depth profile enrichment trends consistent with a kinetic fractionation arising from soil organic carbon (SOC) humification across a northern forest chronosequence (1, 15, 45, 80 and 125+ yrs). Reduced soil C storage that coincided with observed soil profile δ13C‐enrichment patterns which intensified following clearcut harvesting, pointed to losses of SOC in the deeper (>20 cm) mineral soil. This study suggests the δ13C approach may assist in identifying mechanisms responsible for soil C storage changes in disturbed C3 forest ecosystems.

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[1] Developing a better understanding of the processes involved in controlling soil carbon (C) storage and turnover in native forest soils is critical if we are to fully understand the role land management activities play in the global C cycle. Separating soil organic matter (SOM) into discrete fractions has been successfully used to isolate changes in the structure and function of the SOM pool in response to land management activities but investigations in native forest systems are rare. Using a density fractionation procedure, we isolated and characterized three distinct SOM fractions (free, intra-aggregate, and organo-mineral) across a postharvest forest age sequence. We describe age related variations in each of these fractions with respect to their contribution to soil mass, C storage, C concentrations, C-to-N ratios, and d 13 C ratios. In conceptual models of SOM pool structure, the organo-mineral fraction is assumed to be largely stable. We show that harvesting may increase the potential for loss of soil C (i.e., destabilize the soil C pool) and that a significant portion of the soil C pool may be cycling on decadal timescales. Isotopic evidence is consistent with a period of C loss attributable to increased rates of decomposition, with losses below 20 cm driving the trend. We encourage investigators studying the effects of forest harvesting on SOM storage to consider the deeper mineral soil (20+ cm) and how we may increase SOM turnover time and stabilization capacity in a native forest system.

Global declines in postsecondary enrollment in soil science programs over the last several decades have been mainly attributed to an overemphasis on the connection with agronomy and production agriculture but recent enrollment increases in the USA suggest change is afoot. To determine if similar trends are occurring in Canada, we inventoried undergraduate soil science course offerings at postsecondary institutions and conducted a survey to assess the status and projected trends in soil science education. We found that 64% of universities and 37% of colleges offer undergraduate soil science courses as part of degrees or diplomas in which knowledge of soil science is important (e.g., agriculture and resource management). In Canada, there are 149 undergraduate soil science courses taught in universities and 58 at colleges. On average, there are 3.2 courses taught at each university and 1.9 at each college that offer soil science courses. Soil science programs at the

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As the focus of soil science education in Canada and elsewhere has shifted towards nonsoil science majors, it is important to understand if and how this has affected the scope of introductory soil science courses. The objectives of this study were to inventory Canadian postsecondary units that offer introductory soil science courses and to document attributes of instructors, students, and teaching approaches in these courses. We surveyed 58% of the instructors of introductory soil science courses across Canada, and most of these courses were offered by geography and environmental science units. The majority of instructors followed a traditional lecture (86%) and laboratory (76%) delivery format, whereas 36% used online teaching resources. Introductory courses were delivered by primarily one instructor, who held a Ph.D. in a tenure track position and in most cases developed the course themselves. Over half of the instructors surveyed used either a required or a recommended textbook, pointing to the need for creation of a Canadian-authored soil science textbook. Several follow-up studies are needed to evaluate teaching methods used in the upper level soil science courses, students' perceptions of teaching in soil science, and instructors' knowledge of resources available for online and (or) blended learning.

Our goals in this study were to track the incorporation of plant residue into soil organic matter (SOM) and test the effectiveness of different fractionation methods to evaluate this transformation. We incubated soil amended with 13 C-labelled barley (Hordeum vulgare L.) residue and used three fractionation methods based on size (> 250, 53-250, 5-53 and < 5 μm) and density (< 1.7 g cm −3 , i.e. light fraction (LF)) and determined its quantity and the rate of C loss or gain or both in these fractions as decomposition progressed. One method was based on size only, another involved density separation followed by size fractionation and a third separated organic matter fractions by size first and then by density. There were significant quantitative differences between the methods for the amount of residue in the fractions, but there was no effect of fractionation method on the rate of change in the residue that comprised the fractions. The density method did not appear to identify all of the most recently added (i.e. least decomposed) residue in the LF or that there was a redistribution of SOM among the fractions. The amount of residue C and the C:N ratio of the residue in the two smallest fractions increased early during the incubation (0-2 months), but subsequently decreased towards the end. The initially small C:N ratio in the clay fraction probably reflects the accumulation of microbial by-products from the rapid decomposition of water-soluble compounds. The subsequent increase and decrease in both residue C and C:N ratio reflects the balance of the accumulation of sorbed water-soluble compounds and dense plant residue fragments and their mineralization over time. We conclude that clay is a sink for residue C (i.e. microbial metabolites) early during decomposition, and that there is a transfer among fractions and mineralization of residue C as decomposition proceeds. These findings indicate that the clay fraction contains a dynamic pool of C that can cycle within short time-scales.196