Soil microarthropods feed on two distinct yet interconnected resource channels: detrital and root. The detrital channel, historically thought to be dominant, is primarily composed of aboveground plant litters, resources which may be only slowly available in cold boreal forest soils. Root channel resources are derived from recent photosynthate in saps, exudates, and ephemeral fine roots. These high-quality resources are likely available more quickly. To understand photosynthate contributions to belowground soil microarthropods in the Alaskan boreal forests, we selected five approximately 2.7 m tall white spruce trees and trenched 4 m out from the trees cutting off recent photosynthate from outside the plots in mid-July. Approximately 40 days later, we enclosed each tree in clear plastic and labeled photosynthate with 99% 13CO. We collected microarthropods in fall and spring near our experimental sites to determine the δ13C baseline range of 39 abundant taxa. Inside the labeled plots, we collected the same microarthropods for 13C analysis in early and late fall and the following spring to assess 13C enrichment. Root and rhizosphere feeding taxa and their predators were distinctly labeled in fall, often >5‰ enriched within 3-7 days. By spring, most remaining taxa δ13C averages were >2‰ enriched over their baselines. We identified only 8 detritivores where δ13C averages were little changed but even in these taxa, some samples appeared enriched in 13C by late spring. Our results indicate fast widespread contributions of recent photosynthate to many soil microarthropods and interconnections between the root and detrital resource channels.
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