D3049: Following 13CO2 labeled recent photosynthate into boreal forest microarthropod community food webs

Soil microarthropod communities feed on two distinct yet interconnected channels: detrital and grazing. The detrital channel, often thought dominant, is primarily composed of above- and belowground plant litter but these resources may be slowly available in cold boreal forest soils. Grazing channel resources are derived from recent photosynthate in fine roots and root exudates, high-quality resources that are available more quickly. To understand recent photosynthate contributions to belowground soil microarthropod communities within the boreal forest, we selected five relatively isolated ~2.5 m tall white spruce trees and trenched 4 m out from the trees cutting off recent photosynthate contributions from outside of the plot in June. In late August, we enclosed the trees in clear plastic, added 1.6 L of 99% ¹³CO₂ 4 times over ~7 hours to label recent photosynthate, and allowed trees to uptake ¹³CO₂ for 24 hr before removing the plastic bags. Well outside the labeled area, we collected abundant microarthropods in fall and spring to determine the baseline δ¹³C range of each taxon. In the experimental area, we collected microarthropods for ¹³C analysis in early and late fall and the following spring. Stable isotope analysis was done by mass spectrometer on samples greater than 10 µg of microarthropod tissue. Root associated taxa and most predators were clearly labeled in fall and by spring most taxa δ¹³C averages were >2‰ enriched over their baseline values. Our results characterize fast widespread contributions of recent photosynthate to soil microarthropod communities.