Quercus rubra (L.) fine root trait trade-offs, respiration, and biomass across a Midwestern U.S. latitudinal gradient

Regional climate changes may lead to shifts in root traits, affecting forest productivity and carbon release. Fine roots, which can respire significant proportions of fixed carbon dioxide back to the atmosphere, may adjust through changes in their respiration rates, morphology, nitrogen content, or biomass. Across a species’ range, understanding how these characteristics vary in response to their current environments lays the groundwork for predicting their responses to novel environments. We investigated northern red oak ( Quercus rubra L.) fine root trait and biomass responses to growing season temperature and precipitation, and soil properties. We sampled soil and Q. rubr a fine roots at 14 sites from Michigan’s Upper Peninsula to Tennessee, U.S.A. At each site, we measured respiration, biomass, and functional traits of fine roots in the upper 10 cm of soil. We compared these root measurements to soil properties and climatic data using mixed linear modeling and hierarchical partitioning. Roots became more conservative as soil bulk density increased, while trait values along the collaboration axis and fine root respiration decreased with higher precipitation. With increased biomass in sandy soils, this led to greater fine root respiratory carbon release in dry, sandy sites, which also tended to be colder. These results suggest that moisture availability and the soil environment are important determinants of fine root traits and carbon release at the regional scale, though soil and temperature effects could not be fully detangled. Changes to precipitation regimes may affect this substantial carbon flux out of oak-dominated forests.