Effects of rooting, temperature, and organic horizon development on temperate forest soil carbon, nitrogen, and inorganic nutrients in transplanted soils

Complex interactions controlling carbon (C), nitrogen (N), and inorganic nutrients: calcium (Ca), magnesium (Mg), potassium (K), phosphorus (P), in forest soils are difficult to tease apart due to covarying factors (e.g., soil parent material) and reductionist approaches can miss potential synergistic effects. We evaluated if increasing mean annual temperature (MAT), decreased organic horizon development, shallow tree rooting, and accumulation of C, N, and inorganic nutrients. We transplanted 144 mineral soil columns across six temperate forests from Virginia to New Hampshire and collected them 1-year and 4-years later. Our results show that organic horizon C, N, and nutrient pools were negatively associated with MAT with 4 × to 5 × greater pools at the coldest sites than the warmest sites. Since five-years of inputs from litterfall and throughfall monitoring show similar or increasing fluxes with MAT, differences were likely due to faster mineralization and transport from the columns. Transplanted mineral soil C, N, Ca, and P pools did not vary with MAT nor with root-access or root biomass, showing roots and organic horizon masses did not have consistent effects. Mineral soil root and MAT effects may still be developing or impacted by other variables not evaluated. Lastly, we found increases of organic phase Ca, Mg, K, and P from Year 0 to Year 1in the mineral soil across all six sites using Scanning Electron Microscopy- Energy-Dispersive X-ray Spectroscopy (SEM–EDS) imaging but only a significant effect of MAT or root-access for K. Our study highlights that MAT, organic horizon development, and nutrient accumulation and storage are linked but not in the mineral soil.