A reanalysis of nutrient dynamics in coniferous coarse woody debris

We analyzed net N, P, K, Ca, and Mg fluxes from decaying coarse woody debris (CWD) by developing a "volume-adjusted method" and applying it to existing chronosequence studies of CWD in temperate coniferous forests. Unadjusted nutrient concentrations may overestimate the amount of a given nutrient remaining or accumulating in CWD, because mass loss, primarily as microbially respired CO2, occurs during decomposition. This overall mass loss tends to increase nutrient concentrations (e.g., µg N/g CWD) by decreasing the denominator and, therefore, can be misleading as an indicator of nutrient flux. Our volume-adjusted method corrects for mass loss, by assuming a constant volume as CWD decays. Using this method we determined that (i) Ca and K were lost from CWD as decay progressed; (ii) N and P increased or had no net change in amount; and (iii) Mg results were mixed. Several studies showed net gains of Mg and several showed net losses. We discuss the applicability and limitations of the volume adjusted method and propose the use of isotopic and conservative tracers as more accurate, but more difficult, methods of investigating CWD nutrient fluxes. We also discuss possible nutrient flux pathways into and out of CWD.