Soil carbon and nitrogen pools and processes in an old-growth conifer forest 13 years after trenching

We measured surface soil (0-15 cm) C and N pools and processes inside and o utside an area that had been trenched 13 years earlier in an old-growth con ifer forest (>450 years) to assess the long-term impacts of reduced root in puts on C and N turnover. Trenching, combined with frequent clipping of und erstory plants, was originally conducted to prevent nutrient uptake by plan ts, as part of a study of the role of vegetation in ecosystem retention of N. Thirteen years following trenching, the median values of bulk density, p H, total C and N concentrations, annual rates of in situ net N mineralizati on and nitrification, microbial biomass C and N, microbial respiration, and anaerobically mineralizable N in the trenched plot were all within the 25- 75% interquartile range of values found in the replicated, untrenched plots . The trenched plot had higher rates of net N mineralization (41% higher in October, 484% higher in June) and net nitrification (25% higher in October , and lower net NO3- immobilization in June) during laboratory incubation a nd a 22% higher water content in October. In June, soil water content in th e trenched plot was about 8% lower than in the untrenched plots. Our result s suggest that soil C and N dynamics in these old-growth forests are relati vely resistant to perturbations resulting from major reductions in root inp ut to the soil.