Soil compaction and forest litter amendment affect carbon and net nitrogen mineralization in a boreal forest soil

Abstract

Mechanical site preparation in forests often results in soil compaction, mixing of forest litter with mineral soil, and/or displacement of surface organic material in forest ecosystems. We used a 9-month laboratory incubation experiment to examine the effects of soil compaction and forest litter amendment on microbial biomass C (MBC) and N (MBN), soluble organic C and N, and C and net N mineralization rates in a boreal forest soil with a silt loam texture. Four treatments: forest litter unamended and noncompacted (OM0C0, bulk density at 1.1 Mg m −3), forest litter unamended and compacted (OM0C1, 1.5 Mg m −3), forest litter amended and noncompacted (OM1C0), and forest litter amended and compacted (OM1C1) were applied to the soil. Soil compaction reduced MBC, MBN, soluble organic C and N on several sampling dates. Carbon mineralization and net nitrification rates were reduced by soil compaction whether forest litter was amended or not. The total amount of C mineralized from OM0C0, OM0C1, OM1C0, and OM1C1 in 9-month was 1.8, 1.6, 2.6 and 1.7 mg C g −1 soil, respectively. Forest litter amendment alone increased MBC in the early stage of the incubation and soluble organic C and N on every sampling date except the initial one. Forest litter amendment had a positive priming effect on C and net N mineralization and nitrification rates. The total amount of N mineralized from OM0C0, OM0C1, OM1C0, and OM1C1 was 40, 39, 61, and 59 mg N kg −1 soil, respectively. We conclude that soil compaction and forest litter amendment influenced microbial properties and processes in this boreal forest soil under controlled conditions. Our results imply that forest management practices that alter soil porosity (through compaction) and organic matter distribution in the soil profile can dramatically change soil C and N dynamics that may result in the eventual change in soil C and N concentrations or availability.