Soil physicochemical and microbial drivers of temperature sensitivity of soil organic matter decomposition under boreal forests

Soil organic matter (SOM) in boreal forests is an important carbon sink. The aim of this study was to assess and to detect factors controlling the temperature sensitivity of SOM decomposition. Soils were collected from Scots pine, Norway spruce, silver birch, and mixed forests (O horizon) in northern Finland, and their basal respiration rates at five different temperatures (from 4 to 28 °C) were measured. The Q10 values, showing the respiration rate changes with a 10 °C increase, were calculated using a Gaussian function and were based on temperature-dependent changes. Several soil physicochemical parameters were measured, and the functional diversity of the soil microbial communities was assessed using the MicroResp™ method. The temperature sensitivity of SOM decomposition differed under the studied forest stands. Pine forests had the highest temperature sensitivity for SOM decomposition at the low temperature range (0–12 ° C). Within this temperature range, the Q10 values were positively correlated with the microbial functional diversity index (H′mic) and the soil C-to-P ratio. This suggested that the metabolic abilities of the soil microbial communities and the soil nutrient content were important controls of temperature sensitivity in taiga soils.