Denitrification in north temperate forest soils: Relationships between denitrification and environmental factors at the landscape scale

Abstract

Relationships between annual dentrification N loss and soil physical and biological factors were investigated in nine north temperate forest soils of different texture and drainage classes. Soil texture was analyzed numerically by using percentage of sand as a variable and soil wetness was quantified by a continuous drainage index function. Correlations between soil texture, soil drainage, microbial biomass C and N content, the ratio of the flush of C mineralization to the flush of N mineralization following fumigation (C fN f), denitrification enzyme activity (DEA), the ratio DEA-to-biomass C, and annual denitrification N loss were quantified. We found that DEA and the DEA-to-biomass C ratio accounted for up to 96% of the variation in annual denitrification N loss. Percentage sand and soil wetness could also account for a large proportion of the annual variation in denitrification rates among sites ( r 2 = 0.86). Very low rates of denitrification in wet sandy soils were related to high C fN f values in these soils. The ratio DEA-to-biomass C is an indicator of the proportion of the soil microbial population that can denitrify. Differences in this ratio among the soils studied suggest that there is a selective advantage to organisms with the ability to denitrify. By analyzing annual denitification N loss rather than daily or hourly denitrification rates, and by evaluating landscape-scale factors, such as soil texture and drainage, rather than field-scale factors, such as soil moisture, we were able to establish stronger relationships between denitrification and environmental factors than have been achieved hitherto.