Soil Mineralogy Affects Conifer Forest Soil Carbon Source Utilization and Microbial Priming

The cycling of temperate forest soil C is likely to be altered with climate change. Climate change may induce changes in forest litter that promotes priming, or enhanced decomposition of extant soil C. The effects of environmental factors such as temperature, litter quality, and soil mineralogy on priming are not well understood. The objectives of this study were to determine the interaction of temperature and soil mineral assemblage on priming of temperate forest soil C. We incubated soils from three forest types (ponderosa pine, white fir, and red fir), on granite (GR), basalt (BS), and andesite (AN) parent materials at three temperatures (12.5, 7.5, and 5.0°C), with the addition of 13C-labeled ponderosa pine litter. Soil C mineralized from each parent material differed in response to increasing temperature (i.e., relative increases of 38-70% from 5.0-12.5°C), following a pattern of GR > BS > AN. The percentage of C derived from litter and soil C pools varied significantly by parent material and forest type. Andesite soils, dominated by short-range-oder (SRO) aluminosilicates demonstrated decreased priming relative to BS and GR soils across all forest types. Soil C mineralization rate data indicated that the majority of priming effects were short term (within the first 20 d of a 90-d incubation). Regression analysis indicated control of priming by soil C, C/N, and soil C 13C signature, SRO Fe oxyhydroxides, and Al-humus complexes. Variation in the soil mineral assemblage was the dominant control of both cumulative soil C mineralization and soil C priming.