Litter type and soil minerals control temperate forest soil carbon response to climate change

Temperate forest soil organic carbon (C) represents a significant pool of terrestrial C that may be released to the atmosphere as CO₂ with predicted changes in climate. To address potential feedbacks between climate change and terrestrial C turnover, we quantified forest soil C response to litter type and temperature change as a function of soil parent material. We collected soils from three conifer forests dominated by ponderosa pine (PP; Pinus ponderosa Laws.); white fir [WF; Abies concolor (Gord. and Glend.) Lindl.]; and red fir (RF; Abies magnifica A. Murr.) from each of three parent materials, granite (GR), basalt (BS), and andesite (AN) in the Sierra Nevada of California. Field soils were incubated at their mean annual soil temperature (MAST), with addition of native ¹³C-labeled litter to characterize soil C mineralization under native climate conditions. Further, we incubated WF soils at PP MAST with ¹³C-labeled PP litter, and RF soils at WF MAST with ¹³C-labeled WF litter to simulate a migration of MAST and litter type, and associated change in litter quality, up-elevation in response to predicted climate warming. Results indicated that total CO₂ and percent of CO₂ derived from soil C varied significantly by parent material, following the pattern of GR > BS > AN. Regression analyses indicated interactive control of C mineralization by litter type and soil minerals. Soils with high short-range-order (SRO) mineral content exhibited little response to varying litter type, whereas PP litter enriched in acid-soluble components promoted a substantial increase of extant soil C mineralization in soils of low SRO mineral content. Climate change conditions increased soil C mineralization greater than 200% in WF forest soils. In contrast, little to no change in soil C mineralization was noted for the RF forest soils, suggesting an ecosystem-specific climate change response. The climate change response varied by parent material, where AN soils exhibited minimal change and GR and BS soils mineralized substantially greater soil C. This study corroborates the varied response in soil C mineralization by parent material and highlights how the soil mineral assemblage and litter type may interact to control conifer forest soil C response to climate change.