Decomposition of Organic Carbon in Fine Soil Particles Is Likely More Sensitive to Warming than in Coarse Particles: An Incubation Study with Temperate Grassland and Forest Soils in Northern China Fan Ding 1,2 , Yao Huang 1 , Wenjuan Sun 1 *, Guangfu Jiang 1,2 , Yue Chen 1,2 1 State Key Laboratory of Vegetation and Environmental Change, Institute of Botany, Chinese Academy of Sciences, Beijing, China, 2 University of Chinese Academy of Sciences, Beijing, China Abstract It is widely recognized that global warming promotes soil organic carbon (SOC) decomposition, and soils thus emit more CO 2 into the atmosphere because of the warming; however, the response of SOC decomposition to this warming in different soil textures is unclear. This lack of knowledge limits our projection of SOC turnover and CO 2 emission from soils after future warming. To investigate the CO 2 emission from soils with different textures, we conducted a 107-day incubation experiment. The soils were sampled from temperate forest and grassland in northern China. The incubation was conducted over three short-term cycles of changing temperature from 5uC to 30uC, with an interval of 5uC. Our results indicated that CO 2 emissions from sand (.50 mm), silt (2–50 mm), and clay (,2 mm) particles increased exponentially with increasing temperature. The sand fractions emitted more CO 2 (CO 2 -C per unit fraction-C) than the silt and clay fractions in both forest and grassland soils. The temperature sensitivity of the CO 2 emission from soil particles, which is expressed as Q 10 , decreased in the order clay.silt.sand. Our study also found that nitrogen availability in the soil facilitated the temperature dependence of SOC decomposition. A further analysis of the incubation data indicated a power-law decrease of Q 10 with increasing temperature. Our results suggested that the decomposition of organic carbon in fine-textured soils that are rich in clay or silt could be more sensitive to warming than those in coarse sandy soils and that SOC might be more vulnerable in boreal and temperate regions than in subtropical and tropical regions under future warming. Citation: Ding F, Huang Y, Sun W, Jiang G, Chen Y (2014) Decomposition of Organic Carbon in Fine Soil Particles Is Likely More Sensitive to Warming than in Coarse Particles: An Incubation Study with Temperate Grassland and Forest Soils in Northern China. PLoS ONE 9(4): e95348. doi:10.1371/journal.pone.0095348 Editor: Dafeng Hui, Tennessee State University, United States of America Received December 3, 2013; Accepted March 26, 2014; Published April 15, 2014 Copyright: ß 2014 Ding et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Funding: This work was jointly supported by the National Natural Science Foundation of China (Grant No. 41075108), the Ministry of Science and Technology of China (2010CB950604) and the CAS Strategic Priority Research Program (Grant No. XDA05050507). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Competing Interests: The authors have declared that no competing interests exist. * E-mail: sunwj@ibcas.ac.cn Introduction As the largest terrestrial carbon pool, soil plays a vital role in the global carbon cycle [1]. A small change in the magnitude of soil carbon stocks could result in a large impact on the atmospheric enrichment of CO 2 [2]. Soil organic carbon (SOC) loss via soil heterotrophic respiration (i.e., SOC decomposition) is one of the largest components of global CO 2 flux from the terrestrial ecosystem to the atmosphere [3,4]. It is widely recognized that temperature has a profound influence on SOC decomposition [5] and that soils are expected to release CO 2 at faster rates with rising temperature [3]. Therefore, understanding the temperature sensitivity of SOC decomposition is critical for predicting changes in global soil respiration, changes in soil carbon stocks to future warming, and especially, the feedback of soils on climate change [2,6–8]. The temperature sensitivity of SOC decomposition, which is commonly expressed as Q 10 , refers to the change in decomposition rate with a 10uC increase in temperature. A recent study constructed a database of worldwide soil respiration observations matched with high-resolution historical climate data and estimated that global soil respiration had a Q 10 of 1.5 [3]. Nevertheless, soil respiration experiments have unanimously indicated that Q 10 is spatially heterogeneous on a global scale [9,10]. Thus, to accurately predict changes in global soil carbon stocks to future warming, knowing which factors determine the temperature dependence of SOC decomposition on large scales is critical [6]. It is known that the Q 10 of soil heterotrophic respiration varies with temperature [5,11], soil moisture [12,13], and the quantity and quality of SOC [14,15]. However, it is not clear whether SOC decomposition has different warming responses in different soil textures. It is most likely so because the SOC stock in fine-textured soils is less vulnerable to disturbances, e.g., tillage, than in coarse- textured soils [16,17]. Such different vulnerabilities are assumed to result from fine- textured soils having greater fractions of silt-sized or clay-sized particles, whereas coarse-textured soils have more sand-sized particles; these primary particles contain different mineral compositions and provide various affinities to organic matter [18]. Clay and silt particles (e.g., sesquioxides and layer silicates) provide large specific surface areas and numerous reactive sites at which SOC can be sorbed by strong ligand exchange and PLOS ONE | www.plosone.org 1 April 2014 | Volume 9 | Issue 4 | e95348