Pedosphere 27(5): 789{791, 2017 doi:10.1016/S1002-0160(17)60489-2 ISSN 1002-0160/CN 32-1315/P ⃝c 2017 Soil Science Society of China Published by Elsevier B.V. and Science Press Preface Soil Organic Carbon in a Changing World JIA Zhongjun1, Yakov KUZYAKOV2;3, David MYROLD4 and James TIEDJE5 1State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008 (China). E-mail: [email protected] 2Agro-Technology Institute, RUDN University, Moscow 115419 (Russia). E-mail: [email protected] 3Institute of Physicochemical and Biological Problems in Soil Science, RAS, Pushchino 142290 (Russia) 4Department of Crop and Soil Science, Oregon State University, Corvallis OR 97331 (USA). E-mail: [email protected] 5Center for Microbial Ecology, Michigan State University, East Lansing MI 48824-1325 (USA). E-mail: [email protected] Soil contains more than three times as much carbon like compounds. By characterizing soil organic matter (C) as either the atmosphere or terrestrial vegetation. species using solid-state 13C cross polarization magic Soil organic C (SOC) is essentially derived from in- angle spinning (CPMAS) nuclear magnetic resonance puts of plant and animal residues, which are processed (NMR) (13C CPMAS-NMR) spectroscopy of humic by the microbiota (bacteria, archaea, protists, fungi substances and density-based fractions in a forest eco- and viruses) that dominates SOC transformation and system, Ranatunga et al. observed greater fractions of turnover in complex terrestrial environments. A tiny alkyl C, O-alkyl C, and carbohydrate functional gro- change in the SOC pool would have profound impacts ups in response to burning. This implies that burning on global climate, soil fertility and ecosystem produc- might have stimulated soil process of dehydrogena- tivity, food security and sustainable development goals. tion, de-oxygenation and decarboxylation, despite the Consequently, SOC has been one of the central themes fact that low-intensity fire appeared to cause limited in Pedosphere. In fact, more than one quarter of the to- structural changes in the soil organic matter fractions. tal articles published in Pedosphere have been related As soil harbors numerous elements other than C that to soil C and soil organic matter since its establishment could combust (Pribyl, 2010; Jansen et al., 2011), the in 1991. classic loss on ignition (LOI) method may overestimate This special issue in Pedosphere is the first devoted SOC due to co-combustion of other elements (Salehi et to SOC studies. It contains 19 articles, which collec- al., 2011). Touch et al. assessed LOI for organic C mea- tively address a wide range of topics including, but not surement, and concluded that littoral sediment C was limited to, cutting-edge methods, microbial transfor- better represented by burning at 200, 300, and 600 ◦C mation mechanisms, land-use change impacts, agricul- for 4 h using the index of LOI200−300/LOI600, where tural sustainability, global change and model predic- LOI200−300 and LOI600 are the LOI at 200{300 and tions. The organization of this thematic issue allows a 600 ◦C, respectively. retrospective review of SOC studies in Pedosphere and Microbial communities are the engines that drive helps identify the emerging topics in the field. cycles of C, N and most other nutrients (Schimel and Extraction and identification of SOC is a long- Schaeffer, 2012). The fixation of atmospheric CO2 and standing challenge (Guigue et al., 2014), because soil is decomposition of organic C constitute the turnover of arguably considered the most complicated biomineral SOC and are primarily driven by plant and microbial materials on the planet (Young and Crawford, 2004). communities, respectively (Kuzyakov and Gavrichko- The extraction efficiency of SOC largely depends on va, 2010; Schmidt et al., 2011; El-Mahrouky et al., the target components (Xing et al., 2005). In this spe- 2015). Due to the rapid advance in molecular tech- cial issue, Xie et al. showed that the three-dimensional niques, microbially mediated C processing is increa- excitation-emission (EEM) fluorescence spectroscopy singly resolved at the individual and population levels could be a powerful means to characterize the com- (Sofi et al., 2016) rather than at the entire community ponents of dissolved organic matter, and that the ex- level (Liu et al., 2008). Kumar and Ghoshal used phos- traction methods need to be optimized for in-depth pholipid fatty acid composition to investigate the rela- analysis of such groups as protein-, fulvic-, and humic- tionship of microbial community structure with SOC 790 Preface following conversion of natural forest to degraded fo- a Fluvisol in Northeast China. They also showed that rest and agroecosystems in India, and found that the the ISSM had a positive effect on aggregate structure changes in fungal and bacterial abundance could ex- and stability, and improved the quantity and quality of plain 73% and 91% of the SOC variations, respective- SOC based on solid-state 13C NMR analysis. It should ly, across all the land-use types. Using high-throughput be noted that N availability often constrains agricultu- pyrosequencing techniques, Lucheta et al. assessed fun- ral productivity, and Srivastava et al. reviewed recent gal community structure in an attempt to relate its di- advances in studies on interactions between organic C versity with SOC transformation in Amazonian Dark and inorganic N transformations and associated micro- Earth (ADE) and charred black carbon (BC) particles bial processes, and highlighted the multiple effects of in ADE. This study showed phylogenetically distinct abiotic and biotic factors on the generation and decom- fungal populations inhabiting ADE and BC. Neverthe- position of SOC in the context of a changing climate. less, direct evidence is still scarce regarding the relative The changes of SOC pools can readily amplify glo- contribution of fungi and bacteria to the formation of bal climate changes by regulating the sink and source of specific soil organic matter in complex soil environment greenhouse gases including CO2, CH4 and N2O (Lal, (Throckmorton et al., 2012; Kallenbach et al., 2016). 2004). The generation of these gases in soils results Plant residue characteristics influence the quanti- solely from decomposition of SOC that serves as mi- ty and quality of soil organic matter, and soil physio- crobial substrates (Serrano-Silva et al., 2014). Never- chemical properties contribute significantly to its speci- theless, the mechanisms that enable practical and theo- ation and turnover (Schmidt et al., 2011). Jin B S et al. retical scaling up from microbial biogeochemical pro- showed increased SOC sequestration in a tidal marsh cess to global change remain poorly understood (Lai, following the invasion of the exotic C4 plant Spartina 2009; Guillaume et al., 2015). Wang Y H et al. de- alterniflora owing to its greater biomass amount and monstrated that simulated global change of drought lower proportion of labile SOC fractions compared to had significantly negative impacts on SOC and soil en- the native C4 plant Cyperus malaccensis. Jin W H et zyme activities in a Stangic Anthrosol, while this nega- al. demonstrated that rice-wheat rotation system sti- tive feedback could be counteracted to some extent by mulated SOC accumulation to a greater extent than elevated CO2 and soybean cultivation. Heintze et al. poplar plantations in the coastal reclaimed flatlands found that cattle slurry application resulted in greater of eastern China. Mavi and Marschner established a emissions of CO2 and N2O than biogas digestate ap- gradient of salinity and sodicity by manipulating non- plication, but CH4 flux was unaffected, and the magni- saline soils with salts, and found that osmotic potential tude of these effects varied among the three soil types is a better parameter to evaluate the salt effects on that were studied. Thapa et al. further evaluated the dissolved organic matter and microbial activity than effects of EC and moisture content on CO2 and N2O electrical conductivity (EC). Intriguingly, Melas et al. emissions from naturally occurring sulfate-based saline showed no protective effect of biochar on mineraliza- soils, and revealed that potential N mineralization rate tion of SOC, but glucose mineralization strongly de- and CO2 emissions decreased with increasing soil EC. pended on nutrient availability. Both soil moisture and EC played important roles for Soil organic matter forms essential basis of soil fer- denitrification and, thus, for N2O emission. tility and agricultural productivity (Lal, 2004; Kurga- Despite numerous studies of SOC modeling across nova et al., 2014). Intensified agricultural management different scales, there exist large uncertainties on the results in changes of SOC stocks and composition that global SOC budget (Amundson, 2001; Tian et al., are often considered as important indexes of soil ferti- 2015). The SOC stock and sink could be better lity (Tiessen et al., 1994; Williams et al., 2005; Benbi et approximated by optimizing model performance and al., 2015). Wang Y X et al. conducted a county-wide reducing the uncertainties of key variables such as survey of SOC density under intensive cultivation of soil area estimates, annual temperature variabili- citrus orchards from 1982 to 2010, which showed that ty, ground vegetation and microbial communities current management practices enhanced SOC seques- (Cheng et al., 2004; Yu et al., 2007). Were et al. tration. The integrated soil-crop system management employed a novel evolutionary genetic optimization- (ISSM) was invented to generate high crop yield while based adaptive neuro-fuzzy inference system (ANFIS- achieving high nutrient use efficiency, and Zhang et EG) for mapping the spatial patterns of SOC stock- al. revealed higher SOC, water-soluble organic C, easily s, and revealed marginally higher SOC stocks in the oxidizable organic C, particulate organic C and humic forested ecosystems than in the agroecosystems in acid C under ISSM than under conventional regimes in Kenya. Qin et al. performed analysis of sensitivity and Preface 791 uncertainty of DeNitrification-DeComposition (DND- of mechanisms and controls.