Short communication High nitrogen deposition decreases the contribution of fungal residues to soil carbon pools in a tropical forest ecosystem Wei Zhang a , Yanhe Cui a, e , Xiankai Lu b , Edith Bai a , Hongbo He a, * , Hongtu Xie a , Chao Liang a, c , Xudong Zhang a, d, * a Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang,110016, China b Key Laboratory of Vegetation Restoration and Management of Degraded Ecosystems, South China Botanical Garden, Chinese Academy of Sciences, Guangzhou, 510650, China c DOE Great Lakes Bioenergy Research Center, University of Wisconsin, Madison, 53706, USA d National Field Observation and Research Station of Shenyang Agroecosystems, Chinese Academy of Sciences, Shenyang,110016, China e University of Chinese Academy of Science, Beijing, 100049, China article info Article history: Received 16 November 2015 Received in revised form 27 March 2016 Accepted 28 March 2016 Available online 4 April 2016 Keywords: Amino sugars Microbial residues Soil organic matter N deposition abstract Soil carbon (C) dynamics are closely mediated by microorganisms and microbial residues could consti- tute a significant pool of soil organic C (SOC). However, little is known about the nitrogen (N) deposition effect on the contribution of microbial residues to SOC balance in tropical forest ecosystems. Here, we assessed microbial residues using amino sugar biomarkers in surface soils of a tropical forest ecosystem under 11-year continuous N addition at different rates (0, 50, 100 and 150 kg N ha 1 yr 1 ). Nitrogen addition didn't affect either fungal or bacterial residues in soil apparently, but high-N addition (150 kg N ha 1 yr 1 ) significantly decreased the contribution of fungal residues to SOC indicated by both ratios of fungal/bacterial amino sugars and fungal residues/SOC. Consequently, high-N addition whittled down microbial contribution to SOC pools. Those findings may have implications for our predictions of global change impacts on soil C dynamics. © 2016 Elsevier Ltd. All rights reserved. Soil carbon (C) dynamics are heavily influenced by catabolic and anabolic activities of microorganisms (Liang et al., 2011; Schimel and Schaeffer, 2012). Microbial residues represent a significant source of stable C and may play a greater role in long-term C accumulation in soils than traditionally believed (Simpson et al., 2007; Liang et al., 2011). Global change drivers such as nitrogen (N) deposition can exert direct (i.e., altering physiological activity) and indirect (i.e., altering resource supply) influences on soil mi- crobial communities. Consequently, the retention of microbial debris and the regulation in key process in soil C turnover can also be affected by N deposition to some extent (Zak et al., 2011). However, main understanding of N deposition effects on soil microbial-mediated C dynamics is largely based on work in temperate ecosystems, where N is mostly limited (Griepentrog et al., 2014). Comparable data are generally lacking for tropical forest ecosystems, where soil is often N-rich or even N-saturated, thus the systems are featured by rapid N cycling rates and high net primary productivity (Matson et al., 1999; Wright et al., 2011; Brookshire et al., 2012). Meanwhile, most tropical soils are often highly acidic and poorly buffered against acidification (Sollins et al., 1988; Matson et al., 1999). As a result, conclusions based on studies conducted in temperate regions are of little relevance for the tro- pics under elevated N deposition. To our knowledge, there is limited information regarding the effect of N deposition on soil microbial contribution to soil C pools in tropical forest ecosystems, which store approximately 13% of global soil C contributing greatly to the global C cycle (Lu et al., 2013). The dynamics of microbial residues and their contribution to SOC can be indicated by soil amino sugars. They are cell wall components of microorganisms (Lauer et al., 2011) and can be stabilized in soil after cell dies. Amino sugars can serve as a time- integrated biomarker to indicate microbial community structure (Glaser et al., 2004). Muramic acid (MurN) originates exclusively from bacteria, whereas glucosamine (GluN) predominantly origi- nates from fungi (Amelung, 2001). The origin of soil galactosamine * Corresponding authors. Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, 110016, China. E-mail addresses: hehongbo@iae.ac.cn (H. He), xdzhang@iae.ac.cn (X. Zhang). Contents lists available at ScienceDirect Soil Biology & Biochemistry journal homepage: www.elsevier.com/locate/soilbio http://dx.doi.org/10.1016/j.soilbio.2016.03.019 0038-0717/© 2016 Elsevier Ltd. All rights reserved. Soil Biology & Biochemistry 97 (2016) 211e214