Biology and Fertility of Soils https://doi.org/10.1007/s00374-020-01438-z ORIGINAL PAPER Microbial community assembly and metabolic function during wheat straw decomposition under different nitrogen fertilization treatments Yangquanwei Zhong1 & Jin Liu2 & Xiaoyu Jia2 & Zhouping Shangguan2 & Ruiwu Wang1 & Weiming Yan2,3 Received: 8 July 2019 /Revised: 22 January 2020 /Accepted: 27 January 2020 # Springer-Verlag GmbH Germany, part of Springer Nature 2020 Abstract In-depth microbial community characterization, a community-level metabolic function analysis, and biogeochemical assess- ments of residues were performed to understand the principles governing microbial community assembly in wheat straw during decomposition with different N fertilization rates in soil. We identified a suite of decomposition-associated bacterial and fungal groups in straw that contribute to C and N cycling. The decomposition-associated microbial community in straw is likely mainly derived from the original straw, and the bacterial and fungal communities showed different patterns along with the decomposi- tion. Overall, the microbial community composition and function were not substantially affected by the N fertilization rate, but N fertilization significantly increased the straw microbial assembly speed and had significant effects on the abundances of certain taxa and C- and N-related genes, leading to different decomposition rates of straw under different N fertilization rates. Furthermore, the straw quality, especially dissolved organic C (DOC) and lignin, accounted for most observed effects on microbial community development and decomposition. The results provide new insight into the roles of the microbial commu- nity in straw during crop residue decomposition for nutrient cycling in farmland ecosystems. Keywords Microbial community . Metabolic function . Nitrogen fertilization . Crop residue . Decomposition Introduction been lost to the atmosphere due to intensive agricultural produc- tion (Lal 2004). The enhancement of C sequestration by agricul- Soil represents the largest sink of terrestrial C, i.e., 2500 Gt at a tural soils has significant implications for the reduction of atmo- depth of 1 m, and approximately 25% of agricultural soil C has spheric CO2 and alleviation of soil degradation (Banerjee et al. 2016). In addition, approximately 3.8 billion tons of crop resi- dues are produced annually worldwide (Lal 2005),andsuchcrop Electronic supplementary material The online version of this article residues could be returned to the soil to replenish the soil nutri- (https://doi.org/10.1007/s00374-020-01438-z) contains supplementary material, which is available to authorized users. ents and are important sources of organic matter for improving the physical, chemical, and biological properties of soil (Kumar * Ruiwu Wang and Goh 2000, 2003). The decomposition of crop residues in soil [email protected] is a complex process involving the mineralization and transfor- * Weiming Yan mation of organic matter induced by microbes (Dilly et al. 2004; [email protected] Marschner et al. 2011;Patersonetal.2008). Given the impor- tance of straw decomposition in soil C sequestration, there has 1 School of Ecology and Environment, Northwestern Polytechnical been continued interest in elucidating the dynamic changes in ’ ’ University, Xi an 710072, People sRepublicofChina microbial communities occurring during residue decomposition 2 State Key Laboratory of Soil Erosion and Dryland Farming on the and the associated regulatory factors. Loess Plateau, Northwest A&F University, When crop residues are returned to the soil, the specific Yangling 712100, Shaanxi, People’sRepublicofChina microbial taxa established on the surface of straw act as de- 3 Institute of Soil and Water Conservation, Chinese Academy of composers (Bastian et al. 2009; Marschner et al. 2011). Sciences, Xinong Rd. 26, Yangling 712100, Shaanxi, People’s Republic of China During the decomposition of crop residues, the changes in Biol Fertil Soils microbial and biochemical activity result in a series of decom- accompanied by a succession of microbial decomposers with position stages associated with microbial succession (Gao various catabolic capabilities involved in the decomposition et al. 2016). Previous studies have provided evidences de- process (Bastian et al. 2009; Guo et al. 2018; Osono 2006). In scribing the structural and functional changes in microbial addition, the primary factors associated with the residue chem- communities during residue decomposition in different ways. istry characteristics affecting the changes in microbial com- These studies focused on the effects of environmental factors munities and metabolic function under different N fertilization (temperature and soil type) (Sun et al. 2013;Zhouetal.2016a, rates have been poorly studied. 2016b), experimental duration (Marschner et al. 2011; Sun To address these issues, we investigated wheat straw de- et al. 2013), straw quality (Marschner et al. 2011;Zhouetal. composition in a field subjected to long-term N application 2016b), or the return of straw (Banerjee et al. 2016;Chenetal. under three N fertilization rates. We examined the dynamic 2017) on the abundance and composition of soil microbial patterns of the straw microbial community composition and communities. However, few studies have concentrated pri- metabolic functions and the chemical characteristics of the marily on evaluating the changes in the abundance and com- straw and its decomposition. Specifically, we aimed to (1) position of both bacterial and fungal communities in straw determine the dynamic process of the establishment of micro- along with its decomposition. Both bacteria and fungi on litter bial communities (both bacterial and fungal) on straw along play key roles in residue decomposition (Pankratov et al. with the decomposition of straw and determine the primary 2011; Štursová et al. 2012; Voriskova and Baldrian 2013); source of the microbes driving straw decomposition, (2) ex- however, a comprehensive understanding of the microbial plore the effect of N fertilization on straw decomposition and community on straw during decomposition is lacking. microbial community composition and function, and (3) un- In the farmland ecosystem, N fertilization is the most com- derstand the factors affecting microbial community establish- mon agricultural practice, and different N fertilization rates ment and functional dynamics. have varied effects on plant nutrients and soil microbial com- munities (Zhong et al. 2015a). Thus, the effects of N fertiliza- tion on crop residue decomposition is variable and depends on Materials and methods the nutrient content in residues and soil, the microbial com- munity composition, etc. (Hobbie et al. 2012;Lietal.2017; Experimental site and climatic conditions Potthoff et al. 2005). Compared to plants grown in rich nutri- ent soil, soil N deficits can result in a low leaf N concentration, This study was conducted in an experimental field at the lower decomposition rates, and higher C/N ratios (Wang et al. Institute of Soil and Water Conservation, Yangling, Shaanxi 2012). In addition, soil N availability can lead to increased or (34°17′56″ N, 108°04′7″ E) located in the southern boundary decreased microbial diversity and activity (Treseder 2008; of the Loess Plateau. The region experiences a temperate, Zhong et al. 2015a, 2017), which can further influence residue semihumid climate with a mean annual temperature of decomposition. Thus, due to the direct and indirect effects of 13 °C, a mean annual precipitation of 632 mm, and approxi- N application on straw decomposition, a comprehensive study mately 60% of the precipitation occurring between July and considering the straw quality and microbial communities September. The soil type is Lou soil (Eum-Orthic Anthrosol). could enhance our understanding of nutrient cycling, micro- bial succession, and residue decomposition under N fertiliza- tion. In addition, previous studies have reported that the de- Experimental plot design composition process begins before litter enters the soil (Stone 1987) and that the establishment of microbiota on the surface This study adopted a randomized block design involving three of litter from soil is a dynamic process (Voriskova and N fertilization rates, and each treatment included three repli- Baldrian 2013). However, whether the microbes that drive cates. N was applied at the following rates: 0, 180, and 360 kg residue decomposition are derived primarily from the straw Nha−1 (hereafter termed N0, N180, and N360, respectively). before it is buried or are associated with the soil remains Winter wheat (Triticum aestivum L. cv., Changhan No. 58) unclear. was cultivated. Each plot had an area of 2 × 3 m and contained The decomposition of crop residue is governed by both the 20 rows of wheat spaced 15 cm apart, and each plot was sown quantity and quality of the residue (Jensen et al. 2005; with 90 plants. N was applied in the form of urea, while phos- Johnson et al. 2007;Yuetal.2015), climatic conditions (such phate (P) was applied in the form of super P (33 kg P ha−1), as temperature and moisture) (Sun et al. 2013; Zhong et al. and the applications were performed the same across all treat- 2017), and soil properties (Frouz et al. 2015; Zhong et al. ments each year before sowing. No potassium or 2017). Both the residue quality and activity of litter- micronutrients were applied in this study. Furthermore, no associated microorganisms change throughout the