Effects of inorganic nitrogen and litters of Masson Pine on soil organic carbon decomposition

RESEARCH ARTICLE Effects of inorganic nitrogen and litters of Masson Pine on soil organic carbon decomposition Xin Yu ID1,2☯, Lin Chao1,2☯, Weidong Zhang ID1,3*, Longchi Chen1,3, Qingpeng Yang1,3, Guangjie Zhang1,2, Silong Wang1,3* a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 1 Key Laboratory of Forest Ecology and Management, Institute of Applied Ecology, Chinese Academy of Sciences, Shenyang, China, 2 University of Chinese Academy of Sciences, Beijing, China, 3 Huitong Experimental Station of Forest Ecology, Chinese Academy of Sciences, Huitong, China ☯ These authors contributed equally to this work. * (WZ); (SW) Abstract OPEN ACCESS Citation: Yu X, Chao L, Zhang W, Chen L, Yang Q, Zhang G, et al. (2019) Effects of inorganic nitrogen and litters of Masson Pine on soil organic carbon decomposition. PLoS ONE 14(9): e0222973. https://doi.org/10.1371/journal.pone.0222973 Editor: Fuzhong Wu, Sichuan Agricultural University, CHINA Received: July 4, 2019 Accepted: September 11, 2019 Published: September 26, 2019 Copyright: © 2019 Yu 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. Soil organic matter (SOM) mineralization represents one of the largest fluxes in the global carbon cycle. Numerous studies have shown that soil organic carbon decomposition was largely changed owing to the addition of litter, however very few studies have focused on the role of plant organs in the priming effects (PEs). Here, we studied the effects of different Pinus massoniana organs (fresh leaf, leaf litter, twigs, absorptive fine roots, and transport fine roots) on C4 soil respiration by applying the 13C isotopic natural abundance method. Results showed that the effects of plant organs on PEs were significantly different at the end of 210 days incubation, which can be ascribed to contrasting organs traits especially nonstructural carbohydrates and water-soluble compounds. Transport fine roots and fresh leaf induced positive PE, whereas absorptive fine roots induced negative PE. Leaf litter did not change the native SOC decomposition. Plant organ addition can change the microbial community and result in the reduction of bacteria-to-fungi ratio. Our results suggest that with regard to determining the PE of the entire ecosystem, using fresh leaf to represent leaf litter and aboveground to represent underground is implausible. Data Availability Statement: All relevant data are within the manuscript. Introduction Funding: This work received support from: National Natural Science Foundation of China U1805243; key research program of Frontier Sciences of the Chinese Academy of Sciences,Key Laboratory of Drug Research (CN) QYZDBSSWDQC002-03; Youth Innovation Promotion Association of the Chinese Academy of Sciences 2017239 Weidong Zhang; National Key Research and Development Program of China 2016YFA060080203 Weidong Zhang. Soil organic matter (SOM) mineralization represents one of the largest fluxes in the global carbon (C) cycle [1]. Forest SOMs are the biggest C pool in the terrestrial ecosystem; hence, a litter change in these SOMs will vastly affect the global C balance [2]. Understanding the factors that regulate SOM turnover is essential to predict the terrestrial feedback on climate change [3]. On one hand, fresh organic matter can form new soil organic carbon (SOC) during litter decomposition [4]. On the other hand, fresh organic substrates can stimulate the decomposition of stabilized SOC through a phenomenon called the priming effect (PE) [5]. Plant litter typically comprises different organs, such as leaf litter, twigs, fine roots, and others (e.g., reproductive organs, bark, and detritus). Fine roots occupy nearly 48% of the annual PLOS ONE | https://doi.org/10.1371/journal.pone.0222973 September 26, 2019 1 / 19 Effects of litters on soil organic carbon decomposition Competing interests: The authors have declared that no competing interests exist. plant litter input, whereas leaf litter and twigs account for 41% and 11%, respectively [6]. The traditional definition of fine roots are roots with diameters � 2 mm. This definition covered the truth that many traits vary among root orders, and differences in these traits may influence root decomposition rates. Researchers have divided the fine roots into two distinct classes, namely, absorptive (first- to third-order roots) and transport fine roots (higher-order roots) [7], to enable comparisons among functionally similar roots. However, ecological theories generally presume the plant as a whole individual and use leaf traits to represent the whole tree traits[8, 9]. This assumption overlooked the role of other organ traits in regulating the ecosystem’s C cycle to some degree. Previous studies have explored the correlation between the decomposition rates of leaf litter and other organs, but no general conclusion has been addressed yet. Freschet et al. [10] have demonstrated that for structure-related traits, such as lignin, C controls the decomposability for all plant organs. However, Sun et al. [11] studied the decomposition dynamics of the leaf litter and fine root of 35 tree species in a temperate forest ecosystem and discovered that the decomposition mechanisms of fine roots and leaf litter were different. Phenolic substances are the major controlling factors in the decomposition of fine roots, whereas stoichiometry (e.g. C:N, lignin:N) determines leaf litter decomposition. These contrasting results proved that whole-plant ecological strategies are necessary to account for the impact of different plant organs on decomposition processes. Priming effect is characterized by the effect of adding of exogenous substrates on SOM mineralization [12]. Numerous studies have shown that soil organic carbon decomposition was largely changed owing to the addition of external organic matter, and PE has become a universal phenomenon. However, the directions of the PE induced by litter vary, showing positive [13], negative [14, 15], or no PE [16]. The added high-quality litters, such as fresh leaf and absorptive fine roots (lower C:N ratio), act as an energy source for microorganisms in degrading SOM by producing extracellular enzymes. However, according to nitrogen (N) mining theory, added recalcitrant C substrates, such as twigs and transport fine roots (higher C:N ratio), also stimulate SOM-decomposing microorganisms to chase N for alleviated nutrient limitation [17]. Furthermore, previous studies have demonstrated that the quality and quantity of litter can determine the microbial community [18]. For example, the relative abundance of actinomycetes and fungi increases as recalcitrant substrates are added [19], whereas the relative abundance of bacterial increases owing to the addition of labile substrates [20]. Bacteria that thrive o (...truncated)