title: Soil C and N availability determine the priming effect: microbial N mining and stoichiometric decomposition theories.
abstract: The increasing input of anthropogenically derived nitrogen (N) to ecosystems raises a crucial question: how does available N modify the decomposer community and thus affects the mineralization of soil organic matter (SOM). Moreover, N input modifies the priming effect (PE), that is, the effect of fresh organics on the microbial decomposition of SOM. We studied the interactive effects of C and N on SOM mineralization (by natural (13) C labelling adding C4 -sucrose or C4 -maize straw to C3 -soil) in relation to microbial growth kinetics and to the activities of five hydrolytic enzymes. This encompasses the groups of parameters governing two mechanisms of priming effects - microbial N mining and stoichiometric decomposition theories. In sole C treatments, positive PE was accompanied by a decrease in specific microbial growth rates, confirming a greater contribution of K-strategists to the decomposition of native SOM. Sucrose addition with N significantly accelerated mineralization of native SOM, whereas mineral N added with plant residues accelerated decomposition of plant residues. This supports the microbial mining theory in terms of N limitation. Sucrose addition with N was accompanied by accelerated microbial growth, increased activities of β-glucosidase and cellobiohydrolase, and decreased activities of xylanase and leucine amino peptidase. This indicated an increased contribution of r-strategists to the PE and to decomposition of cellulose but the decreased hemicellulolytic and proteolytic activities. Thus, the acceleration of the C cycle was primed by exogenous organic C and was controlled by N. This confirms the stoichiometric decomposition theory. Both K- and r-strategists were beneficial for priming effects, with an increasing contribution of K-selected species under N limitation. Thus, the priming phenomenon described in 'microbial N mining' theory can be ascribed to K-strategists. In contrast, 'stoichiometric decomposition' theory, that is, accelerated OM mineralization due to balanced microbial growth, is explained by domination of r-strategists.
authors.affiliation: State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing, 210008, China; Institute of Plant Nutrition and Soil Science, Christian-Albrecht University Kiel, Kiel, 24118, Germany.
authors.forename: Ruirui
authors.initials: R
authors.lastname: Chen
authors.forename: Mehmet
authors.initials: M
authors.lastname: Senbayram
authors.forename: Sergey
authors.initials: S
authors.lastname: Blagodatsky
authors.forename: Olga
authors.initials: O
authors.lastname: Myachina
authors.forename: Klaus
authors.initials: K
authors.lastname: Dittert
authors.forename: Xiangui
authors.initials: X
authors.lastname: Lin
authors.forename: Evgenia
authors.initials: E
authors.lastname: Blagodatskaya
authors.forename: Yakov
authors.initials: Y
authors.lastname: Kuzyakov
mesh_terms: D002244:Carbon / Q000378:metabolism*; D009584:Nitrogen / Q000378:metabolism*; D012987:Soil / Q000737:chemistry*; D012988:Soil Microbiology; D013395:Sucrose / Q000378:metabolism; D003313:Zea mays / Q000737:chemistry
chemical_list: D012987:Soil; D013395:Sucrose; D002244:Carbon; D009584:Nitrogen
keywords: C cycle; extracellular enzyme activity; microbial growth kinetics; priming mechanisms; r and K strategy; soil microbial biomass; soil organic matter turnover