Journal
GLOBAL CHANGE BIOLOGY
Volume 20, Issue 7, Pages 2356-2367Publisher
WILEY
DOI: 10.1111/gcb.12475
Keywords
C cycle; extracellular enzyme activity; microbial growth kinetics; priming mechanisms; r and K strategy; soil microbial biomass; soil organic matter turnover
Funding
- National Basic Research Program [2014CB954002]
- CAS Strategic Priority Research Program Grant [XDA05020800]
- National Natural Science Foundation of China [41371253]
- CAS [KZCX2-EW-409]
- Chinese Academy of Sciences
- Russian Foundation for Basic Research [12-04-01170-a]
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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 C-13 labelling adding C-4-sucrose or C-4-maize straw to C-3-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 beta-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.
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