Carbon and nitrogen recycling from microbial necromass to cope with C:N stoichiometric imbalance by priming

The impact of increasing amounts of labile C input on priming effects (PE) on soil organic matter (SOM) mineralization remains unclear, particularly under anoxic conditions and under high C input common in microbial hotspots. PE and their mechanisms were investigated by a 60-day incubation of three flooded paddy soils amended with13C-labeled glucose equivalent to 50–500% of microbial biomass C (MBC). PE (14–55% of unamended soil) peaked at moderate glucose addition rates (i.e., 50–300% of MBC). Glucose addition above 300% of MBC suppressed SOM mineralization but intensified microbial N acquisition, which contradicted the common PE mechanism of accelerating SOM decomposition for N-supply (frequently termed as “N mining”). Particularly at glucose input rate higher than 3 g kg−1 (i.e., 300–500% of MBC), mineral N content dropped on day 2 close to zero (1.1–2.5 mg N kg−1) because of microbial N immobilization. To cope with the N limitation, microorganisms greatly increased N-acetyl glucosaminidase and leucine aminopeptidase activities, while SOM decomposition decreased. Several discrete peaks of glucose-derived CO2 (contributing >80% to total CO2) were observed between days 13–30 under high glucose input (300–500% of MBC), concurrently with CH4 peaks. Such CO2 dynamics was distinct from the common exponential decay pattern, implicating the recycling and mineralization of 13C-enriched microbial necromass driven by glucose addition. Therefore, N recycling from necromass was hypothesized as a major mechanism to alleviate microbial N deficiency without SOM priming under excess labile C input. Compound-specific 13C-PLFA confirmed the redistribution of glucose-derived C among microbial groups, i.e., necromass recycling. Following glucose input, more than 4/5 of total 13C-PLFA was in the gram-negative and some non-specific bacteria, suggesting these microorganisms as r-strategists capable of rapidly utilizing the most labile C. However, their 13C-PLFA content decreased by 70% after 60 days, probably as a result of death of these r-strategists. On the contrary, the 13C-PLFA in gram-positive bacteria, actinomycetes and fungi (K-strategists) was initially minimal but increased by 0.5–5 folds between days 2 and 60. Consequently, the necromass of dead r-strategists provided a high-quality C–N source to the K-strategists. We conclude that under severe C excess, N recycling from necromass is a much more efficient microbial strategy to cover the acute N demand than N acquisition from the recalcitrant SOM. © 2020 Elsevier Ltd

Cui J.1, 2, 3 , Zhu Z.1, 2 , Xu X.4 , Liu S.1 , Jones D.L.5 , Kuzyakov Y. 6, 7, 8, 9 , Shibistova O.10 , Wu J.1 , Ge T.1, 2
Elsevier Ltd
  • 1 Key Laboratory of Agro-ecological Processes in Subtropical Region & Changsha Research Station for Agricultural and Environmental Monitoring, Institute of Subtropical Agriculture, Chinese Academy of Sciences, Hunan, 410125, China
  • 2 State Key Laboratory of Organic Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Gongdong, 510640, China
  • 3 Jiangsu Provincial Key Laboratory for Bioresources of Coastal Saline Soils, Jiangsu Coastal Biological Agriculture Synthetic Innovation Center, Yancheng Teachers' University, Yancheng, 224002, China
  • 4 Key Laboratory of Ecosystem Network Observation and Modeling, Institute of Geographic Sciences and Natural Resources Research, Chinese Academy of Sciences, Beijing, 100101, China
  • 5 School of Environment, Natural Resources & Geography, Bangor University, Gwynedd, LL57 2UW, United Kingdom
  • 6 Department of Agricultural Soil Science, Department of Soil Science of Temperate Ecosystems, University of Gӧttingen, Gӧttingen, Germany
  • 7 Institute of Environmental Sciences, Kazan Federal University, Kazan, 420049, Russian Federation
  • 8 Agro-Technological Institute, RUDN University, Moscow, 117198, Russian Federation
  • 9 Departamento de Ciencias Químicas y Recursos Naturales, Universidad de La Frontera, Temuco, Chile
  • 10 VN Sukachev Institute of Forest, SB-RAS, Krasnoyarsk, 660036, Russian Federation
Compound-specific 13C-PLFA analysis; Glucose mineralization; Necromass recycling; Priming effects; Soil carbon; Stoichiometric imbalance
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