Publication Date:
2020
Description:
〈p〉Publication date: March 2020〈/p〉
〈p〉〈b〉Source:〈/b〉 Soil Biology and Biochemistry, Volume 142〈/p〉
〈p〉Author(s): Jun Cui, Zhenke Zhu, Xingliang Xu, Shoulong Liu, Davey L. Jones, Yakov Kuzyakov, Olga Shibistova, Jinshui Wu, Tida Ge〈/p〉
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〈h5〉Abstract〈/h5〉
〈div〉〈p〉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 with〈sup〉13〈/sup〉C-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〈sup〉−1〈/sup〉 (i.e., 300–500% of MBC), mineral N content dropped on day 2 close to zero (1.1–2.5 mg N kg〈sup〉−1〈/sup〉) 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 CO〈sub〉2〈/sub〉 (contributing 〉80% to total CO〈sub〉2〈/sub〉) were observed between days 13–30 under high glucose input (300–500% of MBC), concurrently with CH〈sub〉4〈/sub〉 peaks. Such CO〈sub〉2〈/sub〉 dynamics was distinct from the common exponential decay pattern, implicating the recycling and mineralization of 〈sup〉13〈/sup〉C-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 〈sup〉13〈/sup〉C-PLFA confirmed the redistribution of glucose-derived C among microbial groups, i.e., necromass recycling. Following glucose input, more than 4/5 of total 〈sup〉13〈/sup〉C-PLFA was in the gram-negative and some non-specific bacteria, suggesting these microorganisms as 〈em〉r〈/em〉-strategists capable of rapidly utilizing the most labile C. However, their 〈sup〉13〈/sup〉C-PLFA content decreased by 70% after 60 days, probably as a result of death of these 〈em〉r〈/em〉-strategists. On the contrary, the 〈sup〉13〈/sup〉C-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 〈em〉r〈/em〉-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.〈/p〉〈/div〉
〈/div〉
Print ISSN:
0038-0717
Electronic ISSN:
1879-3428
Topics:
Biology
,
Geosciences
,
Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
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