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A paddy soil, with microbial biomass considerably reduced by chloroform fumigation, was treated with low-crystalline ferrihydrite and high-crystalline goethite and with 13C-labeled acetate. In the first 10 days of the incubation, CH4 was produced mainly from the added acetate (56‒91%). After day 30, however, 3‒11% of the total CH4 emissions originated from the added acetate. Chloroform fumigation reduced the microbial biomass by 43‒87%, leading to the decrease in the CH4 emission from the fumigated soil for 352‒1127 times compared to that from the unfumigated soil. Acetate only contributed to 0‒6% of the total CH4 emission from the fumigated soil during the entire incubation period. Thus, chloroform fumigation largely reduced the abundance of methanogens, and the reduction in the abundance of acetotrophic methanogens was high. Iron oxide additions reduced CH4 emissions from the added acetate and from other sources. The reduction was stronger in the fumigated soil compared to that in the unfumigated soil because the lower abundance of methanogens in the fumigated soil decreased the competition for substrates with iron reducers. The effect of ferrihydrite on CH4 emission from non-acetate sources was stronger than that of goethite before day 6; however, this effect became weaker thereafter, because of the reduced number of reactive sites after acetate sorption by ferrihydrite. We conclude that the marked reduction in the microbial biomass, and especially methanogens, decreased the methane production, changed the CH4 sources, and increased the relative effects of iron oxides on CH4 production. [ABSTRACT FROM AUTHOR]

The effect of mineral fertilization and its application pattern on microbial activity and the subsequent CO2 and CH4 emissions arising from soil organic matter (SOM) or added substrate remains unclear. We quantified the decomposition of 13C-labeled straw and the priming effect (PE) governed by the N and P fertilizer application pattern during a 100-day experiment in a flooded soil. Straw addition increased the total CO2 and CH4 emissions. Straw mineralization increased by 30% and decreased by 19% after full and split NP application, respectively, compared with only straw addition. However, application of NP fertilization (full or split) inhibited straw-derived CH4 emissions compared with only straw addition. SOM decomposition was increased by straw addition, yielding a positive PE for CO2 emission. The application of split NP fertilization along with straw addition improved microbial activity, yielding the highest positive PE for CO2 emission. In contrast, compared with the control (no addition), split NP application decreased the positive PE for CH4 emission. Therefore, the straw-C-derived total CO2 equivalent emission was decreased by split NP application. These results were mainly attributable to the increased Olsen P, microbial biomass, enzyme activity, and straw-derived C microbial use efficiency of split NP application, which negatively affected the PE for CH4 emission; this was supported by the results of standardized total effects determined from structural equation models. Overall, compared with full application, split NP fertilizer application significantly decreased the straw-C mineralization rate and PE for CH4 emission, thereby mitigating greenhouse gas emission and SOM storage in paddy soil. [ABSTRACT FROM AUTHOR]

Phosphorus (P) application is an indispensable practice in agricultural crop production. However, the effect of P on crop and microbial biomass stoichiometries as well as its role in soil nutrient dynamics, remain poorly understood, thereby limiting our ability to predict the ecological consequences of agricultural practices. Herein, we conducted a P application experiment in a subtropical P-limited paddy soil to examine the effect of P addition on soil nutrient availability as well as on rice and the microbial C:N:P stoichiometries. The results showed that soil dissolved organic carbon (DOC) and available P content were simultaneously affected by P application and rice growth stage. Further, addition of P served to increase rice C and N content while decreasing the C: P and N: P stoichiometric ratios, indicating that P input contributed to rice growth and N absorption. Marked increases in soil microbial biomass carbon (MBC) and phosphorus (MBP) were also observed in soil treated with P. Moreover, the microbial C:N:P stoichiometry increased with rice growth stage, suggesting that changes in microbial and plant nutrient demand throughout the rice plant growth cycle causes competition between microorganisms and plants for N and P. Pearson's correlation and redundancy analyses revealed that available nutrients of soil were intercorrelated and regulated the patterns of rice and microbial C:N:P stoichiometries. In conclusions, P enrichment altered soil nutrient composition, microbial nutrient mining strategies, and rice C:N:P stoichiometry, thereby contributing to rice growth and improving crop yield. • P addition increased rice C and N pool and decreased rice stoichiometric ratios of C: P and N: P. • P input induced C and N limitations in the soil and microbial biomass. • The soil microbial ecological C: N: P stoichiometry varied with the rice growth stage. • Altered soil C: N: P stoichiometr affect the P strategy and N fixation of plants. [ABSTRACT FROM AUTHOR]

The author regret that the above article originally published with an error in the equation under "Calculation of GHG emission, PE, C-mineralization, microbial C use efficiency, and enzyme activity" section. The corrected equation is now presented in this article. [ABSTRACT FROM AUTHOR]

The response of stable and labile C pools to global warming is uncertain, especially in paddy soils with very low oxygen availability and the dominance of electron acceptors with low efficiency. To clarify the response of organic matter decomposition to warming, flooded paddy soil was incubated at four temperatures (5, 15, 25, and 35 °C) for 75 days. The 13C-labelled Na-acetate was used as an analogue for root exudates and as a methane (CH 4) source. Soil with acetate had higher C availability to microorganisms leading to 2–2.7 times and 2–153 times higher emission of carbon dioxide (CO 2) and CH 4 on day 75 than from soil without acetate, respectively. Incubation temperature explained >40% of the variance of CO 2 and CH 4 effluxes. Acetate stimulated microbial activities and turnover and so, increased soil organic matter (SOM) mineralisation in the first week, especially at low temperatures (<15 °C) with slow acetate consumption and longer oxygen (O 2) availability. The priming effects measured as CH 4 emissions were especially sensitive to temperatures from 5 to 15 °C. The high Q 10 value of primed CH 4 (Q 10 > 10) at low temperature indicates that flooded paddy fields will contribute greatly to the greenhouse effect in warm winters, which have become common from 1970s. Caution is necessary for interpretations of previous estimates of the temperature sensitivity of SOM decomposition because the priming effect was ignored, especially that of CH 4 under the condition of limited O 2 availability in paddy and other wetland soils. [ABSTRACT FROM AUTHOR]

Labile carbon (C) inputs affect the soil carbon:nitrogen (C:N) ratio and microbial stoichiometric homeostasis, which control the intensity and direction of the priming effect (PE). Here, we clarified how soil microorganisms regulate enzyme production and PE to maintain the C:N stoichiometric balance. Specifically, we conducted an incubation experiment by adding 13C-labeled glucose to four long-term fertilized paddy soils: no fertilization; fertilization with mineral nitrogen, phosphorus, and potassium (NPK); NPK combined with straw; and NPK with manure (NPKM). After glucose addition, the dissolved organic carbon-to-ammonium (DOC:NH 4 +) ratio (24–39) initially increased, but subsequently decreased after day 2 following glucose exhaustion. In parallel, the microbial C:N imbalance [(DOC:NH 4 +):(microbial biomass C:microbial biomass N)] rapidly decreased from day 2 (4.6–7.2) to day 20 (<0.5). Thus, microorganisms became C limited after 20 days of incubation. Excess C, resulting from glucose addition, increased N-hydrolase (chitinase) production and N mining from soil organic matter (SOM) through positive PEs. However, C hydrolase (β -1,4-glucosidase and β-xylosidase) activity increased, while that of N hydrolase (chitinase) decreased, following glucose exhaustion. Consequently, the C:N microbial biomass ratio increased as the DOC:NH 4 + ratio decreased, leading to negative PEs. NPKM-fertilized soil had the largest cumulative PE (2.3% of soil organic carbon) because it had the highest microbial biomass and iron (Fe) reduction rate. Thus, this increased N mining from SOM maintained the microbial C:N stoichiometric balance. We concluded that soil microorganisms regulate C- and N-hydrolase production to control the intensity and direction of PE, maintaining the C:N stoichiometric balance in response to labile C inputs. [Display omitted] • Glucose input into paddy soil increased DOC:NH 4 + ratio and microbial biomass (MB). • High C availability increased activity of N-hydrolases and priming effect (PE). • Decreased MB and N-hydrolase activity induced negative PE with labile C exhaustion. • Highest cumulative PE observed in combined NPK and chicken manure fertilized soil. • C and N hydrolase production is key for regulating C:N stoichiometry of MB and PE. [ABSTRACT FROM AUTHOR]

Root exudates are a labile source of carbon (C) for microorganisms that can lead to increased CO 2 emission. Root exudates can vary in C:N stoichiometric ratio and their impact on microbially driven soil organic matter (SOM) turnover in paddy soils still remains unclear. The objective was to explore the underlying mechanisms involved in SOM decomposition due to root exudate (artificial) addition with three different C:N ratios (10, 20, and 40) during 45 days incubation. Different root exudates C:N ratios were obtained by adding mineral N and exudate components (glucose, oxalic acid, and glutamate) to paddy soil. N-only addition decreased dissolved organic C to limit CO 2 emissions, which is an indicative of C sequestration. Conversely, simulated C:N stoichiometric ratios of root exudates significantly increased both microbial activity and metabolism without altering the microbial biomass C:N ratio. However, soil available dissolved organic C to NH 4 + ratio decreased by exudates addition. The stoichiometric ratio of key C and N compound degrading enzymes activities increased only with C:N = 10 and remained unchanged with exudates C:N = 20 and 40. The q CO 2 values increased with decreasing N-containing compounds in root exudates (i.e. highest CO 2 emission was observed under C:N = 40 exudates addition). The results suggest that increasing exudates C:N ratio intensify CO 2 emission due to high microbial N demand. Overall result show that root exudates C:N ratio and soil available N co-regulate on CO 2 emission, which was controlled by microbial and potential extracellular enzyme activities. • Root exudate analogues significantly increased CO 2 emission from paddy soils. • Exudates addition increased microbial biomass and q CO 2 without altering microbial C:N ratio. • Root exudate inputs increased the accumulation of soil available NH 4 +. • N-only addition limited CO 2 emission and decreased dissolved organic C. [ABSTRACT FROM AUTHOR]