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Dynamics in the Microbial Transformation of Organic C in Soil

Dynamics in the Microbial Transformation of Organic C in Soil. Jinshui Wu Institute of Subtropical Agriculture, the Chinese Academy of Sciences. Outlines. Concepts of soil microbial biomass and soil organic C transformations Methodology for quantifying soil microbial biomass

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Dynamics in the Microbial Transformation of Organic C in Soil

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  1. Dynamics in the Microbial Transformation of Organic C in Soil Jinshui Wu Institute of Subtropical Agriculture, the Chinese Academy of Sciences

  2. Outlines • Concepts of soil microbial biomass and soil organic C transformations • Methodology for quantifying soil microbial biomass • Case studies on dynamics in the microbial transformations of organic C in soil

  3. Outlines • Concepts of soil microbial biomass and soil organic C transformations • Methodology for quantifying soil microbial biomass • Case studies on dynamics in the microbial transformations of organic C in soil

  4. Biogeochemical functions of the soil microbial community Microbial Community OC (N/P/S) CO2/CH4/NxO… HM/Minerals 土壤生物

  5. Biogeochemical functions of the soil microbial community Microbial Community OC (N/P/S) CO2/CH4/NxO… HM/Minerals 土壤生物 Assumption: The soil microbial community mediate the transformation of all organic materials exiting in soil.

  6. Biogeochemical functions of the soil microbial community Microbial Community OC (N/P/S) CO2/CH4/NxO… HM/Minerals 土壤生物 Assumption:The soil microbial community mediate the transformation of all organic materials exiting in soil. Key issue:In which community levels can the fluxes (rates) of C and nutrients be quantified (single cells, species, functional groups, or the whole) ?

  7. Soil microbial community: Population Bacterial species: > 104 g-1 soil (Data from Prof. P. C. Brookes)

  8. The concept of soil microbial biomass(Jenkinson and Brookes) • The sum of the masses of all the soil micro-organisms (as a single pool) • Providing a definitive entity for the bio-chemical assessments of the soil microbial community (e.g. the pool size), and the fluxes of C and nutrients through the biomass pool.

  9. Soil microbial community: Biomass Soil microbial biomass (per ha) 50-350 sheep =

  10. Biogeochemical functions of the soil microbial community Microbial Community OC/ N/P/S CO2/CH4/NxO… HM/Minerals 土壤生物 • Quantity of the microbial biomass • Quantifying the dynamics parameters (the flux rates of OC/N/P/S, and the ratios of the products) • Defining the functional groups involved

  11. Outlines • Concepts of soil microbial biomass and soil organic C transformations • Methodology for quantifying soil microbial biomass • Case studies on dynamics in the microbial transformations of organic C in soil

  12. The fumigation-extraction method ● Lyses > 95% cells.● Does not alter the solubility and mineralizing activity of organic materials. Powlson & Jenkinson (1976), SBB

  13. The fumigation-extraction method Automatic instrument analyses for the extracted biomass C, N, P, and S Flow injection analyzer TOC • Reliable chemistry procedures • Rapid and high accuracy analysis • Suitable for large numbers of samples (Wu et al., 1990, SBB; Shen et al, 1985, SBB;Wu et al., 1994, SBB; Wu et al., 2000, BFS)

  14. The fumigation-extraction method Vance, Brookes and Jenkinson (1987). An extraction method for measuring soil microbial biomass C. Soil Biology & Biochemistry 19, 697-702. Wu, J., R.G. Joergensen, B. Pommerening, R. Chaussod and P.C. Brookes (1990). Measurement of soil microbial biomass by fumigation-extraction - an automated procedure. Soil Biology and Biochemistry 22, 1167-1169. SBB selected papers of the Citation Classics

  15. Combined the automated analysis procedures with 14C labelling technique 14CO2 Turnover Organic C (14C) Biomass 14C Turnover 14C-labeling Metabolic-14C (humic substances)

  16. Outlines • Concepts of soil microbial biomass and soil organic C transformations • Methodology for quantifying soil microbial biomass • Case studies on dynamics in the microbial transformations of organic C in soil

  17. Case 1: The turnover rates of soil microbial biomass C and P Assumption: The turnover of 14C-labelled biomass C follows the first-order kinetics Yt=Y0 e-kt ln(Yt) =ln(Y0) - kt k: The turnover rate 1/k: The turnover time (days)

  18. Paddy soil Upland soil （μg g-1） Incubation time（d） Changes in soil microbial biomass C labelled with 14C (by the amendment with 14C-lablled glucose and incubation at 25oC) (Wu et al., 2012, JSFA)

  19. Turnover rate of microbial biomass C in subtropical upland and paddy soils (China) Site 1 Turnover time Turnover rate At 25℃ Field conditions Upland Paddy Wu et al., 2012, JSFA

  20. The turnover time of biomass C affected by soil clay content and management (NPK) (22% clay)

  21. Case 2: Quantifying the ratio of CO2 from biomass C and non-biomass organic C Soil+14C-glucose CO2 Incubation (20 d at 25℃) Turnover Organic C Biomass C Ad-Rw (5 cycles; incubated for 7 d at 25℃ ) Turnover Metabolites (humic substances) Determinations CO2\Bc\DOC (total\14C-labelled)

  22. 14C-labelled Total (μg C g-1 soil) Incubation time (days) CO2 evolved from a soil following the amendment of 14C-lablled glucose and 5 drying-rewetting cycles (Wu et al., 2005, SBB)

  23. Biomass C (heavily 14C labeled) Organic C (lightly 14C labeled) % Proportions of CO2 evolved in a soil following 5 drying-rewetting Cycles (Wu et al., 2005, SBB)

  24. Case 3: The mechanisms of “priming effect” Priming effects: Responses of the mineralization of soil organic C following the inputs of fresh organic materials.

  25. Responses of CO2 evolution and biomass C to glucose (14C-lablled) addition

  26. PE Mechanism I: Enhanced turnover of the biomass C which results in the ‘replacement’ of native biomass C (unlablled) by the newly formed biomass C (labelled)(Wu et al., 1993, SBB)

  27. Responses of CO2 evolution and biomass C to ryegrass (14C-lablled) addition

  28. Mechanism II:Increased mineralization of the native soil organic C (unlabelled) by the activities of the prolonged increases of the microbial biomass(Wu et al., 1993, SBB)

  29. Case 4: Quantifying the assimilation of atmospheric CO2 by autotrophic micro-organisms in soils

  30. Soils (x 8) (14C-CO2) Incubate in light (no cover, 4 reps) Incubate in dark (foam cover, 4 reps) 12 hr light cycle, incubate for 80 days Soil incubated for 80 d in the growth chamber with 14C-labeled CO2 14C-OC 14C-MBC RubisCo DNA cbbL (1A,1C); cbbL (1D) qPCR, cloning and sequencing Functional micro-organisms

  31. Microbial assimilation of atmospheric CO2 (14C-labelled) in subtropical soils(Yuan et al., 2012, AEM; Ge et al., 2012, SBB) % of total SOC mg C kg-1 soil

  32. Microbial assimilation of atmospheric CO2 (14C-labelled) in subtropical soils(Yuan et al., 2012, AEM; Ge et al., 2012, SBB) Annual C assimilation: 100-500 kg C! % of total SOC mg C kg-1 soil

  33. Light * * Dark * * * * (nmol CO2 g-1 min -1） * nd nd RubisCO activity in the soils incubated for 80 d (Yuan et al., 2012, AEM; Ge et al., 2012, SBB)

  34. Bacterial cbbL genes blue-green cbbL genes * * * * * * * * (×106 copies g-1 ) (×108 copies g-1 ) * * * * * * Non-green cbbL genes * Dark Light * * * Abundance of cbbL genes encoding bacteria, blue-green and non-green algae in the soils (Yuan et al., 2012, AEM) (×106 copies g-1) * * nd * nd

  35. (×107 copies g-1） P1-light P1-dark U1-dark U1-light Ralstonia eutropha Rhodopseudomonas palustris Bradyrhizobium japonicum Bradyrhizobium japonicum Azospirillum lipoferum Thiobacillus denitrificans Rhodopseudomonas palustris Mycobacterium sp. Rhodobacter azotoformans Aminobacter sp. Aminobacter sp. Thiobacillus denitrificans Bacterial cbbL taxa abundance in soils P1 and U1 (Yuan et al., 2012, AEM)

  36. Blue-green algae Oscillatoria sp. Anabaena sp. (×106 copies g-1） Fischerella thermalis Tribonema viride Porphyridium aerugineum Sellaphora auldreekie U1-light P1-light P1-dark U1-dark Non-green algae Algal cbbL taxa abundance in soils P1 and U1 (Yuan et al., 2012, AEM)

  37. Thank for Your Attention !

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