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Dynamics in the Microbial Transformation of Organic C in Soil Jinshui Wu Institute of Subtropical Agriculture, the Chinese Academy of Sciences Slide 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 Slide 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 Slide 4 Microbial Community OC (N/P/S) CO 2 /CH 4 /N x O HM/Minerals Biogeochemical functions of the soil microbial community Slide 5 Microbial Community OC (N/P/S) CO 2 /CH 4 /N x O HM/Minerals Biogeochemical functions of the soil microbial community Assumption: T he soil microbial community mediate the transformation of all organic materials exiting in soil. Slide 6 Microbial Community OC (N/P/S) CO 2 /CH 4 /N x O HM/Minerals Biogeochemical functions of the soil microbial community Assumption: T he 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) ? Slide 7 Soil microbial community: Population Bacteria (No g -1 ) 10 8 - 10 9 Fungal hyphae (m g -1 ) 101000 Bacterial species: > 10 4 g -1 soil (Data from Prof. P. C. Brookes) Slide 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. Slide 9 CompositionsArableGrassland kg ha -1 Dry matter1100-33001600-7500 C500-1400750-3500 N80-230125-500 Soil microbial biomass (per ha) 50-350 sheep = Soil microbial community: Biomass Slide 10 Microbial Community OC/ N/P/S CO 2 /CH 4 /N x O HM/Minerals 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 Biogeochemical functions of the soil microbial community Slide 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 Slide 12 Lyses > 95% cells. Does not alter the solubility and mineralizing activity of organic materials. The fumigation-extraction method Powlson & Jenkinson (1976), SBB Slide 13 TOC Reliable chemistry procedures Rapid and high accuracy analysis Suitable for large numbers of samples The fumigation-extraction method Automatic instrument analyses for the extracted biomass C, N, P, and S (Wu et al., 1990, SBB; Shen et al, 1985, SBB; Wu et al., 1994, SBB; Wu et al., 2000, BFS) Flow injection analyzer Slide 14 The fumigation-extraction method SBB selected papers of the Citation Classics 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. Slide 15 Organic C ( 14 C) Biomass 14 C Metabolic- 14 C (humic substances) 14 CO 2 Turnover Combined the automated analysis procedures with 14 C labelling technique 14 C-labeling Slide 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 Slide 17 Y t =Y 0 e -kt ln(Yt) =ln(Y 0 ) - kt Case 1: The turnover rates of soil microbial biomass C and P Assumption: The turnover of 14 C-labelled biomass C follows the first-order kinetics k: The turnover rate 1/k: The turnover time (days) Slide 18 Changes in soil microbial biomass C labelled with 14 C (by the amendment with 14 C-lablled glucose and incubation at 25 o C) (Wu et al., 2012, JSFA) g g -1 Incubation time d Paddy soilUpland soil Slide 19 Turnover rate of microbial biomass C in subtropical upland and paddy soils (China) Site 1 Upland Paddy Turnover rate Turnover time Field conditions Wu et al., 2012, JSFA At 25 Slide 20 The turnover time of biomass C affected by soil clay content and management Clay Turnover time at 25 Field conditions 393834.0 222012.1 151261.3 Management Turnover time at 25 Field conditions Grassland2122.2 FYM1932.0 Nil1781.9 Fallow1751.8 (22% clay) (NPK) Slide 21 Organic C Biomass C Metabolites (humic substances) CO 2 Turnover Case 2: Quantifying the ratio of CO2 from biomass C and non-biomass organic C Soil+ 14 C-glucose Incubation (20 d at 25 ) Ad-Rw (5 cycles; incubated for 7 d at 25 ) Determinations CO 2 \Bc\DOC (total\ 14 C-labelled) Slide 22 CO 2 evolved from a soil following the amendment of 14 C- lablled glucose and 5 drying-rewetting cycles (Wu et al., 2005, SBB) Total 14 C-labelled (g C g -1 soil) Incubation time (days) Slide 23 Proportions of CO 2 evolved in a soil following 5 drying- rewetting Cycles (Wu et al., 2005, SBB) % Biomass C (heavily 14 C labeled) Organic C (lightly 14 C labeled) Slide 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. Slide 25 Responses of CO 2 evolution and biomass C to glucose ( 14 C-lablled) addition Slide 26 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) PE Slide 27 Responses of CO 2 evolution and biomass C to ryegrass ( 14 C-lablled) addition Slide 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) Slide 29 Case 4: Quantifying the assimilation of atmospheric CO2 by autotrophic micro- organisms in soils Slide 30 Soil incubated for 80 d in the growth chamber with 14 C- labeled CO 2 Soils (x 8) ( 14 C-CO 2 ) Incubate in dark (foam cover, 4 reps) Incubate in light (no cover, 4 reps) 12 hr light cycle, incubate for 80 days 14 C-MBC 14 C-OCDNARubisCo cbbL (1A,1C); cbbL (1D) qPCR, cloning and sequencing Functional micro-organisms Slide 31 mg C kg -1 soil % of total SOC Microbial assimilation of atmospheric CO 2 ( 14 C- labelled) in subtropical soils (Yuan et al., 2012, AEM; Ge et al., 2012, SBB) Slide 32 mg C kg -1 soil % of total SOC Annual C assimilation: 100-500 kg C! Microbial assimilation of atmospheric CO 2 ( 14 C- labelled) in subtropical soils (Yuan et al., 2012, AEM; Ge et al., 2012, SBB) Slide 33 (nmol CO 2 g -1 min -1 RubisCO activity in the soils incubated for 80 d (Yuan et al., 2012, AEM; Ge et al., 2012, SBB) Light Dark nd * * * * * * * Slide 34 (10 8 copies g -1 ) (10 6 copies g -1 ) Bacterial cbbL genes blue-green cbbL genes (10 6 copies g -1 ) Non-green cbbL genes Abundance of cbbL genes encoding bacteria, blue-green and non-green algae in the soils (Yuan et al., 2012, AEM) Light Dark * * * * * * * * * * * * * * * * * * * * * nd Slide 35 Thiobacillus denitrificans Ralstonia eutropha Bradyrhizobium japonicum Azospirillum lipoferum Rhodobacter azotoformans Aminobacter sp. Rhodopseudomonas palustris U1-light P1-dark (10 7 copies g -1 P1-light U1-dark Rhodopseudomonas palustris Bradyrhizobium japonicum Thiobacillus denitrificans Aminobacter sp. Mycobacterium sp. Bacterial cbbL taxa abundance in soils P1 and U1 (Yuan et al., 2012, AEM) Slide 36 (10 6 copies g -1 Algal cbbL taxa abundance in soils P1 and U1 (Yuan et al., 2012, AEM) Blue-green algae Non-green algae P1-lightP1-dark U1-light U1-dark Oscillatoria sp. Anabaena sp. Fischerella thermalis Tribonema viride Porphyridium aerugineum Sellaphora auldreekie Slide 37 Thank for Your Attention !