With its relatively high stability, biochar has been suggested as a means to mitigate climate change through carbon fixation and improve the physicochemical properties of soils. However, our understanding of the effects of biochar on soil microbial diversity and their metabolic activity remain unclear. In order to elucidate how the application of biochar to plantation soils influences microbial biomass and functional diversity (using Biolog EcoPlatesTM), we conducted an experiment to investigate changes in soil microbial communities at four biochar levels (0, 40, 80 and 120 Mg/ha). We found that biochar application altered the metabolic patterns of microbial communities and accelerated the utilization of amino acids, carboxylic acids, polymers and other miscellaneous plant chemical compounds by microbes. Moreover, compared to the control, soil pH increased by 0.23, 0.24, 0.28 units and microbial biomass carbon to nitrogen ratio (MBC/MBN) by 9.20, 20.99 and 17.74, respectively. Meanwhile, soil moisture decreased from 25.7 to 23.8%, 23.7 and 24.4%, and MBN declined by 42.2, 46.2 and 53.8%. Regression analysis showed that soil pH was the primary factor correlated with reduced MBN. Community physiological profiles revealed that high concentrated biochar (120 Mg/ha) elevated microbial metabolic activity, while biochar application did not alter microbial functional diversity represented by the Shannon diversity index (H′) and evenness (E). Furthermore, the application of biochar would affect biogeochemical cycling of carbon and nitrogen through the elevated microbial activity and utilization in different categories of carbon sources (polymers, carboxylic acids etc.) with the reduced MBN.

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Aims:  In this study, we explored the possibility of construction of a ‘universal targeting vector’ by Red/ET recombination to inactivate L gene encoding 3‐amino‐5‐hydroxybenzoic acid (AHBA)‐oxidoreductase in AHBA biosynthetic gene cluster to facilitate the detection of ansamycins production in actinomycetes. Methods and Results:  Based on the conserved regions of linked AHBA synthase (K), oxidoreductase (L) and phosphatase (M) gene clusters, degenerate primers were designed and PCR was performed to detect KLM gene clusters within 33 AHBA synthase gene‐positive actinomycetes strains. Among them, 22 KLM gene cluster‐positive strains were identified. A ‘universal targeting vector’ was further constructed using the 50‐nt homologous sequences chosen from four strains internal L gene in KLM gene clusters through Red/ET recombination. The L gene from nine of the KLM gene cluster‐positive actinomycetes strains was inactivated by insertion of a kanamycin (Km) resistance marker into its internal region from the ‘universal targeting vector’. By comparison of the metabolites produced in parent strains with those in L gene‐inactivated mutants, we demonstrated the possible ansamycins production produced by these strains. One strain (4089) was proved to be a geldanamycin producer. Three strains (3‐20, 7‐32 and 8‐32) were identified as potential triene‐ansamycins producers. Another strain (3‐27) was possible to be a streptovaricin C producer. Strains 24‐100 and 4‐124 might be served as ansamitocin‐like producers. Conclusions:  The results confirmed the feasibility that a ‘universal targeting vector’ could be constructed through Red/ET recombination using the conserved regions of KLM gene clusters to detect ansamycins production in actinomycetes. Significance and Impact of the Study:  The ‘universal targeting vector’ provides a rapid approach in certain degree to detect the potential ansamycin producers from the 22 KLM gene cluster‐positive actinomycetes strains.