Abstract
There are lack of studies regarding the effects of microbial diversity on specific soil functions, such as pesticides degradation. This study evaluated the role of bacterial community diversity and biochar on chlorothalonil (CTN) degradation, using ‘dilution to extinction’ approach, PCR-DGGE/16S rRNA gene technique, and radiorespirometry (14C-CTN). Biochar and microbial community dilution affected structure of the microbial community. In spite of that, CTN mineralization was slow, but dissipation was very fast (D50 < 1.0 d) due to immediate chemical degradation and formation of non-extractable (bound) residues. However, any depletion on soil microbial diversity strongly affected CTN mineralization, suggesting that this function is related to less abundant but specific microbial groups (CTN degraders) or to soil microbial diversity. The extent of these effects will strongly depend on the compound nature (recalcitrance) and soil matrix/substrate (bioavailability). It can be corroborated by the fact that biochar affected CTN sorption, its bioavailability, and subsequently its mineralization rate in the NS. These data indicate a strong relationship between soil microbial diversity and pesticide degradation, which is an acting form to mitigate xenobiotics accumulation in the environment.
Highlights
Despite having a central role in the Earth’s biogeochemical cycles, microbial diversity studies have been neglected until the last decade[1,2]
After biochar and CTN application, the bacterial community was structured in distinct clusters throughout the different sampling periods (1, 21, and 42 d), validated by the R values (R = 0.83 to 0.87 and p < 0.001) that were calculated by the logarithm of Bray Curtis (Supplementary Table S1)
(at 1 d), diluted bacterial communities were maintained in distinct clusters, but no differentiation was observed between the treatments with and without biochar (Figs 1A and 2A)
Summary
Despite having a central role in the Earth’s biogeochemical cycles, microbial diversity studies have been neglected until the last decade[1,2]. CTN degradation involves either displacement of a chlorine by a hydroxyl group forming 4-hydroxy-2,5,6-trichloroisophthalonitrile or oxidation/hydration of a cyano to a corresponding amide and an organic acid group forming 3-cyano-2,4,5,6-tetrachlorobenzamide and 3-carbamyl-2, 4,5-trichlorobenzoic acid[29,30,31] This last metabolite was the most abundant in Brazilian soils, corresponding to 18–25% of the applied amount, whereas the first one was most abundant in other scenarios (mostly at temperate conditions)[32], which causes environmental concerns since it is more acutely toxic (30 times), persistent, and mobile than CTN itself 27,29
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