Agrochemical applications may have side effects on soil biochemical properties related to soil nitrogen (N) mineralization and thus affect N cycling. The present study aimed to evaluate the effects of nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) and fungicide iprodione on soil neutral protease (NPR), alkaline protease (APR), chitinase (CHI), and their functional genes (nprA, aprA, and chiA) related to soil N mineralization. The following four treatments were included: blank control (CK), single DMPP application (DAA), weekly iprodione applications (IPR), and the combined applications of DMPP and iprodione (DI). Compared with the CK treatment, DMPP application significantly inhibited the CHI activity in the first 14 days of incubation, and iprodione applications, particularly when applied alone, decreased the NPR, APR, and CHI activities. Relative to the IPR treatment, extra DMPP application had the potential to alleviate the inhibitory effects of iprodione on the activities of these enzymes. DMPP application significantly increased aprA gene abundances after 14 days of incubation. However, repeated iprodione applications, alone or with the DMPP, decreased nprA and chiA gene abundances. Relative to the CK treatment, DMPP application generated negligible effects on the positive/negative correlations between soil enzyme activities and the corresponding functional gene abundances. However, the positive correlation between the CHI activity and chiA gene abundance was changed to negative correlation by repeated iprodione applications, alone or together with the DMPP. Our results demonstrated that agrochemical applications, particularly repeated fungicide applications, can have inadvertent effects on enzyme activities and functional gene abundances associated with soil N mineralization.
Background: Phyllostachys edulis (moso bamboo) is a key source of non-wood forest products. Clarifying the linkage among bamboo growth, soil nutrient and core microbe can expand the horizon on nutrient management practices and functional endophytic and rhizospheric microbes.Results: In this study, young (0.5-yr), mature (2.5-yr and 4.5-yr) and old (6.5-yr) bamboo plants were selected in a moso bamboo field, and above-ground tissues, below-ground roots (rhizomes) and rhizospheric soils were sampled. The bamboo biomass, soil properties and endophytic microbes were determined and quantify their comprehensive relationships. Bamboo ages had negligible impacts on the bamboo height, diameter at breast height and above-ground biomass. Organic matter and nitrogen (N) contents in the rhizospheric soil of the 0.5-yr bamboo were significantly higher than those of the other three age groups. The rhizospheric soil of the 6.5-yr bamboo had the lowest N mineralization rate and urease activity. Significant differences in bacterial and fungal communities were found in the above-ground tissues but not in the rhizospheric soils associated with plants of different ages. Bacterial and fungal community structures in the above-ground tissues were significantly different from their counterparts in the rhizospheric soils. Conclusions: Bamboo ages significantly affected N transformation rates, functional gene abundances and urease activities of rhizospheric soils and endophytic bacterial community structures. However, niche differentiations outweighed ages in shaping the whole microbial communities of bamboo aboveground tissues, roots and rhizospheric soils. In the future, moso bamboo management should consider balanced applications of ammonium-N and other nutrients and utilisations of Chytridiomycota to stimulate moso bamboo growth.
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