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The crop rotation periodicity has always been a concern of agricultural researchers. This study was the first investigation on the effects of long-term continuous cultivation with rice/cherry tomato rotation on soil microbial community diversity. The main objective was to analyze the optimal rotation years of rice/cherry tomato from a micro-ecology perspective so as to provide theoretical basis for effectively avoiding continuous cropping obstacles of cherry tomato. Soil samples were collected from the surface layers with rice/cherry tomato rotations for 1 year (1a), 3 years (3a), 5 years (5a), 7 years (7a) and 10 years (10a). The microbial community diversity was determined via high-throughput sequencing. The results showed that alpha diversity of soil microbial communities was the highest at 5a and then gradually decreased during 5a to 10a. Beta diversity results revealed that microbial community structure was significantly different among 1a, 3a to 7a and 10a, but there were no clear differences among 3a, 5a and 7a. The abundances of soil beneficial bacteria Gemmatimonadetes, Bacteroidetes, Chloroflexi, Nitrospirae and beneficial fungi Mortierella, Trichoderma, Penicillium were the highest at 5a or 7a. Those of soil pathogenic fungi Fusarium and Aspergillus were the lowest at 5a and 7a, respectively. However, the relative abundances of the above-mentioned beneficial microorganisms began to decline, while those of pathogenic fungi began to increase after 5a or 7a. Soil available phosphorus, available iron and available zinc were common important factors affecting the community structure of bacteria and fungi, as indicated by significant positive correlations between the environmental factors and microbial communities. In conclusion, the soil microbial diversity began to decline and the micro-ecological balance was broken after continuously planting 5a to 7a with rice/cherry tomato rotation, which would lead to new continuous cropping obstacles. [ABSTRACT FROM AUTHOR]

Microbial communities play crucial roles in the biogeochemical cycling of many important soil elements. Pesticides are known to affect non-targeted soil microorganisms. Glyphosate (GP) and diquat (DQ), two commonly used non-selective herbicides, often co-exist in lateritic paddy soil rich in iron/aluminum oxides. However, there is limited information on their co-impact on microbial community structure and diversity in this type of soil. Here, the short-term effects of combined exposure to GP and DQ on microbial diversity and community structure shifts were investigated in lateritic paddy soil from a tropical agricultural region (Hainan, China). The combined utilization dosages of two herbicides were set in three concentrations: low concentration (1 fold of the recommended dosage), medium concentration (10 fold of the recommended dosage) and high concentration (100 fold of the recommended dosage). The structure and diversity of microbial communities were determined via 16S rRNA and ITS gene high-throughput sequencing. The results revealed that Actinobacteria and Proteobacteria were the most sensitive microbial phyla to the combined exposure of GP and DQ in lateritic paddy soil. The combined exposure to GP and DQ increased the abundance of Actinobacteria but significantly inhibited that of Proteobacteria, especially at low and medium concentrations. Compared with CK, mixed herbicide (GP + DQ) had no adverse effects on the richness of bacteria and fungi communities as well as on the diversity of bacteria communities, but it significantly decreased the diversity of fungi communities at high concentrations within 28 days. However, the effects of combined exposure to GP and DQ on soil microbial richness and diversity were not significantly different from those of separate exposure of the two herbicides. In conclusion, the combined application of GP and DQ had no more adverse effects on soil microorganisms. Therefore, these two herbicides can be used reasonably in actual agricultural production. [ABSTRACT FROM AUTHOR]