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BackgroundPrevious studies have focused on linking soil community structure, diversity, or specific taxa to disturbances. Relatively little attention has been directed to crop monoculture soils, particularly potato monoculture. Information about microbial community changes over time between monoculture and non-monoculture treatments is lacking. Furthermore, few studies have examined microbial communities in potato monoculture soils using a high throughput pyrosequencing approach.Methodology/Principal FindingsSoils along a seven-year gradient of potato monoculture were collected and microbial communities were characterized using high throughput pyrosequencing approach. Principal findings are as follows. First, diversity (H Shannon) and richness (S Chao1) indices of bacterial community, but not of fungal community, were linearly decreased over time and corresponded to a decline of soil sustainability represented by yield decline and disease incidence increase. Second, Fusarium, the only soilborne pathogen-associated fungal genus substantially detected, was linearly increased over time in abundance and was closely associated with yield decline. Third, Fusarium abundance was negatively correlated with soil organic matter (OM) and total nitrogen (TN) but positively with electrical conductivity (EC). Fourth, Fusarium was correlated in abundances with 6 bacterial taxa over time.ConclusionsSoil bacterial and fungal communities exhibited differential responses to the potato monoculture. The overall soil bacterial communities were shaped by potato monoculture. Fusarium was the only soilborne pathogen-associated genus associated with disease incidence increase and yield decline. The changes of soil OM, TN and EC were responsible for Fusarium enrichment, in addition to selections by the monoculture crop. Acidobacteria and Nitrospirae were linearly decreased over time in abundance, corresponding to the decrease of OM, suggesting their similar ecophysiologial trait. Correlations between abundance of Fusarium with several other bacterial taxa suggested their similar behaviors in responses to potato monoculture and/or soil variables, providing insights into the ecological behaviors of these taxa in the environment.

Studies were conducted to determine the role of 3-methylthioproprionic acid (MTPA) in the pathogenicity of potato stem canker, Rhizoctonia solani, and the concentrations required to inhibit growth of R. solani under laboratory and plant house-based conditions. The experiments were laid out in a completely randomized design with five treatments and five replications. The treatments were 0, 1, 2, 4, and 8 mM concentrations of MTPA. The purified toxin exhibited maximal activity at pH 2.5 and 30°C. MTPA at 1, 2, 4, and 8 mM levels reduced plant height, chlorophyll content, haulm fresh weight, number of stolons, canopy development, and tuber weight of potato plants, as compared to the control. MTPA significantly affected mycelial growth with 8 mM causing the highest infection. The potato seedlings treated with MTPA concentrations of 1.0–8.0 mM induced necrosis of up to 80% of root system area. Cankers were resulted from the injection of potato seedling stems with 8.0 mM MTPA. The results showed the disappearance of cell membrane, rough mitochondrial and cell walls, change of the shape of chloroplasts, and swollen endoplasmic reticulum. Seventy-six (76) hours after toxin treatment, cell contents were completely broken, cytoplasm dissolved, and more chromatin were seen in the nucleus. The results suggested that high levels of the toxin concentration caused cell membrane and cytoplasm fracture. The integrity of cellular structure was destroyed by the phytotoxin. The concentrations of the phytotoxin were significantly correlated with pathogenicity and caused damage to the cell membrane of potato stem base tissue.

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This study investigated the altering effect of moisture on the emission pattern of gases and the evolutionary dynamics of physicochemical indices in corn straw and cow manure composting. Exploring this effect was reasonable to unravel the use of moisture as a cheap alternative to control gaseous emissions and improve the final properties of compost. The nutrient dynamics of the compost showed 21.6% losses in total organic carbon content, with a 33.3% increase in total nitrogen content at the end of composting. All the gases (CH4, CO2, N2O and NH3) yielded a common emission pattern despite the differences in moisture content. Except for CH4, the peak and stable emission periods of all the gases were observed on the 5th day (thermophilic phase) and after the 27th day (late mesophilic phase) of composting, respectively. Emission reductions of 89%, 91%, 95% and 100% were recorded for CH4, CO2, N2O and NH3, respectively, during the late mesophilic phase of composting. From the study, the 65% moisture content was efficient in reducing the loss rate of the gasses and nutrient contents of the compost. This study would enable farmers to channel organic residues generated into compost while minimizing pollution and nutrient losses associated with the composting process.

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Isatis indigotica planting is the backbone of the medicinal industry in Hexi Oasis, Gansu. In order to solve the problems insufficient water resources and excessive application of nitrogen fertilizer in this area, this paper explored the irrigation and nitrogen levels that can meet the multiple goals of Isatis indigotica. The two-factor split-plot field experiment (2018‒2019) was conducted in Minle County, Gansu Province, China, which contains 9 treatments. There were three levels of irrigation water: W1(low), W2(medium), and W3(high). The soil moisture contents were 60–70%, 70–80%, and 80–90% of the field water-holding capacity, respectively. The nitrogen application rate was classified into three levels, N1(low), N2(medium) and N3(high), which were 150, 200 and 250 kg N/ha, respectively. The standard local irrigation water amount and nitrogen application rate corresponded to W3N3. The results showed that the yield of Isatis indigotica increased first and then decreased with the increase of irrigation amount and nitrogen application rate, the yield of W2N2 is 12.2–17.1% higher than that of W1N1, the yield of W3N3 was 12.1–17.5% lower than that of W2N2. Saving water and reducing nitrogen can improve the quality of Isatis indigotica, compared with W3N3, the indigo, indirubin, (R,S)-epigoitrin and polysaccharides of W2N2 increased by 4.5–5.9%, 2.7–3.1%, 5.2–6.0%, and 1.8–2.1%, respectively. With the increase of nitrogen application rate, the water use efficiency (WUE) first increased and then decreased, as the irrigation volume increases, WUE decreases. Compared with W3N3, the WUE of W2N2 increased by 24.3–27.2%. With the increase of water input, the nitrogen fertilizer use efficiency (NUE) first increased and then decreased, as the nitrogen application rate increases, NUE decreases. Compared with W3N3, the NUE of W2W2 increased by 31.8–34.5%. Therefore, W2N2 can improve quality and increase water and nitrogen utilization efficiency on the basis of ensuring yield.