The improvement of SOC sequestration mediated by soil structure in the greenhouse vegetable soil converted from paddy field

Objective of investigation: Land use conversion strongly alters soil structure and substantially affects soil organic carbon (SOC) sequestration. Changing from an anaerobic paddy field (PF) to a dry land easily causes SOC loss due to stimulation of C decomposition. However, no evidence of SOC loss from PF to intensive vegetable cultivation has been certainly presented. Experimental material: This study was conducted on the long-term cultivated open-field vegetable (OFV) and greenhouse vegetable (GHV) planting area converted from old PF in China. Undisturbed soil cores, natural structured soil, and disturbed soil from top soil layers were using for further analyses. Methods of investigation: To comprehensively investigate SOC and soil structure change in the land use conversion of PF to OFV and PF to GHV, we used 13C-CPMAS NMR spectroscopy to classify the SOC fractions. The soil macropores (> 50 μm) was valued by X-ray computed tomography, and soil aggregates distribution was determined by wet sieving method. Data collection: Data were obtained from the above-mentioned measurements and statistically analyzed in R. Results: The result showed that the SOC stock increased 1-fold from PF to GHV. SOC stability increased with recalcitrant C (aromatic-C and carbonyl-C) raised by 21 %–27 % in GHV bulk soil. Both macropores and macroaggregates (> 250 μm) increased in GHV, accompanied by an accumulation of recalcitrant C in large macroaggregates. Conclusions: we confirmed the expanded GHV cultivation sequestered more belowground SOC than PF, associated with the amplified physical protection by enhancing soil aggregation and by redistributing of soil macropores.

Principles of Irrigation Management for Vegetables

Vegetables have a very high percentage of water content. Some of the vegetables, such as cucumber, tomato, lettuce, zucchini, and celery contain over ninety-five percent of water. As a result of the high-water content in the cells, they are extremely vulnerable plants to water stress and drought conditions. Their yield and quality are affected rapidly when subjected to drought. Therefore, irrigation is essential to the production of most vegetables in order to have an adequate yield with high quality. However, over-irrigating can inhibit germination and root development, decrease the vegetable quality and post-harvest life of the crop. Determination of suitable irrigation systems and scheduling to apply proper amount of water at the correct time is crucial for achieving the optimum benefits from irrigation. This determination requires understanding of the water demand of the vegetable, soil characteristics, and climate factors. All these factors have major impact for the success and sustainability of any vegetable irrigation. This section contains fundamentals of water requirements on different vegetables and summarizes important issues related to soil, water, and vegetable growth relations together with irrigation management concept by evaluating the challenging issues on the selection of proper irrigation system, suitable irrigation timing, and other parameters to increase vegetable yield in an irrigated agriculture.

Analysis of the Distribution Characteristics of Antibiotic Resistance Gene Pollution and Related Moving Factors in the Main Facility Agricultural Soils in Liaoning Province

To understand the distribution characteristics of antibiotic resistance genes (ARGs) and mobile genetic elements (MGEs) in vegetable soil in the main facility agriculture distribution centres of Liaoning Province, 13 soil samples from seven sites including Chaoyang Yandu Xincheng, Zhuanghe, and Fushun were collected to detect the species and abundance of ARGs and MGEs, and analyse their correlation. The results showed that the ARGs were mainly tetracycline and macrolide antibiotic resistance genes, the transportable elements were transposases, and the cell protection and cell discharge pump was the main resistance mechanism. The detection rate of tetm-02, oprj, sul2, blaTEM, fox5, ermX, ermB, and ermF was 100%. The detection rate of integron IntΙ-1 and transposable enzyme tnpA-01 was 100%. The highest content of antibiotic resistance genes was found in Qiandangpu Village, Daying Town, and Zhuanghe City, followed by Wutun Village, Miaojia Village, Daying Town, and Dalian. Correlation analysis showed a correlation between the abundance of ARGs and the abundance of MGEs in agricultural soil. There was a significant positive correlation between the abundance of ARGs and integron (P < 0.05). The results of this study provide data support for the assessment of soil ARG pollution levels and the effective prevention and control of ARG transmission risk in the main protected vegetable fields in Liaoning Province.

Effects of Different Land-use Types on Active Autotrophic Ammonia and Nitrite Oxidizers in Cinnamon Soils

Land-use types with different disturbance gradients show many variations in soil properties, but the effects of different land-use types on soil nitrifying communities and their ecological implications remain poorly understood. Using 13CO2-DNA-based stable isotope probing (DNA-SIP), we examined the relative importance and active community composition of ammonia-oxidizing archaea (AOA) and bacteria (AOB), and nitrite-oxidizing bacteria (NOB) in soils under three land-use types, forest, cropland, and greenhouse vegetable soil, representing three interference gradients. Soil net nitrification rate was in the order forest soil > cropland soil > greenhouse vegetable soil. DNA-SIP showed that active AOA outcompeted AOB in the forest soil, whereas AOB outperformed AOA in the cropland and greenhouse vegetable soils. Cropland soil was richer in NOB than in AOA and AOB. Phylogenetic analysis revealed that ammonia oxidation in the forest soil was predominantly catalyzed by the AOA Nitrosocosmicus franklandus cluster within the group 1.1b lineage. The 13C-labeled AOB were overwhelmingly dominated by Nitrosospira cluster 3 in the cropland soil. The active AOB Nitrosococcus watsonii lineage was observed in the greenhouse vegetable soil, and it played an important role in nitrification. Active NOB communities were closely affiliated with Nitrospira in the forest and cropland soils, and with Nitrolancea and Nitrococcus in the greenhouse vegetable soil. Canonical correlation analysis showed that soil pH and organic matter content significantly affected the active nitrifier community composition. These results suggest that land-use types with different disturbance gradients alter the distribution of active nitrifier communities by affecting soil physicochemical properties. IMPORTANCE Nitrification plays an important role in the soil N cycle, and land-use management has a profound effect on soil nitrifiers. It is unclear how different gradients of land use affect active ammonia-oxidizing archaea and bacteria and nitrite-oxidizing bacteria. Our research is significant because we determined the response of nitrifiers to human disturbance, which will greatly improve our understanding of the niche of nitrifiers and the differences in their physiology.