Contrasting development of soil microbial community structure under no-tilled perennial and tilled cropping during early pedogenesis of a Mollisol

A range of agricultural practices influence soil microbial communities, such as tillage and organic C inputs, however such effects are largely unknown at the initial stage of soil formation. Using an eight-year field experiment established on exposed parent material (PM) of a Mollisol, our objectives were to: (1) to determine the effects of field management and soil depth on soil microbial community structure; (2) to elucidate shifts in microbial community structure in relation to PM, compared to an arable Mollisol (MO) without organic amendment; and (3) to identify the controlling factors of such changes in microbial community structure. The treatments included two no-tilled soils supporting perennial crops, and four tilled soils under the same cropping system, with or without chemical fertilization and crop residue amendment. Principal component (PC) analysis of phospholipid fatty acid (PLFA) profiles demonstrated that microbial community structures were affected by tillage and/or organic and inorganic inputs via PC1 and by land use and/or soil depth via PC2. All the field treatments were separated by PM into two groups via PC1, the tilled and the no-tilled soils, with the tilled soils more developed towards MO. The tilled soils were separated with respect to MO via PC1 associated with the differences in mineral fertilization and the quality of organic amendments, with the soils without organic amendment being more similar to MO. The separations via PC1 were principally driven by bacteria and associated with soil pH and soil C, N and P. The separations via PC2 were driven by fungi, actinomycetes and Gram (−) bacteria, and associated with soil bulk density. The separations via both PC1 and PC2 were associated with soil aggregate stability and exchangeable K, indicating the effects of weathering and soil aggregation. The results suggest that in spite of the importance of mineral fertilization and organic amendments, tillage and land-use type play a significant role in determining the nature of the development of associated soil microbial community structures at the initial stages of soil formation.     

Azospirillum brasilense mitigates water stress imposed by a vascular disease by increasing xylem vessel area and stem hydraulic conductivity in tomato

Water stress, with its negative consequences on plant growth and survival, can be mitigated by Azospirillum brasilense inoculation. In tomato, A. brasilense delays wilting caused by a vascular pathogen, Clavibacter michiganensis subsp. michiganensis, by yet unknown mechanisms. We studied morphological, anatomical and physiological changes induced by A. brasilense in tomato that relate to water stress tolerance, which could explain the deferral in symptom expression. For this purpose, tomato seeds were treated or not with A. brasilense BNM65, and 5 weeks later plants were challenged with C. michiganensis subsp. michiganensis or mock inoculated with water. There was a large growth promotion associated to Azospirillum: treated plants had higher total biomass and leaf area. In relation to water stress tolerance, Azospirillum treated plants had larger xylem vessel area, higher stem specific hydraulic conductivity, thicker stems, and lower shoot/root dry matter and specific leaf area. These changes were opposite to those induced by C. michiganensis subsp. michiganensis. We conclude that A. brasilense favoured a better adjustment of plant-water relations by several mechanisms, and thus, transitorily alleviated symptoms expression of a vascular disease.     

Legume–barley intercropping stimulates soil N supply and crop yield in the succeeding durum wheat in a rotation under rainfed conditions

Legume–cereal intercropping is increasingly being appreciated in dryland areas, where severe climatic conditions and intensive agricultural practices, generally dominated by continuous cereal cultivation, determine depletion of soil nutrient resources and decline of soil fertility. This research aimed to assess whether and to what extent a newly introduced legume-based intercropping system is able to ameliorate the biological fertility status of an arable soil in a way that is still noticeable during the succeeding durum wheat cropping season in terms of changes in bacterial community structure, soil C and N pools, and crop yield. A field experiment was carried out under rainfed conditions in Southern Italy on a sandy clay loam soil cultivated with durum wheat following in the rotation a recently established grain legume (pea, faba bean)–barley intercropping. Soil chemical, biochemical and eco-physiological variables together with compositional shifts in the bacterial community structure by LH-PCR fingerprinting were determined at four sampling times during the durum wheat cropping season. Soil fertility was estimated by using a revised version of the biological fertility index. Results showed that even though the microbial biomass was significantly altered, the preceding legume intercrops stimulated C-related functional variables thus leading to an increased release of mineral N, which was larger in crop treatments succeeding pea-based than faba bean-based intercropping. The increased N made available in soil enabled the succeeding durum wheat to achieve an adequate grain yield with a reduced N-fertilizer use. Soil type and environmental conditions rather than crop treatments were major determinants of bacterial community structure. The biological fertility status was not varied, suggesting that in intensively managed rainfed areas long-term crop rotations with intercropped legumes are needed to consistently ameliorate it.     

Agronomic and physiological contributions to the yield improvement of soybean cultivars released from 1950 to 2006 in Northeast China

Increasing yield is a high priority in most breeding programs. Approximately 600 soybean cultivars had been released by the end of the last century in Northeast China. Understanding the agronomic and physiological changes is essential for planning further plant breeding strategies in soybean. In this study, 45 representative soybean cultivars, from maturity groups 00 and 0, released from 1950 to 2006 in Northeast China were compared in field conditions for 3 consecutive years. A positive correlation between seed yield and year of cultivar release was indicated with a 0.58% average annual increase. Seed number per plant was the most important contributor to yield gain, with a 0.41% increase per year. Pod number per plant and seed size varied slightly with the year of cultivar release. Although variation in protein was from 37.0% to 45.5%, and oil concentration was from 16.7% to 22.0%, their concentrations were not consistently related to year of cultivar release. A 33% increase in the photosynthetic rate, 10.6% increase in plant dry weight and 19.0% increase in harvest index (HI) were found, while leaf area index (LAI) decreased by 17.3%. Modern cultivars have higher photosynthetic rates than their predecessors. The reduced plant height gave increased resistance to lodging, with the lodging score dropping from 3.2 in 1951 to 1.0 in 2006. Seed resistances to disease and pest infestation were also improved. Yield stability was enhanced over years, which could be attributed to the stable pod production across different environments. A flow diagram to explain the contributors to genetic improvement of soybeans in Northeast China was developed.     

Surrounding pressure controlled by water table alters CO2 and CH4 fluxes in the littoral zone of a brackish-water lake

We studied the effect of water table on CO₂ and CH₄ fluxes at different time scales in the littoral zone of Lake Obuchi, a brackish lake in northern Japan. The vegetation formed three distinct zones along the water table gradient, two dominated by emergent aquatic macrophytes (the Phragmites australis-dominated zone and the Juncus yokoscensis-dominated zone) and one dominated by terrestrial macrophytes (Miscanthus sinensis and Cirsium inundatum-dominated zone). To clarify the impact of variations in water table on monthly and yearly summed CO₂ and CH₄ fluxes, we examined the relationship between water table and the ratio of observed flux to calculated flux, whereby the calculated flux was based solely on the exponential relationship between flux and soil temperature for each gas. This study revealed that the impact of variations in water table on monthly and yearly summed CO₂ and CH₄ fluxes differed markedly between the vegetation zones. By taking the temporal change in water table into account in the estimation of both the CO₂ and CH₄ fluxes, the monthly summed CO₂ and CH₄ fluxes in the Phragmites-zone were markedly greater in every month of the year compared to estimation based on temperature alone. In the Juncus-zone, the effect of water table on monthly summed CO₂ and CH₄ fluxes differed between months. In addition, the magnitude of water-table effects controlling monthly summed CO₂ and CH₄ fluxes differed with atmospheric conditions, i.e., between the pressure-falling and low-pressure phase on the one hand and other pressure phases on the other hand. After weighting all the impacts of temporal changes in water table on fluxes, the yearly summed CO₂ and CH₄ fluxes showed a 1.26–6.64-fold increase compared with not taking water table effects into account, and the increase differed among the three vegetation zones.     

Improved guayule lines outperform old lines in south-east Queensland

Guayule (Parthenium argentatum Gray) is a source of high quality rubber and low-allergenic latex as well as resin for use as a wood preservative. Demand for high value latex products has increased with the advent of deadly diseases such as AIDS. The objective of this study was to evaluate the performance of six improved guayule lines (AZ-1 to AZ-6) in south-east Queensland: released jointly by the Agricultural Research Service (ARS) of the United States Department of Agriculture (USDA) and The University of Arizona. Trials were conducted at two sites, Chinchilla and Gatton. Overall performance of improved lines for plant growth and yield of dry matter, rubber and resin was better at both Gatton and Chinchilla than the standard check lines (N 565 and 11591). AZ-1 and AZ-2 maintained the best combinations of desirable traits, including plant uniformity, early vigorous growth, increased dry matter, and increased rubber and resin yields. Of these two, AZ-2 had more uniform plant growth and has commercial potential for Queensland production areas. In the summer harvest at Gatton, 32-month-old AZ-1 and AZ-2 produced rubber yields of 789 kg/ha and 771 kg/ha, respectively, while controls, N 565 and 11591 produced 675 kg/ha and 618 kg/ha, respectively. At Chinchilla, at 33 months, spring harvested AZ-1 and AZ-2 produced rubber yields of 717 kg/ha and 787 kg/ha; these yields were significantly higher than N 565 and 11591 which produced 385 kg/ha and 380 kg/ha, respectively. Thus, rubber yields of AZ-1 and AZ-2 were consistently high across sites. AZ-1 and AZ-2 produced resin yields of 1158 kg/ha and 1115 kg/ha at Gatton and 1318 kg/ha and 1476 kg/ha at Chinchilla. This compared with a mean of 612 kg/ha and 352 kg/ha for the standard check lines at Gatton and Chinchilla. Thus resin yields of AZ-1 and AZ-2 were consistently high across sites. Rubber content appeared to be influenced by time of harvest although this effect is compounded with plant age. At Gatton, in spring, 17-month-old plants produced a mean rubber content of 7.7% (all lines), while, in summer, when the plants were 32-month-olds, rubber content dropped to 6.4%. At Chinchilla, 33-month-old plants harvested in spring produced a mean rubber content of 7.4%, similar to the spring value at Gatton. By contrast, resin content appeared to be little affected by season.     

免疫单扩散法检测牛初乳IgG含量方法改良及牛初乳样品的检测

采用改良后的琼脂免疫单扩散法检测本地荷斯坦奶牛产后7d的初乳样品中IgG含量。结果表明，母牛产犊后7d内。乳汁中IgG含量变化很大，变动范围为118．59～0．86mg／mL。每次挤乳IgG含量下降都很快，特别是前三次挤乳，每次IgG浓度下降率近50％；到第8次，已经降到10mg／mL以下。所以生产乳制品应以前7次挤出的初乳为原料最佳，若笼统地以3d、5d或7d内初乳为原料，产品中IgG含量不仅低，而且每批次差异很大。     

人工湿地去除畜禽养殖废水污染物研究进展

为研究人工湿地在畜禽养殖废水中处理污染物的现状,以“人工湿地”、“畜禽养殖废水或污水”、“畜禽养殖污染”、“营养物质”、“重金属”、“抗生素”和“抗生素基因”等为关键词,搜索ISI web of knowledge、SpringerLink、中国知网、万方数据库等数据库,对2007—2020年发表的相关文献进行归纳和分析。结果表明:1)人工湿地能有效去除畜禽养殖废水中营养物质、重金属、抗生素及ARGs等;2)人工湿地在畜禽养殖废水中的应用尚处于发展阶段,且具有较可观的应用前景,但其去除污染物的机理仍需要深入探;3)研究发现人工湿地综合去除畜禽养殖废水中的污染物能力以及评价人工湿地运行效能是今后的研究发展方向。本研究可为人工湿地处理畜禽养殖废水提供理论参考。     

Response of soil micro- and mesofauna to diversity and quality of plant litter

The abundance and functional structure of soil micro- (nematodes) and mesofauna (collembolans and mites) in relation to species diversity and initial C:N ratio of plant litter were studied in a field mesocosm experiment. A total of five litter treatments were applied to generate an increasing diversity of plant species (one, three and 12 species) and/or differences in initial C:N ratio of the litter (low, intermediate and high ratio). Samples were taken 3, 6 and 24 months after the litter exposure. On each sampling date litter and underlying sand samples were taken. Our results showed that litter quality, but not litter diversity was the factor which affected the three animal groups under study. The effect of litter was dependent on the time of litter exposure. Nematode fauna colonized litter earlier than the two mesofaunal groups. Nematodes responded apparently to litter quality gradient at early stages of litter decomposition. Three months after the start of the experiment the highest density of nematodes was noticed in single species litter of Trifolium pratense. Bacterial-feeding nematodes dominated in all litter treatments; on the first sampling date their percent share in Trifolium litter reached even 99.9%. Opposite to nematodes at late stages of litter decomposition the two mesofaunal groups seemed to show some preferences for low quality litter of Festuca rubra. Collembolan and nematode diversity was affected in similar way by the litter quality; the lowest diversity of the animal communities was found in the litter of the lowest initial C:N ratio. Maturity index of nematode communities was found to be a good index to differentiate between litters of different quality. The abundance and community structure of the three animal groups in underlying sandy soil was not significantly influenced by experimental conditions.