微生物素在果蔬采后保鲜中的应用进展

微生物素在果蔬采后保鲜中有重要的应用价值,但目前实际应用在果蔬采后保鲜领域中的并不多。本文分析了目前已经应用到果蔬保鲜领域的微生物素种类,有乳酸链球菌肽、溶菌酶、木霉发酵液等,分析了其抑菌保鲜原理及研究现状;并结合微生物素的特点,提出了微生物素在未来果蔬采后保鲜中的发展趋势,即面对冷藏技术使用不完善的现象,可以开发利用更多的微生物素种类,如纳他霉素、红曲霉素、短梗霉多糖等,为今后果蔬采后保鲜领域的健康可持续发展提供参考。     

Positionality and protocol in field research: Undertaking community‐based investigations in Samoa

This article considers the experiences of a Samoan female geographer undertaking community‐based field research in her home country, and identifies some lessons for researchers working in similar circumstances. The paper suggests that ethical behaviour in research is ‘place‐specific’, and there is therefore a need to employ culturally sensitive and ‘location‐specific’ methodologies when undertaking community‐based research fieldwork. For the lead researcher, growing up in Samoa played a significant role in gaining an understanding of a set of robust and effective procedures to evaluate citizens' resilience to climatic and other environmental challenges. Fluency in everyday and more formal local languages, and awareness of local differences, each with multi‐layered connections to local communities, understanding cultural nuances and practising respect for va tapuia [sacred space or relationships] protocols, together facilitated the process of knowledge acquisition and helped to confirm the validity of the conclusions derived from the study.     

长期少免耕对中国东北玉米农田土壤呼吸及碳氮变化的影响

在黑土区37年不同耕作模式定位试验田，采用原位法比较常规旋耕灭茬起垄（CT）、旋耕留高茬行间深松-少耕（RT）、免耕（NT）和深翻（PT）4种耕作模式土壤呼吸速率及其与土壤温度和湿度的关系，测定土壤总碳氮、无机氮，微生物碳氮的变化。结果表明，玉米生育期间土壤呼吸呈单峰变化，开花期达最大值，生长季平均呼吸速率依次为RT > NT > CT > PT。4个处理土壤温度与土壤呼吸速率间存在显著指数关系。不同耕作模式0~10 cm土壤温度可解释土壤呼吸速率变异的38.3%~67.9%，温度敏感性系数Q10范围为2.1~5.3；RT和NT处理显著提高0~20 cm土壤碳氮含量；RT处理在0~20 cm土壤中微生物碳含量均高于CT、NT和PT处理。RT处理土壤呼吸对温度响应提高，RT和NT处理显著增加上层土壤总碳氮含量，利于土壤质量提升。     

基于高通量测序技术分析2种菌草根际土壤真菌群落多样性

为了解福州菌草基地巨菌草和绿洲一号2种菌草的根际土壤真菌群落多样性,采用Illumina Miseq高通量测序技术和生物信息学方法,对菌草根际土真菌的多样性及群落结构进行分析。结果表明：从3份土壤样本中获得525 292条ITS序列,在97%序列相似性基础上可划分为7267个可操作分类单元（OTU）。真菌群落的丰富度指数（ACE）以菌草非根际土最低,绿洲一号根际土略高于巨菌草根际土;而多样性指数（Shannon-Wiener和Simpson）菌草根际土高于非根际土,绿洲一号根际土略高于巨菌草根际土。3份样品的优势菌门为子囊菌门（Ascomycota）、担子菌门（Basidiomycota）、接合菌门（Zygomycota）、壶菌门（Chytridiomycota）、球囊菌门（Glomeromycota）;优势菌纲为散囊菌纲（Eurotiomycetes）、粪壳菌纲（ Sordariomycetes）、座囊菌纲（Dothideomycetes）、伞菌纲（Agaricomycetes）、锤舌菌纲（Leotiomycetes）、圆盘菌纲（Orbiliomycetes）、银耳纲（Tremellomycetes）、粘膜菌纲（Wallemiomycetes）;优势菌属为篮状菌属（Talaromyces）、深黄伞形霉属（Umbelopsis）、枝孢菌属（Cladosporium）、暗双孢菌属（Cordana）、镰刀菌属（Fusarium）、隐球菌属（Cryptococcus）、淡紫紫霉属（Purpureocillium）、赤霉菌属 （Gibberella）、灵芝属（Ganoderma）。研究结果表明,菌草根际土真菌群落多样性高于非根际土,为进一步更好地利用菌草提供理论参考依据。     

间作栽培对宁夏南部山区马铃薯根际土壤真菌菌群结构的影响

根据宁夏南部山区气候和作物的生长特点，设计马铃薯‖玉米（P‖M，行比分别为4∶1，3∶2， 2∶3）、马铃薯‖蚕豆（P‖F，行比同前）、马铃薯不同品种（A‖B‖C，行比1∶1∶1）间作栽培模式，以马铃薯连作为对照，研究马铃薯根际土壤真菌多样性和菌群结构的变化，探寻能够减轻宁夏南部山区马铃薯连作障碍的有效栽培模式。采用基于18S rDNA的末端标记限制性片段长度多态性 (Terminal restriction fragment length polymorphism，T-RFLP) 技术研究不同间作栽培模式下马铃薯根际土壤真菌的菌群结构和多样性变化，构建真菌ITS克隆文库，利用Genbank数据库比对各栽培模式中ITS序列的测序结果，并作群落结构组成和功能分析。结果表明，马铃薯间作栽培后真菌Shannon-Wiener指数和Simpson指数均有不同程度降低；马铃薯与玉米、蚕豆间作后根际土壤真菌的物种丰富度在门、纲和目的分类学水平上与连作相比明显下降，菌群结构发生较大变化，成熟期马铃薯‖玉米3∶2行比间作模式与连作的差异最大，属的比例下降67.74%。间作栽培后，黑孢属（Nigrospora）、地丝霉属（Geomyces）、圆盘菌属（Orbilia）、枝顶孢属（Acremonium）、四枝孢属（Tetracladium）等9个属的真菌消失，同时新增刺盘孢属（Colletotrichum）、毛壳属（Chaetomium）、巨孢囊霉属（Gigaspora）、小球腔菌属（Pleosporineae）等13个属的真菌，其中马铃薯‖玉米3∶2行比间作后巨孢囊霉属比例高达60.35%。可见，马铃薯‖玉米间作栽培能有效改善马铃薯根际土壤的真菌菌群结构，使其微环境得以改善，缓解宁夏南部山区马铃薯连作障碍。     

Identification of culturable microbial functional groups isolated from the rhizosphere of four species of mangroves and their biotechnological potential

This study identified microbial functional groups like total culturable bacteria, potential N₂-fixing free living bacteria, N₂-fixing hydrocarbonoclastic bacteria, N-assimilating hydrocarbonoclastic bacteria, total fungi, actinobacteria, P-solubilizers, lipolytic microorganisms, and starch, cellulose, pectin and protein degrading microorganisms, isolated from the rhizosphere of four species of mangroves (Red, Black, White, and Button) from the natural protected area at the Terminos Lagoon, Campeche, México. Overall, microbial populations showed significant differences (P < 0.05) among the four mangrove species. The rhizosphere of White mangrove showed better chemical and textural soil properties, and harbored the highest microbial populations when compared to the remaining mangrove species. The principal component analysis indicated that two components accounted the 85.3% of the total variation. The most significant textural and chemical soil properties were the major components, CP1 (organic matter and total organic carbon) and CP2 (sand and clay). Microbial populations correlated (P < 0.05, Pearson coefficient) with sand and clay particles, and with some soil chemical properties such as organic matter. The total nitrogen and organic carbon significantly correlated with cellulose degraders, while phosphorus with N₂-fixing bacteria, total fungi, and with pectin and starch degraders.     

Artificial neural network modeling of microbial community structures in the Atlantic Forest of Brazil

Microbial communities vary across the landscape in forest soils, but prediction of their biomass and composition is a difficult challenge due to the large numbers of variables that influence their community structures. Here we examine the use of artificial neural network (ANN) models for extraction of patterns among soil chemical variables and microbial community structures in forest soils from three regions of the Atlantic Forest of Brazil. At each location, variations in soil chemical properties and FAME profiles of microbial community structures were mapped at 20 × 20 m intervals within 10 ha parcels. Geostatistical analyses showed that spatial variability in soil physical and chemical variables could be mapped at scale distances of 20 m, but that FAME profiles representing the microbial communities were highly variable and had no spatial dependence at the same scale in most cases. RDA analysis showed that FAME signatures representing different microbial groups were positively associated with soil pH, OM, P and base cations concentrations, whereas microbial biomass was negatively associated with the same environmental factors. In contrast, ANN models revealed clear relationships between microbial community structures at each parcel location, and generated verifiable predictions of variations in FAME profiles in relation to soil pH, texture, and the relative abundances of base cations. The results suggest that ANN modeling provides a useful approach for describing the relationships between microbial community structures and soil properties in tropical forest soils that were not able to be captured using geostatistical and RDA analyses.     

High clay content accelerates the decomposition of fresh organic matter in artificial soils

Clay is generally considered an important stabiliser that reduces the rate of decomposition of organic matter (OM) in soils. However, several recent studies have shown trends contradicting this widely held view, emphasising our poor understanding of the mechanisms underlying the clay effects on OM decomposition. Here, an incubation experiment was conducted using artificial soils differing in clay content (0, 5, and 50%) at different temperatures (5, 15, and 25 °C) to determine the effects of clay content, temperature and their interaction on fresh OM decomposition. CO₂ efflux was measured throughout the experiment. Phospholipid fatty acids (PLFAs), enzyme activities, microbial biomass carbon (MBC), and dissolved organic carbon (DOC) were also measured at the end of the pre-incubation and incubation periods in order to follow changes in microbial community structure, functioning, and substrate availability. The results showed that higher clay contents promoted OM decomposition probably by increasing substrate availability and by sustaining a greater microbial biomass, albeit with a different community structure and with higher activities of most of the extracellular enzymes assayed. Higher clay content induced increases in the PLFA contents of all bacterial functional groups relative to fungal PLFA content. However, clay content did not change the temperature sensitivity (Q₁₀) of OM decomposition. The higher substrate availability in the high clay artificial soils sustained more soil microbial biomass, resulting in a different community structure and different functioning. The higher microbial biomass, as well as the changed community structure and functions, accelerated OM decomposition. From these observations, an alternative pathway to understanding the effects of clay on OM decomposition is proposed, in which clay may not only accelerate the decomposition of organic materials in soils but also facilitate the SOM accumulation as microbial products in the long term. Our results highlight the importance of clay content as a control over OM decomposition and greater attention is required to elucidate the underlying mechanisms.     

Variations in soil chemical properties and microbial biomass in artificial gaps in silver fir stands

Changes in soil chemical and microbiological parameters in small (185 m²) and medium (410 m²) gaps, created in mature silver fir (Abies alba Mill) stands (mean height 30 m) in the Calabrian Apennines (Southern Italy), were studied over 2 years. Medium gaps had high soil temperature and photosynthetically active radiation (PAR) transmittance and low soil moisture. Within small gaps we detected a greater amount of organic matter, with respect to under canopy cover sites and medium gaps. Moreover, a different trend of the organic matter between small and medium gaps was observed. In the medium gaps, with respect to under canopy cover sites and small gaps, we found a relatively low content of organic matter, associated to a lower amount of humic acid, which suggested that the organic substrate undergoes a mineralization rather than a humification process. An opposite trend was observed in small gaps, where the increase of organic matter content, associated to an increase of humic acid and microbial biomass, suggested a better humification process. Moreover, in small gaps the highest level of urease and the greatest fluorescein diacetate (FDA) hydrolysis were observed. The different trend of organic matter observed in small and medium gaps may be related to changes in the environmental conditions. PAR transmittance, significantly higher in medium gaps, contributed to increase soil temperature and decrease soil moisture, affecting soil microbial populations and organic matter trend. These results suggest that the creation of small gaps represents the silvicultural practice with minor environmental impact.     

不同植被恢复模式土壤结构特征与健康评价

对湘西女儿寨流域不同植被恢复类型的土壤结构特征研究和健康评价的结果表明:荒草灌丛容重最高,人工林土壤容重高于天然林及混交林;对土壤孔隙状况的改善作用表现为林分类型优于荒草灌丛类型,天然林优于人工林,0~20 cm土层优于20~40 cm土层;土壤团聚体平均重量直径以油桐人工林、杜仲人工林最高,马尾松天然林、毛竹杉木混交林其次,而润楠次生林、荒草灌丛、杉木人工林较低;各层土壤团聚体分形维数值大小排序为:毛竹杉木混交林>马尾松天然林>荒草灌丛、润楠次生林>杜仲人工林>油桐人工林>杉木人工林;土壤结构健康综合评价的灰色关联分析结果表明,土壤结构以荒草灌丛最差,油桐人工林最好,其余类型介于两者之间.研究结果可为女儿寨流域及我国类似生态脆弱区的植被恢复与重建提供一定依据和参考.