Effect of arbuscular mycorrhizal fungi, organic fertilizer and soil sterilization on maize growth ☆

The effects of inoculation with arbuscular mycorrhizal (AM) fungi, organic fertilizer (F) applications, and soil sterilization on maize growth were evaluated in a pot experiment. The experiment was in a completely randomized factorial design (2 × 4 × 2) with six replicates for each treatment. There were two soil treatments (sterilized soil, SS and unsterilized soil, US), four organic fertilizer treatments (0.0, 0.5, 1.0 and 2.0 g kg^-1 soil), and two AM fungi treatments (inoculation with Glomus mosseae, +AM and uninoculated control, －AM). Inoculated plants generally had greater AM colonization, plant height, dry weight and phosphorus (P) uptake than uninoculated controls, and these parameters were significantly increased as the organic fertilizer application increased up to 0.5 g kg^-1 but decreased or had no significant effect compared to the uninoculated plants at the highest fertilizer rate (2.0 g kg^-1). Plant growth, P uptake and AM colonization of root system were significantly higher in sterilized soil compared to the unsterilized control. Our results indicated that the inoculation of AM fungi in field soil with optimal organic fertilizer application greatly improved maize growth and nutrient uptake, and the effect was greater under sterilized soil condition.     

丛枝菌根真菌在田间的分布特征、代谢活性及其对甘薯生长的影响

研究了大田条件下丛枝菌根(AM)真菌的分布特征、代谢活性及其对甘薯的生长效应.结果表明,接种Glomus intraradices 8周后,甘薯地上部干重,薯块鲜重和薯块个数均明显高于不接种对照;植株地上部和根系的吸磷量显著提高.与不接种对照相比,接种处理的甘薯菌根侵染率、甘薯根外菌丝密度以及甘薯根内菌丝的活性(根内菌丝碱性磷酸酶活性)显著提高.进一步分析甘薯根际不同方位上的菌丝分布,发现接种处理中平行于垄的方向的菌丝密度显著高于苗子下方的菌丝密度,而不接种处理的各个方向总菌丝密度无差异;活菌丝(具琥珀酸脱氢酶活性的菌丝)密度在各个方向的分布规律与总菌丝密度的分布规律一致.接种后根内菌丝活性的增强,根外活性菌丝密度的增加及其分布特征的改变,是甘薯产量增加的主要原因.     

Density of founder cells affects spatial pattern formation and cooperation in Bacillus subtilis biofilms

In nature, most bacteria live in surface-attached sedentary communities known as biofilms. Biofilms are often studied with respect to bacterial interactions. Many cells inhabiting biofilms are assumed to express ‘cooperative traits'', like the secretion of extracellular polysaccharides (EPS). These traits can enhance biofilm-related properties, such as stress resilience or colony expansion, while being costly to the cells that express them. In well-mixed populations cooperation is difficult to achieve, because non-cooperative individuals can reap the benefits of cooperation without having to pay the costs. The physical process of biofilm growth can, however, result in the spatial segregation of cooperative from non-cooperative individuals. This segregation can prevent non-cooperative cells from exploiting cooperative neighbors. Here we examine the interaction between spatial pattern formation and cooperation in Bacillus subtilis biofilms. We show, experimentally and by mathematical modeling, that the density of cells at the onset of biofilm growth affects pattern formation during biofilm growth. At low initial cell densities, co-cultured strains strongly segregate in space, whereas spatial segregation does not occur at high initial cell densities. As a consequence, EPS-producing cells have a competitive advantage over non-cooperative mutants when biofilms are initiated at a low density of founder cells, whereas EPS-deficient cells have an advantage at high cell densities. These results underline the importance of spatial pattern formation for competition among bacterial strains and the evolution of microbial cooperation.     

Charting the course of reed‐warblers across the Pacific islands

Aim Deciphering the complex colonization history of island archipelagos is greatly facilitated by comprehensive phylogenies. In this study we investigate the phylogeny and biogeography of the insular reed‐warblers (genus Acrocephalus) of the tropical Pacific Ocean, from Australia to eastern Polynesia. Location Oceania. Methods We used sequences of mitochondrial DNA (cytochrome b, ND2 and ATP8 genes) to infer the colonization patterns of reed‐warblers endemic to Pacific islands and Australia. We sampled all known taxa of Acrocephalus in the Pacific except A. luscinius nijoi, for which no sample was available. Most taxa were represented by toe‐pad samples from museum specimens collected in the 19th and 20th centuries. With a few exceptions, several specimens per taxon were sequenced independently in two institutions (Smithsonian Institution and Natural History Museum of Geneva). Results Our data indicate that Pacific reed‐warblers do not form a monophyletic group, because A. luscinius luscinius from Guam falls outside the main Pacific radiation. The remaining Pacific taxa are divided into two clades: one clade includes all the reed‐warblers from Micronesia (except Guam) and Australia, and two Polynesian taxa from the Line Islands and the southern Marquesas; the other clade includes all remaining Polynesian taxa. The taxa endemic to three archipelagos (Mariana, Marquesas and Society islands) are polyphyletic, suggesting several independent colonizations. Main conclusions Our results provide evidence for a complex pattern of colonization of the Pacific by reed‐warblers. Calibration analyses suggest that reed‐warbler lineages are much younger than the ages of the islands they occupy. Several remote archipelagos were colonized independently more than once. Consequently, we infer that the colonization of reed‐warblers in the Pacific did not follow a regular, stepping‐stone‐like pattern. The phylogeny also suggests a previously undetected case of reverse colonization (from island to continent) for the Australian lineage and indicates that A. luscinius, as currently defined, is not monophyletic. We discuss the supertramp strategy of reed‐warblers in the Pacific and show that, although Pacific reed‐warblers meet some of the supertramp criteria in their aptitude for colonizing remote archipelagos, their life history characteristics do not fit the model.     

High haplotype diversity with fine-scale structure in a recently established population of an endangered orchid

New populations of endangered plants may establish outside of protected areas if a suitable habitat becomes available. However, it is unclear whether such populations are genetically uniform, as a result of a founder effect, or whether they contain genetic variation resulting from continuous gene flow from source populations, and subsequent recruitment after establishment. We addressed this by examining haplotype variation in the endangered orchid, Anacamptis robusta, which has formed a new population outside of its protected area within the past 20 years. To assess population growth, the number of A. robusta flowering plants were counted every year for 22 years in both the new population and populations within the reserve. Haplotype diversity and fine-scale structure were examined with spatial autocorrelation analysis, both in the new population and representative populations from the protected area. The number of flowering individuals in the new population increased from 9 to 2,277 between 2003 and 2012, whereas within the reserve flowering population sizes varied between years. Seventeen of 23 haplotypes detected for A. robusta were detected in the new population, with seven of these occurring more frequently in the new population than reserve populations. In the new population, there was strong fine-scale spatial structure of haplotypes, similar to patterns found in large populations from the protected area, suggesting multiple colonization events and subsequent local recruitment. This highlights that ongoing demographic and genetic monitoring of plant populations is vital to improve our understanding of population colonization and the conservation of narrow endemics.     

A comparative study of competitive ability between two cactophilic species in their natural hosts

Abstract Competition is a major aspect of the ecology of insect communities exploiting ephemeral and fragmented resources. We analysed the effect of intraspecific (single species culture) and interspecific (mixed species culture) competition on larval viability, developmental time and wing length in the cactophilic Drosophila buzzatii and Drosophila koepferae (Diptera: Drosophilidae) reared in cultured media prepared with fermenting tissues of three common natural cactus hosts in nature at different densities. Our results show that all traits measured were affected by both intra‐ and interspecifc competition, although the effect of competition depended on the Drosophila species and the rearing cactus. In fact, flies tended to have a lower viability, shorter wing size and longer developmental time as a function of increasing density in single species culture in both D. buzzatii and D. koepferae (intraespecific competition). Besides, the performance of both species was seriously affected (shorter body size, slower developmental times, lower viability) by the presence of heterospecific competitors except in the case of D. koepferae reared in its primary host plant, Trichocereus terschekii. We also show that D. koepferae successfully utilized Opuntia quimilo, which is absent in most parts of its distribution range. We discuss the roles of intra‐ and interspecific competition as determinants of the relative abundance of these two species in the arid zones of Southern South America.     

Diverse plant mixtures sustain a greater arbuscular mycorrhizal fungi spore viability than monocultures after 12 years

密集的土地管理可能损害土壤生物多样性,从而危害长期的土壤生产力。丛枝菌根真菌(AMF)通过与植物专一性的共生关系,在促进土壤生产力方面发挥着关键作用。然而,目前尚不清楚植物群落的性质,特别是植物物种丰富度和组成如何影响土壤中AMF种群的生存能力。本研究中,我们测试了来自不同植物功能类群的8种植物的单一栽培和不同植物的混合种植,是否可以维持更有活力的AMF繁殖体。为了回答这个问题,我们从12年的单种植物和混种植物中提取AMF孢子,并通过因子设计将单株AMF孢子与单株植物配对,并考察与AMF孢子来源和植物物种特性的交互作用。研究结果表明,不同植物混合种植的AMF孢子比单一栽培的AMF孢子更能成功地定植于多种植物和植株个体中。此外,我们还发现,来自不同混合种植的AMF孢子比来自单一栽培的AMF更能显著提高白车轴草(Trifolium repens L.)的生物量。 与单一栽培相比,起源于不同植物混合种植的AMF孢子的生存能力和与多种植物相互作用的能力更强。我们的研究结果首次表明,多样的植物群落可以维持土壤中AMF的活力,也证明了多样的植物群落有潜力维持AMF繁殖体的活力对土壤健康和生产力至关重要。     

L.sp.HXQ 001 菌在小鼠肠道定植的实验研究

研究Ｌ·ｓｐ．ＨＸＱ００１菌株对小鼠的有益作用。通过对口服该菌液使之定植于小鼠肠道,分离小鼠粪便、肠段匀浆中该菌菌落及作肠段切片ＨＥ染色,肠道的正常防御机制不能杀灭该菌,并能在小鼠肠道定植,且以结肠为主。该菌定植肠段有淋巴细胞浸润,但无变性坏死等变化,显示生理性炎症反应。Ｌ．ｓｐ．ＨＸＱ００１菌株不是小鼠肠道正常菌群但仍可定植于肠道、激发机体免疫应答。有望成为新的肠道微生态调节剂。     

海南两种红树林植物内生真菌的多样性分析

以海南红树林植物红海榄和秋茄为对象,研究了两种植物的内生真菌的多样性。结果表明:红海榄和秋茄的枝、叶中分别分离到内生真菌30株和27株,内生真菌的优势属分别是茎点霉属和拟盘多毛孢属;同种植物的枝和叶中内生真菌的定殖率差异显著;红海榄和秋茄内生真菌的多样性指数分别为1.7890和1.7473,均匀度指数分别为0.5260和0.5302。两种红树林植物的内生真菌显示出丰富的多样性。