Years Of Monoculture Research Articles

Synergistic changes of rhizosphere bacterial community and soil properties in greenhouse soils under long-term tomato monoculture

Tomato is a dominant vegetable crop in China that is often continuously cultivated in greenhouses, which causes a series of soil quality issues such as nutrient imbalance or microbial degradation. The deterioration caused by long-term monoculture remain poorly understood. Here, we investigated the microbiological and edaphic parameters in a chronosequence of tomato monoculture greenhouse (0–20th years) in Northwest China via 16S rRNA sequencing and soil nutrient determination. We found that the rhizosphere bacteria shifted significantly throughout the 20-year cropping period, but was more closely related to the no monoculture soil bacteria in the last five-year period (15–20th years) than in the first five-years (1–6th year). Soil properties of nitrogen (N), phosphorus (P), and organic carbon (TOC) increased first, then decreased (9th year), and finally remained stable (15–20th year). In addition, monoculture influenced soil properties that subsequently drove the bacterial community change. N, P, and TOC directly affected bacterial composition and potential functions. Intriguingly, functional genes related to stress resistance increased, while others associated with microbial growth decreased, suggesting that monoculture increased the stress of bacterial community. This study revealed how bacteria and their functioning were impacted by 20 years of monoculture, which was strongly associated with the changes of soil properties. This further illustrates the cause of how soil health and quality deterioration in long-term monoculture systems.

青藏高原不同牧草人工草地对土壤线虫群落的影响

为缓解草蓄矛盾，青藏高原人工草地得到快速发展。土壤线虫对环境变化敏感，是草地生态系统的重要组成部分。然而，不同牧草人工草地对土壤线虫群落的影响尚不明确。2016年7月，对多年生禾本科（垂穗披碱草Elymus nutans Griseb.、老芒麦Elymus sibiricus L.、早熟禾Poa annua L.和羊茅Festuca ovina L.）、一年生禾本科燕麦Avena sativa L.和多年生豆科紫花苜蓿Medicago sativa L.等6种单播牧草人工草地（建植期4年）和天然草地（对照）的土壤线虫群落进行了调查。结果表明：（1）土壤线虫隶属于2纲8目32科58属，平均密度为1754个/100 g干土；紫花苜蓿样地的线虫密度最低，为949个/100 g干土；燕麦样地最高，为3267个/100 g干土；（2）与天然草地相比，燕麦样地的线虫群落总密度、多样性以及植食性和杂食-捕食性线虫密度显著增加，而其他人工草地的线虫群落密度、多样性以及植食性、食真菌和食细菌线虫密度均无显著变化；（3）土壤线虫总密度以及各营养类群密度在不同人工草地间差异显著，且均在燕麦样地最高；（4）建植人工草地改变了土壤线虫的群落组成，冗余分析（RDA）表明土壤全钾、碳氮比、全磷和有效钾是影响线虫群落组成的重要因子。研究表明青藏高原建植人工草地通过改变植物群落和土壤理化性质对土壤线虫群落产生影响，其中种植燕麦短期内可显著提高土壤线虫群落的密度和多样性。青藏高原生态环境脆弱，在大面积建植人工草地前应对地下生态过程进一步深入研究。;Artificial grassland with higher productivity has developed rapidly in recent years in order to balance available pasture and stocking rates on the Qinghai-Tibetan Plateau. Soil nematodes are sensitive to environmental changes, which are important components of grassland ecosystems. However, little is known about the effects of the artificial grasslands with the different forage species on the diversity of soil nematode communities. Soil nematode communities in the natural grasslands (control) and artificial grasslands were investigated in July 2016. Four perennial grass (Elymus nutans Griseb., Elymus sibiricus L., Poa annua L., and Festuca ovina L.), one annual grass (Avena sativa L.), and one perennial legume (Medicago sativa L.) were selected. Forages were grown for four years in monoculture in this study. Soil nematodes were extracted from 50 g of fresh soil using Baermann funnels for each composite soil sample. The composite samples were comprised of three soil cores taken from the upper 0-15 cm soil. Soil nematodes were identified into 2 classes,8 orders,32 families,and 58 genera. The results showed that:(1) the average nematodes abundance was 1754 ind./100 g dry soil, ranging from 949 ind./100 g dry soil in the M. sativa to 3267 ind./100 g dry soil in the A. sativa. (2) The total abundances, taxonomic richness, Shannon diversity index of the soil nematodes communities, and the abundances of herbivores and omnivores-predators were significantly higher in the A. sativa grasslands compared to the natural grasslands. However, no significant difference was observed in the total abundances and diversity of the nematode communities and the abundances of fungivores, bacterivores and omnivores-predators between the rest artificial grasslands and natural grasslands. (3) The abundances of the soil nematode communities and each trophic group differed significantly among the different artificial grasslands, with the maximum values occurring in the A. sativa grasslands. (4) Redundancy analysis results showed that soil total K, C/N, total P and available K were the important factors affecting the composition of the soil nematode communities. The results suggested that establishing artificial grasslands with changes in plant communities and soil physico-chemical properties led to the change of soil nematode communities on the Qinghai-Tibetan Plateau, and the abundances and diversity of soil nematode communities were significantly increased by planting A. sativa. Given the vulnerability of ecological environment on the Qinghai-Tibetan Plateau, the changes in soil nematode communities depicted here indicate that underground process should be further studied before the area of artificial grasslands has been greatly increased.

Bombax ceiba is a Good Native Tree Species for Performing Reforestation to Restore Highly Degraded Tropical Forests in Hainan Island, China

Reforestation is an effective way to alleviate deforestation and its negative impacts on ecosystem services. It is widely recognized that the most key step for reforestation is using suitable native species, but selecting suitable native tree species is much more complex and challenging than the selection of non-native tree species that have been widely used for reforestation. Here, we quantify whether the native tree species (Bombax ceiba) can be suitable for performing reforestation to restore a 0.2 km2 highly degraded tropical monsoon forest in Baopoling Mountain (BPL), Sanya, China, due to 20 years of limestone mining for cement production. We found that stomatal closure helped Bombax ceiba develop higher drought stress tolerance than the most dominant native tree species (Bridelia tomentosa) in an undisturbed tropical rainforest in BPL, thereby better adapting well to drought stress in the dry season. These characteristics in turn facilitated it to have high survival rate (92% ± 4%) and fast growth rate, after three years of monoculture in BPL. Thus, Bombax ceiba is very suitable for performing reforestation to recover highly degraded tropical forests in Hainan Island, China.

Assessment of soil clogging and seed productivity of weeds on poplar black landings

Goal. Determination of soil contamination of plots planted for planting black poplar and evaluation of seed productivity of weeds.
 Methods. The level of seed productivity of the weeds was determined by the weighting method in the following sequence. In the experiment, 10 plants of one weed species were cut and manually threshed on a tarpaulin. The purified seeds were weighed and, after determining the mass of 1000 seeds, the average amount (thousand units /plant) of seeds per plant was converted.
 Results. The problem with perennial plantations of bioenergy crops is that the plants are grown for 10—15 years in monoculture on the same section of the field. Consequently, large stocks of certain weeds in the soil can significantly affect the growth and development and productivity level of cultivated plants. So, before planting a plantation, it is necessary to assess the clogging of the plots for the presence of problematic weed species, which can potentially breed on black poplar plantings and impede effective plant care. Virtually all arable land is mothballed with a different weed seed bank. Weed seed stocks depend on the direction of use of the plot, the culture of agriculture, the quality of agricultural operations on care, crop rotation, culture, etc. However, two areas with the same seed reserves in the soil are difficult to find, although the percentage of the main weed species may be identical.
 Conclusions. Weeds traditionally have high seed productivity and form large seed banks in the arable soil, reaching 1.5—2.0 million units / ha. Bioenergy crops, especially perennial species, are extremely sensitive to weeds in the first year of growing season. Because they form rather modest growths of vegetative mass and can not receive photosynthetically active energy to the soil, and therefore it is important to ensure the purity of the field from weeds during the first year of vegetation.

Effect of Habitat and Foliar Fertilization with K, Zn and Mn on Winter Wheat Grain and Baking Qualities

Cereal monoculture causes a series of unfavorable changes in field habitat, for example a decrease in technological quality and yield. This system can lead to a shortage of microelements in the diet of poor communities. Moreover, breeding of highly productive plants caused a significant “dilution effect” of the necessary nutrients, such as Zn and Fe. The aim of this work was to determine the effect of two strategies: crop rotation (after rapeseed and many years of monoculture of Galega orientalis Lam.) and foliar fertilization with microelements on the yield, yield elements, physical quality, and farinograph characteristics of winter wheat grain and flour. Results showed that pre-crop preparation and cultivation year have the highest effect on yield, yield components, and qualitative and farinographic characteristics of winter wheat. Foliar additional feeding favorably affected the yield and its components, although the particular fertilization treatment did not significantly increase the yield. Grain quality, its physical characteristics and the rheological parameters of flour were strongly modified by habitat conditions, including weather conditions. Dough obtained from wheat grown after galega showed significantly higher water absorption and prolonged consistency.

Seasonal Variation and Crop Sequences Shape the Structure of Bacterial Communities in Cysts of Soybean Cyst Nematode.

Soybean cyst nematode (SCN), Heterodera glycines Ichinohe, is the number 1 pathogen of the important economic crop soybean. Bacteria represent potential biocontrol agents of the SCN, but few studies have characterized the dynamics of bacterial communities associated with cysts under different crop rotation sequences. The bacterial communities in SCN cysts in a long-term soybean–corn crop rotation experiment were investigated over 2 years. The crop sequences included long-term soybean monoculture (Ss), years 1–5 of soybean following 5 years corn (S1–S5), years 1 and 2 of corn following 5 years soybean (C1 and C2), and soybean–corn annual rotation (Sa and Ca). The bacterial 16S rRNA V4 region was amplified from DNA isolated from SCN cysts collected in spring at planting, midseason (2 months later), and fall at harvest and sequenced on the Illumina MiSeq platform. The SCN cyst microbiome was dominated by Proteobacteria followed by Actinobacteria, Bacteroidetes, and Verrucomicrobia. The bacterial community composition was influenced by both crop sequence and season. Although differences by crop sequence were not significant in the spring of each year, bacterial communities in cysts from annual rotation (Sa and Ca) or crop sequences of early years of monoculture following a 5-year rotation of the alternate crop (S1 and C1) became rapidly differentiated by crop over a single growing season. In the fall, genera of cyst bacteria associated with soybean crop sequences included Rhizobacter, Leptothrix, Cytophaga, Chitinophaga, Niastella, Streptomyces, and Halangium. The discovery of diverse bacterial taxa in SCN cysts and their dynamics across crop rotation sequences provides invaluable information for future development of biological control of the SCN.

Interactions between soil properties, fungal communities, the soybean cyst nematode, and crop yield under continuous corn and soybean monoculture

Corn (Zea mays) and soybean (Glycine max) production forms an integral part of economies worldwide, but yields are limited by biotic and abiotic factors associated with short rotations and long-term monocultures. The objectives of this study were (i) to investigate the role of corn-soybean crop rotations and continuous monocultures in shaping bulk soil fungal communities, ii) to identify fungal taxa or functional guilds correlated with SCN density, and (iii) to characterize relationships between biotic and abiotic factors and their effects on corn and soybean yields. The study utilized a long-term rotation site with corn and soybean planted in annual rotation, five-year rotation, and long-term monoculture. High throughput sequencing of the ITS1 region of fungal rDNA revealed that soil fungal community structure varied significantly by crop sequence, with fungal communities under five consecutive years of monoculture becoming progressively similar to corresponding communities in long-term monoculture plots. Total fungal alpha diversity was greater under corn, but patterns of diversity and relative abundance of specific fungal functional guilds differed by crop, with more nematophagous fungi proliferating under soybean and more arbuscular mycorrhizal fungi (AMF) proliferating under corn. The relative abundance of nematode-trapping fungi and several putative nematode egg parasites was positively correlated with SCN density at several time points, suggesting that these fungi may proliferate as a result of the availability of the SCN as a nutrition source. Soil properties also varied by crop sequence, with higher pH and P under continuous soybean and higher Fe, Mn, and Cu under continuous corn. Lower levels of P corresponded with the relative abundance of several orders of fungi with roles in P uptake and transfer to plants (Glomerales, Paraglomerales, and Sebacinales), while higher P levels corresponded with the relative abundance of Mortierellales, a fungal order containing phosphate-solubilizing fungi. Structural equation modeling identified the SCN and soil nitrogen as the most important variables explaining soybean yield and fungal pathogens of corn and soil nitrogen as the most important variables explaining corn yield.

Evidence for rapid evolution in a grassland biodiversity experiment.

In long-term grassland experiments, positive biodiversity effects on plant productivity commonly increase with time. Subsequent glasshouse experiments showed that these strengthened positive biodiversity effects persist not only in the local environment but also when plants are transferred into a common environment. Thus, we hypothesized that community diversity had acted as a selective agent, resulting in the emergence of plant monoculture and mixture types with differing genetic composition. To test our hypothesis, we grew offspring from plants that were grown for eleven years in monoculture or mixture environments in a biodiversity experiment (Jena Experiment) under controlled glasshouse conditions in monocultures or two-species mixtures. We used epiGBS, a genotyping-by-sequencing approach combined with bisulphite conversion, to provide integrative genetic and epigenetic (i.e., DNA methylation) data. We observed significant divergence in genetic and DNA methylation data according to selection history in three out of five perennial grassland species, namely Galium mollugo, Prunella vulgaris and Veronica chamaedrys, with DNA methylation differences mostly reflecting the genetic differences. In addition, current diversity levels in the glasshouse had weak effects on epigenetic variation. However, given the limited genome coverage of the reference-free bisulphite method epiGBS, it remains unclear how much of the differences in DNA methylation was independent of underlying genetic differences. Our results thus suggest that selection of genetic variants, and possibly epigenetic variants, caused the rapid emergence of monoculture and mixture types within plant species in the Jena Experiment.

Properties of bacterial community in the rhizosphere soils of Achyranthes bidentata tolerant to consecutive monoculture

Changes in the structure and abundance of plant rhizosphere microbial communities have direct correlation with plant health and fitness. Extensive studies have been carried out on growth inhibition effects of consecutive monoculture on several medicinal plants but there is paucity of information about its effect on Achyranthes bidentata Blume, a suitable species for consecutive monoculture. Our objective was to evaluate the shifts of soil microbial community structure under consecutive monoculture of A. bidentata. The 16S rDNA sequencing results showed that the bacterial communities in 10-year (10 Y) and 30-year (30 Y) monocultured soil samples were different in diversity and abundance from those in newly planted soil (1 Y) and control soil. There was significant enhancement in the abundance of Pseudomonas and Bacillaceae. Furthermore, DGGE profiles revealed distinct changes in Pseudomonas spp. with the increasing years of monoculture. The abundance of Pseudomonas aeruginosa was distinctly higher in consecutively monocultured plots than in the newly planted plot. The results from the LC-MS/MS analysis and in vitro interaction found that phytosterones were one of main substances in root and soil samples, and the allochemicals showed the positive interaction with the dominant beneficial species of P. aeruginosa W9. It is therefore suggested that consecutive monoculture of A. bidentata led to a distinct shift in rhizosphere bacterial community, with the enhancement of the plant beneficial bacteria. The result obtained from the studies are expected to be helpful to unravel the rhizo-biological mechanism of A. bidentata under consecutive monoculture and provide the basis for further understanding the roles of microbiome in overcoming continuous cropping obstacles for other monocultured plants.

Function and Distribution of a Lantipeptide in Strawberry Fusarium Wilt Disease-Suppressive Soils.

Streptomyces griseus S4-7 is representative of strains responsible for the specific soil suppressiveness of Fusarium wilt of strawberry caused by Fusarium oxysporum f. sp. fragariae. Members of the genus Streptomyces secrete diverse secondary metabolites including lantipeptides, heat-stable lanthionine-containing compounds that can exhibit antibiotic activity. In this study, a class II lantipeptide provisionally named grisin, of previously unknown biological function, was shown to inhibit F. oxysporum. The inhibitory activity of grisin distinguishes it from other class II lantipeptides from Streptomyces spp. Results of quantitative reverse transcription-polymerase chain reaction with lanM-specific primers showed that the density of grisin-producing Streptomyces spp. in the rhizosphere of strawberry was positively correlated with the number of years of monoculture and a minimum of seven years was required for development of specific soil suppressiveness to Fusarium wilt disease. We suggest that lanM can be used as a diagnostic marker of whether a soil is conducive or suppressive to the disease.

Arsenic and selenium levels in rice fields from south-west of Spain: influence of the years of monoculture

There is a lack of information regarding the arsenic (As) and selenium (Se) concentrations in Spanish rice (Oryza sativa L.) fields and how soil conditions affect such concentration, especially those derived from the typical monoculture practiced in the studied area. To clarify these aspects, 76 soil samples and 95 grain samples were collected from 19 rice fields along the Vegas Altas area, the most important rice growing area of south-west of Spain. The results suggested a significant increase in the soil total As and Se concentrations as the number of monoculture years increased. While As concentration reached toxic levels in 12 out of the 19 locations, Se concentration in all the analysed fields could be considered as deficient. An increase of the As and Se concentration in soil produced a subsequent increase of the concentration of both elements in the rice grain. Therefore, it might be extremely important to control both levels. It would be necessary to establish different actions, including rotations with other crops, in order to remediate As accumulation and to increase Se intake.

不同连作年限怀牛膝根际土壤理化性质及微生物多样性

PDF HTML阅读 XML下载 导出引用 引用提醒 不同连作年限怀牛膝根际土壤理化性质及微生物多样性 DOI: 10.5846/stxb201606071097 作者: 作者单位: 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金（81303170，81573530，31401950，U1205021）；闽台作物特色种质创制与绿色栽培协同创新中心（2015-75） Analysis of physicochemical properties and microbial diversity in rhizosphere soil of Achyranthes bidentata under different cropping years Author: Affiliation: Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:以不同连作年限怀牛膝根际土壤为材料，采用土壤农化分析技术和磷脂脂肪酸生物标记法，对土壤理化性质以及根际微生物群落结构进行分析。结果表明：怀牛膝连作会使大部分大量元素（全磷、碱解氮、速效磷和速效钾）含量上升，而全氮、全钾的变化并无明显趋势。全量钙、全量镁、全量锰和有效锌的含量也会随着连作年限的增加而增加。研究发现，怀牛膝连作1a的土壤与对照相比，根际土壤微生物群落结构差别不大，但是与连作10a和30a的土壤相比微生物多样性却发生了明显变化。土壤中总PLFAs、细菌、革兰氏阴性菌Gram（-）及真菌含量都随连作年限增加而明显上升，微生物多样性增加，且革兰氏阳性菌Gram（+）/革兰氏阴性菌Gram（-）的比值随着连作年限的增加而下降。此外，土壤中一些嗜热解氢杆菌和真菌等参与土壤物质循环和木质素降解的微生物类群数量明显增加，假单胞菌等有益微生物类群也显著增多，这是牛膝连作促进作用的生物学基础。研究用药用植物怀牛膝证明了植物根际微生物结构和功能多样性对植物连作促进或连作抑制作用的产生与控制的生态学意义。 Abstract:In this study, the rhizosphere soils of Achyranthes bidentata, which was grown in a monoculture for multiple years, were investigated for analyzing the major elements, trace elements and rhizosphere microbial community structure by means of agricultural chemistry and phospholipid fatty acid (PLFA) analysis techniques. The results showed that consecutive monocultures of A. bidentata increased the contents of major elements (total phosphorus, alkaline hydrolysis nitrogen, available phosphorus, and available potassium). However, the ability of consecutive monocultures to change the total nitrogen content and total potassium was not obvious. In addition, total calcium, total magnesium, total manganese, and available zinc contents also increased with the increasing years of monoculture. Further analysis of PLFA profiles showed that there were no obvious differences in the rhizosphere microbial community structures between the control and newly planted A. bidentata. Besides, different results were depicted by 10 years and 30 years of consecutive monoculture, which showed that the total PLFA, bacteria (especially G-), and fungal content increased significantly, and the G+/G- ratio decreased with increasing years of monoculture. Moreover, some microbes involved in material cycling and lignin degradation, such as Hydrogenobacter, fungi (PLFA18:2ω6,9), and some beneficial bacteria including Pseudomonas increased significantly with increasing years of monoculture. These results suggest the important biological basis for the promotion mechanism of A. bidentata under a monoculture system. The case study exemplifies the ecological significance of rhizosphere microbial structure and its functional diversity in monoculture promotion or monoculture inhibition. 参考文献 相似文献 引证文献

Interaction of Pseudostellaria heterophylla with Quorum Sensing and Quorum Quenching Bacteria Mediated by Root Exudates in a Consecutive Monoculture System.

Many plant-pathogenic bacteria are dependent on quorum sensing (QS) to evoke disease. In this study, the population of QS and quorum quenching (QQ) bacteria was analyzed in a consecutive monoculture system of Pseudostellaria heterophylla. The isolated QS strains were identified as Serratia marcescens with SwrIR-type QS system and exhibited a significant increase over the years of monoculture. Only one QQ strain was isolated from newly planted soil sample and was identified as Bacillus thuringiensis, which secreted lactonase to degrade QS signal molecules. Inoculation of S. marcescens to P. heterophylla root could rapidly cause wilt disease, which was alleviated by B. thuringiensis. Furthermore, the expression of lactonase encoded by the aiiA gene in S. marcescens resulted in reduction of its pathogenicity, implying that the toxic effect of S. marcescens on the seedlings was QS-regulated. Meanwhile, excess lactonase in S. marcescens led to reduction in antibacterial substances, exoenzymes, and swarming motility, which might contribute to pathogensis on the seedlings. Root exudates and root tuber extracts of P. heterophylla significantly promoted the growth of S. marcescens, whereas a slight increase of B. thuringiensis was observed in both samples. These results demonstrated that QS-regulated behaviors in S. marcescens mediated by root exudates played an important role in replanting diseases of P. heterophylla.

Insight into structure dynamics of soil microbiota mediated by the richness of replanted Pseudostellaria heterophylla.

Consecutive monoculture of crops causes serious diseases and significant decline in yield and quality, and microbes in the rhizosphere are closely linked with plant health. Here we systematically studied the structure dynamics of soil microbiota in the monocropping system of Pseudostellaria heterophlla. The results illustrated that the successive cropping of P. heterophylla shifts the diversity and structure of microbial community in rhizosphere soil of P. heterophylla, showing that the diversity of microbial community in rhizosphere soil of P. heterophylla was decreased with the increase of planting years while the structure of microbial community became more deteriorative. Moreover, the population size of typical pathogens increased and the beneficial bacterial population decreased with the increasing years of monoculture, which resulted in the microecological imbalance in P. heterophylla rhizosphere, thereby caused serious replanting diseases in monocropping system. Our results suggested that structure dynamics of rhizosphere microbial communities were mediated by the richness of replanted P. heterophylla, and thus the replant disease result from the imbalanced microbial structure with a higher ratio of pathogens/beneficial bacteria in rhizosphere soil under monocropping regimes. This finding provides a clue to open a new avenue for modulating the root microbiome to enhance the crop production and sustainability.

Determining the Role of Plant‐Parasitic Nematodes in the Corn–Soybean Crop Rotation Yield Effect Using Nematicide Application: II. Soybean

Corn (Zea mays L.)–soybean [Glycine max (L.) Merr.] crop rotation is well‐known to increase yields of both crops and is called the rotation effect. This study was conducted to determine the role of plant‐parasitic nematodes—particularly soybean cyst nematode (SCN, Heterodera glycines),—in the rotation effect for soybean. Research was conducted at a site in Waseca, MN, that was established in 1982 to study corn–soybean rotation. Included in the study were treatments in 1 to 5 yr of SCN‐susceptible soybean monoculture following 5 yr of corn, continuous SCN‐susceptible soybean monoculture, and continuous soybean with SCN‐resistant cultivars since 2010. Granular nematicides have been applied to half of each plot since 2010 to minimize nematode populations across crop sequences as a way to determine the role of nematodes in the rotation effect. Because nematicide was similarly effective in each crop sequence, it was not effective for determining if SCN damage varied by crop sequence. Soybean cyst nematode populations increased (P ≤ 0.05) in soybean monoculture and were negatively correlated with soybean yield (P ≤ 0.05). Pratylenchus (lesion nematode) populations decreased significantly in soybean monoculture particularly when comparing first and second year in soybean (P ≤ 0.05). Helicotylenchus (spiral nematode) and Xiphinema (dagger nematode) populations were significantly decreased in continuous soybean compared to most sequences in 5 or fewer years of monoculture (P ≤ 0.05). Trends in nematode populations suggest SCN may have had a role in the rotation effect for soybean yield, but that Pratylenchus, Helicotylenchus, and Xiphinema did not. Growing soybean in monoculture decreases yield. Growing soybean in monoculture increases soybean cyst nematode populations. There was some evidence that soybean cyst nematode can be involved in monoculture yield decline for soybean.

Plant probiotics to the rescue

Soil Biology![Figure][1] Soil-dwelling bacteria can protect strawberry plants from fungal wilt PHOTO: © OLEKSANDR SHEVCHENKO/ALAMY STOCK PHOTO Some soils protect crops against their microbial attackers without any pesticides or fungicides. Cha et al. investigated the microbial and biochemical basis of this effect in a patch of soil that excluded fungal wilt on strawberry plants, despite 15 years of monoculture. Mixing in the protective soil transferred this suppressive effect into neighboring disease-ridden soils, which gained increasingly better disease-control capacity with successive growing cycles. A strain of Streptomyces bacteria, a group renowned for producing antibiotics, emerged as the chief agent that suppressed the pathogenic fungi. The Streptomyces produced an interesting large heat-stable thiopeptide antibiotic with antifungal properties. Thus, much like the development of probiotics to combat gut diseases, probiotics for soil should be feasible. ISME J. 10 , 119 (2016) [1]: pending:yes

Inferring the origin of primary inoculum of Zymoseptoria tritici from differential adaptation of resident and immigrant populations to wheat cultivars

We investigated whether the origin of primary inoculum of the fungal wheat pathogen Zymoseptoria tritici can be inferred from evidence of adaptation to host cultivars. We compared the aggressiveness of two pathogen populations collected locally, the first considered as resident (collected from debris in a wheat cv. Soissons monoculture plot) and the second considered as immigrant (collected from leaf lesions in a 300 m apart wheat cv. Soissons plot containing no debris, exposed to an inoculum pool of distant origin), with the aggressiveness of a third population (collected from early leaf lesions in the same monoculture plot) the origin of which we wanted to determine (local vs. distant). The three populations were sampled twice, in 2009 and 2012, from a 6-year field trial. Latent period and sporulating area of 6 × 12 isolates were assessed in greenhouse on adult plants of cv. Soissons and of Apache, another cultivar commonly grown around the field for several years. Firstly, we detected a differential host adaptation: after several years of monoculture, the resident pathogen populations became less adapted to the other cultivar. Secondly, we showed that when the inoculum pressure was high (2009), the aggressiveness profile of the third pathogen population was more similar to that of the resident populations than of the immigrant. This indicates that early lesions in the monoculture plot were mostly caused by within-field (local) primary inoculum. The comparison of aggressiveness profiles when the inoculum pressure was lower (2012) was less conclusive, suggesting that the tested population could have a mixed origin.

Influence of long-term corn–soybean crop sequences on soil ecology as indicated by the nematode community

In the Midwestern United States, corn–soybean rotation is an essential agricultural practice, but relatively little is known about the impact of different corn–soybean cropping sequences on soil ecology. A long-term research site in Waseca, Minnesota was established in 1982 to study corn–soybean rotation. At the site, various corn–soybean crop sequences can be compared each year including corn and soybean in 1 to 5 years of monoculture and continuous monoculture of each crop. Additionally, granular nematicides (terbufos or aldicarb) have been applied to half of each plot since 2010 to minimize nematode populations, particularly plant-parasitic nematodes, across crop sequences. The nematode community, a sensitive indicator of changes in soil ecology, was assessed at this site to determine the impact of corn–soybean crop sequences and nematicide application on the soil ecosystem. Nematicide application was effective against target nematodes, herbivores, but also impacted non-target nematodes and thus soil ecology. Nematicide application decreased fungivore and bacterivore populations, diversity, and maturity; but significantly increased enrichment compared to no nematicide application. The nematode community and thus soil ecology was significantly different in corn compared to soybean cropping systems and changed most during initial years after switching crops. Cropping systems in corn supported significantly greater fungivore populations, fungal decomposition pathways, more diversity, and a more mature ecosystem compared to soybean systems. Soybean systems supported significantly greater bacterivore populations and a more disturbed, enriched ecosystem. These differences between corn and soybean systems demonstrate that each crop has a distinct impact on the soil ecosystem.

Application of Deep Pyrosequencing to the Analysis of Soil Microbial Communities in Different Lotus Fields

Fusarium oxyporum f. sp. nelumbicola is a very important plant pathogen that can cause lotus Fusarium wilt and lead to vast economic loss in Jiangxi Province, China. Sequencing data of 16S ribosomal RNA genes and internal transcribed spacer regions revealed that different bacterial and fungal communities were present in soil samples from healthy or Fusarium wilt-infected lotus fields with different years of continuous cropping, indicating that the long-term continuous cropping of lotus significantly altered the soil microbial communities. Fungal diversity indexes in the healthy soil samples increased with the years of monoculture, but decreased in the Fusarium wilt-infected soil samples, whereas bacterial community diversity in all the soil samples was relatively stable. A cluster analysis revealed that consecutive cropping time was a key factor for determining fungal community structure, but not for bacterial community structure. The relative abundances of Proteobacteria, Acidobacterial, Ascomycota, and Basidiomycota phyla decreased with the years of lotus monoculture. Compared with the healthy soil samples, the abundances of beneficial bacteria in the Fusarium wilt-infected soil samples significantly decreased with time. These observations indicate that soil weakness and lotus Fusarium wilt disease may be attributed to structural changes of soil microbial communities after long-term continuous cropping, and the changes include reduction of beneficial microorganisms and accumulation of fungal pathogens.

Microbial community structure and its temporal changes in Rehmannia glutinosa rhizospheric soils monocultured for different years

Consecutive monoculture leads to a substantial decline in both yield and quality for Rehmannia glutinosa. The diversity of microbes in rhizosphere can affect plant health. The objective was to investigate the effects of consecutive monoculture of this plant on rhizospheric microbial community composition and catabolic diversity at different stages of plant growth. The results showed that the microbial communities were significantly affected by both longevity of monoculture and plant growth stage. The amounts of phospholipid fatty acids indicative of most microbial functional groups differed significantly between the newly planted and monocultured soils. In addition, a significant correlation was observed between the microbial biomass and the community metabolic activities. The cyclopropyl-to-precursor ratio (cy/pre), an indicator of physiological stress in microbial communities, was significantly higher in the monocultured soils than in the newly planted soil at both the root elongation and expansion stages. Furthermore, the amounts of two pathogenic fungi (Fusarium oxysporum and Aspergillus flavus) significantly increased with increasing years of monoculture. In conclusion, we revealed characteristic differences in the microbial community composition and functions in R. glutinosa rhizosphere after monoculture, which might be attributed to the changes in plant performance and root exudates.