Effects of tobacco–peanut relay intercropping on soil bacteria community structure

A reasonable cultivation pattern is beneficial to maintain soil microbial activity and optimize the structure of the soil microbial community. To determine the effect of tobacco−peanut (Nicotiana tabacum−Arachis hypogaea) relay intercropping on the microbial community structure in soil, we compared the effects of relay intercropping and continuous cropping on the soil bacteria community structure. We collected soil samples from three different cropping patterns and analyzed microbial community structure and diversity using high-throughput sequencing technology. The number of operational taxonomic units (OTU) for bacterial species in the soil was maximal under continuous peanut cropping. At the phylum level, the main bacteria identified in soil were Proteobacteria, Actinobacteria, and Acidobacteria, which accounted for approximately 70% of the total. The proportions of Actinobacteria and Firmicutes increased, whereas the proportion of Proteobacteria decreased in soil with tobacco–peanut relay intercropping. Moreover, the proportions of Firmicutes and Proteobacteria among the soil bacteria further shifted over time with tobacco–peanut relay intercropping. At the genus level, the proportions of Bacillus and Lactococcus increased in soil with tobacco–peanut relay intercropping. The community structure of soil bacteria differed considerably with tobacco–peanut relay intercropping from that detected under peanut continuous cropping, and the proportions of beneficial bacteria (the phyla Actinobacteria and Firmicutes, and the genera Bacillus and Lactococcus) increased while the proportion of potentially pathogenic bacteria (the genera Variibacter and Burkholderia) decreased. These results provide a basis for adopting tobacco–peanut relay intercropping to improve soil ecology and microorganisms, while making better use of limited cultivable land.     

Are traits measured on pot grown plants representative of those in natural communities?

Question: The quantification of functional traits in natural communities can be difficult (e.g. root traits, RGR). Can functional traits measured on pot grown plants be reliably applied to natural communities? Alternatively, can below‐ground plant traits be predicted from above‐ground traits? Location: Southeastern Australia. Methods: We compared 17 shoot, root and whole‐plant morphological traits measured on 14 plant species in a native grassland community to those measured under two different pot conditions: unfertilised and fertilised. Results: The majority of trait values for pot grown plants differed to plants in the field, however, species ranking remained consistent for most leaf traits between the field and the two pot growing conditions. In contrast, species ranking was not consistent for most whole plant traits when comparing field plants to fertilised pot grown plants, providing a caution against the tendency to grow plants in controlled conditions at ‘optimal’ (high) resource levels. Moderate to strong correlations were found between below‐ground and above‐ground plant traits, including between root dry matter content and leaf dry matter content, and between specific root area and specific leaf area. Conclusions: The utility of pot grown plants to quantify traits for field plants is highly dependent on the selection of the growing conditions in the controlled environment. The consistency we observed between above‐ground and below‐ground trait strategies suggests that below‐ground traits may be predictable based on above‐ground traits, reducing the need to quantify root traits on cultured plants.     

Life in earth: the impact of GM plants on soil ecology?

The impact of changes incurred by agricultural biotechnology has led to concern regarding soil ecosystems and, rightly or wrongly, this has focused on the introduction of genetically modified (GM) crops. Soils are key resources, with essential roles in supporting ecosystems and maintaining environmental quality and productivity. The complexity of soils presents difficulties to their inclusion in the risk assessment process conducted for all GM plants. However, a combined approach, informed by both soil ecology and soil quality perspectives, that considers the impacts of GM crops in the context of conventional agricultural practices can provide a regulatory framework to ensure the protection of soils without being overly restrictive.     

Alleviating salt stress in tomato seedlings using Arthrobacter and Bacillus megaterium isolated from the rhizosphere of wild plants grown on saline–alkaline lands

Salt-induced soil degradation is common in farmlands and limits the growth and development of numerous crop plants in the world. In this study, we isolated salt-tolerant bacteria from the rhizosphere of Tamarix chinensis, Suaeda salsa and Zoysia sinica, which are common wild plants grown on a saline–alkaline land, to test these bacteria's efficiency in alleviating salt stress in tomato plants. We screened out seven strains (TF1–7) that are efficient in reducing salt stress in tomato seedlings. The sequence data of 16S rRNA genes showed that these strains belong to Arthrobacter and Bacillus megaterium. All strains could hydrolyze casein and solubilize phosphate, and showed at least one plant growth promotion (PGP)-related gene, indicating their potential in promoting plant growth. The Arthrobacter strains TF1 and TF7 and the Bacillus megaterium strain TF2 and TF3 could produce indole acetic acid under salt stress, further demonstrating their PGP potential. Tomato seed germination, seedling length, vigor index, and plant fresh and dry weight were enhanced by inoculation of Arthrobacter and B. megaterium strains under salt stress. Our results demonstrated that salt-tolerant bacteria isolated from the rhizosphere of wild plants grown on saline–alkaline lands could be used for alleviating salt stress in crop plants.     

Effects of cotton–maize rotation on soil microbiome structure

Verticillium wilt is a disastrous disease in cotton-growing regions in China. As a common management method, cotton rotation with cereal crops is used to minimize the loss caused by Verticillium dahliae. However, the correlation between soil microbiome and the control of Verticillium wilt under a crop rotation system is unclear. Therefore, three cropping systems (fallow, cotton continuous cropping, and cotton–maize rotation) were designed and applied for three generations under greenhouse conditions to investigate the different responses of the soil microbial community. The soil used in this study was taken from a long-term cotton continuous cropping field and inoculated with V. dahliae before use. Our results showed that the diversity of the soil bacterial community was increased under cotton–maize rotation, while the diversity of the fungal community was obviously decreased. Meanwhile, the structure and composition of the bacterial communities were similar even under the different cropping systems, but they differed in the soil fungal communities. Through microbial network interaction analysis, we found that Verticillium interacted with 17 bacterial genera, among which Terrabacter had the highest correlation with Verticillium. Furthermore, eight fungal and eight bacterial species were significantly correlated with V. dahliae. Collectively, this work aimed to study the interactions among V. dahliae, the soil microbiome, and plant hosts, and elucidate the relationship between crop rotation and soil microbiome, providing a new theoretical basis to screen the biological agents that may contribute to Verticillium wilt control.     

Root development of ‘Red Lady’ papaya plants grown on a hillside

Red Lady papaya (Carica papaya L.) seedlings were grown for 7 weeks in one experiment and 17 weeks in a second experiment on a 60% to 70% sloped hillside. Depth and lateral root developmental characteristics were determined to establish a more informed basis for developing management procedures during hillside production of papaya. A trench was dug perpendicular to the contour line, and positioned 10 cm from the stem base of each plant. A 1 cm layer of soil was removed from the profile wall, and the roots on the trench profile were mapped. Thereafter, the intact half of each root system was excavated to determine the dry mass and length distribution. Roots were separated into the taproot system, and the lateral roots of the uphill and downhill sides. The downhill portion of lateral roots accounted for 56% of total length and 64% of total mass after 7 weeks, and 71% of total length and 69% of total mass after 17 weeks. Some lateral roots on the uphill side of the plants developed with a negative gravitropic orientation to maintain a portion of the root system, close to the surface of the slope. After 17 weeks, 34% of the roots on the uphill side of the trench profile walls were located above a horizontal plane positioned at the stem base. Root growth of Red Lady papaya plants growing on hillsides was maintained in all directions, including up the slope. The results signify that there may be no need to modify fertilizer placement practices for hillside production of papaya. However, the higher concentration of roots on the downhill side of these plants indicates a need for placement of soil moisture sensors for irrigation scheduling in uphill and downhill sites.     

Effects of cropland reclamation on soil organic carbon in China's black soil region over the past 35 years

The long-term use of cropland and cropland reclamation from natural ecosystems led to soil degradation. This study investigated the effect of the long-term use of cropland and cropland reclamation from natural ecosystems on soil organic carbon (SOC) content and density over the past 35 years. Altogether, 2140 topsoil samples (0–20 cm) were collected across Northeast China. Landsat images were acquired from 1985 to 2020 through Google Earth Engine, and the reflectance of each soil sample was extracted from the Landsat image that its time was consistent with sampling. The hybrid model that included two individual SOC prediction models for two clustering regions was built for accurate estimation after k-means clustering. The probability hybrid model, a combination between the hybrid model and classification probabilities of pixels, was introduced to enhance the accuracy of SOC mapping. Cropland reclamation results were extracted from the land cover time-series dataset at a 5-year interval. Our study indicated that: (1) Long-term use of cropland led to a 3.07 g kg⁻¹ and 6.71 Mg C ha⁻¹ decrease in SOC content and density, respectively, and the decrease of SOC stock was 0.32 Pg over the past 35 years; (2) nearly 64% of cropland had a negative change in terms of SOC content from 1985 to 2020; (3) cropland reclamation track changed from high to low SOC content, and almost no cropland was reclaimed on the “Black soils” after 2005; (4) cropland reclamation from wetlands resulted in the highest decrease, and reclamation period of years 31–35 decreased when SOC density and SOC stock were 16.05 Mg C ha⁻¹ and 0.005 Pg, respectively, while reclamation period of years 26–30 from forest witnessed SOC density and stock decreases of 8.33 Mg C ha⁻¹ and 0.01 Pg, respectively. Our research results provide a reference for SOC change in the black soil region of Northeast China and can attract more attention to the area of the protection of “Black soils” and natural ecosystems.     

Epichloë endophyte affects the root colonization pattern of belowground symbionts in a wild grass

Plants host multiple symbionts that interact with each other affecting plant performance and regulating their establishment. Here, we analyzed how the association with Epichloë endophytes affects belowground colonization by Dark Septate Endophytes (DSE) and arbuscular mycorrhizal fungi (AMF) in the grass Bromus auleticus. Epichloë-symbiotic (E+) and Epichloë-non symbiotic (E−) plants were sampled from a long-term experimental plot and colonization structures were analyzed in the roots. We also examined the influence of Epichloë exudates on the in vitro growth of DSE Microdochium bolleyi isolated from roots. Epichloë symbiosis increased AMF colonization, although differences were not significant. Despite the lack of differences in total DSE colonization, in concordance with in vitro findings, a higher significant abundance of microsclerotia was observed in E+ plants. A negative correlation between total mycorrhizal and DSE was found. Our findings show a more uniform root colonization pattern in E+ plants, suggesting a root symbiosis modulating role.     

Effects of transportation direction of photosynthate on soil microbial processes in the rhizosphere of Phyllostachys bissetii北大核心CSCD

Aims Clonal integration contributes greatly to the adaption of clonal plants to heterogeneous habitats. However, effects of transportation direction of photosynthate on microbial processes need to be further investigated in the rhizosphere. The purpose of this study is to determine the effects of directional differences in photosynthate transport on microbial processes in the rhizosphere of clonal plant Phyllostachys bissetii. Methods By removing the aboveground parts of the ramets, acropetal treatment and basipetal treatment were applied in this study to control the transportation direction of photosynthate. In acropetal treatment, aboveground parts of distal ramets were cut off (with 20 cm above ground kept), and proximal ramets were left intact. While in basipetal treatment, aboveground parts of proximal ramets were cut off (with 20 cm above ground kept), and distal ramets were left intact. Rhizomes between the two ramets were either connected or severed. Carbon (C) and nitrogen (N) availabilities, and enzyme activities in the rhizosphere soils were measured. Important findings In acropetal treatment, total organic carbon (TOC), dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and soil inorganic nitrogen (NH4 +-N and NO3 --N) content in the rhizosphere soil of distal ramets with connected rhizomes were significantly higher than those with severed rhizome. The activities of urease, polyphenol oxidase (POXase), N-acetyl-β-D-Glucosaminidase (NAGase) were significantly enhanced. Further, clonal integration had a significant effect on C and N availability, and microbial processes in the rhizosphere soil of neighbouring ramets. In basipetal treatment, clonal integration did not show a significant effect on C availability in the rhizosphere soil of proximal ramets, but microbial processes along with soil enzyme activities were altered accordingly. Effects of transportation direction of photosynthate on microbial processes in the rhizosphere of P. bissetii provides insights into the adaptation mechanisms of clonal plant populations. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

Effects of short-Term experimental warming on soil microbes in a typical alpine steppe北大核心CSCD

Aims Soil microbe plays key role in mediating terrestrial carbon cycles. It has been suggested that climate warming may affect the microbial community, which may accelerate carbon release and induce a positive feedback to soil climate warming. However, there is still controversy on how microbial community responds to experimental warming, especially in cold and drought environment. Methods We conducted an open top chambers (OTCs) experiment to explore the effects of warming on soil microbial community in an alpine steppe on Qinghai-Xizang Plateau. During the maximum of the growing seasons (August) of 2015 and 2016, we monitored the biomass and structure of soil microbial community in warming and control plots using phospholipid fatty acids (PLFA) as biomarkers. Important findings Short-Term warming treatment significantly increased the soil temperature by 1.6 and 1.6 C and decreased soil moisture by 3.4% and 2.4% (volume fraction) respectively, but did not alter either soil properties or normalized difference vegetation index (NDVI) during the growing season (from May to October) in 2015 and 2016. During the maximum of growing seasons (August) of 2015 and 2016, the magnitude of microbial biomass carbon (MBC) were 749.0 and 844.3 mg·kg-1, microbial biomass nitrogen (MBN) were 43.1 and 102.1 mg·kg-1, and the microbial biomass C:N ranged between 17.9 and 8.4. Moreover, all three showed no significant differences between warming and control treatments. The abundance of bacteria was the most in microbial community, while arbuscular mycorrhizal fungi was the least, and warming treatment did not alter the abundance of different microbial group and the microbial community structure. Nonetheless, our result revealed that warming-induced changes in MBC had significant positive correlation with changes in soil temperature and soil moisture. These patterns indicate that, microbial community in this alpine steppe may not respond substantially to future climate warming due to the limitation of soil drought. Therefore, estimation of microbial community response to climate change calls for consideration on the combined effect of warming and drought. © 2018 Editorial Office of Chinese Journal of Plant Ecology. All rights reserved.     

α-Domain of human metallothionein IA can bind to metals in transgenic tobacco plants

We have introduced a genetically marked Dissociation transposable element (Ds ^HPT ) into tomato (Lycopersicon esculentum) by Agrobacterium tumefaciens-mediated transformation. Probes for the flanking regions of the T-DNA and transposed Ds ^HPT elements were obtained with the inverse polymerase chain reaction (IPCR) technique and used in RFLP linkage analyses. The RFLP map location of 11 T-DNAs carrying Ds ^HPT was determined. The T-DNAs are distributed on 7 of the 12 tomato chromosomes. To explore the feasibility of gene tagging strategies in tomato using Ds ^HPT , we examined the genomic distribution of Ds ^HPT receptor sites relative to the location of two different, but very closely linked, T-DNA insertion sites. After crosses with plants expressing Ac transposase, the hygromycin phosphotransferase (HPT) marker on the Ds element and the excision markers β-glucuronidase (GUS) and Basta resistance (BAR) facilitated the identification of plants bearing germinally transposed Ds ^HPT elements. RFLP mapping of 21 transposed Ds ^HPT elements originating from the two different T-DNA insertions revealed distinct patterns of reintegration sites.     

Effect of “osmotic stress” on protein and nucleic acid synthesis in isolated tobacco protoplasts

The incorporation of labeled precursors into RNAs and proteins of isolated tobacco (Nicotiana tabacum L.) leaf protoplasts decreases with increasing osmotic pressure in the incubation medium. The incorporation of precursors into RNA and proteins is linear for 15–18 h after the isolation of the protoplasts, irrespective of the osmolarity of the culture media. The uptake of precursors is also affected by the osmolarity of the medium. However, the osmotic stress-induced inhibition of incorporation of precursors into RNA and proteins is also apparent if the differences in uptake are taken into consideration in the calculation. Incorporation of ³²P into TMV-RNA is also inhibited by osmotic stress. As assayed by the double labeling ratio technique, osmotic stress has less unequivocal effect on TMV protein synthesis.Abbreviations PP protoplast - RNase ribonuclease - rRNA ribosomal ribonucleic acid - SDS sodium dodecyl sulfate - SSC 0.1 M Na-acetate in 0.15 M NaCl - TCA trichloroacetic acid - TMV tobacco mosaic virus     

Phosphate aggravates iron chlorosis in sensitive plants grown on model calcium carbonate−iron oxide systems

Background and aims

The possible influence of phosphorus (P) on iron (Fe) deficiency chlorosis in susceptible plants needs elucidation. In this work, we tested the hypothesis that Fe chlorosis can be aggravated at high levels of P in the substrate.

Methods

Chickpea, lupin and peanut (in a preliminary experiment), and lupin and sorghum (in a second, factorial experiment) were successively grown on artificial substrates consisting of mixtures of Fe oxide-coated sand (FOCS), calcium carbonate (calcite) sand (CCS) and quartz sand to which phosphate was added at different doses.

Results

The proportion of FOCS in the substrate had a significant positive effect on leaf chlorophyll concentration (as estimated via SPAD) in all crops. In the factorial experiment, the SPAD value was negatively affected by the proportion of CCS in the dicot (lupin) but not in the monocot (sorghum). In the preliminary experiment, increasing the P dose generally had little effect on the SPAD of plants grown on the FOCS-rich substrate but a negative effect on those grown on the FOCS-poor substrate. In the factorial experiment, the P dose negatively affected SPAD in both lupin and sorghum.

Conclusions

Iron acquisition by the plant is negatively influenced by P probably because the solubility of the Fe oxides decreases with increasing coverage of their surfaces by sorbed phosphate.