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A multicrystalline silicon solar cell was analyzed using Raman microspectroscopy. We measured the prominent Raman modes of silicon, nanocrystalline silicon and silver oxide in various regions of the solar cell to generate insights into the process and material quality of the finished device. First, by comparing the distribution of the transverse optical (TO) phonon peak position and full-width-at-half-maximum (FWHM) of the solar cell with a single crystal silicon wafer, the quality of the multicrystalline silicon surface was ascertained. Second, a similar analysis of the remnant saw marks on the device surface showed a discernably higher and wider distribution of TO phonon peak position and FWHM compared to a multicrystalline silicon surface. This indicated the presence of residual compressive stresses in the saw mark region. Third, by observing the silver fingers and bus bars, a residual silver oxide layer was identified, up to 25 μm away from the line edges. This was attributed to the screen printing of the silver paste and the subsequent firing process. Finally, Raman mapping on an embedded inclusion showed the presence of nanocrystalline silicon phase. The multicrystalline silicon region surrounding the inclusion was under tensile stress. A nondestructive, confocal Raman analysis of the inclusion provided a 3-D visualization of the defect, both inside and above the surface of the multicrystalline silicon wafer.

Genome sequence-driven molecular typing tools have the potential to uncover the population biology and genetic diversity of rapidly evolving plant pathogens like Magnaporthe oryzae. Here, we report a new molecular typing technique -a digitally portable tool for population genetic analysis of M. oryzae to decipher the genetic diversity. Our genotyping tool exploiting allelic variations in housekeeping and virulence genes coupled with pathotyping revealed a prevalence of genetically homogenous populations within a single-field and plant niches such as leaf and panicle. The M. oryzae inciting leaf-blast and panicle-blast were confirmed to be genetically identical with no or minor nucleotide polymorphism in 17 genomic loci analyzed. Genetic loci such as Mlc1, Mpg1, Mps1, Slp1, Cal, Ef-Tu, Pfk, and Pgk were highly polymorphic as indicated by the haplotype-diversity, the number of polymorphic sites, and the number of mutations. The genetically homogenous single field population showed high virulence variability or diversity on monogenic rice differentials. The study indicated that the genetic similarity displayed by the isolates collected from a particular geographical location had no consequence on their virulence pattern on rice differentials carrying single/multiple resistance genes. The data on virulence diversity showed by the identical Sequence Types (STs) is indicative of no congruence between polymorphic virulence genes-based pathotyping and conserved housekeeping genes-based genotyping.

Climate change altered variations in weather trends and rainfall fluctuations could trigger soil slope instability, causing landslides or debris flows. To mitigate such rainfall-induced slope failures, vegetated slopes are considered as an effective mechanism. For that reason, several studies have addressed the restraining of mechanical failures and advantages of evapotranspiration model in soil–plant-slope stability continuum. However, most of these investigations were examined on tree seedlings (1–2 m trunk height), which are relatively atypical and are insufficient to comprehend the vegetated slope mechanism. Besides, the variation of pore water pressure (directly related to slope stability) with different rainfall intensities are unclear. These critical measurements are required for modelling climate change-slope stability models and for practicing in long-term maintenance of man-made slopes. Therefore, this study attempted to investigate the temporal variation (suction distribution) of matured Ivy tree under different rainfall events (return periods equal to 20 years, 2 years and less than 2 years). The suction variations with different rainfall events were measured both vertically and horizontally below the root zones using jet fill tensiometers (± 1 kPa accuracy). The study provides evidence of suction distribution within the root zones, discussing the suction recovery after consecutive rainfall events and natural drying. Based on the observations, it was found that antecedent rainfall plays an effective role in suction recovery rates and changes in soil hydraulic conductivity.

In this study, the local softening characteristic of saturated soft clay was examined through a series of dynamic triaxial test under varying confining pressures. Additionally, the stress strain relationship and pore water pressure development during the process of softening zone formation were recorded. Using the energy based pore pressure model, it has been seen that the pore water pressure and energy dissipation has very good correlation for saturated sands and silty soils. The experimental results prove that the local softening and the development of pore water pressure have a good correlation. The different dynamic stress makes the soil sample to reach the same damage level. The softening area made by the smaller dynamic stress is more clear and concentrated than larger stress.

Biochars produced from different feedstocks (such as wood, pig manure) possess varying physical and chemical properties, which have influence on crack and evaporation rate of biochar-amended soil (BAS). Furthermore, influence of compaction state and drying-wetting cycles on evaporation rate and cracking of BAS has not been investigated comprehensively. The objective of this study was to investigate the effects of biochar types, compaction state of BAS, and drying-wetting cycles on crack propagation and retained water (or evaporation rate). An animal and plant feedstock-based biochars were produced in-house from pig manure (PM) and wood (W), respectively. In addition, nano structured chalk and wheat biochar (CWB) were also produced. Soil amended with individual biochars was compacted in petri-glass discs at two densities. Disc specimens were subjected to multiple drying-wetting cycles, and evaporation rate of specimens and crack area were monitored throughout the experimental period (70 days). Images were captured after every 24 h and processed using image processing technique to obtain the crack intensity factor (CIF). The results show that plant-based W BAS showed the high water retention, i.e., low evaporation rate and low CIF. Furthermore, the crack potential of CW BAS was seen to be higher. In dense compacted soil, maximum CIF% can be reduced from 3.9 to 0.4% for W BAS, from 3.9 to 1.7% for PM BAS, and from 3.9 to 1.6% for CW BAS. WB was able to resist cracking more efficiently than other types of biochar. Evaporation was found to be minimal for plant-based W BAS at 10% biochar percentage. Higher biochar content in soil was seen to increase the water retention of BAS significantly. Dense state of BAS at high biochar content (i.e., 10%) was effective in reducing evaporation rate and crack progression.

Additional file 1. Table S1. Rice defense genes used for the qPCR analysis and their function. Table S2. List of the PCR primers used in the gene expression studies. Table S3. Metagenome read statistics of phyllomicrobiome of rice genotypes grown in two contrasting climatic zone. Table S4. Network analysis of rice phyllosphere microbiome using SparCC correlation coefficients. Table S5. Population size of epiphytic bacteria (Log CFU g_1) on phyllosphere of 15 and 30 days aged rice genotypes grown in Mountain zone. Table S6. Population size of epiphytic bacteria (Log CFU g−1) on phyllosphere of rice genotypes grown in Island zone. Table S7. Identification of bacterial isolates by 16S rRNA gene sequencing. Table S8. Analysis of nature of BVC mediated mycelial inhibition of Magnaporthe oryzae. Table S9. qPCR based transcriptional analysis of defense genes expression in rice seedlings upon phyllobacterization. i. OsCEBiP was found induced in all-time points by bacterization; significant induction by Aureimonas sp.OsEp-Plm-30P7 for all three-time points and Pseudomonas putida OsEp-Plm-15P11 or Pantoea ananatis OsEp-AN-30A848 hour post bacterization. ii. OsPR1.1 was also found induced 72 h post bacterization with significant induction by Aureimonas sp.OsEp-Plm-30P7. iii. OsNPR1 and OsPDF2.2 showed induction at 72 h post-inoculation for all the bacterial treatments. iv. Other genes induced were OsFMO in Pantoea ananatis OsEp-AN-30A8, OsCERK1, andOsPAD4 in Pantoea ananatis OsEp-AN-30A8.

Additional file 2. Fig. S1. Identification of biomarkers based on the linear discriminant analysis (LDA) and effect size (LEfSe) pipeline; (A) Two genotypes (PRR78 and Pusa1602); (B) Two locations (Palampur and Port Blair). Fig. S2. Network analysis of rice phyllosphere microbiome using SparCC correlation coefficients (Normal group). Fig. S3. Extended error bar plot at various taxonomic hierarchy levels for phyllomicrobiome of rice genotypes, PRR78 and Pusa1602. Fig. 4. Extended error bar plot at various taxonomic hierarchy levels for phyllomicrobiome of rice grown in Palampur, Himachal Pradesh and Port Blair, Andaman Island. Fig. 5. Relative abundance of phyllosphere bacterial communities on rice genotypes grown in two agroclimatic zones of India. Fig. S6. Relative abundance of phyllosphere bacterial communities at genus level on two rice genotypes representing contrasting agroclimatic zones of India. Fig. 7. BOX PCR fingerprinting of cultured bacterial isolates of rice phyllosphere; M: DNA size marker; Lanes: Isolates of bacteria isolated from the phyllosphere of rice leaf. Fig. 8. Amplification of 16S rRNA of bacterial isolates of rice phyllosphere. Fig. 9a. Colonies of cultured Acidovorax species from rice phyllomicrobiome. Fig. S9b. Colonies of cultured Acinetobacter species from rice phyllomicrobiome. Fig. 9c. Colonies of cultured Agrobacterium species from rice phyllomicrobiome. Fig. S9d. Colonies of cultured Aureimonas species from rice phyllomicrobiome. Fig. S9e. Colonies of cultured Curtobacterium species from rice phyllomicrobiome. Fig. 9f. Colonies of cultured Enterobacter species from rice phyllomicrobiome. Fig. S9g. Colonies of cultured Erwinia species from rice phyllomicrobiome. Fig. 9h. Colonies of cultured Exiguobacterium species from rice phyllomicrobiome. Fig. S9i. Colonies of cultured Microbacterium species from rice phyllomicrobiome. Fig. S9j. Colonies of cultured Micrococcus species from rice phyllomicrobiome. Fig. S9k. Colonies of cultured Pantoea species from rice phyllomicrobiome. Fig. S9l. Colonies of cultured Pseudomonas species from rice phyllomicrobiome. Fig. 9m. Colonies of cultured Sphingomonas species from rice phyllomicrobiome. Fig. S10. Secreted metabolite mediated in vitro antifungal activity of rice phyllosphere bacterial isolates on Magnaporthe oryzae. Fig. S11. Volatile mediated in vitro antifungal activity of rice phyllosphere bacterial isolates on Magnaporthe oryzae. Fig. S12. Analysis of nature of BVC mediated growth inhibition of Magnaporthe oryzae. Fig. S13. Effect of phyllobacterization on rice blast disease incited by Magnaporthe oryzae. Fig. S14. qPCR based transcriptional analysis of defense genes expression in rice seedlings upon phyllobacterization.

Background The fundamental role and contributions of phyllosphere habitat in shaping plant functional ecology are poorly investigated, and often underestimated. Phyllosphere -the harsh and dynamic foliar-photosynthetic-habitat is continuously exposed to vagaries of changing weather events during the entire plant life. With its adapted microbiota, the phyllosphere-niche brings microbial diversity to the plant-holobiont pool and potentially modulates a multitude of plant and agronomic traits. The phyllomicrobiome structure and the consequent ecological functions are vulnerable to a host of biotic (Genotypes) and abiotic-factors (Environment) which is further compounded by agronomic-transactions on domesticated agricultural crops. However, the ecological forces driving the phyllomicrobiome assemblage and functions are among the most under-studied aspects of plant biology. Despite the reports on the occurrence of diverse prokaryotic phyla such as Proteobacteria, Firmicutes, Bacteroides, and Actinobacteria on phyllosphere habitat, the functional characterization leading to their utilization for agricultural sustainability is not yet adequately explored.Currently, the metagenomic-Next-Generation-Sequencing (mNGS) technique scanning the conserved V3-V4 region of ribosomal RNA gene is a widely adopted strategy for microbiome-investigations. However, the structural and functional validation of mNGS annotations by microbiological methods is not integrated into the microbiome exploration-programs. In the present study, we combined the high throughput mNGS approach with conventional microbiological methods to decipher the core-functional-phyllomicrobiome of contrasting rice genotypes varying in their response to blast disease grown in contrasting agroclimatic zones in India. We, further, scanned the rice phyllosphere by electron microscopy to show the microbial communities on leaf. Magnaporthe oryzae-the phyllosphere pathogen inciting necrotic lesion on cereal crops is managed by the deployment of ‘non-durable’blast resistance genes and ‘toxic’ fungicidal molecules. Nowadays, there is a growing consensus for devising an alternative strategy for mitigating blast owing to a recent ban on the use of most commonly used fungicidal molecule, tricyclazole. In the present work, we further identified phyllosphere- core-functional microbial groups leading tothe proposal of phyllomicrobiome assisted rice blast management strategy.Multi-pronged activities of phyllomicrobiome against Magnaporthe oryzae (antifungal activity), rice innate immunity (defense elicitation), and rice blast disease (disease suppression) have beenelaborated for effective management of blast by phyllomicrobiome re-engineering. ResultsRice phyllomicrobiome of tropical “Island-Zone” displayed marginally more bacterial community diversity than that of temperate ‘Mountain-Zone’. Principal coordinate analysis based on Bray Curtis and ANoSIM method indicated nearly converging-phyllomicrobiome profiles on two contrasting rice genotypes grown in the same agroclimatic zone. However, the rice genotype grown in the contrasting Mountain-zone and Island-zone displayed diverse-phyllomicrobiome profiles indicating a strong influence of environmental factors rather than the genotype on phyllomicrobiome structure and assembly. The predominance of Phyla such as Proteobacteria, Actinobacteria, and Firmicutes was observed on the rice phyllosphere irrespective of the genotypes and environmental conditions. The core-microbiome analysis showed multi-microbiota-core consisting of Acidovorax, Arthrobacter, Bacillus, Clavibacter, Clostridium, Cronobacter, Curtobacterium, Deinococcus, Erwinia, Exiguobacterium, Hymenobacter, Kineococcus, Klebsiella, Methylobacterium, Methylocella, Microbacterium, Nocardioides, Pantoea, Pedobacter, Pseudomonas, Salmonella, Serratia, Sphingomonas and Streptomyceson phyllosphere of rice genotypes grown in contrasting agroclimaticzones. The linear discriminant analysis (LDA) effect size (LEfSe) method revealed ten and two distinct bacterial genera in blast-resistant and -susceptible genotypes, respectively. The analysis further indicated 15 and 16 climate-zone specific bacterial genera for Mountain and Island zone, respectively. SparCC based network analysis of phyllomicrobiome showed hundreds of complex intra-microbial cooperative or competitive interactions on the rice genotypes and agroclimatic zones. Our microbiological validation of mNGS data further confirmed the presence of resident Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, andSphingomonason the rice phyllosphere.Strikingly,the two contrastingagroclimatic zones displayed genetically identical bacterial isolates on the phyllosphere that could be attributed to the spatio-temporal transmission of core-phyllomicrobiome, perhaps, aided by rice seeds. A total of 59 distinct bacterial isolates were obtained, identified, and evaluated for their functional attributes on Magnaporthe oryzae and rice plant. The phyllomicrobiome associated core-bacterial communities showed secreted-metabolite and volatile-compound mediated antifungal activity on M. oryzae.Uponphyllobacterization (a term coined for spraying of bacterial cells on the phyllosphere), the core bacterial species such as Acinetobacter baumannii, Aureimonas sp., Pantoea ananatis, P. eucrina,andPseudomonas putidaelicited plant defense and contributed significantly to blast disease suppression. Transcriptional analysis by qPCR indicated induction of rice innate immunity associated genes such as OsPR1.1, OsNPR1, OsPDF2.2, OsFMO, OsPAD4, OsCEBiP, andOsCERK1in phyllobacterized rice seedlings. ConclusionsThe rice genotypes growing in a particular agroclimatic zone showed a convergent phyllomicrobiome assemblage and composition. Conversely, diverging phyllomicrobiome assembly was observed on rice genotype cultivated in the contrasting agroclimatic zones.Agroclimatic zones and the associated climatic-factors rather than plant-genotypesper se appeared to drive phyllomicrobiome structure and composition on the rice genotypes. Our integrated mNGS method and microbiological validation divulged Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, andSphingomonasas core phyllomicrobiome of rice. Genetically identical bacterial communities belonging to Pantoea intercepted on the phyllosphere of rice grown in the two contrasting agroclimatic zones are suggestive of spatio-temporal transmission of phyllomicrobiome aided by seed. The core-microbiome mediated phyllobacterization showed potential for blast disease suppression by direct-antibiosis and defense elicitation. The identification of phyllosphere adapted functional core-bacterial communities in our study and their co-occurrence dynamics presents an opportunity to devise novel strategies for rice blast management through phyllomicrobiome reengineering in the future.

In rice farming, the blast disease caused by Magnaporthe oryzae (T.T. Hebert) M.E. Barr. is one of the primary production constraints worldwide. The current blast management options such as blast-resistant varieties and spraying fungicides are neither durable nor commercially and environmentally compatible. In the present study, we investigated the antifungal and defense elicitor activity of potassium phosphite (Phi) against M. oryzae on elite rice cultivar BPT5204 (popularly known as Samba Mahsuri in India) and its transgenic rice variant (ptxD-OE) over-expressing a phosphite dehydrogenase enzyme. The Phi was evaluated both preventively and curatively on rice genotypes where the preventive spray of Phi outperformed the Phi curative application with significant reductions in both rice blast severity (35.67-60.49%) and incidence (22.27-53.25%). Moreover, the application of Phi increased the levels of photosynthetic pigments (Chlorophyll and Carotenoids) coupled with increased activity of defense enzymes (PAL, SOD, and APx). Besides, Phi application also induced the expression of defense-associated genes (OsCEBiP and OsPDF2.2) in the rice leaf. Furthermore, the Phi application reduced the reactive Malondialdehyde (lipid peroxidation) to minimize the cellular damage incited by Magnaporthe in rice. Overall, the present study showed the potential of Phi for blast suppression on rice as an alternative to the current excessive use of toxic fungicides.

A fully finished, aluminum back-surface field, multi crystalline silicon solar cell was analyzed using Raman microspectroscopy. New insights into the process and material quality of the finished device is obtained. First, the image scan obtained on the multi crystalline silicon surface is reflective of the textured surface contributing to the surface topology. Second, the analysis helps to identify differences in the Raman spectra of the remnant saw marks on the silicon surface when compared to a textured silicon surface. Third, Raman analysis of the silver line shows a clear silver oxide signal that is detected up to 25 μm away from the edge of the silver line thus, quantifying the quality and effectiveness of the screen-printing and firing process. Finally, inclusions embedded inside the silicon surface are unambiguously identified as nanocrystalline silicon. Using confocal Raman microspectroscopy 3D tomography of the inclusions are constructed and the state of compressive stress around these particulates are measured. Taken together, these results demonstrate Raman microspectroscopy as a valuable tool for identification of micron-scale feature sizes and defects, otherwise too small to be identified using current metrology techniques.

Doped polycrystalline silicon (poly-Si) passivating contacts featuring a thin tunneling oxide have emerged as one of the most promising carrier selective contacts for crystalline silicon (c-Si) solar cells due to their very low recombination and resistive losses, as well as a high thermal stability compared to amorphous silicon (a-Si:H) heterojunctions. This contact technology consists of a heavily doped poly-Si layer on top of a c-Si substrate with an interfacial ultra-thin silicon oxide layer (SiO x ). To implement poly-Si passivating contacts into an industrial silicon solar cell production line, a cost-effective and high-throughput deposition process is required. Atmospheric pressure chemical vapor deposition (APCVD) process is a single side deposition process that requires no vacuum or plasma systems and is very well suited for high volume manufacturing. In this work, we present an in-line APCVD process for depositing heavily phosphorus doped poly-Si films to form low recombination electron contacts using silane (SiH 4 ) and phosphine (PH 3 ) as precursor gases. The as-deposited samples went through different post deposition annealing processes for solid phase crystallization, dopant activation and dopant diffusion. We have studied the effect of different process parameters like deposition temperature, precursor gas ratio and different post deposition treatments etc. on the surface passivation quality of this contact.

Plant roots affect soil water regime through root-water uptake upon transpiration. This process induces soil matric suction, which affects soil hydraulic conductivity, soil shear strength and hence shallow soil stability. This is referred to as plant hydrological reinforcement in the soil bioengineering application. Recent experimental evidence put forward by the authors has demonstrated that plant hydrological reinforcement should not be exclusively limited to the effects of root-water uptake and plant transpiration. The presentation will provide some new evidence of other potential aspects of plant hydrological reinforcement, namely (1) root-induced changes in soil hydraulic properties, (2) root water-dependent bio-hydro-mechanical properties. In aspect (1), laboratory test results on how root growth dynamic alter the soil pore size distribution and hence affect both the soil water retention curve and hydraulic conductivity will be presented. To highlight the effects of these root-induced changes in soil properties on slope water regime and slope stability, numerical simulation employing a dual-permeability water transport model in unsaturated rooted soil will be discussed. In aspect (2), a new concept, hysteretic root water retention curve (relationship between root water content and root water potential), will be introduced with support of some preliminary data. How root water retention affects the root biomechanical properties including not only tensile strength and Young’s modulus that have received wide attention in the soil bioengineering literature but also breakage strain will be presented. New data will be provided in order to attempt to use root water content to explain the large variability of biomechanical properties observed in the literature.

Background The fundamental role and contributions of phyllosphere habitat in shaping plant functional ecology are poorly investigated, and often underestimated. Phyllosphere -the harsh and dynamic foliar-photosynthetic-habitat is continuously exposed to vagaries of changing weather events during the entire plant life. With its adapted microbiota, the phyllosphere-niche brings microbial diversity to the plant-holobiont pool and potentially modulates a multitude of plant and agronomic traits. The phyllomicrobiome structure and the consequent ecological functions are vulnerable to a host of biotic (Genotypes) and abiotic-factors (Environment) which is further compounded by agronomic-transactions on domesticated agricultural crops. However, the ecological forces driving the phyllomicrobiome assemblage and functions are among the most under-studied aspects of plant biology. Despite the reports on the occurrence of diverse prokaryotic phyla such as Proteobacteria, Firmicutes, Bacteroides, and Actinobacteria on phyllosphere habitat, the functional characterization leading to their utilization for agricultural sustainability is not yet adequately explored.Currently, the metagenomic-Next-Generation-Sequencing (mNGS) technique scanning the conserved V3-V4 region of ribosomal RNA gene is a widely adopted strategy for microbiome-investigations. However, the structural and functional validation of mNGS annotations by microbiological methods is not integrated into the microbiome exploration-programs. In the present study, we combined the high throughput mNGS approach with conventional microbiological methods to decipher the core-functional-phyllomicrobiome of contrasting rice genotypes varying in their response to blast disease grown in contrasting agroclimatic zones in India. We, further, scanned the rice phyllosphere by electron microscopy to show the microbial communities on leaf. Magnaporthe oryzae -the phyllosphere pathogen inciting necrotic lesion on cereal crops is managed by the deployment of ‘non-durable’ blast resistance genes and ‘toxic’ fungicidal molecules. Nowadays, there is a growing consensus for devising an alternative strategy for mitigating blast owing to a recent ban on the use of most commonly used fungicidal molecule, tricyclazole. In the present work, we further identified phyllosphere- core-functional microbial groups leading to the proposal of phyllomicrobiome assisted rice blast management strategy. Multi-pronged activities of phyllomicrobiome against Magnaporthe oryzae (antifungal activity), rice innate immunity (defense elicitation), and rice blast disease (disease suppression) have been elaborated for effective management of blast by phyllomicrobiome re-engineering. ResultsRice phyllomicrobiome of tropical “Island-Zone” displayed marginally more bacterial community diversity than that of temperate ‘Mountain-Zone’. Principal coordinate analysis based on Bray Curtis and ANoSIM method indicated nearly converging-phyllomicrobiome profiles on two contrasting rice genotypes grown in the same agroclimatic zone. However, the rice genotype grown in the contrasting Mountain-zone and Island-zone displayed diverse-phyllomicrobiome profiles indicating a strong influence of environmental factors rather than the genotype on phyllomicrobiome structure and assembly. The predominance of Phyla such as Proteobacteria, Actinobacteria, and Firmicutes was observed on the rice phyllosphere irrespective of the genotypes and environmental conditions. The core-microbiome analysis showed multi-microbiota-core consisting of Acidovorax, Arthrobacter, Bacillus, Clavibacter, Clostridium, Cronobacter, Curtobacterium, Deinococcus, Erwinia, Exiguobacterium, Hymenobacter, Kineococcus, Klebsiella, Methylobacterium, Methylocella, Microbacterium, Nocardioides, Pantoea, Pedobacter, Pseudomonas, Salmonella, Serratia, Sphingomonas and Streptomyces on phyllosphere of rice genotypes grown in contrasting agroclimatic zones. The linear discriminant analysis (LDA) effect size (LEfSe) method revealed ten and two distinct bacterial genera in blast-resistant and -susceptible genotypes, respectively. The analysis further indicated 15 and 16 climate-zone specific bacterial genera for Mountain and Island zone, respectively. SparCC based network analysis of phyllomicrobiome showed hundreds of complex intra-microbial cooperative or competitive interactions on the rice genotypes and agroclimatic zones. Our microbiological validation of mNGS data further confirmed the presence of resident Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, and Sphingomonas on the rice phyllosphere. Strikingly, the two contrasting agroclimatic zones displayed genetically identical bacterial isolates on the phyllosphere that could be attributed to the spatio-temporal transmission of core-phyllomicrobiome, perhaps, aided by rice seeds. A total of 59 distinct bacterial isolates were obtained, identified, and evaluated for their functional attributes on Magnaporthe oryzae and rice plant. The phyllomicrobiome associated core-bacterial communities showed secreted-metabolite and volatile-compound mediated antifungal activity on M. oryzae. Upon phyllobacterization (a term coined for spraying of bacterial cells on the phyllosphere), the core bacterial species such as Acinetobacter baumannii, Aureimonas sp., Pantoea ananatis, P. eucrina, and Pseudomonas putida elicited plant defense and contributed significantly to blast disease suppression. Transcriptional analysis by qPCR indicated induction of rice innate immunity associated genes such as OsPR1.1, OsNPR1, OsPDF2.2, OsFMO, OsPAD4, OsCEBiP, and OsCERK1 in phyllobacterized rice seedlings. ConclusionsThe rice genotypes growing in a particular agroclimatic zone showed a convergent phyllomicrobiome assemblage and composition. Conversely, diverging phyllomicrobiome assembly was observed on rice genotype cultivated in the contrasting agroclimatic zones. Agroclimatic zones and the associated climatic-factors rather than plant-genotypes per se appeared to drive phyllomicrobiome structure and composition on the rice genotypes. Our integrated mNGS method and microbiological validation divulged Acinetobacter, Aureimonas, Curtobacterium, Enterobacter, Exiguobacterium, Microbacterium, Pantoea, Pseudomonas, and Sphingomonas as core phyllomicrobiome of rice. Genetically identical bacterial communities belonging to Pantoea intercepted on the phyllosphere of rice grown in the two contrasting agroclimatic zones are suggestive of spatio-temporal transmission of phyllomicrobiome aided by seed. The core-microbiome mediated phyllobacterization showed potential for blast disease suppression by direct-antibiosis and defense elicitation. The identification of phyllosphere adapted functional core-bacterial communities in our study and their co-occurrence dynamics presents an opportunity to devise novel strategies for rice blast management through phyllomicrobiome reengineering in the future.

Permanent wilting point (PWP) is generally used to ascertain plant resistance against abiotic drought stress and designated as the soil water content (θ) corresponding to soil suction (ψ) at 1500 kPa obtained from the soil water retention curve. Determination of PWP based on only pre-assumed ψ may not represent true wilting condition for soils with contrasting water retention abilities. In addition to ψ, there is a need to explore significance of additional plant parameters (i.e., stomatal conductance and photosynthetic status) in determining PWP. This study introduces a new framework for determining PWP by integrating plant leaf response and ψ during drought. Axonopus compressus were grown in two distinct textured soils (clayey loam and silty sand), after which drought was initiated till wilting. Thereafter, ψ and θ within the root zone were measured along with corresponding leaf stomatal conductance and photosynthetic status. It was found that coarse textured silty sand causes wilting at much lower ψ (≈ 300 kPa) than clayey loam (≈ 1600 kPa). Plant response to drought was dependent on the relative porosity and mineralogy of the soil, which governs the ease at which roots can grow, assimilate soil O2, and uptake water. For clay loam, the held water within the soil matrix does not facilitate easy root water uptake by relatively coarse root morphology. Contrastingly, fine root hair formation in silty sand facilitated higher plant water uptake and doubled the plant survival time.

Biochar produced from the pyrolysis of plant-based feedstock has been advocated as an alternative soil amendment for landfill cover. Previous literature indicated that the pyrolysis temperature influences the intra-pore distribution and surface functional groups (especially hydroxyl groups), resulting in “love-hate relationship” of the biochar-amended soil (BAS) with water. From the purview of geotechnical engineering, the effects of pyrolysis temperature on geotechnical properties are rarely investigated. In total, three biochar rates (0, 5, and 10%) were considered for a set of geotechnical experiments in sand clay mixture soil with biochar produced at 350°C and 550°C. Test results show that biochar addition in soil, in general regardless of pyrolysis temperature, increased the optimum moisture content (OMC), plasticity index, and soil water retention characteristics (SWRC) and decreased the maximum dry density (MDD), shear strength parameters (cohesion, friction), and erosion rates. Whilst comparing the pyrolysis temperature effects on two biochar-amended soils, only marginal effects (in terms of magnitude) on SWRC were observed. The most significant decrease of MDD (or increase of OMC) for 5% (w/w) and 10% (w/w) biochar additions occurred at pyrolysis temperatures of 550 °C and 350°C, respectively. In addition, biochar produced at lower pyrolysis temperature (350 °C) was more effective in reducing cracks and enhancing shrinkage area ratio. Ten percent of biochar addition with pyrolysis temperature of 350 °C was the optimum combination in resisting soil erosion. The study provides evidence that the geotechnical properties of biochar-amended soils for landfill cover soil applications could be tailor made by controlling the pyrolysis temperature.

Biochar has been recently investigated as an eco-friendly material in bio-engineered slopes/landfill covers. A majority of recent studies have focused on analyzing water retention behavior while very few have examined dynamic behavior (i.e., cyclic loading due to earthquake, wind, or wave) of biochar amended soil. As far as the authors are aware, there is no study on the dynamic behavior of biochar amended soils. Considering the above mentioned study as a major objective, field excavated soil was collected and mixed with in-house produced biochar from peach endocarps, at three amendment rates (5%, 10%, and 15%). The un-amended bare soil and biochar amended soil were imposed to a cyclic load in a self-designed apparatus and the corresponding stress-strain parameters were measured. Dynamic parameters such as shear modulus and damping ratio were computed and the results were compared between bare and biochar amended soil. Furthermore, the residual cyclic strength of each soil types were correlated with an estimated void ratio to understand the interrelation between dynamic loading responses and biochar amended soils. The major outcomes of this study show that the addition of biochar decreases the void ratio, thereby increasing the shear modulus and residual cyclic strength. However, the modulus and strength values attenuates after 15 cycles due to an increase in pore water pressure. In contrary, at higher amendment rates, Biochar Amended Soils (BAS) forms clay-carbon complex and decreases both shear modulus and residual cyclic strength.