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At least 883 records · Page 49

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DOE OSTI2019

Photoelectron spectroscopy and theoretical studies of PCSe-, AsCS-, AsCSe-, and NCSe-: Insights into the electronic structures of the whole family of ECX- anions (E = N, P, and As; X = O, S, and Se)

The newly synthesized, phosphorus- and arsenic-containing analogues of the thio- and seleno-cyanate anions, PCSe-, AsCS-, and AsCSe-, as well as the known ion NCSe-, were investigated in the gas phase by negative ion photoelectron spectroscopy (NIPES), velocity-map imaging (VMI) spectroscopy, and quantum chemical computations. The electron affinities (EA), spin-orbit (SO) splittings, and “symmetric” / “antisymmetric” stretching frequencies (?1 and ?2) of the neutral radicals ECX• (E = N, P and As, X = S and Se), generated by electron detachment from the corresponding anions, were obtained from the spectra. The calculated EAs, SO splittings, and vibrational frequencies are in excellent agreement with the measured values. These newly obtained values, when combined with those previously determined for the lighter analogues, show interesting trends on descending the pnictogen and chalcogen series. These trends are rationalized on the basis of electronegativity arguments, the electron distribution in the HOMO, and NBO/NRT analyses.

Yuan, Qinqin↗

DOE OSTI2020

Sulfidation and selenidation of nickel nanoparticles

Abstract Transition metal chalcogenide nanoparticles (NPs) are of interest for energy applications, including batteries, supercapacitors, and electrocatalysis. Many methods have been established for synthesizing Ni NPs, and conversion chemistry to form Ni oxide and phosphides from template Ni NPs is well‐understood. Sulfidation and selenidation of Ni NPs have been much less explored, however. We report a method for the conversion of Ni template NPs into sulfide and selenide product NPs using elemental sulfur, 1‐hexadecanthiol, thiourea, trioctylphosphine sulfide, elemental selenium, and selenourea. While maintaining mole ratios of 2 mmol sulfur/selenium precursor: mmol Ni, products with phases of Ni 3 S 2 , Ni 9 S 8 , NiS, NiSO 4 ·6H 2 O, Ni 3 S 4 , Ni 3 Se 2 , and NiSe have been obtained. The products have voids that form through the Kirkendall effect during interdiffusion. Trends relating the chemical properties of the precursors to the phases of the products have been identified. While some precursors contained phosphorus, there was no significant incorporation of phosphorus in any of the products. An increase of the NP size during sulfidation and selenidation is consistent with ripening. The application of Ni sulfide and selenide NPs as electrocatalysts for the hydrogen evolution reaction is also demonstrated.

Lynch, Brian B.↗

DOE OSTI2025

Pyrrole‐Imine Macrocycle: Self‐Organizing Cross‐Reactive Anion Receptor and Sensor

Self-organizing macrocyclic receptor-sensors for phosphorus oxyanions, phosphates, and phosphonates comprising imine moieties were prepared by condensation of dipyrrolylmethane dicarbaldehyde with diethylene triamine. The incorporation of flexible ethylene moieties endows the macrocycle with unprecedented flexibility and ability to accommodate numerous phosphorus oxyanions from orthophosphate to large anions such as ATP or phosphonate glyphosate. The anion binding was elucidated by NMR titrations, low-temperature NMR, and NOESY NMR. The incorporation of dansyl fluorophore enables sensing of anions using the fluorescence signal, whereas the changes in fluorescence intensity, width of the fluorescence band, and position of the maxima are analyte-specific and useful in recognition and identification of eleven different P-oxyanions in water. The affinity (K assoc ) for Na + salts was H 2 PO 4 − ≈ Methylphosphonate > H 2 P 2 O 7 2− > Phenylphosphonate- > Glyphosate 2− > AMP 2− > ADP 2− > ATP 2− . Interestingly, phosphonates, including methylphosphonate and glyphosate anions, were also found to display a strong affinity (K assoc ∼10 6 M −1 ) while halides, nitrate, carbonates, or hydrogen sulfate did not show a significant affinity. The determined fluorescence spectral parameters were used to classify the 12 analytes (11 anions and water) using Linear Discriminant Analysis (LDA). Quantification was performed using LDA and Support Vector Machine (SVM), and the phosphonate concentrations in unknown samples were determined with an error of 3.5% or lower.

anions↗

DOE OSTI2025

New Phosphoranylideneketenes and Phosphoranylidenethioketenes‐Synthesis, Structure, Spectroscopy, and Lewis Base Properties

Posphoranylideneketene Ph 3 PCCO and its sulfur analogue, Ph 3 PCCS, are cumulated ylides that exhibit diverse reactivity and distinct structural features. Herein, we present the first systematic study of substituent effects on the structures and bonding of a series of aryl- and alkyl-substituted phosphoranylideneketenes, R 3 PCCO [R = Et, cyclohexyl, NMe 2 , 4-Me 2 N-C 6 H 4 , 4-MeO-C 6 H 4 , 4-CF 3 -C 6 H 4 , 3,5-(CF 3 ) 2 -C 6 H 3 ], prepared from the corresponding phosphonium salts, [R 3 PCH 2 COOEt]X (X = Br, I) and two equivalents of Na[N(SiMe 3 ) 2 ]. Multinuclear NMR and IR spectroscopy, supported by single-crystal X-ray diffraction, revealed that the bond strength within the central P═C═C═O fragment increases with the electron-deficiency of the aryl substituents at phosphorus. The corresponding phosphoranylidenethioketenes, R 3 PCCS (R = Et, cyclohexyl, NMe 2 , 4-Me 2 N-C 6 H 4 , 4-MeO-C 6 H 4 , 4-CF 3 -C 6 H 4 ), were obtained by reactions of R 3 PCCO with CS 2 . Here, the rate of conversion of R 3 PCCO into R 3 PCCS decreases with increasing electron deficiency at phosphorus. Both R 3 PCCO and R 3 PCCS act as relatively weak ambidentate Lewis donors, yet they form stable acid-base adducts with strong Lewis acids such as B(C 6 F 5 ) 3 and Al(C 6 F 5 ) 3 .

Lewis acid-base adduct↗

DOE OSTI2021

Bringing function to structure: Root–soil interactions shaping phosphatase activity throughout a soil profile in Puerto Rico

Abstract Large areas of highly productive tropical forests occur on weathered soils with low concentrations of available phosphorus (P). In such forests, root and microbial production of acid phosphatase enzymes capable of mineralizing organic phosphorus is considered vital to increasing available P for plant uptake. We measured both root and soil phosphatase throughout depth and alongside a variety of root and soil factors to better understand the potential of roots and soil biota to increase P availability and to constrain estimates of the biochemical mineralization within ecosystem models. We measured soil phosphatase down to 1 m, root phosphatase to 30 cm, and collected data on fine‐root mass density, specific root length, soil P, bulk density, and soil texture using soil cores in four tropical forests within the Luquillo Experimental Forest in Puerto Rico. We found that soil phosphatase decreased with soil depth, but not root phosphatase. Furthermore, when both soil and root phosphatase were expressed per soil volume, soil phosphatase was 100‐fold higher that root phosphatase. Both root and soil factors influenced soil and root phosphatase. Soil phosphatase increased with fine‐root mass density and organic P, which together explained over 50% of the variation in soil phosphatase. Over 80% of the variation in root phosphatase per unit root mass was attributed to specific root length (positive correlation) and available (resin) P (negative correlation). Synthesis : Fine‐root traits and soil P data are necessary to understand and represent soil and root phosphatase activity throughout the soil column and across sites with different soil conditions and tree species. These findings can be used to parameterize or benchmark estimates of biochemical mineralization in ecosystem models that contain fine‐root biomass and soil P distributions throughout depth.

59 BASIC BIOLOGICAL SCIENCES↗

DOE OSTI2025

Clarifying the trophic state concept to advance macroscale freshwater science and management

For over a century, ecologists have used the concept of trophic state (TS) to characterize an aquatic ecosystem's biological productivity. However, multiple TS classification schemes, each relying on a variety of measurable parameters as proxies for productivity, have emerged to meet use‐specific needs. Frequently, chlorophyll a, phosphorus, and Secchi depth are used to classify TS based on autotrophic production, whereas phosphorus, dissolved organic carbon, and true color are used to classify TS based on both autotrophic and heterotrophic production. Both classification approaches aim to characterize an ecosystem's function broadly, but with varying degrees of autotrophic and heterotrophic processes considered in those characterizations. Moreover, differing classification schemes can create inconsistent interpretations of ecosystem integrity. For example, the US Clean Water Act focuses exclusively on algal threats to water quality, framed in terms of eutrophication in response to nutrient loading. This usage lacks information about non‐algal threats to water quality, such as dystrophication in response to dissolved organic carbon loading. Consequently, the TS classification schemes used to identify eutrophication and dystrophication may refer to ecosystems similarly (e.g., oligotrophic and eutrophic), yet these categories are derived from different proxies. These inconsistencies in TS classification schemes may be compounded when interdisciplinary projects employ varied TS frameworks. Even with these shortcomings, TS can still be used to distill information on complex aquatic ecosystem function into a set of generalizable expectations. The usefulness of distilling complex information into a TS index is substantial such that usage inconsistencies should be explicitly addressed and resolved. To emphasize the consequences of diverging TS classification schemes, we present three case studies for which an improved understanding of the TS concept advances freshwater research, management efforts, and interdisciplinary collaboration. To increase clarity in TS, the aquatic sciences could benefit from including information about the proxy variables, ecosystem type, as well as the spatiotemporal domains used to classify TS. As the field of aquatic sciences expands and climatic irregularity increases, we highlight the importance of re‐evaluating fundamental concepts, such as TS, to ensure their compatibility with evolving science.

classification↗

DOE OSTI2021

Rhizosphere bacteria containing ACC deaminase decrease root ethylene emission and improve maize root growth with localized nutrient supply

Abstract Localized nutrient supply can enhance maize root proliferation, but also increase root ethylene production. Whether engineering ethylene signalling in the rhizosphere can further enhance root growth and nutrient uptake remains unknown. Here, field and column experiments for maize ( Zea mays . L) were designed as different nutrient treatments (broadcast or localized nutrient supply containing ammonium and phosphorus) with or without inoculation with rhizobacterium Variovorax paradoxus 5C‐2 containing the 1‐aminocyclopropane‐1‐carboxylate (ACC) deaminase. Rhizobacterial inoculation increased shoot biomass by 12% and root length density by 50% with localized nutrient supply. Meanwhile, localized nutrient supply increased root ethylene production by 54% compared with broadcast, and rhizobacterial inoculation prevented the increase in root ethylene. Reduced root ethylene production following V. paradoxus 5C‐2 inoculation was highly associated with a greater proportion of fine root proliferation under localized nutrient supply, which may account for the increased nitrogen and phosphorus uptake. Our work sheds light on the understanding of the interactions between root and microbe through taking hormone into consideration to dissect the relationship between below ground and above ground. It is useful to explore the strategy of soil–crop management by introducing rhizosphere microorganisms to regulate plant ethylene signal and then benefit sustainable agriculture.

Jin, Kemo↗

DOE OSTI2023

Effects of Livestock Exclusion on Stream Habitat and Aquatic Biota: A Review and Recommendations for Implementation and Monitoring

Abstract To inform riparian restoration, research, and monitoring and to provide management recommendations, we reviewed published studies evaluating the physical and biological effectiveness of livestock exclusion and grazing reduction on various metrics in riparian and aquatic areas. We identified 95 North American studies that reported the effects of livestock grazing reduction on physical habitat (channel morphology, mesohabitats, substrate, and bank stability), biological assemblages (riparian vegetation, macroinvertebrates, fish, and birds), and water quality metrics (temperature, nitrates, phosphorus, and turbidity). Most studies reported that methods to reduce or exclude livestock decreased channel width, width-to-depth ratio, bank erosion, soil bulk density, bare ground, water temperature, nitrogen, and phosphorus and increased riparian vegetation (cover, height, productivity, biomass, and abundance), riparian bird abundance, and young-of-the-year fishes. Results for channel depth, instream substrate, mesohabitats, water depth, juvenile and adult fishes, and macroinvertebrates showed no consistent response to exclusion. Project success was influenced by the time since exclusion; whether there was complete exclusion or continued grazing; and local climate, geology, and soils. Apart from bank erosion and stability, most of the physical and biological metrics took more than a decade to respond to livestock exclusion. However, coupling exclusion with planting and other restoration measures decreased the recovery time. Complete exclusion of livestock produced more consistent improvements in riparian condition and other metrics than rest–rotation or other grazing management strategies. Understanding how physical and biological metrics respond to livestock exclusion will require (1) focused, long-term studies using before–after or before–after, control–impact designs; and (2) monitoring of metrics that most consistently respond to exclusion. Ultimately, the design of exclusions should be driven by local climate, geology, biophysical conditions, and management history. Our results highlight the need for watershed-scale approaches to excluding livestock from broad areas and the need for implementation monitoring to ensure that fencing and other exclusion measures continue to exclude livestock and produce the desired responses.

Krall, Michelle↗

DOE OSTI2021

Morphology, microstructure, and doping behaviour: A comparison between different deposition methods for poly-Si/SiO x passivating contacts

In this work, we study how crystallographic structures, optoelectronic properties, and nanoscale surface morphologies of ex situ phosphorus-doped polycrystalline silicon (poly-Si)/SiO x passivating contacts, formed by different deposition methods (sputtering, plasma-enhanced chemical vapour deposition [PECVD], and low-pressure chemical vapour deposition [LPCVD]), are investigated and compared. Across all these deposition technologies, we noted the same trend: higher diffusion temperatures yield films that are more crystalline but that have rougher surface morphologies due to bigger surface crystal grains. Also, the recrystallization process of the as-deposited Si films starts from the SiO x interface, rather than from the film surface and bulk. However, there are some distinct differences among these technologies. First, the LPCVD method yields the lowest deposition rate, roughest surfaces, and smallest degree of crystallinity on finished poly-Si films. In contrast, the PECVD method has the highest deposition rate and smoothest surfaces for both as-deposited Si and annealed poly-Si films. Second, as-deposited sputtered and PECVD Si films contain only an amorphous phase, whereas as-deposited LPCVD films already has some crystalline phase. Third, the LPCVD phosphorus in-diffusion into the substrate depends strongly on the initial film thickness, whereas for the other two methods, it is weakly dependent on thickness. Finally, the passivation quality of every poly-Si film type has different responses to the film thickness and diffusion temperature, suggesting that the ex situ doping optimization should be performed independently.

14 SOLAR ENERGY↗

DOE OSTI2015

Lattice dynamics and thermoelectric properties of nanocrystalline silicon-germanium alloys: Lattice dynamics and thermoelectric properties of nc Si-Ge alloys

The lattice dynamics and thermoelectric properties of sintered phosphorus-doped nanostructured silicon–germanium alloys obtained by gas-phase synthesis were studied. Measurements of the density of phonon states by inelastic neutron scattering were combined with measurements of the elastic constants and the low-temperature heat capacity. A strong influence of nanostructuring and alloying on the lattice dynamics was observed. The thermoelectric transport properties of samples with different doping as well as samples sintered at different temperature were characterized between room temperature and 1000°C. A peak figure of merit zT=0.88 at 900°C is observed and is comparatively insensitive to the aforementioned parameter variations.

36 MATERIALS SCIENCE↗

DOE OSTI2014

Sources and resources: importance of nutrients, resource allocation, and ecology in microalgal cultivation for lipid accumulation

Regardless of current market conditions and availability of conventional petroleum sources, alternatives are needed to circumvent future economic and environmental impacts from continued exploration and harvesting of conventional hydrocarbons. Diatoms and green algae (microalgae) are eukaryotic photoautotrophs that can utilize inorganic carbon (e.g., CO 2 ) as a carbon source and sunlight as an energy source, and many microalgae can store carbon and energy in the form of neutral lipids. In addition to accumulating useful precursors for biofuels and chemical feed stocks, the use of autotrophic microorganisms can further contribute to reduced CO 2 emissions through utilization of atmospheric CO 2 . Because of the inherent connection between carbon, nitrogen, and phosphorus in biological systems, macronutrient deprivation has been proven to significantly enhance lipid accumulation in different diatom and algae species. However, much work is needed to understand the link between carbon, nitrogen, and phosphorus in controlling resource allocation at different levels of biological resolution (cellular versus ecological). An improved understanding of the relationship between the effects of N, P, and micronutrient availability on carbon resource allocation (cell growth versus lipid storage) in microalgae is needed in conjunction with life cycle analysis. This mini-review will briefly discuss the current literature on the use of nutrient deprivation and other conditions to control and optimize microalgal growth in the context of cell and lipid accumulation for scale-up processes.

09 BIOMASS FUELS↗

DOE OSTI2018

Spatial Variation of Soil CO 2 , CH 4 and N 2 O Fluxes Across Topographical Positions in Tropical Forests of the Guiana Shield

The spatial variation of soil greenhouse gas fluxes (GHG; carbon dioxide—CO 2 , methane—CH 4 and nitrous oxide—N 2 O) remains poorly understood in highly complex ecosystems such as tropical forests. Here, we used 240 individual flux measurements of these three GHGs from different soil types, at three topographical positions and in two extreme hydric conditions in the tropical forests of the Guiana Shield (French Guiana, South America) to (1) test the effect of topographical positions on GHG fluxes and (2) identify the soil characteristics driving flux variation in these nutrient-poor tropical soils. Surprisingly, none of the three GHG flux rates differed with topographical position. CO 2 effluxes covaried with soil pH, soil water content (SWC), available nitrogen and total phosphorus. The CH 4 fluxes were best explained by variation in SWC, with soils acting as a sink under drier conditions and as a source under wetter conditions. Unexpectedly, our study areas were generally sinks for N 2 O and N 2 O fluxes were partly explained by total phosphorus and available nitrogen concentrations. This initial work describing the spatial variation of soil fluxes of the three main GHGs measured simultaneously in forests of the Guiana Shield lays the foundation for specific studies of the processes underlying the observed patterns.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2018

Microbial community structure and functions differ between native and novel (exotic-dominated) grassland ecosystems in an 8-year experiment

Aims Grasslands dominated by non-native (exotic) species have replaced purely native-dominated areas in many parts of the world forming ‘novel’ ecosystems. It is still poorly understood how soil microbial communities and their functions are affected between these native- and exotic-dominated sites. Methods We sampled 64 experimental grassland plots in central Texas with plant species mixtures of either all native or all exotic species; half with summer irrigation. We tested how native vs. exotic plant species mixtures and summer irrigation affected bacterial and fungal community composition and structure, microbial phylotype co-occurrence, and rates of mineralization across sampling years. Results Plant origin significantly affected fungal community composition and structure, but not diversity, throughout the length of the study, while changes in bacterial communities were limited to certain years. Nitrogen and phosphorus mineralization rates were higher under native plant mixtures, and correlated with changes in particular fungal species. Microbial communities were more structured in exotic than native grassland plots, especially for the fungal community. Conclusions The results indicate that conversion of native to exotic grasslands will more strongly impact fungal than bacterial communities structure. Furthermore, these impacts can alter ecosystem functioning belowground via changes in nitrogen and phosphorus cycling.

54 ENVIRONMENTAL SCIENCES↗

DOE OSTI2019

Thermally Assisted Adhesion Enhancement in High-Phosphorous Electroless Nickel Plating

High-phosphorus electroless nickel is a widely recognized protective plating for oilfield metallic parts subject to corrosion and wear. In the present investigation, thermally activated diffusion treatment was applied to enhance electroless nickel (10-13 wt.% P) plating adhesion on low-alloy steel (UNS G41400) and reduce the risks of spalling. High-phosphorus electroless nickel (10-13 wt.% P) was applied to a variety of UNS G41400 low-alloy steel test samples as per ASTM B733 that were subsequently heat-treated in air for four distinct temperatures, i.e., 510, 540, 570, and 600 °C for 2-10 h. Following post-plating diffusion heat treatments, the initial amorphous electroless nickel was replaced by Ni{sub 3}P precipitates dispersed in a crystalline nickel-rich phase, with an average hardness improvement from 500 to 700 HK. An increased atomic interdiffusion (from 400 to 3.5 µm) was observed at plating–substrate interfaces, resulting in enhanced adhesion and reduced susceptibility toward spalling. This improvement in adhesion was measured repeatedly through post-bending crack analyses and subsequently validated by interface microindentation. Along with diffusion across plating–substrate interface, nickel oxide formation on surface by oxidation was observed to grow at quasi-parabolic rate with no detrimental impact on spalling. In all cases, plating adhesion was improved by heat treatments due to the diffusion-controlled formation of a seemingly ductile layer.

36 MATERIALS SCIENCE↗

DOE OSTI2015

Life Cycle Assessment of Switchgrass Cellulosic Ethanol Production in the Wisconsin and Michigan Agricultural Contexts

Spatial variability in yields and greenhouse gas emissions from soils has been identified as a key source of variability in life cycle assessments (LCAs) of agricultural products such as cellulosic ethanol. This study aims to conduct an LCA of cellulosic ethanol production from switchgrass in a way that captures this spatial variability and tests results for sensitivity to using spatially averaged results. The Environment Policy Integrated Climate (EPIC) model was used to calculate switchgrass yields, greenhouse gas (GHG) emissions, and nitrogen and phosphorus emissions from crop production in southern Wisconsin and Michigan at the watershed scale. These data were combined with cellulosic ethanol production data via ammonia fiber expansion and dilute acid pretreatment methods and region-specific electricity production data into an LCA model of eight ethanol production scenarios. Standard deviations from the spatial mean yields and soil emissions were used to test the sensitivity of net energy ratio, global warming potential intensity, and eutrophication and acidification potential metrics to spatial variability. Substantial variation in the eutrophication potential was also observed when nitrogen and phosphorus emissions from soils were varied. This work illustrates the need for spatially explicit agricultural production data in the LCA of biofuels and other agricultural products.

Acidification↗

DOE OSTI2019

Impact of Lubricant Oil Additives on the Performance of Pd-Based Three-Way Catalysts

As alternative lubricant anti-wear additives are sought to reduce friction and improve overall fuel economy, it is important that these additives are also compatible with current emissions control catalysts. In the present work, a second-generation oil-miscible phosphorous-containing ionic liquid (IL), is evaluated for its impact on Pd-based three-way catalyst (TWC) reactivity and benchmarked against the industry standard zinc dialkyl-dithio-phosphate (ZDDP). The TWCs are exposed to the lubricant additives in an engine bench under four different scenarios: base case with no additive (NA), ZDDP-only, IL-only, and IL + ZDDP. The engine-aged TWC samples, along with the as-received TWC, are characterized through various analytical techniques including catalyst reactivity evaluation in a bench-flow reactor. The temperature of 50% conversion (T 50 ) for the ZDDP-aged TWC increases by 11, 21, and 36 °C for CO, C 3 H 6 , and C 3 H 8 , respectively, as compared with the no-additive case. Similarly, the T50 for IL-only and IL + ZDDP-aged TWCs also increase as compared with the no-additive case. Even though the water-gas-shift (WGS) reactivity is similar for all engine-aged samples, the IL-aged TWC had higher oxygen storage capacity than the ZDDP-aged TWC. EPMA analysis reveals penetration of phosphorus deep into the washcoat for all engine-aged TWCs. Results from XRD indicate the presence of CePO 4 and AlPO 4 on the washcoat of IL, ZDDP, and IL + ZDDP-aged TWC samples but not on the fresh and NA TWC samples. Additionally, ICP-OES results show a large amount of phosphorus in the washcoat of IL, ZDDP and IL + ZDDP-aged TWC samples and a lesser amount in NA TWC samples.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗

DOE OSTI2018

The limiting layer of fish scales: structure and properties

Fish scales serve as a flexible natural armor that have received increasing attention across the materials community. Most efforts in this area have focused on the composite structure of the predominately organic elasmodine, and limited work addresses the highly mineralized external portion known as the Limiting Layer (LL). This coating serves as the first barrier to external threats and plays an important role in resisting puncture. In this investigation the structure, composition and mechanical behavior of the LL were explored for three different fish, including the arapaima (Arapaima gigas), the tarpon (Megalops atlanticus) and the carp (Cyprinus carpio). The scales of these three fish have received the most attention within the materials community. Features of the LL were evaluated with respect to anatomical position to distinguish site-specific functional differences. Results show that there are significant differences in the surface morphology of the LL from posterior and anterior regions in the scales, and between the three fish species. The calcium to phosphorus ratio and the mineral to collagen ratios of the LL are not equivalent among the three fish. Results from nanoindentation showed that the LL of tarpon scales is the hardest, followed by the carp and the arapaima and the differences in hardness are related to the apatite structure, possibly induced by the growth rate and environment of each fish.

Arola, Dwayne D.↗

DOE OSTI2016

Zinc concentration affects the functional groups of microbial communities in sugarcane-cultivated soil

The addition of zinc (Zn) to the soil has significant gains in sugarcane productivity. The understanding of the consequences of zinc application requires insight into ecological aspects of changes in soil microbial communities. Here, we evaluated the effects of zinc application on richness, diversity, evenness and structure of microbial functional genes in sugarcane-cultivated soil, and response thresholds of abundance for groups of microbial functional genes on different zinc concentrations added to the soil (0, 5, 10 and 20 kg Zn ha -1 ) in two sugarcane fields in the Northeastern São Paulo state, Brazil. Using a high-density functional gene array termed GeoChip 5.0, which contains 101,796 distinct probes belonging to gene categories involved in zinc transport, secondary metabolism, stress, virulence and nutrient cycling, differences were observed in the functional gene structure of microbial communities and abundance of specific gene families with a threshold between 5 and 10 kg Zn ha -1 . However, the richness, diversity and evenness of functional genes did not differ across the zinc gradients in soil. Cluster analysis based on microbial functional subcategories revealed variation in abundances across the gradient of zinc concentrations in soil mainly for virulence, stress, secondary metabolism, and carbon- and phosphorus-cycling-related gene families. A threshold in abundance was observed between 5 and 10 kg Zn ha -1 with high abundance of microbial gene families associated with zinc transporter proteins, antioxidant enzymes, exoenzymes associated with infection, secretion proteins, virulence regulatory genes, carbon fixation, and phosphorus utilization in soils supplemented with up to 5 kg Zn ha -1 . In these same soils, reduced abundance was observed for gene families associated with methanogenesis, metabolism of halogen and carotenoid, and antiphagocytosis compared with soil supplements with 10 or 20 kg Zn ha -1 . The results suggest that changes in microbial functional gene structure and abundance could be used to evaluate the impact of soil management practices on soil microbial communities in sugarcane production fields.

54 ENVIRONMENTAL SCIENCES↗