Nitrogen fixation is an important biological process in terrestrial ecosystems and for global crop production. Legume nodulation and N2 fixation have been improved using nodule‐enhancing ...rhizobacteria (NER) under both regular and stressed conditions. The positive effect of NER on legume–rhizobia symbiosis can be facilitated by plant growth‐promoting (PGP) mechanisms, some of which remain to be identified. NER that produce aminocyclopropane‐1‐carboxylic acid deaminase and indole acetic acid enhance the legume–rhizobia symbiosis through (i) enhancing the nodule induction, (ii) improving the competitiveness of rhizobia for nodulation, (iii) prolonging functional nodules by suppressing nodule senescence and (iv) upregulating genes associated with legume–rhizobia symbiosis. The means by which these processes enhance the legume–rhizobia symbiosis is the focus of this review. A better understanding of the mechanisms by which PGP rhizobacteria operate, and how they can be altered, will provide opportunities to enhance legume–rhizobial interactions, to provide new advances in plant growth promotion and N2 fixation.
Electromagnetic ion cyclotron (EMIC) waves can act as a loss process for both ring current ions and radiation belt electrons, and the spatial and temporal characteristics of these waves are important ...for quantifying their effects on energetic particles. Here we utilize observations from multiple spacecraft to constrain the azimuthal and radial dimensions as well as the duration of an EMIC wave event occurring on the nightside of the inner magnetosphere on 7 July 2013. These combined observations reveal waves limited to a narrow radial extent but persisting ~10+ hr and spanning ~12 hr in local time. The solar wind conditions, geomagnetic activity, and plasma environment are also examined to better understand the conditions under which persistent nightside EMIC waves can occur. Relativistic electron phase space density profiles during this event reveal local minima concurrent with the wave activity, consistent with EMIC‐driven scattering and loss of radiation belt electrons.
Plain Language Summary
Various oscillating electric and magnetic fields, or waves, can interact with high‐energy particles in near‐Earth space and cause a change in the particles' energy and/or direction of motion. Where and when these waves occur can have a significant impact on how they interact with particles. Here we combine measurements from multiple spacecraft around the Earth to study one specific wave mode. While these waves are often thought to be localized and of short durations, we observe an event on 7 July 2013 where waves persist for over 10 hr and span the entire nightside of the Earth. We explore the dynamics of the Earth's magnetic field, in response to activity on the Sun, to better understand what causes these widespread, long‐lasting waves. Changes in the energetic particle environment around the Earth are also presented to examine the effects of these waves. Events like these have the potential to cause significant effects in the particle populations around the Earth.
Key Points
Sustained, azimuthally extended EMIC waves are observed spanning the nightside of the inner magnetosphere on 7 July 2013
Wave structure lies at the inner edge of the plasma sheet overlaping the outer plasmasphere and plumes following enhanced Kp activity
Local minima in phase space density are observed concurrent with wave activity, consistent with EMIC‐driven MeV electron scattering
Aims
Since most phosphate solubilizing bacteria (PSB) also produce 1‐aminocyclopropane‐1‐carboxylate (ACC) deaminase, we investigated if there was an association between these two plant ...growth‐promoting properties under in vitro conditions.
Methods and Results
A total of 841 bacterial isolates were obtained using selective and enrichment isolation methods. ACC deaminase was investigated using in vitro methods and by sequencing the acdS gene. The effect of ACC deaminase on P solubilization was investigated further using five efficient PSB. ACC deaminase production ability was found amongst a wide range of bacteria belonging to the genera Bacillus, Burkholderia, Pseudomonas and Variovorax. The amount of ACC deaminase produced by PSB was significantly associated with the liberation of Pi from Ca‐P when ACC was the sole N source. Ca‐P solubilization was associated with the degree of acidification of the medium. Additionally, the P solubilization potential of PSB with (NH4)2SO4 was determined by the type of carboxylates produced. An in‐planta experiment was conducted using Burkholderia sp. 12F on chickpea cv. Genesis‐863 in sand : vermiculite (1 : 1 v/v) amended with rock phosphate and inoculation of this efficient PSB significantly increased growth, nodulation and P uptake of chickpea fertilized with rock phosphate.
Conclusion
ACC deaminase activity influenced the capacity of PSB to solubilize P from Ca‐P when ACC was the sole N source and Burkholderia sp. 12F promoted the chickpea‐Mesorhizobium symbiosis.
Significance and Impact of the Study
ACC deaminase activity could enhance the P solubilizing activity of rhizobacteria that improve plant growth.
Imaging the Global Distribution of Plasmaspheric Oxygen Goldstein, J.; Chappell, C. R.; Davis, M. W. ...
Journal of geophysical research. Space physics,
March 2018, 2018-03-00, 20180301, Letnik:
123, Številka:
3
Journal Article
Recenzirano
This paper investigates the potential for 83.4 nm imaging of the plasmaspheric dense oxygen torus, using simple models for core plasma density and composition to constrain a simulated image code. We ...derive the requirements for plasmaspheric O+ imaging, and the expected performance of an imager based on a slightly modified version of the IMAGE extreme ultraviolet camera. We find that such an imager can achieve a sensitivity of 0.69(s R pixel)−1, sufficient to capture the dense torus 83.4 nm signal with 25 min integration time. The background rejection ratios for this design are 1.5 × 10−4 at 58.4 nm and 7.4 × 10−8 for Lyman‐α. We discuss the effects of ion temperature and motion, and O++ glow. We compute simulated O+ images of the formation and global distribution of the dense torus. We also examine the possibility of direct observation of oxygen outflow from the ionosphere.
Plain Language Summary
This paper investigates the potential to use an extreme ultraviolet (or EUV) camera to capture the glow from the torus of ionized oxygen that surrounds the Earth in space. Imaging this oxygen torus will help understand its formation and influence on space weather.
Key Points
Simple density models are used to study 83.4 nm imaging of dense oxygen torus
Imager can achieve sensitivity sufficient for 25 min integrated images
O+ imaging can measure torus formation and structure and dense outflow
Objectives: To measure survival, haemodynamic function and functional class in patients with systemic sclerosis associated pulmonary arterial hypertension (SSc-PAH) in two treatment eras. Methods: ...Six year longitudinal study of 92 consecutive patients with SSc-PAH diagnosed by cardiac catheterisation. Data were collected both prospectively and retrospectively. Patients were given basic treatment (diuretics, digoxin, oxygen and warfarin). Where clinically indicated, a prostanoid was used as advanced treatment (historical control group). From 2002, the range of treatments available expanded to include bosentan, which was generally the preferred treatment (current treatment era group). Survival was measured from the date of diagnosis of pulmonary hypertension by cardiac catheterisation. Six minute walking distance and haemodynamic function were measured at the time of diagnosis and at least one month after treatment was started. Results: The historical control group comprised 47 patients, all of whom received basic treatment; 27 of these were also treated with prostanoids. The current treatment era group comprised 45 patients, all of whom received bosentan as preferred treatment. Kaplan–Meier survival in the historical control group was 68% at one year and 47% at two years. Survival in the current treatment era group was 81% and 71% (p = 0.016) at one and two years, respectively. Pulmonary vascular resistance increased in the historical control group (by 147 dyn·s·cm−5), whereas in the current treatment era group, it remained stable over an average of nine months (decrease of 16 dyn·s·cm−5, p < 0.006). Conclusion: Survival of selected patients with SSc-PAH has improved in the current treatment era. In contrast to patients treated historically with basic drugs and prostanoids, patients treated in the current treatment era had improved survival associated with a lack of deterioration in cardiac haemodynamic function.
The warm plasma cloak is a source of magnetospheric plasma that contain significant O+. When the O+ density in the magnetosphere near the magnetopause is >0.2 cm‐3 and the H+ density is <1.5 cm‐3, ...then O+ dominates the magnetospheric ion mass density by more than a factor of 2. A survey is conducted of such O+‐rich warm plasma cloak intervals and their effect on reconnection at the Earth's magnetopause. The survey uses data from the Magnetospheric Multiscale mission (MMS) and the results are compared and combined with a previous survey of the warm plasma cloak. Overall, the warm plasma cloak and the O+‐rich warm plasma cloak reduce the magnetopause reconnection rate by >20% due to mass‐loading only about 2% to 4% of the time. However, during geomagnetic storms, O+ dominates the mass density of the warm plasma cloak and these mass densities are very high. Therefore, a separate study is conducted to determine the effect of the warm plasma cloak on magnetopause reconnection during geomagnetically disturbed times. This study shows that the warm plasma cloak reduces the reconnection rate significantly about 25% of the time during disturbed conditions.
Key Points
The magnetospheric warm plasma cloak is O+‐rich during geomagnetically active times
The warm plasma cloak reduces the magnetic reconnection rate at the magnetopause ~2‐4% of the time
During geomagnetic storms, the O+‐rich warm plasma cloak reduces the reconnection rate by >20% sometime during 25% of the storms
Effects of whistler mode hiss waves in March 2013 Ripoll, J.‐F.; Santolík, O.; Reeves, G. D. ...
Journal of geophysical research. Space physics,
July 2017, 2017-07-00, 20170701, Letnik:
122, Številka:
7
Journal Article
Recenzirano
We present simulations of the loss of radiation belt electrons by resonant pitch angle diffusion caused by whistler mode hiss waves for March 2013. Pitch angle diffusion coefficients are computed ...from the wave properties and the ambient plasma data obtained by the Van Allen Probes with a resolution of 8 h and 0.1 L shell. Loss rates follow a complex dynamic structure, imposed by the wave and plasma properties. Hiss effects can be strong, with minimum lifetimes (of ~1 day) moving from energies of ~100 keV at L ~ 5 up to ~2 MeV at L ~ 2 and stop abruptly, similarly to the observed energy‐dependent inner belt edge. Periods when the plasmasphere extends beyond L ~ 5 favor long‐lasting hiss losses from the outer belt. Such loss rates are embedded in a reduced Fokker‐Planck code and validated against Magnetic Electron and Ion Spectrometer observations of the belts at all energy. Results are complemented with a sensitivity study involving different radial diffusion and lifetime models. Validation is carried out globally at all L shells and energies. The good agreement between simulations and observations demonstrates that hiss waves drive the slot formation during quiet times. Combined with transport, they sculpt the energy structure of the outer belt into an “S shape.” Low energy electrons (<0.3 MeV) are less subject to hiss scattering below L = 4. In contrast, 0.3–1.5 MeV electrons evolve in an environment that depopulates them as they migrate from L ~ 5 to L ~ 2.5. Ultrarelativistic electrons are not affected by hiss losses until L ~ 2–3.
Key Points
Computations of daily pitch angle diffusion coefficients and electron lifetimes from properties of hiss waves observed in March 2013
Good agreement found between MagEIS flux observations and 1‐D Fokker‐Planck simulations based on our hiss loss term for quiet times
Combined with transport, hiss waves loss drives the daily energy structure of the radiation belts, with a typical S‐shaped outer belt
The evolution of the radiation belts in L‐shell (L), energy (E), and equatorial pitch angle (α0) is analyzed during the calm 11‐day interval (4–15 March) following the 1 March 2013 storm. Magnetic ...Electron and Ion Spectrometer (MagEIS) observations from Van Allen Probes are interpreted alongside 1D and 3D Fokker‐Planck simulations combined with consistent event‐driven scattering modeling from whistler mode hiss waves. Three (L, E, α0) regions persist through 11 days of hiss wave scattering; the pitch angle‐dependent inner belt core (L ~ <2.2 and E < 700 keV), pitch angle homogeneous outer belt low‐energy core (L > ~5 and E~ < 100 keV), and a distinct pocket of electrons (L ~ 4.5, 5.5 and E ~ 0.7, 2 MeV). The pitch angle homogeneous outer belt is explained by the diffusion coefficients that are roughly constant for α0 ~ <60°, E > 100 keV, 3.5 < L < Lpp ~ 6. Thus, observed unidirectional flux decays can be used to estimate local pitch angle diffusion rates in that region. Top‐hat distributions are computed and observed at L ~ 3–3.5 and E = 100–300 keV.
Plain Language Summary
We study the evolution of the radiation belts during quiet geomagnetic times from satellite observations and numerical codes. We reach a global understanding of the trapped electrons variation with time, space, energy, and pitch angle (the angle of the velocity vector with the magnetic field). We exhibit three stable regions, which are less sensitive to scattering from hiss waves, while, on the other hand, hiss causes flux decay over 12 days that forms the slot region between the inner and outer belt. The existing theory explains why the outer belt electron decay is independent of pitch angle but dependent upon energy. This implies that satellite observations can reveal local pitch angle diffusion rates, themselves intimately connected with the wave properties. Thus, a connection is made between observed wave properties and observed/computed scattered electron flux, consistent with theory. Regions where the flux is pitch angle dependent are isolated in the low‐energy slot region where we show that the real shape is a smoothed version of the ideal top‐hat distribution computed from theory. The impact of this work is improved understanding of the belt evolution for space weather prediction, with a proposed event‐driven method that accurately (within ×2) predicts the electron flux decay after storms.
Key Points
Global computations of the (L, E, α0) structure of the evolving radiation belt during quiet times agree well with observations
The inner belt decay is pitch angle dependent, while the outer belt is much more homogeneous with two distinct (L, E) regions
The homogeneity of the pitch angle diffusion coefficient due to hiss waves explains the uniform outer belt decay and why 1D and 3D simulations agree
Data from the Van Allen Probes Helium, Oxygen, Proton, and Electron (HOPE) spectrometers reveal hitherto unresolved spatial structure and dynamics in ion populations. Complex regions of O+ dominance, ...at energies from a few eV to >10 keV, are observed throughout the magnetosphere. Isolated regions on the dayside that are rich in energetic O+ might easily be interpreted as strong energization of ionospheric plasma. We demonstrate, however, that both the energy spectrum and the limited magnetic local time extent of these features can be explained by energy‐dependent drift of particles injected on the nightside 24 h earlier. Particle tracing simulations show that the energetic O+ can originate in the magnetotail, not in the ionosphere. Enhanced wave activity is colocated with the heavy ion‐rich plasma, and we further conclude that the waves were not a source of free energy for accelerating ionospheric plasma but rather the consequence of the arrival of substorm‐injected plasma.
Key Points
Enhanced O+ fluxes mimic local acceleration—shown to result from plasma transport from an injection 24 h earlier
Enhanced wave power is colocated with the enhanced O+—the wave power is enhanced due to arrival of drifting plasma
Time history of previous injections must be accounted for when interpreting in situ observations
Bulk plasma properties at geosynchronous orbit Denton, M. H.; Thomsen, M. F.; Korth, H. ...
Journal of Geophysical Research - Space Physics,
July 2005, Letnik:
110, Številka:
A7
Journal Article
Recenzirano
Odprti dostop
We present a comprehensive study of plasma properties at geosynchronous orbit for electron and ion energies between ∼1 eV and ∼45 keV, between 1990 and 2001. The variations of temperature and density ...are analyzed as functions of local time, magnetospheric convection strength, and the strength of the ring current. Various parameters derived from temperature and density are calculated to elucidate the temporal and spatial location of delivery of plasma sheet material into the inner magnetosphere. We find that the electron and proton densities are greatest in the dawn region for the periods of highest convection and ring current strength. We perform a superposed epoch analysis of 283 geomagnetic storms which occurred between 1991 and 2001 and examine the temporal variation of the plasma at geosynchronous orbit as a function of storm phase. This analysis demonstrates the local time variability of delivery from the plasma sheet into the inner magnetosphere and the concurrent changes in temperature and pressure. We demonstrate that the density of electrons in the plasma sheet is strongly dependent upon the magnetospheric convection strength and, for the first time, upon solar activity. Electron density at geosynchronous orbit is strongly correlated with solar activity. The average plasma sheet electron density at solar maximum can be a factor of two or more higher than that at solar minimum. We also outline a method to estimate the composition of the plasma sheet from MPA measurements and calculate the O+ and H+ density variations with solar cycle as a function of Kp and local time. We show that the O+ and H+ plasma sheet densities increase with increasing solar activity, as does the O+/H+ density ratio. During times of high solar activity and strong convection, the O+ and H+ densities may be comparable.
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