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•Seven key soil health indicators (SHIs) were identified from a 168 SHI dataset.•Identified key SHIs were sensitive to long-term crop rotation and fertilization.•Despite some ...differences, the key SHIs were consistent with other publications.•A site-specific soil health score was significantly correlated to crop yields.
Long-term agricultural management practices affect soil health, but identifying measurable soil properties that reflect soil health (soil health indicators – SHIs) is a challenge. Five long-term (>40 years) crop rotations with varying cropping frequency, crop diversity, fertility and lime treatments were sampled as part of the Soil Heath Institute’s North American Project to Evaluate Soil Health Measurements (NAPESHM) at the University of Albert Breton Plots research site in 2019, and additional samples were collected in 2020 for additional indicator measurements. Many soil health frameworks such as the Cornell Assessment of Soil Health (CASH) generate soil health scores based on key SHIs identified from a large, multivariate database using principal component analysis (PCA). For our dataset, we adopted the PCA-based approach with the following questions in mind: 1) Were the key SHIs that explain a large portion of the total dataset variance also the key SHIs that were most sensitive to the rotation, fertilizer and lime management? 2) Were the key SHIs identified with PCA associated with soil health, soil fertility or inherent soil characteristics? We identified seven key SHIs with PCA that explained 86.8% of the database variance. Results of a permutational MANOVA suggested that crop rotation and fertilizer management significantly influenced the total variance of the identified key SHIs. Four of the seven identified key SHIs primarily reflected soil health and three SHIs primarily reflected soil fertility and/or inherent soil properties but were also positively associated with soil health at this site. Overall, the PCA-based approach used to develop the site-specific soil health score (SSpeSHS) proved to be a helpful screening tool for the identification of key SHIs that are sensitive to soil-health-promoting management practices from a large dataset.
The variation in the radiative output of the Sun, described in terms of solar irradiance, is important to climatology. A common assumption is that solar irradiance variability is driven by its ...surface magnetism. Verifying this assumption has, however, been hampered by the fact that models of solar irradiance variability based on solar surface magnetism have to be calibrated to observed variability. Making use of realistic three-dimensional magnetohydrodynamic simulations of the solar atmosphere and state-of-the-art solar magnetograms from the Solar Dynamics Observatory, we present a model of total solar irradiance (TSI) that does not require any such calibration. In doing so, the modeled irradiance variability is entirely independent of the observational record. (The absolute level is calibrated to the TSI record from the Total Irradiance Monitor.) The model replicates 95% of the observed variability between April 2010 and July 2016, leaving little scope for alternative drivers of solar irradiance variability at least over the time scales examined (days to years).
An increase in intensive cropping would benefit society by providing food to a growing population, and vegetable production is an excellent example of intensive cropping systems that are indeed on ...the rise. Vegetable cropping systems are high-input and generally require large quantities of fertilization, frequent irrigation, and repeated tillage operations. Consequently, an increase in global vegetable production may have seriously negative impacts on soil health and ecosystem services. Yet, not only maintaining but improving soil health is critical to enhancing the sustainability of food production systems. Previous agricultural research mainly focused on field crop systems and largely ignored vegetable cropping systems; consequently, this represents a conspicuous research gap, one that must be addressed in order to make progress towards sustainable food production. Here, we review the literature to gain a better understanding of how management has influenced various soil health indices (soil biology, chemistry, and physical dynamics) and to evaluate the implications for soil ecosystem services in vegetable cropping systems. We found that alternative modifications to conventional vegetable production systems, which resemble methods used in organic or conservation agriculture, tended to improve aspects of soil health. For example, soil amendments generally improved soil chemical indices of health – soil carbon levels and nitrogen reserves in particular. Incorporation of cover crops to vegetable crop rotations tended to improve nitrogen recycling via reduced nitrate leaching risks, increased soil carbon levels, and weed suppression. Reduced tillage systems were rare, presenting an important challenge and opportunity for further improving soil health dynamics in vegetable production. Notably, adopting alternative practices generally had no effect on crop yields, which implies little risk of yield penalties when agronomic management is carefully planned. Our results indicate that future sustainable vegetable cropping systems may embody a blend between organic and conventional ideologies to better maintain or improve soil ecosystem functioning.
ABSTRACT
Magnetic features on the surface of stars, such as spots and faculae, cause stellar spectral variability on time-scales of days and longer. For stars other than the Sun, the spectral ...signatures of faculae are poorly understood, limiting our ability to account for stellar pollution in exoplanet transit observations. Here we present the first facular contrasts derived from magnetoconvection simulations for K0, M0, and M2 main-sequence stars and compare them to previous calculations for G2 main-sequence stars. We simulate photospheres and immediate subsurface layers of main-sequence spectral types between K0 and M2, with different injected vertical magnetic fields (0 G, 100 G, 300 G, and 500 G) using MURaM, a 3D radiation-magnetohydrodynamics code. We show synthetic spectra and contrasts from the UV (300 nm) to the IR (10 000 nm) calculated using the ATLAS9 radiative transfer code. The calculations are performed for nine viewing angles to characterize the facular radiation across the disc. The brightness contrasts of magnetic regions are found to change significantly across spectral type, wavelength, and magnetic field strength, leading to the conclusion that accurate contrasts cannot be found by scaling solar values. This is due to features of different size, apparent structure and spectral brightness emerging in the presence of a given magnetic field for different spectral types.
Phospholipid fatty acids (PLFAs) are key components of microbial cell membranes. The analysis of PLFAs extracted from soils can provide information about the overall structure of terrestrial ...microbial communities. PLFA profiling has been extensively used in a range of ecosystems as a biological index of overall soil quality, and as a quantitative indicator of soil response to land management and other environmental stressors. The standard method presented here outlines four key steps: 1. lipid extraction from soil samples with a single-phase chloroform mixture, 2. fractionation using solid phase extraction columns to isolate phospholipids from other extracted lipids, 3. methanolysis of phospholipids to produce fatty acid methyl esters (FAMEs), and 4. FAME analysis by capillary gas chromatography using a flame ionization detector (GC-FID). Two standards are used, including 1,2-dinonadecanoyl-sn-glycero-3-phosphocholine (PC(19:0/19:0)) to assess the overall recovery of the extraction method, and methyl decanoate (MeC10:0) as an internal standard (ISTD) for the GC analysis.
ABSTRACT
Variability observed in photometric light curves of late-type stars (on time-scales longer than a day) is a dominant noise source in exoplanet surveys and results predominantly from surface ...manifestations of stellar magnetic activity, namely faculae and spots. The implementation of faculae in light-curve models is an open problem, with scaling typically based on spectra equivalent to hot stellar atmospheres or assuming a solar-derived facular contrast. We modelled rotational (single period) light curves of active G2, K0, M0, and M2 stars, with Sun-like surface distributions and realistic limb-dependent contrasts for faculae and spots. The sensitivity of light-curve variability to changes in model parameters such as stellar inclination, feature area coverage, spot temperature, facular region magnetic flux density, and active band latitudes is explored. For our light-curve modelling approach we used actress, a geometrically accurate model for stellar variability. actress generates two-sphere maps representing stellar surfaces and populates them with user-prescribed spot and facular region distributions. From this, light curves can be calculated at any inclination. Quiet star limb darkening and limb-dependent facular contrasts were derived from MURaM 3D magnetoconvection simulations using ATLAS9. 1D stellar atmosphere models were used for the spot contrasts. We applied actress in Monte Carlo simulations, calculating light-curve variability amplitudes in the Kepler band. We found that, for a given spectral type and stellar inclination, spot temperature and spot area coverage have the largest effect on variability of all simulation parameters. For a spot coverage of $1{{\ \rm per\ cent}}$, the typical variability of a solar-type star is around 2 parts per thousand. The presence of faculae clearly affects the mean brightness and light-curve shape, but has relatively little influence on the variability.
Modifying the rhizosphere microbiome through targeted plant breeding is key to harnessing positive plant-microbial interrelationships in cropping agroecosystems. Here, we examine the composition of ...rhizosphere bacterial communities of diverse
genotypes to identify: (1) taxa that preferentially associate with genotypes, (2) core bacterial microbiota associated with
, (3) heritable alpha diversity measures at flowering and whole growing season, and (4) correlation between microbial and plant genetic distance among canola genotypes at different growth stages. Our aim is to identify and describe signature microbiota with potential positive benefits that could be integrated in
breeding and management strategies. Rhizosphere soils of 16 diverse genotypes sampled weekly over a 10-week period at single location as well as at three time points at two additional locations were analyzed using 16S rRNA gene amplicon sequencing. The
rhizosphere microbiome was characterized by diverse bacterial communities with 32 named bacterial phyla. The most abundant phyla were Proteobacteria, Actinobacteria, and Acidobacteria. Overall microbial and plant genetic distances were highly correlated (
= 0.65). Alpha diversity heritability estimates were between 0.16 and 0.41 when evaluated across growth stage and between 0.24 and 0.59 at flowering. Compared with a reference
genotype, a total of 81 genera were significantly more abundant and 71 were significantly less abundant in at least one
genotype out of the total 558 bacterial genera. Most differentially abundant genera were Proteobacteria and Actinobacteria followed by Bacteroidetes and Firmicutes. Here, we also show that
genotypes select an overall core bacterial microbiome with growth-stage-related patterns as to how taxa joined the core membership. In addition, we report that sets of
core taxa were consistent across our three sites and 2 years. Both differential abundance and core analysis implicate numerous bacteria that have been reported to have beneficial effects on plant growth including disease suppression, antifungal properties, and plant growth promotion. Using a multi-site year, temporally intensive field sampling approach, we showed that small plant genetic differences cause predictable changes in canola microbiome and are potential target for direct and indirect selection within breeding programs.
Reclamation practices in the oil sands region of Alberta involve the reconstruction of soil profiles using a combination of salvaged mineral substrates and organic-matter-rich surface materials, ...including peat–mineral mix (PM) and forest floor – mineral mix (FFM). The successful re-establishment of vegetation on reclaimed sites is for a large part dependent on the nutrients these materials can provide. Hence, the overall objective of this study was to compare carbon (C), nitrogen (N), and phosphorus (P) release rates from PM and FFM materials used to cap reconstructed sandy soils. A 325 d laboratory incubation was conducted to measure these rates. The two materials released comparable amounts of N on a per kilogram of soil basis (111–118 mg N kg-1). However, when results were normalized based on each material’s organic C content, N release was six times greater for FFM than for PM, in accordance with results of previous studies. In addition, overall C mineralization and P release rates were over one order of magnitude higher with FFM than with PM. As opposed to N, however, P release seemed to be controlled more by abiotic processes than by organic matter mineralization. While the FFM material overall released more N and P, it also degraded faster; in comparison, PM may provide a smaller but more stable release of N.
Aspen (Populus tremuloides Michx.) and white spruce (Picea glauca (Moench) Voss) are archetypal species of the boreal forest of western Canada. With the many new and varied environmental pressures ...(e.g., fire, harvesting, climate change) on, this boreal forest biome, we were interested in understanding the importance of potential changes in organic matter inputs to its soil microbial community structure and function. Double -labeled (15N and 13C) aspen leaf litter was utilized as an amendment to the forest floor of two stands, an aspen and a spruce, in a 16-month paired field experiment, where amended mesocosms were compared to control mesocosms with no litter added. Nitrogen mineralization from the aspen leaf litter occurred within both stand types, as evidenced by higher δ15N values in roots and live aboveground vegetation. In term of carbon fluxes, stable isotope 13C analysis of the forest floor microbial phospholipid fatty acid (PLFAs) indicated a slight initial enrichment within all amended mesocosms, likely due to leaching of 13C enriched solubles from the labeled aspen litter. Within the aspen stand, continued 13C enrichment of most PLFAs demonstrated that incorporation of the litter-derived carbon by a wide range of microorganisms was maintained through both growing seasons. Response of the spruce microbial community differed from that of aspen. Its overall structural composition did not alter in response to aspen litter addition; yet, δ13C values of several PLFA biomarkers decreased at the end of the first growing season, suggesting that priming stimulated mineralization of a 13C-depleted pool. These results indicate that while nitrogen mineralization was maintained, the deep forest floor carbon stocks of spruce stands may be vulnerable to increased decomposition rates with changing organic matter input.
•Aspen leaf litter was enriched in 15N and 13C and added to a field incubation.•Microbial phospholipids under aspen were enriched in 13C after aspen litter addition.•Spruce phospholipids were either less enriched or depleted in13C following addition.•Aspen litter addition did not change the structure of the spruce microbial community.•Live vegetation growing on both spruce and aspen soils was enriched in 15N.
Canada's interest in agricultural lands has changed with time from a desire of crop yields at Confederation through to discussions in the Senate on adaptation and resilience in 2018. Long-term ...research experiments (LTRs) have been present and utilized by federal and university researchers to provide answers throughout. Here we highlight the importance of LTRs by identifying the historical context of LTRs and soil health research in Canada. We then briefly describe the history and key results from select LTRs and illustrate the wealth of information collected from the North American Project to Evaluate Soil Health Measurements cross-country point-in-time soil sampling from these LTRs. We discuss the LTRs, and the knowledge gained from them, with the hope that by showing the distinctive narratives associated with each of these study sites, researchers will be inspired to use them to address their research questions and make sound predictions to facilitate the adaptation of Canadian agroecosystems to climate challenges. Through identifying the value generated by these unique LTRs, we hope that the importance of these sites will inspire not only their continued maintenance but also the next generation of LTRs.
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