•The impact of grazing on SOC is climate-dependent.•Grazing increases SOC for C4 but decreases it for C3 and C3-C4 mixed grasslands.•Grazing increases TN and BD but has no effect on soil pH.
...Livestock grazing intensity (GI) is thought to have a major impact on soil organic carbon (SOC) storage and soil quality indicators in grassland agroecosystems. To critically investigate this, we conducted a global review and meta-analysis of 83 studies of extensive grazing, covering 164 sites across different countries and climatic zones. Unlike previous published reviews we normalized the SOC and total nitrogen (TN) data to a 30cm depth to be compatible with IPCC guidelines. We also calculated a normalized GI and divided the data into four main groups depending on the regional climate (dry warm, DW; dry cool, DC; moist warm, MW; moist cool, MC). Our results show that taken across all climatic zones and GIs, grazing (below the carrying capacity of the systems) results in a decrease in SOC storage, although its impact on SOC is climate-dependent. When assessed for different regional climates, all GI levels increased SOC stocks under the MW climate (+7.6%) whilst there were reductions under the MC climate (−19%). Under the DW and DC climates, only the low (+5.8%) and low to medium (+16.1%) grazing intensities, respectively, were associated with increased SOC stocks. High GI significantly increased SOC for C4-dominated grassland compared to C3-dominated grassland and C3-C4 mixed grasslands. It was also associated with significant increases in TN and bulk density but had no effect on soil pH. To protect grassland soils from degradation, we recommend that GI and management practices should be optimized according to climate region and grassland type (C3, C4 or C3-C4 mixed).
While many laboratory studies have focused on the short term effects of biochar addition to soil), there have been comparatively few tracing its longer term effects in the field. This study ...investigated the multiyear impact of biochar on crop performance and soil quality with specific emphasis on carbon (C) and nitrogen (N) cycling over a 3 y period. Biochar was added to an agricultural field at 0, 25 and 50tha−1 and planted with maize (year 1) and grass (years 2 and 3). Biochar addition affected plant performance in the grass crop with significant increases in foliar N (year 2) and above-ground biomass (year 3). Below-ground, biochar increased soil respiration, fungal and bacterial growth rate and turnover in year 2. This change coincided with a shift toward a bacterial dominated decomposer community, suggesting a decrease in the potential for microbially mediated C sequestration. Biochar did not affect dissolved organic C (DOC) and N (DON), NO3− or NH4+ pool sizes. Similarly, biochar addition had limited effects on the turnover of 14C-labelled SOC (plant litter), DOC (sugars and organic acids) and DON (amino acids) and no long term effect on N mineralization, NH3 volatilization, denitrification and NH4+ sorption. After 3 years in the field, the alkalinity associated with the biochar had been fully neutralized and biochar lost most of its cations (K, Na, Ca) but had built up an associated microbial community. We conclude that biochar addition to soil causes small and potentially transient changes in a temperate agroecosystem functioning. Importantly, many of the short-term effects of biochar on plant growth and soil behavior reported from laboratory studies were not observed in the field emphasizing the need for long term field trials to help inform agronomic management decisions involving biochar.
► Biochar induced temporary shifts in soil respiration and microbial community structure. ► Biochar induced only small changes in soil carbon and nitrogen cycling. ► Biochar had no observed negative effects on soil quality or crop production. ► Short term effects of biochar observed in the laboratory were not apparent in the field.
The photochemical activation of dimagnesium(I) compounds, and subsequent high yielding, regioselective reactions with inert arenes are reported. Irradiating benzene solutions of {(ArNacnac)Mg}2 ...(ArNacnac=HC(MeCNAr)2−; Ar=2,6‐diisopropylphenyl (Dip) or 2,4,6‐tricyclohexylphenyl (TCHP)) with blue or UV light, leads to double reduction of benzene and formation of the “Birch‐like” cyclohexadienediyl bridged compounds, {(ArNacnac)Mg}2(μ‐C6H6). Irradiation of {(DipNacnac)Mg}2 in toluene, and each of the three isomers of xylene, promoted completely regio‐ and chemo‐selective C−H bond activations, and formation of (DipNacnac)Mg(Ar′) (Ar′=meta‐tolyl; 2,3‐, 3,5‐ or 2,5‐dimethylphenyl), and {(DipNacnac)Mg(μ‐H)}2. Fluorobenzene was cleanly defluorinated by photoactivated {(DipNacnac)Mg}2, leading to biphenyl and {(DipNacnac)Mg(μ‐F)}2. Computational studies suggest all reactions proceed via photochemically generated magnesium(I) radicals, which reduce the arene substrate, before C−H or C−F bond activation processes occur.
The photochemical activation of dimagnesium(I) compounds, and subsequent high yielding double reductions, and regioselective C−H bond activations, of a range of normally inert arene substrates are reported (see picture, Dip=2,6‐diisopropylphenyl). Such transition‐metal‐free selective C−H bond activations hold considerable potential for organic synthesis.
Biochar application to soil has been proposed as a mechanism for improving soil quality and the long term sequestration of carbon. The implications of biochar on pesticide behavior, particularly in ...the longer term, however, remains poorly understood. Here we evaluated the influence of biochar type, time after incorporation into soil, dose rate and particle size on the sorption, biodegradation and leaching of the herbicide simazine. We show that typical agronomic application rates of biochar (10–100 t ha
−1) led to alterations in soil water herbicide concentrations, availability, transport and spatial heterogeneity. Overall, biochar suppressed simazine biodegradation and reduced simazine leaching. These responses were induced by a rapid and strong sorption of simazine to the biochar which limits its availability to microbial communities. Spatial imaging of
14C-labeled simazine revealed concentrated hotpsots of herbicide co-localized with biochar in the soil profile. The rate of simazine mineralization, amount of sorption and leaching was inversely correlated with biochar particle size. Biochar aged in the field for 2 years had the same effect as fresh biochar on the sorption and mineralization of simazine, suggesting that the effects of biochar on herbicide behavior may be long lasting. We conclude that biochar application to soil will reduce the dissipation of foliar applied pesticides decreasing the risk of environmental contamination and human exposure via transfer in the food chain, but may affect the efficacy of soil-applied herbicides.
► Biochar sequesters carbon in soil and significantly affects pesticide behavior. ► Biochar prevents pesticide leaching but enhances pesticide persistence in soil. ► Pesticides preferentially associate with biochar causing concentrated hotspots in soil. ► The effect of biochar on pesticide behavior lasts for long periods in soil (>2 years). ► Biochar may potentially suppress the effectiveness of pre-emergent herbicides in soil.
The application of biochar to soil has been shown to cause an apparent increase in soil respiration. In this study we investigated the mechanistic basis of this response. We hypothesized that ...increased CO2 efflux could occur by: (1) Biochar-induced changes in soil physical properties (bulk density, porosity, moisture content); (2) The biological breakdown of organic carbon (C) released from the biochar; (3) The abiotic release of inorganic C contained in the biochar; (4) A biochar-induced stimulation of decomposition of native soil organic matter (SOM) which could occur both biotically or abiotically; (5) The intrinsic biological activity of the biochar results in the liberation of CO2. Our results show that most of the extra CO2 produced after biochar addition to soil came from the equal breakdown of organic C and the release of inorganic C contained in the biochar. Using long-term 14C-labelled SOM, we show that biochar repressed native SOM breakdown, counteracting the release of CO2 from the biochar. A range of mechanisms to describe this negative priming response is presented. Although biochar-induced significant changes in the physical characteristics of the soil, overall this made no contribution to changes in soil respiration. Similarly, the evidence from our study suggests that changes in soluble polyphenols do not help explain the respiration response. In summary, biochar induced a net release of CO2 from the soil; however, this C loss was very small relative to the amount of C stored within the biochar itself (ca. 0.1%). This short-term C release should therefore not compromise its ability to contribute to long-term C sequestration in soil environments.
A major new contribution to college student development theory, this book brings "third wave" theories to bear on this vitally important topic.
The first section includes a chapter that provides an ...overview of the evolution of student development theories as well as chapters describing the critical and poststructural theories most relevant to the next iteration of student development theory. These theories include critical race theory, queer theory, feminist theories, intersectionality, decolonizing/indigenous theories, and crip theories. These chapters also include a discussion of how each theory is relevant to the central questions of student development theory.
The second section provides critical interpretations of the primary constructs associated with student development theory. These constructs and their related ideas include resilience, dissonance, socially constructed identities, authenticity, agency, context, development (consistency/coherence/stability), and knowledge (sources of truth and belief systems). Each chapter begins with brief personal narratives on a particular construct; the chapter authors then re-envision the narrative's highlighted construct using one or more critical theories.
The third section will focus on implications for practice. Specifically, these chapters will consider possibilities for how student development constructs re-envisioned through critical perspectives can be utilized in practice.
The primary audience for the book is faculty members who teach in graduate programs in higher education and student affairs and their students. The book will also be useful to practitioners seeking guidance in working effectively with students across the convergence of multiple aspects of identity and development.
The loss of organic and inorganic carbon from roots into soil underpins nearly all the major changes that occur in the rhizosphere. In this review we explore the mechanistic basis of organic carbon ...and nitrogen flow in the rhizosphere. It is clear that C and N flow in the rhizosphere is extremely complex, being highly plant and environment dependent and varying both spatially and temporally along the root. Consequently, the amount and type of rhizodeposits (e.g. exudates, border cells, mucilage) remains highly context specific. This has severely limited our capacity to quantify and model the amount of rhizodeposition in ecosystem processes such as C sequestration and nutrient acquisition. It is now evident that C and N flow at the soil-root interface is bidirectional with C and N being lost from roots and taken up from the soil simultaneously. Here we present four alternative hypotheses to explain why high and low molecular weight organic compounds are actively cycled in the rhizosphere. These include: (1) indirect, fortuitous root exudate recapture as part of the root's C and N distribution network, (2) direct re-uptake to enhance the plant's C efficiency and to reduce rhizosphere microbial growth and pathogen attack, (3) direct uptake to recapture organic nutrients released from soil organic matter, and (4) for inter-root and root-microbial signal exchange. Due to severe flaws in the interpretation of commonly used isotopic labelling techniques, there is still great uncertainty surrounding the importance of these individual fluxes in the rhizosphere. Due to the importance of rhizodeposition in regulating ecosystem functioning, it is critical that future research focuses on resolving the quantitative importance of the different C and N fluxes operating in the rhizosphere and the ways in which these vary spatially and temporally.
There have been many advances in insulin with a realistic possibility of mimicking nature to improve insulin replacement, with a view to achieving improved metabolic control. Lessons can be learnt ...from the evolution of insulin, insulin development, and new advances in technology. This may lead to fewer side effects of therapy resulting in a lower risk of hypoglycaemia and less weight gain, which could in turn could reduce long‐term complications for people with diabetes.
What's new?
Numerous strategies involving amino acid substitutions and chemical modifications have been adopted for therapeutic benefit to make more rapidly acting and longer‐acting insulins.
This review explores lessons from evolution and from pharmaceutical manipulation of the insulin molecule to reduce predictable side effects of subcutaneous insulin treatment.
This could result in a lower risk of hypoglycaemia and weight gain and could reduce long‐term complications for people with diabetes.
An extremely bulky, symmetrical three-coordinate magnesium(i) complex, {(
Nacnac)Mg}
(
Nacnac = {(TCHP)NCMe}
CH
, TCHP = 2,4,6-tricyclohexylphenyl) has been prepared and shown to have an extremely ...long Mg-Mg bond (3.021(1) Å) for such a complex. It was shown not to react with either DMAP (4-dimethylaminopyridine) or CO. Three unsymmetrical 1 : 1 DMAP adducts of less bulky Mg-Mg bonded species have been prepared,
(
Nacnac)Mg-Mg(DMAP)(
Nacnac) (
Nacnac = (ArNCMe)
CH
Ar = 2,6-xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), and their reactivity toward CO explored. Like the previously reported bulkier complex, (
Nacnac)Mg-Mg(DMAP)(
Nacnac) (Dip = 2,6-diisopropylphenyl), (
Nacnac)Mg-Mg(DMAP)(
Nacnac) reductively trimerises CO to give a rare example of a deltate complex, {(
Nacnac)Mg(μ-C
O
)Mg(DMAP)(
Nacnac)}
. In contrast, the two smaller adduct complexes react with only two CO molecules, ultimately giving unusual ethenediolate complexes {(
Nacnac)Mg{μ-OC(H)double bond, length as m-dashC(DMAP
)O}Mg(
Nacnac)}
(Ar = Xyl or Mes). DFT calculations show the latter reactions to proceed
reductive dimerizations of CO, and subsequent intramolecular C-H activation of Mg-ligated DMAP by "zig-zag" C
O
fragments of reaction intermediates. Calculations also suggest that magnesium deltate complexes are kinetic products in these reactions, while the magnesium ethenediolates are thermodynamic products. This study shows that subtle changes to the bulk of the reacting 1 : 1 DMAP-magnesium(i) adduct complexes can lead to fine steric control over the products arising from their CO reductive oligomerisations. Furthermore, it is found that the more activated nature of the adduct complexes, relative to their symmetrical, three-coordinate counterparts, {(
Nacnac)Mg}
, likely derives more from the polarisation of the Mg-Mg bonds of the former, than the elongated nature of those bonds.
A significant proportion of the total nutrient in soil solution can be bound to organic molecules and these often constitute a major loss from soil to freshwater. Our purpose was to determine whether ...chemical extractants used for measuring inorganic N could also be used to quantify dissolved organic nitrogen (DON) and carbon (DOC) in soil. In a range of soils, DOC and DON were extracted with either distilled water or 2
M KCl and the amount recovered compared with that present in soil solution recovered by centrifugal-drainage. The recovery of DON and DOC from soil was highly dependent upon the method of extraction. Factors such as soil sampling strategy (number of samples over space and time), sample preparation (sieving and drying), soil storage, extraction temperature, shaking time, and soil-to-extractant volume ratio all significantly affected the amount of DOC and DON extracted from soil. To allow direct comparison between independent studies we therefore propose the introduction of a standardized extraction procedure: Replicate samples of unsieved, field-moist soil extracted as soon as possible after collection with distilled water, 0.5
M K
2SO
4 or 2
M KCl at a 1:5
w/v ratio for 1
h at 20
°C.
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