Predicting the response of fine roots to increased atmospheric CO₂concentration has important implications for carbon (C) and nutrient cycling in forest ecosystems. Root architecture is known to play ...an important role in how trees acquire soil resources in changing environments. However, the effects of elevated CO₂on the fine‐root architecture of trees remain unclear. We investigated the architectural response of fine roots exposed to 14 yr of CO₂enrichment and 6 yr of nitrogen (N) fertilization in a Pinus taeda (loblolly pine) forest. Root traits reflecting geometry, topology and uptake function were measured on intact fine‐root branches removed from soil monoliths and the litter layer. CO₂enrichment resulted in the development of a fine‐root pool that was less dichotomous and more exploratory under N‐limited conditions. The per cent mycorrhizal colonization did not differ among treatments, suggesting that root growth and acclimation to elevated CO₂were quantitatively more important than increased mycorrhizal associations. Our findings emphasize the importance of architectural plasticity in response to environmental change and suggest that changes in root architecture may allow trees to effectively exploit larger volumes of soil, thereby pre‐empting progressive nutrient limitations.
The application of FTIR spectroscopy to concentrated solutions of tetrolic acid shows, for the first time, a direct relationship between molecular self association in solution and H-bonded motifs in ...the subsequently crystallised solid phases.
Multi-drug resistant bacteria are a persistent problem in modern health care, food safety and animal health. There is a need for new antimicrobials to replace over used conventional antibiotics. Here ...we describe engineered triple-acting staphylolytic peptidoglycan hydrolases wherein three unique antimicrobial activities from two parental proteins are combined into a single fusion protein. This effectively reduces the incidence of resistant strain development. The fusion protein reduced colonization by Staphylococcus aureus in a rat nasal colonization model, surpassing the efficacy of either parental protein. Modification of a triple-acting lytic construct with a protein transduction domain significantly enhanced both biofilm eradication and the ability to kill intracellular S. aureus as demonstrated in cultured mammary epithelial cells and in a mouse model of staphylococcal mastitis. Interestingly, the protein transduction domain was not necessary for reducing the intracellular pathogens in cultured osteoblasts or in two mouse models of osteomyelitis, highlighting the vagaries of exactly how protein transduction domains facilitate protein uptake. Bacterial cell wall degrading enzyme antimicrobials can be engineered to enhance their value as potent therapeutics.
The residence time of fine-root carbon in soil is one of the least understood aspects of the global carbon cycle, and fine-root dynamics are one of the least understood aspects of plant function. ...Most recent studies of these belowground dynamics have used one of two methodological strategies. In one approach, based on analysis of carbon isotopes, the persistence of carbon is inferred; in the other, based on direct observations of roots with cameras, the longevity of individual roots is measured. We show that the contribution of fine roots to the global carbon cycle has been overstated because observations of root lifetimes systematically overestimate the turnover of fine-root biomass. On the other hand, isotopic techniques systematically underestimate the turnover of individual roots. These differences, by virtue of the separate processes or pools measured, are irreconcilable.
The term “frustration” in the context of magnetism was originally used by P. W. Anderson and quickly adopted for application to the description of spin glasses and later to very special lattice ...types, such as the kagomé. The original use of the term was to describe systems with competing antiferromagnetic interactions and is important in current condensed matter physics in areas such as the description of emergent magnetic monopoles in spin ice. Within molecular magnetism, at least two very different definitions of frustration are used. Here we report the synthesis and characterization of unusual nine-metal rings, using magnetic measurements and inelastic neutron scattering, supported by density functional theory calculations. These compounds show different electronic/magnetic structures caused by frustration, and the findings lead us to propose a classification for frustration within molecular magnets that encompasses and clarifies all previous definitions.
Fine roots acquire essential soil resources and mediate biogeochemical cycling in terrestrial ecosystems. Estimates of carbon and nutrient allocation to build and maintain these structures remain ...uncertain because of the challenges of consistently measuring and interpreting fine-root systems. Traditionally, fine roots have been defined as all roots ≤ 2 mm in diameter, yet it is now recognized that this approach fails to capture the diversity of form and function observed among fine-root orders. Here, we demonstrate how order-based and functional classification frameworks improve our understanding of dynamic root processes in ecosystems dominated by perennial plants. In these frameworks, fine roots are either separated into individual root orders or functionally defined into a shorter-lived absorptive pool and a longer-lived transport fine-root pool. Using these frameworks, we estimate that fine-root production and turnover represent 22% of terrestrial net primary production globally – a c. 30% reduction from previous estimates assuming a single fine-root pool. Future work developing tools to rapidly differentiate functional fine-root classes, explicit incorporation of mycorrhizal fungi into fine-root studies, and wider adoption of a two-pool approach to model fine roots provide opportunities to better understand below-ground processes in the terrestrial biosphere.
Climate changes will influence soil organisms both directly (warming) and indirectly (warming and elevated CO₂) via changes in quantity and quality of plant-mediated soil C inputs. Elevated ...atmospheric CO₂ commonly stimulates flow of organic C into the soil system, increases root production and exudation, but decreases litter quality. There is little evidence that atmospheric CO₂ enrichment will increase total soil organic matter content because greater C flow into soil stimulates the soil food web, often leading to equivalent increases in soil CO₂ efflux. Effects of warming on C allocation belowground, on the other hand, will depend largely on the temperature optima of different plant species. Warming is likely to increase the rate of soil organic matter decomposition by stimulating soil heterotrophic respiration, although some degree of acclimatization to warming is likely. Mycorrhizal and N₂-fixing relationships are generally enhanced by CO₂ enrichment, but effects of warming are highly variable. Data suggest that energy flow through fungal pathways may be enhanced relative to bacterial pathways by both warming and atmospheric CO₂ enrichment. Whether the shift toward fungal domination of soils will increase soilborne fungal disease occurrence in the future is still an open question. Plant heat and drought tolerance, along with resistance to pathogens in warmer and wetter soils, may be achieved, to some unknown extent, by exploitation and management of beneficial soil organisms. Further study is needed to develop a more holistic understanding of the effects of climate change on belowground processes.
Efforts to characterize carbon (C) cycling among atmosphere, forest canopy, and soil C pools are hindered by poorly quantified fine root dynamics. We characterized the influence of ...free-air-CO₂-enrichment (ambient +200 ppm) on fine roots for a period of 6 years (Autumn 1998 through Autumn 2004) in an 18-year-old loblolly pine (Pinus taeda) plantation near Durham, NC, USA using minirhizotrons. Root production and mortality were synchronous processes that peaked most years during spring and early summer. Seasonality of fine root production and mortality was not influenced by atmospheric CO₂ availability. Averaged over all 6 years of the study, CO₂ enrichment increased average fine root standing crop (+23%), annual root length production (+25%), and annual root length mortality (+36%). Larger increase in mortality compared with production with CO₂ enrichment is explained by shorter average fine root lifespans in elevated plots (500 days) compared with controls (574 days). The effects of CO₂-enrichment on fine root proliferation tended to shift from shallow (0-15 cm) to deeper soil depths (15-30) with increasing duration of the study. Diameters of fine roots were initially increased by CO₂-enrichment but this effect diminished over time. Averaged over 6 years, annual fine root NPP was estimated to be 163 g dw m⁻² yr⁻¹ in CO₂-enriched plots and 130 g dw m⁻² yr⁻¹ in control plots (P= 0.13) corresponding to an average annual additional input of fine root biomass to soil of 33 g m⁻² yr⁻¹ in CO₂-enriched plots. A lack of consistent CO₂x year effects suggest that the positive effects of CO₂ enrichment on fine root growth persisted 6 years following minirhizotron tube installation (8 years following initiation of the CO₂ fumigation). Although CO₂-enrichment contributed to extra flow of C into soil in this experiment, the magnitude of the effect was small suggesting only modest potential for fine root processes to directly contribute to soil C storage in south-eastern pine forests.
A Star of David catenane Leigh, David A; Pritchard, Robin G; Stephens, Alexander J
Nature chemistry,
11/2014, Letnik:
6, Številka:
11
Journal Article
Recenzirano
We describe the synthesis of a 2catenane that consists of two triply entwined 114-membered rings, a molecular link. The woven scaffold is a hexameric circular helicate generated by the assembly of ...six tris(bipyridine) ligands with six iron(II) cations, with the size of the helicate promoted by the use of sulfate counterions. The structure of the ligand extension directs subsequent covalent capture of the catenane by ring-closing olefin metathesis. Confirmation of the Star of David topology (two rings, six crossings) is provided by NMR spectroscopy, mass spectrometry and X-ray crystallography. Extraction of the iron(II) ions with tetrasodium ethylenediaminetetraacetate affords the wholly organic molecular link. The self-assembly of interwoven circular frameworks of controlled size, and their subsequent closure by multiple directed covalent bond-forming reactions, provides a powerful strategy for the synthesis of molecular topologies of ever-increasing complexity.
Root systems are important for global models of below‐ground carbon and nutrient cycling. Notoriously difficult sampling methods and the fractal distribution of root diameters in the soil make data ...being used in these models especially susceptible to error resulting from under‐sampling. We applied the concept of species accumulation curves to root data to quantify the extent of under‐sampling inherent to minirhizotron and soil coring sampling for both root uptake and carbon content studies. Based on differences in sample size alone, minirhizotron sampling missed approximately one third of the root diameters observed by soil core sampling. Sample volumes needed to encounter 90% of root diameters averaged 2481 cm3 for uptake studies and 5878 cm3 for root carbon content studies. These results show that small sample volumes encounter a non‐representative sample of the overall root pool, and provide future guidelines for determining optimal sample volumes in root studies.
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