Early changes due to sorghum biofuel cropping systems in soil microbial communities and metabolic functioning

Evaluation of biofuel production cropping systems should address not only energy yields but also the impacts on soil attributes. In this study, forage sorghum (Sorghum bicolor L. Moench) cropping systems were initiated on a low organic matter soil (<0.9 %) with a history of intensively tilled low-input cotton production in the semiarid Southern High Plains of the U.S. Sorghum cropping systems were evaluated in a split-plot design with sorghum cultivar as the main plot and the combination of irrigation level (non-irrigated and deficit irrigated) and aboveground biomass removal rate (50 % and 100 %) as the split plot. The sorghum cultivars used varied in yield potential and lignin content, which are important features for feedstock-producing crops. Within 1 year, the transition from long-term cotton cropping systems to sorghum biofuel cropping systems resulted in increased soil microbial biomass C (16 %) and N (17 %) and shifts in the microbial community composition as indicated by differences in fatty acid methyl ester (FAME) profiles. Additionally, enzyme activities targeting C, N, P and S cycles increased 15–75 % (depending on the enzyme) after two growing seasons. Increased enzyme activities (16–19 %) and differences in FAME profiles were seen due to irrigation regardless of aboveground biomass removal rate. Biomass removal rate and the cultivar type had little effect on the soil microbial properties during the time frame of this study. Early results from this study suggest improvements in soil quality and the sustainability of sorghum biofuel cropping for low organic matter agricultural soils.     

Pyrosequencing and mid-infrared spectroscopy reveal distinct aggregate stratification of soil bacterial communities and organic matter composition

This study integrated physical, chemical, and molecular techniques to assess relationships between soil bacterial community structures and the quantity and quality of soil organic carbon (SOC) at the soil microenvironment scale (e.g., within different aggregate size-fractions). To accomplish this goal, soil samples (0–5 cm) were collected from the Texas High Plains region under a variety of dryland and irrigated cropping systems. The soil was separated into macroaggregates, microaggregates, and silt + clay fractions that were analyzed for (1) bacterial diversity via pyrosequencing of the 16s rRNA gene and (2) SOC quantity and quality using a combustion method and mid-infrared diffuse reflectance spectroscopy (mid-IR), respectively. Results from pyrosequencing showed that each soil microenvironment supported a distinct bacterial community. Similarly, mid-IR data revealed distinct spectral features indicating that these fractions were also distinguished by organic and mineral composition. Macroaggregates showed relatively high abundance of Actinobacteria (excluding order Rubrobacteriales) and α-Proteobacteria and contained the most SOC. Microaggregates showed high relative abundance of Rubrobacteriales and the least amount of SOC. Predominance within the soil microenvironment and correlations along the mid-IR spectra were different between members of the order Rubrobacteriales compared with all other members of the Actinobacteria phyla, suggesting they have different ecological niches. Mid-IR results revealed microaggregates had greater absorbance in the 1370–1450 cm^?1 region for phenolic and alkyl groups (possibly recalcitrant C). Silt + clay fractions were distinguished by Gemmatimonadetes and OP10 phyla, which positively correlated with spectral absorption in the1250–1150 cm^?1 range (indicating both degradable and recalcitrant C forms). In contrast to general diversity index measurements, distributions of the more rare bacterial phyla (phyla representing <6% of the identified population) were more important for differentiating between communities in soil microenvironments. To our knowledge, this is the first study to investigate soil bacterial communities among soil aggregates using pyrosequenging and to associate these communities to specific soil C chemistries as indicated by mid-IR absorbance.     

Land use effects on microbial biomass C, β-glucosidase and β-glucosaminidase activities,and availability,storage, and age of organic C in soil

Microbial biomass, β-glucosidase and β-glucosaminidase activities, and availability, storage, and age of soil organic C were investigated after 26 years of conversion from sugarcane (Saccharum officinarum) to forest (Eucaliptus robusta or Leucaena leucocephala), pasture (mixture of tropical grasses), and to vegetable cropping (agriculture) in a vertisol in Puerto Rico. Soil organic C (SOC) at 0–100 cm was similar under Leucaena (22.8 kg C/m²), Eucalyptus (18.6 kg C/m²), and pasture (17.2 kg C/m²), which were higher than under agriculture (13.0 kg C/m²). Soil organic N (SON) at 0–100 cm was similar under the land uses evaluated which ranged from 1.70 (under agriculture) to 2.28 kg N/m² (under Leucaena forest). Microbial biomass C (MBC) and N (MBN) of the 0–15-cm soil layer could be ranked as: pasture > Leucaena = Eucalyptus > agriculture. The percentages of SOC and SON present as MBC and MBN, respectively, were nearly 1% in pasture and less than 0.50% in forest under Leucaena or Eucalyptus and agricultural soil. The activity of β-glucosidase of the 0–15-cm soil layer could be ranked as: Leucaena = Eucalyptus > pasture > agriculture; while β-glucosaminidase activity was ranked as: Eucalyptus > Leucaena = pasture > agriculture. The soil δ ¹³C changed from 1996 to 2006 in forest under Eucalyptus (18.7‰ to 21.2‰), but not under Leucaena (20.7‰ to 20.8‰). The soil under Leucaena preserved a greater proportion of old C compared to the forest under Eucalyptus; the former had an increased soil mineralizable C from the current vegetation inputs. The soil under agriculture had the lowest enzyme activities associated with C cycling, lowest percentage of SOC as MBC, highest percentage of SOC present as mineralizable C, and highest percentage of MBC present as mineralizable C compared to the other land uses.     

Fast and simple method for the simultaneous evaluation of the capacity and efficiency of food antioxidants in trapping peroxyl radicals in an intestinal model system

A simple oxygraphic method, for which the theoretical and experimental bases have been recently revised, has been successfully applied to evaluate the peroxyl radical chain-breaking characteristics of some typical food antioxidants in micelle systems, among which is a system that reproduces conditions present in the upper part of the digestive tract, where the absorption and digestion of lipids occur. This method permits one to obtain from a single experimental run the peroxyl radical trapping capacity (PRTC, that is, the number of moles of peroxyl radicals trapped by a given amount of food), the peroxyl radical trapping efficiency (PRTE, that is, the reciprocal of the amount of food that reduces to half the steady-state concentration of peroxyl radicals), and the half-life of the antioxidant ( t(1/2)) when only a small fraction of peroxyl radicals reacts with the antioxidants present in foods. Examples of application of the method to various types of foodstuffs have been reported, assessing the general validity of the method in the simple and fast evaluation of the above-reported fundamental antioxidant characteristics of foods.     

Exploitation shifted trophic ecology and habitat preferences of Mediterranean and Black Sea bluefin tuna over centuries

During recent decades, the health of ocean ecosystems and fish populations has been threatened by overexploitation, pollution and anthropogenic-driven climate change. Due to a lack of long-term ecological data, we have a poor grasp of the true impact on the diet and habitat use of fishes. This information is vital if we are to recover depleted fish populations and predict their future dynamics. Here, we trace the long-term diet and habitat use of Atlantic bluefin tuna (BFT), Thunnus thynnus, a species that has had one of the longest and most intense exploitation histories, owing to its tremendous cultural and economic importance. Using carbon, nitrogen and sulphur stable isotope analyses of modern and ancient BFT including 98 archaeological and archival bones from 11 Mediterranean locations ca. 1st century to 1941 CE, we infer a shift to increased pelagic foraging around the 16th century in Mediterranean BFT. This likely reflects the early anthropogenic exploitation of inshore coastal ecosystems, as attested by historical literature sources. Further, we reveal that BFT which migrated to the Black Sea–and that disappeared during a period of intense exploitation and ecosystem changes in the 1980s–represented a unique component, isotopically distinct from BFT of NE Atlantic and Mediterranean locations. These data suggest that anthropogenic activities had the ability to alter the diet and habitat use of fishes in conditions prior to those of recent decades. Consequently, long-term data provide novel perspectives on when marine ecosystem modification began and the responses of marine populations, with which to guide conservation policy.     

Fumonisins: probable role as effectors in the complex interaction of susceptible and resistant maize hybrids and Fusarium verticillioides

Fusarium verticillioides is best known for its worldwide occurrence on maize resulting in highly variable disease symptoms, ranging from asymptomatic to severe rotting and wilting and fumonisin production. The aim of this study was to investigate the influence of hybrid genotypes in the early stages of F. verticillioides infection, and the role of fumonisins as effectors in the outcome of this complex interaction. Disease symptoms, growth parameters, root morphology, and fungal colonization were evaluated at 7, 14, and 21 days after planting in seedlings from maize seeds of resistant (RH) and susceptible (SH) hybrids inoculated with F. verticillioides or watered with solutions of fumonisins. F. verticillioides induced growth enhancement or retardation depending on the plant genetic background and the fungal colonization rate, while fumonisins caused severe reduction in biomass and fitness. Seedlings watered with high fumonisin concentrations displayed lesions similar to those seen in F. verticillioides maize seedling disease, and also elicited inhibitory effects on root growth and morphology and on functional properties. In summary, these data strongly suggest a dual role for fumonisins in the F. verticillioides-maize interaction, acting as pathogenic factors at high concentrations, or triggering the plant detoxification mechanisms at low levels.     

Rad51 is an accessory factor for Dmc1-mediated joint molecule formation during meiosis

Meiotic recombination in budding yeast requires two RecA-related proteins, Rad51 and Dmc1, both of which form filaments on DNA capable of directing homology search and catalyzing formation of homologous joint molecules (JMs) and strand exchange. With use of a separation-of-function mutant form of Rad51 that retains filament-forming but not JM-forming activity, we show that the JM activity of Rad51 is fully dispensable for meiotic recombination. The corresponding mutation in Dmc1 causes a profound recombination defect, demonstrating Dmc1's JM activity alone is responsible for meiotic recombination. We further provide biochemical evidence that Rad51 acts with Mei5-Sae3 as a Dmc1 accessory factor. Thus, Rad51 is a multifunctional protein that catalyzes recombination directly in mitosis and indirectly, via Dmc1, during meiosis.