Biogenic emissions of CO2 and N2O at multiple depths increase exponentially during a simulated soil thaw for a northern prairie Mollisol

The fate of carbon (C) and nitrogen (N) belowground is important to current and future climate models as soils warm in northern latitudes. Currently, little is known about the sensitivity of microbial respiration to temperature changes at depths below 15 cm. We used whole-core (7.6 cm dia. × 90 cm) laboratory incubations to determine if temperature response quotients (Q₁₀) for CO₂ and N₂O varied with depth for undisturbed prairie while plants were senescent and clipped at the surface. We collected intact soil cores from an undisturbed prairie in central North Dakota and uniformly subjected them to freezing (5 to ?15 °C) and thawing (?15 to 5 °C). We measured rates of CO₂ and N₂O emissions at 5 °C temperature increments at 0, 15, 30, 45, 60, and 75 cm depths. During freezing, active and sterilized core emissions occurred only between 0 and ?10 °C. During thawing, a simple first-order exponential model, E = αe^βT, fit observed CO₂ and N₂O emissions (R² = 0.91 and 0.99, respectively). Parameter estimates for β were not significantly different across depths for CO₂ and for N₂O (Q₁₀ = 4.8 and 13.7, respectively). Parameter estimates for α (emissions when temperature is 0 °C) exponentially declined with depth for both gases for similar depth-response curves. Stepwise regressions of soil properties on α parameter estimates indicated emissions of CO₂ and N₂O at 0 °C during thawing were positively correlated (R² > 0.6) with soil porosity. Results indicate pedogenic properties associated with depth may not necessarily influence temperature response curves during thawing but will affect emissions at 0 °C for both CO₂ and N₂O.     

Interplay Between Oxytetracycline and the Homozygote kdr (L1014F) Resistance Genotype on Fecundity in Anopheles gambiae (Diptera: Culicidae) Mosquitoes

The insecticide resistance in Anopheles gambiae mosquitoes has remained the major threat for vector control programs but the fitness effects conferred by these mechanisms are poorly understood. To fill this knowledge gap, the present study aimed at testing the hypothesis that antibiotic oxytetracycline could have an interaction with insecticide resistance genotypes and consequently inhibit the fecundity in An. gambiae. Four strains of An. gambiae: Kisumu (susceptible), KisKdr (kdr (L1014F) resistant), AcerKis (ace-1 (G119S) resistant) and AcerKdrKis (both kdr (L1014F) and ace-1 (G119S) resistant) were used in this study. The different strains were allowed to bloodfeed on a rabbit previously treated with antibiotic oxytetracycline at a concentration of 39·10^–5 M. Three days later, ovarian follicles were dissected from individual mosquito ovaries into physiological saline solution (0.9% NaCl) under a stereomicroscope and the eggs were counted. Fecundity was substantially lower in oxytetracycline-exposed KisKdr females when compared to that of the untreated individuals and oxytetracycline-exposed Kisumu females. The exposed AcerKis females displayed an increased fecundity compared to their nontreated counterparts whereas they had reduced fecundity compared to that of oxytetracycline-exposed Kisumu females. There was no substantial difference between the fecundity in the treated and untreated AcerKdrKis females. The oxytetracycline-exposed AcerKdrKis mosquitoes had an increased fecundity compared to that of the exposed Kisumu females. Our data indicate an indirect effect of oxytetracycline in reducing fecundity of An. gambiae mosquitoes carrying kdr^R (L1014F) genotype. These findings could be useful for designing new integrated approaches for malaria vector control in endemic countries.     

Aggregate and organic matter dynamics in reclaimed soils as indicated by stable carbon isotopes

Recovery of belowground ecosystem processes, such as soil aggregation and organic matter (OM) accumulation, in reconstructed soils is crucial to successful reclamation of disturbed lands. Objectives of this study were to track soil aggregate recovery in combination with aggregate associated OM on a chronosequence of reclaimed surface mine sites and a native, undisturbed reference site. Macroaggregate and micro-within-macroaggregate proportions increased with reclamation age, while microaggregate proportions decreased. Organic carbon (C) and total nitrogen (N) concentrations increased with reclamation age for each aggregate fraction and were higher in the OM fraction observed within soil aggregates than in the free OM fraction found between soil aggregates. Naturally occurring isotopic signatures of ¹³C decreased rapidly with reclamation age, indicating over 50% of total aggregate C to be new C from predominately C₃ plant community inputs after 26 years of reclamation. Soil aggregate size distribution trends of increasing macroaggregation and micro-within-macroaggregates along with rapid rates of OM accumulation with time indicated that reclaimed soils had recovered structurally towards a native soil condition after a period of 10-15 years.     

Effect of processing on flatus producing oligosaccharides in cowpea (Vigna unguiculata) and the tropical African yam bean (Sphenostylis stenocarpa)

The effect of dehulling, soaking and soaking/cooking on sucrose, raffinose and stachyose in mature dry seeds of nine varieties of cowpea (Vigna unguiculata) and one variety of tropical African yam bean (Sphenostylis stenocarpa) were investigated. The results showed a progressive decrease in sucrose, raffinose, and stachyose contents. Soaking for 12 hours and cooking for 30 min eliminated most of the sucrose, raffinose and stachyose. The sugar contents in whole raw cowpea were sucrose 0.73–4.58%, raffinose 0.71–6.86% and stachyose 2.38–3.87%, and for tropical African yam bean sucrose 4.08%, raffinose 1.08% and stachyose 4.14% while the seeds soaked for 12 hours and cooked for 30 min had for cowpea sucrose 0.03–0.81%, raffinose 0.04–0.20% and stachyose 0.12–0.72%, and tropical African yam bean sucrose 0.70%, raffinose 0.40% and stachyose 0.41%.     

Assessing Impacts of Crested Wheatgrass AND Native Species Establishment on Soil Characteristics in Reclaimed LAND Using Bayesian Posterior Predictive Distributions

We examined the interacting effects of drastic disturbance and re‐vegetation communities on the development of soil properties over time. We compared soil characteristics from an undisturbed reference site with reclaimed mine sites that differed by vegetation type and time since reclamation: Three sites were seeded solely with crested wheatgrass (Agropyron cristatum) (11, 16, and 29 years old), and two were seeded with native cool‐season grass mixes (14 and 26 years old). We sampled soil at two depths (0–5 and 5–15 cm) for soil macroaggregate and microaggregate weights, aggregate carbon to nitrogen (C : N) ratios, and microbial abundance. We employed a Bayesian bivariate model to account for potential correlations in soil properties across depths and compared soil properties across sites using posterior predictive distributions. We found that all reclaimed soils, regardless of vegetation type, had total aggregate weights that were similar to the undisturbed reference soil but had a larger proportion of macroaggregates than the reference soil. Aggregate C : N ratios were similar between the undisturbed reference and crested wheatgrass soils, while the reclaimed native cool‐season grass soils had lower C : N ratios in the top 5 cm. Total microbial abundance in soils seeded with crested wheatgrass was an order of magnitude lower than that in soils occupied by native species (both reclaimed and undisturbed). The presence of crested wheatgrass on the reclaimed sites alone did not differentiate all soil properties across our reclamation sites, but seeding this single, aggressive species may have contributed to maintaining different belowground characteristics on reclaimed soils. Copyright © 2015 John Wiley & Sons, Ltd.