Sudden increase in atmospheric CO2 concentration reveals strong coupling between shoot carbon uptake and root nutrient uptake in young walnut trees

We studied the short-term (i.e., a few days) effect of a sudden increase in CO2 uptake by shoots on nutrient (NO3-, P ion, K+, Ca2+ and Mg2+) uptake by roots during vegetative growth of young walnut (Juglans nigra x J. major L.) trees. The increase in CO2 uptake was induced by a sudden increase in atmospheric CO2 concentration ([CO2]). Twelve 2-year-old trees were transplanted and grown in perlite-filled pots in a greenhouse. Rates of CO2 uptake and water loss by individual trees were determined by a branch bag method from 3 days before until 6 days after [CO2] was increased. Nutrient uptake rates were measured concurrently by a hydroponic recirculating nutrient solution system that provided non-limiting supplies of water and nutrients. Six control trees were kept in ambient [CO2] (360 ppm), and [CO2] was increased to 550 ppm for one set of three trees and to 800 ppm for another set of three trees. Before imposing the elevated [CO2] treatments, all trees exhibited similar daily water loss, CO2 uptake and nutrient uptake rates when expressed per unit leaf area to account for the tree size effect. Daily water loss rates were only slightly affected by elevated [CO2]. Carbon dioxide uptake rates greatly increased with increasing atmospheric [CO2], and nutrient uptake rates were proportional to CO2 uptake rates during the study period, except for P ion. Our results show that, despite the important carbon and nitrogen storage capacities previously observed in young walnut trees, nutrient uptake by roots is strongly coupled to carbon uptake by shoots over periods of a few days.     

Spatial and temporal variations in leaf area index, specific leaf area and leaf nitrogen of two co-occurring savanna tree species

Foliage growth, mass- and area-based leaf nitrogen concentrations (Nm and N a) and specific leaf area (SLA) were surveyed during a complete vegetation cycle for two co-occurring savanna tree species: Crossopteryx febrifuga (Afzel. ex G. Don) Benth. and Cussonia arborea A. Rich. The study was conducted in the natural reserve of Lamto, Ivory Coast, on isolated and clumped trees. Leaf flush occurred before the beginning of the rainy season. Maximum leaf area index (LAI), computed on a projected canopy basis for individual trees, was similar (mean of about 4) for both species. Seasonal courses of the ratio of actual to maximum LAI were similar for individuals of the same species, but differed between species. For C. febrifuga, clumped trees reached their maximum LAI before isolated trees. The LAI of C. arborea trees did not differ between clumped and isolated individuals, but maximum LAI was reached about 2 months later than for C. febrifuga. Leaf fall was associated with decreasing soil water content for C. arborea. For C. febrifuga, leaf fall started before the end of the rainy period and was independent of changes in soil water content. These features lead to a partial niche separation in time for light resource acquisition between the two species. Although Nm, N a and SLA decreased with time, SLA and N a decreased later in the vegetation cycle for C. arborea than for C. febrifuga. For both species, N a decreased and SLA increased with decreasing leaf irradiance within the canopy, although effects of light on leaf characteristics did not differ between isolated and clumped trees. Given relationships between N a and photosynthetic capacities previously reported for these species, our results show that C. arborea exhibits higher photosynthetic capacity than C. febrifuga during most of the vegetation cycle and at all irradiances.     

Luminex-based triplex immunoassay for the simultaneous detection of soy, pea, and soluble wheat proteins in milk powder

An automated fluorescent microsphere-based flow cytometric triplex immunoassay, using the Luminex 100 flow analyzer with MultiAnalyte Profiling (xMAP) technology, was developed for the simultaneous detection of proteins from three vegetable sources as potential fraudulent adulterants in milk powder. In the final triplex inhibition immunoassay, soluble wheat proteins (SWP) and proteins from soy and pea were coupled to three different microsphere sets. A mixture of these microsphere sets was transferred to a microtiter plate well together with the sample and a mixture of three affinity-purified polyclonal antibodies raised against the proteins and labeled with a fluorophore (Alexa 532). After incubation for 1.5 h at room temperature in the dark, the fluorescence intensities on the microspheres were directly measured (no wash procedure) in the Luminex during 10 s per well (100 microspheres per set). The sensitivities of the three assays for plant protein extracts were determined as 0.5-0.6 microg/mL at 50% inhibition. For the detection of the vegetable proteins in milk powder, the samples were dissolved in buffer (0.1 g in 10 mL) and further diluted (20 times) to create a 50% inhibition at approximately 0.5% of the vegetable proteins in the total protein content of milk powder. With the help of calibration standards, prepared under conditions comparable to those for sample materials, the triplex immunoassay proved to be quantitative above 0.1%, although concentrations in high-heated milk powders were underestimated. Due to the xMAP technology, in which 100 different microsphere sets can be distinguished, this triplex immunoassay can easily be extended to detect other possible adulterants.     

Fetal protection against bovine viral diarrhoea type 1 virus infection after one administration of a live-attenuated vaccine

A modified-live vaccine has been shown previously to prevent fetal infection with bovine viral diarrhoea virus (BVDV)-2 and, to some extent BVDV-1, when used in association with an inactivated vaccine in a two-step vaccination protocol. In this challenge study, the modified-live vaccine used alone was able to protect 13 heifers between 49 and 96 days of gestation at challenge from leucopenia and virus replication and, for a 4-month period, to prevent fetal infection. The efficacy of the BVDV-1f 22146/Han81 challenge was demonstrated by virus isolation from the fetuses of all nine non-vaccinated, control heifers. However, the small number of heifers tested meant that the vaccination failure rate could be as high as 10% in the field.     

Adaptation to climate across the Arabidopsis thaliana genome

Understanding the genetic bases and modes of adaptation to current climatic conditions is essential to accurately predict responses to future environmental change. We conducted a genome-wide scan to identify climate-adaptive genetic loci and pathways in the plant Arabidopsis thaliana. Amino acid-changing variants were significantly enriched among the loci strongly correlated with climate, suggesting that our scan effectively detects adaptive alleles. Moreover, from our results, we successfully predicted relative fitness among a set of geographically diverse A. thaliana accessions when grown together in a common environment. Our results provide a set of candidates for dissecting the molecular bases of climate adaptations, as well as insights about the prevalence of selective sweeps, which has implications for predicting the rate of adaptation.     

Effect of Microbial Activity and Nitrogen Mineralization on Free-living Nitrogen Fixation in Permanent Grassland Soils

Free‐living nitrogen (N) fixation can be important for sustainable soil fertility, particularly in extensively managed soils with low abundance of leguminous plant species. However, the factors affecting free N₂‐fixation in situ are still poorly documented. We investigated the role of microbial active biomass activity, particularly substrate‐induced respiration (SIR) and net N mineralization, on the free‐living N₂ fixation in soils under a semi‐natural grassland ecosystem in France. Analysis of replicated bulk soil and rhizospheric soil samples obtained from sites experiencing contrasting grazing regimes revealed highly significant negative relationships (P < 0.01) between free‐living N₂‐fixation and SIR or N‐mineralization with a significant rhizosphere effect. The study has demonstrated that the activity of free‐living N₂‐fixers is more important in soils having low active microbial biomass and low N‐mineralization rates in these permanent grasslands.     

Refining the interpretation of orthic horizons in South Africa

The relationship between soil water regime and soil profile morphology could contribute towards improving catchment water yield. This paper proposes refinements to the interpretation of orthic A horizons (ochric), defined in Soil Classification — A Taxonomic System for South Africa, to aid interpretation for hydrological purposes. Soil water contents have been measured for six years in the Weatherley catchment in South Africa and used to classify orthic A horizons in terms of wetness classes defined in the Soil Survey Manual. The well drained class is applicable to orthic A horizons overlying red apedal B, yellow-brown apedal B (agric or ferralic) or neocutanic B (cambic) horizons. The moderate poorly and poorly drained classes are applicable to orthic A horizons overlying E (albic), soft plinthic B (ferric) or G (gleyic) horizons. The occurrence of mottles and matrix colour can be used for differentiation between the latter two wetness classes. Interpretation of orthic A horizons can therefore be enhanced by wetness classification, utilizing the nature of the underlying horizon, the occurrence of mottles and matrix colour.