Predicting available phosphate ions from physical–chemical soil properties in acidic sandy soils under pine forests

Purpose  

For economic and environmental reasons, and for biomass production, appropriate concepts and diagnostic systems based on relevant processes are required to assess the phosphorus (P) supply capacity of the soils in the long term and to adapt P fertilization accordingly in forests. The amount of available phosphate ions (iP) can be quantified using an isotopic dilution procedure. However, this method is difficult to apply since it requires the use of radioactivity (³²P or ³³P). Our objective was thus to build pedotransfer functions for the prediction of available iP from physical–chemical soil properties.     

Wheat gluten phenolic acids: occurrence and fate upon mixing

Ferulic acid (FA, 4.9-17.7 microg/100 mg), sinapic acid (SA, 1.4-3.5 microg/100 mg), and traces of p-coumaric acid and vanillic acid were detected after saponification of six wheat glutens from industrial and pilot-scale origins. FA and SA occurred mostly as soluble-bound and insoluble-bound forms according to their extractability by acetone/methanol/water (7:7:6, v/v/v). The major part of FA (50-95%) was found in the unextractable fraction, whereas SA was mostly extractable (64-85%). The carbohydrate contents of the glutens were determined also after acid hydrolysis. The highest levels of glucose, arabinoxylan, and FA were obtained from the unextractable fractions of the pilot-scale extracted glutens, probably in relation with a lower efficiency of washing during extraction compared to industrial processes. On the other hand, SA compounds were in similar concentrations in all samples, suggesting their involvement in specific interactions during gluten protein agglomeration. Saponification of the soluble-bound phenolic acids released mainly glucose, whereas a beta-glucosidase treatment had no effect. FA and SA extractability, especially that of soluble-bound ones, decreased strongly in overmixed gluten/water doughs. These low molecular weight conjugates of phenolic acids could be involved in the dough breakdown phenomenon.     

Impact of protein size distribution on gluten thermal reactivity and functional properties

Wheat gluten structure was modified in different ways: Disulfide bonds were reduced by sulfitolysis, or protein chains were enzymatically hydrolyzed at three different degrees of proteolysis. A kinetic study of the thermal reactivity of the modified glutens showed that gluten aggregation kinetic was slowed in consequence to the shift of gluten size distribution toward smaller proteins. In contrary to sulfitolysis, proteolysis also affected the gluten reactivity potential because of the formation of numerous nonreactive species. Moreover, the thermally induced browning reaction was greatly enhanced by proteolysis, which increased the amount of free amine residues, substrates of the Maillard reaction. On the contrary, a whitening effect was observed for reduced gluten with bisulfite. Proteolysis was also found to decrease plasticized gluten viscosity, to increase gluten-based materials water solubility, and to enhance gluten adhesiveness properties but to reduce its mechanical performance. Sulfitolysis was considered as a possible way of extending gluten processability by extrusion or injection molding, whereas proteolysis was found to confer enhanced gluten stickiness that suggests new potential end uses of gluten in the pressure sensitive adhesives domain.     

Bioaccumulation of mercury and methylmercury

The factors controlling the accumulation of mercury in fish are poorly understood. The oft invoked lipid solubility of MMHg is an inadequate explanation because inorganic Hg complexes, which are not bioaccumulated, are as lipid soluble as their MMHg analogs and, unlike other hydrophobic compounds, MMHg in fish resides in protein rather than fat tissue. We show that passive uptake of the lipophilic complexes (primarily HgCl₂ and CH₃HgCl) results in high concentrations of both inorganic and MMHg in phytoplankton. However, differences in partitioning within phytoplankton cells between inorganic mercury — which is principally membrane bound — and MMHg — which accumulates in the cytoplasm — lead to a greater assimilation of MMHg during Zooplankton grazing. Most of the discrimination between inorganic and MMHg thus occurs during trophic transfer while the major enrichment factor is between water and phytoplankton. As a result, MMHg concentrations in fish are ultimately determined by water chemistry which controls MMHg speciation and uptake at the base of the food chain.     

Assessing turnover of microbial biomass phosphorus: Combination of an isotopic dilution method with a mass balance model

Microbial biomass phosphorus (P) can play an important role in P cycling and availability to plants by acting as a source (remineralization) or sink (immobilization) of phosphate ions (iP). To assess the role of the microbial P pools, both the dynamics (i.e. the turnover) and the size of the microbial P pools were studied in forest soils. Combining an isotopic dilution method with a modelling approach, we showed the existence of two pools of microbial P with different dynamics and therefore of different importance in soil P availability and cycling. In particular, we showed that the largest pool of microbial P (80%) had a fast turnover (nine days). Microbial P increased with an increase in soil organic matter and represented up to 53% of total P in contrasting forest soils. By combining these results with the turnover times of microbial P obtained in the modelling study, we evaluated that 8.5-17.3 kg P ha⁻¹ of microbial P could turn over in a few days. This suggests that microbial biomass P is a potentially significant source of available iP, and that micro-organisms can play a major role in P cycling in the forest studied here. However, microbial biomass can also be in competition with the trees since most of the remineralized P could be immobilized again in the microbial turnover.     

A proton buffering role for silica in diatoms

For 40 million years, diatoms have dominated the reverse weathering of silica on Earth. These photosynthetic protists take up dissolved silicic acid from the water and precipitate opaline silica to form their cell wall. We show that the biosilica of diatoms is an effective pH buffer, enabling the enzymatic conversion of bicarbonate to CO2, an important step in inorganic carbon acquisition by these organisms. Because diatoms are responsible for one-quarter of global primary production and for a large fraction of the carbon exported to the deep sea, the global cycles of Si and C may be linked mechanistically.     

The mosquito genome--a breakthrough for public health

The Anopheles gambiae genome sequence will accelerate identification of new insect vector target genes leading to improved strategies for malaria control.