Mechanisms of aluminum tolerance in triticum aestivum L. (wheat) III. Long‐term pH changes induced in nutrient solutions by winter cultivars differing in tolerance to aluminum

Five winter cultivars of Triticum aestivum L., representing a known range of tolerance to aluminum (Al), were grown in nutrient solutions with and without Al for 41 days to determine long‐term changes in solution pH. Plant‐induced pH of the nutrient solutions declined for 16 to 17 days. Subsequently, the pH induced by Al‐sensitive plants grown without Al and Al‐tolerant plants grown with Al and without Al increased rapidly, presumably reflecting depletion of NH₄ ⁺ from the nutrient solutions. Aluminum‐sensitive plants grown with Al showed a less pronounced pH rise after 16 to 17 days of treatment.

After nutrient solutions were renewed on days 26 and 34, plant‐induced pH patterns were similar to those during days 1 to 26. However, the time required for the onset of the rapid rise in pH decreased. In these subsequent pH cycles, the pH patterns induced by Al‐tolerant plants grown with Al progressively approximated those induced by plants grown without Al. Aluminum‐sensitive plants grown with Al did not induce a rapid rise In pH of nutrient solutions.

Differential tolerance to Al was apparent visually after three to five days growth. Cultivar tolerance to Al was correlated with the initial rate of the pH decline (days 1 to 26) as well as final pH of solutions discarded on days 26, 34, and 41. These results support the hypothesis that differential uptake of NH₄ ⁺ and NO₃ ^‐ causes cultivar differences in plant‐induced pH of nutrient solutions and affects the relative growth of cultivars in Al‐toxic nutrient solutions.     

Salt tolerance of rapid‐cycling brassica species in relation to potassium/sodium ratio and selectivity at the whole plant and callus levels

The potassium/sodium (K/Na) ratio in the shoots of six rapid‐cycling Brassica species was greatly reduced by seawater salinity. It proportionally decreased with increasing salinity from 4 dS/m to 12 dS/m. This decrease was correlated with salt‐induced growth reduction (expressed as the percentage of control) within a species. The change in K/Na ratio with increasing salinity, however, was not correlated with K‐Na selectivity. The change in K/Na ratio at the callus level corresponded to that at the whole plant level. Both K/Na ratio and K‐Na selectivity were not found to be correlated with the relative salt tolerance of these Brassica species, indicating that the maintenance of a high K/Na ratio as a mechanism for salt tolerance in these Brassica species was not operative. These results also suggest that a high shoot K/Na ratio or K‐Na selectivity may not be reliable selection criteria for salinity resistance in some species.     

Is the decline of soil microbial biomass in late winter coupled to changes in the physical state of cold soils?

During winter when the active layer of Arctic and alpine soils is below 0 °C, soil microbes are alive but metabolizing slowly, presumably in contact with unfrozen water. This unfrozen water is at the same negative chemical potential as the ice. While both the hydrostatic and the osmotic components of the chemical potential will contribute to this negative value, we argue that the osmotic component (osmotic potential) is the significant contributor. Hence, the soil microorganisms need to be at least halotolerant and psychrotolerant to survive in seasonally frozen soils. The low osmotic potential of unfrozen soil water will lead to the withdrawal of cell water, unless balanced by accumulation of compatible solutes. Many microbes appear to survive this dehydration, since microbial biomass in some situations is high, and rising, in winter. In late winter however, before the soil temperature rises above zero, there can be a considerable decline in soil microbial biomass due to the loss of compatible solutes from viable cells or to cell rupture. This decline may be caused by changes in the physical state of the system, specifically by sudden fluxes of melt water down channels in frozen soil, rapidly raising the chemical potential. The dehydrated cells may be unable to accommodate a rapid rise in osmotic potential so that cell membranes rupture and cells lyse. The exhaustion of soluble substrates released from senescing plant and microbial tissues in autumn and winter may also limit microbial growth, while in addition the rising temperatures may terminate a winter bloom of psychrophiles.Climate change is predicted to cause a decline in plant production in these northern soils, due to summer drought and to an increase in freeze-thaw cycles. Both of these may be expected to reduce soil microbial biomass in late winter. After lysis of microbial cells this biomass provides nutrients for plant growth in early spring. These feedbacks, in turn, could affect herbivory and production at higher trophic levels.     

Is pH increasing in the noncalcareous topsoils of France under agricultural management? A statistical framework to overcome the limitations of a soil test database

Soil pH is one of the most common and important measurements used to assess soil quality and manage soil fertility. Soil acidification is a slow process that can have large consequences. Therefore, it is important to detect soil changes early. Using a French soil test database, we show that the soil pH increased in 36% of arable soils monitored from 1996 to 2010, which suggests that soils became less acidic across the country. Conversely, decreases in pH were rarely detected. To perform this assessment, we used a statistical framework to analyse 488 717 soil test results from the French national soil test database. We excluded calcareous soils due to their relatively stable pH. Two periods were analysed: 1996 to 2000 (period 1) and 2006 to 2010 (period 2). Then, we performed nonparametric Mann–Whitney U tests following a resampling step to account for the noncontrolled selection of spatial and temporal localization in the observations. Our statistical framework smoothed the effects of some limitations of the database related to the variable number of samples collected during both periods and uncertainties in sampling locations. Overall, this study demonstrates the potential of using this type of database and a relevant statistical framework to detect long‐term changes in soil properties.     

Are dietary diversity scores related to the socio-economic and anthropometric status of women living in an urban area in Burkina Faso?

OBJECTIVES: To study dietary diversity and its relationship with socio-economic and nutritional characteristics of women in an urban Sahelian context. DESIGN: A qualitative dietary recall was performed over a 24-h period. Dietary diversity scores (DDS = number of food groups consumed) were calculated from a list of nine food groups (DDS-9) or from a list of 22 food groups (DDS-22) which detailed both micronutrient- and energy-dense foods more extensively. Body mass index (BMI), mid upper-arm circumference and body fat percentage were used to assess the nutritional status of the women. SETTING AND SUBJECTS: Five hundred and fifty-seven women randomly selected in two districts of Ouagadougou, the capital of Burkina Faso. RESULTS: The mean DDS-9 and DDS-22 were 4.9 +/- 1.0 and 6.5 +/- 1.8 food groups, respectively. In the high tertile of DDS-22, more women consumed fatty and sweetened foods, fresh fish, non-fatty meat and vitamin-A-rich fruits and vegetables. The DDS-9 was not associated with the women's socio-economic characteristics whereas the DDS-22 was higher when the women were younger, richer and had received at least a minimum education. Mean BMI of the women was 24.2 +/- 4.9 kg m-2 and 37% of them were overweight or obese (BMI > or = 25 kg m-2). Neither the DDS-9 nor the DDS-22 was associated with the women's anthropometric status, even though there was a trend towards fewer overweight women in the lowest tertile of DDS-22. CONCLUSION: In this urban area, the qualitative measurement of dietary diversity is not sufficient to identify women at risk of under- or overweight.     

Is the adapted Radimer/Cornell questionnaire valid to measure food insecurity of urban households in Tehran, Iran?

OBJECTIVE: To assess the validity of the adapted Radimer/Cornell questionnaire to measure food insecurity in low-income urban households in Tehran, the capital of Iran. DESIGN: The Radimer/Cornell questionnaire was modified and used to assess the applicability, validity and reliability of such a measure in a culturally different context of urban households in Tehran. Factor analysis and Cronbach's alpha were used to assess validity and reliability, respectively. Socio-economic characteristics and food consumption frequency of the household were used to assess the criterion validity of the questionnaire. SETTING: District 20 of Tehran. SUBJECTS: A sample of 250 Iranian nuclear households with at least one child aged 1-18 years and a non-pregnant, non-lactating woman of reproductive age, selected through a multistage random sampling method. RESULTS: Three scales, labelled as household, individual and child hunger, were extracted through factor analysis using varimax rotation. Internal consistency of the scales was 0.897, 0.820 and 0.796, respectively. Individual insecurity and child hunger were inversely correlated with monthly per capita income, father's education, mother's education and father's occupational status, and positively correlated with household size, as expected. However, household insecurity did not follow the same pattern. Consumption frequency of fruits, vegetables, dairy, red meat and rice declined as food insecurity status worsened, while bread and potato consumption increased. CONCLUSION: The results show that a modified version of the Radimer/Cornell questionnaire is a valid and reliable instrument to measure household food insecurity in a culturally different context. However, further modifications seem necessary to measure food insecurity at household level. Results lend support to the utility and applicability of experience-based measures in varying cultural communities.     

Is soil water repellency a function of soil order and proneness to drought? A survey of soils under pasture in the North Island of New Zealand

We conducted a survey of the occurrence of soil water repellency (SWR) in the top 40 mm of soils across 50 sites under pastoral land use in the North Island of New Zealand. The sites represented ten soil orders and covered five classes of proneness to drought. We found at least a moderate persistence of SWR in 35 out of 50 sites (70%) in summer 2009/2010 and a moderate potential persistence of SWR in 49 out of 50 sites (98%) after drying the soils. The soil orders had an influence on the degree and persistence of SWR. Both the degree and persistence of SWR were greatest for the soil orders Podzol, Organic and Recent, and least for the soil order Allophanic. On average, all soil orders had contact angles larger than 94°, with the exception of the soil order Allophanic. We found no relationship between SWR and drought‐proneness. The degree of SWR and its persistence for air‐dried samples were positively correlated with soil carbon and nitrogen contents and negatively with soil bulk density. The persistence of SWR for field‐fresh samples was additionally negatively correlated with the soil water content. We identified a close relationship (R² = 0.84) between the degree and persistence of SWR. The survey results indicate that SWR is at least moderately persistent in a soil with a contact angle larger than 93.8°. Using a water‐drop penetration time of 60 s as the threshold for SWR being moderately persistent, we found that moderately persistent SWR occurred only for volumetric water contents below 45% or a relative saturation of 60%. The latter can be considered to be a generic value of the critical water content for the onset of SWR at the scale of the North Island of New Zealand.     

Ecological sustainability and the use of chemicals: Is ecotoxicological risk assessment doing its job properly? An introduction to chemical time bombs

Ten million chemical substances are registered scientifically, but only 1 per cent, 100000, are known to be traded internationally, and only a fraction of these are assessed to establish (eco)toxicological risks through international and national authorities. Only a few of the substances are natural or systemic; most are xenobiotic and poorly evaluated with respect to their environmental effects. It is not only the chemical accidents that make newspaper headlines, but the creeping accumulation of pollutants in soils, sediments and groundwater which degrade the environment for future generations. Ecotoxicological risk assessment still neglects this ‘hidden pollution’, as it usually deals only with the bioavailable fractions of chemicals in the environment. the ‘lost’ (residue) fractions, however, can have non-linear and time-delayed effects (chemical time bombs). As governments need to protect their natural resources (soils, sediments, groundwaters) against negative impacts from chemicals, an ecosystem approach May, help them to overcome the shortsightedness of current ‘acute’ ecotoxico-logical risk assessments. the Netherlands' risk philosophy on chemicals in the environment is discussed as an example. the National Environmental Policy Plan-2 (1994) stresses the chain of events associated with a chemical from the raw material, The side effects of its transport, production, use and disposal, to its final effects in the ecosystem, including the time-delayed responses of pollution. a revised ecotoxicological assessment policy under the new NEPP will have to take account of such chemical time bombs.     

Influence of redox processes on clay mineral transformation in Retisols in the Carpathian Foothills in Poland. Is a ferrolysis process present?

Purpose

Ferrolysis is a soil-forming process, which involves destruction of clay minerals due to cyclic reduction and oxidation in acidic and periodically wet soils. The main objectives of this study were as follows: (1) to determine the influence of redox processes on clay mineral transformation in Retisols (Albeluvisols) in the Carpathian Foothills in Poland and (2) to verify the occurrence of ferrolysis in Retisols showing various degrees of bleaching.

Materials and methods

Twelve representative soil profiles were selected for analysis. All were formed entirely from loess except for two profiles, in which the lowermost horizons (2C) had developed from weathered flysch rocks residuum. Soil mineral analysis was done using x-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and Mössbauer spectroscopy (MS).

Results and discussion

The obtained results indicate that the qualitative and quantitative mineral compositions of the clay fraction in the E and Eg horizons obtained from Retisols in the Carpathian Foothills exhibiting marked differences in bleaching (strong, moderate, weak, and lack of bleaching) caused by periodic stagnation of water above a slowly permeable fragipan and cyclic redox processes are the same. The E and Eg horizons are characterized by the presence of 2:1 clay minerals with likely organic interlayer fillings, dioctahedral mica, kaolinite, and chlorite.

Conclusions

The results indicate that (1) redox processes occurring in the soils do not affect clay mineral transformation in Retisols of the Carpathian Foothills in Poland and (2) ferrolysis is not the main soil-forming process operating in these soils. This is most likely because iron-bearing minerals are not abundant in the Retisols and/or undergo eluviation to the lower part of the soil profiles. The lower content of the clay fraction in the E and Eg horizons versus that in the lower soil horizons of the Retisols is related to clay illuviation (lessivage), and not to clay decomposition due to ferrolysis.

     

Is ‘grey literature’ a reliable source of data to characterize soils at the scale of a region? A case study in a maritime pine forest in southwestern France

Soil scientists are receiving increasing numbers of requests for expert advice on soil over large areas, but at a high resolution. We tested the use of the soil data contained in sources of information that are not directly accessible (referred to as ‘grey’ data) to accomplish this task. We collected grey data about a pine forest, which is currently the subject of drastic, and questionable, changes in management, including a rapid rate of biomass removal. These grey data (from 266 sites) were compared with soil data obtained directly from our field sampling (83 sites). Our comparisons showed that the two sources of data were consistent when the variables concerned had been sampled and analysed by using methods shared by the soil scientists such as particle‐size distribution. Conversely, significant discrepancies appeared for variables for which different methods existed, such as for CEC. For the latter, using corrective equations gave contrasting results, depending on the soil variable. The final database was used to characterize the soils of the study region. Results showed that soils of the study region (mainly sandy podzols and arenosols) were acidic and particularly oligotrophic. Several important properties (CEC, phosphorus cycling, pH, bulk density) were related to the organic fraction or carbon (C) content of soils. For instance, CEC values were linearly and exclusively dependent on C content. The most oligotrophic sites of the study region were clearly not suitable for the new intensive management of the forest in the long term. For the other sites, the question remains open because some specific data are still needed before drawing conclusions. We conclude that as a complement to conventional soil studies, the grey literature is a useful source of data and information to characterize soils at a regional scale.