Metal uptake in maize, willows and poplars on impoldered and freshwater tidal marshes in the Scheldt estuary

Foliar Cd and Zn concentrations in Salix, Populus and Zea mays grown on freshwater tidal marshes were assessed. Soil metal concentrations were elevated, averaging 9.7 mg Cd kg^?1 dry soil, 1100 mg Zn kg^?1 dry soil and 152 mg Cr kg^?1 dry soil. Cd (1.1–13.7 mg kg^?1) and Zn (192–1140 mg kg^?1) concentrations in willows and poplars were markedly higher than in maize on impoldered tidal marshes (0.8–4.8 mg Cd kg^?1 and 155–255 mg Zn kg^?1). Foliar samples of maize were collected on 90 plots on alluvial and sediment‐derived soils with variable degree of soil pollution. For soil Cd concentrations exceeding 7 mg Cd kg^?1 dry soil, there was a 50% probability that maize leaf concentrations exceeded public health standards for animal fodder. It was shown that analysis of foliar samples of maize taken in August can be used to predict foliar metal concentrations at harvest. These findings can therefore contribute to anticipating potential hazards arising from maize cultivation on soils with elevated metal contents.     

Opportunities for domesticating the African baobab (Adansonia digitata L.): multi-trait fruit selection

Among the priority species identified for domestication in the Sahel region of Sub-Sahara Africa is the baobab (Adansonia digitata L.) tree. The quantification of the variation in nutrient content and fruit morphological traits of trees is one of the most important steps in identifying superior planting material for domestication. Ten provenances in Mali covering all the different agro-ecological zones were selected and the fruit morphological traits, vitamin C, calcium, iron and colour were studied. Mean pulp content was 2,149 ± 1,117 , 2,406 ± 776  and 25 ± 17 mg kg^?1 for vitamin C, calcium and iron, respectively. Fruit pulp colour varied from white, creamy to pink and a significant correlation between pulp vitamin C content and reflectance in the green and blue bands was observed. Significant negative correlations were found between rainfall and pulp vitamin C content and between mean annual temperature and fruit and pulp weight and pulp fraction, suggesting that these traits are influenced by the environment. Pulp iron content correlated positively with topsoil sodicity and base saturation. Similarly, pulp vitamin C content correlated positively with topsoil sand fraction. Pulp reflectance in the blue and green bands correlated negatively with topsoil pH water and base saturation, respectively. The variation in nutritive and morphological traits offers the opportunity for selecting plus trees with a combination of desired traits for domestication.     

Availability and plant uptake of nutrients following the application of paper pulp and lime to tropical acid soils

Availability and plant uptake of nutrients were evaluated in three tropical acid soils (Kandiudult) amended with paper pulp and lime under greenhouse conditions. Amendments were applied to attain target pH values of 5.5, 6.0, and 6.5. A control treatment (no paper pulp or lime added) was also included. Rye grass (Lolium perenne L.) as a test plant was grown for three successive cycles of 40 days each. Extractable nutrients and cumulative nutrient uptake were determined. The application of paper pulp or lime resulted in a significant increase in exchangeable Ca and K and a decrease in exchangeable Mg and extractable Fe, Mn, and Zn. Amendment of soils with paper pulp or lime increased plant uptake of Ca and Mg and decreased that of K, Mn, and Zn. Both amendments behaved similarly, but the effect of lime seemed generally greater than that of paper pulp. Paper pulp in tropical acid soils behaved as a liming agent rather than an organic amendment. Similar to lime, amendment of soils with paper pulp resulted in an increase in availability of Ca and Mg and in a decrease in availability of K, Mn, and Zn for plants. Soil extractions appeared to be appropriate for assessing the availability of Ca, Mn, and Zn. Soil pH and effective cation exchange capacity positively influenced the availability of Ca and negatively the availability of Mn and Zn. Thus, the precision of predicting nutrient availability in paper pulp amended tropical acid soils could be improved by including soil pH or effective cation exchange capacity in relevant regression equations.     

Spatial eco-evolutionary feedback in plant-pathogen interactions

In recent years the potential for evolutionary change to drive ecological dynamics, and vice versa, has been widely recognized. However, the convincing examples of eco-evolutionary dynamics mainly stem from highly artificial experimental systems, with conspicuously few examples contributed by field systems. While rarely considered in the eco-evolutionary literature, the gene-for-gene hypothesis inherently recognizes the tight link between evolutionary and ecological dynamics. The boom-and-bust dynamics of some agricultural pathogens are an extreme demonstration of this. In this perspective, we place plant-pathogen systems in a spatial eco-evolutionary framework, which recognizes that ecology and evolution are tightly linked, take place at the same time scale and are strongly influenced by spatial structure. Specifically, we: i) exemplify how the ecological process of dispersal modifies rapid local coevolutionary dynamics and thereby shapes spatial variation in resistance, infectivity, and local adaptation; and ii) illustrate how the outcome of coevolution (spatial distribution in resistance, infectivity and local adaptation) drives ecological metapopulation processes. Overall, we conclude that both agricultural and wild pathosystems provide a unique illustration of the high relevance of spatial eco-evolutionary feedback in understanding species interactions.     

Influence of farm yard manure,poultry manure and forest litter on copper solubility in soil and uptake by Phaseolus vulgaris

Long term and intensive use of copper‐based fungicides on coffee farms may contaminate soils with copper. The legacy of copper pollution may pose the risk of contaminating food crops cultivated on these soils. A randomized block design field experiment at Kilimanjaro, Tanzania was designed to investigate the effects of different application rates of cattle manure, poultry manure and forest litter on aqua regia, EDTA and CaCl₂ extractable copper in soils and copper uptake by bean plants grown on this long‐term copper‐contaminated soil (more than 50 yr of copper application). It was important to examine the potential of the organic amendments in mobilizing or immobilizing copper and assess the risks of contaminating bean crops at a farm, where the application of organic amendments was common practice. At harvest, rhizosphere soils were collected and analysed. The soils were found to have large concentrations of copper, greatly exceeding international standard levels. Poultry manure applied at 40 tons/ha significantly increased CaCl₂ extractable copper compared with the control treatment. Organic carbon, cation exchange capacity, EDTA extractable copper, aqua regia extractable copper and copper concentrations in bean seeds or leaves were not significantly changed by the organic matter treatments. The concentration of copper was significantly less in bean seeds than in bean leaves (P < 0.01). The bean plants did not take up excessive quantities of copper, and therefore, the risk of copper contamination of bean crops in this farm appears to be small.     

Mangrove species zonation and soil redox state,sulphide concentration and salinity in Gazi Bay (Kenya), a preliminary study

The relationship between soil redox state, sulphide concentration, salinity and spatial patterns of mangrove species distribution was investigated in the mangrove forest of Gazi Bay (Kenya). Field measurements were conducted to examine the relationship between species distribution along a band transect of 280m and soil redox potential (Eh) and sulphide patterns, as well as the indirectly related (through flooding regimes) soil salinity. Of the three major species Avicenniamarina, Ceriops tagal and Rhizophoramucronata present along the transect, only the distribution of the latter correlated with the measured soil variables, R. mucronata being absent from the lessreduced zone with high salinity. Bruguieragymnorhiza and Heritieralittoralis occur in minor populations, they are restricted to the saline, sulphidepoor and lessreduced substrates. From the results it is concluded that soil redox potential (Eh), sulphide concentration and salinity may contribute to structure mangroves through the distribution of dominant species, however in combination with other environmental conditions and processes of vegetation dynamics.     

Water Extractability of Trace Metals from Soils: Some Pitfalls

Water soluble and/or dissolved metals represent the most ecotoxicologically relevant fraction of metals in the environment. However, water extractions may be prone to errors. This study aims to evaluate the performance of 5 filters as well as Rhizon soil moisture samplers, with respect to metal adsorption and/or release by the filter. In addition, the effect of equilibration time on water extractions of different types of soils was evaluated (silty loam, silty clay loam, loamy sand). Filtrations of synthetic solutions containing 40 μg 1^?1 Zn, 20 μg 1^?1 Cu, Ni and Pb, 10 μg 1^?1 Cr and 2 μg 1^?1 Cd were conducted using the different filters. The synthetic solutions either contained (i) no other competitive cations (Ca, Mg, Na, K, Fe, Mn, Al) (A ₁), (ii) competitive cations at concentrations similar to those observed in soil solutions (A ₂), (iii) competitive cations at 10 times lower concentrations than those in the synthetic soil solution (A ₃). Whiteband filters were observed to retain considerable amounts of trace metals (except Cr), both in the presence and absence of other competitive cations. Millipore filters did not exhibit metal retention. Rhizon soil moisture samplers did not retain trace metals from the synthetic soil solution (A ₂), whereas at lower concentrations of competitive cations (A ₁, A ₃) retention of Cu and Pb was observed. Whiteband filters without a predefined pore diameter allowed colloidal material of unknown particle size to pass into the filtrate, making interpretation of results very difficult and comparison between studies using different filters impossible. Millipore filters with a predefined pore diameter are to be recommended for this purpose. However, particular attention must be paid to potential constitutive Zn release by the sintered glass filter holders, the effect of which can be reduced by rigorous acid washing prior to and following every use. Rhizon samplers were also considered to be useful tools with well-defined and sufficiently small pore diameters to withhold colloidal material. However, in the absence or at reduced concentrations of competitive cations (A ₁, A ₃) retention of trace metals by the Rhizons, particularly Cu and Pb, was observed. Finally, short equilibration times may be insufficient for full assessment of the water extractable pool of trace metals in the soil.     

Feeding experiments on the larvae of the fiddler crab Uca pugilator (Brachyura,Ocypodidae), reared in the laboratory

Larvae of Uca pugilator (Bosc) were reared in the laboratory from hatching to the megalopa stage on three different diets: (1) newly hatched Artemia salina nauplii (diet A), (2) the rotifer Brachionus plicatilis (O.F. Müller) and a ciliate Euplotes sp. (diet RC), and (3) a combination of the above two diets (diet ARC). The survival rate of zoeae fed diet A (90.0%) and diet ARC (93.8%) was much higher than that of the larvae fed diet RC (22.5%). The duration of the zoeal stages was significantly shorter for the larvae fed diet ARC than for those fed diets A and RC. The survival rate of megalopa larvae (reared on diets A and ARC in the zoeal stages) was high (above 90%) for megalopa fed Artemia nauplii only, as well as for those fed a combination of Artemia nauplii and shrimp. No significant differences in duration of the megalopa stage were found between the latter diet groups.     

Use of selenium fertilizers for production of Se‐enriched Kenaf (Hibiscus cannabinus): Effect on Se concentration and plant productivity

Due to selenium (Se) deficiency, Se fortification of food and feed is applied in many countries. Therefore, potential use of Se‐enriched kenaf was investigated based on its Se accumulation, its potential to transform accumulated Se to other Se species, and effect of Se accumulation on its growth. Kenaf was grown with different levels of two Se fertilizers (selenite and selenate) at concentrations ranging from 0 to 4 mg Se (kg soil)^–1. Total Se concentrations in the plants grown on selenate‐treated soil amounted to (1019 ± 136) mg Se (kg dry weight)^–1 and were much higher compared to plants grown on selenite‐treated soil. Identified Se species were selenite, selenate, Se‐methionine, and Se‐cystine. Biomass yield, net photosynthesis, and chlorophyll index of the plants decreased when plants were grown on soils treated with high doses of selenate.