Soil solution dynamics and plant uptake of cadmium and zinc by durum wheat following phosphate fertilization

A growth chamber study was conducted to evaluate the effect of application of phosphate fertilizer on soil solution dynamics of cadmium (Cd) and Cd accumulation in durum wheat (Triticum turgidum L. var. durum). Treatments consisted of three phosphate fertilizer sources containing 3.4, 75.2, and 232 mg Cd kg^?1 applied at three rates (20, 40 and 80 mg P kg^?1) plus a no fertilization control. An unplanted treatment at 40 mg P kg^?1 was included to separate the effects on soil solution Cd dynamics of the crop from that of the fertilizer. Soil solution samples were obtained using soil moisture samplers every 10 days after germination. The experimental results indicated that plant biomass significantly increased with P application rates and decreased with increased Cd concentration in the phosphate fertilizers. Total cadmium concentration in soil solution was not consistently affected by phosphate fertilization rate and fertilizer sources, and therefore Cd concentration in the fertilizer. Application of phosphate fertilizer, however, increased the concentration and accumulation of Cd and shoot Cd/Zn ratio, and decreased shoot Zn concentration in durum wheat. Phosphate sources had a marginally significant effect (P?=?0.05) on shoot Cd concentration and did not affect Cd accumulation in durum wheat. Concentration of Cd in soil solution was unrelated to Cd concentration in durum wheat. These results suggest that the immediate increase in Cd concentration and Cd accumulation in durum wheat with phosphate application is due more to competition between Zn and Cd for absorption into plants, enhanced root to shoot translocation and enhanced root development, than to a direct addition effect from Cd contained in phosphate fertilizer. In the short term, application of phosphate fertilizers can increase Cd concentration in the crops, regardless of the Cd concentration of the fertilizer. An optimal P fertilization, possibly in combination with Zn application, may offer an important strategy for decreasing Cd concentration and accumulation in crops.     

Crop residue incorporation negates the positive effect of elevated atmospheric carbon dioxide concentration on wheat productivity and fertilizer nitrogen recovery

Background and purpose

Rapid increases in atmospheric carbon dioxide concentration ([CO₂]) may increase crop residue production and carbon: nitrogen (C:N) ratio. Whether the incorporation of residues produced under elevated [CO₂] will limit soil N availability and fertilizer N recovery in the plant is unknown. This study investigated the interaction between crop residue incorporation and elevated [CO₂] on the growth, grain yield and the recovery of ¹⁵N-labeled fertilizer by wheat (Triticum aestivum L. cv. Yitpi) under controlled environmental conditions.

Methods

Residue for ambient and elevated [CO₂] treatments, obtained from wheat grown previously under ambient and elevated [CO₂], respectively, was incorporated into two soils (from a cereal-legume rotation and a cereal-fallow rotation) 1 month before the sowing of wheat. At the early vegetative stage ¹⁵N-labeled granular urea (10.22 atom%) was applied at 50 kg?N ha^?1 and the wheat grown to maturity.

Results

When residue was not incorporated into the soil, elevated [CO₂] increased wheat shoot (16 %) and root biomass (41 %), grain yield (19 %), total N uptake (4 %) and grain N removal (8 %). However, the positive [CO₂] fertilization effect on these parameters was absent in the soil amended with residue. In the absence of residue, elevated [CO₂] increased fertilizer N recovery in the plant (7 %), but when residue was incorporated elevated [CO₂] decreased fertilizer N recovery.

Conclusions

A higher fertilizer application rate will be required under future elevated [CO₂] atmospheres to replenish the extra N removed in grains from cropping systems if no residue is incorporated, or to facilitate the [CO₂] fertilization effect on grain yield by overcoming N immobilization resulting from residue amendment.     

Cadmium uptake kinetics and plants factors of shoot Cd concentration

Background and aims

Accumulation of Cd in the shoots of plants grown on Cd contaminated soils shows considerable variation. A previous preliminary experiment established that one major reason for this variation was the rate of Cd influx into the roots (mol Cd cm^?2 root s^?1). However, this experiment did not distinguish between solubilization of soil Cd on the one hand and difference in Cd uptake kinetics on the other. The main objectives of the present study were thus to characterize Cd uptake kinetics of plants continuously exposed to Cd concentrations similar to those encountered in soils. Furthermore we determined the factors responsible for differences in shoot Cd concentration such as net Cd influx, root area-shoot dry weight ratio, shoot growth rate and proportion of Cd translocated to the shoot.

Materials and methods

Maize, sunflower, flax and spinach were grown in nutrient solution with five constant Cd concentrations varying from 0 to 1.0 μmol?L^?1. Root and shoot parameters as well as Cd uptake were determined at two harvest dates and from these data Cd net influx and shoot growth rates were calculated.

Results and conclusions

Cadmium uptake kinetics, i.e. the net Cd influx vs. Cd solution concentration followed a straight line. Its slope is the root absorbing power, α, $ \left( {\alpha ={{{\mathrm{Cd}\;\mathrm{net}\;\mathrm{influx}}} \left/ {{\mathrm{Cd}\;\mathrm{solution}\;\mathrm{concentration}}} \right.}} \right) $ . The α values of spinach and flax were about double that of maize and sunflower (5?×?10^?6?cm?s^?1 vs. 2.5?×?10^?6?cm?s^?1). Spinach and flax had a 3–5 times higher shoot Cd concentration than maize and sunflower. The difference in shoot Cd concentration was partly due to the higher Cd influx but also to a higher translocation of Cd from root to shoot and also to a slower shoot growth rate.     

The reduction in zinc concentration of wheat grain upon increased phosphorus-fertilization and its mitigation by foliar zinc application

Background and aims

Malnutrition resulting from zinc (Zn) and iron (Fe) deficiency has become a global issue. Excessive phosphorus (P) application may aggravate this issue due to the interactions of P and micronutrients in soil crop. Crop grain micronutrients associated with P applications and the increase of grain Zn by Zn fertilization were field-evaluated.

Methods

A field experiment with wheat was conducted to quantify the effect of P applications on grain micronutrient quality during two cropping seasons. The effect of foliar Zn applications on grain Zn quality with varied P applications was tested in 2011.

Results

Phosphorus applications decreased grain Zn concentration by 17–56%, while grain levels of Fe, manganese (Mn) and copper (Cu) either remained the same or increased. Although P applications increased grain yield, they restricted the accumulation of shoot Zn, but enhanced the accumulation of shoot Fe, Cu and especially Mn. In 2011, foliar Zn application restored the grain Zn to levels occurring without P and Zn application, and consequently reduced the grain P/Zn molar ratio by 19–53% than that without Zn application.

Conclusions

Foliar Zn application may be needed to achieve both favorable yield and grain Zn quality of wheat in production areas where soil P is building up.     

Preceding crop and phosphorus fertilization affect cadmium and zinc concentration of flaxseed under conventional and reduced tillage

Field studies were conducted over 4 years at two locations in Manitoba, Canada to evaluate effects of preceding crop, tillage and phosphorus (P) fertilization on Cd and Zn concentration in oilseed flax (linseed—Linum usitatissimum L.). Canola (Brassica napus L.) and spring wheat (Triticum aestivum L.) were grown under conventional and reduced tillage with three rates of monoammonium phosphate. Flax was seeded the year following the spring wheat or canola, with or without P fertilizer, and Cd and Zn concentration and accumulation were determined in the flax tissue at 5 weeks and in the mature seed. Flax following canola had lower Zn concentration and accumulation and higher Cd concentration and Cd:Zn ratio in the tissue and seed relative to flax following wheat. Phosphorus fertilization tended to increase Cd concentration and Cd:Zn ratio and decrease Zn concentration in the tissue and seed. Effects of tillage and interactions among tillage, preceding crop, and P fertilization were inconsistent. Changes in flax Cd and Zn concentration may be due to changes in mycorrhizal colonization or by the high concentration of Cd in the decomposing canola residue. Crop sequence and P management can be used to improve flaxseed food quality, by increasing Zn and decreasing Cd concentration.     

Spatial and technological variability in the carbon footprint of durum wheat production in Iran

Purpose

The purpose of this study was to quantify the spatial and technological variability in life cycle greenhouse gas (GHG) emissions, also called the carbon footprint, of durum wheat production in Iran.

Methods

The calculations were based on information gathered from 90 farms, each with an area ranging from 1 to 150 ha (average 16 ha). The carbon footprint of durum wheat was calculated by quantifying the biogenic GHG emissions of carbon loss from soil and biomass, as well as the GHG emissions from fertilizer application and machinery use, irrigation, transportation, and production of inputs (e.g., fertilizers, seeds, and pesticides). We used Spearman’s rank correlation to quantify the relative influence of technological variability (in crop yields, fossil GHG emissions, and N₂O emissions from fertilizer application) and spatial variability (in biogenic GHG emissions) on the variation of the carbon footprint of durum wheat.

Results and discussion

The average carbon footprint of 1 kg of durum wheat produced was 1.6 kg CO₂-equivalents with a minimum of 0.8 kg and a maximum of 3.0 kg CO₂-equivalents. The correlation analysis showed that variation in crop yield and fertilizer application, representing technological variability, accounted for the majority of the variation in the carbon footprint, respectively 76 and 21%. Spatial variation in biogenic GHG emissions, mainly resulting from differences in natural soil carbon stocks, accounted for 3% of the variation in the carbon footprint. We also observed a non-linear relationship between the carbon footprint and the yield of durum wheat that featured a scaling factor of ?2/3. This indicates that the carbon footprint of durum wheat production (in kg CO₂-eq kg^?1) typically decreases by 67% with a 100% increase in yield (in kg ha^?1 year^?1).

Conclusions

Various sources of variability, including variation between locations and technologies, can influence the results of life cycle assessments. We demonstrated that technological variability exerts a relatively large influence on the carbon footprint of durum wheat produced in Iran with respect to spatial variability. To increase the durum wheat yield at farms with relatively large carbon footprints, technologies such as site-specific nutrient application, combined tillage, and mechanized irrigation techniques should be promoted.

     

Metal concentration and metal mass of metallicolous, non metallicolous and serpentine Noccaea caerulescens populations, cultivated in different growth media

Aims

Evaluate the genetic and environmental variability of metal concentration and metal mass of Noccaea caerulescens, from metalliferous (MET), non metalliferous (NMET) and serpentine (SERP) soils.

Methods

18 populations were cultivated in 18 different growth conditions, such as a soil mine tailing, soils amended with zinc (Zn), cadmium (Cd) and nickel (Ni) salts (in mixtures or in monometallic salts) and a hydroponic solution with two Zn concentrations.

Results

MET populations had Zn concentrations lower than NMET and SERP in the different soils but higher Cd mass (the product of aerial biomass and foliar metal concentration). SERP had the highest Ni concentration and Ni mass values. The addition of Cd or Ni to a Zn-contaminated soil significantly decreases Zn concentration. In hydroponics, MET and NMET had equivalent Zn concentrations but these were three times higher than those obtained in soil experiments. Zn mass of NMET was significantly lower than MET with the latter having Zn mass values largely above those obtained in mine soil.

Conclusions

Results showed a large heterogeneity of responses among populations depending on the substrate used, and it was not possible to correctly assign a single population to its accurate origin with only one experiment. Finally, data on metal concentration obtained in culture soils are closer to those in field soils than those from hydroponics so that they could give a more accurate information on the accumulating capacity of Noccaea caerulescens and its use in phytoextraction of metals in field conditions.     

Properties of anthropogenic soils in ancient run-off capturing agricultural terraces in the Central Negev desert (Israel) and related effects of biochar and ash on crop growth

Background and aims

In the Central Negev hills (Israel) many ancient terraced wadis exist, which captured run-off and caused gradual soil aggradation, which enabled agricultural practices. In these terraces, dark colored soil horizons were observed, containing charcoal, as can be found in Terra Preta soils, suggesting higher fertility compared to natural soils. The aim of our investigation was to investigate these anthropogenic soils and to study the effects of charcoal and ash addition on soil properties and crop growth.

Methods

We investigated 12 soil profiles, focusing on possible differences between light and dark colored soil horizons. We also investigated the effects of amendment of charcoal and ash on the growth of wheat (Triticum Aestivum L.) in a 40-day pot experiment involving two water regimes.

Results

Results show that charcoal content in light and dark horizons were both low (<0.2 %), but significantly lower bulk densities were found in dark colored horizons. In the crop experiment, charcoal addition resulted in decreased crop growth, while, in the water deficit regime, ash addition resulted in increased crop growth.

Conclusions

Considering the observed charcoal and the results from the crop experiment, we hypothesize that, in ancient run-off capturing agricultural systems, ash was purposefully added as fertilizer.     

Mapping QTLs for yield and nitrogen-related traits in wheat: influence of nitrogen and phosphorus fertilization on QTL expression

Key message

The present study identified some new important genomic regions and demonstrated the availability of conditional analysis in dissecting QTLs induced by environmental factors.

Abstract

The high input and low use efficiency of nutrient fertilizers require knowledge of the genetic control of crop reaction to nutrient supplements. In this study, 14 morphological and 8 physiological traits of a set of 182 wheat (Triticum aestivum L.) recombinant inbred lines (Xiaoyan 54 × Jing 411) were investigated in six environments to map quantitative trait loci (QTLs). The influence of nitrogen (N) and phosphorus (P) fertilization on QTL expression was studied by unconditional and conditional analysis. A total of 117 and 30 QTLs were detected by unconditional and conditional analysis, respectively, among which 21 were common for both methods. Thirty-four QTL clusters were identified. Eighteen conserved QTLs (15.4 % of the 117 QTLs) between years, but within nutritional treatment were found. The three major QTLs on chromosomes 2D, 4B and 6A were coincident with Rht8, Rht-B1b and TaGW2, respectively. The other two important intervals on chromosomes 4B and 7A for yield component traits were newly detected QTLs that warrant further study. By conditional analysis, spikelet number per spike was found to be induced by P fertilization mostly, whereas N fertilization had more effects on the expression of the QTLs for nitrogen concentration and utilization efficiency traits. QTLs that respond to N and P interactions were also detected. The results are helpful for understanding the genetic basis of N utilization efficiency in wheat under different N and P supplement environments and provide evidence for the availability of conditional analysis in dissecting QTLs induced by environmental factors.     

The effect of transpiration on thallium uptake and mobility in durum wheat and spring canola

Aims

The objective of this study was to investigate the role of transpiration on accumulation and distribution of thallium (Tl) in young durum wheat (Triticum turgidum L. var ‘Kyle’) and spring canola (Brassica napus L. cv ‘Hyola 401’) plants.

Methods

Seedlings were grown hydroponically and exposed to Tl(I) under different high relative humidity (RH) conditions which resulted in different rates of transpiration among treatments. Plants were harvested prior to exposure, after a dark period of 9 (wheat) or 10?h (canola), and after 24?h of exposure. Harvested plant material was digested and analyzed for Tl by GFAAS.

Results

Our results indicated that accumulation and distribution of Tl by plants was dependent on plant species, Tl(I) dose, duration of exposure and RH, but that the effect of RH was influenced by plant species and Tl dose. Plants exposed to Tl(I) under different RH conditions did not accumulate more Tl overall. In wheat, shoots with higher transpiration rates contained a higher Tl concentration. In canola, the rate of transpiration did not consistently affect the concentration of Tl in shoots.

Conclusions

Overall, our results suggest that accumulation and translocation of Tl by plants is influenced by environmental factors that affect transpiration, in addition to soil characteristics.     

Influence of CdCl2 and CdSO4 supplementation on Cd distribution and ligand environment in leaves of the Cd hyperaccumulator Noccaea (Thlaspi) praecox

Background and aims

The aim was to investigate whether different Cd salts in the nutrient solution of the Cd/Zn hyperaccumulator Noccaea (Thlaspi) praecox alter leaf Cd distribution and Cd ligand environment, and plant fitness.

Methods

Plants were grown for 8 weeks with 100/300 μM CdCl₂ or CdSO₄. Leaf biomass, and total chlorophyll, anthocyanin, Cd, Cl, S and P concentrations were monitored. Cd localisation and ligand environment in leaves were analysed using quantitative synchrotron-based micro-X-ray fluorescence imaging, and Cd K-edge X-ray absorption fine structure and Cd L₃-edge micro-X-ray absorption near-edge structure measurements.

Results

Cd uptake and plant fitness were comparable for CdCl₂ and CdSO₄ treatments, and depended on applied Cd concentration. In all treatments, Cd preferentially accumulated with high concentrations of Cl in vacuoles of large vacuolarised epidermal cells, bound mainly to oxygen-based (O)-ligands. In the mesophyll of CdCl₂? treated plants, Cd was preferentially sequestered in vacuoles, while for CdSO₄, Cd accumulated preferentially in the apoplast. In the symplast, O-ligands increased with increasing Cd concentrations; in the apoplast, sulphur-based (S)-ligands prevailed.

Conclusions

Cd partitioning between leaf mesophyll apoplast and symplast and the Cd ligand environment in N. praecox depend on the Cd salt type and concentration added to the nutrient solution.     

Root-induced processes controlling phosphate availability in soils with contrasted P-fertilized treatments

Aims

In this study we identified the nature of the root-induced chemical processes controlling changes in phosphate (P) availability in a soil with two P loadings resulting from long-term fertilization treatments.

Methods

We used a set of mechanistic adsorption models (surface complexation and ion exchange) within the framework of the component additive approach to simulate the effect of durum wheat roots on P availability. We had to consider the influence of adsorption of other ions to ensure the goodness-of-fit of the simulations.

Results

We found that Ca²⁺ uptake, in addition to P uptake and root-induced alkalization, controlled P availability in the rhizosphere regardless of the fertilization level. The relative influence of these three processes depends primarily on the extractant used to estimate P availability. Calcium uptake was the most significant process in water extracts, whereas P uptake was the dominant root-induced chemical process in CaCl₂ extracts. Under low Ca concentrations, Ca²⁺ uptake decreased the promoting influence of Ca²⁺ adsorption on P adsorption.

Conclusions

In addition to confirming the validity of our approach to model P availability, the present investigation indicated that root-induced processes markedly affect P availability irrespective of the fertilization level.     

Pyrosequencing reveals how pulses influence rhizobacterial communities with feedback on wheat growth in the semiarid Prairie

Background and Aims

Evidence shows that plants modify their microbial environment leading to the “crop rotation effect”, but little is known about the changes in rhizobacterial community structure and functionality associated with beneficial rotation effects.

Methods

Polymerase chain reaction (PCR) and 454 GS FLX amplicon pyrosequencing were used to describe the composition of the rhizobacterial community evolving under the influence of pea, a growth promoting rotation crop, and the influence of three genotypes of chickpea, a plant known as an inferior rotation crop. The growth promoting properties of these rhizobacterial communities were tested on wheat in greenhouse assays.

Results

The rhizobacterial communities selected by pea and the chickpea CDC Luna in 2008, a wet year, promoted durum wheat growth, but those selected by CDC Vanguard or CDC Frontier had no growth-promoting effect. In 2009, a dry year, the influence of plants was mitigated, indicated that moisture availability is a major driver of soil bacterial community dynamics.

Conclusion

The effect of pulse crops on soil biological quality varies with the crop species and genotypes, and certain chickpea genotypes may induce positive rotation effects on wheat. The strength of a rotation effect on soil biological quality is modulated by the abundance of precipitation.     

Mechanistic studies of perfluorooctane sulfonate, perfluorooctanoic acid uptake by maize (Zea mays L. cv. TY2)

Aims

There is a need to predict trace metal concentration in plant organs at given development stages. The aim of this work was to describe the Cd hyperaccumulation kinetics in the different plant organs, throughout the complete cultivation cycle, independently of a possible soil effect.

Methods

Plants of Noccaea caerulescens were exposed in aeroponics to three constantly low Cd concentrations and harvested at 6 to 11 dates, until siliquae formation.

Results

Dry matter allocation between roots and shoots was constant over time and exposure concentrations, as well as Cd allocation. However 86 % of the Cd taken up was allocated to the shoots. Senescent rosette leaves showed similar Cd concentrations to the living ones, suggesting no redistribution from old to young organs. The Cd root influx was proportional to the exposure concentration and constant over time, indicating that plant development had no effect on this. The bio-concentration factor (BCF), i.e. [Cd]_plant/[Cd²⁺]_solution for the whole plant, roots or shoots was independent of the exposure concentration and of the plant stage.

Conclusions

Cadmium uptake in a given plant part could therefore be predicted at any plant stage by multiplying the plant part dry matter by the corresponding BCF and the Cd²⁺ concentration in the exposure solution.     

Comparative analysis of Cd and Zn impacts on root distribution and morphology of Lolium perenne and Trifolium repens: implications for phytostabilization

Backgrounds and aims

The phytostabilization potential of plants is a direct function of their root systems. An experimental design was developed to investigate the impact of Cd and Zn on the root distribution and morphology of Lolium perenne and Trifolium repens.

Methods

Seedlings were transplanted into columns filled with washed quartz and irrigated daily with Cd- or Zn-containing nutrient solutions during 1 month. Root biomass, root length density (RLD) and diameter were subsequently quantified as a function of depth. Pot experiments were also performed to quantify metal, lignin and structural polysaccharides concentrations as well as cell viability.

Results

Lolium perenne accumulated Cd and Zn in the roots whereas T. repens was unable to restrict heavy metal translocation. Cadmium and Zn reduced rooting depth and RLD but induced thick shoot-borne roots in L. perenne. Cd-induced root swelling was related to lignification occurring in the exodermis and parenchyma of central cylinder. Hemicelluloses and lignin did not play a key role in root metal retention. Cadmium slightly reduced mean root cell viability whereas Zn increased this parameter in comparison to Cd.

Conclusions

Even though plant species like Lolium perenne and Trifolium repens may appear suitable for a phytostabilization scheme based on their shoot metal tolerance, exposure to toxic heavy metals drastically impairs their root distribution. This could jeopardize the setting up of phytostabilization trials. The metal-induced alterations of root system properties are clearly metal- and species-specific. At sites polluted with multiple metals, it is therefore recommended to first test their impact on the root system of multiple plant species so as to select the most appropriate species for each site.     

Soil CO2 efflux in response to the addition of water and fertilizer in temperate semiarid grassland in northern China

Background and aims

Knowledge about the effects of water and fertilizer on soil CO₂ efflux (SCE) and Q ₁₀ is essential for understanding carbon (C) cycles and for evaluating future global C balance. A two-year field experiment was conducted to determine the effects of water, fertilizer, and temperature on SCE in semiarid grassland in northern China.

Methods

SCE, as well as environmental factors was measured in two grasslands, one with bunge needlegrass (BNE, Stipa bungeana) and one with purple alfalfa (ALF, Medicago sativa), with four treatments: CK (unwatered and unfertilized); W (50 mm water addition yr^?1); F (50 kg phosphorus (P) fertilizer ha^?1 yr^?1 for ALF, 100 kg nitrogen (N)?+?50 kg P fertilizer ha^?1 yr^?1 for BNE); and W + F.

Results

During the 11-month experimental period from July 2010 to October 2011, the addition of water consistently stimulated mean SCE in BNE and ALF, and the positive effects were relatively stronger during dry seasons. P fertilization consistently enhanced SCE in ALF, and the positive effect was strongly dependent on the availability of soil water. The effects of N plus P fertilization on SCE in BNE varied seasonally from significant increases to small reductions to no response. Water addition increased the Q ₁₀ of SCE in ALF by 11 % but had no effect in BNE. Fertilization, however, reduced the Q ₁₀ of SCE by 21 % and 13 % for BNE and ALF, respectively. Models that rely only on Q ₁₀ underestimated the emissions of soil CO₂ by 8–15 % at the study site, which was mediated by species and treatment.

Conclusions

Responses of SCE and its temperature sensitivity to water and fertilizer may vary with species and depend on the period of measurement. Models of SCE need to incorporate the availability of ecosystemic water and nutrients, as well as species, and incorporate different environmental factors when determining the impact of water, nutrients, and species on SCE.     

Soil fertility and its significance to crop productivity and sustainability in typical agroecosystem: a summary of long-term fertilizer experiments in China

Aims and background

Soil fertility quality index is a useful indicator that helps to improve sustainable land use management and achieve economical yield in agriculture production. The objectives of this study were to evaluate the changes of soil fertility quality between the 1980s and 2000s in different cropping systems and its significance to crop productivity and sustainability.

Methods

We collected all published data on crop yields and soil parameters from 58 long-term experiments in three typical double-cropping systems in China, including maize-wheat (M-W), rice-rice (R-R) and rice-wheat (R-W) cropping systems, and selected seven fertilizer treatments in each experiment, including inorganic fertilizer [nitrogen and phosphorus fertilizer (NP), nitrogen and potassium fertilizer (NK), phosphorus and potassium fertilizer (PK) and balanced mineral fertilizer (NPK)], combined NPK with farmyard manure (NPKM) or crop straw (NPKS), and no fertilizer application (served as control). For comparison, an integrated fertility quality index (IFQI) was used to estimate the variations in soil fertility in different cropping systems. Moreover, the mean production variability index (PVI, %) in each cropping system was calculated to evaluate the stability of crop production.

Results

Over cropping systems, the averaged relative yields of PK, NK and NP ranged from 38.0 to 97.4 %, while the mean yields can be increased by 2.4–5.1 % in NPKM, compared to NPK. The mean yields were similar between NPK and NPKS for maize and wheat crops, but the yield was increased by 4.3–10.0 % in NPKS. Among the different treatments, the highest variability of cereal productivity was obtained in NK, PK or Control, while the lowest value was mostly recorded in NPKM or NPKS in these three cropping systems. Relative to the control, the IFQIs in fertilization treatments were increased by 9.4–150.0 %, 6.2–41.5 % and 1.3–17.5 % in M-W, R-W and R-R systems, respectively (except for PK treatment in R-R system). However, changes of IFQI in topsoil differed among fertilizer treatments, and greater increases existed in the treatments receiving organic residues (NPKM and NPKS).

Conclusions

The increase in crop yield is exponentially correlated with the increased IFQI over treatments in three cropping systems. Over the treatments and systems, production variability among years is shown to be negatively, linearly related to IFQI (P?<?0.001). Therefore, the high grain yield and low production variability can be simultaneously achieved by increasing soil fertility in all three cropping systems.     

Role of roots in cadmium accumulation of two water spinach cultivars: reciprocal grafting and histochemical experiments

Background and Aims

Cultivars of water spinach (Ipomoea aquatica Forsk.) differ widely in their shoot cadmium (Cd) concentration. Previously, we suggested that low-Cd cultivars are better able to retain Cd in their roots and thus prevent root-to-shoot Cd translocation. In this study, we explored the roles of roots and shoots in Cd accumulation in a high-Cd (T308) and low-Cd cultivar (QLQ).

Methods

We used reciprocal grafting to determine the importance of roots and shoots in Cd accumulation, and a dithizone histochemical method to investigate Cd distribution in the roots.

Results

The T308 scion with QLQ rootstock accumulated less Cd than the shoot of non-grafted T308. The QLQ scion with T308 rootstock showed a significantly higher Cd concentration than that in the shoot of non-grafted QLQ. Cadmium induced thicker phellem formation in the main roots of QLQ than in those of T308 and only QLQ showed thickening of the outer cortex cell walls in lateral roots.

Conclusions

Shoot Cd accumulation was primarily determined by root-to-shoot Cd translocation, not root Cd uptake. The thicker phellem and outer cortex cell walls in QLQ than in T308 may be one reason why QLQ roots were able to retain more Cd, and thus reducing Cd translocation to shoots.     

Temporal variability of solution Cd2+ concentration in metal-contaminated soils as affected by soil temperature: consequences on lettuce (Lactuca sativa L.) exposure

The aim of this study was to assess how the solubility and the speciation of Cd in soil solution were affected over time by the soil temperature for three metal-contaminated soils. The changes of solution Cd concentration (either total or free ionic) and other physico-chemical parameters (e.g. pH, ionic strength, the concentrations of ${\text{NO}}_3^ - $ , ${\text{SO}}_4^{2 - } $ , Ca, Mg and dissolved organic carbon) were monitored over a 28-day culture of lettuce (Lactuca sativa L.) in soils incubated at 10°C, 20°C or 30°C. The major result of this study was that Cd²⁺ concentration greatly varied over time in soil solution. The Cd²⁺ concentration declined over time in soil solution as did the concentration of cations that may compete for adsorption (Ca²⁺, Mg²⁺). The rise in soil temperature primarily impacted on the concentration of Cd²⁺ via promoting the microbial C-degradation and, thus, the complexation of Cd in soil solution. The integration of the temporal variations in Cd²⁺ concentration through the calculation of the root exposure to solution Cd (E _Cd) provided a fairly close and robust prediction of Cd concentration in lettuce roots. The present work thus provided new insights on the fate of Cd in contaminated soils that may be relevant for predicting the root uptake of Cd.     

Predictability of the Zn and Cd phytoextraction efficiency of a Salix smithiana clone by DGT and conventional bioavailability assays

Aims

Phytomanagement of metal-polluted soils requires information on plant responses to metal availability in soil, but the predictability of metal accumulation in plant shoots and/or roots may be limited by metal toxicity and inherent shortfalls of the bioavailability assays.

Methods

We measured the uptake of Cd and Zn in a Salix smithiana clone grown in a pot experiment on soils with different characteristics and metal availabilities, determined by conventional soil single extractions (0.05 M Na₂-EDTA and 1 M NH₄NO₃), soil solution obtained by centrifugation, and diffusive gradients in thin films (DGT). The Cd and Zn phytoavailability after a 2-year phytoextraction by willow was assessed by metal accumulation in the straw of the following barley culture.

Results

The phytoextraction efficiency was largest on a moderately polluted acid soil. Biomass and shoot Zn concentrations of S. smithiana were better predicted by DGT-measured Zn concentrations in soil solution (C _DGT) than by Zn concentrations in the soil solution and extractable soil fractions. The weaker correlation for Cd in shoots may be related to relative Cd enrichment in the plant tissues. The metal accumulation in barley straw was unaffected or increased after a 2-year phytoextraction.

Conclusions

The shoot Zn and Cd removal of the tested Salix clone can be predicted by C _DGT concentrations and is highest on either calcareous or moderately polluted acid soils. Single extraction with NH₄NO₃ and the C _DGT value of Cd were not able to predict shoot Cd removal on the tested soils. Only shoot removal of Zn was predicted fairly well by the C _DGT value.