Showing papers in "Plant and Soil in 2004"

Rare earth elements in soil and plant systems - A review

Abstract: The rare earth elements (REEs) form a chemically uniform group and include yttrium (Y), lanthanum (La) and the lanthanides cerium (Ce), praseodymium (Pr), neodymium (Nd), promethium (Pm), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu) Their average abundance in the Earth’s crust range from 66µg g−1 in Ce to 05µg g−1 in Tm and «01µg g−1 in Pm Recent great improvements in more routine analytical technique, the use of REEs as fertilisers, at least in East Asian agriculture, and the importance of these elements as indicators in both pedological and physiological processes and reactions have contributed to an increased interest in these previously less considered elements in environmental sciences This review of recent and current literature deals with REEs in primary and secondary soil minerals, concentrations in surface soils, factors influencing adsorption, solubility and transport in soils, including weathering and transformations of REE minerals, and vertical distribution in soil profiles Reviewed and discussed are also concentrations, distribution and localisation of REEs in plants and plant organs, soil-plant relationships and interactions, effects on plant growth and crop production and their importance in plant physiology and biochemistry The REEs are found, usually several elements together, as phosphates, carbonates and silicate minerals finely dispersed especially in magmatic and metamorphic rocks REE concentrations in surface soils of humid climates, such as the A(E)-horizons of Podzols and Laterites, are usually lower than in the parent material, due to higher weathering and leaching rates than of the average soil constituents Some fractionation may occur due to the formation of more element-specific secondary minerals Transfer from soil to plant is usually low, but extreme accumulators are found, eg, among several species of ferns Roots have generally higher concentrations than shoots Possible uptakemechanisms of REEs are discussed Uptake is positively, though often weakly, correlated with soil acidity and easily soluble concentrations of the elements, but rarely well related to their total concentrations in the soil Under certain conditions, low concentrations of at least some REEs seem to favour plant growth and productivity, but the physiological mechanisms are still not well understood Some considerations concerning the boundary between essential and non-essential micro nutrients are discussed

Cadmium tolerance and hyperaccumulation in a new Zn-hyperaccumulating plant species (Sedum alfredii Hance)

Abstract: Sedum alfredii Hance has been identified as a new zinc (Zn) hyperaccumulating plant species. In this study, the effects of cadmium (Cd) supply levels (control, 12.5, 25, 50, 100, 200, 400, 800 µmol Cd L −1 ) on the growth and cadmium accumulation and Zn supply on Cd accumulation in S. alfredii Hance were studied. The results showed that no reduction in shoot and root dry matter yields were noted when the plants were grown at Cd supply levels up to 200 µmol L −1 in nutrient solution. Slight stimulation on shoot growth was noted at relatively low Cd levels (25 to 100µmol L −1 ). Cadmium concentrations in leaves and stems increased with increasing Cd supply levels, and reached a maximum of approximately 9000 and 6500 mg kg −1 (DW) at 400 µmol Cd L −1 , respectively. Root Cd concentration increased sharply only at relatively high Cd levels. Cadmium distribution in different parts of the

Development of specific rhizosphere bacterial communities in relation to plant species, nutrition and soil type

Abstract: Rhizosphere microbial communities are important for plant nutrition and plant health. Using the culture-independent method of PCR-DGGE of 16S rDNA for community analyses, we conducted several experiments to investigate the importance of pH, soil type, soil amendment, nutritional status of the plant, plant species and plant age on the structure of the bacterial community in the rhizosphere. At the same time, we assessed the spatial variability of bacterial communities in different root zone locations. Our results showed that the bacterial community structure is influenced by soil pH and type of P fertilization. In a short-term experiment (15–22 days) with cucumber and barley growing in a N deficient or a P deficient soil, the bacterial community structure in the rhizosphere was affected by soil type and fertilization but not by plant species. In a 7.5-week experiment with three plant species (chickpea, canola, Sudan grass) growing in three different soils (a sand, a loam and a clay), the complex interactions between soil and plant effects on the rhizosphere community were apparent. In the sand and the loam, the three plant species had distinct rhizosphere communities while in the clay soil the rhizosphere community structures of canola and Sudan grass were similar and differed from those of chickpea. In all soils, the rhizosphere community structures of the root tip were different from those in the mature root zone. In white lupin, the bacterial community structure of the non-cluster roots differed from those of the cluster roots. As plants matured, different cluster root age classes (young, mature, old) had distinct rhizosphere communities. We conclude that many different factors will contribute to shaping the species composition in the rhizosphere, but that the plant itself exerts a highly selective effect that is at least as great as that of the soil. Root exudate amount and composition are the key drivers for the differences in community structure observed in this study.

Sugar beet and barley yields in relation to inoculation with N2-fixing and phosphate solubilizing bacteria

Abstract: Recently, there has been a resurgence of interest in bioorganic fertilizers as part of sustainable agricultural practices to alleviate drawbacks of intensive farming practices N2-fixing and P-solubilizing bacteria are important in plant nutrition increasing N and P uptake by the plants, and playing a significant role as plant growth-promoting rhizobacteria in the biofertilization of crops A study was conducted in order to investigate the effects of two N2-fixing (OSU-140 and OSU-142) and a strain of P-solubilizing bacteria (M-13) in single, dual and three strains combinations on sugar beet and barley yields under field conditions in 2001 and 2002 The treatments included: (1) Control (no inoculation and fertilizer), (2) Bacillus OSU-140, (3) Bacillus OSU-142, (4) Bacillus M-13, (5) OSU-140 + OSU-142, (6) OSU-140 + M-13, (7) OSU-142 + M-13, (8) OSU-140 + OSU-142 + M-13, (9) N, (10) NP N and NP plots were fertilized with 120 kg N ha−1 and 120 kg N ha−1 + 90 kg P ha- for sugar beet and 80 kg N ha−1 and 80 kg N ha−1 + 60 kg P ha−1 for barley The experiments were conducted in a randomized block design with five replicates All inoculations and fertilizer applications significantly increased leaf, root and sugar yield of sugar beet and grain and biomass yields of barley over the control Single inoculations with N2-fixing bacteria increased sugar beet root and barley yields by 56–110% depending on the species while P-solubilizing bacteria alone gave yield increases by 55–75% compared to control Dual inoculation and mixture of three bacteria gave increases by 77–127% over control as compared with 207–259% yield increases by NP application Mixture of all three strains, dual inoculation of N2-fixing OSU-142 and P-solubilizing M-13, and/or dual inoculation N2-fixing bacteria significantly increased root and sugar yields of sugar beet, compared with single inoculations with OSU-140 or M-13 Dual inoculation of N2-fixing Bacillus OSU-140 and OSU-142, and/or mixed inoculations with three bacteria significantly increased grain yield of barley compared with single inoculations of OSU-142 and M-13 In contrast with other combinations, dual inoculation of N2-fixing OSU-140 and P-solubilizing M-13 did not always significantly increase leaf, root and sugar yield of sugar beet, grain and biomass yield of barley compared to single applications both with N2-fixing bacteria The beneficial effects of the bacteria on plant growth varied significantly depending on environmental conditions, bacterial strains, and plant and soil conditions

Salinity effects on germination, growth, and seed production of the halophyte Cakile maritima

Abstract: Cakile maritima (Brassicaceae) is a halophyte that thrives on dunes along the Tunisian seashore. Besides its ecological interest for soil fixation, this plant produces seeds rich in lipids (40% on dry weight basis), making it a potential source of oil for industrial use. The purpose of the present work was to study the salt tolerance of this species at germination, vegetative growth and fruiting stages. NaCl inhibited germination only at concentrations higher than 200 mM, mainly by an osmotic effect (fully reversible after seed transfer to water). At the vegetative stage, the plant exhibited a typical halophytic behaviour, requiring the presence of a moderate salt concentration (50 to 100 mM NaCl) to express its maximal growth potentialities. Growth activity was maintained up to 500 mM NaCl. Salt tolerance of C maritima at the vegetative stage seemed to be mainly based on: (i) the capacity to preserve the biomass production within the range of optimal salt concentrations; (ii) the ability to maintain the tissue water status; and (iii) the efficiency of selective K+ uptake, in spite of high Na+ concentration in the medium. Indirect evidence of Na+ utilisation by the plant for osmotic adjustment was obtained. Seed production was stimulated at 50 to 100 mM NaCl as compared to control treatment, and severely restricted at higher salt levels. Individual seed mass was moderately diminished by increasing NaCl concentrations.

QTL mapping of root hair and acid exudation traits and their relationship to phosphorus uptake in common bean

Abstract: The relationship between root-hair growth, acid exudation and phosphorus (P) uptake as well as the quantitative trait loci (QTLs) associated with these traits were determined for a recombinant inbred line (RIL) population derived from the cross of two contrasting common bean (Phaseolus vulgaris L.) genotypes, DOR364 and G19833, which were grown in solution culture and under field conditions with low-P availability. In the solution-culture study, root-hair density, root-hair length, H+ exudation and total acid exudation were measured. Substantial genotypic variability was observed for these traits and their response to P availability. The P-efficient parent G19833 had greater root-hair density, longer root-hair length, and greater exudation of H+ and total acid than the P-inefficient genotype DOR364. These traits segregated continuously in the RIL population, with obvious tendency of trait transgression. Genetic analysis revealed that the root traits measured had various heritabilities, with hb2 ranging from 43.24 to 86.70%. Using an integrated genetic map developed for the population, a total of 19 QTLs associated with root hair, acid exudation and P-uptake traits were detected on 8 linkage groups. P uptake in the field was positively correlated with total acid exudation, basal root-hair length, and basal root-hair density. Acid-exudation traits were intercorrelated, as were root-hair traits. Total acid exudation was positively correlated with basal root-hair density and length. Linkage analysis revealed that some of the root-trait QTLs were closely linked with QTLs for P uptake in the field. We propose that marker-assisted selection (MAS) might be a feasible alternative to conventional screening of phenotypic root traits.

Decomposition and nutrient release from logging residues after clear-cutting of mixed boreal forest

Abstract: Elevated dissolved carbon (C), nitrogen (N) and phosphorus (P) concentrations are frequently observed in surface water soon after clear-cutting of boreal coniferous forests. It has been suggested that they originate from the fine logging residues whose decomposition may be accelerated as a result of changes in soil temperature and moisture conditions. In the present study, the decomposition rate and release of C, N, and P from Scots pine (Pinus sylvestris L.), Norway spruce (Picea abies Karsten) and silver birch (Betula pendula Roth.) logging residues (fine roots ∅≤2 mm, branches ∅≤10 mm and foliage) were investigated during three years with the litterbag method in a clear-cut area and in an adjacent Norway spruce dominated, mixed boreal forest in eastern Finland (63°51′ N, 28°58′ E, 220 m asl). The mass loss of the logging residues decreased in the order: foliage > roots > branches. Birch leaves were the only fraction that showed significantly higher losses of mass and C at the clear-cut plot than at the forest plot; otherwise there was no tendency for accelerated decomposition or mineralization at the clear-cut plot. After three years the initial C pool in the logging residues had declined by 33% and that of P by 49% but there was no net release of N as more N accumulated in roots and branches than was released from foliage. The results indicate that 1) logging residues release relatively large and rapid fluxes of CO2 to the atmosphere 2) are potential source of elevated P in surface waters soon after clear-cutting 3) are not a net source of N immediately after clear-cutting.

Root traits as tools for creating phosphorus efficient crop varieties

Abstract: This paper provides a brief assessment of the genetic variation in root properties (root morphology, including root hairs), mycorrhizal symbiosis, uptake kinetics parameters and root-induced changes (pH, organic acids and acid phosphatase) in the rhizosphere of various crop species and their genotypes and then briefly discusses the opportunities and challenges of using such knowledge for enhancing P efficiency of future crop genotypes by genetic means. Wide genotypic variation and heritability of root morphology, root hair length and density and thereby P acquisition provide opportunities for selection and breeding for root characteristics for increasing P acquisition. The progress is challenged by the concerns of high carbon cost of larger root systems and by the lack of cost effective methods to determine root length of a large number of genotypes under field conditions. The carbon cost of root hairs is low. Furthermore, low cost methods now exist to compare root hair formation of field grown genotypes. The development and application of sophisticated methods has advanced our knowledge on the role of mycorrhizal symbiosis in P acquisition and also on the molecular basis of fungi and plant interactions. However, extensive studies to explore genotypic variation in mycorrhizal responsiveness are rare, which makes it difficult to assess, how mycorrhizal symbiosis can be manipulated through breeding efforts. The promising variation found in P uptake kinetics parameters of crop genotypes in few studies indicates that more genotypes may be screened by relatively simple nutrient solution culture techniques. The genetic manipulation of the overall differences in cation-anion uptake, which is the main cause of rhizosphere pH change, may be difficult. For manipulation of rhizosphere pH, agronomic measures such as applications of ammonium or nitrate fertilisers may be more useful than breeding approaches. Also it seems difficult to assess what kind of genetic analysis should be performed to support the breeding efforts. Phosphorus mobilisation effect of pH depends on soil P compounds, therefore will differ with soil type. Both the enhanced release of organic acids and higher acid phosphatase activity in the rhizosphere may be useful for increasing P acquisition from inorganic and organic P pools, respectively. Modification of these traits by genetic means should be considered. For successful breeding programmes, the role of various root traits needs to be targeted in an integrated manner and then methods need to be developed for studying their importance under natural soil conditions, so that the genotypic variation can be explored and their ecological significance in P acquisition can be established.

Microbial growth under the snow: Implications for nutrient and allelochemical availability in temperate soils

Abstract: Recent work has shown that plant litter inputs fuel microbial growth in autumn and winter resulting in a large increase of microbial biomass under the snow pack in tundra soils. This winter-adapted microbial community can grow at low temperatures (−5 to 3 °C) and depletes the litter of easily degraded constituents, such as simple phenolic compounds, and immobilizes nitrogen. During snowmelt there is a die-off of this winter microbial community (due to starvation and intolerance to higher soil temperature) resulting in a release of nitrogen that can be utilized by plants and the summer microbial community. The summer microbial community can tolerate higher temperatures (5 to 20 °C) and utilizes mostly plant root exudates for growth. These yearly cycles of microbial growth dynamics have profound implications for both nutrient and alleochemical availability to plants. Firstly, these results show that release (from litter) and degradation of plant phenolic compounds (potential alleochemicals) occurs before plant growth commences in the spring. Secondly, nitrogen (N) immobilized by over-winter microbial growth is released back to the soil during and after snowmelt, thus becoming available to plants. Both of these results need to be incorporated in the design of experiments to explore plant-plant interactions. Many experiments in which chemicals (or fresh litter) are incorporated during plant growth do not reflect the fact that these two events are temporally uncoupled in many natural systems.

Stand fine root biomass and fine root morphology in old-growth beech forests as a function of precipitation and soil fertility

Abstract: Only very limited information exists on the plasticity in size and structure of fine root systems, and fine root morphology of mature trees as a function of environmental variation. Six northwest German old-growth beech forests (Fagus sylvatica L.) differing in precipitation (520 – 1030 mm year−1) and soil acidity/fertility (acidic infertile to basic fertile) were studied by soil coring for stand totals of fine root biomass (0–40 cm plus organic horizons), vertical and horizontal root distribution patterns, the fine root necromass/biomass ratio, and fine root morphology (root specific surface area, root tip frequency, and degree of mycorrhizal infection). Stand total of fine root biomass, and vertical and horizontal fine root distribution patterns were similar in beech stands on acidic infertile and basic fertile soils. In five of six stands, stand fine root biomass ranged between 320 and 470 g m−2; fine root density showed an exponential decrease with soil depth in all profiles irrespective of soil type. An exceptionally small stand fine root biomass (<150 g m−2) was found in the driest stand with 520 mm year−1 of rainfall. In all stands, fine root morphological parameters changed markedly from the topsoil to the lower profile; differences in fine root morphology among the six stands, however, were remarkably small. Two parameters, the necromass/biomass ratio and fine root tip density (tips per soil volume), however, were both much higher in acidic than basic soils. We conclude that variation in soil acidity and fertility only weakly influences fine root system size and morphology of F. sylvatica, but affects root system structure and, probably, fine root mortality. It is hypothesized that high root tip densities in acidic infertile soils compensate for low nutrient supply rates, and large necromasses are a consequence of adverse soil chemical conditions. Data from a literature survey support the view that rainfall is another major environmental factor that influences the stand fine root biomass of F. sylvatica.

Arbuscular mycorrhiza can depress translocation of zinc to shoots of host plants in soils moderately polluted with zinc

Abstract: There is increasing and widespread interest in the maintenance of soil quality and remediation strategies for management of soils contaminated with organic pollutants and trace metals or metalloids. There is also a growing body of evidence that arbuscular mycorrhizal (AM) fungi can exert protective effects on host plants under conditions of soil metal contamination. Research has focused on the mechanisms involved and has raised the prospect of utilizing the mutualistic association in soil re-vegetation programmes. In this short paper we briefly review this research, summarize some recent work and highlight some new data which indicate that the alleviation of metal phytotoxicity, particularly Zn toxicity, by arbuscular mycorrhiza may occur by both direct and indirect mechanisms. Binding of metals in mycorrhizal structures and immobilization of metals in the mycorrhizosphere may contribute to the direct effects. Indirect effects may include the mycorrhizal contribution to balanced plant mineral nutrition, especially P nutrition, leading to increased plant growth and enhanced metal tolerance. Further research on the potential application of arbuscular mycorrhiza in the bioremediation or management of metal-contaminated soils is also discussed.

Root Typ: a generic model to depict and analyse the root system architecture

Abstract: Dynamic models of root system development and architecture integrate various developmental processes and let simulate multiple dynamic interactions. They are recognised as valuable tools to study the soil–plant–atmosphere continuum. In the recent years, some models have emerged from fractal descriptions. Others arose from developmental approaches but most efforts met little success for genericity. Among the difficulties with models are their growing complexity and they inability to detail evenly all important mechanisms often due to a deficit of independent and suitable data for model testing. We propose here a generic model called `Root Typ' dedicated to quantitative and global analyses of root system architectures and simplified representation of architectural diversity. It aims at (i) detailing evenly a large range of developmental processes, (ii) generalising the concept of root type and (iii) representing in a very simplified way soil effects on developmental processes. The model implements several developmental processes including: root emission, axial and radial growth, sequential branching, reiteration, transition, decay and abscission, which are all discussed in details. Finally, it's ability to mimic a diversity of root architectures is tested against representative root systems depicted in the book of Kutschera (1960) which represents an independent database collected on a large number of plant species and soil conditions, and gives an overall synthetic view upon root systems.

Barley genotypes with long root hairs sustain high grain yields in low-P field

Abstract: Superior root traits, like long root hairs, enhance phosphorus (P) uptake and hence the selection for root hair trait offers the possibility to sustain yields in low-P soils. It is yet unknown whether root hair promoted P uptake of barley genotypes is related to the grain yield in low -P field soil. To investigate this, a set of barley genotypes was pre-screened using hydroponics for long (about 1 mm, cvs. Pongo, Linus Barke, Tofta, Henni) and short root hairs (about 0.5 mm, cvs. AC91/5606/17, Meltan, Scarlett, Century, Otira, and Cecilia). The selected genotypes were cultivated in low-P field plots (no P in 35 years, 3 μM P in soil solution) and in plots amended by moderate (10 kg P ha−1, 6 μM P in soil solution) and high (20 kg P ha−1, 10 μM P in soil solution) P fertilisation. The ranking of the genotypes root hairs in laboratory remained consistence in the field, except for cv. Barke (1.05 mm). The genotypes varied in specific root length (SRL, m g−1) and root hair length (RHL), but the estimated volume of soil explored by root system clearly depended on RHL. The correlations of RHL (R 2=0.60***), volume of soil explored by root system (R 2=0.57***) and SRL (R 2=0.40**) with the P uptake in the field were highly significant. The correlation of root-shoot ratio with the P uptake was non-significant (R 2=0.11). The genotypes with long root hairs preserved economical stable grain yield in low, moderate and high P plots. In contrast, the genotypes with short root hairs produced lower grain yield in low P soil, but they responded to moderate and high P fertilisation by significant increase in their grain yields. From the results of this field-based case study, it is concluded that barley genotypes with long root hairs are better adapted in low P soils and they express high yield potentials both in low and high P soils.

Estimating length, average diameter and surface area of roots using two different Image analyses systems

Abstract: Image analyses systems provide a quick determination of various root morphological parameters. Generally, a specific testing procedure should be conducted at the beginning of every measurement process. In this study, the performance of two image analyses programs using different measuring algorithms was compared: a commercial package WinRHIZO and a freeware ROOTEDGE. Roots of field grown cereal crops, wheat (Triticum durumDesf.) and barley (Hordeum vulgare L.), were used. Several types of tests were executed: 1. Comparison of image analyses and manually conducted measurements of root length; 2. Comparison between root length, average diameter and surface area measurements performed with ROOTEDGE and WinRHIZO; 3. Tests of root arrangement to assess the importance of random orientation of the scanned roots for accurate measurements; 4. Evaluation of the maximum acceptable scanning density (cm scanned root length per cm2 scanning area). The results suggest that ROOTEDGE and WinRHIZO provide fairly correct measurements of root morphological parameters. There were small differences between manually and image analyses measurements of root length, in particular using a transparent light unit for scanning. Ratios of image analyses to manual estimations ranged from 0.95 to 1.03 for different root samples of winter barley. Comparisons of the programs generated almost equal root estimates. Discrepancies between diameter and surface area were slightly higher than between length measurements. The average root diameter was a little overestimated by ROOTEDGE compared to WinRHIZO. The most significant source for these discrepancies presumably was the difference between the fixed threshold for ROOTEDGE and the flexible threshold, automatically optimized for every single image by WinRHIZO. ROOTEDGE and WinRHIZO image analyses showed small sensitivity to root sample orientation. Estimations of root length, average diameter and surface area were well reproducible. For the scanning density to 3 cm cm−2 CV values for the replicated measurements varied between 0.3% and 3.4% by both programs. High scanning density of roots resulted in increasing underestimation of root length and overestimation of root average diameter. For the common scanning density range in root research between 1 and 3 cm cm−2 discrepancies did not exceed 5%. Higher scanning densities than 3 cm cm−2 are not recommended.

Nitrous oxide emissions from silage maize fields under different mineral nitrogen fertilizer and slurry applications

Abstract: Intensive dairy farming systems are a large source of emission of the greenhouse gas nitrous oxide (N2O), because of high nitrogen (N) application rates to grasslands and silage maize fields. The objective of this study was to compare measured N2O emissions from two different soils to default N2O emission factors, and to look at alternative emission factors based on (i) the N uptake in the crop and (ii) the N surplus of the system, i.e., N applied minus N uptake by the crop. Twelve N fertilization regimes were implemented on a sandy soil (typic endoaquoll) and a clay soil (typic endoaquept) in the Netherlands, and N2O emissions were measured throughout the growing season. Highest cumulative fluxes of 1.92 and 6.81 kg N2O-N ha-1for the sandy soil and clay soil were measured at the highest slurry application rate of 250 kg N ha-1. Background emissions from unfertilized soils were 0.14 and 1.52 kg N2O-N ha-1for the sandy soil and the clay soil, respectively. Emission factors for the sandy soil averaged 0.08, 0.51 and 0.26% of the N applied via fertilizer, slurry, and combinations of both. For the clay soil, these numbers were 1.18, 1.21 and 1.69%, respectively. Surplus N was linearly related to N2O emission for both the sandy soil (R2=0.60) and the clay soil (R2=0.40), indicating a possible alternative emission factor. We concluded that, in our study, N2O emission was not linearly related to N application rates, and varied with type and application rate of fertilizer. Finally, the relatively high emission from the clay soil indicates that background emissions might have to be taken into account in N2O budgets.

Effect of root contact on interspecific competition and N transfer between wheat and fababean using direct and indirect 15N techniques

Abstract: Pot experiments were carried out to investigate the complementary N use between intercropped fababean (Vicia faba L. cv. Linxia Dacandou) and wheat (Triticum aestivum L cv. 8354). These pots were separated into two compartments, either by a solid barrier to prevent root contact and N movement, by a nylon mesh (30 μm) to prevent root contact, but allow N exchange, or no root barrier between the compartments to allow root intermingling. Root contact enhanced 15N acquisition of wheat but decreased that of fababean. Nitrogen derived from fertilizer (Ndff) by wheat was 73, 91 and 130 mg pot−1 in the treatment with solid barrier, with mesh barrier and without barrier, respectively. For fababean, these values were 38, 25 and 8 mg pot−1, respectively. Accordingly, increased competition from wheat roots resulted in a decrease in soil and fertilizer N uptake by fababean, and correspondingly, higher percentage of N derived from atmosphere N2 (%Ndfa). The %Ndfa of fababean was 58%, 80%, and 91% in the treatment with solid barrier, with mesh barrier and without barrier, respectively. Nitrogen transfer from fababean to wheat was estimated by the indirect 15N isotope dilution technique and by direct plant labeling via petiole injection of a 15N solution. With the indirect method, N transferred from fababean to the associated wheat was 2 mg with a mesh barrier and 6 mg without barrier. Using direct labeling method, N transferred from fababean to companion wheat was 7 mg, equal to 15% of total N in wheat.

Root exudates and arsenic accumulation in arsenic hyperaccumulating Pteris vittata and non-hyperaccumulating Nephrolepis exaltata

Abstract: This study compared the roles of root exudates collected from two fern species, the As hyperaccumulating Chinese Brake fern (Pteris vittata L.) and the As-sensitive Boston fern (Nephrolepis exaltata L.), on As-mobilization of two As minerals (aluminum arsenate and iron arsenate) and a CCA (chromated copper arsenate)-contaminated soil as well as plant As accumulation. Chinese Brake fern exuded 2 times more dissolved organic carbon (DOC) than Boston fern and the difference was more pronounced under As stress. The composition of organic acids in the root exudates for both ferns consisted mainly of phytic acid and oxalic acid. However, Chinese Brake fern produced 0.46 to 1.06 times more phytic acid than Boston fern under As stress, and exuded 3–5 times more oxalic acid than Boston fern in all treatments. Consequently, root exudates from Chinese Brake fern mobilized more As from aluminum arsenate (3–4 times), iron arsenate (4–6 times) and CCA-contaminated soil (6–18 times) than Boston fern. Chinese Brake fern took up more As and translocated more As to the fronds than Boston fern. The molar ratio of P/As in the roots of Chinese Brake fern was greater than in the fronds whereas the reverse was observed in Boston fern. These results suggested that As-mobilization from the soil by the root exudates (enhancing plant uptake), coupled with efficient As translocation to the fronds (keeping a high molar ratio of P/As in the roots), are both important for As hyperaccumulation by Chinese Brake fern.

Relationships between soil characteristics, topography and plant diversity in a heterogeneous deciduous broad-leaved forest near beijing, china

Abstract: Patterns of biodiversity affect soil properties at different scales, conversely, soil characteristics and landscape features influence biodiversity. It is important to determine these relationships for understanding ecosystem processes. Many studies have carried out during the last few years mainly concentrated on factors that influence plant diversity in grassland or shrubland. Focused on the topography and forest heterogeneity for a warm temperate-zone deciduous broad-leaved forest in the Donglingshan Mountains near Beijing, detailed plant diversity, topography and soil features of 76 plots were investigated in a small watershed. To discern the complex relationships, multivariate statistical analysis techniques (Principal Component Analysis (PCA), Cluster Analysis (CA) and Canonical Correlation Analysis (CCA)) were employed. The results of PCA and CA showed that soil organic matter (SOM) is an important indicator to soil fertility. The coverage, richness and α-diversity index of three layers of plants (tree, shrub and herb) have unique features under different soil fertilities. High fertility plots often exist on south-facing slopes, in upper slope positions, and have gentle slope gradients. The coverage, richness and α-diversity index (Shannon index) of tree and shrub layers are the highest in mid-fertility plots, which have the highest available phosphorus (AP) and potassium (AK) contents, but those same summary descriptors for herbs are the least. CCA analysis elucidated the relationships of three different index groups (topography, soil and plant). Elevation and aspect have a close relationship with shrub richness and α-diversity. Elevation is also an important factor influencing SOM. SOM and total nitrogen have the greatest effect on plant characteristics (mainly shrub coverage) among all soil factors.

Effects of aluminum and cadmium toxicity on growth and antioxidant enzyme activities of two barley genotypes with different Al resistance

Abstract: A hydroponic experiment was carried out to study genotypic differences in effect of Al and Cd on growth and antioxidant enzyme activities by using 2 two-row winter barley genotypes (Hordeum vulgare L.) with different Al resistance, the relatively resistant Gebeina and the sensitive Shang 70–119. The seedling growth, presented as shoot height, root length and dry weight of root and shoot, and tillers per plant were inhibited by all stress treatments, including low pH, 100 µM Al (pH 4.0) and 1.0 µM Cd+100 µM Al (pH 4.0), while 1.0 µM Cd showed a slight stimulation of growth. The inhibition was more severe in 1.0 µ MC d+100 µM Al (pH 4.0) than in 100 µ MA l (pH 4.0), indicating that the effect of Cd and Al is synergistic. Al-sensitive genotype Shang 70–119 was more inhibited than Al-resistant genotype Gebeina. Proline concentration in leaves was significantly increased when plants were exposed to all stress treatments, being more pronounced in Shang 70–119 than in Gebeina. A highly significant increase in malonaldehyde (MDA) concentration, and a stimulation of superoxide dismutase (SOD) and peroxidase (POD) activities were recorded in the plants subjected to low pH, 100 µM Al (pH 4.0) and 1.0 µ MC d +100 µM Al(pH 4.0) treatments, and the extent of the increase varied greatly depending on concentration and time of exposure. Shang 70–119 had a higher MDA concentration, and less increase in SOD activity when first exposed than Gebeina had. Abbreviations: ROS – reactive oxygen species; CAT – catalase; MDA – malondialdehyde; POD – peroxidase; SOD – superoxide dismutase.

Nitrogen fixation and N transfer from peanut to rice cultivated in aerobic soil in an intercropping system and its effect on soil N fertility

Abstract: The novel cultivation of paddy rice in aerobic soil reveals the great potential not only for water-saving agriculture, but also for rice intercropping with legumes and both are important for the development of sustainable agriculture. A two-year field experiment was carried out to investigate the yield advantage of intercropping peanut (Arachis hypogaea L., Zhenyuanza 9102) and rice (Oryza sativa L., Wuyujing 99-15) in aerobic soil, and its effect on soil nitrogen (N) fertility. A pot experiment was also conducted to examine the N2-fixation by peanut and N transfer from peanut to rice at three N fertilizer application rates, i.e., 15, 75 and 150 kg N ha−1 using a 15N isotope dilution method. The results showed that the relative advantage of intercropping, expressed as land equivalent ratio (LER), was 1.41 in 2001 and 1.36 in 2002. Both area-adjusted yield and N content of rice were significantly increased in the intercropping system while those of peanut were not significantly different between intercropping and monocropping systems. The yields of rice grain and peanut, for example, were increased by 29–37% and 4–7% in the intercropping system when compared to the crop grown in the monocropping system. The intercropping advantage was mainly due to the sparing effect of soil inorganic N contributed by the peanut. This result was proved by the higher soil mineral N concentration under peanut monocropping and intercropping than under the rice monocropping system.%Ndfa (nitrogen derived from atmosphere) by peanut was 72.8, 56.5 and 35.4% under monocropping and 76.1, 53.3 and 50.7% under the intercropping system at N fertilizer application rates of 15, 75 and 150 kg ha−1, respectively. The 15N-based estimates of N transfer from peanut (%NTFL) was 12.2, 9.2 and 6.2% at the three N fertilizer application rates. N transferred from peanut accounted for 11.9, 6.4 and 5.5% of the total N accumulated in the rice plants in intercropping at the same three N fertilizer application rates, suggesting that the transferred N from peanut in the intercropping system made a contribution to the N nutrition of rice, especially in low-N soil.

Using stable oxygen isotopes to quantify the water source used for transpiration by native shrubs in the San Luis Valley, Colorado U.S.A.

Abstract: An understanding of the water source used by phreatophytic desert shrubs is critical for understanding how they function and respond to man-caused groundwater drawdowns. Shrubs can use primarily groundwater, precipitation recharged soil water, or a mixture of the two. If shrubs use primarily groundwater, a water table decline may reduce water availability and lead to high plant mortality. However, if shrubs can acquire precipitation recharged soil water, then groundwater decline could have less impact on plants. This study took place in the San Luis Valley, a large, arid, high elevation closed basin in south-central Colorado. We examined stable oxygen isotopes in precipitation, soil water from several depths, groundwater and plant xylem water to identify the likely water sources for the three most abundant shrubs in the valley: Sarcobatus vermiculatus (Hooker) Torrey, Chrysothamnus nauseosus (Pallas) Britton subsp. consimilis (Greene) Hall & Clements, and Chrysothamnus greenei (Gray) Greene. C. greenei is not known to be phreatophytic while S. vermiculatus and C. nauseosus may be phreatophytic. Mean annual San Luis Valley precipitation during the two years of study was 121 mm, with 67% occurring during the summer monsoon season of July through September. We found differences in water acquisition patterns by species, season, and along a depth to water table gradient. C. greenei only occurred in sites with a water table > 2.0 m deep, and utilized only soil water recharged by precipitation. At sites with a water table less then 2 m depth, S. vermiculatus and C. nauseosus utilized soil water from the top 0.5 m and shallow groundwater during the pre-monsoon and monsoon periods. A more complex water use pattern was found at sites with a water table deeper then 2 m. S. vermiculatus and C. nauseosus used both deep soil water and groundwater during 1996. During the pre-monsoon period in 1997, both shrubs utilized predominantly groundwater. However, during the 1997 monsoon season both species switched to utilize primarily precipitation recharged water acquired from the upper 0.3–0.4 m of soil. This is the first report that C. nauseosus can utilize summer precipitation. Our results support the hypothesis that plants utilize more summer rain recharged soil water in regions receiving a substantial proportion of annual precipitation during the summer.

Relative effectiveness of calcium and magnesium in the alleviation of rhizotoxicity in wheat induced by copper, zinc, aluminum, sodium, and low pH

Abstract: Root elongation in short-term experiments with wheat (Triticum aestivum L.) seedlings demonstrated that the following ions were rhizotoxic in the order Cu2+>Al3+≫ H+>Zn2+≫ Na+. Additions of Ca2+ and Mg2+ alleviated the toxicity, but the relative ameliorative effectiveness of Ca2+ and Mg2+ depended upon the toxicant. The effectiveness of Mg2+ relative to Ca2+ was 0.098 for Na+, 0.37 for H+, 1.0 for Al3+, 2.1 for Cu2+, and 170 for Zn2+. The mechanisms of inhibition are mainly unknown, but the mechanisms of alleviation are better understood. Mechanism I entails ameliorant-induced reduction of the negativity of the plasma membrane (PM) surface electrical potential (ψ0). The consequence is a reduced activity of the toxicant at the PM surface because of reduced electrostatic attraction. Ca2+ and Mg2+ are equally effective agents of Mechanism I alleviation but are less effective than H+ and more effective than Na+ for reasons described by electrostatic principles. Mechanism II alleviation is specific for Ca2+ and entails the restoration of Ca2+ at the PM surface if surface Ca2+ has been reduced by the toxicant to growth-limiting levels. This occurs more commonly in Na+ and H+ toxicities than in the others, though in no case is it the principal mechanism of alleviation. Mechanism III alleviation is the collective ameliorative effect of an ion beyond Mechanisms I and II. Differences between Ca2+ and Mg2+ in ameliorative effectiveness are mainly attributable to Mechanism III which, in the case of Zn2+, may entail an internal detoxification and, in the case of Na+, may entail the blockade of a Na+ uptake channel. This study demonstrates that appropriate nonlinear equations incorporating cell-surface ion activities enable the dissection of multiple toxic and ameliorative effects of the ions.

Changes in water extractable metals, pH and organic carbon concentrations at the soil-root interface of forested soils

Abstract: Soluble metals are of nutritional and ecotoxicological interest as they are the most readily available form to the biota. Metal solubility in soils is mostly controlled by pH and the organic matter content. The rhizosphere is generally considered as an environment enriched in organic matter and often more acidic (depending on nutritional status of the plant) than the bulk soil. Yet, there is a lack of consensus on the distribution of metals at the soil-root interface. Consequently, the specific objectives of this paper are to compare the chemical properties and the water extractable metal concentrations of the rhizosphere and the bulk soil of forest soil (1) along a gradient in soil contamination and (2) under different tree species. Two study areas were used: (1) Rouyn-Noranda (Canada) where samples were collected along a gradient in metal contamination at a distance of 0.5, 2 and 8 km downwind from a copper smelter; (2) Saint-Hippolyte (Canada) where the effect of three tree species (Abies balsamea, Acer saccharum and Betula papyrifera) was studied. In the field, the rhizosphere was operationally defined as the soil adhering to the roots after agitation, soil falling from the roots and the rest of the soil composing the bulk soil. Once in laboratory, a second agitation was performed to separate the rhizosphere into an inner and an outer component. Water extractable metal concentrations (Al, Ca, Cd, Co, Cr, Cu, Fe, Li, Mg, Mn, Ni, Pb and Zn) were quantified either with an ICP-AES or a GFAAS. Measurements of pH, electrical conductivity (EC), water-extractable organic carbon (WEOC) and solid phase organic carbon (SPOC) were performed. Results systematically indicate that EC, WEOC and SPOC follow the sequence inner rhizosphere > outer rhizosphere > bulk soil. The pH is always lower in the inner rhizosphere than in the bulk soil, while the outer rhizosphere frequently shows an inconstant behaviour. The results also show a clear gradient following inner rhizosphere > outer rhizosphere > bulk soil for water extractable Al, Ca, Cd, Cu, Fe, Mg, Mn, Ni, Pb and Zn. Li, Co and Cr levels were below method detection limit in all cases. WEOC seems to be the main variable related to the water-extractable metals concentrations. The gradient in metal contamination at Rouyn-Noranda was not as expected in the water extracts with the site at 2 km frequently presenting higher metal concentrations than the sites at 0.5 and 8 km. Moreover, a tree species effect did not clearly immerge for any of the chemical properties studied. However, the water extractable Ca concentrations were higher in the soil under Acer saccharum. The effects of the metal gradient and of the tree species may be more pronounced if stronger extractants are used. The addition of an outer rhizosphere component is useful as its behaviour is not consistently intermediate between the inner rhizosphere and bulk soil.

Incidence of Fusarium wilt in Cucumis sativus L. is promoted by cinnamic acid, an autotoxin in root exudates

Abstract: The effects of Fusarium oxysporum f. sp. cucumerinum, the pathogen causing Fusarium wilt in cucumber and cinnamic acid, a principal autotoxic component in the root exudates of cucumber (Cucumis sativus L.), on plant growth, Photosynthesis and incidence of Fusarium wilt in cucumber were studied in order to elucidate the interaction of autotoxins and soil-borne pathogens in the soil sickness. F. oxysporum. f. sp. cucumerinum (FO) and cinnamic acid (CA) at 0.1 or 0.25 mM significantly decreased net photosynthetic rate, stomatal conductance and the quantum yield of Photosystem II photochemistry (ΦPSII), followed by a reduction of plant biomass production, but did not induce photoinhibition. Pretreatment with CA before inoculation with FO increased the effectiveness of FO, together with a slight photoinhibition. CA pretreatment significantly increased percentage of plants affected by Fusarium wilt, browning index of vascular bundle and Fusarium population in the nutrient solution. All these results indicate that CA enhanced Fusarium wilt by predisposing cucumber roots to infection by FO through a direct biochemical and physiological effect. It is likely that soil sickness results from an interaction of many factors. Abbreviations: CA – cinnamic acid; CFU – colony forming units; Ci – intercellular CO2 concentration; FO –Fusarium oxysporum (Schlechtend.:Fr) f. sp. cucumerinum (Owen) Snyder & Hansen; Fv/Fm– maximal quantum efficiency of PS II; Fv′/Fm′– the efficiency of excitation capture by open PS II centers; Gs – stomatal conductance; NPQ – non-photochemical quenching coefficient; Pn – net photosynthetic rate; PS II – Photosystem II; ΦPS II– the quantum yield of PS II photochemistry; qP – photochemical quenching coefficient.

Quantifying the regional source strength of N-trace gases across agricultural and forest ecosystems with process based models

Abstract: The process-based models DNDC and PnET-N-DNDC were evaluated with regard to their potential to calculate regional inventories of N-trace gas emissions from agricultural and forest soils. To extend the model predictions to regional scale, we linked the models to a detailed GIS-database for Saxony, Germany, which was holding all the spatially and temporally differentiated input information and other model drivers. Total annual N2O-emissions from agricultural soils in Saxony ranged from 0.5–26.0 kg N2O-N ha−1 yr−1 and were calculated to amount to approx. 5475 t N2O-N yr−1 in the year 1995, which compares quite well with previous estimates based on the IPCC approach (4892 t N2O-N yr−1). Compared to the agricultural soils, N2O-emissions from forest soils in Saxony (range: 0.04–19.7 kg N2O-N ha−1 yr−1) were much lower and amounted to 1011 t N2O-N yr−1. In comparison with other sources of N2O in Saxony our estimates show, that – even in such a highly industrialised region like Saxony – soils contribute more than 50% to the total regional N2O source strength. Simulated emissions of NO from the agricultural and forest soils were approx. in the same magnitude than for N2O. The modelled NO-emission rates ranged from 0.4–26.3 kg NO-N ha−1 yr−1 for the agricultural soils and 0.04–28.3 kg NO-N ha−1 yr−1 for the forest soils with total emissions of 8868 t NO-N yr−1 (agricultural soils) and 4155 t NO-N yr−1 (forest soils). Our results indicated that the agricultural and forest soils were a significant source, which contributed 17.9% of the total NOx emissions from various sources in Saxony. Furthermore, a series of sensitivity tests were carried out, which demonstrated that variations in soil organic carbon content (SOC) and soil texture significantly effect the modelled N-trace gas emissions from agricultural soils at the regional scale, whereas, in addition, for forest soils also the soil pH is within the sensitive factors. Finally, multi-year simulations were conducted for the region with observed meteorological data from 1994–1996. The results demonstrated that the modelled interannual variations, which were obviously induced by only the climate conditions, in the N-gas emissions were as high as 36%. The high interannual variations imply that multi-year (e.g., 5–10 years), instead of single baseline year, simulations would produce more reliable estimates of mean soil N2O-emissions at regional scale. With respect to the Kyoto protocol this means that the mean N2O-emissions from soils in the period 1988–1992 should be evaluated instead of focusing on a single year, 1990.

Increasing drought decreases phosphorus availability in an evergreen Mediterranean forest

Abstract: Mediterranean ecosystems are water-limited and frequently also nutrient-limited. We aimed to investigate the effects of increasing drought, as predicted by GCM and eco-physiological models for the next decades, on the P cycle and P plant availability in a Mediterranean forest. We conducted a field experiment in a mature evergreen oak forest, establishing four drought-treatment plots and four control plots (150 m 2 each). After three years, the runoff and rainfall exclusion reduced an overall 22% the soil moisture, and the runoff exclusion alone reduced it 10%. The reduction of 22% in soil moisture produced a decrease of 40% of the accumulated aboveground plant P content, above all because there was a smaller increase in aerial biomass. The plant leaf P content increased by 100 ± 40 mg m −2 in the control plots, whereas it decreased by 40 ± 40 mg m −2 in the drought plots. The soil Po-NaHCO3 (organic labile-P fraction) increased by 25% in consonance with the increase in litterfall, while the inorganic labile-P fraction decreased in relation to the organic labile-P fraction up to 48%, indicating a decrease in microbial activity. Thus, after just three years of slight drought, a clear trend towards an accumulation of P in the soil and towards a decrease of P in the stand biomass was observed. The P accumulation in the soil in the drought plots was mainly in forms that were not directly available to plants. These indirect effects of drought including the decrease in plant P availability, may become a serious constraint for plant growth and therefore may have a serious effect on ecosystem performance.

Gel observation chamber for rapid screening of root traits in cereal seedlings

Abstract: A simple gel chamber is described for measurement of seedling root traits Seedlings are located between two closely spaced flat layers of transparent gel, on plastic plates (at least one of which is transparent) Root system traits can be non-destructively recorded in two-dimensions using a flatbed scanner Easily measured rooting traits include root length, elongation rate, longest root, deepest root, seminal root number, and angular spread of roots Examples of wild, landrace, and cultivated barleys were grown in the gel chambers, between gel layers or in loosely packed soil Root growth on the gel plates was similar to that in loose soil, with the cultivated barley having the most seminal axes (about 7), and widest angular spread of roots (about 120 °), and wild barley the fewest seminal axes (about 3), and narrowest angular spread of roots (about 40 °) Landrace barley lines tested were intermediate between wild barley and modern cultivars Separate experiments were performed to study the effect of grain mass and grain size on these rooting traits These experiments included parents of genetic mapping populations Seminal root number was most strongly dependent on grain mass in the modern cultivar Chime Grain size significantly influenced root number in the modern cultivar Derkado, the breeding line B83-12/21/5, and a selection from a landrace Tadmor, suggesting that grain size should be controlled in any screening exercise

Critical N:P values: Predicting nutrient deficiencies in desert shrublands

Abstract: Many terrestrial ecosystems are nutrient limited. Koerselman and Meuleman (1996) proposed critical foliar N:P values that could predict wetland nutrient deficiencies (N:P 16, P limitation). Although critical N:P values have potential as ecological and diagnostic tools, species differences in N and P requirements must be tested. The objectives of our experiments were 1) to determine if two desert species share critical N:P values, and 2) to assess the N:P tool's applicability in a non-wetland system. We studied two common, co-occurring North American desert shrubs, Chrysothamnus nauseosus spp. consimilis and Sarcobatus vermiculatus. Based on leaf N and P concentrations, effective mycorrhizal status, and leaf N:P, we predicted Chrysothamnus would be N limited and Sarcobatus would be P limited. During the 2000 and 2001 growing seasons, juvenile shrubs received N, P, N+P, or control treatments. To assess interaction with water limitation, other shrubs were irrigated and fertilized in 2001 (N+IR, P+IR, N+P+IR, control IR). Contrary to the predicted N limitation in Chrysothamnus, stem growth was 1.7-fold greater in P+IR plants relative to IR controls, although without irrigation Chrysothamnus did not respond to P addition. Also, contrary to the predicted P limitation in Sarcobatus, stem growth was 2.7-fold and 1.5-fold greater in N and N+IR plants, respectively, relative to their controls. Leaf N was significantly higher in N-treated Sarcobatus, both with and without irrigation. Our study suggests species-specific critical N:P values and that the N:P tool does not effectively predict desert shrub nutrient limitations. Species adapted to low nutrient conditions may not respond to increased nutrient availability due to water and nutrient co-limitation, lack of plasticity, or lower tissue nutrient requirements.

Photosynthesis controls of CO2 efflux from maize rhizosphere

Abstract: The effects of different shading periods of maize plants on rhizosphere respiration and soil organic matter decomposition were investigated by using a 13 C natural abundance and 14 C pulse labeling simultaneously. 13 C was a tracer for total C assimilated by maize during the whole growth period, and 14 C was a tracer for recently assimilated C. CO2 efflux from bare soil was 4 times less than the total CO2 efflux from planted soil under normal lighting. Comparing to the normal lighting control (12/12 h day/night), eight days with reduced photosynthesis (12/36 h day/night period) and strongly reduced photosynthesis (12/84 h day/night period) resulted in 39% and 68% decrease of the total CO2 efflux from soil, respectively. The analysis of 13 C natural abundance showed that root-derived CO2 efflux accounted for 82%, 68% and 56% of total CO2 efflux from the planted soil with normal, prolonged and strongly prolonged night periods, respectively. Clear diurnal dynamics of the total CO2 efflux from soil with normal day-night period as well as its strong reduction by prolonged night period indicated tight coupling with plant photosynthetic activity. The light-on events after prolonged dark periods led to increases of root-derived and therefore of total CO2 efflux from soil. Any factor affecting photosynthesis, or substrate supply to roots and rhizosphere microorganisms, is an important determinant of root-derived CO2 efflux, and thereby, total CO2 efflux from soils. 14 C labeling of plants before the first light treatment did not show any significant differences in the 14 CO2 respired in the rhizosphere between different dark periods because the assimilate level in the plants was high. Second labeling, conducted after prolonged night phases, showed higher contribution of recently assimilated C ( 14 C) to the root-derived CO2 efflux by shaded plants. Results from 13 C natural abundance showed that the cultivation of maize on Chromic Luvisol decreased soil organic matter (SOM) mineralization compared to unplanted soil (negative priming effect). A more important finding is the observed tight coupling of the negative rhizosphere effect on SOM decomposition with photosynthesis.

Bioavailability and crop uptake of trace elements in soil columns amended with sewage sludge products

Abstract: In order to assess the potential impact of long-term sewage sludge application on soil health, the equivalent of about 25 years of agronomic applications of low-metal (`EQ') sewage sludge products were made to greenhouse soil columns. After a 6-year period of `equilibration', during which time successive crops were grown with irrigation by simulated acid rain, the plant-available quantities of trace elements were estimated in the soils by extraction with 0.01 M CaCl2 at 90 °C, and measured directly by uptake into a crop of red clover (Trifolium pratense L.). Soil pH had a strong influence on the level of extractable and plant-available metals, and because the tested sludge products affected soil pH differently, pH was directly factored into the comparison of different sludge treatments with controls. CaCl2-extractable levels of several metals (Cu, Zn, Mo), sulfur and phosphorus were found to be higher in the soils amended with organic-rich sludge products than in the control soils. However, extractable Cd and Ni were not significantly elevated by the sludge amendments, presumably because of the low total loading of these metals. Copper, Zn and Mo applied in the form of sludge ash had low soil extractability, suggesting that these trace metals were trapped in high-temperature mineral phases formed during sludge incineration, and resisted subsequent weathering in the soil environment. Extractable soil metals in the alkaline-stabilized sludge treatment were also generally low. Phytotoxicity from the sludge metal loadings (Zn≤125, Cu≤135 kg/ha), was not clearly indicated as long as soil pH was maintained in the 6–7 range by lime amendment. Nevertheless, unexplained depressions in yield were noted with some of the sludge products applied, particularly the dewatered and composted materials. On limed soil columns, the most consistent effect of sludge product amendment on red clover composition was a marked increase in plant Mo.