Pathogenic Potential of Soil Fusaria from Malaysian Oil Palm Habitats

A total of 353 Fusarium isolates consisting of 8 species and 2 varieties obtained from the soils of 22 sampling sites in oil palm habitats in Peninsular Malaysia was tested on 2-leaf stage oil palm seedlings. None of the isolates tested produced any symptoms of vascular wilt or other diseases. However, some of the isolates did have an adverse effect on the growth and vigour of the palms. They were found to cause significant reduction in palm growth. Isolates causing a reduction in the growth of the oil palm seedlings were not confined to a certain type of soil or a particular location.     

Responses of the Fructose-1,6-bisphosphatase and Glutamate Dehydrogenase Activities of Alfalfa to Boron,Gypsum, and Limestone Amendments of Soil

Plants cultivated on acid soils that contain toxic levels of Al³⁺ usually produce low yields. A multi-factorial treatment of gypsum (G), boron (B), and limestone (Lm) was applied to such soil in order to determine the biochemical basis of the best management plan for ameliorating the soil acidity for sustainable growth of alfalfa. The alfalfa shoots were subjected to analysis for hexose, protein, nucleotide, and chlorophyll (Chl) contents, fructose 1,6-bisphosphatase (FBPase) activity, and the RNA synthetic activity of glutamate dehydrogenase (GDH). Hexose and protein contents of control alfalfa without B and G, but with Lm (672 g m^–2) amendment were 0.87 and 38.30 g, respectively, per kg shoot. Increasing the G doses at fixed moderate doses of 0.15 and 0.30 g m^–2 B decreased the FBPase activity by 53 and 31 %, respectively. However, increasing the B doses at higher fixed G (1 kg m^–2= G_1.0) increased the FBPase activity by 91 % thus indicating that G₁ optimized the saccharide metabolism by neutralizing the soil acidity. In the absence of B, increasing the G doses also maximized the hexose and Chl contents, but minimized the nucleotide amount. In the absence of G, increasing the B doses maximized the RNA synthetic activity of GDH, but lowered the hexose and Chl contents as well as the FBPase activity without affecting the protein contents, thereby permitting the selection of B (0.45 g m^–2) with Lm as the best amendment for the sustainable growth of alfalfa. Treatment with 0.45 g B and 0.5 kg G (= G_0.5) induced the strongest B-Ca antagonism by maximizing the hexose and Chl contents but severely suppressing the FBPase activity and the RNA synthetic activity of GDH. Therefore, the coordinate optimization of saccharide metabolism through the G-dependent neutralization of soil acidity, and of RNA metabolism through the B-dependent detoxification of Al³⁺ are the biochemical options for the mitigation of the adverse effects of soil acidity for the optimization of sustainable alfalfa production.     

Calcium sulphate,phosphogypsum and calcium carbonate in the amelioration of acid subsoils for root growth

The chemical barrier to root development existing in the subsoils of acid soils is a subject of increasing interest. In order to better understand the factors involved in the amelioration of subsoil acidity, the effects of calcium sulphate, phosphogypsum and calcium carbonate on the properties of the solid and liquid phases of subsoil samples and on the growth and nutrient uptake by maize (Zea mays L.) were evaluated. The soils used were two alic red-yellow latosols, two acric dusky red latosols and one alic dark-red latosol from the State of São Paulo, Brazil. A vertical split-root technique was used in a greenhouse experiment, with the plants initially grown in a small pot with 130 g fertile soil, which was introduced in a larger pot containing 2 dm³ of the subsoil samples. The treatments consisted of a control (C) and applications of calcium carbonate (CC), calcium sulphate (CS) and phosphogypsum (PG) at the rate of 10 mmol_c Ca²⁺ dm^-3. CS and PG reduced soil acidity, but in a much smaller proportion than CC. Calcium carbonate reduced the activity of Al³⁺ because of the increase in pH. Total aluminum and calcium contents in the soil solution were much higher for the red-yellow latosols than for the other soils, indicating lower sorption of Ca²⁺ and in these soils. The activity of Al in the soil solution was decreased in different ways for the five soils, depending on the ionic strength and the formation of the ionic pair and, in the case of PG, the formation of complexes of Al with F (AlF²⁺, and ). The subsoil samples presented severe restrictions for maize root growth and all three treatments were equally effective in increasing root development, which could be attributed to the supply of calcium in one of the acric dusky red latosols and a combined effect of the amendment in reducing the activity of Al and increasing the activity of Ca in the soil solution in the other soils. As a consequence the three treatments increased in the same manner water, N and K uptake from the subsoil and the dry matter production of maize. It can be concluded that, for the soils considered in this research, phosphogypsum is an effective amendment for acid subsoils containing low calcium or toxic aluminum contents.     

Effects of limestone and gypsum application to a Malaysian ultisol on soil solution composition and yields of maize and groundnut

A field experiment was conducted on an Ultisol in Malaysia to assess changes in soil solution composition and their effects on maize and groundnut yields, resulting from limestone and gypsum application. The results showed that soil solution Ca in the lime treatment remained mainly in the zone of incorporation, but in the gypsum treatment some Ca moved into 15–30 cm zone. Al³⁺ and AlSO₄ ⁺ were dominant Al species in the soil solution of nil treatment. Liming decreased Al³⁺ and AlSO₄ ⁺, but increased hydroxy-Al monomer activities. However, gypsum application resulted in an increase of AlSO₄ ⁺ activity and in a decrease of Al³⁺ activity. Relative maize and groundnut yields were negatively correlated with Al³⁺, Al(OH)²⁺ and Al_sum activities. Likewise, relative yields were negatively correlated with Al concentration and the Al concentration ratio and positively correlated with soil solution Mg concentration and Ca/Al ratio.     

Effect of liming and phosphorus application on performance ofLeucaena leucocephala in acid soils

Pot experiments were conducted to assess the lime and phosphorus requirements ofLeucaena leucocephala (LAM.) De Wit grown on three acid soils (Ultisols) from southeastern Nigeria. Liming and phosphorus application significantly enhanced growth ofL. leucocephala. Ammakama soil showed best effect to phosphorus application, while acidity problems were more pronounced on Onne and Isienu soils. High lime rate (2000 ppm) reduced plant growth in Isienu soil probably due to nutrient imbalance. Potassium, manganese and zinc levels in the plants were reduced with increasing lime rates. On Onne and Isienu soils plant tops correlated better with total acidity and extractable Al⁺³ level than with soil pH-H₂O.     

<Emphasis Type="Italic">Streptomyces sanglieri</Emphasis> which colonised and enhanced the growth of <Emphasis Type="Italic">Elaeis guineensis</Emphasis> Jacq. seedlings was antagonistic to <Emphasis Type="Italic">Ganoderma boninense</Emphasis> in in vitro studies

Actinomycete strain AUM 00500 was 99.5 % similar to Streptomyces sanglieri NBRC 100784^T and was evaluated for antagonistic activity towards Ganoderma boninense, the causative fungus of basal stem rot of oil palm. The strain showed strong antifungal activity towards G. boninense in in vitro and SEM analysis showed various modes of inhibition of the fungus. Ethyl acetate extracts of single culture and inhibition zone of cross-plug culture by HPLC indicated that strain AUM 00500 produced two different antibiotics of the glutarimide group namely cycloheximide and actiphenol. In greenhouse trials, oil palm seed treated with spores of S. sanglieri strain AUM 00500 at 10⁹ cfu/ml showed significant (P < 0.05) increase in oil palm seedlings growth when compared to the control. Streptomyces sanglieri strain AUM 00500 successfully colonised the epidermal surface of the roots of treated oil palm seedlings and it was recovered from root fragments plated on starch casein agar.     

Nutrient uptake estimates for woody species as described by the NST 3.0, SSAND, and PCATS mechanistic nutrient uptake models

The effect of soil acidity on root and rhizosheath development in wheat and barley seedlings was investigated in an acid Ferrosol soil to which various amounts of lime (CaCO₃) were applied to modify soil Al concentrations (pH (CaCl₂): 4.22 to 5.35 and Al (CaCl₂ extract): 17.7 to 0.4 mg kg^?1 soil; respectively), and Ferrosol soil from an adjacent location at the same site which had a higher Al concentration (pH 4.19; 29.2 mg kg^?1 Al). The cereal lines were selected on the basis of differences in their rate of root growth, Al-resistance and root hair morphology. Root morphology was assessed after 7 days of growth. The length of fine (mainly lateral) roots of Al-sensitive genotypes was more sensitive to soil Al concentrations than that of the coarse (mainly primary) roots. The experiments demonstrated that even where root growth was protected by expression of the TaALMT1 gene for Al-resistance, root-soil contact was diminished by soil acidity because root hair length (in many lines), and root hair density and rhizosheath formation (all lines) were adversely affected by soil acidity. In the case of Al-sensitive lines, fine root growth and rhizosheath mass were reduced over much the same range of soil Al concentrations (i.e. >3–6 mg kg^?1 Al). Although Al-resistant lines could maintain fine root length under these conditions, they were similarly unable to maintain rhizosheath mass. This finding may help to explain why Al-resistant wheats which yield relatively well in deep acid soils, may also benefit from application of lime to the surface layers of the soil.     

The effect of soil strength on the growth of pigeonpea radicles and seedlings

The effect of soil strength on the growth of pigeonpea radicles and seedlings was investigated in cores of three clay soils prepared at different water contents and bulk densities in the laboratory.Radicle elongation directly into soil cores was reduced from 50–70 mm d^-1 at strengths less than 0.5 MPa to 0 mm d^-1 at 3.5–3.7 MPa. The response to soil strength was affected by the water content of the soil, presumably as a result of reduced oxygen availability in wetter soil. This effect was apparent in soils wet to air-filled porosities less than 0.15 m³ m^-3.Radicles were more sensitive to high soil strength (>1.5 MPa) than were seedling roots which encountered the same conditions at 60 mm in the profile. Radicle growth ceased at 3.5 MPa which reduced seedling root growth by only 60%.Despite a 60% reduction in root length in the high strength zone, seedling roots compensated in zones of loose soil above and below the compacted layer, and total root length and shoot growth were unaffected. There was no evidence of a root signal response which results in reduced shoot growth in some species in response to high soil strength.The proliferation of roots in surface layers and the delayed penetration of the root system to depth in compacted soil are likely to expose seedlings to a greater risk of water-deficit in the field, particularly under dryland conditions where plants rely on stored subsoil water for growth.     

Short‐term soil carbon sink potential of oil palm plantations

Oil palm plantations cover ≈14.6 million ha worldwide and the total area under cultivation is expected to increase during the 21st century . Indonesia and Malaysia together account for 87% of global palm oil production and the combined harvested area in these countries has expanded by 6.5 million ha since 1990. Despite this, soil C cycling in oil palm systems is not well quantified but such information is needed for C budget inventories. We quantified soil C storage (root biomass, soil organic matter (SOM) and microbial biomass) and losses [potential soil respiration (R_s) and soil surface CO₂ flux (F_s)] in mineral soils from an oil palm plantation chronosequence (11–34 years since planting) in Selangor, Malaysia. There were no significant effects of plantation age on SOM, microbial biomass, R_s or F_s, implying soil C was in dynamic equilibrium over the chronosequence. However, there was a significant increase in root biomass with plantation age, indicating a short‐term C sink. Across the chronosequence, R_s was driven by soil moisture, soil particle size, root biomass and soil microbial biomass N but not microbial biomass C. This suggests that the nutrient status of the microbial community may be of equal or greater importance for soil CO₂ losses than substrate availability and also raises particular concerns regarding the addition of nitrogenous fertilizer, i.e. increased yields will be associated with increased soil CO₂ emissions. To fully assess the impact of oil palm plantations on soil C storage, initial soil C losses following land conversion (e.g. from native forest or other previous plantations) must be accounted for. If initial soil C losses are large, our data show that there is no accumulation of stable C in the soil as the plantation matures and hence the conversion to oil palm would probably represent a net loss of soil C.     

The effect of phosphate rock dissolution on soil chemical properties and wheat seedling root elongation

Soils of the Appalachian region of the United States are acidic and deficient in P. North Carolina phosphate rock (PR), a highly substituted fluoroapatite, should be quite reactive in these soils, allowing it to serve both as a source of P and a potential ameliorant of soil acidity. An experiment was conducted to evaluate the influence of PR dissolution on soil chemical properties and wheat (Triticum aestivum cv. Hart) seedling root elongation. Ten treatments including nine rates of PR (0, 12.5, 25, 50, 100, 200, 400, 800, and 1600 mg P kg^-1) and a CaCO₃ (1000 mg kg^-1) control were mixed with two acidic soils, moistened to a level corresponding to 33 kPa moisture tension and incubated for 30 days. Pregerminated wheat seedlings were grown for three days in the PR treated soils and the CaCO₃ control. Root length was significantly (P<0.05) increased both by PR treatments and CaCO₃, indicating that PR dissolution was ameliorating soil acidity. The PR treatments increased soil pH, exchangeable Ca, and soil solution Ca while lowering exchangeable Al and 0.01 M CaCl₂ extractable soil Al. Root growth in PR treatments was best described by an exponential equation (P<0.01) containing 0.01 M CaCl₂ extractable Al. The PR dissolution did not reduce total soil solution Al, but did release Al complexing anions into soil solution, which along with increased pH, shifted Al speciation from toxic to nontoxic forms. These results suggest that North Carolina PR should contribute to amelioration of soil acidity in acidic, low CEC soils of the Appalachian region.     

Selection of Bradyrhizobium strains and provenances of Acacia mangium and Faidherbia albida: Relationship with their tolerance to acidity and aluminium

This work was designed to determine the role of the acidity and aluminium stress in the selection of partners in the Acacia symbioses with relevance to the persistence of the microsymbiont Bradyrhizobium in the soil and the growth and nodulation of the host plant respectively. Fifteen strains of Bradyrhizobium from Acacia mangium and Faidherbia albida formed a very homogenous acid tolerant group as indicated by their ability to grow better in a medium at pH 4.5 than in a medium at pH 6.8. By contrast, a growth experiment using an acid liquid media (pH 4.5), containing different concentrations of aluminium successfully identified strains sensitive to aluminium toxicity and those able to grow even in the presence of 100 M AlCl₃.Our results suggest that high amounts of aluminium in the soil rather than acidity (pH 4.5) were a major soil factor for selection of Bradyrhizobium strains capable of establishing a permanently high population under natural conditions.Unlike the behaviour of the microsymbiont, growth and nodulation of Acacia mangium and Faidherbia albida were not affected by aluminium, even at 100 M, but they might be significantly affected by medium acidity (pH 4.5) depending on plant provenances. It is therefore suggested that ability of the host plant to tolerate acidity stress should be taken into account first when screening effective Acacia-Bradyrhizobium combinations for use in afforestation trials.     

The presence of aluminum in arbuscular mycorrhizas of Clusia multiflora exposed to increased acidity

In this work, we present the results obtained after 9 months of watering with acidic solutions seedlings of Clusia multiflora, inoculated with arbuscular mycorrhizal fungi (AMF). The fungi were isolated from acid and neutral soil. C.multiflora is a tropical woody species that naturally grows on acid soils high in soluble Al. The research evaluated if arbuscular mycorrhizas (AM) could be responsible at least partially for the tolerance to acidity and to aluminum of C.multiflora and if an inoculum of AM fungi (AMF) coming from acid soils contributes more to the tolerance of acidity of C. multiflora than one coming from neutral soils. Results showed that in the absence of AMF (control treatment), the seedlings of C. multiflora did not grow, indicating that this species is highly dependent on AMF. When C. multiflora was exposed to a very acidic solution (pH 3), plants inoculated with AMF from acid soils were taller than those inoculated with AMF from neutral soils. Acidity affected root growth and root length. Plants inoculated with AMF from neutral soils showed thicker roots and lower shoot-root relationships than those inoculated with AMF from acid soils. Acidity did not affect root growth of C. multiflora inoculated with AMF from acid soils even when they were watered with solutions of pH 3. All plants accumulated high quantities of Al in roots (>10000 mg.kg ^–1), but plants inoculated with AMF from acid soils, accumulated less aluminum in roots than plants from the other treatments. A histochemical study of the distribution of Al in roots showed that in mycorrhizal plants, the aluminum was bound to the cell walls in the mycelium of the fungus, mainly in the vesicles or in auxiliary cells, a fact showed for the first time in this work.     

Effects of elevated CO2 and nitrogen on nutrient uptake in ponderosa pine seedlings

This paper reports on the results of a controlled-environment study on the effects of CO₂ (370, 525, and 700 mol mol^-1) and N [0, 200, and 400 g N g soil^-1 as (NH₄)SO₄] on ponderosa pine (Pinus ponderosa) seedlings. Based upon a review of the literature, we hypothesized that N limitations would not prevent a growth response to elevated CO₂. The hypothesis was not supported under conditions of extreme N deficiency (no fertilizer added to a very poor soil), but was supported when N limitations were less severe but still suboptimal (lower rate of fertilization). The growth increases in N-fertilized seedlings occurred mainly between 36 and 58 weeks without any additional N uptake. Thus, it appeared that elevated CO₂ allowed more efficient use of internal N reserves in the previously-fertilized seedlings, whereas internal N reserves in the unfertilized seedlings were insufficient to allow this response. Uptake rates of other nutrients were generally proportional to growth. Nitrogen treatment caused reductions in soil exchangeable K⁺, Ca²⁺, and Mg²⁺ (presumably because of nitrification and NO₃ ^- leaching) but increases in extractable P (presumably due to stimulation of phosphatase activity).The results of this and other seedling studies show that elevated CO₂ causes a reduction in tissue N concentration, even under N-rich conditions. The unique response of N is consistent with the hypothesis that the efficiency of Rubisco increases with elevated CO₂. These results collectively have significant implications for the response of mature, N-deficient forests to evevated CO₂.     

Impact of the TaMATE1B gene on above and below-ground growth of durum wheat grown on an acid and Al3+-toxic soil

Background and aims

Subsoil acidity with a high aluminium (Al³⁺) soil content inhibits root growth and proliferation of durum wheat (tetraploid AABB, Triticum turgidum) leading to poor nutrient and water uptake. This study evaluated the impact of Al³⁺-tolerantTaMATE1B allele on root and shoot traits of durum wheat grown in an acidic soil with a high Al³⁺concentration.

Methods

Two durum wheat lines, Jandaroi–TaMATE1B with the TaMATE1B gene introgressed from Al³⁺-tolerant bread wheat and Jandaroi–null (a sister line lacking the Al³⁺-tolerant TaMATE1B allele), were grown in rhizoboxes in a glasshouse. We mapped root growth and proliferation over time and measured shoot traits and grain yield.

Results

Introgression of the Al³⁺-tolerant TaMATE1B allele into durum wheat enabled root growth and proliferation below 0.25 m of the soil profile, where the soil pH was low (4.1, CaCl₂ extract) with high Al³⁺ content (16.5 mg kg⁻¹), and increased total root length and biomass at 42 days after sowing (DAS; Z₃₃) by 38.3 and 22%, respectively, relative to the Jandaroi–null. Differences in root growth between the two lines were apparent from tillering stage (Z₃₃) and by 50% anthesis (Z₆₄), respectively. Jandaroi–TaMATE1B had 69.2% greater root biomass, 76.2% greater root length, 5.89% greater leaf area and 18% greater shoot biomass than Jandaroi–null at 50% anthesis (Z₆₄). Time to anthesis and physiological maturity was delayed 6–7 days in Jandaroi–TaMATE1B, compared to Jandaroi–null. Jandaroi–TaMATE1B tended to have relatively greater, but not significantly different, shoot biomass, grain yield and yield components than Jandaroi–null.

Conclusions

Introgression of the Al³⁺-tolerant TaMATE1B allele into durum wheat enabled root growth and proliferation down an acidic soil profile with a high Al³⁺ concentration. We assume that in the field where plants need to acquire water at depth differences in above-ground parameters would be amplified.

     

Effects of air pollutant-temperature interactions on mineral-N dynamics and cation leaching in reciplicate forest soil transplantation experiments

Increased emissions of nitrogen compounds have led to atmosphericdeposition to forest soils exceeding critical loads of N overlarge parts of Europe. To determine whether the chemistry offorest soils responds to changes in throughfall chemistry, intactsoil columns were reciprocally transplanted between sites, withdifferent physical conditions, across a gradient of N and Sdeposition in Europe.The transfer of a single soil to the various sites affected itsnet nitrification. This was not simply due to the nitrificationof different levels of N deposition but was explained bydifferences in physical climates which influenced mineralizationrates. Variation in the amount of net nitrification between soiltypes at a specific site were explained largely by soil pH.Within a site all soil types showed similar trends in netnitrification over time. Seasonal changes in net nitrificationcorresponds to oscillations in temperature but variable time lagshad to be introduced to explain the relationships. WithArrhenius law it was possible to approximate gross nitrificationas a function of temperature. Gross nitrification equalled netnitrification after adaptation of the microbial community oftransplanted soils to the new conditions. Time lags, andunderestimates of gross nitrification in autumn, were assumed tobe the result of increased NH ₄ ⁺ availability due either tochanges in the relative rates of gross and net N transformationsor to altered soil fauna-microbial interactions combined withimproved moisture conditions.Losses of NO ₃ ^- were associated with Ca²⁺and Mg²⁺ in non-acidified soil types and with losses ofAl³⁺ in the acidified soils. For single soils the ionequilibrium equation of Gaines-Thomas provided a useful approximationof Al³⁺ concentrations in the soil solution as a functionof the concentration of Ca²⁺. The between site deviationsfrom this predicted equilibrium, which existed for single soils, couldbe explained by differences in throughfall chemistry which affectedthe total ionic strength of the soil solution.The approach of reciprocally transferring soil columnshighlighted the importance of throughfall chemistry, interactingwith the effect of changes in physical climate on forest soilacidification through internal proton production, in determiningsoil solution chemistry. A framework outlining the etiology offorest die-back induced by nitrogen saturation is proposed.     

Microscale heterogeneity of acidity related stress-parameters in the soil solution of a forested cambic podzol

Acid related stress in soils might be caused by high concentrations of H⁺ and Al³⁺ in soil solution. Sampling of soil solution so far integrates over a relatively large soil volume, in the range of dm³. In order to study the microscale heterogeneity of acidity related stress-parameters the soil profile of a podzolic cambisol was covered by a 10×6 matrix of micro suction cups with a grid distance of 2 cm. The soil solution collected at 10 sampling events was analyzed for free cations and anions by capillary electrophoresis and for total metal content by a micro injection technique on ICP-OES. pH and UV absorption were also measured.There was a general trend of increasing pH and decreasing UV absorption with increasing soil depth, however without a clear correlation of concentration isolines to soil horizon borders. The latter was also true for total Al (Al_tot) and Al³⁺, with the exception of the soil horizon border A_he/B_h,which was very well reflected by Al³⁺ and also by the fraction of bound Al. In the A_he horizon less than 30%, in deeper mineral soil less than 50% of Al_tot were present as free Al³⁺. This fact is critical when calculating Ca/Al ratios as a stress parameter, because total metal content measured by ICP clearly overestimates the risk of root damage, even in deeper horizons of acid forest soils, where organic complexation of Al is of minor importance. The heterogeneity of soil solution chemistry and toxicity parameters on the cm-scale was found to be significant, for example with gradients of more than 0,5 pH-units within 2 cm. Because plant roots also experience soil on a microscale, high resolution investigations of soil solution chemistry offer a new approach for looking at the chemical environment relevant for root growth and plant nutrition.     

Will CO<Subscript>2</Subscript> Emissions from Drained Tropical Peatlands Decline Over Time? Links Between Soil Organic Matter Quality,Nutrients, and C Mineralization Rates

Conversion, drainage, and cultivation of tropical peatlands can change soil conditions, shifting the C balance of these systems, which is important for the global C cycle. We examined the effect of soil organic matter (SOM) quality and nutrients on CO₂ production from peat decomposition using laboratory incubations of Indonesian peat soils from undrained forest in Kalimantan and drained oil palm plantations in Kalimantan and Sumatra. We found that oil palm soils had higher C/N and lower SOM quality than forest soils. Higher substrate quality and nutrient availability, particularly lower ratios of aromatic/aliphatic carbon and C/N, rather than total SOM or carbon, explained the higher rate of CO₂ production by forest soils (10.80 ± 0.23 µg CO₂–C g C h^?1) compared to oil palm soils (5.34 ± 0.26 µg CO₂–C g C h^?1) from Kalimantan. These factors also explained lower rates in Sumatran oil palm (3.90 ± 0.25 µg CO₂–C g C h^?1). We amended peat with nitrogen (N), phosphorus (P), and glucose to further investigate observed substrate and nutrient constraints across the range of observed peat quality. Available N limited CO₂ production, in unamended and amended soils. P addition raised CO₂ production when substrate quality was high and initial P state was low. Glucose addition raised CO₂ production in the presence of added N and P. Our results suggest that decline in SOM quality and nutrients associated with conversion may decrease substrate-driven rates of CO₂ production from peat decomposition over time.     

Aluminium localization and toxicity symptoms related to root growth inhibition in rice (<Emphasis Type="Italic">Oryza sativa</Emphasis> L.) seedlings

We correlated root growth inhibition with aluminium (Al³⁺) localization and toxicity symptoms in rice roots using seedlings of two genotypes (tolerant and sensitive) that were exposed to different AlCl₃ concentrations. Al³⁺ localization was evaluated by hematoxylin in primary roots and by morin in cross-sections of the root tips. Neutral invertase enzyme activity and callose (1→3, β-d-glucan) accumulation were observed and compared with Al³⁺ accumulation sites. Root growth was inhibited by Al³⁺ in a concentration-specific manner and proportional to the increase of hematoxylin staining, being more pronounced in the sensitive genotype. Morin staining showed the presence of Al³⁺ deep within the roots of the sensitive genotype, indicating that the metal was able to penetrate beyond the first few cell layers. In the tolerant genotype, Al³⁺ penetration was restricted to the first two cell layers. Ruptures in exodermis and epidermis layers by lateral root protrusions in both genotypes allowed Al³⁺ to enter into the roots. More intense activity of invertase in roots of the tolerant genotype was also observed, which could be related to greater root growth of this cultivar when submitted to Al³⁺ stress. Moreover, Al³⁺-induced callose accumulation was a late response occurring in the same areas where Al³⁺ was present.     

Microbial populations in trifluralin-treated soil

Summary This study examined the effects of trifluralin (,,-trifluoro-2,6-dinitro-N,N-dipropyl-p-toluidine), a soil incorporated herbicide, on soil microflora both in the general soil environment and in the rhizosphere of trifluralin damaged wheat roots. Two Dark Brown Chernozemic soils were treated with various trifluralin rates in the growth chamber and wheat [Triticum aestivum L. Neepawa] was seeded. Trifluralin generally had no effect on fungi, bacteria, or actinomycete populations in either the general soil or in the rhizosphere. CO₂ evolution was unchanged when trifluralin was added to the soil. In wheat plots, at two field locations, there were no significant effects of trifluralin (1.0 kg ha^–1) on soil fungi, bacteria, actinomycete, denitrifying bacteria, and nitrifying Nitrobacter propulations. A pure culture study with 42 soil microorganisms showed that many isolates were inhibited at 400 to 100,000 g g^–1 but not at concentrations <16 g g^–1. Similar data were obtained from tests on four different soils. These studies indicate that trifluralin is unlikely to cause changes in the numbers of soil microorganisms when used at recommended levels.     

Aluminium pre-treatment induces activation of defense responses against <Emphasis Type="Italic">Fusarium</Emphasis> infection in <Emphasis Type="Italic">Triticum aestivum</Emphasis>

Pre-treatment with low dose of aluminium sulphate [Al₂(SO₄)₃] was assayed on wheat (Triticum aestivum L.) seedlings for its ability to induce resistance against Fusarium oxysporum infection. Pre-treatment of seven days old germinated wheat seedlings with 50 μM concentration of Al₂(SO₄)₃ reduced the severity of the disease. In Al₂(SO₄)₃ pre-treated seedlings inoculated with fungus reduction in disease severity was correlated with suppression of fungal mycelia development inside the leaf tissues. The activities of peroxidase, polyphenol oxidase, and phenylalanine ammonia lyase were determined as resistance markers. F. oxysporum inoculation induced significant increase of all these enzymes. Such responses were expressed earlier and with much higher magnitude when Al₂(SO₄)₃ pre-treated seedlings were challenged with the pathogen. Slower disease development in Al₂(SO₄)₃ pre-treated seedlings might be due to increased deposition of total phenolic compounds and enhanced level of salicylic acid which restricts pathogen entry.