Phosphate,aluminium and iron in the soil solution of three different soils in relation to varying concentrations of citric acid

Several plant species excrete di- and tricarboxylic acids as a reaction to P and Fe deficiency. Therefore, the effect of citric acid on P, Al, and Fe soil solution concentrations of three soils was investigated in an incubation experiment. Citric acid additions of 10–50 μmole/g soil increased P, Al, and Fe solubility. The effect was strongly pronounced in the podzol with humic-P complexes as the main P fraction. The maximum increase was about 80 μmole P/L in the luvisol, 500 μmole P/L oxisol, and 3000 μmole P/L in the podzol. The Fe and Al solubility increased parallel to that of P with a ratio of Fe+Al_solubized/P_solubized of 10 or more. The solubization effect by citric acid was strong even after 90 days. Possible solubization reactions are discussed.     

Organic acid concentrations in soil solution: effects of young coniferous trees and ectomycorrhizal fungi

Organic acids may play a key role in rhizosphere and pedogenic processes. The effects of young trees and ectomycorrhizas on the soil solution concentrations of low molecular weight organic acids (LMWOAs) were studied in soil columns (E horizon) in the presence or absence of Pinus sylvestris and Picea abies with or without three ectomycorrhizal fungi. Several LMWOAs were identified at concentrations ranging from <0.1 to 11 μM. Compared to soil columns without tree seedlings, the presence of non-mycorrhizal or mycorrhizal tree seedlings sometimes resulted in small but statistically significant increases in citrate, formate, malonate and oxalate concentration. The general nutrient concentration and low P had little short-term effect on soil solution organic acid concentrations. The results suggest that biodegradation rather than production may be the major factor regulating soil solution organic acid concentrations.     

Growth, P uptake and rhizosphere properties of intercropped wheat and chickpea in soil amended with iron phosphate or phytate

Intercropping has been shown to increase total yield and nutrient uptake compared to monocropping. However, depending on crop combinations, one crop may dominate and decrease the growth of the other. Interactions in the soil, especially in the rhizosphere, may be important in the interactions between intercropped plant genotypes. To assess the role of the rhizosphere interactions, we intercropped a P-inefficient wheat genotype (Janz) with either the P-efficient wheat genotype (Goldmark) or chickpea in a soil with low P availability amended with 100 mg P kg⁻¹ as FePO₄ (FeP) or phytate. The plants were grown for 10 weeks in pots where the roots of the genotypes could intermingle (no barrier, NB), were separated by a 30 μm mesh (mesh barrier, MB), preventing direct root contact but allowing exchange of diffusible compounds and microorganisms, or were completely separated by a solid barrier (SB). When supplied with FeP, Janz intercropped with chickpea had higher shoot and grain dry weight (dw) and greater plant P uptake in NB and MB than in SB. Contact with roots of Janz increased shoot, grain and root dw, root length, shoot P concentration and shoot P uptake of chickpea compared to SB. Root contact between the two wheat genotypes, Janz and Goldmark, had no effect on growth and P uptake of Janz. Shoot and total P uptake by Goldmark were significantly increased in NB compared to MB or SB. In both crop combinations, root contact significantly increased total plant dw and P uptake per pot. Plant growth and P uptake were lower with phytate and not significantly affected by barrier treatment. Differences in microbial P, available P and phosphatase activity in the rhizosphere among genotypes and barrier treatments were generally small. Root contact changed microbial community structure (assessed by fatty acid methyl ester (FAME) analysis) and all crops had similar rhizosphere microbial community structure when their roots intermingled.     

Effects of phosphate carriers,iron, and indoleacetic acid on iron nutrition and productivity of peanut on a calcareous soil

Results of a field experiment designed to assess the effects of phosphate carriers, iron (Fe), and indoleacetic acid (IAA) on the Fe nutrition of peanut grown on a calcareous soil showed that single superphosphate (SSP) was more effective than diammonium phosphate (DAP) in improving Fe nutrition and chlorophyll synthesis. Increased phosphorus (P) and Fe contents of chlorotic leaves showing symptoms of Fe deficiency suggested that Fe, despite absorption and uptake, was subjected to inactivation, and that the Fe content per se was not the cause of the observed chlorosis. Better amelioration of chlorosis with the SSP treatment as compared with DAP indicated a role of sulphur (S) in preventing inactivation of Fe, possibly caused by excessive P accumulation. A foliar spray of Fe‐EDDHA corrected the chlorosis, but a ferric citrate foliar treatment did not. This further suggested that the mobility of Fe was impaired in chlorotic plants. An IAA foliar spray only also tended to improve Fe nutrition. Significant increase in peanut productivity was observed following improvement in Fe nutrition both with soil and foliar treatments.     

Effects of growing roots of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) on rhizosphere soil solution chemistry

The chemical conditions of the rhizosphere can be very different from that of bulk soil. Up to now, little attention has been given to the problem of spatial heterogeneity and temporal dynamics of rhizosphere soil solution and little is known about the influence of different tree species on rhizosphere chemistry. In the present study, we used micro suction cups to collect soil solution from the rhizosphere of Norway spruce (Picea abies [L.] Karst.) and European beech (Fagus sylvatica L.) seedlings in high spatial resolution and capillary electrophoresis for the determination of major cations and anions. The results indicate, that in a soil with a base saturation of about 20—25% and a pH of 6.5, growing roots of beech and spruce lower the concentrations of nutrient cations and nitrate in the rhizosphere soil solution and decrease significantly the pH. The H⁺ release leads to an enhanced mineral weathering as indicated by an increase of CEC and base saturation and to a mobilization of soluble Al, however, on a very low concentration level. In our experiment rhizosphere effects of spruce have been more pronounced than those of beech, indicating, that with respect to below ground activity young spruce trees have a better competitive power than beech.     

The involvement of iron and aluminum in the bonding of phosphorus to soil humic acid

Abstract

With a peat soil similar amounts of phosphorus (P) were coprecipitated with humic acid from alkali extracts over a limited range of strongly acidic pH, whereas with a mineral soil the amount was pH dependent. The difference between the two soils relates to the much greater total amounts of inorganic P and aluminum (Al) present in the extract of the mineral soil. In this acid mineral soil, Al rather than iron (Fe) may be involved in the formation of metal bridges in humic acid‐metal‐inorganic P complexes. Neither Al or Fe were implicated in binding of organic P to humic acid. The P species observed in humic acids was dependent on the pH at which they were precipitated from the alkali extracts. In the peat soil the inorganic P was an order of magnitude lower than the organic P.     

Diversity of 16S-rRNA and nifH genes derived from rhizosphere soil and roots of an endemic drought tolerant grass,Lasiurus sindicus

Lasiurus sindicus is a highly nutritive, drought tolerant, perennial grass, endemic to the Thar Desert of Rajasthan, India. In order to characterize the diversity of bacteria associated with roots of this grass that had survived severe drought stress, 16S-rRNA gene clone libraries were established from RT-PCR amplified products of the total RNA extracted from the washed roots and rhizosphere soil samples. Eight major bacterial taxa were identified in a total of 121 16S-rRNA gene clones. The majority of sequences belonged to Gram-positive bacteria, Actinobacteria being the most predominant ones, closely followed by Firmicutes. Most of the sequences showed similarity with sequences from cultivated bacteria or uncultivated environmental clones associated with arid, semi-arid environments, cold deserts and contaminated soils. PCR amplification of nifH genes using total DNA as template produced a total of 48 nifH clones from the rhizosphere soil and root samples and revealed a predominance of nifH sequences closely affiliated to Pseudomonas pseudoalcaligenes, isolated in a previous study from root samples of Lasiurus sindicus. Some nifH sequences showed close similarity to cultivated diazotrophs like Azospirillum brasilense, Rhizobium sp., and a variety of uncultured nitrogen fixing bacteria. Thus, this study provides us with evidence that L. sindicus harbors a diversity of bacteria with potential for nitrogen fixation.     

Agronomic evaluation of phosphate rock and slag on an upata acid soil in Bolivar State,Venezuela

Abstract

An agronomic evaluation of phosphate rock and slag on the acid soils of Upata, Bolivar State was conducted to measure their effect on the chemical properties of the soil and growth of Brachiaria decumbens. A field experiment was established using a split plot design with three replications. The treatments were, i) three sources of phosphate rock (Riecito and Lizardo of Falcon State and Monte Fresco of Tachira State) at four rates of P₂O₅/ha (0, 50, 100, and 200), ii) one source of high‐solubility P [triple superphosphate (TSP) at the same rates], and iii) three levels of calcium applied as basic slag from the Orinoco Steel Company (0, 300, and 600 kg Ca/ha). A basic fertilization was applied to all plots (217 kg/ha Urea, 50 kg/ha KCl, and 78 kg/ha magnesium sulphate). The pasture species used was Brachiaria decumbens. Pasture and soil samples were taken at 2, 3, 5, 7, 12, 14, 16, 17, 24, 27, and 31 months after planting. The pasture samples were analyzed for dry matter production (DM), and percentage content of nitrogen (N), phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg). Soil samples were analyzed for pH, cation exchange capacity (CEC), and available calcium (Ca) and phosphorus (P). The relative agronomic effectiveness (RAE), calculated using the formula: RAE (%) = DM of the rock ‐ DM of the check plot/DM of TSP ‐ DM of check plot × 100 was applied for each harvest time. The best RAE values at each sampling time were obtained with the Monte Fresco phosphate rock at the rate of 200 kg P₂O₅/ha and 600 kg Ca/ha as slag. There was a tendency for the RAE value to improve with each sampling apparently due to the slow release of phosphorus from the phosphate rock and its residual effect. There are also values of RAE that show better dry matter production than the high soluble source of TSP.

Soil available P and Ca increased with phosphate rock and slag application from 5 and 200 mg/kg to 25 and 400 mg/kg, respectively, after 2.5 years of the experiment. Phosphorus uptake changed from 0.1% in the check plot, which is insufficent to supply the P requirement of grazing cattle in the tropics to a value higher than 0.2%, depending on the sampling time. Soil pH increased slightly from 5.2 to 5.6 with phosphate rock, and to 6.2 when basic slags were applied.     

Effects of moist storage and different drying temperatures on the extractability of iron,copper, manganese,and zinc in soil samples

Abstract

The objective of this study was to investigate the effect of different pretreatments on the extraction of cationic micronutrients [iron (Fe), copper (Cu), manganese (Mn), and zinc (Zn)] from four different soils. Samples were either stored in the field‐moist state for seven days before drying or dried immediately. Three drying treatments were used: air‐dried (72 hours), oven‐dried at 40°C (48 hours), or oven‐dried at 105°C (24 hours). Micronutrients were then extracted with 0.1N HC1 or diethenetriamine‐pentacetic acid (DTPA). Storage, drying temperature, extractant, and soil type all influenced micronutrient extractability. In general, a higher temperature increased the level of micronutrient extracted. However, the reverse effect was also observed. The effect of storage was variable and probably depended on the sample moisture content. We conclude that the results from routine analysis and experimentally determined indices can only be compared if soil samples are subjected to the same pretreatments. Hence, rigorous standardization of the sample preparations is imperative for accurate determination of plant‐available micronutrients.     

Increased phosphorus availability to corn resulting from the simultaneous applications of phosphate rock, calcareous rock, and biochar to an acid sandy soil

Phosphorus (P) deficiency is one of the main constraints on crop production in Arenosols (acid sandy soil). The high cost of P fertilizers may represent an insurmountable obstacle in many poor countries, leaving the exploitation of their own calcareous and phosphate rocks as the only low-cost and long-term alternative. Biochar is suggested to have positive effects on soil properties; however, there is no published research on the synergistic effects of biochar and rocky materials in modifying soil properties. The aim of this study was to investigate the chemical and biochemical responses of an acid Arenosol treated with phosphate rock (PR), calcareous rock (CR), and biochar (BC), and the implications for corn yield. A soil from Marracuene District, Mozambique was used, where corn was grown for 90 d with the soil treated with:no addition (control), water-soluble zinc phosphite fertilizer (WSP), PR, WSP+CR, WSP+BC, WSP+CR+BC, PR+BC, and PR+CR+BC. Biochar was produced by pyrolysis of babycorn peels for 4 h at 450℃ and applied at 11 g kg^-1. The soil pH_H2O increased from about 4.54 in the control to 7.38 in the PR+CR+BC treatment. Easily oxidizable organic carbon, cation exchange capacity, and available P were higher in the treatments containing BC than in the control. The treatments containing CR and/or BC led to the highest activities of alkaline phosphomonoesterase, phosphodiesterase, and α-glucosidase, which increased P availability and gave the greatest biomass and yields. We suggest that biochar provides additional soluble P and supplies adsorption sites for phosphate, preventing its evolution to unavailable forms. Thus, PR applied together with BC contributed to an 840% yield increase compared to the control. The treatments containing WSP and BC facilitated phosphite oxidation to phosphate and increased crop yield.     

Organic and inorganic soil phosphates and acid phosphatase activity in the rhizosphere of 80-year-old Norway spruce [Picea abies (L.) Karst.] trees

Summary Inorganic and organic phosphates (P) were measured in bulk soil, rhizosphere soil and mycorrhizal rhizoplane soil of Norway spruce. Various methods of P extraction and estimation were compared. In addition, acid phosphatase activity and mycelial hyphae length were determined. In soil solutions from various locations, about 50% (range 35%–65%) of the total P was present as organic P. Compared to the bulk soil, the concentrations of readily hydrolysable organic P were lower in the rhizosphere soil and in the rhizoplane soil; this difference was particularly marked in the humus layer. In contrast, the concentrations of inorganic P either remained unaffected or increased. A 2- to 2.5-fold increase was found in the activity of acid phosphatase in the rhizoplane soil in comparison to the bulk soil. There was a positive correlation (r = 0.83^***) between phosphatase activity and the length of mycelial hyphae. The results stress the role of organic P and of acid phosphatase in the rhizosphere in the P uptake by mycorrhizal roots of spruce trees grown on acid soils.     

Effects of lime and phosphate additions on changes in enzyme activities,microbial biomass and levels of extractable nitrogen,sulphur and phosphorus in an acid soil

Summary The effects of adding lime and/or phosphate to an acid, phosphate-deficient soil on microbial activity, enzyme activities and levels of biomass and extractable N, S and P were studied under laboratory conditions. Following rewetting there was, as expected, an initial flush in microbial growth and activity, as shown by large increases in CO₂ evolution, in levels of biomass N, S and P and by accumulation of extractable mineral N and sulphate in the soil. Following rewetting, additions of lime and phosphate further stimulated mineralization of C, N and S. In the first 4 weeks of incubation, the mineralized N accumulated in the soil as ammonium N and there was a concomitant rise in soil pH. After this initial period, nitrification increased substantially and soil pH decreased again. Additions of lime generally increased protease and sulphatase activities but decreased phosphatase activity. Additions of phosphate decreased the activities of all three enzymes. The positive effect of liming on protease and sulphatase activities persisted for the duration of the experiment while accumulation of mineral N and sulphate effectively ceased after about 4 weeks. Furthermore, although phosphate additions decreased the activities of protease and sulphatase they increased the accumulation of mineral N and sulphate. Thus, protease and sulphatase activities were not reliable indicators of the relative amounts of mineral N and sulphate accumulated in the soil during incubation. Some uncertainty surrounded the validity of biomass S and P values estimated by the chloroform fumigation technique because differing proportions of the sulphate and phosphate released from the lysed cells may have been extracted from the different treatments.     

Temporal and spatial dynamics of soil solution C and N concentrations during Lolium perenne L. sward establishment and the effects of elevated CO2 and N additions

There is now clear evidence for a prolonged increase in atmospheric CO₂ concentrations and enrichment of the biosphere with N. Understanding the fate of C in the plant-soil system under different CO₂ and N regimes is therefore of considerable importance in predicting the environmental effects of climate change and in predicting the sustainability of ecosystems. Swards of Lolium perenne were grown from seed in a Eutric Cambisol at either ambient (ca. 350 μmol mol⁻¹) or elevated (700 μmol mol⁻¹) atmospheric pCO₂ and subjected to two inorganic N fertilizer regimes (no added N and 70 kg N ha⁻¹ month⁻¹). After germination, soil solution concentrations of dissolved organic C (DOC), dissolved inorganic N (DIN), dissolved organic N (DON), phenolics and H⁺ were measured at five depths down the soil profile over 3 months. The exploration of soil layers down the soil profile by roots caused transient increases in soil solution DOC, DON and phenolic concentrations, which then subsequently returned to lower quasi-stable concentrations. In general, the addition of N tended to increase DOC and DON concentrations while exposure to elevated pCO₂ had the opposite effect. These treatment effects, however, gradually diminished over the duration of the experiment from the top of the soil profile downwards. The ambient pCO₂ plus added N regime was the only treatment to maintain a notable difference in soil solution solute concentration, relative to other treatments. This effect on soil solution chemistry appeared to be largely indirect resulting from increased plant growth and a decrease in soil moisture content. Our results show that although plant growth responses to elevated pCO₂ are critically dependent upon N availability, the organic chemistry of the soil solution is relatively insensitive to changes in plant growth once the plants have become established.     

Seasonal effects of liming,irrigation, and acid precipitation on microbial biomass N in a spruce (Picea abies L.) forest soil

Summary Seasonal effects of liming, irrigation, and acid precipitation on microbial biomass N and some physicochemical properties of different topsoil horizons in a spruce forest (Picea abies L.) were measured throughout one growing season. The highest biomass N was recorded in autumn and spring in the upper soil horizons, while the lowest values were obtained in summer and in deeper horizons. The clearest differences between the different soil treatments were apparent in autumn and in the upper horizons. Liming increased the microbial biomass N from 1.7% of the total N content to 6.8% (Olf₁ layer) and from 1% to 2% of the total N content in the Of₂ layer. The main inorganic-N fraction in the deeper horizons was NO _inf3 ^sup- . An increase in cation exchange capacity was observed down to the Oh layer, while soil pH was only slightly higher in the Olf₁ and Of₂ layers after liming. The effects of irrigation were less marked. The microbial biomass N increased from 1.7% of total N to 4.8% in the Olf₁ layer and from 1% to 2% of total N in the Of₂ layer. In the Olf₁ layer an increase in C mineralization was observed. Acid precipitation decreased the microbial biomass N in the upper horizons from 4.8% of total N to 1.8% in the Olf₁ layer and from 2% to 0.5% in the Of₂ layer. No significant changes in soil pH were observed, but the decrease in cation exchange capacity may result in a decrease in the proton buffering capacity in the near future.     

Diversity of total,nitrogen‐fixing and denitrifying bacteria in an acid forest soil

To assess the diversity of total, denitrifying and N₂‐fixing bacteria in a nitrogen (N)‐limited, acid forest soil, isolated DNA was analysed for the genes 16S rRNA, nosZ and nifH. Sequence information for these genes was obtained from clone libraries and from our TReFID computer program, which employs terminal restriction patterns for bacteria using multiple restriction enzymes. Both approaches indicated that Proteobacteria (α‐ and γ‐groups) and Acidobacteria dominated. A comprehensive list of bacteria retrieved from this soil is provided and compared with literature data on the bacterial community compositions from other sites. The study indicated that the current PCR conditions with the primers employed allowed retrieval of only a portion of the bacteria occurring in soils. Massive treatment of a soil plot with NH₄NO₃ caused an increase in the N content, which was rapidly followed by an enhancement of carbon (C) content. Thus the C/N ratio stayed below 16.0 and the soil remained N‐limited. This may explain why the bacterial diversity did not undergo drastic shifts as was tentatively inferred from the available data sets.     

Inhibition of iron uptake by phytic acid, tannic acid, and ZnCl2: studies using an in vitro digestion/Caco-2 cell model.

The objective of this study was to document the effects of phytic acid, tannic acid, and zinc on iron uptake in an in vitro digestion/Caco-2 cell culture model. The effects of phytic acid and tannic acid on iron uptake were measured at increasing molar ratios of FeCl3 to phytic acid or tannic acid. Maximal inhibition of iron uptake by phytic acid occurred at a 1:10 ratio of Fe to phytic acid. Dialyzable Fe decreased with a low Fe to phytic acid ratio but increased with Fe:phytic acid ratios greater than 1:3 indicating that more iron was soluble at higher phytic acid levels but less available. As in human studies, heme iron was less inhibited by phytic acid than nonheme iron. Tannic acid was a more potent inhibitor of nonheme iron uptake, as maximal inhibition (97.5%) of iron uptake occurred at a ratio of 1:1 or less. The addition of ZnCl2 to the digest at ratios of 1:0.5 and 1:1 decreased iron uptake by 57 and 80%, respectively. Overall, the results agree qualitatively with studies in humans and demonstrate the relative effects of these compounds on iron uptake in this model system. This study provides key information for determining iron availability under more complex meal conditions.     

Growth of Lumbricus terrestris and Aporrectodea caliginosa in an acid forest soil, and their effects on enchytraeid populations and soil properties

A laboratory experiment was carried out to test the hypothesis that the earthworms Lumbricus terrestris and Aporrectodea caliginosa are able to maintain their populations and reproduce in the acid forest soil of a deciduous forest where no lumbricids were found in the field. The experiment was conducted in 45-l containers in which layers of mineral subsoil, humus and organic topsoil collected from the site were established. Both species survived and at least L. terrestris reproduced during the 60 weeks’ incubation. Burrows and middens of L. terrestris were recorded and quantities of litter were consumed. The presence of lumbricids increased the organic matter content of humus, reduced the acidity of the topsoil and humus layers, and suppressed the population of the enchytraeid Cognettia sphagnetorum. A dense population of Enchytraeus albidus was found in L. terrestris middens. It is concluded that edaphic factors do not explain the absence of earthworms, but isolation from cultural landscapes and lack of opportunity to colonize the site from the surroundings is the decisive factor.     

Soil particle surface electrochemical property effects on abundance of ammonia-oxidizing bacteria and ammonia-oxidizing archaea, NH4 activity, and net nitrification in an acid soil

Soil surface electrochemical properties may have a strong influence on nitrifying microorganisms, H⁺ and NH₄⁺ activities, and therefore on the nitrification process. A gradient of surface electrochemical parameters was obtained by amendment of a subtropical acid pine soil (Oxisol) with 0% (control), 3%, 5%, 8%, 10% and 12% pure Ca-Montmorillonite by weight. The H⁺ and NH₄⁺ activities, the abundance of the ammonia-oxidizing bacterial (AOB) and archaeal (AOA) amoA gene copies, and time-dependent kinetics of net nitrification were investigated. Soil particle surface specific area ranged from 53 to 103 m² g⁻¹ and increased with increasing montmorillonite application rate. Similar to specific area, surface charge quantity, surface charge density, electric field strength and surface potential increased after montmorillonite amendment. The H⁺ and NH₄⁺ activities decreased linearly after montmorillonite addition. AOB amoA gene copy number was 1.82 × 10⁵ copies g⁻¹ for unamended soil, and the highest AOB amoA gene copy numbers were found for the 10% montmorillonite amendment (3.11 × 10⁷ g⁻¹ soil), which was more than 150 times higher than unamended soil. AOA amoA gene copy numbers were 9.19 × 10³ copies g⁻¹ dry unamended soil, and the highest AOA amoA gene copy numbers were found in the 8% montmorillonite amendment (1.22 × 10⁵ g⁻¹ soil). Although pH significantly decreased during the first three weeks of incubation, no significant difference was observed between the unamended control and different rates of montmorillonite addition treatments during the whole incubation. The largest net nitrification (103 mg N kg⁻¹) was observed in the 10% montmorillonite amendment and the lowest in unamended soil (62 mg N kg⁻¹). While montmorillonite did not change the kinetic patterns of net nitrification, the highest nitrification potential (275 mg N kg⁻¹) for the 10% montmorillonite treatment was more than 3 times higher than unamended soil from simulation of time-dependent kinetics. Nitrification was significantly stimulated after montmorillonite amendment in acid soil mainly due to an increase in the quantity and activity of AOB and AOA. We concluded that soil particle surface parameters can significantly influence nitrification, especially in acid soils.     

Regulating the mobility of Cd, Cu and Pb in an acid soil with amendments of phosphogypsum, sugar foam, and phosphoric rock

When acid soil has been contaminated by metals as a result of industrial discharges, accidental spills, or acid mine drainage it may be desirable to retain the metals in the soil rather than allow them to leach away. We have investigated the potential of phosphogypsum (PG), sugar foam (SF), and phosphoric rock (PR) to regulate the availability and mobility of Pb, Cd and Cu. We have also identified changes in attenuation during incubation for 1 year and the effect of aging on metal speciation in amended soils. We studied miscible displacement in columns of undisturbed soil previously treated with solutions of the amendments and soluble metals and, subsequently, single and sequential chemical metal extractions. All amendments increased the soil's metal retention capacity. This, in turn, increased the amount of metal extractable by diethylenetriaminepentaacetic acid (DTPA). However, over time the amounts of DTPA‐extractable metal decreased, particularly for Cu and Pb. Both Cu and Cd were held preferentially within the acetic acid‐extractable fraction (operationally defined exchangeable fraction – EX fraction), whereas Pb was associated mainly with the hydroxylammonium‐extractable fraction (operationally defined bound to Fe and Al hydroxides – OX fraction). Both Pb and Cu in the oxide and organic fractions increased in the PG‐ and SF‐treated soils. In general, the distribution of metal did not change in the PR‐treated columns after the incubation. Finally, scanning electron microscopy in back‐scattered electron mode (SEM–BSE) showed the formation of Al‐hydroxy polymers which provides the soils with additional cation sorption capacity. In the PG‐ and PR‐treated columns, P and S were associated with these formations. The three metals were associated with the Al polymers, probably through direct coordination or the formation of ternary complexes with the inorganic ligands phosphate and sulphate.     

Enhancement in growth and quality parameters of tea [Camellia sinensis (L.) O. Kuntze] through inoculation with arbuscular mycorrhizal fungi in an acid soil

The present study was undertaken to determine the effect of inoculation with arbuscular mycorrhizal fungi (AMF) from natural and cultivated tea rhizospheres (NTR and CTR, respectively) on growth as well as on quality parameters of tea [Camellia sinensis (L.) O. Kuntze]. Seeds (after germination) and cuttings were inoculated with AMF consortia from NTR and CTR in non-sterilized acid soil (pH 5.0). Seedlings and cuttings were grown under net-house conditions and the data on growth and quality parameters were recorded up to 2 years. Tea plants were found to be highly colonized by AMF (74–83%) after 1 year. The significant increase in most of the growth parameters (root/shoot length, dry weight; r/s ratio) was recorded in AMF-treated plants, which also showed better tea quality parameters than noninoculated plants. Maximum significant increases up to 31% and 100%, over control, were recorded in amino acids and total protein content, respectively. Similarly, maximum increase in total polyphenols (15%) and caffeine content (34%) over control was also significant. Enhanced sugar content (maximum 16% in total soluble sugars, maximum 45% in reducing sugars, and maximum 69% in non-reducing sugars) was recorded in AMF-inoculated plants. In most cases, better response was observed in tea plants inoculated with AMF consortia from NTR. These results indicate that growth and quality of tea can be improved by AMF inoculations in acid soils.