Showing papers in "Plant and Soil in 1988"
TL;DR: A new genus and species are proposed and namedSaccharobacter nitrocaptans, which is an aerobic rod, motile by 1 to 3 lateral flagella, fixes N2 in semisolid media under air but not in liquid media except when a starter dose of N is added.
Abstract: During surveys of bacteria possibly responsible for N2 fixation in sugarcane, root and stem samples were collected in four sugarcane-growing regions in Brazil. A new microaerobic N2-fixing bacterium was isolated from most samples of washed roots and stems from all regions. Isolation procedures were based on semisolid diluted sugarcane juice medium followed by replication to N-free 10% sugar medium acidified with acetic acid to pH 4.5. The new bacterium is an aerobic rod, motile by 1 to 3 lateral flagella, fixes N2 in semisolid media under air but not in liquid media except when a starter dose of N is added. It has no nitrate, reductase and N2 fixation proceeds in the presence of 10mM NO
3
−
. Best growth occurs with high sucrose concentrations (10%). Growth occurs up to 30% sucrose but not at 35%. Acid is formed reaching a final pH of below 3.0. Growth and N2 fixation proceed at this acidity. Ethanol is used for growth and is “overoxidised” (oxidized to CO2 and H2O). Acetic and lactic acids are also oxidized to CO2 and H2O. Acids produced from glucose are consumed with precipitation of CaCO3. Dark brown colonies are formed on potato agar with 10% sugar and dark orange colonies on N poor agar (20 mg yeast extract per 1) containing bromothymol blue. In view of the distinct characteristics which do not allow identification within either Frateuria, Gluconobacter, Acetobacter or any known N2-fixing bacterium a new genus and species are proposed and namedSaccharobacter nitrocaptans.
625 citations
TL;DR: Investigation of the reasons for different P efficiencies of seven plant species found species of low efficiency such as onion, tomato and bean had low influx rates and low root-shoot ratios, whereas species of medium to high efficiency had either high influx rates (rape and spinach) or high root- shoot ratios (ryegrass and wheat).
Abstract: Plant species differ in their P efficiency, i.e. the P content in soil needed to reach their maximum yield. The differences in external P requirements can be attributed to either a lower internal P requirement for optimum growth or higher uptake efficiency of the plant. The objective of this research was to investigate the reasons for different P efficiencies of seven plant species. Onion, ryegrass, wheat, rape, spinach, tomato and bean were grown in a P-deficient subsoil fertilized with 0, 2, 5, 10, 20, 40 and 80mg P 100 g 1. All species showed a strong yield increase due to P fertilization. To reach 80% of maximum yield onion and tomato needed 17 and 11 mg P 100 g-~ respectively, corresponding to a soil solution concentrations of 6.9 and 5.7/~mol P 1 -~, whereas ryegrass, wheat and rape needed about 5mg P 100g 1 corresponding to only 1.4#mol P 1 ~ in soil solution. These differences in external P requirement cannot be explained by differences in their internal P requirement since onion, with the highest external P requirement, only contained 0.14% P in the shoot at 80% of maximum yield, while wheat, as the most P efficient species, contained 0.28%. P efficiency was related to the uptake efficiency of the plant which is determined by both root-shoot ratio and absorption rate per unit of root (influx). Species of low efficiency such as onion, tomato and bean had low influx rates and low root-shoot ratios, whereas species of medium to high efficiency had either high influx rates (rape and spinach) or high root-shoot ratios (ryegrass and wheat). The combination of both high influx rate and high root-shoot ratio was not found in any of the species studied.
337 citations
TL;DR: In this paper, the root growth is modeled in terms of growing time, number of axes, initiation times, growth rates and branching characteristics of the roots, and characteristics governing the direction of root growth.
Abstract: A model is described which simulates the growth of fibrous root systems. The root growth is specified in terms of growing time, numbers of axes, initiation times of axes, growth rates and branching characteristics of the roots, and characteristics governing the direction of root growth. The model generates a representation of the root system in which the locations of all branches and root tips are recorded in three-dimensional coordinates, and updates this representation in discrete time steps until the specified growing time is reached.
244 citations
TL;DR: The results demonstrate that decomposition and N and S mineralization of crop residues, under conditions prevalent in the experiment, are primarily a function of their nutrient concentrations rather than biochemial composition related to crop species.
Abstract: The mineralization of C, N, and S from residues of three different crop species (wheat, lentil, and rape) grown under diverse nutritional regimes was measured over a 12-week incubation period under controlled conditions The rate of decomposition, as measured by CO2 evolution, varied considerably among treatments and appeared to be controlled almost entirely by N content of the residue (R2=098) Similarly, N mineralization was strongly tied to N concentration The critical N concentration, below which significant immobilization of N occurred, declined over time, ranging from 19% at day 14 to 11% at day 84 Mineralization of S was positively correlated with initial S concentration (R2=095) and negatively related to N concentration, apparently because of a dilution effect The results demonstrate that decomposition and N and S mineralization of crop residues, under conditions prevalent in the experiment, are primarily a function of their nutrient concentrations rather than biochemial composition related to crop species As a result, it should be possible to enhance rate of residue decomposition, increase quantities of N and S mineralized, and avert detrimental immobilization losses in the following year by governing the nutritional regime under which the crop is grown
188 citations
TL;DR: The results indicate that sensitivity toB toxicity in barley and wheat is governed by the ability of cultivars to excludeB, and cultivars have the same ranking whether cultured at a normal or excessB supply.
Abstract: The mechanism of resistance toB toxicity in barley and wheat was studied in a solution culture experiment using several cultivars displaying a large range of sensitivity to excessB supply. Plants were cultured for 35 d atB concentrations ranging from normal to excessive (15 to 5000 μM, respectively) then examined for dry matter production and theB distribution between roots and shoots.
187 citations
TL;DR: Strains of Rhizobium meliloti isolated onto low pH media were, in general, more acid-tolerant than sister isolates from high pH media, when tested in both the laboratory and field.
Abstract: In the selection of acid-tolerantRhizobium meliloti, procedures for the collection and isolation of rhizobia, and the assessment of acid tolerance, have not been critically evaluated. Such procedures form the basis of this study. Root nodules were collected fromMedicago spp. found growing on acid soil in Sardinia. Their encumbent bacteria were isolated directly onto media adjusted over a range of pH values, and then assessed for acid tolerance in both the laboratory and field. Strains ofRhizobium meliloti isolated onto low pH media were, in general, more acid-tolerant than sister isolates from high pH media, when tested in both the laboratory and field. Dilution (10 or 100 fold) of the inocula used in the laboratory assessment did not greatly influence the rating derived, although there was some effect of bacterial colony type on growth rating. The link between polysaccharide production and acid tolerance was not strong. There was a poor correlation between the growth ratings derived from the laboratory screening and acid tolerance as expressed in the field.
186 citations
TL;DR: It is concluded that the whole legume-Rhizobium symbiosis should be considered when improving legume growth and yield under nutrient stress conditions.
Abstract: Mineral nturient defiencies are a major constraint limiting legume nitrogen fixation and yield. In this review general techniques for assessing nutrient involvement in symbiotic nitrogen fixation are described and specific methods are outlined for determining which developmental phase of the symbiosis is most sensitive to nutrient deficiency. The mineral nutrition of the Rhizobium component of the symbiosis is considered both as the free living organism in the soil and as bacteroids in root nodules. Rhizobial growth and survival in soils is not usually limited by nutrient availability. Multiplication of rhizobia in the legume rhizosphere is limited by low Ca availability. Nodule initiation is affected by severe Co deficiency through effects on rhizobia. Nodule development is limited by severe B deficiency via an effect on plant cell growth. Fe deficiency limits nodule development by affecting rhizobia and strains of rhizobia differ widely in their ability to acquire sufficient Fe for their symbiotic development. Nodule function requires more Mo than does the host plant, and in some symbioses nitrogen fixation may be specifically limited by low availability of Ca, Co, Cu and Fe. The importance of the peribacteriod membrane in determining nutrient availability to bacteroids is considered. It is concluded that the whole legume-Rhizobium symbiosis should be considered when improving legume growth and yield under nutrient stress conditions. Differences among rhizobial strains in their ability to obtain mineral nutrients from their environment may be agronomically important.
181 citations
TL;DR: In this paper, seasonal changes in soil water and nitrogen availability were related to the phenology and growth of plants in California annual grassland, showing that plants were in the vegetative growth phase, roots were growing rapidly and soil moisture was high.
Abstract: Seasonal changes in soil water and nitrogen availability were related to the phenology and growth of plants in California annual grassland. Plant accumulation of nitrogen was mainly confined to two short periods of the year: fall and early spring. At these times, plants were in the vegetative growth phase, roots were growing rapidly and soil moisture was high. During these periods, soil nitrate was low or depleted. High flux of nitrogen in this ecosystem, however, is indicated by the rapid disappearance of the previous year's detrital material, high microbial biomass, and high mineralizable nitrogen and nitrification potential. At the end of the summer drought, significant amounts of the previous year's detrital material had disappeared, chloroform-labile N (expressed as microbial biomass N) was at its seasonal maximum, and soil inorganic nitrogen pools were high. This suggests inorganic nitrogen flux during the drought period. The ‘drought escaper’ life history characteristics of annual grasses in California annual grassland, however, may prevent plants from utilizing available nitrogen during a large part of the year.
177 citations
TL;DR: The endophyte apparently confers drought tolerance to Kentucky 31 tall fescue, and this effect may be at least partially mediated through enhanced resistance to soil-borne nematodes.
Abstract: The presence of the endophytic fungusAcremonium coenophialum Morgan-Jones et Gams in tall fescue (Festuca arundinacea Schreb.) induces toxicity when this grass is grazed by cattle; however, there is evidence that removing the endophyte reduces the stand vigor and longevity of fescue. A field trial was conducted to determine the effects of water supply and the presence of the endophytic fungus on plant growth, drought tolerance, and soil nematode populations in ‘Kentucky 31’ tall fescue. The design included two factors, level of endophyte infection (0 and 75%) and irrigation regime (none, low, and high). Where water deficits occurred, herbage yield and leaf area were lower, and percentage dead tissue and canopy minus air temperature were greater in endophyte-free compared with endophyte-infected fescue. Soil populations ofPratylenchus scribneri andTylenchorhynchus acutus were substantially higher in the noninfected than in the endophyte-infected plots. The endophyte apparently confers drought tolerance to Kentucky 31 tall fescue, and this effect may be at least partially mediated through enhanced resistance to soil-borne nematodes.
167 citations
TL;DR: While the single inoculation of Rhizobium increased the nodulation and nitrogenase activity, the ‘phosphate-solubilizers’ increased the available phosphorus content of the soil and also the dry matter content, the grain yield and nitrogen and phosphorus uptake significantly over the uninoculated control.
Abstract: Combined inoculation of Rhizobium and ‘Phosphate-solubilizing’Pseudomonas striata orBacillus polymyxa with and without added chemical fertilizer on chickpea yield and nutrient content was studied under greenhouse conditions. While the single inoculation of Rhizobium increased the nodulation and nitrogenase activity, the ‘phosphate-solubilizers’ increased the available phosphorus content of the soil. Combined inoculation of Rhizobium andP. striata orB. polymyxa increased the above parameters and also the dry matter content, the grain yield and nitrogen and phosphorus uptake significantly over the uninoculated control. The inoculation effects were more pronounced in the presence of added fertilizers. The possibilities of saving half the dose of N and replacing superphosphate with rockphosphate and inoculation with ‘phosphate-solubilizers’ are discussed.
149 citations
TL;DR: Seedlings of rice (Oryza sativa L. var. IR42) were inoculated with nitrogen-fixingAzospirillum lipoferum by immersing the roots in the inoculum for 6 h and bacterial population counts suggested that A. lipoferUM survived on the roots till the end of the experiment.
Abstract: Seedlings of rice (Oryza sativa L. var. IR42) were inoculated with nitrogen-fixingAzospirillum lipoferum (strain 34H) by immersing the roots in the inoculum for 6 h. The plants were grown in the prescence of NH4+-N for 47 days in a hydroponic system under greenhouse conditions. Inoculation significantly enhanced PO4-ion uptake of the plants in 4 of the 7 samplings tested while the uptake of NH4-ion was significantly increased in two samplings and was decreased in one sampling. Inoculation reduced root length significantly and caused significant increases in shoot fresh and dry weights. Root surface area was not affected by inoculation. Bacterial population counts suggested thatA. lipoferum survived on the roots till the end of the experiment.
TL;DR: In this paper, the development of coherent soil sheaths on the distal 30-cm of maize roots, and the loss of the sheaths further back, led to the differences in surface structure, anatomy, carbon exudation and microflora of sheathed and bare zones.
Abstract: Recent work in our laboratory provides evidence for a revised view of the functioning of roots of maize, and probably of all the grasses. The development of coherent soil sheaths on the distal 30-cm of these roots, and the loss of the sheaths further back, led us to investigate the differences in surface structure, anatomy, carbon exudation and microflora of the sheathed and bare zones. The significant differences are summarized. But the fact which underlies all these differences is the maturation of the late metaxylem (LMX). In the sheathed zones the LMX elements are still alive and non-conducting; only the early metaxylem (EMX) and protoxylem are open. In the bare zones they are open vessels. This leads directly to the dryness of bare zones and the wetness of sheathed zones, and indirectly to the other differences noted. Branch root junctions are shown to be structures of great significance. Besides connecting the branches to the axile systems, they serve also to connect the EMX and LMX vessels, and contain a tracheid barrier which prevents air embolisms entering the main vessels. These discoveries force us to revise the traditional view of water uptake by the root hair zone, and to suggest that much water must also enter bare roots, possibly via the laterals. There is some published evidence for this. The living LMX elements of the sheathed zone accumulate large concentrations of potassium which must join the transpiration water at the transition to the bare zone. Calculations suggest that this may be only a tenth of the requirement of a mature plant, and that the balance may enter the bare zones with the transpiration water.
TL;DR: In this paper, the spatial arrangement of maize roots was studied in a clay loam field in order to test the regularity of root arrangement, which is implicitly assumed when distances between neighbouring roots are calculated.
Abstract: The spatial arrangement of maize roots was studied in a clay loam field in order to test the regularity of root arrangement, which is implicitly assumed when distances between neighbouring roots are calculated. For that. we carried out a mapping of root contacts on six superposed horizontal planes which cut the rooting volume of several area samples. Three situations were studied: (i) one inter-row out of two was compacted down to the base of the ploughed layer (28 cm), but not in non-tilled layers (28 to 200 cm); (ii) a mechanical obstacle was placed at the base of the ploughed layer; (iii) one inter-row out of two was compacted down to half the depth of the ploughed layer. On all horizontal planes, the spatial arrangement or root contacts followed a non-regular, clustered pattern for a 10−2m scale of study, even in parts of soil which had not been disturbed by compactions. In the first two situations, where obstacles met the base of the ploughed layer, root density in non-tilled layers was several times lower below the obstacles than below the remaining parts of the ploughed layer. This caused a 10−1 m sized variability which was superimposed on to the 10−2 m one. Conversely in the third situation, obstacles had no appreciable effect on root density in non-tilled layers. Obstacles located at the base of the ploughed layer therefore prevented root access to non-tilled layer and caused a ‘shadow effect’ in the non-tilled layers. This effect is probably due to the main vertical direction of roots in these layers.
TL;DR: In this article, the theoretical basis of fine root turnover estimation in forest soils is discussed, in relation to appropriate experimental techniques of measurement, and the correct expression is the sum of significant positive increments of live and dead roots of various diameter categories, to which the transfer of dead roots to organic matter derived from roots, OMDR, has to be added.
Abstract: The theoretical basis of fine root turnover estimation in forest soils is discussed, in relation to appropriate experimental techniques of measurement. After sequential coring, the correct expression is the sum of significant positive increments of live and dead roots of the various diameter categories, to which the transfer of dead roots to organic matter derived from roots, OMDR, has to be added. This should not be confounded with dead root mineralization. The transfer rates should first be estimated in root dimensions and not in weight of dry matter.
TL;DR: Some recent progress in this field is reviewed, particularly at the institute in Rio de Janeiro, concerning specificity of selected Azospirillum strains in the infection of cereal roots and the promotion of responses in the host plants.
Abstract: Over the last few years research in the area of biological nitrogen fixation (BNF) associated with cereals and grasses has become divided into two areas. On the one hand there have been a large number of reports of responses of field-grown plants to inoculation with N2-fixing bacteria, principallyAzospirillum spp. On the other hand there have been several reports of significant contributions of associated BNF to the nutrition of several crops, including wetland rice, sugar cane and some forage grasses. However, where BNF contributions have definitely been established no certain information is available as to the diazotrophic organisms responsible. Furthermore, certain recent reports indicate that, at least in some cases, responses of plants to inoculation withAzospirillum spp. have been shown not to be due to BNF contributions.
TL;DR: In this paper, labelled urea or ammonium nitrate was applied to winter wheat growing on a loamy soil in Northern France, and two applications of fertilizer were given: 50 kg N ha−1 at tillering (early March) and 110 kg N h− 1 at the beginning of stem elongation (mid-April).
Abstract: Labelled urea or ammonium nitrate was applied to winter wheat growing on a loamy soil in Northern France. Two applications of fertilizer were given: 50 kg N ha−1 at tillering (early March) and 110 kg N ha−1 at the beginning of stem elongation (mid-April). The kinetics of urea hydrolysis, nitrification of ammonium and the disappearance of inorganic nitrogen were followed at frequent intervals. Inorganic nitrogen soon disappeared, mainly immobilized by soil microflora and absorbed by the crop. Net immobilization of fertilizer N occured at a very similar rate for urea and ammonium nitrate. Maximum immobilization (16 kg N ha1) was found at harvest for the first dressing and at anthesis for the second dressing (23 kg N ha1). During the nitrification period, the labelled ammonium pool was immobilized two to three times faster than the labelled nitrate pool. No significant net15N remineralization was found during the growth cycle. The actual denitrification and volatilization losses were probably more important than indicated from calculations made by extrapolation of fluxes measured over short intervals. However microbial immobilization was the most important of the processes which compete with plant uptake for nitrogen.
TL;DR: The estimated size of the root system at 8 weeks after planting was not significantly different from the size at silking or harvest, and the largest root:shoot ratio was found in the vegetative stage and decreased throughout the rest of the season.
Abstract: Two methods for estimating the size of the maize (Zea mays l.) root system from soil cores taken in the field were compared. The spatially weighed block method of estimation accounted for variation in root density by using 18 samples per plant which varied in distance from plant and soil depth. This method was compared to an estimation which averaged all of the 18 samples together. Both methods gave surprisingly similar estimates for total root growth. Increased root growth in the surface soil layers, due to tillage and N fertilization, did not impact on the estimation of total root growth. Total root length remained unchanged or increased with N fertilization, while root weight remained the same or decreased. Root mass per length decreased with N fertilization. The estimated size of the root system was used to calculate root:shoot weight ratios. The largest root:shoot ratio was found in the vegetative stage and decreased throughout the rest of the season. In this field experiment, the estimated size of the root system at 8 weeks after planting was not significantly different from the size at silking or harvest. Nitrogen fertilization significantly decreased the root:shoot weight ratio. However, tillage did not significantly change the ratio.
TL;DR: It is suggested that co-inoculation of legumes with antibiotic-producing microorganisms and root-nodule bacteria resistant to those antibiotics is a promising means of promoting nodulation and possibly nitrogen fixation.
Abstract: A study was conducted to determine whether colonization of legume roots and nodulation byRhizobium meliloti andBradyrhizobium japonicum could be enhanced by using inocula containing microorganisms that produce antibiotics suppressing soil or rhizosphere inhabitants but not the root-nodule bacteria. An antibiotic-producing strain of Pseudomonas and one of Bacillus were isolated, and mutants ofR. meliloti andB. japonicum sp. resistant to the antibiotics were used. The colonization of the alfalfa rhizosphere and nodulation byR. meliloti were enhanced by inoculation of soil withPseudomonas sp. in soil initially containing 2.7×105R. meliloti per g. The colonization of soybean roots byB. japonicum was enhanced by inoculating soil with three cell densities ofBacillus sp., and nodulation was stimulated byBacillus sp. added at two cell densities. In some tests, the dry weights of soybeans and seed yield increased as a result of these treatments, and co-inoculation with Bacillus also increased pod formation. Inoculation of seeds withBacillus sp. and the root-nodule bacterium enhanced nodulation of soybeans and alfalfa, but colonization byB. japonicum andR. meliloti was stimulated only during the early period of plant growth.
TL;DR: The results present evidence that the ability of the soil to retain plant-derived N is strong in comparison with the able of the subsequent crop and different loss mechanisms to remove it.
Abstract: Release of N, retention in soil, availability to a subsequent crop and total recovery of N derived from different15N-labelled plant materials decomposing in soil was investigated in two field experiments. In the first experiment five different plant species (white clover, red clover, subterranean clover, field bean and timothy) and in the second subterranean clover of different maturity (2,3 and 4 months old) were buried in mesh bags in the soil and allowed to decompose for 10 and 4 months, respectively. Most of the N released from the decaying plant materials was retained in the soil (27–46% of input). The subsequent crop (barley) took up 6–25% of input. The uptake correlated with the amount of N released from the decomposing material (r=0.936*, I experiment). Similar amounts of subterranean clover N were taken up by barley regardless to whether the material was buried in soil in the previous autumn or just before sowing of the crop. At the end of the experiments, the total recovery of the introduced plant-derived N varied between 89 and 102%. The results present evidence that the ability of the soil to retain plant-derived N is strong in comparison with the ability of the subsequent crop and different loss mechanisms to remove it.
TL;DR: In this paper, a study was conducted to screen 25 rice cultivars (Oryza sativa L.) at low, medium, and high levels of soil P. Positive correlations were found among growth parameters such as plant height, tillers, root and shoot weight, and P content of roots and shoots.
Abstract: Phosphorus deficiency is one of the most growth-limiting factors in acid soils in various parts of the world. The objective of this study was to screen 25 rice cultivars (Oryza sativa L.) at low, medium, and high levels of soil P. Number of tillers, root length, plant height, root dry weight and shoot dry weight were related to tissue P concentrations, P uptake and P-use efficiency. Shoot weight was found to be the plant parameter most sensitive to P deficiency. Significant cultivar differences in P use efficiency were found. Phosphorus use efficiency was higher in roots than shoots and decreased with increasing levels of soil P. Positive correlations were found among growth parameters such as plant height, tillers, root and shoot weight, and P content of roots and shoots. These results indicate selection of rice cultivars for satisfactory performance under low P availability can be carried out using shoot and root dry weight as criteria.
TL;DR: If establishment of the inoculated strain is demonstrated in plants grown in15N-labelled soil, the15N enrichment of the plants will reveal if any observed responses in N yield are due to N2-fixation or increased soil/fertilizer-N uptake.
Abstract: Diazotrophs have been isolated from the rhizosphere or roots of plants by many workers. To recognize a certain diazotroph as the most abundant bacterium at a certain site or as the principal agent responsible for N2-fixation is much more difficult. It is probable that many diazotrophs, including possibly the most efficient ones, have not been identified yet. The use of proper selective media which simulate the environment of the various diazotrophs in situ has led to the discovery of 10 new root-associated diazotrophs, three of them during 1986/1987 (Azospirillum halopraeferans, Herbaspirilium seropedicae and the recently proposed Acetobacter diazotrophicus). The importance of using a variety of carbon substrates in the growth media with pH indicators, and the use of N-free semi-solid media, is discussed. Recognition of plant-bacteria interactions requires, in addition to the identification of the bacteria, the demonstration of effects of the plant on the bacteria and of the bacteria on the plant. Confirmation of the identity of diazotrophs responsible for response of plants to inoculation must be made in experiments with strains labelled with antibiotic resistance or other markers. If establishment of the inoculated strain is demonstrated in plants grown in 15N-labelled soil, the 15N enrichment of the plants will reveal if any observed responses in N yield are due to N2-fixation or increased soil/fertilizer-N uptake.
TL;DR: There was a slow build up of mycorrhizal propagules late in the season irrespective of the treatment in the preceding season, and the effect of crop rotation of native vesicular arbuscular mycorRhizal fungi was studied.
Abstract: The effect of crop rotation of native vesicular arbuscular mycorrhizal fungi was studied. Finger millet was grown as the first season crop in 15 plots. In the second season a mycorhizal host (cowpea) and a non-mycorrhizal host (mustard) were grown in 5 plots each, and the remaining 5 plots were left fallow. In the third season cowpea was grown in all the plots. Leaving the land fallow reduced the mycorrhizal propagules by 40% while growing a non-mycorrhizal host reduced it by 13%. Cowpea grown in the third season coincided with a slow build up of mycorrhizal propagules in soil. There was a slow build up of mycorrhizal propagules late in the season irrespective of the treatment in the preceding season.
TL;DR: In this article, a rapid colourimetric method of determination of nitrate was modified, which eliminated the use of barium sulphate and introduced diazotization of sulphanilamide by the nitrite ion obtained by the reduction of Nitrate and subsequent coupling with N-1-naphthyethelenediamine dihydrochloride.
Abstract: A rapid colourimetric method of determination of nitrate was modified. Proposed modifications eliminated the use of barium sulphate and introduced diazotization of sulphanilamide by the nitrite ion obtained by the reduction of nitrate and subsequent coupling with N-1-naphthyethelenediamine dihydrochloride. Introduction of filtration in place of centrifugation of coloured solution simplified the procedure. Determinations were highly reproducible with coefficient of variation of 2.2 and 2.9% for soil and plant extracts respectively.
TL;DR: In this article, the authors measured calcium, magnesium and potassium dynamics in decomposing litter of three tree species over a two-year period, and compared the relative mobility of all six elements examined in relation to mass loss after two years.
Abstract: Calcium, magnesium and potassium dynamics in decomposing litter of three tree species were measured over a two-year period. The speices studied were flowering dogwood (Cornus florida), red maple (Acer rubrum) and chestnut oak (Quercus prinus). The order of decomposition was:C. florida>A. rubrum>Q. prinus. Calcium concentrations increased following any initial leaching losses. However, there were net releases of Ca from all three litter types since mass loss exceeded the increases in concentration. Net release of Ca by the end of two years from all three species combined was 42% of initial inputs in litterfall. Magnesium concentrations increased in the second year, following decreases due to leaching during the first year inC. florida andA. rubrum litter. Net release of Mg by the end of two years was 58% of initial inputs. Potassium concentrations decreased rapidly and continued to decline throughout the study. Net release of K by the end of two years was 91% of initial inputs. These data on cation dynamics, and similar data on N, S and P dynamics from a previous study, were combined with annual litterfall data to estimate the release of selected nutrients from foliar litter of these tree species at the end of one and two years of decomposition. The relative mobility of all six elements examined in relation to mass loss after two years was; K>Mg>mass>Ca>S>P>N.
TL;DR: Ectomycorrhizal colonization can protect Pinus and Picea seedlings from heavy metal toxicity at low or intermediate soil concentrations of Cd, Cu, Ni, Pb and Zn.
Abstract: Pinus banksiana andPicea glauca inoculated or not with the ectomycorrhizal fungusSuillus luteus were grown in a sandy loam soil containing a range of Cd, Cu, Ni, Pb and Zn concentrations. Ectomycorrhizal colonization rates were significantly reduced on Pinus and Picea seedlings by the heavy metals, particularly Cd and Ni. Needle tissue metal concentrations were lower in ectomycorrhizal seedlings at low soil metal concentrations. However, at higher soil concentrations, heavy metal concentrations of needle tissue were similar in ectomycorrhizal and nonmycorrhizal plants. The growth of nonmycorrhizal seedlings exposed to heavy metals was reduced compared to those inoculated withSuillus luteus. Apparently ectomycorrhizal colonization can protect Pinus and Picea seedlings from heavy metal toxicity at low or intermediate soil concentrations of Cd, Cu, Ni, Pb and Zn.
TL;DR: In this paper, the effects of liquid and solid fertilizers on fine-root development were studied in a 130-year-old Scots pine (Pinus sylvestris L.) stand.
Abstract: The effects of liquid and solid fertilizers on fine-root development were studied in a 130-year-old Scots pine (Pinus sylvestris L.) stand. Ingrowth cores,viz. initially root-free mesh bags with sieved mineral soil taken outside the plots and driven to a depth of 30 cm from the soil surface, were subsequently resampled and the amount of fine roots was estimated.
TL;DR: The rapidity of the responses in P. major ssp pleiosperma and preliminary determinations of the contents of several ions raised the question about the decisive role of the availability of minerals in growth regulation.
Abstract: In Plantago major L. an enormous genetic variability is present for a large number of plant traits (Van Dijk and Van Delden, 1981; Kuiper, 1982, 1983; Kuiper and Smid, 1985). Differences in relative growth rates (RGR) for shoot and roots were observed among inbred lines of P. major. Inbred lines also differed largely in the rate of growth responses, when plants were transferred from a nutrient-rich growth solution (100%) to a 50 times diluted nutrient solution (2%) and vice versa. Quick growth responses in plants of an inbred line belonging to subspecies pleiosperma (Pilger) transferred from a 100% to a 2% solution (100–2% plants) were accompanied by a rapid decrease in shoot to root ratio (S/R). The rapidity of the responses in P. major ssp pleiosperma and preliminary determinations of the contents of several ions raised the question about the decisive role of the availability of minerals in growth regulation.
TL;DR: In this article, the amounts of mineral-nitrogen extracted by 2MKCL and the net amounts of N mineralized (δ Min-N) during a 10-day incubation of field-moist soils, air-dried then rewetted samples, and chloroform-fumigated samples, were measured in a range of 20 topsoils from grasslands.
Abstract: The amounts of mineral-nitrogen (NH4−N+NO3−N) extracted by 2MKCL and the net amounts of N mineralized (δ Min-N) during a 10-day incubation of field-moist soils, air-dried then rewetted samples, and chloroform-fumigated samples, were measured in a range of 20 topsoils from grasslands. Air-drying generally increased extractable-N and the δ Min-N of the remoistened soils, but decreased the Min-N flush after fumigation. The C∶N ratios (CO2−C production: net Min-N production) over 10 days decreased significantly from an average of 25 to 12 after initial air-drying, suggesting that substrates of low C∶N ratio, such as microbial cells, were contributiong to the extra N mineralized after the air-drying treatment. A procedure to quantify the contribution from microbial-N to the increased δ Min-N after air-drying was only partially successful, but indicated a large proportion of this increase was derived from microbial cells killed by desccation.
TL;DR: In this article, a field experiment was conducted using 15N methodology to study the effect of cultivation of faba bean (Vicia faba L), pea (Pisum sativum L.), and barley (Hordeum vulgare L.) on the N status of soil and their residual N effect on two succeeding cereals (sorghum (Sorghus vulga) followed by barley).
Abstract: A field experiment was conducted using15N methodology to study the effect of cultivation of faba bean (Vicia faba L.), pea (Pisum sativum L.) and barley (Hordeum vulgare L.) on the N status of soil and their residual N effect on two succeeding cereals (sorghum (Sorghum vulgare) followed by barley). Faba bean, pea and barley took up 29.6, 34.5 and 53.0 kg N ha−1 from the soil, but returned to soil through roots only 11.3, 10.8 and 5.7 kg N ha−1, respectively. Hence, removal of faba bean, pea and barley straw resulted in a N-balance of about −18, −24, and −47 kg ha−1 respectively. A soil nitrogen conserving effect was observed following the cultivation of faba bean and pea compared to barley which was of the order of 23 and 18 kg N ha−1, respectively. Cultivation of legumes resulted in a significantly higher AN value of the soil compared to barley. However, the AN of the soil following fallow was significantly higher than following legumes, implying that the cultivation of the legumes had depleted the soil less than barley but had not added to the soil N compared to the fallow. The beneficial effect of legume cropping also was reflected in the N yield and dry matter production of the succeeding crops. Cultivation of legumes led to a greater exploitation of soil N by the succeeding crops. Hence, appreciable yield increases observed in the succeeding crops following legumes compared to cereal were due to a N-conserving effect, carry-over of N from the legume residue and to greater uptake of soil N by the succeeding crops when previously cropped to legumes.
TL;DR: Anin situ resin bag technique was used to measure the relative availabilities of N and P along a chronosequence of soils in southern New Mexico, and was compared to two more common indices of nutrient availability.
Abstract: Anin situ resin bag technique was used to measure the relative availabilities of N and P along a chronosequence of soils in southern New Mexico, and was compared to two more common indices of nutrient availability. Accumulations of N and P during 10-week intervals over an 18 month period were separable into wet season (September–January) and dry season (February–August) groups, with wet season values significantly greater than dry season values. Only accumulations during the wet season showed significant differences among sites, thus stressing the role of field water regime in interpreting resin accumulation results. Total mineral N (NO3+NH4) sorbed by resins was significantly correlated to laboratory N mineralization rates. Although accumulation patterns of N and P were similar to patterns of %N and %P in shrub species growing along the chronosequence, these similarities were not statistically significant. A laboratory experiment demonstrated that bicarbonate-form anion resins are preferable to hydroxyl-form resins, as long as standards are made from solutions extracted by resins to account for variable ion recovery efficiencies.