The effect of grass maturing and root decay on N2O production in soil

The N₂O flux from the surface of grass-covered pots was only significant following grass maturing. Removal of the above-ground plant material resulted in an immediate and long-lasting increase in N₂O production in the soil. The results suggest that easily available organic matter from the roots stimulates the denitrification when the plants are damaged. Grass cutting might therefore result in a marked nitrogen loss through denitrification. The quantitative effect was equal in soil with and without succinate added. The size of the anaerobic zone around the roots is therefore sufficient to allow for denitrification activity mediated by increased organic matter availability because of plant cutting.     

The effect of lime on phosphorus adsorption and barley growth in three acid soils

For three acid soils from Santa Catarina, Brazil, lime application and time of incubation with lime had little effect on the adsorption of added phosphorus. In two soils with high contents of exchangeable aluminium, solution P and isotopically exchangeable P were decreased by incubating with lime for 1 month: phosphorus was probably adsorbing on freshly precipitated aluminium hydrous oxides. In one soil with less exchangeable aluminium, P in solution was increased by liming. After 23 months lime increased solution and exchangeable P possibly due to crystallization of aluminium hydrous oxides reducing the number of sites for P adsorption. All these changes were however small. In a pot experiment, lime and phosphorus markedly increased barley shoot and root dry matter and P uptake. Although liming reduced P availability measured by solution P, isotopically exchangeable P and resin extractable P, it increased phosphorus uptake by reducing aluminium toxicity and promoting better root growth. The soil aluminium saturation was reduced by liming, but the concentration of aluminium in roots changed only slightly. The roots accumulated aluminium without apparently being damaged.     

Effects of ethylene oxide on soil microbial content and some soil chemical characteristics

The effects of ethylene oxide (EtO) on survival of soil microflora and on selected chemical properties of a sandy-loam soil were examined. Soil sterilization was achieved after 8 hours exposure to EtO. Ethylene oxide treatment increased soil pH and organic matter content. Extractable Mn and Fe slightly increased whereas P content decreased. Total N was not affected by the treatment.     

A study of nodulation and nitrogen fixation of alder on the purplish soils in China

Summary The alder has a perennial nodule cluster. The nodule amount on the roots increases with tree age. The N₂-fixing activity of nodules decreases with nodule age. Purple coloured soils with various soil pHs and CaCO₃ contents are, in the main, the ones which influence nodulation and N₂-fixing. Higher N₂-fixing capacity existed in the neutral and low calcium soils. High calcium soils and acid soils can restrain nodulation and the N₂-fixing rate significantly. On the slope, where calcarous light loams are found, the annual nitrogen fixation capacity of alder and cypress mixed plantations, less than 10 years old, is 16 or 17 kg/ha yr, but in the valley, a pure alder plantation can reach 40 kg/ha yr.     

Growth measurements of terrestrial microbial species by a continuous-flow technique

A continuous nutrient flow system has been developed to measure microbial activity in soil with various concentrations of added substrate. The system consists of a thin soil layer through which substrate was added continuously over periods up to 4.5 days. Substrate utilization was determined by effluent analysis. Respiration was measured manually by injecting a sample into a gas chromatograph or automatically by coupling the growth chamber to a computer-controlled gas sampling valve. This permitted respiratory CO₂ to be measured by the gas chromatograph at intervals selected by the investigator. Software controlling the valve and gas chromatograph not only automated gas phase sampling, but also provided a scan of CO₂ evolution and a preliminary data summary. This included the date and time of sample, peak height, and percent CO₂ in the gas phase. Data for growth on glucose using a microbial population native to a California annual grassland soil demonstrated that the direct cell count and respiratory techniques for biomass estimation give comparable results. This procedure provides the potential for detailed analyses of substrate utilization in studies of the growth and maintenance of soil microorganisms.     

Influence of various soil factors on the effects of ferulic acid on leaf expansion of cucumber seedlings

Summary Cucumber seedlings were grown in a Portsmouth soil-sand system to study how varying soil clay and organic matter content might modify cucumber seedling response to ferulic acid, a reported allelopathic agent. Leaf area expansion of cucumber seedlings, soil respiration, and soil solution concentrations of ferulic acid were monitored. Leaf area, mean absolute rates of leaf expansion, and shoot dry weight of cucumber seedlings were significantly reduced by ferulic acid concentrations ranging from 10 to 70 μg/g dry soil. Ferulic acid was applied every other day, since it rapidly disappeared from soil solution as a result of retention by soil particles, utilization by microbes and/or uptake by roots. The amount of ferulic acid retained (i.e., adsorbed, polymerized,etc.) by soil particles appeared to be secondary to microbial utilization and/or uptake by roots. Varying clay (5.3 to 9.8 g/cup) and organic matter (2.0 to 0.04g/cup) contents of the soil appeared to have little impact on the disappearance of ferulic acid from soil solution under “ideal” growth conditions for cucumber seedlings unless larger amounts of ferulic acid were added to the soil; in this case 200 μg/g. The addition of ferulic acid to the soil materials substantially increased the activity of the soil microbes. This latter conclusion is based on recovery of ferulic acid from soil solution and soil respiration measurements. Paper No. 10347 of the Journal Series of the North Carolina Agricultural Research Service, Raleigh, N C 27695-7601. The use of trade names in this publication does not imply endorsement by the North Carolina Agricultural Research Service of the product named, nor criticism of similar ones not mentioned.     

Prediction of heavy-metal concentrations in mature plants by chemical analysis of seedlings

Five plant species were cultivated on a soil from the Neckar alluvial fan near Heidelberg (FRG) polluted by the emissions of a cement plant. Thallium, cadmium and lead concentrations in seedlings and mature plants were determined by atomic absorption analysis. AdditionallyBrassica napus L.napus was grown on soils containing 5 different concentrations of heavy metals, achieved by mixing two similar soils, from the same area but with different metal concentrations. Thallium and cadmium were shown to be taken up by roots whilst lead which was also absorbed, was deposited mainly on the plant surface. However during cultivation in the winter months, a remarkable deposit of lead via the roots was found. Thallium in the soil from a anthrorogen source was more available to plants than thallium of geological origin. During the lifetime of a plant concentrations of thallium and cadmium were always highest in the seedling. The decrease in metal concentration with maturity depended on the plant species and the element, but was not a function of the metal concentration in the soil.     

The organic content of the surficial sediment: a method for the study of ecosystems development in abandoned river channels

To characterise different abandoned river channels, a simple index of the surface sediment was developed i.e. the content of organic matter (expressed as C × N) plotted in relation to that of CaCO₃. The age of the channels studied ranges from 20 to 300 years. Some of them still contain water; others are silted up. Two types are distinguished. The ecosystems of the first one are closed and show a slow rate of development governed by autogenous processes. Those of the second type are more open and show a fast rate of development mainly controlled by allogenous processes. These distinctions are used in a diagrammatic model of the dynamics of Rhône River alluvial plain to be used in fundamental or applied future research.     

Exogenous inorganic carbon sources for photosynthesis in seawater by members of the Fucales and the Laminariales (Phaeophyta): ecological and taxonomic implications

Summary Characteristics of inorganic carbon assimilation by photosynthesis in seawater were investigated in six species of the Fucales (five Fucaceae, one Cystoseiraceae) and four species of the Laminariales (three Laminariaceae, one Alariaceae) from Arbroath, Scotland. All of the algae tested could photosynthesise faster at high external pH values than the uncatalysed conversion of HCO ₃ ^- to CO₂ can occur, i.e. can use external HCO ₃ ^- . They all had detectable extracellular carbonic anhydrase activity, suggesting that HCO ₃ ^- use could involve catalysis of external CO₂ production, a view supported to some extent by experiments with an inhibitor of carbonic anhydrase. All of the algae tested had CO₂ compensation concentrations at pH 8 which were lower than would be expected from diffusive entry of CO₂ supplying RUBISCO as the initial carboxylase, consistent with the operation of energized entry of HCO ₃ ^- and / or CO₂ acting as a CO₂ concentrating mechanism. Quantitative differences among the algae examined were noted with respect to characteristics of inorganic C assimilation. The most obvious distinction was between the eulittoral Fucaceae, which are emersed for part of, or most of, the tidal cycle, and the other three families (Cystoseiraceae, Laminariaceae, Alariaceae) whose representatives are essentially continually submersed. The Fucaceae examined are able to photosynthesise at high pH values, and have lower CO₂ compensation concentrations, and lower K_1/2 values for inorganic C use in photosynthesis, at pH 8, than the other algae tested. Furthermore, the Fucaceae are essentially saturated with inorganic C for photosynthesis at the normal seawater concentration at pH 8 and 10°C. These characteristics are consistent with the dominant role of a CO₂ concentrating mechanism in CO₂ acquisition by these plants. Other species tested have characteristcs which suggest a less effective HCO ₃ ^- use and CO₂ concentrating mechanism, with the Laminariaceae being the least effective; unlike the Fucaceae, photosynthesis by these algae is not saturated with inorganic C in normal seawater. Taxonomic and ecological implications of these results are considered in relation to related data in the literature.     

The response of stomata to CO2 relates to its effect on respiration and ATP level

External ATP enhanced stomatal opening of Commelina communis L. differently from EDTA. ATP was more effective in opening stomata than EDTA, when both were applied in amounts yielding equivalent free Ca²⁺ concentration. The stimulation by ATP depended upon its de-phosphorylation and was not due to the P₁ released. Hence an energetical contribution of external ATP appears possible. Increase in CO₂ concentration increased the stimulation of stomatal opening by ATP and diminished the internal ATP level, ATP/(ADP+AMP) ratio and respiration rate.