Influence of vegetation on low-molecular-weight carboxylic acids in soil solution—a review

Low-molecular-weight (LMW) carboxylic acids found in soils and soil solutions comprise mainly aliphatic mono-, di- and tricarboxylic acids and substituted benzoic and cinnamic acids. This review compiles current information on the content of LMW carboxylic acids in soil solutions collected by centrifugation and in lysimeters, and soil extracts in relation to type of vegetation, soil type and soil depth. Contents of LMW carboxylic acids are highest in soil solution from the upper soil layers where carbon in LMW carboxylic acids constitutes up to 10% of DOC. The concentrations of aliphatic LMW di-/tricarboxylic acids (oxalic, malonic, malic, succinic, tartaric and citric acid) are usually in the range 0–50 μM with the higher concentrations in soil solutions from meadow, permanent pasture and forest soils as compared to ley and cultivated soils. In contrast, the concentrations of aliphatic LMW monocarboxylic acids (formic, acetic, propionic, butyric, valeric and lactic acid) are commonly in the range 0–1 mM with high concentrations found in soil solutions from both cultivated and forested soils. Especially insence cedar (Calocedrus decurrens (Torr.) Florin), ponderosa pine (Pinus ponderosa Dougl.), Douglas fir (Pseudotsuga menziesii Franco) and Norway spruce (Picea abies (L.) Karst.) seem to cause higher contents of LMW carboxylic acids in soils and soil solutions as compared to other tree species. Soil solution concentrations of substituted benzoic and cinnamic acids are submicromolar for all vegetations, whereas similar amounts in the range 0–800 μmol kg⁻¹ of aliphatic LMW carboxylic acids and substituted benzoic and cinnamic acids are extractable from mineral soils with alkaline and dilute acid extractants. Seasonal variations are observed in soil solutions isolated by centrifugation and soil extracts with highest concentrations in 2–4 months in a period from mid spring to early summer, minimum concentrations around early autumn, and increasing concentrations during autumn.     

Effects of permafrost thawing on vegetation and soil carbon pool losses on the Qinghai–Tibet Plateau,China

Bearing a total organic carbon (TOC) content of 9.3–10.7 kg C/m², alpine grassland soils of the Qinghai–Tibet plateau's permafrost region bear a greater organic carbon pool than do grassland soils in other regions of China or than tropical savannah soils. The easily released light fraction organic carbon (LFOC) accounts for 34–54% of the TOC and is particularly enriched in the topsoil (0–0.10 m). The LFOC in the organic carbon pool of alpine cold meadow and alpine cold steppe soils decreased at exponential and quadratic rates, respectively, as the vegetative cover decreased. When the vegetative cover of alpine cold meadows decreased from > 80 dm²/m² to 60 dm²/m², the topsoil TOC and LFOC dropped by 20.4% and 38.4%, respectively. Similarly, when the vegetative cover of alpine cold meadow decreased from 50 dm²/m² to 30 dm²/m² and < 15 dm²/m², the topsoil LFOC content dropped by 60% and 86.7%, respectively. Under climatic warming, the degradation of permafrost and vegetation have resulted in serious soil organic carbon (SOC) loss from the carbon pool. Land cover changes that occurred between 1986 and 2000 are estimated to have resulted in a 1.8 Gg C (120 Mg C/yr) loss in SOC, and a concomitant 65% decrease in the LFOC, in the 0–0.30 m soil layer in the Qinghai–Tibet plateau's permafrost regions. Since the region's ecosystems are quite sensitive to global climate changes, if global warming persists, alpine cold grassland ecosystems are expected to further degrade. Hence, the influence of global climatic change on soil carbon emissions from alpine grasslands should receive more attention.     

Studies on microörganisms and their activities in soil Part. 2. Virgin and cultivated soil of the same origin

The nature of soil is modified differently depending upon the artificial condition such as its utilization or management. It is therefore expected that the microbiological characteristic of soil is changed also. Greaves¹⁾ and Williams²⁾ reported that the reclamation of virgin soil brought about a change of bacterial count. Suzuki et al³⁾ observed that the kind of fungi differed between a virgin and a cultivated soil and that the vegetative mycelium was numerous in the former than in the latter. On the other hand, according to W aksman and Starkey⁴⁾, the bacterial count differed depending upon the fertility of soil. Singh⁵⁾ reported also that the number of fungi and actinomycetes was higher in a fertile than in an infertile soil. Lochhead⁶⁾, and Lochhead and Chasen studied the bacterial flora of a fertile (long-continued application of manure) and an infertile (no fertilizer for many years) soil and found that a certain difference could be observed when morphological, physiological and nutritional classification are tried.     

PM—Power and Machinery: Development of a Slow Active Suspension for Stabilizing the Roll of Spray Booms,Part 2: Controller Design

To prevent local under- or over-application of chemicals, a spray boom must be kept parallel to the soil. On a slanted field, the operator, driving a sprayer equipped with a passive boom suspension, has to turn the boom manually in a skewed position. This paper presents the development of a slow active controller to do this automatically and to add damping to the suspension. A controller, designed for a cable suspension, captures the signals of two ultrasonic sensors, measuring the distance between the boom and the soil, and activates a low-power electrical DC motor which positions the boom automatically. Different control strategies have been tried out in simulation and in a laboratory experiment on a six-post electro-hydraulic shaking table. The best controller was implemented on a real spraying machine and validated under field conditions.     

Studies on soil fumigation—I: Effects on ammonium,nitrate and phosphate in soil and on the growth,nutrition and yield of wheat

Fumigation of field soil with chloropicrin alone or followed by methyl bromide, each at 220Kg·ha^?1, released 20–30 parts/10⁶ NH⁺₄-N which persisted for 75 days; such fumigation also doubled the amount of bicarbonate-extractable phosphate 28 days after fumigation. Soil fumigation increased both the vegetative and grain yields as well as increasing the content of N in the grain and the content of K and Cl in the tops at ear emergence. Root growth and the phosphate uptake activity of the roots were increased by soil fumigation.     

The impact of vegetation and soil on runoff regulation in headwater streams on the east Qinghai–Tibet Plateau,China

Vegetation type is one of many factors that affect watershed hydrology and is an especially important influence on surface hydrological processes. Canopy and ground cover vegetation provide a natural cushion against the impact energy of rainfall in headwater portions of a stream basin, increasing water filtration into the soil and reducing surface runoff, but effects of different vegetation types are not fully understood. We sought to evaluate the capacity of different vegetation communities to regulate surface runoff in an alpine landscape. We collected water samples for stable hydrogen and oxygen isotopic analyses from precipitation, throughfall, soils, streams, and rivers and compared their isotopic signatures. Results indicated that different vegetation types had different capacities for water conservation. Forested vegetation types were best able to regulate surface runoff. Land use changes have dramatically affected water conservation in the study area in the past several decades; if forested land cover existed at the levels present in 1986 or 1974, the ability of the watershed to intercept surface runoff would increase by about 7% and 3%, respectively, over its capacity in 2000.     

Relationship between archaeal community structure and vegetation type in a fen on the Qinghai–Tibetan Plateau

The contribution of different methanogenic precursors probably depends on vegetation in the cold Zoige peatlands. This study was carried out to elucidate the relationship between archaeal community dynamics and vegetation type over growing season. Soil samples were collected monthly during the growing season from two vegetation types (communities dominated by Carex muliensis vs. Eleocharis valleculosa) on an open fen at the Wetland National Nature Reserve of the Zoige peatlands on the Qinghai–Tibetan Plateau. Archaeal community structure was determined with terminal restriction fragment length polymorphism analysis of the 16S rRNA gene fragment. Methanosarcinales, Methanosaeta, Methanomicrobiales, Methanobacteriales, uncultured RC-II, and uncultured Crenarchaeota were detected in both vegetation types. The results suggested that seasonal change affects the activity rather than the structure of the archaeal community over the growing season. Ordination analyses indicated that archaeal community composition was related to vegetation type and plant height.     

Studies on soil fumigation—II: Effects on bacteria

In a South Australian wheat-field soil the viable counts of “total” aerobic bacteria and of fluorescent pseudomonads were initially greatly depressed by fumigation with 220 kg·ha^?1 chloropicrin (CP) or with a combined application of 220 kg·ha^?1 of chloropicrin and 220 kg·ha^?1 methyl bromide (F). Bacterial numbers rose sharply within 10 days of the completion of fumigation. For a further 14 days the fluorescent pseudomonads formed the major part of the aerobic bacterial population counted and over 5 months later their numbers in F-treated soil remained about 10 times higher than in untreated soil. Numbers of aerobic spore-formers rose more slowly after CP or F treatment. but then remained significantly higher over the 159 days of the trial. Fumigation with 220 kg·ha^?1 of methyl bromide alone (MB) had little effect on soil bacterial numbers.A check of random isolates revealed a predominance of Gram-negative organisms in soil treated with CP, this dominance decreasing with time, whereas MB treatment did not result in any detectable change.Fluorescent pseudomonads from rhizospheres of wheat plants in soil fumigated with CP contained smaller proportions of strains antagonistic in vitro to Gaeumannomyces graminis var. tritici than isolates from MB-treated soil or from untreated soil.     

Studies on soil fumigation—IV: Effects on fungi

The effect of soil fumigation with a chloropicrin-methyl bromide mixture(1:1) at 440 kg·ha^?1 on the fungal flora of a wheat-field has been investigated. Recolonization of fumigated soil and the occurrence of fungi on roots of wheat growing in fumigated and untreated soil were also followed. Very few fungi survived in fumigated soil that had been covered with polythene sheeting, but in uncovered fumigated soil some fungi survived especially at or near the soil surface.Study of recolonization of covered fumigated soil showed that some fungi, notably species of Chaetomium and Mortierella, appeared to survive fumigation and then increase in number, but many of the fungi recolonizing surface soil (2.5 cm), Alternaria, Stemphylium, Mucor, Cladosporium, Epicoccum), appeared to have come from the air. Recolonization of surface soil was not uniform; high counts were often due to the spores of one or a few fungi and samples collected a few cm apart might show different fungi in high number. In subsurface soil (5–22.5 cm) recolonization was much slower and even 117 days after fumigation the number of colonies and species of fungi was low compared with untreated soil.The common fungi on roots of plants grown in uncovered fumigated or untreated soil were very similar though initially there were fewer fungi on roots from fumigated soil. The main differences recorded were that Chaetomium species were more frequent on roots from fumigated soil and that. in general, Cylindrocarpon destruetans, Embellisia chlamydospora, species of Pythium and Rhizoctonia, and Gaeumannomyces graminis were more common on roots in untreated soil.     

P ‐ Mo interactions on the yield and nodulation of white clover grown on limed‐lignite overburden materials

Abstract

A greenhouse study using lignite overburden surface soil from a lignite mine in northwest Louisiana was conducted to determine the yield response and nodulation of inoculated and non‐inoculated white clover (Trifolium repens L.) to P (0, 40, and 80 kg/ha) and Mo (0, 90, and 180 g/ha) fertilization. Results manifested a highly significant response of inoculated white clover to a single application of P and Mo. Application of P at the rate of 40 and 80 kg/ha increased the dry matter yield (DMY) of white clover by 164% and 154%, while Mo fertilization at the rate of 90 and 180 g/ha increased the dry matter yield (DMY) by 21% and 37%, respectively, over the control. The yield of white clover was also significantly affected by Rhizobium inoculation. Yield was increased from 2.1 to 2.5 Mg/ha which is equivalent to a 19% yield improvement over the non‐inoculated plants.

Nodule formation (NF), likewise, was significantly favored by P and Mo fertilization. Results also revealed that Rhizobium inoculation had remarkably improved the nodule count of white clover. Nodule count was increased from 0.4 to 5.5 or 1375% improvement between the inoculated and non‐inoculated plants. The non‐inoculated white clover also responded significantly to P fertilization, but not to Mo addition. Nodule formation, however, was not observed from the non‐inoculated white clover except at the highest rate of P and Mo additions. Increasing P supply significantly increased the concentrations of P, S, Na, and Ca but decreased the concentration of K in the clover. Mo additions resulted in increased concentrations of P and Ca. No significant P‐Mo interaction effects were observed on the nutrient concentration of white clover.     

SW—Soil and Water: Construction of an Artificial Perched Watertable,Part 1: Air Permeability of Soils and Aspects of Soil Failure

The annual precipitation in the Three-river Plain of the People's Republic of China is only 500–600 mm and, besides, the rainfall is uneven; 60–70% of the annual precipitation occurs in July and August and there is almost no rainfall in the winter and spring seasons. Experiments were conducted to form the artificial perched watertable where the runoff caused in summer could preferably be held, by injecting high-pressure air into the soil. A horizontal soil cavity is required, so this paper deals with the determination of the air permeability of soils and the difference in the soil failure mechanisms due to the different air permeabilities.The results show that the air permeability k of 10 m² s⁻¹ MPa⁻¹ defined the situation between the fluidization and the V-shaped soil failure. When the value of k was from 10 to 0·1 m² s⁻¹ MPa⁻¹, the V-shaped soil failure took place and when it was less than 0·1 m² s⁻¹ MPa⁻¹, the soil cavity production took place. In order to produce the soil cavity in the B horizon of the planosol or Cg1 horizon of the meadow soil by air injection, the value of k for these soils should be less than 0·1 m² s⁻¹ MPa⁻¹ and the soil water content of these soils should be more than 30% d.b.     

Studies on soil fumigation—III: Effects on enzyme activities,bacterial numbers and extractable ninhydrin reactive compounds

Fumigation of a field soil with chloropicrin and methyl bromide, either singly or in combination, differentially decreased soil enzyme activities and viable bacterial numbers and increased the amounts of ninhydrin reactive compounds extractable with acidified Tris buffer. Chloropicrin treatment was more effective than methyl bromide.The rates of hydrolysis of both an amide and a peptide derivative were decreased by chloropicrin treatment and remained relatively low despite changes in activities over 325 days. By contrast, caseinase activity initially was decreased by both chloropicrin and methyl bromide fumigation, but activities of the fumigated soils recovered to exceed those of untreated soils. Thereafter, caseinase activities of fumigated and untreated soils exhibited relatively large fluctuations, which were partly associated with seasonal drying of the soils in the field.Chloropicrin but not methyl bromide fumigation markedly depressed the viable bacterial populations, which subsequently increased to be above those of the untreated soils. There was no consistent relationship between the release of ninhydrin reactive compounds following fumigation and changes in bacterial numbers or changes in enzyme activity. Autolytic reactions are probably important in the early stages of amino-nitrogen release in fumigated soils. Net gains in caseinase activity may be partly due to the production de novo of extracellular proteases by microorganisms or to the release of intracellular proteases from killed cells.     

PH—Postharvest Technology: Diffusive Drying Kinetics in Wheat,Part 2: applying the Simplified Analytical Solution to Experimental Data

Reanalysis of the drying background in wheat showed that analytical solutions may be employed in this grain to estimate diffusion coefficients by using the simplified equation for short times instead of the time-consuming series. Sixteen thin-layer drying curves of hard wheat were measured (airflow ≈ 0·3 kg m⁻²s⁻¹) covering four air temperatures (35–70°C) at each of four initial moisture content levels (0·189–0·269 decimal, d.b.). Experimental curves of the moisture ratio versus time grouped by initial moisture content showed the expected strong accelerating effect of temperature on drying rate. Besides, when the same curves were grouped by temperature, the moisture ratios corresponding to higher initial moisture contents fell, after some time, consistently faster, showing that the diffusion coefficient should increase somehow with water concentration. The short time simplified diffusive equation fitted each curve very well, with values of the coefficient of determination above 0·99. Values of the diffusion coefficient for the whole kernel ranged from 1·4×10⁻¹¹to 7·1×10⁻¹¹m⁻²s⁻¹, presenting the classical Arrhenius temperature dependency (activation energy ≈ 27·0 kJ mol⁻¹), but with a pre-exponential factor that depends linearly on initial moisture content. This diffusive kinetics is expected to be useful for fast and accurate dryer simulation.     

Cationic antimicrobial (ε-polylysine)-anionic polysaccharide (pectin) interactions: influence of polymer charge on physical stability and antimicrobial efficacy

The cationic biopolymer ε-polylysine (ε-PL) is a potent food-grade antimicrobial that is highly effective against a range of food pathogens and spoilage organisms. In compositionally complex systems such as foods and beverages, cationic ε-PL molecules may associate with anionic substances, leading to increased turbidity, sediment formation, and reduced antimicrobial activity. This study therefore characterized the interactions between cationic ε-PL and anionic pectins with different degrees of esterification (DE) and then investigated the influence of these interactions on the antimicrobial efficacy of ε-PL. The nature of the interactions was characterized using isothermal titration calorimetry (ITC), microelectrophoresis (ME), and turbidity measurements. High (DE 61%), medium (DE 51%), and low (DE 42%) methoxyl pectins interacted with ε-PL molecules through electrostatic forces, forming either soluble or insoluble complexes with various electrical charges, depending on the relative mass ratio of pectin and ε-PL. The interaction of pectin with ε-PL increased as the negative charge density on the pectin molecules increased, that is, with decreasing DE. The antimicrobial efficacy of ε-PL against two acid-resistant spoilage yeasts (Zygosaccharomyces bailii and Saccharomyces cerevisiae) decreased progressively in the presence of increasing levels of all three pectins. Nevertheless, the low DE pectin decreased the antimicrobial efficacy of ε-PL much more dramatically, likely due to strong electrostatic binding of ε-PL onto low DE pectin molecules reducing its interaction with anionic microbe surfaces. This study provides knowledge that will facilitate the rational application of ε-PL as an antimicrobial in complex food systems.     

AE—Automation and Emerging Technologies: Fungal Spore Detection on Tomatoes using Spectral Fourier Signatures

Fusarium oxysporum was detected on the majority of the tomato plantations in the state of Sinaloa, Mexico, reducing yields to 50%. Fusarium rot and Rhizopus rot appeared in storage rooms producing high postharvest losses. Actually, it takes a day to determine whether the sample is infected, by isolating fungal spores on nutrient agar plates. Laboratory equipment capable of detecting spores quickly and with high sensitivity is required in packing houses to increase tomato quality and reduce postharvest losses. Visible and near infrared (NIR) spectra were obtained before and after inoculating tomatoes with Fusarium oxysporum and Rhizopus stolonifer conidia. Spectral signatures in the frequency domain were analysed using discriminant analysis and models capable of detecting spore-free and inoculated tomatoes were obtained. Tomatoes containing Fusarium oxysporum and Rhizopus stolonifer conidia on their surfaces were detected with high success rates and could also be distinguished accurately.     

Regeneration of vegetation on Santa Fé and Pinta islands,Galápagos,after the eradication of goats

Analysis of 13 permanent sample plots (quadrats) in the Galápagos showed that recent elimination or reduction of the populations of feral goats has been followed by a regeneration of the vegetation. On Santa Fé, where the vegetation is dry season deciduous, goats were eradicated in 1971; since then the density of woody plants in the quadrats has increased. However, only about half the woody species present participate in the recolinisation, and some of the remaining species appear to have been reduced so much in number that re-establishment will be very slow or even impossible. On Pinta island about 40 000 feral goats were shot during the period 1971–1977 and it is estimated that only a few thousand are left. In the arial lowlands a rapid regeneration is under way: the density and number of woody plant species occurring in the quadrats is increasing. Almost all species of woody plants appear to have survived in sufficient numbers to enable recolonisation of the area as soon as the grazing pressure is diminished. Some of the species seem to increase in abundance by means of rapid growth and maturity, subsequent large seed production, and rapid establishment of seedlings. In the evergreen vegetation types of the humid highlands of Pinta a rapid regeneration is also taking place, but here much probably takes place as regrowth from old stems and rhizomes. Both the density and number of woody plant species is increasing, and at the same time the herb cover is changing into more fern-rich communities.     

Regional chemical characteristics of lakes in North America: Part I — Eastern Canada

Data defining the major ion chemistry of lakes located in eastern Canada have been compiled for the purpose of evaluating the current status of surface water quality in relation to acidic deposition. A companion paper for lakes in the eastern United States (i.e. Part II, Linthurst et al., 1986) has been prepared also. Data sources in Canada included the National Inventory Survey, the Ontario Lake Sensitivity data set, and the National Aquatic Data base which provided an overall data base of approximately 5700 lakes. Only recently collected data (largely 1980 or later) were used in the analysis. Frequency distribution statistics were obtained for pH, acid neutralizing capacity (ANC), SO₄ and organic anion (A^?) concentrations. Acidic and low ANC waters in eastern Canada occur in a pattern explained by a combination of biogeochemical factors and atmospheric deposition. Nova Scotia contained the highest proportion of acidic and ultralow ANC lakes of any region surveyed in eastern North America; since this region receives approximately 20 kg.ha^?1.yr^?1 wet SO₄ deposition, the proposed target loading may be too high to protect the highly sensitive waters of Maritime Canada. Compared to the rest of eastern Canada, lakes in Ontario have relatively high ANCs due to the influence of CaCO₃ contained in the glacial till of the area. Variation in the SO₄ concentration of lakes approximately follows expected gradients in wet SO₄ deposition. Naturally occurring organic acids do not play a dominating role in the acidification of eastern Canadian lakes.     

PM—Power and Machinery: Development of a Slow Active Suspension for Stabilizing the Roll of Spray Booms,Part 1: Hybrid Modelling

In this paper, a hybrid model of a spray boom with cable suspension is developed. It combines an analytical modelling procedure with identification techniques to cope with the limited power in the excitation actuator. The analytical model was used to optimize the passive boom suspension, while the identification part is the first step in the design of a slow active suspension.