Zinc fractions and availability to soybeans in representative soils of Northeast China

Purpose  

Limited information exists about the zinc (Zn) status of major soils in northeast China, and their ability to supply Zn to soybeans. This study aims to establish the critical concentrations of Zn in soil for plant growth, to characterize the Zn forms in soil, to correlate the concentration of various Zn forms with Zn uptake by soybeans, and to identify the most effective means of Zn application.     

Use of partition and redistribution indexes for heavy metal soil distribution after contamination with a multi-element solution

Purpose  

Tessier's sequential extraction method is usually used to study metal parting among different phases in soils. The main objective of this study was to determine the redistribution of trace metals which were added simultaneously to a sandy loam soil by use of the fractional distribution and reduced partition indexes and the risk of assessment code (RAC).     

Model organic compounds differ in their effects on pH changes of two soils differing in initial pH

The mechanisms by which organic materials affect soil pH are not fully understood. This study for the first time compared the short-term effect of various model organic compounds on pH change of two soils differing in initial pH (Podosol of pH 4.4 and Tenosol of pH 6.1). Eight organic compounds, representing common compounds in plant residues, were selected based on the number and type of chemical functional groups. The addition of organic acids (acetic, malic, citric, and benzoic acid) reduced soil pH immediately due to H⁺ dissociation. The magnitude of pH decrease depended on the rate of application, degree of dissociation of the acids, and initial soil pH. During a subsequent incubation, pH was slowly restored as these compounds were decomposed. The degree to which pH was restored was reduced with increasing addition rate. The production of H⁺ ions was increased with increasing rate of acid addition and decreased over time. When potassium citrate (organic anion) was added, soil pH increased due to H⁺ consumption upon decomposition. Compounds with amine groups (glucosamine hydrochloride) and less easily decomposable compounds (phenol) did not significantly alter pH during 16-day shaking. Changes in pH after glucose addition were relatively small compared with other compounds and were not expected because hydroxyl chemical groups of glucose are neutral. The present study demonstrated that the addition of model organic compounds to soil caused soil pH to increase, decrease, or remains unaffected. The extent and direction of pH change was dependent on the chemical functional group, addition rate, decomposition, and the initial soil pH.     

Fungal degradation of chlorpyrifos by <Emphasis Type="Italic">Acremonium</Emphasis> sp. strain (GFRC-1) isolated from a laboratory-enriched red agricultural soil

The organophosphorus insecticide, chlorpyrifos, has been widely applied in agriculture; in veterinary, against household pests; and in subterranean termite control. Due to its slow rate of degradation in soil, it can persist for extended periods in soil with a significant threat to environment and public health. The mixed and pure fungi were isolated from three soils by enrichment technique. The enriched mixed fungal cultures were capable of biodegrading chlorpyrifos (300 mg L⁻¹) when cultivated in Czapek Dox medium. The identified pure fungal strain, Acremonium sp., utilized chlorpyrifos as a source of carbon and nitrogen. The highest chlorpyrifos degradation (83.9%) by Acremonium sp. strain GFRC-1 was found when cultivated in the nutrient medium with full nutrients. Desdiethyl chlorpyrifos was detected as a major biodegradation product of chlorpyrifos. The isolated fungal strain will be used for developing bioremediation strategy for chlorpyrifos-polluted soils.     

Genetic differentiation and diversity of phenotypic characters in Chinese wild soybean (<Emphasis Type="Italic">Glycine soja</Emphasis> Sieb. et Zucc.) revealed by nuclear SSR markers and the implication for intraspecies phylogenic relationship of characters

Genetic diversity is reduced from wild soybean to cultivars and from landraces to modern varieties. However, intraspecies genetic diversity loss between characters or phenotypes also existed in wild soybean. We revealed the phylogenic relationship of character types in Chinese wild soybean using 42 SSR markers. We conjectured that white flower, no-seed bloom, grey pubescence, and four seed coat colours were evolutionarily acquired phenotypes. There were a small decrease (∆H = 0.1–6.46%) of gene diversity and a moderate reduction (∆Na = 10.81–53.54%) of number of alleles but a violent loss (80.74–98.59%) of unique alleles in the acquired phenotypes. Our results seemed to suggest that ovoid and elliptic leaves were differentiated at the earliest and subsequently lanceolate leaf appeared before the domestication of soybeans within wild soybean, and that G. gracilis type was another earliest type, maybe emerged since the appearance of soybeans or it was concomitant with the domestication of soybean.     

Soil pH controls nitrification and carbon substrate utilization more than urea or charcoal in some highly acidic soils

Understanding the mechanism and key controlling factors of nitrification in highly acidic soils is important from both ecological and environmental perspectives. Many acid soils are also characterized by vegetation that produces polyphenolic and terpene compounds that inhibit microbial activity. We investigated the potentially ameliorative effects of lime, charcoal, and urea additions on soil nitrification and carbon substrate utilization (using the MicroResp method). Four soils were studied from widely different environments but with similar pH and inputs of phytochemicals to determine the relative effects of these potentially controlling factors. The addition of charcoal had no significant effect on net nitrification, but charcoal significantly increased soil basal respiration and altered C substrate utilization in the two Scottish soils. Urea greatly increased nitrification in both the Chinese soils, but there was no effect of urea on nitrification in the two Scottish soils. Lime application increased nitrification in all the soils except for the Chinese mixed forest soil. Multivariate analysis of the C source utilization data revealed that lime altered C substrate utilization more than urea or charcoal in these highly acidic soils. Our results suggest that acid-tolerant nitrifiers do exist in these soils and have potential for high activity, and pH (lime addition) and N-substrate (urea) most often increased nitrification. However, no single factor controlled nitrification in every soil, suggesting an interaction between abiotic and nitrifier community composition as a result of land use and soil type interactions.     

N<Subscript>2</Subscript>-fixation along a gradient of long-term disturbance in tropical mangroves bordering the gulf of Mexico

Microbial processes are key elements in determining the productivity of mangroves, and reductions in these processes reflect the loss of microbial biodiversity and function due to fabricated disturbances. Because nitrogen is a major limiting nutrient for the productivity of these ecosystems, the goal of this study was to determine profiles of inorganic nitrogen combined with several environmental parameters, all in relation to the degree of long-term hydraulic impairment of a tropical, monospecific black mangrove (Avicennia germinans) forest that showed degradation ranging from total loss of mangrove cover to no disturbance. N₂-fixation, oxygen levels, and nitrite contents decreased significantly with the severity of the disturbance, and almost null levels were reached in the completely degraded zone, whereas salinity achieved very high values. Concomitantly, total N, ammonium, and P contents and ammonia volatilization increased significantly. Pore-water temperature and pH increased moderately. Other soil physical properties (sand, silt, clay, organic matter, and total C), which varied among the sampling sites, were not correlated with the level of disturbance. Principal component analyses, including environmental and biological parameters, suggested that the most significant finding was the considerable loss of N₂-fixation with increasing impairment, which was concomitant with significant increases in volatilization of ammonia and salinity. The results show that microbial N-cycling processes are highly sensitive to salinity and to man-made disturbances that modify the water level and flow.