Mineral cycling in a tropical palm forest

Nutrient cycling and biomass characteristics of a tropical palm forest dominated byOrbignya cohune were found to be different from thsoe of hardwood dominated forests. The cohune palm forest had a high proportion of biomass in leaves (5%), a reduced sapling layer, a large amount of standing forest litter and an exceptionally low decomposition rate factor (0.1 year^–1). Mineral concentrations in palm leaves were generally lower than in hardwood species with the exception of Na, which was exceptionally high inOrbignya cohune. Biomass was estimated at 226 tons ha^–1 containing 1173 kg ha^–1 N; 126 kg ha^–1 P; 437 kg ha^–1 K; 1869 kg ha^–1 Mg; 125 kg ha^–1 Ca, and 2177 kg ha^–1 Na. Soils of cohune association did not differ significantly from those of neighbouring hardwood dominated associations with the exception of Na which occurred in higher concentration because of bioaccumulation in the dominant. The results suggest that the growth habits and physiology of a dominant can strongly influence some of the ecological parameters used to describe aforest association.     

Arsenic in orchard and potato soils and plant tissue

Summary The total and water soluble arsenic contents of orchard and potato field soils are significantly higher where arsenic has been applied. Orchards with a record of past and present applications show average values as high as 99.57 ppm total arsenic and 1.99 ppm water-soluble arsenic. Orchards with a low or no arsenic application show 27.21 ppm total and 0.20 ppm water-soluble arsenic. Potato fields situated on ex-orchard plantings have an average of 38.70 ppm total and 0.32 ppm water-soluble arsenic, whereas those on non-orchard soils showed values of 9.63 and 0.04 ppm respectively. Highest soil arsenic concentrations were found in the 0–10 cm surface layer and at a distance of one meter from the tree trunk. In plant tissue the apple leaf, peel and pulp all were significantly higher for recently arsenic treated orchards, while only the apple pulp showed significance where applications had been discontinued for the past 10–15 years. Potato leaf and peel were significantly higher in arsenic on exorchard soil while the pulp was not.     

A method for preventing sorbitol interference with the determination of inorganic phosphate

A technique is described for preventing interference of sorbitol with the assay of P₁ by modifying the procedure of B. N. Ames (1966, in Methods in Enzymology, E. F. Neufeld and V. Ginsburg, eds., Vol. 8, pp. 115–118, Academic Press, New York). The new method relies on the ability of precipitated protein to bind phosphomolybdate and so allow separation of the P₁ from the soluble sorbitol. The conditions for the formation and precipitation of phosphomolybdate-protein complex and for the subsequent assay of P₁ are described. No unique set of conditions could be found which prevented interference at all sorbitol concentrations tested. Instead, conditions for the elimination of interference by particular sorbitol concentration ranges were established. The application of the procedure to samples containing 0–150 nmol of P₁ and 10–100 μmol of sorbitol is described. Complete recovery of P₁ was achieved after precipitation. Standard plots were linear. Coefficients of variation ranged from 9% with low amounts of P₁ (≤25 nmol) to 2.5% at higher levels (150 nmol). One hundred nanomoles of P₁ gave an absorbance at 700 nm of 0.87. Modifications are described to extend the technique to different sorbitol concentration ranges and other applications of the method are mentioned.     

Understanding molecular mechanisms for improving phytoremediation of heavy metal-contaminated soils

Heavy metal pollution of soil is a significant environmental problem with a negative potential impact on human health and agriculture. Rhizosphere, as an important interface of soil and plants, plays a significant role in phytoremediation of contaminated soil by heavy metals, in which, microbial populations are known to affect heavy metal mobility and availability to the plant through release of chelating agents, acidification, phosphate solubilization and redox changes, and therefore, have potential to enhance phytoremediation processes. Phytoremediation strategies with appropriate heavy metal-adapted rhizobacteria or mycorrhizas have received more and more attention. In addition, some plants possess a range of potential mechanisms that may be involved in the detoxification of heavy metals, and they manage to survive under metal stresses. High tolerance to heavy metal toxicity could rely either on reduced uptake or increased plant internal sequestration, which is manifested by an interaction between a genotype and its environment.A coordinated network of molecular processes provides plants with multiple metal-detoxifying mechanisms and repair capabilities. The growing application of molecular genetic technologies has led to an increased understanding of mechanisms of heavy metal tolerance/accumulation in plants and, subsequently, many transgenic plants with increased heavy metal resistance, as well as increased uptake of heavy metals, have been developed for the purpose of phytoremediation. This article reviews advantages, possible mechanisms, current status and future direction of phytoremediation for heavy-metal–contaminated soils.     

Adsorption of insecticidal toxin from Bacillus thuringiensis subsp. Kurstaki by some Chinese soils: effects of organic acid ligands addition

We have investigated the effects of low molecular weight organic acid ligands on the adsorption of the insecticidal toxin from Bacillus thuringiensis (Bt) by the colloidal (<2 μm particle-size) fraction of some soils. The desorption of the bound toxin by NaCl and phosphate buffer has also been measured. The soils used were a red soil (Ultisol), a latosol (Oxisol), a yellow brown soil (Alfisol) and a yellow cinnamon soil (Alfisol) from central and southern China. The adsorption isotherms were all of the L-type, and the data fitted the Langmuir equation (R² > 0.97). When present at low concentrations, organic acids (acetate, oxalate, citrate) had an inhibitory effect on toxin adsorption. Uptake, however, was promoted when the organic acid concentration exceeded 10 mM. The toxin was very strongly bound by the soils but the soil-toxin interaction weakened in the presence of organic acids. A small portion of the toxin was adsorbed by electrostatic and ligand exchange interactions. The addition of organic acids appeared to enhance these interactions. Responsible Editor: Thomas B. Kinraide     

A Tropical Freshwater Wetland: I. Structure,Growth, and Regeneration

Forested wetlands dominated by Terminalia carolinensis are endemic to Micronesia but common only on the island of Kosrae, Federated States of Micronesia. On Kosrae, these forests occur on Nansepsep, Inkosr, and Sonahnpil soil types, which differ in degree of flooding and soil saturation. We compared forest structure, growth, nutrition, and regeneration on two sites each on Nansepsep and Inkosr soils and one site on the much less common Sonahnpil soil type. Terminalia tree sizes were similar on all three soil types, but forests differed in total basal area, species of smaller trees, and total plant species diversity. Terminalia regeneration was found only on the Inkosr soil type, which had the highest water table levels. Other Terminalia species are relatively light demanding, and T. carolinensis exhibited similar characteristics. It is therefore likely that Terminalia requires periodic, but perhaps naturally rare, stand-replacing disturbances (e.g., typhoons) in order to maintain its dominance, except on the wettest sites, where competition from other species is reduced. Terminalia swamps in the Nansepsep soil type appeared to be at the greatest risk of conversion to other uses, but swamps on all three types may face greater pressure as Kosrae's population increases and the island's infrastructure becomes more developed.     

内蒙古典型草原主要土壤类型和植物硫状况的研究（英文）

通过对内蒙古典型草原4种主要土壤类型及122种主要植物硫含量的分析,并与主要放牧家畜的营养需要相结合,综合评价了内蒙古典型草原硫的营养状况.研究表明4种主要土壤类型不同层次(0.2～0.4m,0.1～0.2m和0～0.1m)的土壤中有机硫的含量变化很大,为17～397μg*g-1,有机硫的含量与土壤中有机碳和全氮含量呈高度正相关.土壤中平均无机硫含量低于10μg*g-1,但黑钙土土壤中无机硫的含量较高,达20μg*g-1左右.土壤中微生物硫含量占土壤中全硫含量的1.78%～2.80%.所测定的122种主要植物中有75%的植物体内硫含量低于0.16%,氮/硫比大于14∶1;与主要放牧家畜的营养需要相比,有约80%的植物缺硫.植物体中硫的含量与土壤中有效硫的含量显著正相关.     

Vegetation:environment relationships and water management in Shark Slough,Everglades National Park

The hydrologic regime of Shark Slough, the most extensive long hydroperiod marsh in Everglades National Park, is largely controlled by the location, volume, and timing of water delivered to it through several control structures from Water Conservation Areas north of the Park. Where natural or anthropogenic barriers to water flow are present, water management practices in this highly regulated system may result in an uneven distribution of water in the marsh, which may impact regional vegetation patterns. In this paper, we use data from 569 sampling locations along five cross-Slough transects to examine regional vegetation distribution, and to test and describe the association of marsh vegetation with several hydrologic and edaphic parameters. Analysis of vegetation:environment relationships yielded estimates of both mean and variance in soil depth, as well as annual hydroperiod, mean water depth, and 30-day maximum water depth within each cover type during the 1990's. We found that rank abundances of the three major marsh cover types (Tall Sawgrass, Sparse Sawgrass, and Spikerush Marsh) were identical in all portions of Shark Slough, but regional trends in the relative abundance of individual communities were present. Analysis also indicated clear and consistent differences in the hydrologic regime of three marsh cover types, with hydroperiod and water depths increasing in the order Tall Sawgrass < Sparse Sawgrass < Spikerush Marsh. In contrast, soil depth decreased in the same order. Locally, these differences were quite subtle; within a management unit of Shark Slough, mean annual values for the two water depth parameters varied less than 15 cm among types, and hydroperiods varied by 65 days or less. More significantly, regional variation in hydrology equaled or exceeded the variation attributable to cover type within a small area. For instance, estimated hydroperiods for Tall Sawgrass in Northern Shark Slough were longer than for Spikerush Marsh in any of the other regions. Although some of this regional variation may reflect a natural gradient within the Slough, a large proportion is the result of compartmentalization due to current water management practices within the marsh. We conclude that hydroperiod or water depth are the most important influences on vegetation within management units, and attribute larger scale differences in vegetation pattern to the interactions among soil development, hydrology and fire regime in this pivotal portion of Everglades.     

Bioaccumulation of heavy elements by Armadillidium vulgare (Crustacea,Isopoda) exposed to fallout of a municipal solid waste landfill

This paper reports the response of isopods exposed to fallout of a municipal solid waste landfill located in central Italy. Soil samples and specimens of Armadillidium vulgare were collected at different distances from the landfill and analyzed to determine the concentrations of heavy elements such as As, Cd, Co, Cr, Cu, Ni, Pb, Sb, V and Zn. The isopod analysis was performed on unpurged and purged specimens. Analytical data indicate that the soil contents of heavy elements were quite uniform and within the respective local geochemical background. Slight enrichments of Cu and Pb were found in some soils collected within the solid waste. Purged isopods showed an accumulation of As, Co, Cr, Ni, Sb and V whose body levels decreased as the distance from the landfill increased. Cd, Cu, Pb and Zn concentrations in purged specimens were rather uniform and no significant variation trend occurred. This result probably was due to the fact that the isopods are provided with physiological mechanisms of regulation for these heavy elements. Analytical data also indicate the ability of A. vulgare to adsorb differently the heavy elements according to the following order: As > Co > Ni > Pb > V. The contents of heavy elements in unpurged specimens were higher than in purged ones. This finding suggested that the defecation has marked effects on the tissue levels of heavy elements in isopods. This study indicates that the isopods provide useful information about environmental quality in areas characterized by low and discontinuous emission of heavy elements and their low accumulation in soil.