The sorption behaviors of 4 cyclic and linear volatile methyl siloxane (VMS) compounds between water and organic matter in 3 United Kingdom soils were studied by a batch equilibrium method using13C-enriched sorbates. Sorption and desorption kinetics and isotherms were determined for octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), octamethyltrisiloxane (L3), and decamethyltetrasiloxane (L4). Concentrations of [13C]-VMS in the soil and aqueous phases were measured directly by extraction and gas chromatography–mass spectrometry techniques. All VMS compounds were sorbed rapidly, reaching constant distributions in all soils by 24 h. Desorption kinetics were very rapid, with reattainment of equilibrium within 1 h. In the main, linear isotherms were observed for aqueous concentrations at or below 4% of the solubility limits. The average sorption organic carbon partition coefficient (log KOC) values across soils were 4.23 for D4, 5.17 for D5, 4.32 for L3, and 5.13 for L4, with standard deviations of 0.09 to 0.34. Desorption KOC values were systematically greater by 0.1 log units to 0.3 log units. The linear isotherms and low variation in KOC values across soils suggested partitioning-dominated sorption of the VMS. Compared with traditional hydrophobic organic compounds, KOC values for the VMS compounds were significantly lower than expected on the basis of their octanol–water partition coefficients. A linear free energy relationship analysis showed that these differences could be rationalized quantitatively in terms of the inherent characteristics of the VMS compounds, combined with the differences in solvation properties of organic matter and octanol. Environ Toxicol Chem 2014; 33:1937–1945.

Plant xylem pressure potentials and leaf conductances to water loss were measured in the spring and summer at two sites in the western Cape Province, Republic of South Africa. The measurements were to test the hypothesis that the fynbos of South Africa was equivalent to the chaparral of California, therefore a period of plant water stress, similar to the period measured in chaparral species, should occur in flynbos species during the dry summer. The measurements indicated little or no plant water stress in most fynbos species at both sites. The sites were similar in plant water relations in spite of a more than twofold difference in annual precipitation. The minor differences in plant water relations can be explained in terms of different vegetation cover and different vapor pressure deficits during the measurements. The results support the conclusion that the arid fynbos may be equivalent to chaparral, but the majority of the fynbos is equivalent to coniferous and broad-leaved evergreen forest in California.

Hazanlia orcuttii (A. Gray) Greene is a 5-10 dm tall perennial shrub that is native to coastal sage scrub communities of southern California and northern Baja California. This species was listed as threatened by the California Department of Fish and Game in 2002 and is a federal candidate species, and the only known population in the U.S. is on a 1.6 ha mesa located in Encinitas, California. Very httle IS known about the general ecology of this species, thus, the goal of this research was to characterize the basic soil physical and chemical properties and plant community characteristics associated with this species. Research was conducted between January 2004 and July 2005 in 12.56 mrandomly-located plots that either contained or lacked H. orcuttii. Soil in plots containing H. orcuttii had significantly higher clay, soil organic matter, total N, and soil moisture content than plots lacking H. orcuttii, while plots lacking H. orcuttii had significantly more surface litter content. Significant differences were also observed in plant species abundance between plots containing and lacking H. orcuttii, indicating fundamental differences in plant community composition associated with patches of H. orcuttii. Our data support the notion that H. orcuttii is a soil endemic; however, it is unclear whether H. orcuttii prefers soil richer in clay or is restricted to these soils because of other factors. Given the restricted nature of H. orcuttii, and the proximity of the extant population to residential areas, habitat protection from human degradation and fire should be a high priority. ResumenHcizarclia orcuttii (A.Gray) Greene es un arbusto perenne que mide 5-10 dm de alto que es nativo a la comunidad perteneciente de la salvia chaparro costeno en el sur de California y el la parte fronterizo de Baja California Norte. Esta especie fue enumerada como una que eata bajo de amenaza por el Departamento de California pescaderia y casa en el 2002, y la unica poblacion en los Estados Unidos esta en una mesa de 1 .6 ha ubicado en Encinitas, Calif Poco se sabe sobre la ecologia general de esta especie, asi, el fm de esta inverrstigacion era de caracterisar las propiedades basicos fisicos y quimicos de la tierra y las carecteristicas planta associadas con esta comunidad de esta especie. Invistigaciones fueron condujidos entre Enero 2004 y Julio 2005 en 12.65 m-en parcelas establecidas al azar unos conteniendo y otros careciendo H. orcuttii. Tierra en parcelas conteniendo H. orcuttii tenian significativamente alto niveles de barro, mater organica del suelo, nitrogeno total, y contenido de humedad del suelo que las parcelas careciendo H. orcuttii tenian significatimante mas contenido de revoltura al superficie. Diferencias significativas fueron observados en la abundancia de especie de plantas entre parcelas conteniendo y careciendo de H. orcuttii, indicando diferencias esenciales en el compuesto de la comunidad de las plantas asociado con parches de H. orcuttii. Nuestros datos apoyan la nocion que H. orcuttii es endemica de la tierra s...