Late Quaternary eolian dust in surficial deposits of a Colorado Plateau grassland: Controls on distribution and ecologic effects

In a semi-arid, upland setting on the Colorado Plateau that is underlain by nutrient-poor Paleozoic eolian sandstone, alternating episodes of dune activity and soil formation during the late Pleistocene and Holocene have produced dominantly sandy deposits that support grass and shrub communities. These deposits also contain eolian dust, especially in paleosols. Eolian dust in these deposits is indicated by several mineralogic and chemical disparities with local bedrock, but it is most readily shown by the abundance of titaniferous magnetite in the sandy deposits that is absent in local bedrock. Magnetite and some potential plant nutrients (especially, P, K, Na, Mn, and Zn) covary positively with depth (3–4 m) in dune-crest and dune-swale settings. Magnetite abundance also correlates strongly and positively with abundances of other elements (e.g., Ti, Li, As, Th, La, and Sc) that are geochemically stable in these environments. Soil-property variations with depth can be ascribed to three primary factors: (1) shifts in local geomorphic setting; (2) accumulation of relatively high amounts of atmospheric mineral dust inputs during periods of land-surface stability; and (3) variations in dust flux and composition that are likely related to changes in dust-source regions. Shifts in geomorphic setting are revealed by large variations in soil texture and are also expressed by changes in soil chemical and magnetic properties. Variable dust inputs are indicated by both changes in dust flux and changes in relations among magnetic, chemical, and textural properties. The largest of these changes is found in sediment that spans late Pleistocene to early Holocene time. Increased dust inputs to the central Colorado Plateau during this period may have been related to desiccation and shrinkage of large lakes from about 12 to 8 ka in western North America that exposed vast surfaces capable of emitting dust. Soil properties that result from variable dust accumulation and redistribution in these surficial deposits during the late Quaternary are important to modern ecosystem dynamics because some plants today utilize nutrients deposited as long ago as about 12–15 ky and because variations in fine-grained (silt) sediment, including eolian dust, influence soil-moisture capacity.     

Induction of high affinity nitrate and ammonium uptake systems in wheat

Abstract

The ability of 7 day old wheat seedlings to take up nitrate or ammonium from hydroponic solution was measured. Seedlings were grown under fully aerated hydroponic conditions. The growth solution consisted of either 0.5 mM CaSO₄ alone or in combination with high nitrate (5 mM NO₃ ^‐ ), high ammonium (2 mM NH₄ ⁺) or modified 1/10 Hoaglands solution with nitrate N only (14 mM) or ammonium N only (2 mM). After washing the roots for one hour in CaSO₄, nitrate or ammonium uptake was measured with an ion selective electrode. Plants grown in high nitrate were unable to take up nitrate from a 0.1 mM external solution. Those grown in CaSO₄ were able to take up nitrate at the same external concentration (flux = 10.2 +/‐ 3.0 μmol nitrate/g dry wtlbh). The same result was seen for plants grown in high ammonium vs those grown in CaSO₄ (flux = 21.0 +/‐ 10.0 μmol/g dry wtlbh). Similar results were obtained when modified Hoagland's solution was substituted for the high N solutions. These data indicate that wheat roots possess both high and low affinity nitrate and ammonium uptake systems. The data further indicate that, for a given ion, the high and low affinity systems do not operate simultaneously under high N conditions. The high affinity system is switched off in the range of 1 mM for both ionic forms of N. Developmental studies show that the expression of the high affinity trait is reversible and may be induced (repressed) by conditioning for 24 h in low (high) N media. Plants grown in high N solutions showed efflux of the ion under assay conditions. Neither ion interfered with the induction/repression of the high affinity trait for the other under the conditions used in this study.     

Humoral immune responses to phocine herpesvirus-1 in Pacific harbor seals (Phoca vitulina richardsii) during an outbreak of clinical disease

Infection with phocine herpesvirus type-1 (PHV-1) has been associated with morbidity and high mortality in neonatal harbor seals (Phoca vitulina). A PHV-1 specific indirect enzyme linked immunosorbent assay (ELISA) was developed to sequentially measure the serological status of 106 harbor seal neonates admitted to a Pacific coast rehabilitation center (total number of sera tested was 371). Early in the season (February-April), the majority of pups had low serum levels of PHV-1 specific antibody. A dramatic increase in PHV-1 specific antibody, involving the majority of hospitalized pups, was observed during a 4-week period in May. This coincided with a high incidence of PHV-1 associated adrenal lesions and mortality. Although there was overall agreement between the timing of seroconversion to PHV-1 and histological evidence of PHV-1 infection, 82.4% of individual pups with adrenalitis had no evidence of a humoral response to PHV-1 at the time of their death. This suggests either a rapid disease course, or an inability to develop a humoral response in some neonatal seals.     

Comparative phospholipid analogue distributions of Porphyromonas gingivalis isolated from cats in Australia and the USA

DNA-DNA homology measurements and phospholipid (PL) analogue profiling have shown heterogeneity of Porphyromonas gingivalis. The aim of this study was to determine whether there were differences between cat strains of P. gingivalis from Australia and USA with respect to PL analogue distribution. Lipids were extracted with chloroform-methanol and examined by fast atom bombardment-mass spectrometry (FAB-MS) in negative-ion mode, using published methods. For PL analogues, the major anions included those with mass-to-charge (m/z)=634, 648, 662, 705, 932, 946 and 960, respectively, corresponding to expected presence of PE (28:0), PE (29:0), PE (30:0), PG (32:1), and three unknown homologues of a glycero-phospholipid with a single nitrogen. Analyses were compared to calculate a matrix of Pearson coefficients of linear correlation from which a dendrogram was produced of strains clustered by single linkage. One cluster was comprised solely of Australian cat-to-cat bite isolates and a second cluster included exclusively USA cat- and dog-to-human bite isolates except for one Australian cat-to-cat bite isolate (VPB 5089). The US cluster included three outliers, one of which was the Australian cat isolate VPB 5089. The human type strain (ATCC 33277) was quite remote from all dog and cat strains. It was shown that P. gingivalis human and non-human animal isolates have distinct PL analogue profiles from each other. Furthermore, the cat strains from the USA and those from Australia showed quantitative differences in polar lipid profiles that correlated largely with country of isolation.     

Coordination between water-transport efficiency and photosynthetic capacity in canopy tree species at different growth irradiances

Plasticity in hydraulic architecture of five dominant Atlantic forest species differing in light requirements and growth rates was evaluated in saplings grown at different irradiances to determine if hydraulic architecture changes in coordination with photosynthetic capacity. Saplings were grown in shade-houses at 10, 30, 45 and 65% of full solar irradiance for 4 months. In four of the five species, maximum relative growth rates were observed at intermediate irradiances (30 and 40% of full sun). Slow-growing species had lower maximum electron transport rates (ETR(max)) than fast-growing species. A positive correlation between ETR(max) and maximum leaf hydraulic conductivity (K(L)) was found across species, suggesting that species-specific stem hydraulic capacity and photosynthetic capacity were linked. Species with relatively high growth rates, such as Cedrela fissilis Vell., Patagonula americana L. and Cordia trichotoma (Vell.) Arrab. Ex Stend, exhibited increased K(L) and specific hydraulic conductivity (K(S)) with increased growth irradiance. In contrast, K(S) and K(L) did not vary with irradiance in the slower-growing and more shade-tolerant species Balfourodendron riedelianum (Engl.) Engl. and Lonchocarpus leucanthus Burkart, despite a relatively large irradiance-induced variation in ETR(max). A correlation between K(S) and ETR(max) was observed in fast-growing species in different light regimes, suggesting that they are capable of plastic changes in hydraulic architecture and increased water-transport efficiency in response to changes in light availability resulting from the creation of canopy gaps, which makes them more competitive in gaps and open habitats.     

Cloning and Characterization of Glutamate Receptors in Californian Sea Lions (Zalophus californianus)

Domoic acid produced by marine algae has been shown to cause acute and chronic neurologic sequelae in Californian sea lions following acute or low-dose exposure. Histological findings in affected animals included a degenerative cardiomyopathy that was hypothesized to be caused by over-excitation of the glutamate receptors (GluRs) speculated to be present in the sea lion heart. Thus tissues from five sea lions without lesions associated with domoic acid toxicity and one animal with domoic acid-induced chronic neurologic sequelae and degenerative cardiomyopathy were examined for the presence of GluRs. Immunohistochemistry localized mGluR 2/3, mGluR 5, GluR 2/3 and NMDAR 1 in structures of the conducting system and blood vessels. NMDAR 1 and GluR 2/3 were the most widespread as immunoreactivity was observed within sea lion conducting system structures. PCR analysis, cloning and subsequent sequencing of the seal lion GluRs showed only 80% homology to those from rats, but more than 95% homologous to those from dogs. The cellular distribution and expression of subtypes of GluRs in the sea lion hearts suggests that exposure to domoic acid may induce cardiac damage and functional disturbances.