Fluoride injury of wheat roots and calcium nutrition

Wheat roots growing in a saturated atmosphere were treated 5min with various concentrations of calcium sulfate and the growthresponse recorded. Roots treated with optimum calcium followedby a delayed treatment with inorganic fluoride, or the reversesequence of treatments, caused responses very similar to thoseresulting from calcium deficiency. Potassium oxalate, sodiumethylenediaminetetraacetate and sodium monofluoroacetate allcaused responses that corresponded to various states of calciumdeficiency. Results suggest but do not confirm that the majoradverse effects of inorganic fluoride are the result of precipitationand depletion of available calcium in cells. Response of monofluoroacetatemight also in part be attributed to its release of inorganicfluoride in vivo. Results also indicate a depletion of a criticalconcentration of calcium from the elongation zone of roots bya 5-min treatment in any solution low in calcium will initiatechanges which cannot be reversed by treatment of calcium, andwhich will result in tissue damage. The meristematic cells areless sensitive. ¹This research was supported in part by Public Health ServiceGrant AP 00276-01 from the Division of Air Pollution. Journalpaper no. 761. Utah Agricultural Experiment Station. ²Present address: Department of Water Science and Engineering,University of California, Davis. (Received April 19, 1969; )     

A portable system for measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of sampling

SUMMARY. This paper describes the design, construction and testing of a portable monitoring system capable of measuring water temperature, conductivity, dissolved oxygen, light attenuation and depth of operation. The unit is powered by rechargeable batteries and can be used to provide instantaneous readings or continuous records of each variable when used with a suitable chart recorder. Circuits for measuring conductivity and light-ratio are of a novel design. The conductivity circuit measures conductance by the voltage drop across a low-value resistor connected in series with the conductivity cell. The light-ratio circuit measures light intensities by digitizing signals from two photocells and comparing their ratios over short periods of time. The paper includes examples of results obtained with the instrument in a wide range of applications and compares the performance of the Mackereth oxygen electrode with, and without, a small water-circulating attachment.     

The spatial distribution of nutrients in the South Basin of Windermere

SUMMARY. The vertical and horizontal distribution of electrical conductivity, soluble reactive phosphorus (SRP), total phosphorus, ammonia-nitrogen and nitrate-nitrogen in the South Basin of Windermere is described and related, where possible, to spatial variations in phytoplankton and zooplankton. For most variables, the maximum range of horizontal variation on a single day was greater than the maximum range of seasonal variation measured at a single station over a full year. Horizontal variations in SRP and ammonia were particularly high, with coefficients of variation often exceeding 100%. The errors associated with sampling at a single station were most pronounced when local accumulations of zooplankton or phytoplankton occurred in the lake. Horizontal variations in conductivity were primarily influenced by the discharge of treated sewage effluent into the central region and the mass transport of water from the more oligotrophic North Basin. Occasionally, more widespread variations in conductivity appeared to be related to spatial variations in photosynthetic activity. The major factor influencing the horizontal distribution of SRP was the discharge of treated effluent into the central region. Despite the intensive recycling of phosphorus, SRP concentrations were nearly always 10–30% higher near the sewage works than elsewhere in the basin. On a few occasions, significant horizontal differences in SRP concentration were also detected within downwind accumulations of crustacean zooplankton. Horizontal variations in total phosphorus were produced by spatial differences in SRP concentration or by local accumulations of phytoplankton or zooplankton. Horizontal differences in ammonia concentration appeared to be produced, both by the effluent discharge and by the turbulent transfer of nutrients from sediments in shallow water. Observations of effluent movement and dispersion demonstrate that wind-induced water movements tend to recirculate nutrient-rich water in the central region and limit mixing along the axis of the basin. The statistical implications of nutrient heterogeneity are discussed in relation to sampling strategy and the possible effects of persistent nutrient concentration gradients on phytoplankton patch formation are assessed.     

Molecular genetics and speciation in Elliptio and its relationships to other taxa of North American Unionidae (Bivalvia)

The genetic relationships among 30 populations of 11 species and five genera of North American Unionidae were assessed by using standard allozyme procedures. Emphasis was on relationships among populations and species of Elliptio and Fusconaia. Multi-dimensional scaling based on a matrix of Nei's (1972) genetic distances substantiated the immunoelectrophoretic results of Davis&Fuller 1981, which demonstrated the distinct and divergent taxonomic groups Anodontinae, Margaritiferinae, and Ambleminae, plus die close relationship of Elliptio and Fusconaia , which justifies their inclusion within the same tribe. Genetic distance appears to increase regularly with time since divergence of taxa. The E. complanata species group is an apparently recent radiation and probably is actively radiating today. The I values among species of this group range from 0.90 to 0.99. Considerable heterozygosity, numerous polymorphic loci, and much interpopuladon phenotypic diversity was also recorded for this group. Some taxa mat have been considered synonyms are demonstrated to be valid species. Reasons for the low genetic distances among unionid taxa are discussed. Standard allozyme analyses are shown to be of great value for assessing relationships among unionid taxa.