Alkaline phosphatase activity and cellular phosphorus as an index of the phosphorus status of phytoplankton in Minnesota lakes

SUMMARY. Total alkaline phosphatase activity is inversely related to cellular phosphorus in the particulate organic matter of waters above and below the thermocline in nine Minnesota lakes. Diagnostic criteria for assessing surplus and limiting levels of phosphorus are proposed. When applied to seasonal changes in phosphorus status in Lake Josephine, they demonstrate severe phosphorus starvation in late summer and autumn.     

Salt Tolerance in the Triticeae: Leymus sabulosus

Elymus dahuhcus, Leymus giganteus, L. angustus, L. sabulosusand, to a lesser extent, L. triticoides, were found to tolerate200 mol m^–3 NaCl in solution culture. Elymus dahuricusdiffered from the Leymus species in its ion-uptake characteristics,showing a greater uptake of Cl and Na and a greater loss ofK from the shoots. In a more detailed experiment on Leymus sabulosusit was found that transpiration rates altered rapidly in responseto changes in external salinity whereas the accumulation ofNa and Cl in the leaves exhibited a lag of several days. Insalt stressed L. sabulosus Cl partially replaced the high levelsof nitrate found in the leaves of control plants. Glycinebetainelevels increased in the leaves from 8.0 mol m^–3 plantsap in the controls to 28 mol m^–3 plant sap at 250 molm^–3 NaCl. Key words: Salt stress, Transpiration, Solute accumulation, Leymus     

Photosynthesis, transpiration and salt fluxes through leaves of Leptochloa fusca L. Kunth

Abstract Salt excretion by glands on the leaves of Leptochloa fusca was studied. The rate of excretion was strongly dependent on temperature up to 39°C, which is near the optimum for photosynthesis in this thermophilic C₄ grass. The concentration of salt in the xylem required to sustain the observed rate of excretion was low (about two orders of magnitude less than the external concentration). Salt excretion is concluded to be a secondary mechanism of salt tolerance, with exclusion at the roots being the major mechanism. The rate of salt excretion was strongly dependent on temperature.     

Salt Tolerance in the Triticeae: K/Na Discrimination in Aegilops Species

Inorganic ion concentrations were measured in the leaves ofAegilops species growing in 50 or 75 mol m^–3 NaCl (+2.5or 3.75 mol m–3 CaCl₂). The low leaf Na and high leafK concentrations characteristic of the enhanced K/Na discriminationcharacter, originally found in Aegilops squarrosa and in hexaploidwheat, were also found in other Aegilops species containingthe D genome, but not in Ae. ventricosa. The S genome diploidAegilops species (section Sitopsis) all lacked the enhancedK/Na discrimination trait, as did the C genome species Ae. caudataand the N genome species Ae. uniaristata. Most of the U genomespecies (section Polyeides), except Ae. biuncialis, Ae. kotschyiand Ae. variabilis, also exhibited the trait. Examination ofamphiploid hybrids suggested that the trait was dominant incrosses involving Ae. squarrosa or Ae. umbellulata with otherspecies in which the trait was absent. Key words: Salt, ion transport, D genome, Aegilops spp     

Salt Tolerance in the Triticeae: Salinity-induced Changes in the Leaf Solute Composition of Some Perennial Triticeae

Changes in the leaf solute composition of a number of perennialTriticeae in response to salinity are described. There was variationboth within and between species in the extent of Na and Cl accumulationin the leaves. In almost all cases leaf nitrate concentrationsdecreased substantially and orthophosphate concentrations increasedin response to salinity. There was no overall decrease in arange of soluble nitrogen-containing compounds nor in totalnitrogen. In Thinopyrum scirpeum there was an inverse relationshipbetween proline and glycinebetaine contents of different tissues,with proline levels higher in older leaves. Concentrations ofboth compounds were higher in salt-stressed plants. Key words: Triticeae, salinity, leaf solute composition     

Response of Melanthera biflora to Salinity and Water Stress

Melanthera biflora (Asteraceae) is a moderately salt-tolerantplant from the Indo-Pacific region. In laboratory studies itsgrowth was inhibited by salt above 50 mol m^–3, but itwas able to survive salinities approaching that of seawater,namely 400 mol m^–3. Shoot potassium concentrations weremaintained over a range of salinities up to 400 mol m^–3,while sodium and chloride accumulation followed closely theincrease in external osmotic pressure. In contrast, the increasein osmotic pressure of the leaf sap of Melanthera biflora, subjectedto water stress, was due mainly to a decrease in the ratio offresh weight/dry weight. 3-dimethylsulphoniopropionate (3-DMSP)and glycinebetaine were identified by fast atom bombardmentmass and ¹H -NMR spectroscopy, with 3-DMSP being the main oniumcompound and glycinebetaine absent in some accessions. Onium(quaternary ammonium and/or tertiary sulphonium) compounds andproline increased during salt and water stress due mainly toa decrease in the fresh weight/dry weight ratio of tissue, althoughpart of the increase in salt-stressed tissue was due to an increasein the accumulation of the onium compound. This salt-inducedincrease in 3-DMSP was inhibited in conditions of low sulphursupply and there was no compensatory increase in proline. Key words: Melanthera biflora, Asteraceae, salinity, glycinebetaine, 3-dimethylsulphonioproprionate     

The Iron and Manganese Content of Plants present in the Natural Vegetation of the English Lake District

Estimations of iron and manganese have been made on ninety-sixspecies of plants (including fungi, mosses, ferns, and floweringplants) from a wide range of natural habitats. These plantsnormally contain more of both elements than is usual in cropplants grown on cultivated fields, probably owing to the greateracidity and humus content of the natural soils. The amount presentvaries with the individual species, the plant group, and thetype of habitat. While some species and groups tend to takeup iron or manganese selectively, both the absolute amountsand the ratio of the two elements may vary widely without apparentinjury to the plant. In general, these elements accumulate mostin aquatic plants growing on organic and anaerobic muds. Thelowest amounts are found in species characteristic of flushedbrown earths and in plants from drained acid peats. The fruitingbodies of fungi contain little of either element.