Phytoplankton nutrient limitation in Colorado mountain lakes

SUMMARY. 1. Limiting nutrients for phytoplankton were studied experimentally in eight mountain lakes of central Colorado between May and November of 1984.
2. Five categories of phytoplankton limitation were identified: no limitation, N limitation, P limitation, concurrent limitation (stimulation only by simultaneous additions of N and P), and reciprocal limitation (stimulation by addition of either N or P). The phytoplankton communities of three lakes were primarily N-limited, one was primarily phosphorus-limited, and four showed primarily combined limitation (concurrent or reciprocal). Switching between categories of limitation was also observed within lakes. Nitrogen was the most frequently limiting nutrient; N, either alone or in combination with P, accounted for 79% of all observed instances of limitation.
3. Nine indices were tested for effectiveness in predicting phytoplankton limitation by N and P. The best indices for discriminating all limitations were ratios of dissolved inorganic N: total P (84% accuracy) and dissolved inorganic N:total dissolved P (80% accuracy). The effectiveness of these indices may be explained by the degree to which they represent N and P fractions actually available to the phytoplankton.     

Intermediary metabolism and shell growth in the brachiopod Terebratalia transversa

Juvenile Terebratalia transversa (Brachiopoda) metabolize carbohydrates in the anterior-most marginal mantle at a rate of 0.46 μM glucose/g/hr (in vitro incubation of mantle in C¹⁴-glucose in a carrying medium of 10^-3 M non-radioactive glucose). The rate declines to 0.18μM glucose/g/hr in full-grown specimens. Carbohydrate metabolism in the marginal (anterior-most) mantle averages approximately 3.7 times greater than metabolism in (a portion of the ‘posterior’) mantle situated between the coelomic canals and the marginal mantle. This ratio remains constant in specimens of all sizes (i.e. an ontogenetic trend in the ratio is absent at p≤ 0.05). Organic acids are not detectable within the mantle (HPLC techniques) even after simulated anoxia (N₂ bubbling during mantle incubation). Glucose metabolism in vitro declines in both the marginal and ‘posterior’ mantles during anoxia and the metabolic ratio between marginal/‘posterior’ mantles becomes 1/1. We found no difference (at p≤ 0.05) in mean metabolic activity or in sue-related metabolic trends among populations from depths ranging between mean sea level and 70 m. However, the activity within the ‘posterior’ mantle was more variable in specimens from 70 m than in those from shallower habitats (10 m - mean sea level). The size of the specimens analyzed was most variable in the groups obtained from the shallowest habitats and least variable at 70 m depth. Our results may help define the energetics of fossil as well as living brachiopod shell growth. Brachiopod shell growth is known to be very slow relative to that of bivalves and our results indicate that this is a result of the animals' slow metabolism. The inflation of the valves in T. transversa is, in part, a function of the high ratio of intermediary metabolism in the marginal vs‘posterior’ mantle (i.e. parallels the relative growth rates at the shell margin vs‘posterior’ areas). We found that the bivalve, Chlamys hastata, which is commonly associated with T. transversa, has a lower ratio of metabolic activities in the ventral/dorsal mantle areas than the brachiopod has in the anterior/posterior. The difference produces a flatter shell in the bivalve in accord with allometric principles. The higher metabolic rate in the marginal vs‘posterior’ brachiopod mantle and its more pronounced decline with anaerobiosis is reflected in the greater definition of growth increments in the outer shell layer. Our results do not support recent generalizations that correlate shell thickness of a wide variety of invertebrates inversely with metabolic rate. Growth rate as determined from width of shell growth increments is a better index of metabolic rate. Although the genetic basis of glucose metabolism is unknown, the observed metabolic variability is consistent with suggestions that populations of marine organisms living in stable offshore environments are genetically more variable but morphologically more uniform than populations from shallow water. Furthermore, our results support suggestions that bivalved molluscs and brachiopods are very different metabolically, but the data are neutral with respect to theories of competitive exclusion of the two taxa throughout geologic history.     

A classification of the genus Nothofagus (Fagaceae)

PHILIPSON, W. R. & PHILIPSON, M. N., 1988. A classification of the genus Nothofagus (Fagaceae). The genus Nothofagus is subdivided into two subgenera, two sections and three subsections, employing characters of the pollen, cupule and vernation, together with the incidence of leaf-fall. The subdivision into subgenera also agrees with present geographical distribution and with characters of the secondary xylem. One subgeneric and one subsectional name are new. Reasons are given for departures from previous classifications.     

Wounding and the Regulation of Apoplasmic Retrieval in Source Leaf Tissue 5Spinacia oleracea L.

Kinetic studies were performed on fresh-cut and aged leaf discsof Spinacia oleracea L. in order to investigate the regulatoryprocesses involved in sugar transport across the mesophyll plasmamembrane. A comparison of the kinetic profiles for fructose,glucose, sucrose and arginine obtained on freshly-cut and ageddiscs revealed that during wound-recovery, uptake is enhanced,but that this enhancement varies considerably for the differentsubstrates tested. Variation in the saturable and first-orderkinetic components of uptake was also observed. The involvementof a phosphoinositide-signalling mechanism in the wounding processwas examined by pretreating spinach leaves with lithium. Lithiuminhibited the enhancement of uptake and this effect was reversedby the addition of miro-inositol. However, in some experimentsthe tissue appeared to be insensitive to Li⁺. Gas chromatographicanalyses performed on cut discs indicated that ethylene wasproduced in response to wounding and that the addition of cobaltto the ageing media inhibited this ethylene production. Comparativekinetic studies of control and cobalt-treated discs indicatedthat ethylene was essential for the enhancement of transportacross the plasma membrane. However, addition of ethylene touncut tissue caused only a partial increase in the uptake offructose, which indicates that some additional wound-signallingcomponent is involved. Addition of cycloheximide to the recoverymedia completely inhibited this enhancement phenomenon. Thecycloheximide-response was not due to an inhibition of ACC synthasesynthesis nor to a reduction of ATP levels. We concluded thatthe effect of cycloheximide was on protein synthesis. Our resultsare discussed in terms of possible cellular and molecular mechanismsregulating sugar transport. Key words: Sugar transport, wounding, ethylene production, spinach leaves     

Functional Aspects of the Salt Glands of the Plumbaginaceae

X-ray microanalysis and diffuse reflectance infrared Fouriertransform spectrometry were used to determine the presence andratios of elements in salt secretions from salt glands of greenhouseand experimentally-manipulated leaves of five species of thePlumbaginaceae Sodium, magnesium, silica, sulphur, phosphorus,chloride, potassium, calcium and carbonate were detected insecretions of greenhouse-grown plants. The salt glands of excisedleaves challenged by solutions of KI, KCl, NaCl, Na₂SO₄, MgCl₂and MgSO₄ secreted principally the ions of the challenging solutions. Key words: Ion transport, secretion     

A Comparison of Endogenous Development of Three Isolates of Cryptosporidium in Suckling Mice1

ABSTRACT. Suckling mice were used as a model host to compare the endogenous development of three different isolates of Cryptosporidium: one from a naturally infected calf, one from an immunocompetent human with a short-term diarrheal illness, and one from a patient with acquired immune deficiency syndrome (AIDS) and persistent, life-threatening, gastrointestinal cryptosporidiosis. After oral inoculation of mice with oocysts, no differences were noted among developmental stages of the three isolates in their sites of infection, times of appearance, and duration, morphology, and fine structure. Sporozoites excysted within the lumen of the duodenum and ileum, penetrated into the microvillous region of villous enterocytes, and developed into type I meronts with six or eight merozoites. Type I merozoites penetrated enterocytes and underwent cyclic development as type I meronts or they became type II meronts with four merozoites. Type II merozoites did not exhibit cyclic development but developed directly into sexual forms. Microgamonts produced £16 small, bullet-shaped microgametes, which were observed attaching to and penetrating macrogametes. Approximately 80% of the oocysts observed in enterocytes had a thick, two-layered wall. After sporulating within the parasitophorous vacuole, these thick-walled oocysts passed through the gut unaltered and were the resistant forms that transmitted the infection to a new host. Approximately 20% of the oocysts in enterocytes consisted of four sporozoites and a residuum surrounded only by a single oocyst membrane that ruptured soon after the parasite was released from the host cell. The presence of thin-walled, autoinfective oocysts and recycling of type I meronts may explain why a small oral inoculum can produce an overwhelming infection in a suitable host and why immune deficient persons can have persistent, life-threatening cryptosporidiosis in the absence of repeated oral exposure to thick-walled oocysts.     

Hydroxyl- and Bicarbonate-Associated Transport Processes in Chara corallina: Studies on the Light-Dark Regulation Mechanism

Lucas, W. J. and Ogata, K. 1985. Hydroxyl– and bicarbonate–associatedtransport processes in Chara corallintr. Studies on the light–darkregulation mechanism.—J. exp. Bot. 36: 1947–1958.Experiments were undertaken on the fresh water alga Chara corallinato investigate the nature of the coupling between the chloroplastsand the light–dependent OH^– and -associated plasmalemma transport systems. Electrophysiologicalexperiments, in which DCMU was employed, revealed that thischemical could elicit a hyperpolarization of the membrane potentialthat was identical to that normally obtained by turning offthe light. This DCMU–induced hyperpolarization was obtainedunder control () and phosphate–decoupled conditions (). Measurements of the extracellular electric potentialswhich are associated with the acidic () and alkaline (OH^–) regions, indicated that, in the presenceof control ()or phosphate–decoupled conditions, normal profiles were established under air, oxygenor nitrogen environments. These results indicate that the generationof the control signal(s) is related to events associated withchloroplast electron transport, rather than to changes in theflow or levels of carbon intermediates within the reductivepentose phosphate or photorespiratory cycles. Although the levelof oxygen was found to have no effect on the light–inducedactivation of the OH regions, we found that in pure oxygen thedark–induced inactivation of the OH^– efflux systemwas delayed, and that partial transport function could be maintainedin the dark. The possible involvement of changes in either theratio of oxidized to reduced ferridoxin or NADP^? to NADPH, aspart of this light–mediated control signal, is discussed. Key words: Chara corallina, Plasma membrance transport, OH^– and , regulation     

Aerenchyma (Gas-space) Formation in Adventitious Roots of Rice (Oryza sativa L.) is not Controlled by Ethylene or Small Partial Pressures of Oxygen

Jackson, M. B., Fenning, T. M., and Jenkins, W. 1985 Aerenchyma(gas-space) formation in adventitious roots of rice (Oryza sativaL.) is not controlled by ethylene or small partial pressuresof oxygen.—J. exp. Bot. 36: 1566–1572. The extent of gas-filled voids (aerenchyma) within the cortexof adventitious roots of vegetative rice plants (Oryza sativaL. cv. RB3) was estimated microscopically from transverse sectionswith the aid of a computer-linked digitizer drawing board. Gas-spacewas detectable in 1-d-old tissue and increased in extent withage. After 7 d, approximately 70% of the cortex had degeneratedto form aerenchyma. The extent of the voids in 1-4-d-old tissuewas not increased by stagnant, poorly-aerated external environmentscharacterized by sub-ambient oxygen partial pressures and accumulationsof carbon dioxide and ethylene. Treatment with small oxygenpartial pressures, or with carbon dioxide or ethylene appliedin vigorously stirred nutrient solution also failed to promotethe formation of cortical gas-space. Furthermore, ethylene productionby rice roots was slowed by small oxygen partial pressures typicalof stagnant conditions. Silver nitrate, an inhibitor of ethylene action, did not retardgas-space formation; similarly when endogenous ethylene productionwas inhibited by the application of aminoethoxyvinylglycine(A VG), aerenchyma development continued unabated. Cobalt chloride,another presumed inhibitor of ethylene biosynthesis, did notimpair formation of the gas in rice roots nor did it decreasethe extent of aerenchyma even if A VG was supplied simultaneously.These results contrast with those obtained earlier using rootsof Zea mays L. We conclude that in rice, aerenchyma forms speedily even inwell-aerated environments as an integral part of ordinary rootdevelopment There seems to be little or no requirement for ethyleneas a stimulus in stagnant root-environments where aerenchymais likely to increase the probability of survival. Key words: Rice (Oryza sativa L.), ethylene, flooding, aeration, aerenchyma, environmental stress