Influence of cytosolic pH changes on the organisation of the endoplasmic reticulum in epidermal cells of onion bulb scales: Acidification by loading with weak organic acids

Summary The anastomosing ER system of epidermal cells of onion bulb scales is composed of three modifications: lamellar and tubular elements, located in the cell periphery, and long tubular stands located deeper in the cytoplasm. Cytoplasmic acidification of epidermal cells by loading with weak organic acids like acetic or propionic acid causes the decay of the lamellar elements and the disappearance of long tubular strands. Organelle movement is also inhibited. The effects depend on the pH of the incubation medium and on the administered acid concentration, and are characterized by a distinct lag phase of about 7 min. The induced ER changes are transient with adaptation starting after about 50min. Buffer components alone have little influence on the cellular ER organization within a pH-range of 4.0–8.0. However, the pH of the medium strongly affects the time course of the effects as well as recovery after omitting the administered acid. Both modulation and recovery occur more rapidly at neutral or slightly alkaline pH. Actin filaments, which play a major role in ER organization and organelle movement, are not affected by cytosolic acidification.Dedicated to the memory of Professor Oswald Kiermayer     

Growth, dry weight partitioning and wood properties of Pinus radiata D. Don after 2 years of CO2 enrichment

Abstract Advanced selections (families 20010 and 20062) of P. radiata D. Don were exposed to either 340 or 660 μmol CO₂ mol ¹ for 2 years to establish if growth responses to high CO₂ would persist during the development of woody tissues. The experiment was carried out in glasshouses and some of the trees at each CO₂ concentration were subjected to phosphorus deficiency and to periodic drought. CO₂ enrichment increased whole-plant dry matter production irrespective of water availability, but only when phosphorus supply was adequate. The greatest increase occurred during the exponential period of growth and appeared to be tied to increased rates of photosynthesis, which caused accelerated production of leaf area. The increase in whole-plant dry matter production was similar for both families; however, family 20010 partitioned larger amounts of dry weight to the trunks than family 20062. which favoured the roots and branches. Wood density was generally increased by elevated CO₂ and for family 20010 this increase was due to thickening of the tracheid walls. Tracheid length was similar at both CO₂ levels but differed between families. These results suggest that, as the atmospheric CO₂ concentration rises, field-grown P. radiata should produce more dry weight at sites where phosphorus is not acutely deficient, even where drought limits growth; however, increases in wood production are likely only for genotypes which continue to partition at least the same proportion of dry weight to wood in the trunk.     

Sulfur dynamics in mineral horizons of two northern hardwood soils. A column study with 35S

Sulfur dynamics of two Spodosols were ascertained using soil columns constructed from homogenized mineral soil from nothern hardwood ecosystems at the Huntington Forest (HF) in the Adirondack Mountains of New York and Bear Brook Watershed in Maine (BBWM). Columns were leached for 20 weeks with a simulated throughfall solution with³⁵SO₄ ^2-. Sulfur constituents were similar to those of other Spodosols, with the organic S fractions (C-bonded S and ester sulfate) constituting over 90% of total S. HF soil columns had higher total S (14.9 mol S g^-1) than that for the BBWM soil columns (7.4 mol g^-1) primarily due to higher C-bonded S in the former.Initially, adsorbed SO₄ ^- accounted for 5 and 4% of total S for the BBWM and HF soil columns, respectively. After 20 weeks, adsorbed SO₄ ^2- decreased (81%) in BBWM and increased (33%) in HF soil columns. For both HF and BBWM soil columns, C-bonded S increased and ester sulfate decreased, but only for HF columns was there a net mineralization of organic S (5.6% of total S). The greatest decrease in ester sulfate occurred at the top of the columns.Leaching of³⁵S was less than 0.5% of the³⁵S added due to its retention in various S constituents. There was an exponential decrease in³⁵S with column depth and most of the radioisotope was found in C-bonded S (70–88 and 70–91% for BBWM and HF, respectively). The rapid turnover of adsorbed SO^2- ₄ was reflected in its high specific activity (834 and 26 kBq mol^-1 S for BBWM and HF, respectively). The lower specific activity of adsorbed SO₄ ^2- in HF was attributable to greater isotopic dilution by non-radioactive SO^2- ₄ derived from greater organic S mineralization in the HF versus the BBWM columns.Both soil columns initially had high levels of NO^- ₃ which resulted in the generation of H⁺ and net retention of SO₄ ^2- in the early phase of the experiment due to pH dependent sulfate adsorption; later NO₃ ^- decreased and SO₄ ^2- was desorbed. Leaching of NIO₃ ^- and SO₄ ^2- was correlated with losses of Mg²⁺ and Ca²⁺ of which the latter was the dominant cation.Analyses using both S mass balances and radioisotopes corroborate that for BBWM soil columns, SO^2- ₄ adsorption-desorption dominated the S biogeochemistry while in HF soil columns, organic S mineralization-immobilization processes were more important. It is suggested that similar techniques can be applied to soils in the field to ascertain the relative importances of SO₄ ^2- adsorption processes and organic S dynamics.     

Aluminum geochemistry in peatland waters

The chemical speciation of aluminum was examined in surface water samples from Sphagnum peatlands in north-central Minnesota, from peatlands along the Canadian east coast, and from bogs in the Pennine Mountain area of England. In highly organic ([DOC] 50 mg L^–1 ), low pH waters, 80–90% of total dissolved Al was complexed with organic matter (OM), while in waters with low DOC ([DOC] 5 mg L^–1) 54–86% of total dissolved Al existed as Al⁺³ or other inorganic Al species. Batch titrations of OM with Al revealed a high Al binding capacity, 1.4–2.8 mol (mg DOC)^–1, that generally was unsaturated with Al. Titrations of OM with Al in conjunction with a continuous distribution model were used to determine Al-OM conditional stability constants. Binding capacity (mol Al (mg DOC)^–1) and strength (formation constant) increased from pH 3 to 5 but decreased above pH 5 due to formation of AI-hydroxy species including A1(OH)₃ (s). The high binding capacity of OM in bog waters facilitates metal mobility, especially in low pH (< 5) wetlands where metal solubility is high and OM concentrations are highest. Results showed that the relative degree of organic matter saturation with metal ions was important in modeling AI speciation in bog waters.     

Determination of trace elements in aerosol samples by Instrumental Neutron Activation Analysis

Two nuclear techniques, Energy-Dispersive X-Ray Fluorescence Analysis (EDXRF) and Instrumental Neutron Activation Analysis (INAA), were used to analyze aerosol samples collected in the city of São Paulo, Brazil. Na, Cl, Mn, V, Al, Sm, Mo, W, La, As, Br, Sb, K, Ba, Se, Th, Cr, Rb, Ca, Fe, Ce, and Sc were determined by INAA, and Al, Si, P, S, Cl, K, Ca, Ti, V, Cr, Mn, Fe, Ni, Cu, Zn, Ga, As, Se, Br, Rb, Sr, Hg, and Pb were determined by EDXRF. A preliminary identification of the main source of the atmospheric aerosol was performed based on enrichment factor and correlation coefficient calculations.

     

A long-term perspective of dissolved organic carbon transport in Sycamore Creek, Arizona, USA

Dissolved organic carbon (DOC) dynamics were examined over five years (1989–1993) in Sycamore Creek, a Sonoran Desert stream, specifically focusing on DOC concentration in surface and hyporheic waters, and rates of export. In 1989 and 1990, the years of lowest stream discharge (0.08 and 0.04 m³ s^–1 annual mean of daily discharge, respectively), DOC was high, averaging 7.37 and 6.22 mgC l^–1 (weighted annual means). In contrast, from 1991 through 1993, a period of increased flow (1.1, 1.2 and 4.3 m³ s^–1), concentration was significantly lower (P<0.001) with annual mean concentrations of 3.54, 3.49 and 3.39 mgC l^–1. Concentration exhibited little spatial variation between two sampling stations located 6 km apart along the mainstem or between surface and hyporheic waters. Annual export of DOC from Sycamore Creek varied 100-fold over the five-year period from a mean rate of only 24 kgC d^–1 in 1990 to 2100 kgC d^–1 in 1993. Ninety percent of DOC was exported by flows greater than 2.8 m³ s^–1, and 50% during flows greater than 27 m³ s^–1; flows of 2.8 and 24 m³ s^–1 occurred only 9 and 1% of the time. The export of organic matter in Sycamore Creek appears to be coupled to El Niño-Southern Oscillation phenomena. The years of highest export, 1991–1993, had El Niño conditions while 1989 and 1990 had medial conditions.     

Changes of the forest-savanna boundary in Brazilian Amazonia during the Holocene revealed by stable isotope ratios of soil organic carbon

The possibility of ecosystem boundary changes in northern Brazilian Amazonia during the Holocene period was investigated using soil organic carbon isotope ratios. Determination of past and present fluctuations of the forest-savanna boundary involved the measurement of natural ¹³C isotope abundance, expressed as ¹³C, in soil organic matter (SOM). SOM ¹³C analyses and radiocarbon dating of charcoal fragments were carried out on samples derived from soil profiles taken along transects perpendicular to the ecotonal boundary. SOM ¹³C values in the upper soil horizons appeared to be in equilibrium with the overlying vegetation types and did not point to a movement of the boundary during the last decades. However, ¹³C values obtained from deeper savanna and forest soil layers indicated that the vegetation type has changed in the past. In current savanna soil profiles, we observed the presence of mid-Holocene charcoals derived from forest species: fire frequency at that time was probably greater, and more extensive savanna may have resulted. Isotope data and the presence of these charcoals thus suggest that the forest-savanna boundary has shifted significantly in the recent Holocene period, forest being more extensive during the early Holocene than today. During the middle Holocene, the forest could have strongly regressed, and fires appeared, with a maximum development of the savanna vegetation. At the beginning of the late Holocene, the forest may have invaded a part of this savanna, and fires occurred again.     

A native nitrogen-fixing shrub facilitates weed invasion

Invasions by exotic weedy plants frequently occur in highly disturbed or otherwise anthropogenically altered habitats. Here we present evidence that, within California coastal prairie, invasion also can be facilitated by a native nitrogen-fixing shrub, bush lupine (Lupinus arboreus). Bush lupines fix nitrogen and grow rapidly, fertilizing the sandy soil with nitrogen-rich litter. The dense lupine canopy blocks light, restricting vegetative growth under bushes. Heavy insect herbivory kills lupines, opening exposed nitrogen-rich sites within the plant community. Eventual re-establishment of lupine occurs because of an abundant and long-lived seed bank. Lupine germination, rapid growth, shading and fertilization of sites, and then death after only a few years, results in a mosaic of nutrient-rich sites that are available to invading species. To determine the role of bush lupine death and nitrogen enrichment in community composition, we examined nutrient dynamics and plant community characteristics within a site only recently colonized by lupine, comparing patches where lupines had recently died or were experimentally killed with adjacent areas lacking lupine. In experimentally killed patches, instantaneous pool sizes of exchangeable ammonium and nitrate nitrogen were higher than in adjacent sites free of lupine. Seedlings of the introduced grass Bromus diandrus accumulated 48% greater root biomass and 93% more shoot biomass when grown in a greenhouse in soil collected under experimentally killed lupines compared to B. diandrus seedlings grown in soil collected at least 1 m away from lupines. At the end of the spring growing season, total above-ground live plant biomass was more than twice as great in dead lupine patches as in the adjacent lupine-free grassland, but dead lupine patches contained 47% fewer plant species and 57% fewer native species. Sites where lupines have repeatedly died and reestablished during recent decades support an interstitial grassland community high in productivity but low in diversity, composed of mostly weedy introduced annual plants. In contrast, at a site only recently colonized by bush lupines, the interstitial grassland consists of a less productive but more diverse set of native and introduced species. We suggest that repeated bouts of lupine germination, establishment, and death can convert a rich native plant community into a less diverse collection of introduced weeds.     

Behavioral changes in pottos (Perodicticus potto): Effects of naturalizing an exhibit

Observations of the potto (Perodicticus potto),a nocturnal prosimian primate,indicated a limited behavioral repertoire and prompted renovation of their exhibit at the Frankin Park Zoo (Boston, MA). We used the natural history of this species to direct the exhibit modifications, which used only nonsynthetic items. We added live plants, soil, bamboo, shelf fungi, grapevines, a hollow tree, and a log containing an insect dispenser to the exhibit at little expense. They provided new textures, odors, pathways, stimulation and cover for this secretive species. The changes produced a heightened aesthetic appeal to the nocturnal exhibit and improved its educational value by representing the animals’ habitat more accurately. The exhibit modifications also resulted in a significant increase in activity, an expansion of the pottos’ behavioral repertoire,the emergence of sexual behaviors, and an increased visibility to the public.     

Halcyon days with Bill Arnold

The circumstances that led to the discovery that plants luminesce after they are illuminated are described, as are other discoveries that would not have been possible were it not for the fortuitous association I had with my dear and most admirable friend, W.A. Arnold, to whom this special issue is dedicated.