Nutritional differentiation among populations of the mediterranean shrub Dittrichia viscosa (Asteraceae) in siliceous and calcareous habitats

Summary Dittrichia (ex Inula) viscosa is a ruderal species that has recently become an invading plant in the northwest Mediterranean basin. A previous study failed to demonstrate the occurrence of morphologically differentiated ecotypes among populations of the species but suggested the existence of nutritional ecotypes. This latter possibility is examined here by comparing the ability of plants from contrasting habitats to control cation accumulation balance. Dittrichia viscosa plants, from eight siliceous habitats and nine calcareous habitats of southern France and neighbouring Spain and Italy, were cloned and grown together hydroponically with a solution simulating an acid soil with an aluminium constraint. Two independent hydroponic units containing solution supplemented with two levels of Al were used (2 Al levels x17 populations x3 genotypes x3 replicates). The growth and cation content (K, Ca, Mg and Na) of plant shoots and the chemical composition of the soil of each habitat were analysed. At the high Al level (1.1mm), populations differed in K, Ca and Mg plant proportions. Two groups could be distinguished: one containing all but one siliceous populations and the other containing all but one calcareous populations. Plants of the siliceous group accumulated proportionally more K and less Ca, and had better growth, than plants of the calcareous group, in the same way as calcifuge and calcicole species when grown on acid soil. At the lowest Al level (0.37mm), differences between siliceous and calcareous populations were less marked. The results suggest that differences in the ability of plants to control K and Ca balance, which appear to be of adaptive significance, could have arisen through selection, and that Dittrichia viscosa has evolved calcifuge and calcicole nutritional ecotypes in siliceous and calcareous habitats respectively. Various degrees of calcifugy, and to a lesser extent of calcicoly, can thus be suggested to occur among the studied populations, some in relation to the intensity of mineral stress in the natural habitats. So far, only functional traits have provided evidence of ecotypic differentiations within Dittrichia viscosa.deceased     

Effects of plant size on photosynthesis and water relations in the desert shrub Prosopis glandulosa (Fabaceae)

The Jornada del Muerto basin of the Chihuahuan Desert of southern New Mexico, USA, has undergone a marked transition of plant communities. Shrubs such as mesquite (Prosopis glandulosa) have greatly increased or now dominate in areas that were previously dominated by perennial grasses. The replacement of grasses by shrubs requires an establishment phase where small shrubs must compete directly with similar-sized grass plants. This is followed by a phase in which large, established shrubs sequester nutrients and water within their biomass and alter soil resources directly under their canopy, creating “islands” of fertility. We hypothesized that these two phases were associated with shrubs having different physiological response capacities related to their age or size and the resource structure of the environment. As a corollary, we hypothesized that responses of small shrubs would be more tightly coupled to variation in soil moisture availability compared to large shrubs. To test these hypotheses, we studied gas exchange and water relations of small (establishing) and large (established) shrubs growing in the Jornada del Muerto as a function of varying soil moisture during the season. The small shrubs had greater net assimilation, stomatal conductance, transpiration, and xylem water potential than large shrubs following high summer rainfall in July, and highest seasonal soil moisture at 0.3 m. High rates of carbon assimilation and water use would be an advantage for small shrubs competing with grasses when shallow soil moisture was plentiful. Large shrubs had greater net assimilation and water-use efficiency, and lower xylem water potential than small shrubs following a dry period in September, when soil moisture at 0.3 m was lowest. Low xylem water potentials and high water-use efficiency would allow large shrubs to continue acquiring and conserving water as soil moisture is depleted. Although the study provides evidence of differences in physiological responses of different-sized shrubs, there was not support for the hypothesis that small shrubs are more closely coupled to variation in soil moisture availability than large shrubs. Small shrubs may actually be less coupled to soil moisture than large shrubs, and thus avoid conditions when continued transpiration could not be matched by equivalent water uptake.     

Effects of host plant environment and Ustilago maydis infection on the fungal endophyte community of maize (Zea mays)

The focus of many fungal endophyte studies has been how plants benefit from endophyte infection. Few studies have investigated the role of the host plant as an environment in shaping endophyte community diversity and composition. The effects that different attributes of the host plant, that is, host genetic variation, host variation in resistance to the fungal pathogen Ustilago maydis and U. maydis infection, have on the fungal endophyte communities in maize (Zea mays) was examined. The internal transcribed spacer (ITS) region of the rDNA was sequenced to identify fungi and the endophyte communities were compared in six maize lines that varied in their resistance to U. maydis. It was found that host genetic variation, as determined by maize line, had significant effects on species richness, while the interactions between line and U. maydis infection and line and field plot had significant effects on endophyte community composition. However, the effects of maize line were not dependent on whether lines were resistant or susceptible to U. maydis. Almost 3000 clones obtained from 58 plants were sequenced to characterize the maize endophyte community. These results suggest that the endophyte community is shaped by complex interactions and factors, such as inoculum pool and microclimate, may be important.     

Effect of mosquitofish (Gambusia affinis) and sestonic food abundance on the invertebrate community within a constructed treatment wetland

1. The effect of mosquitofish (Gambusia affinis) predation on the invertebrate community in a hypereutrophic constructed treatment wetland in southern California was investigated at two nutrient levels that influenced sestonic food abundance. 2. Gambusia affinis and insect predators in the wetland had a significant impact on larval mosquito density in the wetland irrespective of nutrient level. At the end of the 5‐month study, cladoceran abundance in predator exclusion enclosures was 2–3 orders of magnitude greater than in the treatments that allowed access by planktivores. Chironomids were the most abundant insect group collected in emergence traps, and midge production from the high nutrient location of the wetland was greater than from the low nutrient location, but was not affected significantly by G. affinis. The presence of abundant alternative prey in this highly enriched wetland may have weakened the predation impact of G. affinis on mosquitoes. 3. The abundances of six invertebrate groups in dipper samples and of four insect groups in emergence trap collections were analysed using a multivariate distance‐based linear model. Fish treatment and location interactions with sampling date explained significant amounts of the variation in the abundance of invertebrate groups. 4. Multivariate multiple regression analysis showed that chlorophyll‐a concentration explained a large portion of the variability in non‐predatory insect and zooplankton abundance at the high nutrient location, whereas bacterial density explained a large portion of the variability in the abundances of these taxa at the low nutrient location. Predatory insects were not directly coupled to the bottom‐up influence of bacterial abundance and chlorophyll‐a.     

Root xylem transport of amino acids in the root hemiparasitic shrub Olax phyllanthi (Labill) R.Br. (Olacaceaea) and its multiple hosts

The amino acid compositions of the root xylem saps of Olax phyllanthi and a range of its common hosts were examined in native coastal heath in Western Australia and in pot cultures of Olax reliant on single hosts. When hosts specializing in the xylem transport of one major solute (asparagine, glutamine, histidine, arginine or proline) were exploited, the endophytic tissue of haustoria and the xylem sap of Olax showed much lower proportions of this than of other solutes, suggesting pronounced metabolic transformation prior to xylem loading by the parasite. However, the xylem sap of Olax did partly reflect the compositions of its hosts; for example, djenkolic acid and pipecolic acid were present when Olax was parasitic on species of Acacia, and levels of citrulline and aspartic acid were higher than normal when it exploited hosts transporting large amounts of these compounds. Back-flow of S-ethenyl cysteine, a novel amino acid specific to Olax, was observed to another root hemiparasite (Exocarpos sparteus) in native habitat and to certain non-parasitic hosts in water-stressed pot cultures. Haustoria exhibited high levels of glutamine synthetase but showed appreciable in vivo nitrate reductase activity only when on hosts with high xylem levels of nitrate.     

黑麦草根系分泌物剂量对污染土壤芘降解和土壤微生物的影响

模拟根际根系分泌物梯度递减效应,研究了黑麦草根系分泌物剂量对污染土壤中芘降解特征和土壤微生物生态特征的影响.结果表明:污染土壤中芘残留量随根系分泌物添加剂量的增加呈现先下降后上升的非线性变化,达到最低芘残留量的添加剂量是总有机碳(TOC) 32.75 mg·kg-1,说明此浓度下根系分泌物显著促进了芘的降解;土壤微生物生物量碳和微生物熵的变化趋势与污染土壤中芘残留量变化趋势相反,表明土壤微生物与污染土壤 中芘残留量存在密切关系.芘污染土壤中微生物群落以细菌占主导地位,且细菌变化趋势与芘降解变化一致,表明芘以细菌降解为主,根系分泌物主要通过影响细菌数量,进而影响芘的降解.能催化有机物质脱氢反应的土壤微生物胞内酶——脱氢酶活性的变化与土壤微生物变化趋势一致,进一步证明微生物及其生物化学特性变化是污染土壤中芘残留量随根系分泌物添加剂量变化的生态机制.     

The effect of the desert cobra (Walterinnesia aegyptia) crude venom and its protein fractions on the metabolic activity of cultured human fibroblasts

Fibroblast cultures were used to study the effect of crude venom and six venom protein fractions (F₂–F₇) fromWalterinnesia aegyptia) on their metabolic activity. This was done by incubation of six fibroblast cultures with 10 g of crude venom for 3 h at 37°C. The activities of phosphofructokinase, lactate dehydrogenase, and citrate synthase were significantly lowered upon incubation with all fractions except F₂. Glycogen phosphorylase activity was significantly increased, leading to a significant concurrent drop of glycogen content. This effect was only seen for fractions F₃ and F₅. Creatine kinase activity and cellular ATP levels rose significantly upon incubation with all venom proteins except fractions F₂ and F₇. Increases were seen for aspartate and alanine amino-transferases by all venom proteins except fractions F₂ and F₄. Incubation of cell sonicates with all the venom proteins did not significantly alter activities of any of the parameters. Thus, fibroblasts in culture under such conditions appear to mobilize glycogen, phosphocreatine, and protein for ATP production to compensate for decreased glucose.Abbreviations ALT alanine aminotransferase - AST aspartate aminotransferase - ATP adenosine 5-triphosphate - CS citrate synthhase - GP glycogen phosphorylase - LDH lactate dehydrogenase - PFK phosphofructokinase     

Diurnal, seasonal and annual variation in the net ecosystem CO2 exchange of a desert shrub community (Sarcocaulescent) in Baja California, Mexico

Estimates of net ecosystem exchange (NEE) of CO₂ have been measured on a variety of ecosystems world wide including grasslands, savannahs, boreal, pine, deciduous, Mediterranean and tropical rain forests as well as arctic tundra. While there have been numerous comparisons between net primary productivity of arid and semiarid grasslands and shrublands, notably lacking are estimates of NEE with a few exceptions. The objective of this study was to characterize the seasonal and annual carbon flux of a desert shrub ecosystem using the eddy covariance technique to determine the sensitivity of the system to the timing and varying amounts of precipitation. Measurements began in July of 2001, a year with 339 mm of rainfall, considerably above the long‐term average of 174 mm and preceded by 2 years of below average rainfall (50–62 mm). Over the 2 complete years of measurements, precipitation was 147 and 197 mm in 2002 and 2003, respectively. In all years, the majority of the precipitation fell between August and September. The site was a sink of ?39 g C m^?2 yr^?1 in 2002 with a relatively strong uptake in the early part of the year and reduced uptake after the suboptimal rainfall in September. This contrasts with 2003 when the ecosystem took up ?52 g C m^?2 yr^?1 concentrated in the fall after significant rain in August and September. Likely, extremely low rainfall years would result in a carbon loss while a strengthening of the typical winter secondary peak in precipitation (notably absent in the 2 years of measurements) may extend uptake into the spring resulting in more carbon accumulation. The system appears to be buffered against variations in annual rainfall attributed to water storage in the stems and roots.     

Effect of La(III) on the growth and aging of root of loquat plantlet in vitro

The effect of lanthanum on the adventitious root growth, activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), O₂ production rate, MDA content, and the relative plasma membrane permeability in roots of loquat test-tube plantlet were studied. Addition of lanthanum chloride (0.5 μmol/L) to the culture medium significantly increased the length of roots, increased the dry weight, enhanced the activities of SOD, CAT, and POD, decreased O₂ production rate, malondialdehyde (MDA) contents, and the relative plasma membrane permeability. The relatively stable membrane structure of cell could defer the root aging of the plantlet in vitro. There are important theory meaning and practical value in applying LaCl₃ in the rooting medium to raise the rate of rooting and transplant for wood plant.     

Effects of european alder (Alnus flutinosa (L.) Gaertn) rhizobacteria on nodular metabolism and root development

The effects of 3 Bacillus and 7 Pseudomonas strains on development of the root system and nodular metabolism, evaluating CO₂ production and acetylene reduction activity (ARA), of Alnus glutinosa, were studied. All experiments were done on nodulated plants (N) with the symbiont Frankia and on non-nodulated plants (NN).An increase in root length (RL) and root surface (RS) was detected when growth culture media from three different Bacillus free of bacteria were assayed, both in N and NN plants. However, Pseudomonas growth culture media reduced RS in N plants, and a decrease in RL parallel to an increase in RS in NN plants. Bacillus growth cultyre media caused an increase: and CO₂ production while Pseudomonas culture media caused lower ARA and a noticeable increase in nodular respiration. Results are discussed considering nutritional and/or hormonal (Bacillus) or phytotoxic factors (Pseudomonas).     

A comparison of the effects of auxin on cluster root initiation and development in Grevillea robusta Cunn. ex R. Br. (Proteaceae) and in the genus Lupinus (Leguminosae)

The effect of NAA (naphthaleneacetic acid) on the development of cluster roots in members of the Proteaceae and Leguminosae was investigated. The exogenous addition of NAA led to initiation of cluster roots in phosphate conditions normally inhibitory for their development, but initiation took place within the limits of the cluster pattern under –P conditions. There was no change in spacing within the cluster root nor between cluster roots in Grevillea robusta Cunn. ex R. Br. or in rootlet length or cluster root length. In Lupinus albus L., change in rootlet length and cluster root length was noted at 10^-10 and 10¹² M NAA. In L. albus, the length of time that roots were exposed to NAA does not appear to be important, with similar levels of cluster root initiation after 48 h and 7 days. Cluster root production in G. robusta differed from that in L. albus in terms of the concentration of NAA needed to induce initiation, and in the effects of extremely low levels of NAA on rootlet numbers and lengths. L. arboreus L. does not produce cluster roots under –P conditions. Furthermore, neither L. arboreus L., L. angustifolius L., L. luteus L. nor L. mutabilis L. were induced to produce cluster roots under –P conditions, nor under +P conditions in the presence of exogenous NAA. Thus, exogenous NAA only leads to the induction of cluster roots, at levels of P normally inhibitive of their development, in species of Lupinus that produce them under –P conditions. Auxin-induced cluster roots develop within the same constraints as those developing under –P conditions. NAA does not induce cluster roots in species of Lupinus that do not produce them under –P conditions.     

Effects of choline and ethanolamine on the synthesis and breakdown of the inositol phospholipid (PI) system in Tetrahymena

Lower concentrations of choline chloride and ethanolamine (10^?3 M ; 10^?5 M ) increased phosphatidyl inositol (PI), phosphatidyl inositol monophosphate (PIP) and phosphatidyl inositol bisphosphate (PIP₂) level of Tetrahymena, while higher concentrations (10^?2 M ) decreased them. These two substances also influenced, however in a less obvious way, the transformation of inositol phospholipids. The experiments draw attention to the sensitivity of the precursors of the second messenger system at a phylogenetically low level.     

Effects of genotype,habitat, and seasonal variation on iridoid glycoside content of Plantago lanceolata (Plantaginaceae) and the implications for insect herbivores

Summary We investigated the effects of genotype, habitat, and seasonal variation on production of the iridoid glycosides, aucubin and catalpol, in leaves of the common weed Plantago lanceolata. Two genotypes, one each from a lawn and an adjacent abandoned hayfield population, were clonally replicated in the greenhouse, and then planted back into the two habitats. One quarter of the plants from each treatment were harvested on each of four dates, at approximately two-week intervals. Over the course of the growing season, and in both habitats, we found a significant increase in the concentration of both aucubin and catalpol in P. lanceolata leaves. The genotypes differed in their response to environmental variation, both in time and between sites, as indicated by significant genotype x date and genotype x site interactions. Early in the season, habitat (lawn or field) had a greater effect on iridoid glycoside concentration than did plant genotype, but later in the season, plant genotype was more influential in determining the iridoid glycoside concentration. Thus, the relative palatability of Plantago genotypes to specialist and generalist herbivores may vary in time and space.     

Distribution,habitat and conservation status of desert pupfish (Cyprinodon macularius) in the Lower Colorado River Basin,Mexico

In order to better determine the currentstatus of desert pupfish populations (Cyprinodon macularius macularius) in the LowerColorado River Basin of Mexico, bimonthly fishsampling and habitat evaluations were carriedout from September 1996 to August 1997 in sixlocalities of Baja California and Sonora.Desert pupfish were collected using minnowseines and traps. Four sampling sites are inSonora, in shallow marginal habitats of theCiénega Santa Clara (Hunters' Camp, Outletof the Welton-Mohawk channel, El Doctor andFlor del Desierto) and two are in BajaCalifornia (Cerro Prieto and streams south ofCerro Prieto). The most abundant fish speciessampled was native desert pupfish (C.macularius, 59%) followed by sailfin molly(Poecilia latipinna, 19%), redbellytilapia (Tilapia cf. zilli, 10%) and western mosquito fish (Gambusiaaffinis, 7%). Significant temporalfluctuations in distribution and abundance ofdesert pupfish populations, as previouslyreported for these populations, was againdocumented. The main anthropogenic factorsaffecting distribution and abundance of desertpupfish populations in the Mexican portion ofthe Lower Colorado River Basin are progressivealteration of aquatic and riparian habitats, aswell as presence of exotic fishes that havecaused the displacement or elimination ofnative fish populations. Both habitat andpresence of the desert pupfish populations inthe study area are controlled by theperiodicity, quality and volume of dischargesinto the Mexican portion of the basin from theUnited States.     

Effects of pollen quantity and quality on reproduction and offspring vigor in the rare plant Scorzonera humilis (Asteraceae)

We studied the effects of pollinator exclusion, interparental distance, and supplementary hand pollination on reproduction and progeny vigor in Scorzonera humilis (Asteraceae), a rare plant of fragmented, nutrient-poor grasslands. Caged flowers produced no seeds and selfed flowers only very rarely, indicating that S. humilis is mainly self-incompatible. Seed production, seed mass, and seed germination following between-population crosses were consistently, but not significantly, higher than after within-population crosses. Seed set increased with local density of conspecifics, indicating that the reduced plant density in fragmented populations may reduce plant reproductive success. Seed set was pollen limited in all four populations studied. Supplementary hand-pollination strongly increased the survival of offspring, indicating that either pollinators transferred pollen from related individuals resulting in inbreeding depression in spite of the incompatibility system or that higher pollen loads increased pollen competition and the selectivity among gametes. In one of the populations, adding pollen from a different population strongly increased progeny fitness compared with both natural pollination and pollen supplementation from the same population. The results indicate that S. humilis is sensitive to inbreeding and that pollen limitation can reduce both the number and quality of offspring.     

Effects of Proteus vulgaris growth on the establishment of a cheese microbial community and on the production of volatile aroma compounds in a model cheese

Aims:  To investigate the impact of Proteus vulgaris growth on a multispecies ecosystem and on volatile aroma compound production during cheese ripening.
Methods and Results:  The microbial community dynamics and the production of volatile aroma compounds of a nine-species cheese ecosystem were compared with or without the presence of P. vulgaris in the initial inoculum. Proteus vulgaris was able to colonize the cheese surface and it was one of the dominant species, representing 37% of total isolates at the end of ripening with counts of 9·2 log₁₀ CFU g⁻¹. In the presence of P. vulgaris , counts of Arthrobacter arilaitensis , Brevibacterium aurantiacum and Hafnia alvei significantly decreased. Proteus vulgaris influenced the production of total volatile aroma compounds with branched-chain aldehydes and their corresponding alcohols being most abundant.
Conclusions:  Proteus vulgaris was able to successfully implant itself in a complex cheese ecosystem and significantly contributed to the organoleptic properties of cheese during ripening. This bacterium also interacted negatively with other bacteria in the ecosystem studied.
Significance and Impact of the Study:  This is the first time that the impact of a Gram-negative bacterium on cheese microbial ecology and functionality has been described.     

Possible impact of global warming on cabbage root fly (Delia radicum) activity in the UK

A program for simulating the patterns of egg-laying by populations of the cabbage root fly was used to model the effects of global warming on future cabbage root fly attacks. An increase of 3°C in mean daily temperature would cause the cabbage root fly to become active about a month earlier in the year than at present. Under such conditions, the emergence of flies from the overwintering population would be less synchronised, as the completion of diapause and post-diapause development would occur at the same time in different individuals within the population. However, there would continue to be only three generations of fly each year, even in the south of England. With temperature increases of 5°C or 10°C, the fly would complete four generations each year and aestivation would seriously disrupt egg-laying. These rises in temperature would have a major impact on cabbage root fly activity and would require new strategies for controlling this pest.