Polyphyly,asexual reproduction and dual trophic mode in Buchwaldoboletus

Most Boletaceae form ectomycorrhizas but species in two sister groups (subfamily Chalciporoideae and the genus Pseudoboletus) have unclear trophic modes and are putatively mycoparasitic. Chalciporoideae is the earliest diverging lineage in Boletaceae and includes Chalciporus and Buchwaldoboletus. Buchwaldoboletus species fruit on wood and were thought to be saprobes, but the type species Buchwaldoboletus lignicola is mycoparasitic on the wood decay fungus Phaeolus schweinitzii. However, the nutritional mode and host range of B. lignicola and other Buchwaldoboletus remain unclear. We obtained fresh collections and axenic cultures of B. lignicola, B. hemichrysus and B. sphaerocephalus from the southeastern USA. We use cultures to examine the phylogenetic relationships among taxa in Chalciporoideae, elucidate the trophic mode of Buchwaldoboletus species and test the effect that Buchwaldoboletus species have on wood decay. Our analysis supports the hypothesis that the Chalciporus lineage is sister to all other Boletaceae but suggests that Buchwaldoboletus is not monophyletic. Confrontation experiments on agar suggest that Buchwaldoboletus species might parasitize a wide range of decay fungi. Buchwaldoboletus hemichrysus and B. sphaerocephalus produce abundant conidia in culture whereas the more distantly related B. lignicola produces sclerotia. Wood decay assays show that Buchwaldoboletus species did not have a significant effect on the decay caused by wood decay fungi. Interestingly, when B. lignicola or B. hemichrysus were inoculated alone on wood both species decayed wood, producing a brown rot that can cause 35–65% mass loss over 6 months. Our results suggest that Buchwaldoboletus species have a dual trophic mode as saprobes and mycoparasites.     

褶纹冠蚌和背角无齿蚌对水体营养盐和浮游植物的影响

2009年5月31日-6月20日在广东省大沙河水库利用微型生态系统比较不同放养密度的褶纹冠蚌(Cristaria plicata)和背角无齿蚌(Anodonta woodiana)对水体氮、磷及浮游植物的影响,探讨两种蚌在控制南亚热带水库富营养化水体藻类水华上的可行性。实验结果表明,在褶纹冠蚌和背角无齿蚌处理组中,总氮、总磷和叶绿素a浓度显著增加,而铵氮的浓度显著下降;褶纹冠蚌和背角无齿蚌导致了浮游植物群落组成结构的改变和数量的增加,实验过程中绿藻所占的比例迅速上升。两种蚌之间没有显著的差异,只是在不同的作用强度下,时间上的响应不同。综合实验结果,褶纹冠蚌和背角无齿蚌难以有效地运用于我国华南地区水库的水质改善与富营养化控制。     

The effect of predation on the structure and invasibility of assembled communities

Summary Fifty four microcosmic communities were assembled over 4 months from a 28-species source pool of phytoplankton using nine different invasion patterns each replicated six times. Three communities from each set of replicates then were invaded with a cladoceran that feeds on phytoplankton. All communities were then treated identically for an additional 4 months. In all nine invasion categories species richness was greater in predated communities. Predation opened communities to invasion by increasing the representation of infrequently sampled species at the expense of more common species. Invasion rate was four times more influential than predation and over eleven times more important than either invasion order or the timing pattern of interspecific arrivals in determining species richness in this system of communitites.     

Does Tetranychus urticae (Acari: Tetranychidae) use flying insects as vectors for phoretic dispersal?

Whether the spider mite Tetranychus urticae uses flying insects as vectors for phoretic dispersal was experimentally tested. Two bean plants were placed in a microcosm, and a mite population was introduced onto one of the plants. Either Phaenicia cuprina Wiedemann (Diptera: Calliphoridae) or Helicoverpa armigera Hübner (Lepidoptera: Noctuidae) was then introduced into the microcosms as a hypothetical vector insect. T. urticae populations on the second bean plant were monitored to detect any evidence of phoretic dispersal. Instances of dispersal were detected at extremely low frequency, suggesting that phoretic dispersal of T. urticae mediated by winged insects is probably rare in the wild.     

森林叶凋落物混合分解的研究Ⅰ.缩微(Microcosm)实验

采用缩微实验法,初步系统研究了杉木叶凋落物分别与火力楠、红栲和木荷3个阔叶树种之一的叶凋落物两两混合分解的动态变化,以探明凋落物混合分解过程中可能存在的相互作用.结果表明,杉木叶凋落物与3种阔叶树种叶凋落物两两混合分解时所表现出不同的相互作用形式:杉木与木荷表现出抑制作用,杉木与红栲或火力楠表现为较弱的促进作用.     

Experimental tests of trophic dynamics: towards a more penetrating approach

The complex interactions between primary producers, herbivores, carnivores, and detritivores have resulted in the burgeoning field of trophic dynamics. One important contribution is the Fretwell and Oksanen theory (FO theory). The FO theory proposes that the productivity of the environment determines the length of the trophic chain, which, they suggest, is directly related to whether the system is being controlled by top-down forces (odd numbered length of trophic chain) or bottom-up forces (even numbered length of trophic chain). Recent evidence from experiments by L.H. Fraser and J.P. Grime claims to support the FO theory but the methodology has been criticised by D.C. Moon, P. Stiling and M.V. Cattell for hidden treatments and pseudoreplication. We reject these criticisms and recommend an approach to the study of trophic dynamics involving the aggregation of organisms into functional groups, direct quantitative measurements of trophic processes using field manipulations, inferences based upon the use of field probes and synthesis of ecosystems in closed microcosms. Received: 15 December 1998 / Accepted: 10 December 1998     

The extracellular nuclease of Serratia marcescens: studies on the activity in vitro and effect on transforming DNA in a groundwater aquifer microcosm

A quantitative endonuclease assay, which relies on the introduction of single and double strand breaks into supercoiled plasmid DNA, was used to study the activity of the extracellular nuclease of Serratia marcescens SM6 in buffer and in groundwater. The parallel enzyme concentration-dependent production of relaxed and linear plasmid molecules suggests that the nuclease produces single and double strand breaks in duplex DNA. Bovine serum albumin stimulated the nuclease activity towards DNA and RNA and increased the stability of the enzyme against thermal inactivation. The DNase activity at 4 °C and 50 °C was almost half of that at the optimum temperature (37 °C). The nuclease was active in groundwater, although the specific activity was lower than in buffer. In a groundwater aquifer microcosm, mineral-adsorbed transforming DNA was substantially less accessible to the nuclease than was dissolved DNA. The data suggest that the extracellular nuclease of Serratia marcescens may contribute to DNA turnover in the environment and that adsorption of DNA to minerals provides protection against the nuclease.Abbreviations GW groundwater GWA groundwater aquifer     

Effect of organic loading on nitrification and denitrification in a marine sediment microcosm

Abstract The effects of organic additions on nitrification and dentrification were examined in sediment microcosms. The organic material, heat killed yeast, had a C/N ratio of 7.5 and was added to sieved, homogenized sediments. Four treatments were compared: no addition (control), 30 g dry weight (dw) m⁻² mixed throughout the 10 cm sediment column (30M), 100 g dw m⁻² mixed throughout sediments (100M), and 100 g dw m⁻² mixed into top 1 cm (100S). After the microcosms had been established for 7–11 days, depth of O₂ penetration, sediment-water fluxes and nitrification rates were measured. Nitrification rates were measured using three different techniques: N-serve and acetylene inhibition in intact cores, and nitrification potentials in slurris. Increased organic additions decreased O₂ penetration from 2.7 to 0.2 mm while increasing both O₂ consumption, from 30 to 70 mmol O₂ m⁻² d⁻¹, and NO₃⁻ flux into sediments. Nitrification rates in intact cores were similar for the two methods. Highest rates occurred in the 30M treatment, while the lowest rate was measured in the 100S treatment. Total denitrification rates (estimated from nitrification and nitrate fluxes) increased with increased organic addition, because of the high concentrations of NO₃⁻ (40 μM) in the overlaying water. The ratio of nitrification: denitrification was used as an indication of the importance of nitrification as the NO₃⁻ supply for denitrificaion. This ratio decreased from 1.55 to 0.05 iwth increase organic addition.     

罗非鱼对微型生态系统营养物水平的影响

本文总结了罗非鱼不同放养密度的微型生态系统中N、P浓度及P分布动态观测结果。在罗非鱼的影响下,微型生态系统中氨氮、颗粒磷和总磷浓度不同程度地高于对照组,而正磷酸盐浓度和沉积物磷的量显著地低于对照组。不同密度组某些指标的观测值虽有显著差异,但未见任何指标依罗非鱼放养密度而有规律地变动。微型生态系统中正磷酸盐浓度同浮游动、植物密度和初级生产力显著相关,氨氮浓度与浮游植物密度之间亦有显著的相关关系。然而,浮游植物密度与总磷浓度之间不存在营养级联假说所预见的下行影响,相反有前者决定于后者的上行影响的趋向。微型生态系统中P分布的变化可揭示罗非鱼促进系统中营养物循环,从而加速其富营养化的主要机制。     

Individual vs. population plastic responses to elevated CO2, nutrient availability, and heterogeneity: a microcosm experiment with co-occurring species

We conducted an experiment to evaluate the plastic phenotypic responses of individuals, growing under intra-specific competition, and populations of three co-occurring grassland species (Lolium perenne, Plantago lanceolata, and Holcus lanatus) to joint variations in atmospheric CO₂ partial pressure (P _CO2; 37.5 vs. 70 Pa), nutrient availability (NA; 40 vs. 120 mg N added as organic material), and the spatial pattern of nutrient supply (SH; homogeneous vs. heterogeneous nutrient supply). At both the population and individual levels, the aboveground biomass of the three species significantly increased when the nutrients were heterogeneously supplied. Significant two- (SH × NA) and three-term (P _CO2 × NA × SH) interactions determined the response of traits measured on populations (aboveground biomass and below: aboveground biomass ratio, BAR) and individuals (aboveground biomass and specific leaf area). The combination of a high SH and NA elicited the highest plasticity of aboveground biomass in populations and individuals of the three species evaluated, and of BAR in Holcus. Soil heterogeneity and elevated P _CO2 elicited the highest plasticity in the SLA of Plantago and Lolium individuals. Our results show that populations, and not only individuals, respond to soil heterogeneity in a plastic way, and that plastic responses to elevated P _CO2 are complex since they vary across traits and species, and are influenced by the availability of nutrients and by their spatial distribution. They also emphasize the importance of soil heterogeneity as a modulator of plant responses to global change drivers. Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. Responsible Editor: Angela Hodge