Collembolan associations in natural versus improved pastures of the New England Tableland,NSW: Distribution of native and introduced species

Native Australian species of Collembola dominated natural pasture in numbers of species present and in abundance, while introduced Collembola dominated fertilized pasture sown to exotic species. Those collembolan species which were restricted to one pasture type only were mainly epigeal and hemiedaphic species of the herbage and litter. Increased grazing by sheep decreased species richness and increased uniformity of Collembola in both pasture types. The abundance of introduced Collembola was positively associated with phosphorus content of litter.     

Carbohydrate-Free Media for Crithidia

SYNOPSIS. The insect trypanosomatid Crithidia fasciculata grew well at pH 3.8–6.3 in defined carbohydrate-free media containing arginine (an essential amino acid) + proline + glutamic acid as substrates; glycerol was effective by itself. Precipitation of hemin in the acid media did not hinder growth. Further addition of succinic acid permitted growth matching that with carbohydrate. At pH 6.9–7.5 growth in this medium without carbohydrate with the aforementioned non-fermentable substrates was slight; added carbohydrate (as sucrose or sorbitol) permitted good growth. Utilization of non-carbohydrate substrates may contribute to Crithidia 's ability (and presumably to that of pathogenic trypanosomatids as well) to multiply in the insect gut and to the ability of some Trypanosoma species to multiply in the insect hemocoel and salivary gland.     

A POLARLY FLAGELLATED MEMBER OF THE ENTEROBACTERIACEAE

SUMMARY: An organism which has been frequently isolated from the rhizosphere of plants of Lolium perenne (Perennial Rye-grass) is described; it has the typical morphology and flagellation of Pseudomonas but the biochemical reactions of Klebsiella.     

Genetic relatedness and disrupted social structure in a poached population of African elephants

We use genetic measures of relatedness and observations of female bonding to examine the demographic signature of historically heavy poaching of a population of free-ranging African elephants. We collected dung samples to obtain DNA and observed behaviour from 102 elephant families over a 25-month period in 2003–2005 in Mikumi National Park, Tanzania. Poaching reduced the population by 75% in the decade prior to the 1989 ivory trade ban; park records indicate that poaching dropped significantly in Mikumi following the ban. Using 10 microsatellite loci, DNA was genotyped in 203 elephants and pair-wise relatedness was calculated among adult females within and between groups. The Mikumi population is characterized by small group size, considerable variation in group relatedness, females with no first-order adult relatives and females that form only weak social bonds. We used gene-drop analysis and a model of a genetically intact pedigree to compare our observed Mikumi group relatedness to a simulated genetically intact unpoached expectation. The majority of groups in Mikumi contain 2 to 3 adults; of these, 45% were classified as genetically disrupted. Bonding, quantified with a pair-wise association index, was significantly correlated with relatedness; however only half of the females formed strong bonds with other females, and relatedness was substantially lower for a given bond strength as compared to an unpoached population. Female African elephants without kin demonstrated considerable behavioural plasticity in this disturbed environment, grouping with other females lacking kin, with established groups, or remaining alone, unable to form any stable adult female-bonds. We interpret these findings as the remaining effect of poaching disturbance in Mikumi, despite a drop in the level of poaching since the commercial trade in ivory was banned 15 years ago.     

Plasma membrane H+-ATPase-dependent citrate exudation from cluster roots of phosphate-deficient white lupin

White lupin ( Lupinus albus L.) is able to grow on soils with sparingly available phosphate (P) by producing specialized structures called cluster roots. To mobilize sparingly soluble P forms in soils, cluster roots release substantial amounts of carboxylates and concomitantly acidify the rhizosphere. The relationship between acidification and carboxylate exudation is still largely unknown. In the present work, we studied the linkage between organic acids (malate and citrate) and proton exudations in cluster roots of P-deficient white lupin. After the illumination started, citrate exudation increased transiently and reached a maximum after 5 h. This effect was accompanied by a strong acidification of the external medium and alkalinization of the cytosol, as evidenced by in vivo nuclear magnetic resonance (NMR) analysis. Fusicoccin, an activator of the plasma membrane (PM) H⁺-ATPase, stimulated citrate exudation, whereas vanadate, an inhibitor of the H⁺-ATPase, reduced citrate exudation. The burst of citrate exudation was associated with an increase in expression of the LHA1 PM H⁺-ATPase gene, an increased amount of H⁺-ATPase protein, a shift in pH optimum of the enzyme and post-translational modification of an H⁺-ATPase protein involving binding of activating 14-3-3 protein. Taken together, our results indicate a close link in cluster roots of P-deficient white lupin between the burst of citrate exudation and PM H⁺-ATPase-catalysed proton efflux.     

Effects of experimental drought on soil respiration and radiocarbon efflux from a temperate forest soil

Soil moisture affects microbial decay of SOM and rhizosphere respiration (RR) in temperate forest soils, but isolating the response of soil respiration (SR) to summer drought and subsequent wetting is difficult because moisture changes are often confounded with temperature variation. We distinguished between temperature and moisture effects by simulation of prolonged soil droughts in a mixed deciduous forest at the Harvard Forest, Massachusetts. Roofs constructed over triplicate 5 × 5 m² plots excluded throughfall water during the summers of 2001 (168 mm) and 2002 (344 mm), while adjacent control plots received ambient throughfall and the same natural temperature regime. In 2003, throughfall was not excluded to assess the response of SR under natural weather conditions after two prolonged summer droughts. Throughfall exclusion significantly decreased mean SR rate by 53 mg C m^?2 h^?1 over 84 days in 2001, and by 68 mg C m^?2 h^?1 over 126 days in 2002, representing 10–30% of annual SR in this forest and 35–75% of annual net ecosystem exchange (NEE) of C. The differences in SR were best explained by differences in gravimetric water content in the Oi horizon (r²=0.69) and the Oe/Oa horizon (r²=0.60). Volumetric water content of the A horizon was not significantly affected by throughfall exclusion. The radiocarbon signature of soil CO₂ efflux and of CO₂ respired during incubations of O horizon, A horizon and living roots allowed partitioning of SR into contributions from young C substrate (including RR) and from decomposition of older SOM. RR (root respiration and microbial respiration of young substrates in the rhizosphere) made up 43–71% of the total C respired in the control plots and 41–80% in the exclusion plots, and tended to increase with drought. An exception to this trend was an interesting increase in CO₂ efflux of radiocarbon‐rich substrates during a period of abundant growth of mushrooms. Our results suggest that prolonged summer droughts decrease primarily heterotrophic respiration in the O horizon, which could cause increases in the storage of soil organic carbon in this forest. However, the C stored during two summers of simulated drought was only partly released as increased respiration during the following summer of natural throughfall. We do not know if this soil C sink during drought is transient or long lasting. In any case, differential decomposition of the O horizon caused by interannual variation of precipitation probably contributes significantly to observed interannual variation of NEE in temperate forests.     

Flow cytometric analysis for ploidy level differentiation of 45 hairy vetch accessions

Determining the ploidy of plant germplasm is a necessary step in breeding or genetic studies in species. The purpose of this research was to determine the presence of ploidy level differentiation of hairy vetch (Vicia villosd) germplasm. Flow cytometry and root tip chromosome squashing methods were employed to assess 45 accessions labeled V. villosa available through the USDA germplasm collection. Flow cytometry determined that 43 of the accessions were 2C, one accession was 4C, and one accession was 6C. Analysis of accessions by root tip chromosome counts indicated that all accessions were diploid. The 2C accession contains 14 chromosomes and their chromosomes were approximately one-half and one-third in size as compared to the chromosomes of the 4C and 6C accessions, respectively. The 4C accession was observed to have 16 chromosomes and the 6C accession was observed to have 14 chromosomes. The large-scale differences in DNA amounts were due to chromosomal size variability as opposed to ploidy differences. This revealed the incidence of species misidentification of these two V. villosa accessions to be Vicia pannonica. All the V. villosa accessions were observed to be diploid and have similar DNA amounts. Flow cytometry proved to be useful in the efficient assessment of these accessions.     

Rapid and reversible modifications of extension capacity of cell walls in elongating maize leaf tissues responding to root addition and removal of NaCl

A creep extensiometer technique was used to provide direct evidence that short (20 min) and long-term (3d) exposures of roots to growth inhibitory levels of salinity (100mol m^-3 NaCl) induce reductions in the irreversible extension capacity of cell walls in the leaf elongation zone of intact maize seedlings (Zea mays L.). The long-term inhibition of cell wall extension capacity was reversed within 20 min of salt withdrawal from the root medium. Inhibited elongation of leaf epidermal tissues was also reversed after salt removal. The salt-induced changes in wall extension capacity were detected using in vivo and in vitro assays (shortly after localized freeze/thaw treatment of the basal elongation zone). The rapid reversal of the inhibition of wall extensibility and leaf growth after salt removal from root medium of long-term salinized plants, suggested that neither deficiencies in growth essential mineral nutrients nor toxic effects of NaCl on plasmamembrane viability were directly involved in the inhibition of leaf growth. There was consistent agreement between the scale, direction and timing of salinity-induced changes in leaf elongation growth and wall extension capacity. Rapid metabolically regulated changes in the physical properties of growing cell walls, caused by osmotic (or other) effects, appear to be a factor regulating maize leaf growth responses to root salinization.