Transmission of the mycoparasite Coniothyrium minitans by collembolan Folsomia Candida (Collembola: Entomobryidae) and glasshouse sciarid Bradysia sp. (Diptera: Sciaridae)

Folsomia Candida was maintained on potato dextrose agar (PDA) plates precolonised by the mycoparasite Coniothyrium minitans for 3 yr but the sciarid Bradysia sp. survived for a maximum of only three generations. Collembolans and sciarid larvae from these cultures were able to transmit C. minitans to uninoculated PDA plates through the survival of spores in faecal pellets. Adult and larval sciarids also transmitted C. minitans from PDA culture to uninoculated PDA plates by contamination on the cuticle. In soil and sand both sciarids and collembolans were able to transmit C. minitans from C. m/m'tans-inoculated to uninoculated sclerotia of Sclerotinia sclerotiorum. Inoculation of sclerotia with C. minitans enabled greater populations of larger collembolans to develop. In the glasshouse where C. minitans had been applied to the soil, one adult sciarid and four collembolans out of 70 and 101 insects collected respectively yielded C. minitans on placement onto PDA + Aureomycin.     

Evaluation of automated analysis of 15N and total N in plant material and soil

Simultaneous determination of ¹⁵N and total N using an automated nitrogen analyser interfaced to a continuous-flow isotope ratio mass spectrometer (ANA-MS method) was evaluated. The coefficient of variation (CV) of repeated analyses of homogeneous standards and samples at natural abundance was lower than 0.1%. The CV of repeated analyses of ¹⁵N-labelled plant material and soil samples varied between 0.3% and 1.1%. The reproductibility of repeated total N analyses using the automated method was comparable to results obtained with a semi-micro Kjeldahl procedure. However, the automated method gave results which were 3% to 5% higher than those obtained with the Kjeldahl procedure. Since only small samples can be analysed, careful sample homogenization and fine grinding are very important. Evaluation of a diffusion method for preparing nitrate and ammonium in solution for automated ¹⁵N analysis showed that the recovery of inorganic N in the NH₃ trap was lower when the N was diffused from water than from 2 M KCl. The results also indicated that different proportions of the NO₃ ^- and the NH₄ ⁺ in aqueous solution were recovered in the trap after combined diffusion. The method is most suited for diffusing either NO₃ ^- or NH₄ ⁺ alone, but can be used for combined diffusion of the two ions.     

Root responses to legume plants integrate information on nitrogen availability and neighbour identity

Rhizobial symbiosis is known to increase the nitrogen availability in the rhizosphere of legumes. Therefore, it has been hypothesized that other plants’ roots should forage towards legume neighbours, but avoid non-legume neighbours. Yet, root distribution responding to legume plants as opposed to non-legumes has not yet been rigorously tested and might well be subject to integration of multiple environmental cues.In this study, wedevised an outdoor mesocosm experiment to examine root distributions of the two plant species Pilosella officinarum and Arenaria serpyllifolia in a two-factorial design. While one factor was ‘neighbour identity’, where plants were exposed to different legume or non-legume neighbours, the other factor was ‘nitrogen supply’. In the latter the nutrient-poor soil was supplemented with either nitrogen-free or with nitrogen-containing fertilizer.Unexpectedly, of all treatments that included a legume neighbour (eight different species or factor combinations), we found merely one case of root aggregation towards a legume neighbour (P. officinarum towards Medicago minima under nitrogen-fertilized conditions). In this very treatment, also P. officinarum root–shoot allocation was strongly increased, indicating that neighbour recognition is coupled with a contesting strategy.Considering the various response modes of the tested species towards the different legume and non-legume neighbours, we can conclude that roots integrate information on neighbour identity and resource availability in a complex manner. Especially the integration of neighbour identity in root decisions must be a vital aptitude for plants to cope with their complex biotic and abiotic environment in the field.     

BioEssays 10/2020

Frequent independent origins of environmental sex determination (ESD) are assumed within amniotes. However, the phylogenetic distribution of sex-determining modes suggests that ESD is likely very ancient and may be homologous across ESD groups. Sex chromosomes are demonstrated to be old and stable in endothermic (mammals and birds) and many ectothermic (non-avian reptiles) lineages, but they are mostly non-homologous between individual amniote lineages. The phylogenetic pattern may be explained by ancestral ESD with multiple transitions to later evolutionary stable genotypic sex determination. It is pointed out here that amniote ESD shares several key aspects with sequential hermaphroditism of fishes such as a lack of sex differences in genomes, biased population sex ratios, and potentially also molecular mechanism related to general stress responses. Here, it is speculated that ESD evolves via a heterochronic shift of the sensitive period of sex change from the adult to the embryonic stage in a hermaphroditic amniote ancestor. Also see the video abstract here https://youtu.be/q2mjtlCefu4 .