Seasonal dynamics of edaphic bacterial communities in the hyper-arid namib desert

>Magister Scientiae - MScThe Namib Desert is a hyper-arid, coastal desert with limited bioavailable water and nutrients; characteristics which collectively impose constraints on edaphic microbial communities. Several studies in the Namib Desert have investigated changes in soil microbial communities across space. However, the temporal variation of edaphic bacterial community in response to seasonal microenvironmental variation in the Namib Desert gravel plains has never been investigated in situ.The edaphic bacterial community dynamics were evaluated over short (57 days) and long-term (1 year) sampling intervals using an extensive sampling strategy in combination with community fingerprinting by T-RFLP analyses and microenvironmental characterization. The short-term study was conducted on three distinct locations in the Namib Desert gravel plains. Soil bacterial communities were found to be more similar within habitats than between habitats, with the differences likely shaped by soil pH. These findings are consistent with the concept of habitat filtering.Investigation of edaphic bacterial communities over 1 year in an 8100 m2 sampling site revealed seasonal patterns of variation in community structure. Soil moisture,phosphorus, potassium and magnesium were identified as significant abiotic drivers of community temporal dynamics. β diversity was found to increase over time, while the environment remained relatively static. These findings support previous observations that desert communities are likely structured by stochastic and deterministic processes.Taken together, these findings advance understanding of temporal variation of edaphic communities in the Namib Desert

Seasonal dynamics of edaphic bacterial communities in the hyper-arid Namib desert

>Magister Scientiae - MScThe aim of this study is to investigate the edaphic bacterial community dynamics over short (57 days) and long-term (1 year) sampling intervals using an extensive sampling strategy in combination with community fingerprinting by T-RFLP analyses and micro environmental characterization. The short-term study was conducted on three distinct locations in the Namib Desert gravel plains. Soil bacterial communities were found to be more similar within habitats than between habitats, with the differences likely shaped by soil pH. These findings are consistent with the concept of habitat filtering. Investigation of edaphic bacterial communities over 1 year in an 8100 m2 sampling site revealed seasonal patterns of variation in community structure. Soil moisture, phosphorus, potassium and magnesium were identified as significant abiotic drivers of community temporal dynamics. β diversity was found to increase over time, while the environment remained relatively static. These findings support previous observations that desert communities are likely structured by stochastic and deterministic processes. Taken together, these findings advance understanding of temporal variation of edaphic communities in the Namib deser

Towards a new model of grit within a cognitive-affective framework of self-regulation

Grit – passion and perseverance for long-term goals – has been empirically shown to be a positive predictor of success across multiple contexts. The current study developed a new framework of grit within a framework of self-regulatory behaviours. Here, a qualitative approach was assumed to obtain interview data from chief innovation officers and chief information officers within technologically intensive industries. Empirical evidence was used to inductively determine the underlying cognitive-affective processing that influences gritty behaviour. Overall, six strategies were identified: temporal perspective, perpetual evaluation, motivational orientation, strength and resource gathering, system thinking and framing. Organisations may utilise the grit model developed here to enhance the grittiness of their innovation leaders by building effective cognitive-affective strategies

Temporal dynamics of hot desert microbial communities reveal structural and functional responses to water input

8 páginas, 4 figuras. -- The first publication is available at https://www.nature.comThe temporal dynamics of desert soil microbial communities are poorly understood. Given the implications for ecosystem functioning under a global change scenario, a better understanding of desert microbial community stability is crucial. Here, we sampled soils in the central Namib Desert on sixteen different occasions over a one-year period. Using Illumina-based amplicon sequencing of the 16S rRNA gene, we found that α-diversity (richness) was more variable at a given sampling date (spatial variability) than over the course of one year (temporal variability). Community composition remained essentially unchanged across the first 10 months, indicating that spatial sampling might be more important than temporal sampling when assessing β-diversity patterns in desert soils. However, a major shift in microbial community composition was found following a single precipitation event. This shift in composition was associated with a rapid increase in CO2 respiration and productivity, supporting the view that desert soil microbial communities respond rapidly to re-wetting and that this response may be the result of both taxon-specific selection and changes in the availability or accessibility of organic substrates. Recovery to quasi pre-disturbance community composition was achieved within one month after rainfall.We gratefully acknowledge financial support from the National Research Foundation of South Africa (grant no.81779 and TTK2008052000003), the Research Council of Norway (grant No. 180352) and the University of the Western Cape. Partial support was also provided under the Laboratory Directed Research and Development Program at PNNL, a multiprogram national laboratory operated by Battelle for the U.S. Department of Energy under contract DE-AC05-76RL01830.Peer reviewe

Niche-Partitioning of Edaphic Microbial Communities in the Namib Desert Gravel Plain Fairy Circles

<div><p>Endemic to the Namib Desert, Fairy Circles (FCs) are vegetation-free circular patterns surrounded and delineated by grass species. Since first reported the 1970's, many theories have been proposed to explain their appearance, but none provide a fully satisfactory explanation of their origin(s) and/or causative agent(s). In this study, we have evaluated an early hypothesis stating that edaphic microorganisms could be involved in their formation and/or maintenance. Surface soils (0–5cm) from three different zones (FC center, FC margin and external, grass-covered soils) of five independent FCs were collected in April 2013 in the Namib Desert gravel plains. T-RFLP fingerprinting of the bacterial (16S rRNA gene) and fungal (ITS region) communities, in parallel with two-way crossed ANOSIM, showed that FC communities were significantly different to those of external control vegetated soil and that each FC was also characterized by significantly different communities. Intra-FC communities (margin and centre) presented higher variability than the controls. Together, these results provide clear evidence that edaphic microorganisms are involved in the Namib Desert FC phenomenon. However, we are, as yet, unable to confirm whether bacteria and/or fungi communities are responsible for the appearance and development of FCs or are a general consequence of the presence of the grass-free circles.</p></div

One-way ANOSIM statistics comparing the bacterial and fungal community structures the predefined zones of each FC studied.

<p>R: ANOSIM statistic; p: probability level. *: Significantly different (p <0.05).</p><p>One-way ANOSIM statistics comparing the bacterial and fungal community structures the predefined zones of each FC studied.</p

Fairy Circle sampling.

<p>Photograph of a Fairy Circle in the gravel plains of the Namib Desert (A) with the schematic of the sampling strategy employed (B).</p

Models hypothesizing microbial community assembly in Namib Desert Fairy Circles.

<p>Arrow indicate the assembly processes (purple: stochastic/black: niche-partitioning/blue: neutral). Colors are represent virtually the FC zones (Green: vegetated covered control soils/Yellow: FC margins/Red: FC Centers) where these processes occur. Red arrows indicate the origin in time and length of the environmental disturbance responsible for FC appearance. The x-axis does not reflect proportionally the time scale.</p

Results of two-way crossed ANOSIM tests based on Bray-Curtis similarity matrices from square-root transformed bacterial and fungal T-RFLP profiles.

<p>R: ANOSIM statistic; p: probability level. *: Significantly different (p <0.05).</p><p>Results of two-way crossed ANOSIM tests based on Bray-Curtis similarity matrices from square-root transformed bacterial and fungal T-RFLP profiles.</p