Tripartite Associations Research Articles

Tripartite associations: A bacterial symbiont of fungi promotes plant growth without compromising the benefits conferred by an Epichloë endophyte

Few studies have evaluated the effects of bacteria that form associations with fungi on plant-microbial symbioses. We investigated the effects of a novel symbiotic bacterium (E226) of Epichloë, a well-researched mutualistic fungal endophyte of grasses, on perennial ryegrass (Lolium perenne) also associated with Epichloë. We hypothesised that E226 would promote plant growth but would not interfere with the in-planta growth of Epichloë and its production of antiherbivore alkaloids. E226, identified as Micrococcus luteus, formed an ectosymbiotic relationship with Epichloë when cultured on artificial media (i.e., bacterial cells were located on the hyphal surface) and possessed plant-growth promoting traits identified through whole genome analysis. Seeds of L. perenne, already colonised by an Epichloë strain, were inoculated with E226. The bacterium established within the seedlings, and the abundance of M. luteus populations initially increased with plant age. In agreement with our hypotheses, plant inoculation with E226 enhanced the production of leaves and did not affect the growth of Epichloë or the concentration of Epichloë-derived alkaloids. The putative abilities of E226 to solubilise phosphate and produce vitamins and metabolic cofactors may explain the observed plant growth promotion.

Arbuscular Mycorrhizal Fungi and Diazotrophic Diversity and Community Composition Responses to Soybean Genotypes from Different Maturity Groups

Soybeans can simultaneously form tripartite symbiotic associations with arbuscular mycorrhizal fungi (AMF) and diazotrophs. However, no studies have explored whether soybean genotypes differing in their maturity groups (MGs) may have implications for the recruitment of rhizosphere soil AMF and diazotrophs. We investigated the diversity and community compositions of AMF and diazotrophs in three soybean genotypes differing in their maturity groups (MG) using high-throughput sequencing. The soybean MGs were MG1.4, MG2.2, and MG3.8, representing early, standard, and late maturity, respectively, for the study region. Soil chemical properties and yield-related traits were determined, and co-occurrence network patterns and drivers were also analyzed. The results obtained demonstrated that AMF richness and diversity were relatively stable in the three soybean genotypes, but noticeable differences were observed in diazotrophs, with late maturity being significantly higher than early maturity. However, there were differences in AMF and diazotrophic composition among different MG genotypes, and the changes in the proportion of dominant species in the community were necessarily related to MG genotypes. Co-occurrence network analysis showed that the positive correlation between AMF and diazotrophs gradually decreased in earlier MG genotypes than in the other later MG genotypes. The results of the structural equation model analysis showed that soil organic carbon, AMF, diversity of soil nutrients, and extracellular enzyme activities were important factors driving soybean yield change, with organic carbon accounting for more than 80% of the pathways analyzed. These results suggest that soybean genotype selection based on MG plays an important role in recruiting both AMF and diazotrophic communities, and in comparison to AMF, diazotrophs are more responsive to the different MG genotypes.

Sodalis glossinidius and Wolbachia infections in wild population of Glossina morsitans submorsitans caught in the area of Lake Iro in the south of Chad

Investigations on the bacterial fauna and their association with trypanosome infections in tsetse fly have revealed contrasting results. This study aimed to detect Wolbachia and S. glossinidius in wild populations of G. m. submorsistans and subsequently, understand the influence that these bacteria may have on the vectorial competence of this tsetse species. Tsetse flies were captured in the area of Lake Iro in the south of Chad using biconical traps. After DNA extraction from each tsetse fly, Sodalis glossinidius and Wolbachia were detected using specific primers. Sodalis glossinidius and Wolbachia infection rates were compared and association studies involving trypanosome infections and S. glossinidius or Wolbachia were performed. From 345 G. m. submorsitans analyzed, 9.0% and 14.5% were respectively infected with S. glossinidius and Wolbachia. Only 2.31% of all tsetse flies were co-infected by the 2 bacteria. Of all trypanosome-infected flies, 7.1% and 9.8% harbored, respectively, S. glossinidius and Wolbachia. No association was observed between Wolbachia and trypanosome infections while a significant association (r = 4.992; P = 0.025) was found between S. glossinidius and the presence of trypanosomes. A significant association (r = 3.147; P = 0.043) was also observed between S. glossinidius and T. simiae; and none with T. congolense or T. godfreyi. This study revealed S. glossinidius and Wolbachia in G. m. submorsitans of the area of lake Iro. It showed that co-infections between Wolbachia and S. glossinidius are rare in wild populations of G. m. submorsitans and that the tripartite associations vary according to trypanosome species as well as symbiotic mricroorganisms.

Recreating in vitro tripartite mycorrhizal associations through functional bacterial biofilms.

Arbuscular mycorrhizal fungi (AMF) and beneficial bacteria are found naturally associated with most terrestrial plant roots. While it is now well known that bacteria colonize AMF and can form aggregates and biofilms, little is known about how interactions between bacterial communities and AMF take place under both in situ and in vitro conditions. We investigated the impact of inoculation with AMF-associated bacteria (AABs) of AMF by in vitro recreation of the interaction on synthetic growth media in a two-compartment Petri plate system. The inoculated AABs were found to be associated with the mycorrhizal co-culture and were found to migrate along growing AMF hyphae and to be associated with the spore surface. AABs differentially influenced the growth of the AMF and their functional capability demonstrated by analysis of phosphate solubilization, nitrogen fixation, and biofilm formation. We have thus characterized these important interactions adding to a further understanding of the synergistic relationship between the two cross-kingdom microbial partners. KEY POINTS: • An in vitro assay was utilized to recreate functional biofilms with AMF-associated bacteria. • AMF-associated bacteria formed a biofilm and enhanced sporulation of Rhizophagus irregularis. • AMF-bacterial interactions through biofilm formation influence the functional capability of both partners.

Tripartite interactions: how immunity, microbiota and pathogens interact and affect pathogen virulence evolution.

The bipartite interactions between insect hosts and their bacterial gut microbiota, or their bacterial pathogens, are empirically and theoretically well-explored. However, direct, and indirect tripartite interactions will also likely occur inside a host. These interactions will almost certainly affect the trajectory of pathogen virulence evolution, an area that is currently under researched. The interactions within tripartite associations can be competitive, that is, exploitative-competition, interference-competition or apparent-competition. Competitive interactions will be significantly influenced by non-competitive effects, for example, immunopathology, immunosuppression, and microbiota-mediated tolerance. Considering a combination of these interactions and effects, will enable an increased understanding of the evolution of pathogen virulence. This new perspective allows us to identify several novel research questions, which we hope will be a useful framework for future research.

Prophages encoding human immune evasion cluster genes are enriched in Staphylococcus aureus isolated from chronic rhinosinusitis patients with nasal polyps.

Prophages affect bacterial fitness on multiple levels. These include bacterial infectivity, toxin secretion, virulence regulation, surface modification, immune stimulation and evasion and microbiome competition. Lysogenic conversion arms bacteria with novel accessory functions thereby increasing bacterial fitness, host adaptation and persistence, and antibiotic resistance. These properties allow the bacteria to occupy a niche long term and can contribute to chronic infections and inflammation such as chronic rhinosinusitis (CRS). In this study, we aimed to identify and characterize prophages present in Staphylococcus aureus from patients suffering from CRS in relation to CRS disease phenotype and severity. Prophage regions were identified using PHASTER. Various in silico tools like ResFinder and VF Analyzer were used to detect virulence genes and antibiotic resistance genes respectively. Progressive MAUVE and maximum likelihood were used for multiple sequence alignment and phylogenetics of prophages respectively. Disease severity of CRS patients was measured using computed tomography Lund–Mackay scores. Fifty-eight S. aureus clinical isolates (CIs) were obtained from 28 CRS patients without nasal polyp (CRSsNP) and 30 CRS patients with nasal polyp (CRSwNP). All CIs carried at least one prophage (average=3.6) and prophages contributed up to 7.7 % of the bacterial genome. Phage integrase genes were found in 55/58 (~95 %) S. aureus strains and 97/211 (~46 %) prophages. Prophages belonging to Sa3int integrase group (phiNM3, JS01, phiN315) (39/97, 40%) and Sa2int (phi2958PVL) (14/97, 14%) were the most prevalent prophages and harboured multiple virulence genes such as sak, scn, chp, lukE/D, sea. Intact prophages were more frequently identified in CRSwNP than in CRSsNP (P=0.0021). Intact prophages belonging to the Sa3int group were more frequent in CRSwNP than in CRSsNP (P=0.0008) and intact phiNM3 were exclusively found in CRSwNP patients (P=0.007). Our results expand the knowledge of prophages in S. aureus isolated from CRS patients and their possible role in disease development. These findings provide a platform for future investigations into potential tripartite associations between bacteria-prophage-human immune system, S. aureus evolution and CRS disease pathophysiology.

Co-inoculations with rhizobia and arbuscular mycorrhizal fungi alters mycorrhizal composition and lead to synergistic growth effects in cowpea that are fungal combination-dependent

Cowpea can effectively form tripartite symbiotic associations with nitrogen-fixing bacteria (NFB) and arbuscular mycorrhizal fungi (AMF) although the selection of compatible AMF species and rhizobial strains which are promoting cowpea growth remains a challenge. The aims of the current study were 1) to evaluate the response of cowpea plants to a symbiotic NFB and a multi-AMF inoculum and 2) to explore any interaction between the symbiotic NFB and the different AMF isolates. In a pot gnotobiotic trial, cowpea plants grown under limited N supply, were inoculated with or without a symbiotic nitrogen-fixing bacterium, Sinorhizobium meliloti, and combinations of three different AMF species namely Dominikia disticha, Claroideoglomus etunicatum and Rhizophagus irregularis. Experimental evaluation was determined through the measurement of above ground biomass, nutrient content and AMF root colonization. The presence of AMF species on cowpea roots was also determined with cloning and sequencing. Inoculation with both AMF and S. meliloti led to increased cowpea biomass production compared to inoculation with AMF only, but the presence of a positive effect depended on the specific AMF partners used. Inoculation with AMF alone had a highly positive impact on the growth and P uptake of cowpea, but the NFB inoculation was needed to address N deficiency in planta. The presence of both symbionts generally led to increased AMF colonization of the cowpea roots, however, plant colonization depended on the AMF species, and became even negative, when all three AMF inocula were used together. The AMF composition in plant roots was also altered in the presence of the S. meliloti. Plant nitrogen content of cowpea plants significantly increased under the presence of both symbionts compared to AMF alone, while phosphorus content was hardly affected by dual inoculations. The results show positive synergistic effects of the different AMF species and S.meliloti. Inoculation with all AMF isolates and S. meliloti led to high above ground biomass production and accumulation of N. The presence of S. meliloti increased P content in plants not inoculated with AMF. Finally, the efficiency of synergism depends on the specific AMF partners used and it is not related to their colonization levels.

<p><strong>Rooting Hebelomas: The Japanese ‘<em>Hebeloma radicosum’</em> is a distinct species, <em>Hebeloma sagarae</em> sp. nov. (Hymenogastraceae, Agaricales)</strong></p>

Hebeloma radicosum, known for its long ‘root’ and membranous ring, has regularly been recorded in Japan and been the subject of many studies revolving around ectomycorrhizal fungi exposed to high levels of nitrogen compounds and tripartite associations between fungi, host trees and mammals, including moles, wood mice and shrews. However, the species recorded in Japan is in fact not H. radicosum but a closely related species, also in Hebeloma section Myxocybe, described here as Hebeloma sagarae. This mushroom is macroscopically very similar to Hebeloma radicosum, also with a long ‘root’ and membranous ring, but distinct molecularly and in its distribution. We also examine other ‘rooting’ Hebeloma species from Japan: H. luchuense and H. radicosoides; both are shown to be members of H. sect. Scabrispora. A fourth ‘rooting’ Hebeloma from Japan is shown to be the same as or a close relative of Hebeloma danicum originally described from Europe.

Cophylogenetic patterns in algal symbionts correlate with repeated symbiont switches during diversification and geographic expansion of lichen-forming fungi in the genus Sticta (Ascomycota, Peltigeraceae)

Species in the fungal genus Sticta form symbiotic associations primarily with either green algae or cyanobacteria, but tripartite associations or photosymbiodemes involving both types of photobionts occur in some species. Sticta is known to associate with green algae in the genus Symbiochloris. However, previous studies have shown that algae from other genera, such as Heveochlorella, may also be suitable partners for Sticta. We examined the diversity of green algal partners in the genus Sticta and assessed the patterns of association between the host fungus and its algal symbiont. We used multi-locus sequence data from multiple individuals collected in Australia, Cuba, Madagascar, Mauritius, New Zealand, Reunion and South America to infer phylogenies for fungal and algal partners and performed tests of congruence to assess coevolution between the partners. In addition, event-based methods were implemented to examine which cophylogenetic processes have led to the observed association patterns in Sticta and its green algal symbionts. Our results show that in addition to Symbiochloris, Sticta associates with green algae from the genera Chloroidium, Coccomyxa, Elliptochloris and Heveochlorella, the latter being the most common algal symbiont associated with Sticta in this study. Geography plays a strong role in shaping fungal-algal association patterns in Sticta as mycobionts associate with different algal lineages in different geographic locations. While fungal and algal phylogenies were mostly congruent, event-based methods did not find any evidence for cospeciation between the partners. Instead, the association patterns observed in Sticta and associated algae, were largely explained by other cophylogenetic events such as host-switches, losses of symbiont and failure of the symbiont to diverge with its host. Our results also show that tripartite associations with green algae evolved multiple times in Sticta.

Impact of multilateral place dimensions on corporate brand attractiveness and identification in higher education: Business school insights

This study scrutinizes how places meaningfully burnish corporate brand attractiveness and identification. To date, extant research adopts a mono-lateral, rather than multi-lateral perspective. Marshalling the corporate brand identification theoretical perspective, the findings make a theoretical advance by explicating how a nascent corporate brand can be enhanced through its positive associations with places. The research setting for this study was a newly-established business school and the research focused on international postgraduate students who are a key business school constituency. In this study, the tripartite place associations which meaningfully enhanced customer corporate brand attractiveness and identification were found to be country, city, and corporate locale.

Detection of Wolbachia and different trypanosome species in Glossina palpalis palpalis populations from three sleeping sickness foci of southern Cameroon

BackgroundAfrican trypanosomiases are caused by trypanosomes that are cyclically transmitted by tsetse. Investigations aiming to generate knowledge on the bacterial fauna of tsetse have revealed distinct symbiotic microorganisms. Furthermore, studies addressing the tripartite association between trypanosomes-tsetse-symbionts relationship have so far been contradictory. Most studies included Sodalis glossinudius and, consequently, the association involving Wolbachia is poorly understood. Understanding the vectorial competence of tsetse requires decrypting these tripartite associations. In this study, we identified Wolbachia and trypanosomes in Glossina palpalis palpalis from three human African trypanosomiasis (HAT) foci in southern Cameroon.MethodsTsetse flies were captured with pyramidal traps in the Bipindi, Campo and Fontem HAT foci. After morphological identification, DNA was extracted from whole tsetse flies and Wolbachia and trypanosomes were identified by PCR using different trypanosome-specific primers and two Wolbachia-specific primers (Wolbachia surface protein and 16S rRNA genes). Statistical analyses were performed to compare the trypanosome and Wolbachia infection rates between villages and different foci and to look for an association between these microorganisms.ResultsFrom a total of 2122 tsetse flies, 790 G. p. palpalis were analyzed. About 25.32% of flies hosted Wolbachia and 31.84% of non-teneral flies were infected by at least one trypanosome species. There was no significant difference between the global Wolbachia prevalence revealed by the two markers while some differences were observed between HAT foci. From 248 G. p. palpalis with trypanosome infections, 62.90% were with T. vivax, 34.68% with T. congolense forest, 16.13% with T. brucei (s.l.) and 2.42% with T. congolense savannah. Of all trypanosome-infected flies, 29.84% hosted Wolbachia and no association was observed between Wolbachia and trypanosome co-infections.ConclusionsThis study revealed differences in the prevalence of Wolbachia and trypanosomes in G. p. palpalis according to HAT foci. The use of only one marker has underestimated the prevalence of Wolbachia, thus more markers in subsequent studies may improve its detection. The presence of Wolbachia seems to have no impact on the establishment of trypanosomes in G. p. palpalis. The tripartite association between tsetse, Wolbachia and trypanosomes varies according to studied areas. Studies aiming to evaluate the genetic polymorphism of Wolbachia and its density in tsetse flies could help to better understand this association.

The role of affective temperaments assessed by the Temperament Evaluation of Memphis, Pisa and San Diego-Autoquestionnaire (TEMPS-A) in the relationship between morningness-eveningness and bipolarity

BackgroundGrowing number of studies indicates a link between eveningness chronotype, affective temperaments and bipolarity, both in patients with mood disorders and in general population. Given these tripartite associations, we hypothesized that the effect of circadian preferences on the bipolarity may be mediated by the temperamental traits. MethodsThe study included 1449 subjects (402 men and 1047 women). They all fulfilled a web-based questionnaire, consisting of the Composite Scale of Morningness (CSM), Mood Disorder Questionnaire (MDQ), Hypomania Checklist-32 (HCL-32) and the Temperament Evaluation of the Memphis, Pisa and San Diego-Autoquestionnaire (TEMPS-A). The role of temperamental traits in the relationship between morningness-eveningness and bipolarity was assessed using mediation analysis. ResultsMorningness is correlated with lower bipolarity measured by the MDQ and HCL-32, and to lower scores of depressive, cyclothymic, irritable and anxious temperaments of the TEMPS-A. There is no significant association between morningness and hyperthymic traits. Cyclothymic and irritable traits are full mediators of the association between chronotype and bipolarity, influencing bipolarity independently from circadian preferences. Depressive and anxious traits are partial mediators of this association, increasing the effect of eveningness on bipolarity. LimitationsThe indirectness of the findings in the web-based study and disproportion of participants’ gender. ConclusionsOur study confirmed that eveningness is associated with bipolarity. In case of depressive and anxious temperaments, bipolarity is associated stronger with eveningness than with the TEMPS-A scores. On the other hand, cyclothymic and irritable temperaments were associated with bipolarity independently from circadian preferences.

Schizoxylon as an experimental model for studying interkingdom symbiosis.

Experiments to re-synthesise lichens so far focused on co-cultures of fungal and algal partners. However, recent studies have revealed that bacterial communities colonise lichens in a stable and host-specific manner. We were therefore interested in testing how lichenised fungi and algae interact with selected bacteria in an experimental setup. We selected the symbiotic system of Schizoxylon albescens and the algal genera Coccomyxa and Trebouxia as a suitable model. We isolated bacterial strains from the naturally occurring bacterial fraction of freshly collected specimens and established tripartite associations under mixed culture experiments. The bacteria belong to Actinobacteria, Firmicutes and Proteobacteria and corresponded to groups already found associated with fungi including lichens. In mixed cultures with Coccomyxa, the fungus formed a characteristic filamentous matrix and tightly contacted the algae; the bacteria distributed in small patches between the algal cells and attached to the cell walls. In mixed cultures with Trebouxia, the fungus did not develop the filamentous matrix, but bacterial cells were observed to be tightly adhering to the fungal hyphae. Our experiments show that this tripartite fungal-algal-bacterial model system can be maintained in culture and can offer multiple opportunities for functional studies based on experiments under controlled conditions in the laboratory.

Functional analysis of liverworts in dual symbiosis with Glomeromycota and Mucoromycotina fungi under a simulated Palaeozoic CO2 decline.

Most land plants form mutualistic associations with arbuscular mycorrhizal fungi of the Glomeromycota, but recent studies have found that ancient plant lineages form mutualisms with Mucoromycotina fungi. Simultaneous associations with both fungal lineages have now been found in some plants, necessitating studies to understand the functional and evolutionary significance of these tripartite associations for the first time. We investigate the physiology and cytology of dual fungal symbioses in the early-diverging liverworts Allisonia and Neohodgsonia at modern and Palaeozoic-like elevated atmospheric CO2 concentrations under which they are thought to have evolved. We found enhanced carbon cost to liverworts with simultaneous Mucoromycotina and Glomeromycota associations, greater nutrient gain compared with those symbiotic with only one fungal group in previous experiments and contrasting responses to atmospheric CO2 among liverwort–fungal symbioses. In liverwort–Mucoromycotina symbioses, there is increased P-for-C and N-for-C exchange efficiency at 440 p.p.m. compared with 1500 p.p.m. CO2. In liverwort–Glomeromycota symbioses, P-for-C exchange is lower at ambient CO2 compared with elevated CO2. No characteristic cytologies of dual symbiosis were identified. We provide evidence of a distinct physiological niche for plant symbioses with Mucoromycotina fungi, giving novel insight into why dual symbioses with Mucoromycotina and Glomeromycota fungi persist to the present day.

Tripartite associations among bacteriophage WO, Wolbachia, and host affected by temperature and age in Tetranychus urticae

A phage density model of cytoplasmic incompatibility (CI), which means lytic phages reduce bacterial density associated with CI, significantly enhances our understanding of the tripartite associations among bacteriophage WO, Wolbachia and host. However, WO may alternate between lytic and lysogenic life cycles or change phage production under certain conditions including temperature, host age and host species background. Here, extreme temperatures can induce an alteration in the life cycle of WO and change the tripartite associations among WO, Wolbachia and CI. Based on the accumulation of the WO load, WO can transform into the lytic life cycle with increasing age. These findings confirmed that the environment plays an important role in the associations among WO, Wolbachia and host.

Effects of co-inoculation with arbuscular mycorrhizal fungi and rhizobia on soybean growth as related to root architecture and availability of N and P

Soybean plants can form tripartite symbiotic associations with rhizobia and arbuscular mycorrhizal (AM) fungi, but little is known about effects of co-inoculation with rhizobia and AM fungi on plant growth, or their relationships to root architecture as well as nitrogen (N) and phosphorus (P) availability. In the present study, two soybean genotypes contrasting in root architecture were grown in a field experiment to evaluate relationships among soybean root architecture, AMF colonization, and nodulation under natural conditions. Additionally, a soil pot experiment in greenhouse was conducted to investigate the effects of co-inoculation with rhizobia and AM fungi on soybean growth, and uptake of N and P. Our results indicated that there was a complementary relationship between root architecture and AMF colonization in the field. The deep root soybean genotype had greater AMF colonization at low P, but better nodulation with high P supply than the shallow root genotype. A synergistic relationship dependent on N and P status exists between rhizobia and AM fungi on soybean growth. Co-inoculation with rhizobia and AM fungi significantly increased soybean growth under low P and/or low N conditions as indicated by increased shoot dry weight, along with plant N and P content. There were no significant effects of inoculation under adequate N and P conditions. Furthermore, the effects of co-inoculation were related to root architecture. The deep root genotype, HN112, benefited more from co-inoculation than the shallow root genotype, HN89. Our results elucidate new insights into the relationship between rhizobia, AM fungi, and plant growth under limitation of multiple nutrients, and thereby provides a theoretical basis for application of co-inoculation in field-grown soybean.

Plants, Mycorrhizal Fungi, and Bacteria: A Network of Interactions

This review focuses on interactions among plants, mycorrhizal fungi, and bacteria, testing the hypothesis whether mycorrhizas can be defined as tripartite associations. After summarizing the main biological features of mycorrhizas, we illustrate the different types of interaction occurring between mycorrhizal fungi and bacteria, from loosely associated microbes to endobacteria. We then discuss, in the context of nutritional strategies, the mechanisms that operate among members of the consortium and that often promote plant growth. Release of active molecules, including volatiles, and physical contact among the partners seem important for the establishment of the bacteria/mycorrhizal fungus/plant network. The potential involvement of quorum sensing and Type III secretion systems is discussed, even if the exact nature of the complex interspecies/interphylum interactions remains unclear.

Ant‐plants and fungi: a new threeway symbiosis

Symbioses between plants and fungi, fungi and ants, and ants and plants all play important roles in ecosystems. Symbioses involving all three partners appear to be rare. Here, we describe a novel tripartite symbiosis in which ants and a fungus inhabit domatia of an ant-plant, and present evidence that such interactions are widespread. We investigated 139 individuals of the African ant-plant Leonardoxa africana for occurrence of fungus. Behaviour of mutualist ants toward the fungus within domatia was observed using a video camera fitted with an endoscope. Fungi were identified by sequencing a fragment of their ribosomal DNA. Fungi were always present in domatia occupied by mutualist ants but never in domatia occupied by opportunistic or parasitic ants. Ants appear to favour the propagation, removal and maintenance of the fungus. Similar fungi were associated with other ant-plants in Cameroon. All belong to the ascomycete order Chaetothyriales; those from L. africana formed a monophyletic clade. These new plant-ant-fungus associations seem to be specific, as demonstrated within Leonardoxa and as suggested by fungal phyletic identities. Such tripartite associations are widespread in African ant-plants but have long been overlooked. Taking fungal partners into account will greatly enhance our understanding of symbiotic ant-plant mutualisms.

Topographic position modulates the mycorrhizal response of oak trees to interannual rainfall variability

California coast live oak (Quercus agrifolia) forms tripartite symbiotic associations with arbuscular (AMF) and ectomycorrhizal (EMF) fungi. We selected oak individuals differing in topographic position and depth to groundwater (mesic valley vs. xeric hill sites) to investigate changes of tree mycorrhizal status in response to interannual rainfall variability. EMF root colonization, as well as hyphal abundance and viability in upper rhizosphere soil (0-30 cm), were negatively affected by severe multi-year drought, although not to the same extent in each topographic location. Oak trees growing in hill sites showed EMF colonization levels <1% in upper roots during drought. By contrast, oaks in valley sites maintained much higher EMF colonization (>19%) in upper roots during drought. EMF root colonization increased sharply at both topographic positions during the ensuing wet year (78% in valley, 49% in hill), which indicates that the mycorrhizal status of roots in upper rhizosphere soil is highly responsive to interannual rainfall variability. Across sites and years, percentage EMF colonization and soil hyphal density and viability were strongly positively correlated with soil moisture potential, but percentage AMF root colonization was not. Interestingly, changes in percentage EMF root colonization and density of viable hyphae between a wet and a dry year were proportionally much greater in xeric hill sites than in mesic valley sites. The mycorrhizal status of oak trees was particularly responsive to changes in soil moisture at the hill sites, where roots in upper rhizosphere soil shifted from almost exclusively AMF during severe drought to predominantly EMF during the ensuing wet year. By contrast, the mycorrhizal status of oaks in the valley sites was less strongly coupled to current meteorological conditions, as roots in upper soil layers remained predominantly EMF during both a dry and a wet year. Canopy shading and hydraulic lift by oaks in valley sites likely contributed to maintain the integrity and viability of EMF roots and extraradical hyphae in upper rhizosphere soil during extended drought. Our results suggest that oak woodlands in water-limited ecosystems may become increasingly reliant on the AMF symbiosis under future climate change scenarios for the U.S. southwest and other world regions.

Geodynamic significance of S-type granites in circum-Pacific orogens

Research Article| July 01, 2008 Geodynamic significance of S-type granites in circum-Pacific orogens W.J. Collins; W.J. Collins 1School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4814, Australia Search for other works by this author on: GSW Google Scholar S.W. Richards S.W. Richards 2Research School of Earth Sciences, Australian National University, Canberra 0200, Australia Search for other works by this author on: GSW Google Scholar Author and Article Information W.J. Collins 1School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4814, Australia S.W. Richards 2Research School of Earth Sciences, Australian National University, Canberra 0200, Australia Publisher: Geological Society of America Received: 29 Nov 2007 Revision Received: 04 Apr 2008 Accepted: 09 Apr 2008 First Online: 02 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2008 Geological Society of America Geology (2008) 36 (7): 559–562. https://doi.org/10.1130/G24658A.1 Article history Received: 29 Nov 2007 Revision Received: 04 Apr 2008 Accepted: 09 Apr 2008 First Online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation W.J. Collins, S.W. Richards; Geodynamic significance of S-type granites in circum-Pacific orogens. Geology 2008;; 36 (7): 559–562. doi: https://doi.org/10.1130/G24658A.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract In Phanerozoic circum-Pacific orogenic belts, most “post-collisional” S-type granites and associated high-temperature, low-pressure metamorphic complexes formed during early arc extension. The granites are part of a tripartite association consisting of (1) inboard S-type granite, (2) outboard oceanic arc, and (3) intervening, turbidite-filled backarc basin. S-type granites herald the formation of new outboard oceanic arc and extensional backarc systems, but thickening of a preexisting, sediment-dominated back-arc basin is a prerequisite for their generation. In these environments, S-type plutonism is triggered by renewal of arc magmatism following thickening, when hot basaltic magmas are intruded into the thickened backarc crust once slab retreat is reestablished. With ongoing extension during retreat, the crust becomes progressively thinned, the sedimentary contribution is diminished, and the granites lose their S-type character. Such tripartite associations involving S-type granite are probably diagnostic of repeated slab-retreat episodes, and the Jurassic U.S. cordillera might be an example. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.