Internalizing Conservation through Our Own Microbes

This is the peer reviewed version of the following article: BA Sikes (2012) Internalizing Conservation through our own Microbes. Conservation Biology, 26(2): 198. http://dx.doi.org/10.1111/j.1523-1739.2012.01834.x, which has been published in final form at http://doi.org/10.1111/j.1523-1739.2012.01834.x. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving

When do arbuscular mycorrhizal fungi protect plant roots from pathogens?

This is an Accepted Manuscript of an article published by Taylor & Francis in Plant Signaling and Behavior on March 10, 2010, available online: http://www.tandfonline.com/10.4161/psb.5.6.11776.Arbuscular mycorrhizal (AM) fungi are mainly thought to facilitate phosphorus uptake in plants, but they can also perform several other functions that are equally beneficial. Our recent study sheds light on the factors determining one such function, enhanced plant protection from root pathogens. Root infection by the fungal pathogen Fusarium oxysporum was determined by both plant susceptibility and the ability of an AM fungal partner to suppress the pathogen. The non-susceptible plant species (Allium cepa) had limited F. oxysporum infection even without AM fungi. In contrast, the susceptible plant species (Setaria glauca) was heavily infected and only AM fungi in the family Glomeraceae limited pathogen abundance. Plant susceptibility to pathogens was likely determined by contrasting root architectures between plants, with the simple rooted plant (A. cepa) presenting fewer sites for infection.AM fungal colonization, however, was not limited in the same way in part because plants with fewer, simple roots are more mycorrhizal dependent. Protection only by Glomus species also indicates that whatever the mechanism(s) of this function, it responds to AM fungal families differently. While poor at pathogen protection, AM fungal species in the family Gigasporaceae most benefited the growth of the simple rooted plant species. Our research indicates that plant trait differences, such as root architecture can determine how important each mycorrhizal function is to plant growth but the ability to provide these functions differs among AM fungi

Catfacing of tomatoes as influenced by pruning and growth regulator applications

Field studies were conducted at the University of Tennessee Agricultural Experiment Station at Knoxville in 1974 and 1975 to determine the influence of pruning and auxin on the incidence of catfacing in fresh market tomatoes (Lycopersicon esculentum, cv. Manapal). It was found that time of pruning affected catfacing more than did the amount of pruning. A 2 stem, delayed pruning system produced a lower percentage of catfaced fruit than either 1 or 2 stem early priming systems. Catfacing occurred on plants in an unpruned system equal to that of the delayed pruning system, but early marketable yields were lower with unpruned plants. Nitrogen fertilization had no effect on the incidence of catfacing. Results indicated that certain concentrations of applied synthetic auxin (α -napthalene-acetic acid) could mitigate the increased catfacing response of early-pruned treatments. Plants receiving auxin applications were observed to have vegetative characteristics similar to those of delay-pruned plants which had no auxin applied. These findings and the characteristic nature of the deformity suggest that growth regulator balance may influence the information of catfaced fruit

Suppression of root-endogenous fungi in persistently inundated Typha roots

This is an Accepted Manuscript of an article published by Taylor & Francis in Mycologia in 2019, available online: https://www.tandfonline.com/toc/umyc20/currentWetland soils are defined by anoxic and reducing conditions that impose biogeochemically hostile conditions on plant roots and their endogenous fungal communities. The cosmopolitan wetland plant Typha L. mitigates root-zone anoxia efficiently, such that roots of these plants may constitute fungal habitats similar to roots in subaerially-exposed soils. Alternatively, fungi may compete with plant cells for limited oxygen in inundated roots. We hypothesized that extrinsic environmental factors may reduce fungal incidence and affect fungal community structure within inundated roots as compared to those in subaerially-exposed soils. We sampled roots of Typha spp. plants across inundation gradients in constructed reservoirs; root subsamples were microscopically examined for fungal structures, and morphologically-distinct fungal endophytes were cultured and isolated from surface sterilized subsamples. We found that the incidence of fungal hyphae was suppressed for all types of vegetative mycelia when roots were inundated, regardless of depth, but that there were no obvious differences in community composition of fungi cultured from roots growing in inundated vs subaerially-exposed soils. This suggests that the suppression of hyphae we observed in root samples did not result from changes in community composition. Instead, low hyphal incidence in inundated Typha roots may reflect germinal inhibition or unsuccessful initial colonization, possibly owing to plant-mediated redox dynamism in the surrounding soil. No variation was seen in the incidence of asexual spores, or chytridiomycetes, nor were there significant differences between geographically disparate sampling sites. Communities of root-endogenous fungi may therefore be influenced more strongly by external environmental factors, than by the environments that plant roots comprise

Method or madness: does OTU delineation bias our perceptions of fungal ecology?

This is the author's manuscript. The definitive version is available at www.newphytologist.co

Arbuscular mycorrhizal fungal communities change among three stages of primary sand dune succession but do not alter plant growth

Plant interactions with soil biota could have a significant impact on plant successional trajectory by benefiting plants in a particular successional stage over others. The influence of soil mutualists such as mycorrhizal fungi is thought to be an important feedback component, yet they have shown benefits to both early and late successional plants that could either retard or accelerate succession. Here we first determine if arbuscular mycorrhizal (AM) fungi differ among three stages of primary sand dune succession and then if they alter growth of plants from particular successional stages. We isolated AM fungal inoculum from early, intermediate or late stages of a primary dune succession and compared them using cloning and sequencing. We then grew eight plant species that dominate within each of these successional stages with each AM fungal inoculum. We measured fungal growth to assess potential AM functional differences and plant growth to determine if AM fungi positively or negatively affect plants. AM fungi isolated from early succession were more phylogenetically diverse relative to intermediate and late succession while late successional fungi consistently produced more soil hyphae and arbuscules. Despite these differences, inocula from different successional stages had similar effects on the growth of all plant species. Host plant biomass was not affected by mycorrhizal inoculation relative to un-inoculated controls. Although mycorrhizal communities differ among primary dune successional stages and formed different fungal structures, these differences did not directly affect the growth of plants from different dune successional stages in our experiment and therefore may be less likely to directly contribute to plant succession in sand dunes

Field-based effects of allelopathy in invaded tallgrass prairie

Allelopathic phytochemicals have been linked to invasion success, but their role in the invasion process remains unclear. Toxicity effects demonstrated with lab bioassays may be neutralized in soils, and their role in population expansion can be intertwined with nonallelopathic processes that also influence dispersal and establishment. Here, we use greenhouse experiments to test the soil-based impacts of invasive fine fescue (Festuca rubra L.) on recruitment in tallgrass prairie. Fescue roots release the growth inhibitor m-tyrosine. Using root washes and fescue-conditioned soils to mimic field potency, we determined allelopathic impacts on recruitment, including intraspecific limitation. We also tested whether nonallelopathic factors (propagule pressure, disturbance, and fertility) influence invasion into constructed fescue and prairie mesocosms, and whether root washes inhibit arbuscular mycorrhizal (AM) fungi. We observed significant negative effects of fescue soils and root washes on germination and seedling survival, including on fescue itself. Mesocosm invasion, however, was determined more by nonallelopathic mechanisms (propagule pressure and rapid growth). In prairie mesocosms, fescue invasion was higher than its own understory, with no effects of disturbance or fertility. Tallgrass species had difficulty establishing in all environments, regardless of propagule pressure. Impacts on AM fungal hyphal length and spore production were insignificant. Our results suggest that nonallelopathic traits may be sufficient to explain fescue invasion, with allelopathy likely emerging as a final "coup de grâce" for recruiting native grasses once dominance has been attained. Allelopathic species, including fine fescue, may thus not necessarily be invasive unless nonallelopathic traits facilitate establishment prior to the accumulation of soil-based toxins

Plant and fungal identity determines pathogen protection of plant roots by arbuscular mycorrhizas

This is the peer reviewed version of the following article: BA Sikes, K Cottenie and JN Klironomos. (2009) Plant and fungal identity determines pathogen protection of plant roots by arbuscular mycorrhizas. Journal of Ecology 97: 1274-1280. http://dx.doi.org/10.1111/j.1365-2745.2009.01557.x, which has been published in final form at http://doi.org/10.1111/j.1365-2745.2009.01557.x This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.1. A major benefit of the mycorrhizal symbiosis is that it can protect plants from below-ground enemies, such as pathogens. Previous studies have indicated that plant identity (particularly plants that differ in root system architecture) or fungal identity (fungi from different families within the Glomeromycota) can determine the degree of protection from infection by pathogens. Here, we test the combined effects of plant and fungal identity to assess if there is a strong interaction between these two factors. 2. We paired one of two plants (Setaria glauca, a plant with a finely branched root system and Allium cepa, which has a simple root system) with one of six different fungal species from two families within the Glomeromycota. We assessed the degree to which plant identity, fungal identity and their interaction determined infection by Fusarium oxysporum, a common plant pathogen. 3. Our results show that the interaction between plant and fungal identity can be an important determinant of root infection by the pathogen. Infection by Fusarium was less severe in Allium (simple root system) or when Setaria (complex root system) was associated with a fungus from the family Glomeraceae. We also detected significant plant growth responses to the treatments; the fine-rooted Setaria benefited more from associating with a member of the family Glomeraceae, while Allium benefited more from associating with a member of the family Gigasporaceae. 4. Synthesis. This study supports previous claims that plants with complex root systems are more susceptible to infection by pathogens, and that the arbuscular mycorrhizal symbiosis can reduce infection in such plants – provided that the plant is colonized by a mycorrhizal fungus that can offer protection, such as the isolates of Glomus used here

Plant and root endophyte assembly history: interactive effects on native and exotic plants

Funded by Society for Conservation Biology; National Research Initiative of the USDA Cooperative State Research, Education and Extension Service; Terman Fellowship of Stanford UniversityDifferences in the arrival timing of plants and soil biota may result in different plant communities through priority effects, potentially affecting the success of native vs. exotic plants, but experimental evidence is largely lacking. We conducted a greenhouse experiment to investigate whether the assembly history of plants and fungal root endophytes could interact to influence plant emergence and biomass. We introduced a grass species and eight fungal species from one of three land-use types (undisturbed, disturbed, or pasture sites in a Florida scrubland) in factorial combinations. We then introduced all plants and fungi from the other land-use types 2 weeks later. Plant emergence was monitored for 6 months, and final plant biomass and fungal species composition assessed. The emergence and growth of the exotic Melinis repens and the native Schizacharyium niveum were affected negatively when introduced early with their “home” fungi, but early introduction of a different plant species or fungi from a different site type eliminated these negative effects, providing evidence for interactive priority effects. Interactive effects of plant and fungal arrival history may be an overlooked determinant of plant community structure and may provide an effective management tool to inhibit biological invasion and aid ecosystem restoration

Deciphering the relative contributions of multiple functions within plant-microbe symbioses

This is the publisher's version, also available electronically from http://www.esajournals.org/doi/abs/10.1890/09-1858.1For microbial symbioses with plants, such as mycorrhizas, we typically quantify either the net effects of one partner on another or a single function a symbiont provides. However, many microbial symbioses provide multiple functions to plants that vary based on the microbial species or functional group, plant species, and environment. Here we quantified the relative contributions of multiple functions provided by arbuscular mycorrhizal (AM) fungi to symbiont-mediated changes in plant biomass. We used two published data sets, one that measured multiple functions (pathogen protection and nutrient uptake) on a single plant and one that measured a single function (pathogen protection) on multiple plants. Using structural equation modeling, we observed strong variation in the functional pathways by which AM fungi altered plant growth; changes in plant biomass were associated with different functions (and different AM fungal functional groups) for the different plant species. Utilizing this methodology across multiple partners and environments will allow researchers to gauge the relative importance of functions they isolate and, perhaps more importantly, those they did not consider. This baseline information is essential for establishing the specific mechanisms by which microbial symbioses influence plant diversity and to more effectively utilize these organisms in agriculture, restoration and conservation