Adding Authenticity to Inquiry in a First-Year, Research-Based, Biology Laboratory Course.

Course-based undergraduate research experiences (CUREs) are an effective way to integrate research into an undergraduate science curriculum and extend research experiences to a large, diverse group of early-career students. We developed a biology CURE at the University of Miami (UM) called the UM Authentic Research Laboratories (UMARL), in which groups of first-year students investigated novel questions and conducted projects of their own design related to the research themes of the faculty instructors. Herein, we describe the implementation and student outcomes of this long-running CURE. Using a national survey of student learning through research experiences in courses, we found that UMARL led to high student self-reported learning gains in research skills such as data analysis and science communication, as well as personal development skills such as self-confidence and self-efficacy. Our analysis of academic outcomes revealed that the odds of students who took UMARL engaging in individual research, graduating with a degree in science, technology, engineering, or mathematics (STEM) within 4 years, and graduating with honors were 1.5-1.7 times greater than the odds for a matched group of students from UM's traditional biology labs. The authenticity of UMARL may have fostered students' confidence that they can do real research, reinforcing their persistence in STEM.

Investigation of Plant Interactions Across Common Mycorrhizal Networks Using Rotated Cores.

Arbuscular mycorrhizal (AM) fungi influence plant mineral nutrient uptake and growth, hence, they have the potential to influence plant interactions. The power of their influence is in extraradical mycelia that spread beyond nutrient depletion zones found near roots to ultimately interconnect individuals within a common mycorrhizal network (CMN). Most experiments, however, have investigated the role of AM fungi in plant interactions by growing plants with versus without mycorrhizal fungi, a method that fails to explicitly address the role of CMNs. Here, we propose a method that manipulates CMNs to investigate their role in plant interactions. Our method uses modified containers with conical bottoms with a nylon mesh and/or hydrophobic material covering slotted openings, 15N fertilizer, and a nutrient-poor interstitial sand. CMNs are left either intact between interacting individuals, severed by rotation of containers, or prevented from forming by a solid barrier. Our findings suggest that rotating containers is sufficient to disrupt CMNs and prevent their effects on plant interactions across CMNs. Our approach is advantageous because it mimics aspects of nature, such as seedlings tapping into already established CMNs and the use of a suite of AM fungi that may provide diverse benefits. Although our experiment is limited to investigating plants at the seedling stage, plant interactions across CMNs can be detected using our approach which therefore can be applied to investigate biological questions about the functioning of CMNs in ecosystems.

Arbuscular common mycorrhizal networks mediate intra- and interspecific interactions of two prairie grasses.

Arbuscular mycorrhizal fungi form extensive common mycorrhizal networks (CMNs) that may interconnect neighboring root systems of the same or different plant species, thereby potentially influencing the distribution of limiting mineral nutrients among plants. We examined how CMNs affected intra- and interspecific interactions within and between populations of Andropogon gerardii, a highly mycorrhiza dependent, dominant prairie grass and Elymus canadensis, a moderately dependent, subordinate prairie species. We grew A. gerardii and E. canadensis alone and intermixed in microcosms, with individual root systems isolated, but either interconnected by CMNs or with CMNs severed weekly. CMNs, which provided access to a large soil volume, improved survival of both A. gerardii and E. canadensis, but intensified intraspecific competition for A. gerardii. When mixed with E. canadensis, A. gerardii overyielded aboveground biomass in the presence of intact CMNs but not when CMNs were severed, suggesting that A. gerardii with intact CMNs most benefitted from weaker interspecific than intraspecific interactions across CMNs. CMNs improved manganese uptake by both species, with the largest plants receiving the most manganese. Enhanced growth in consequence of improved mineral nutrition led to large E. canadensis in intact CMNs experiencing water-stress, as indicated by 13C isotope abundance. Our findings suggest that in prairie plant communities, CMNs may influence mineral nutrient distribution, water relations, within-species size hierarchies, and between-species interactions.

Common mycorrhizal networks amplify competition by preferential mineral nutrient allocation to large host plants.

Arbuscular mycorrhizal (AM) fungi interconnect plants in common mycorrhizal networks (CMNs) which can amplify competition among neighbors. Amplified competition might result from the fungi supplying mineral nutrients preferentially to hosts that abundantly provide fixed carbon, as suggested by research with organ-cultured roots. We examined whether CMNs supplied (15) N preferentially to large, nonshaded, whole plants. We conducted an intraspecific target-neighbor pot experiment with Andropogon gerardii and several AM fungi in intact, severed or prevented CMNs. Neighbors were supplied (15) N, and half of the target plants were shaded. Intact CMNs increased target dry weight (DW), intensified competition and increased size inequality. Shading decreased target weight, but shaded plants in intact CMNs had mycorrhizal colonization similar to that of sunlit plants. AM fungi in intact CMNs acquired (15) N from the substrate of neighbors and preferentially allocated it to sunlit, large, target plants. Sunlit, intact CMN, target plants acquired as much as 27% of their nitrogen from the vicinity of their neighbors, but shaded targets did not. These results suggest that AM fungi in CMNs preferentially provide mineral nutrients to those conspecific host individuals best able to provide them with fixed carbon or representing the strongest sinks, thereby potentially amplifying asymmetric competition below ground.

Eucalyptus obliqua seedling growth in organic vs. mineral soil horizons.

Eucalyptus obliqua, the most widespread timber tree in Tasmania, is a pioneer after fire which can eliminate the organic layer of forest soil, exposing the underlying mineral soil. We compared seedling growth, mycorrhiza formation, and mineral nutrient limitation in organic layer vs. mineral soil. We grew E. obliqua seedlings separately in pots of organic layer and mineral soil in a glasshouse. Additional treatments of organic soil only, involved fully crossed methyl-bromide fumigation and fertilization. Fertilization comprised chelated iron for 121 days after transplant (DAT) followed by soluble phosphorus. At 357 DAT, whole plant dry weight was three times greater in ambient organic than in mineral soil. In organic soil, fumigation halved ectomycorrhiza abundance and reduced seedling growth at 149 DAT, but by 357 DAT when negative effects of fumigation on seedling growth had disappeared, neither fumigation nor fertilization affected mycorrhiza abundance. Iron fertilization diminished seedling growth, but subsequent phosphorus fertilization improved it. E. obliqua seedlings grow much better in organic layer soil than in mineral soil, although phosphorus remains limiting. The prevalent forestry practice of burning to mineral soil after timber harvest exposes a poor growth medium likely only partially compensated by fire-induced mineral soil alterations.

Phosphorus limits Eucalyptus grandis seedling growth in an unburnt rain forest soil.

Although rain forest is characterized as pyrophobic, pyrophilic giant eucalypts grow as rain forest emergents in both temperate and tropical Australia. In temperate Australia, such eucalypts depend on extensive, infrequent fires to produce conditions suitable for seedling growth. Little is known, however, about constraints on seedlings of tropical giant eucalypts. We tested whether seedlings of Eucalyptus grandis experience edaphic constraints similar to their temperate counterparts. We hypothesized that phosphorous addition would alleviate edaphic constraints. We grew seedlings in a factorial experiment combining fumigation (to simulate nutrient release and soil pasteurization by fire), soil type (E. grandis forest versus rain forest soil) and phosphorus addition as factors. We found that phosphorus was the principal factor limiting E. grandis seedling survival and growth in rain forest soil, and that fumigation enhanced survival of seedlings in both E. grandis forest and rain forest soil. We conclude that similar to edaphic constraints on temperate giant eucalypts, mineral nutrient and biotic attributes of a tropical rain forest soil may hamper E. grandis seedling establishment. In rain forest soil, E. grandis seedlings benefited from conditions akin to a fire-generated ashbed (i.e., an "ashbed effect").

Arbuscular-mycorrhizal networks inhibit Eucalyptus tetrodonta seedlings in rain forest soil microcosms.

Eucalyptus tetrodonta, a co-dominant tree species of tropical, northern Australian savannas, does not invade adjacent monsoon rain forest unless the forest is burnt intensely. Such facilitation by fire of seedling establishment is known as the "ashbed effect." Because the ashbed effect might involve disruption of common mycorrhizal networks, we hypothesized that in the absence of fire, intact rain forest arbuscular mycorrhizal (AM) networks inhibit E. tetrodonta seedlings. Although arbuscular mycorrhizas predominate in the rain forest, common tree species of the northern Australian savannas (including adult E. tetrodonta) host ectomycorrhizas. To test our hypothesis, we grew E. tetrodonta and Ceiba pentandra (an AM-responsive species used to confirm treatments) separately in microcosms of ambient or methyl-bromide fumigated rain forest soil with or without severing potential mycorrhizal fungus connections to an AM nurse plant, Litsea glutinosa. As expected, C. pentandra formed mycorrhizas in all treatments but had the most root colonization and grew fastest in ambient soil. E. tetrodonta seedlings also formed AM in all treatments, but severing hyphae in fumigated soil produced the least colonization and the best growth. Three of ten E. tetrodonta seedlings in ambient soil with intact network hyphae died. Because foliar chlorosis was symptomatic of iron deficiency, after 130 days we began to fertilize half the E. tetrodonta seedlings in ambient soil with an iron solution. Iron fertilization completely remedied chlorosis and stimulated leaf growth. Our microcosm results suggest that in intact rain forest, common AM networks mediate belowground competition and AM fungi may exacerbate iron deficiency, thereby enhancing resistance to E. tetrodonta invasion. Common AM networks-previously unrecognized as contributors to the ashbed effect-probably help to maintain the rain forest-savanna boundary.

Common mycorrhizal networks amplify size inequality in Andropogon gerardii monocultures.

Arbuscular mycorrhizal fungi can interconnect plant root systems through hyphal common mycorrhizal networks, which may influence the distribution of limiting mineral nutrients among interconnected individuals, potentially affecting competition and consequent size inequality. Using a microcosm model system, we investigated whether the members of Andropogon gerardii monocultures compete via common mycorrhizal networks. We grew A. gerardii seedlings with isolated root systems in individual, adjacent containers while preventing, disrupting or allowing common mycorrhizal networks among them. Fertile soil was placed within the containers, which were embedded within infertile sand. We assessed mycorrhizas, leaf tissue mineral nutrient concentrations, size hierarchies and the growth of nearest neighbors. Plants interconnected by common mycorrhizal networks had 8% greater colonized root length, 12% higher phosphorus and 35% higher manganese concentrations than plants severed from common mycorrhizal networks. Interconnected plants were, on average, 15% larger and had 32% greater size inequality, as reflected by Gini coefficients, than those with severed connections. Only with intact common mycorrhizal networks were whole-plant dry weights negatively associated with those of their neighbors. In the absence of root system overlap, common mycorrhizal networks likely promote asymmetric competition below ground, thereby exaggerating size inequality within A. gerardii populations.

Characterizing variation in mycorrhiza effect among diverse plant varieties.

Exploitation of arbuscular mycorrhizal fungi may be an important approach for development of reduced-input agriculture. We discuss the use of linear models to analyze variation in mycorrhiza response among diverse plant varieties in order to assess the value of mycorrhizas. Our approach allows elimination of variation linked to differences in plant performance in the absence of mycorrhizas and the selection of plant lines that might harbor genetic variation of use to improve the mycorrhizal symbiosis in agriculture. We illustrate our approach by applying it to previously published and to novel data. We suggest that in dealing with a relative trait such as mycorrhiza effect, the choice of measure used to quantify the trait greatly affects interpretation. In the plant populations under consideration, we find evidence for a greater potential to increase mycorrhiza benefit than previously suggested.

Furuncular myiasis caused by Dermatobia hominis in a returning traveler.

Furuncular myiasis caused by Dermatobia hominis is endemic throughout Central and South America. We report a case of furuncular myiasis in a traveler returned from Costa Rica. The case is unique because the primary care physician obtained magnetic resonance images. The images, however, do not show any characteristic features that assist in diagnosis.

Plant responsiveness to mycorrhizas differs from dependence upon mycorrhizas.

Soil phosphorus response curves of plants with and without mycorrhizas reflect two different, but complementary, phenomena. The first, plant responsiveness to mycorrhizas, is represented by the difference in growth between plants with and without mycorrhizas at any designated level of phosphorus availability. This is also a measure of mycorrhizal fungus effectiveness. The second, the lowest level of phosphorus availability at which plants can grow without mycorrhizas, is here termed dependence upon mycorrhizas. The latter definition differs from conventional usage which fails to distinguish dependence from responsiveness. Sigmoid curves generated by the three-parameter, logistic equation generally can model the responses of plants to mycorrhizas and phosphorus addition and can be used to assess responsiveness, effectiveness, and dependence. Such curves reveal that plant responsiveness or fungus effectiveness determined at a single level of phosphorus availability may be misleading when used to compare different host species' intrinsic capacities to respond to different mycorrhizal fungus species. Instead, the same relative position should be evaluated among phosphorus response curves for different species combinations. Dependence of a plant species known to benefit from mycorrhizas can be assessed with reference to only the phosphorus response curve of plants without mycorrhizas. Dependence is a constitutive property of plant species that can be used to classify them as facultatively or obligately mycotrophic. Dependence is a plant attribute upon which natural selection can act, but responsiveness and effectiveness cannot be selected directly because they are emergent properties of the interaction between plant and fungus species.

Arbuscular mycorrhizal fungi colonize decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp.

Hyphae and vesicles of arbuscular mycorrhizal fungi (AMF) were found within the decomposing leaves of Myrica parvifolia, M. pubescens and Paepalanthus sp. at three montane sites in Colombia. Hyphae, vesicles, and arbuscule-like structures were also found within scale-like leaves of the rhizomes of Paepalanthus sp. The litter found in the vicinity of the roots was divided into three decomposition layers. The highest AMF colonization occurred in the most decomposed leaves, which were in close association with roots. In contrast, there were no differences in AMF colonization of roots present in the different decomposition layers. Colonization of decomposing leaves by AMF did not differ between the two closely related species M. parvifolia and M. pubescens, nor between two sites (Guatavita and Zipacón, Colombia) differing in soil fertility. Occurrence of vesicles in decomposing leaves was correlated with abundant AMF extraradical hyphae among the leaves. We propose that AMF enter decomposing leaves mechanically through vascular tissue. As a consequence, AMF are well positioned to obtain and efficiently recycle mineral nutrients released by decomposer microorganisms before their loss by leaching or immobilization in soil.