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= Mycorrhizal Association in Lycopods =

Arbuscular Mycorrhizal History
Arbuscular mycorrhizal fungi (AMF) are soil fungi that colonize plant roots. In which the majority of species belong to the phylum Glomeromycota. Arbuscular mycorrhizae form symbiotic associations with Lycopodiaceae, among many other plant species, allowing the host plant to gain essential mineral nutrients. The fungal symbiont provides nutrients, such as phosphorus, in exchange for fixed carbon. AM fungi facilitate the uptake of nutrients, as well as improve water use efficiency allowing plants to survive in highly competitive, nutrient poor and water stressed environments. These mycorrhizae are usually mutualistic and form symbiotic interactions with roots of ~80% of all terrestrial plant species. Two major morphological forms of AMF exist: Arum and Paris-type.

Lycopodiaceae History
Lycopodiaceae is an ancient family and sister to all other extant vascular plants. This family is characterized by a life cycle with long-lived autotrophic sporophytes and mycoheterotrophic gametophytes (which obtains all organic carbon from fungal symbionts). Members of the Lycopodiaceae family can be found throughout the world, from wet alpine meadows to tropical rain forests. Their habitats can range from terrestrial to epiphytic. Although arbuscular mycorrhizal fungi associations have been well studied, there are only few studies of AMF associations with Lycopodiaceae.

Influence of Arbuscular Mycorrhizae Associations
Winther et al. 2008 reported that this family sometimes has AMF associations only found within individuals of a single species and some species were never found to have AMF association at all. For this to occur, there must be other factors that come into play to form this symbiotic relationship. These factors could be the host species, AMF species, and environmental factors, such as soil nutrients, availability, light intensity, and temperature. Such factors can cause the host plant to have either a negative or positive response to colonization by AMF. The maximum benefit the host plant can obtain from AMF is achieved with a single, most efficient AMF species, although increasing the mycorrhizal diversity would not bring further benefits. Although, to acquire the most phosphorus and support growth rates of the host plant, depends on the host plant identity and time of harvest. There are some plants that acquire maximal benefits by colonization by two different AMF species. It has been shown that in Allium porrum (leeks) colonization by both Glomus claroideum and G. intraradics results in more phosphorus acquisition than with either of the two AMF separately.

Lycophytes are a paraphylum known as pteridophytes. Pteridophytes are the only vascular plants whose gametophytes and sporophytes live independently, with ecological differences, but confined to the same spot. AMF benefit the host plant by providing an refined supply of phosphorus, nitrogen, micronutrients, water, resistance to pathogens and a higher recovery rate from herbivory due to enhanced productivity. Studies have shown that AMF have a crucial role in supporting the establishment of some plants through mycoheterotrophy by enabling carbon transfer between plants. According to a study, only 63% of Lycopodiaceae species form mycorrhizal associations. AMF association can be found throughout all stages of life: from the gametophyte, to the young sporophyte that is still attached to the gametophyte, to the mature sporophyte. Most interactions only occur in the sporophyte stage, however, in some cases gametophytes are mycoheterotrophic when colonized by AMF. In long-lived perennial and evergreen species and many other species of Lycopodiaceae, tend to have long-term fungal reward with plant carbohydrate from sporophytes. It is possible that distinct lineages of plants interacting with AMF will only associate with a certain subset of Glomus A. If this were true, it could be evidence of coevolution of mycoheterotrophic plants with Glomas A and/or other specificity based on ecological and physiological differences between individual Glomas A phylotypes. Studies have found that recruited Glomus phylotypes that form AM mycoheterotrophic associations may be more dependent on location, enviroment, and specific availability of Glomus A and less on the phylogenetic affinity of the plant species.

Distribution of Arbuscular Mycorrhizae Symbiont
The pattern of AMF morphology is mostly Paris-type and intermediate-type because the host plants have slow growth rates. Paris-types tend to grow optimally in these root conditions, whereas Arum-type would occur in roots with high growth rates. In Lycopodiaceae, Paris-type and intermediate-types are characterized by the orientation of the fungal hyphae. The hyphae are linear and form coils inter- or intracellularly within the cells. The AMF enters the host plant mostly by penetrating the roots through either the root hairs or directly through the rhizoids, where the apices are also swollen. AMF association can be spotted under the microscope as dense, striking coils of fine hyphae. At this point of penetration, the evidence of active interaction with nutrient transfer is when the AMF intracellular hyphae induce the cytoplasmic proliferation with the increase of cell organelles. Therefore causing the interface of matrix material thinner and increasing distance from the point of penetration until only a few loose fibrils surrounds the hyphae within the inner cortical cells. While the host plant species can provide insight into fungi present, the environment will also determine if a symbiotic relationship will occur at all. Anaerobic conditions, characteristic of aquatic and marshy habitats, tend to lack mycorrhizae. This is because hydrophytes absorb nutrients, not only through the roots, but also through the shoots and leaves, which may render the hydrophytes less dependent on mycorrhizal fungi. There have been reports of Lycopodiaceae from epiphytic and epilithic habitats to have AMF structures in their roots. A study shows that neighboring photosynthetic conspecific and/or heterospecific plants are likely to contributre organic carbon through shared glomalean networks by exploitation. Spores and other propagules of glomeromycota do not disperse through air, but the dispersal of soil inoculum by vectors such as animals. To be independent from mycorrhizae can be seen as a response to abiotic conditions when the costs outweight the benefits to the plants, either when photosynthetic rates are low (under CO2 limitations) or when there's excess amounts of micronutrients. To conclude a consistent result, gathering samples are important. Mycorrhizal colonization can change in the course of the year and may be undetectable if the roots are not sampled at the right time. AMF have a restricted lifespan in a given part of the root and have to be formed anew as the roots grow.

III. Lycopodiaceae interactions with Dark Septate Endophytes
Aside from arbuscular mycorrhizal associations, many plants also have other fungal interactions, such as endophytes. In Lycopodiaceae, there are studies that show both symbiosis of arbuscular mycorrhiza fungi (AMF) and dark septate endophytes (DSE). Dark septate endophytes are defined as conidial or sterile fungi that colonize living plant roots without causing any apparent negative effects. The difference between DSE and AMF is that DSE possesses melanized or hyaline hyphae that often form cerebriform-like microsclerotia or molininform cells within root cortical cells. DSE prefers aging root tissues, so it can recycle nutrients from senscent or dead roots back into the active roots. Studies have shown that DSE stimulate the host plant's growth and/or increase phosphorus concentration. Although DSE may serve the similar function of providing nutrients to the host as AMF, they also assist in other ways. For example, DSE can protect the host plants against pathogens and herbivores through minimizing the carbon availability in the rhizosphere or through the production of secondary metabolites.

Studies have reported DSE occurring simultaneously with AMF or ectomycorrhizal fungi. Although the degree of association is dependent on the host species, DSE is non-host specific meaning they will colonize many different types of plant species. DSE and AMF are similar in many ways. It has been suggested that DSE associations exists as a back-up system that will take over the functions of AMF under conditions that are unfavorable for AMF. DSE enter the host plants by penetrating the root hairs to enter the cortical layer. Once in the epidermal layer, the hyphae can grow parallel to the main axis of the host's roots. During the intracellular colonization, endophytes form clusters of inflated, rounded, thick-walled within the cortical cells, “thick-pseudoparenchymatic mass or sclerotia”. There is evidence that shows DSE colonization prefers to form in older parts of the root system. This is the means by which DSE is able to recycle nutrients from senescent or dead roots cells back into the active (young) roots. The identity and number of fungal species in DSE are uncertain. The reproduction and dispersal of DSE are also uncertain, but suggest that dispersal by conidiospores is possible.