What makes Funaria hygrometrica the “Wildfire Moss?”
Funaria hygrometrica is a well known cosmopolitan species of temperate North America. It is commonly and affectionately referred to as the “Wildfire Moss” (Grout 1928, Hoffman 1966). It is mostly known as a pioneer species, the first to immediately colonize and dominate the landscape of recent wildfire burns, and in a manner comparable to and consistent with any other invasive plant species (Hoffman 1962).
It has been found to be the earliest and primary colonizer of wildfire burns and slash burns, even dominating post wildfire sites for up to 18 months after the initial burn (Southington 1977). It is also found in waste places and other areas of bare soil but mostly in burns where the concentration of salts is often higher (Steere 1963). The following research was compiled to better understand the relevance of wildfire in relation to the distribution and proliferation of this interesting moss species.
Factors for Successful Wildfire Regeneration
Funariaceae is a unique family of moss that inhabits wildfire burn sites. The openness, substrate sterility, and lack of competing vegetation are merely the obvious features of wildfire burn sites that makes them an ideal habitat for F. hygrometrica or any species to proliferate. However there is a greater diversity of contributing factors in the success of this unique species, such as reproduction mechanisms, biotic and abiotic habitat conditions, seasonal life cycle, and interactions with other species.
Wildfire Chemistry as Habitat
It is well known that one the most important parameter effecting species distribution in plantlike species is growth substrate chemical composition. Specifically, Ph is the most indicative chemical parameter and determiner of species distribution in mosses, especially in temperate areas (Hedenas and Kooijmen 1996, Kooijman and Hedenas 1991). Although F. hygrometrica ‘s relevance to Ph has also been correlated with other chemical factors such as Calcium (Ca) content (Sjors 1983, Wheeler and Proctror 2012), wildfire burns have a higher Ph than other soils primarily due to heavy mineral content, and an unbalanced carbon ratio due to the abundance of Lye (wood ash). When Ph was tested in 60 localities across a 135,000 acre Idaho wildfire, the Ph ranged from 7.0-8.0 even after one year later(Marshall 1928). Funaria hygrometrica grows best in these alkaline soils even if it can survive at a moderately acid substrate, as do vascular plants (Armentand and Caponetti 1972). In addition, during laboratory experiments F. hygrometrica protonema increased in dry weight significantly at each successive Ph increase. It slows growth as Ph decreases, and as in most plantlike species, it will not grow at all at low Ph such as 3.5. Moreover, Funaria hygrometrica is mostly found in wildfire burns where nitrogen is sometimes concentrated. F. hygrometrica responds well by rapid growth to high concentrations of Nitrogen in wildfire burn soils (Southington 1977) but after successive plant competition for light, water and nutrients it declines (Longton 1988, Hoffman 1966).
Symbiotic Species as Contributing Factor
Unlike F. hygrometrica, many plant species that colonize recently burned or cleared substrates are nitrophiles or nitrogen fixing species (Bodenberg 1954). Because of the seemingly harsh growing conditions left after a wildfire, it is easy to consider in the case of F. hygrometrica that there is a nitrogen fixing symbiont in the survival equation. Blue-Green Algae species such as Nostoc sp. and Anabaena sp. live mutualistically with F. hygrometrica as symbiotic algal species. These symbionts are heterocystous epiphytes, meaning they are found living on the surface of F. hygrometrica leaves. They were not just resting losely on the leaf, and the heterocysts and akinetes were distinguished from vegetative cells. Nitrogen fixing algal symbiont species were also found in the F. hygromtrica moss rhizosphere. Although the root-like rhizoids of moss do not transport nutrients to the moss cells the same way a vascular system does in a plant with the same symbiosis, the close proximity of the rhizoids with the moss cells and nitrogen fixing algal species could be an additional contributing factor in the uptake of limiting nutrients and ultimatlty to this moss species success.
Wildfire Copper Concentrations Inhibit Development
Although F. hygrometrica may have adapted to some aspects of the substrate chemistry of wildfire burns, copper may be a detrimental factor for survival because copper has been shown to inhibit growth in F. hygrometrica in lab studies. Wildfire burns often have a high copper content, which is inhibiting to the growth of most species.
In laboratory experiments with F. hygrometrica, high Copper levels inhibited spore germination. In addition, high Copper levels that were added to living specimen of F. hygrometrica resulted in the cessation of protonemal growth. Wildfire Moss are dichotomous to the “Copper Mosses” which evidently require high copper levels in order to germinate (Noguchi and Furado 1956). Zinc is also found in higher concentrations in wildfire burned soils and also has been found to inhibit F. hygrometrica growth. Although Copper was determined to be more toxic than Zinc, Zinc was more effective at preventing spore germination (Nakosteen 1974).
Peristome & Reproduction
There is biological and physiological uniqueness to that may also contribute to its prosperity. Until recently, classification of this species has been based on architectural and morphological features of the peristome teeth. The peristome teeth are like featherlike filters that line the capsule mouth of the sporophyte which is the spore bearing sexual reproductive organ. It reproduces sexually by releasing an excessive number of spores that are distributed widely (During 1987). Spores from previous years were suggested for use in other experiments, suggesting viability and persistence in the soil(Porter 1935).
The peristome of F. hygrometrica is composed of 2 rows, the Endostome segments are positioned opposite of the Exostome teeth, with 32 identical cells of perfectly symetrical divisions, and have perfectly aligned IPL and PPL cell walls. This is different than other double peristome teeth moss species such as Haplolipidae and Encalyptinae which have adjacent instead of aligned cell walls, or in the case of single peristomes where only the endostome is present like in other species of Haplolipidae (Shawn et al.1989a).
Not only has F. hygrometrica developed differentiating sexual reproductive dispersal mechanisms, it also reproduces asexually as an exact clone (Reese 1955). F. hygrometrica is able to regenerate at the paraphyses by using the paraphysis as an asexual propagule (Hill 1903). In laboratory experiments, Funaria hygrometrica protonemal filaments arose from the lowest filament of a paraphysis in one quarter (25%) of attempts on Beneck’s nutrient Agar (Heald 1898, Lakue 1930).
Life Cycle-Protonema induction and Gametophyte bud formation
F. hygrometrica is a perennial moss species with a seasonal life cycle, but can also be cultured from a spore in a laboratory setting. Studies have notes photoperiodic and thermal effects on all bryophytes and suggests their distribution is influenced by altitude and latitude or more specifically light quality and climate, as much as it is by substrate chemistry and gentics (Heslop and Harris 1964). Protonema are the first structures to grow from a germinated spore. In other mosses, sunlight is necessary for the second stage of growth, the initiation of gametophyte bud formation on protonema( Klebs 1893). Photosynthesis normally supports the growth of the bud (Naf 1962). Uniquely, in F. hgrometrica, gametophyte bud formation was induced in darkness in laboratory studies (Chopra 1967). F. hygrometrica is also known to thrive in annual grasslands due to tolerance to low light levels (Young et al 1987).
However, In one lab setting sporophyte ripening entailled a total of 96 days (Krupa 1969). In another laboratory study germination occurred in 2 days, branching protonema took 6-8 days, and gametophyte bud formation another 10 days totalling merely 20 days (Porter 1935). In field studies life cycles seemed variable as well, and dependent on how the biologist characterized the different life cycle changes. One study generally explained, sporophyte capsules expanded from mid October to June and ripened and released spores from June to December (Hackner 1939).
In another, the life cycle began prior to sporophyte capsule elongation and ended with meiosis which occurred when the red color of the annulus (which is the hat on the end of the capsule) begins to deepen while the peristome teeth inside are still green, and totaling 60-65 days to maturity (Garner and Paolillo 1973). In one study suggested sporophytes elongated for two weeks (True 1906), and another suggested 3 more days totalling 17 days(Garner 1973). Despite the descrepincy over days, overall it is understood that F. hygrometrica develops and matures 2 times a year and only during part of the normal growing season for plants, from roughly Jan to May or June and June to December (Taylor 1921, Crum 1973, Brown 1919, Nakosteen and Hughs 1978). And the differences in life cycle times may be explained by different strains and ecotypes. Differentces in visual cues such as elongation, color changes, and expansion differences are merely morphological variations amid strains that are being observed (Heslop and Harris 1964).
Wildfires generally occur during the summer months including June and July analogous with the beginning of Funaria hygronetrica life cycle. Funaria hygrometrica could even have developed ecological races through the behavior of reproductive stages of the life cycle (Dietert 1980). The changes and adaptations by F. hygrometrica where other mosses did not may be additional contributing factors for success.
Funaria hygrometrica has adapted to wildfires for a variety of reasons . By adapting to the wildfire habitat F. hygrometrica developed the ability to take up the little nutrients available under a Ph range that other plants would suffer from nutrient lock. Their unique perisotme formation advantageousness…to be continued