Propagation and Mycorrhizal Inoculation of Indigenous Florida Plants for Phosphate Mine Revegetation
Revegetation of uplands and sandtailings on phosphate mined lands has not been considered a priority. Sites mined prior to 1975 are, for the most part, unreclaimed and colonized by herbaceous, weedy species, and those mined after this date are primarily maintained as pasture or planted with pine. Florida Administrative Code (Chapter 16C – 16.0051) requires that 10% of the lands mined after 1975 be returned to their original condition. This demands a considerable assortment of plants, much the same as existed on the site prior to mining. Lack of pertinent information and difficulty in obtaining a sufficient number of native taxa for accomplishment of the task has hampered such efforts. This report, while far from being comprehensive, lays the foundation for development of a database of fundamental information on selection and propagation of some native species for phosphate mine revegetation.
Vegetative propagation of 34 species (collected from W. R. Grace’s Bonny Lake and Four Corners Mines and the Occidental’s Suwannee River Mine), selected on the basis of a set of criteria, was attempted. Of these, 24 rooted from 75 to l00%, the rooting for six of the species ranged from 45 to 74%, and four species, including Crataegus flava, Diospyros virginiana, and two Quercus spp. were unsuccessful. While seed propagation of many of the taxa used in this research is known, several are either difficult to germinate and a few, such as Persea spp. may be considered impossible, due to lack of seeds with viable embryo. The greater potential for genetic diversity in seed grown plants is acknowledged, but faster growth and nearly immediate maturity of the vegetatively propagated material are factors which should be given serious consideration. Genetic diversity may be maintained by selecting the cutting materials from 25 or more plants, when possible. Furthermore, to maintain the ecotypic variation shown by nearly all species, plants must be collected from no more than a radius of 50 miles or less of any given mine.
The goal of micropropagation (tissue culture) was to make available those woody species which may be required in large numbers, and species that are “difficult” to propagate. This task, however, proved to be overly ambitious, particularly since micropropagation of woody species has been largely restricted to species which are not difficult to root. Nevertheless, shoot multiplication and rooting protocols were successfully developed for Aronia arbutifolia, Nyssa sylvatica, and Persea palustris, and considerable progress was made on several other taxa. Thus, the potential use of plant micropropagation for the mass production of native woody species is demonstrated. As in the case of cutting propagation the problem of genetic uniformity, which in this case is a serious drawback to revegetation, may be overcome by selecting the source material from several plants. Although the time necessary for initial establishment and stock culture regeneration of a given species may exceed nine months, shoot regeneration is logrithmic and within a year astronomical numbers of plants can be produced. For example, the yearly production potential of Aronia arbutifolia is estimated to be 1.8 X. Unquestionably, macropropagation is a particularly viable production system for elite colonal lines, where monoculture of a certain taxon is desired or necessary.
Reduced populations of microorganisms, such as vesicular-arbuscular mycorrhizal fungi (VAM), in disturbed soils are known to limit successful establishment of mycorrhizal-dependent plants. Since it is not feasible to inoculate large tracts of land with VAM fungi, vegetatively produced plant material may be inoculated during the propagation phase. The utility of such a system was determined in a series of experiments, beginning with establishment of single-species pot cultures of native VAM fungi from the mine sites. Isolates differed markedly in their ability to promote plant growth and screening of a larger number of isolates is recommended. Establishment of VAM fungi on the native species in container stages of production resulted in a significant increase in shoot growth and root mass. Plants of Cornus foemina were two times as large, and those of Hex glabra were five times as large, when inoculated, as compared to the non-inoculated plants. Two other species were not affected by the mycorrhizal inoculation. Establishment of VAM on roots of cuttings in the propagation bed was effective on all species tested, except on Viburnum nudum. The inoculum had no effect on root initiation of any species.
In general, establishment of mycorrhizal fungi on nursery-grown plants can be problematic due to the high organic matter content of the media, a problem which may be circumvented by inoculation of cuttings at the rooting stage. Additional research is necessary to determine the proper inoculum for each species. Ecological significance of mycorrhizal fungi on the native plants and the mine ecosystem was also investigated.