Serpentine Soils

Serpentine soils are weathered products of a range of ultramafic rocks composed of ferromagnesian silicates. Serpentine more accurately refers to a group of minerals, including antigorite, chrysotile, and lizardite, in hydrothermally altered ultramafic rocks. Common ultramafic rock types include peridotites (dunite, wehrlite, harzburgite, lherzolite) and the secondary alteration products formed by their hydration within the Earth’s crust, including serpentinite, the primary source of serpentine soil. Serpentine soils are generally deficient in plant essential nutrients such as nitrogen, phosphorus, potassium, and sulfur; have a calcium-to-magnesium (Ca:Mg) molar ratio of less than 1; and have elevated levels of heavy metals such as nickel, cobalt, and chromium. Although physical features of serpentine soils can vary considerably from site to site and within a site, serpentine soils are often found in open, steep landscapes with substrates that are generally shallow and rocky, often with a reduced capacity for moisture retention. Due to the intense selective pressure generated by such stressful edaphic conditions, serpentine soils promote speciation and the evolution of serpentine endemism, contributing to unique biotas worldwide, including floras with high rates of endemism and species with disjunct distributions. The biota of serpentine soils has contributed greatly to the development of ecological and evolutionary theory, as well as to the study of the genetics of adaptation and speciation. Plants growing on serpentine soils also provide genetic material for phytoremediation and phytomining operations. Habitats with serpentine soils are undergoing drastic changes due to ever-expanding development, deforestation,mining for heavy metals and asbestos, exotic-species invasions, climate change, and atmospheric deposition of previously limiting nutrients such as nitrogen. Such changes can have drastic impacts on serpentine floras and affect bacteria, fungi, and fauna associated with serpentine plants and soils. Habitats with serpentine soils provide ample opportunities for conservation- and restoration-oriented research directed at finding ways to better manage these biodiversity hotspots

A Comparative Study of the Flora and Soils of Great Duck and Little Duck Islands, Maine, USA

Strong environmental gradients and varied land-use practices have generated a mosaic of habitats harboring distinct plant communities on islands on the coast of Maine. Botanical studies of Maine\u27s islands, however, are generally limited in number and scope. Baseline studies of Maine\u27s islands are necessary for assessing vegetation dynamics and changes in habitat conditions in relation to environmental impacts imposed by climate change, rising sea levels, invasive species, pests and pathogens, introduced herbivores, and human disturbance. We conducted a survey of the vascular plants and soils of forest, field, and ocean-side communities of Great Duck and Little Duck Islands, ME. These islands differ in environmental and land-use features, and in particular the presence of mammalian herbivores; Great Duck Island has had over a century of continuous mammalian herbivory while Little Duck Island has been largely free of mammalian herbivores over the last 100 years. We recorded 235 vascular plant species in 61 families on the Duck Islands, 106 of which were common to both islands. The composition, abundances, and diversity of plant species substantially differed within similar plant communities between the islands. These differences were particularly evident in the forest communities where Little Duck Island had significantly greater sapling regeneration and a more recent peak in tree recruitment. Soil properties also significantly differed between these islands, with a higher pH in all three communities and higher P, Ca, and K in field, forest, and ocean-side communities, respectively, on Little Duck Island, and higher soluble salts in forest and ocean-side communities of Great Duck Island. Together, our findings suggest that soil characteristics and the dominance and regeneration of vascular plant species can differ substantially even between adjacent islands with otherwise similar geologic characteristics and glacial history, and that mammalian herbivory along with other ecological factors may be important drivers of these differences

Ecotypic Differentiation of Mid-Atlantic \u3ci\u3eQuercus\u3c/i\u3e Species in Response to Ultramafic Soils

Spatial heterogeneity of soil conditions combined with intraspecific variation confer site-specific edaphic tolerance, resulting in local adaptation and speciation. To understand the geoecological processes controlling community assembly of woodland tree species on serpentine and mafic soils, we investigated resource gradients and provenance (geographic area of propagule collection) as variables affecting typical representative upland oak (Quercus) species distribution. Accordingly, we conducted a year-long reciprocal transplant experiment in the greenhouse with serpentine and mafic soils, using seedlings of five oak species (Quercus marilandica, Q. stellata, Q. montana, Q. michauxii and Q. alba). All seedlings, regardless of provenance or soil depth, displayed more robust growth in the mafic soils. Soil depth was an important determinant, with all species exhibiting increased growth in the deeper-soil treatments. Fitness surrogates such as stem height, relative growth rate, and leaves per plant were greater when seedlings were grown in their home soil than when they were grown in the non-resident soil, suggesting an ecotypic effect. Mean stomatal conductance and stem growth were positively correlated with soil depth in all treatments. Taken together, the study showed provenance-specific growth responses of oak seedlings to soil type and depth, providing a better understanding of the mechanisms controlling species assembly in woodland communities

Limestone Flora of the Simonton Corner Quarry Preserve, Rockport, Maine, USA

Limestone is a distinctive substrate that has significant effects on soils and plants. The present study characterizes the diversity of vascular plants, bryophytes, and lichens at the Simonton Corner Quarry Preserve, an abandoned limestone quarry in Rockport, Maine, USA, which was in operation in the late 1800s. We document vascular plant diversity and associated edaphic features (i.e., soil pH and elemental chemistry) using 30 5×5 meter plots spread throughout the site. For vascular plants, 114 species in 96 genera and 50 families were observed; few of these species are known to prefer calcareous environments, and 38% are nonnative. Conversely, the soil- and rock-dwelling cryptogam biota, which comprises 21 moss species in 13 families and eight lichen species in three families, contains many calciphilic species. The bryoflora conspicuously lacks liverworts, whereas the lichen biota is dominated by cyanolichens. This study will inform future conservation and reclamation work at this and other human-altered limestone sites in Maine and floristically similar areas and contribute to our understanding of the geoecology of New England

Diversity and Soil-Tissue Elemental Relations of Vascular Plants of Callahan Mine, Brooksville, Maine, U.S.A

Metal-contaminated soils provide numerous stressors to plant life, resulting in unique plant communities worldwide. The current study focuses on the vascular plants of Callahan Mine in Brooksville, ME, USA, a Superfund site contaminated with Cu, Zn, Pb, and other pollutants. One hundred and fifty-five taxa belonging to 50 families were identified, with the Asteraceae (21%), Poaceae (11%), and Rosaceae (9%) as the most species-rich families. Ninety-six species encountered at the Mine were native to North America (62%), including 11 taxa (7%) with rarity status in at least one New England state. Fifty-one species were non-native (33%), including nine taxa (6%) considered invasive in at least one New England state. We characterized how the plant community changed across different habitats at the Mine, from disturbed and exposed (waste rock piles, tailings pond) to inundated and relatively undisturbed (wetland, shore), and documented concurrent shifts in the ionic content of the soils across the habitats. We found substantial differences in both the plant community and soil chemical features among habitats. Habitats separated out along a single axis of an ordination of the plant community, with wetland and shore habitats at one extreme and tailings pond and waste rock-pile habitats at the other. The first principal component axis of the 21 soil variables was significantly predicted by the ordination of the plant community, indicating a gradient of increasing organic matter, Fe, Mg, Mn, total N, Na, and K roughly parallel to the gradient of increasing wetland vegetation. None of the plant species tested accumulated substantial concentrations of metals in their leaf tissue except Salix bebbiana and Populus balsamifera, which accumulated 1070 ppm and 969 ppm Zn in dry leaf tissue, respectively—approximately one-third of the concentration considered as hyperaccumulation for Zn

A preliminary study of the role of nickel in enhancing flowering of the nickel hyperaccumulating plant \u3ci\u3eAlyssum inflatum\u3c/i\u3e Nyár. (Brassicaceae)

Alyssum inflatum is a native of serpentine soils and is able to hyperaccumulate nickel (Ni), but the importance of Ni to reproduction in the species is unknown. We investigated if reproductive fitness is enhanced by Ni in the growth medium, and included a treatment involving a relatively high level of Mg to provide a comparison with elevated levels of another metal. Seedlings were grown in a modified Hoagland solution culture in an inert medium of Perlite and were treated with Ni (100 μM), a high concentration of Mg (5 mM), or under control conditions (solution culture without Ni or the addition of high Mg) for 14 months. We documented survival, as well as the proportion of individuals that flowered. We also quantified flower production as an indicator of plant fitness. Survival was not affected by treatment (87–90% for all treatments), but significantly more Ni-treated plants (63%) flowered compared with Mg-treated (19%) or control plants (12%). In addition, inflorescences per plant, inflorescence length, and number of open flowers per inflorescence were all significantly greater for Ni-treated plants relative to plants from the other treatments. Although high levels of Ni are not essential for growth and reproduction of the species, we suggest that Ni stimulates flowering in A. inflatum and may result in greater fitness for the species on serpentine soils

Ultramafic geoecology of South and Southeast Asia

Globally, ultramafic outcrops are renowned for hosting floras with high levels of endemism, including plants with specialised adaptations such as nickel or manganese hyperaccumulation. Soils derived from ultramafic regoliths are generally nutrient-deficient, have major cation imbalances, and have concomitant high concentrations of potentially phytotoxic trace elements, especially nickel. The South and Southeast Asian region has the largest surface occurrences of ultramafic regoliths in the world, but the geoecology of these outcrops is still poorly studied despite severe conservation threats. Due to the paucity of systematic plant collections in many areas and the lack of georeferenced herbarium records and databased information, it is not possible to determine the distribution of species, levels of endemism, and the species most threatened. However, site-specific studies provide insights to the ultramafic geoecology of several locations in South and Southeast Asia. The geoecology of tropical ultramafic regions differs substantially from those in temperate regions in that the vegetation at lower elevations is generally tall forest with relatively low levels of endemism. On ultramafic mountaintops, where the combined forces of edaphic and climatic factors intersect, obligate ultramafic species and hyperendemics often occur. Forest clearing, agricultural development, mining, and climate change-related stressors have contributed to rapid and unprecedented loss of ultramafic-associated habitats in the region. The geoecology of the large ultramafic outcrops of Indonesia’s Sulawesi, Obi and Halmahera, and many other smaller outcrops in South and Southeast Asia, remains largely unexplored, and should be prioritised for study and conservation

Adaptive Differentiation in Response to Water Stress by Edaphic Races of \u3ci\u3eLasthenia californica\u3c/i\u3e (Asteraceae)

Two edaphic races of Lasthenia californica sensu Ornduff (races A and C) grow in parapatry on a serpentine outcrop at Jasper Ridge Biological Preserve, California. The races occupy distinct edaphic habitats that have different water‐holding capacities. We predict that the two races will show differentiation in reproductive strategies related to their response to water stress. In order to test this hypothesis, we performed a greenhouse experiment to characterize the reaction norms of the two races exposed to a gradient in water availability. We measured the response of five variables to the watering treatments: early survivorship, days to flowering, root/shoot dry mass ratio, total dry mass, and a measure of reproductive fitness, number of flower heads. We found that the races differ in their allocation patterns to roots compared with shoots and in days to flowering, indicating genetic differentiation for these traits. Race A consistently allocates relatively more biomass to roots while race C flowers earlier. However, the reaction norms of the two races for all nonreproductive traits are parallel, indicating that races do not differ in their plastic response to drought stress. The number of flower heads, our measure of reproductive fitness, did, however, exhibit differential response to water availability between the two races. Under low watering treatment, race C plants are able to maintain flower head production, while race A plants show a monotonic decrease in head production as water stress increases. Results indicate that race C plants are better adapted to drought; they are able to maintain a high reproductive output under low water availability. However, as the phenotype of race A is affected by drought, reproductive output decreases, as we would predict for plants that rarely experience drought in their natural environment