Growth and nickel uptake by serpentine and non-serpentine populations of Fimbristylis ovata (Cyperaceae) from Sri Lanka

Compared with serpentine floras of Southeast Asia, the serpentine vegetation of Sri Lanka is impoverished in regard to serpentine endemics and nickel hyperaccumulators. All species so far documented from the serpentine outcrops of Sri Lanka also have non-serpentine populations; it is unclear whether the serpentine populations are physiologically distinct and deserve ecotypic recognition. We conducted a preliminary study to examine whether serpentine and non-serpentine populations of Fimbristylis ovata represent locally adapted ecotypes by investigating their growth and potential for nickel uptake and tolerance under greenhouse conditions. Although both populations of F. ovata showed a similar growth pattern in serpentine soil during short-term exposure (21 days), the non-serpentine population was unable to survive in serpentine soil under long-term exposure (4 months). Both populations were able to uptake nickel from serpentine soil during short-term exposure (21 days). The serpentine population, however, translocated significantly more nickel from its roots to shoots (translocation factor 0.43) than the non-serpentine population (translocation factor 0.29). Our preliminary investigations suggest that the serpentine and non-serpentine populations of F. ovata may be locally adapted to their respective soils. However, additional studies are required to determine whether the populations deserve ecotypic recognition.

Serpentine Plant Assemblages: A Global Overview

Serpentine substrates are found in many parts of the world, but there is considerable variation in the structure, composition, and diversity of the flora they support. To place western North America in a worldwide context, this chapter provides a brief sketch of global patterns in serpentine plant life, drawing on the reviews by Brooks (1987), Baker et al. (1992), and Roberts and Proctor (1992), as well as other sources. Following this is an overview of some of the main physical factors known to cause variation in the vegetation on serpentine both at the regional and local levels. Finally, we discuss what is known about the roles of competition, fire, herbivory, and other ecological processes in shaping plant assemblages on serpentine. The availability of botanical information varies considerably around the world. In most countries where serpentine occurs, it is possible to name at least some of the plant species and vegetation types found on it. But in countries where surveys are incomplete, or where information has not been synthesized at a national or larger level, it is generally not possible to estimate the number of serpentine-endemic taxa or to describe patterns of variation within the serpentine vegetation. Indonesia, Malaysia, the Phillippines, and Brazil are particularly notable as countries with serpentine floras that are potentially rich but in need of more study. With this caveat, however, some of the major global trends can be described based on available knowledge. Flora and vegetation of selected parts of the world are summarized in table 10-1, and global contrasts between the vegetation of serpentine and other soils are summarized in table 10-2. New Caledonia and Cuba lead the world in known serpentine endemic diversity with 900+ species each, >90% of which are also endemics to these islands. Depending on elevation, rainfall, and fire history, the serpentine vegetation on both islands varies from sclerophyllous scrubland that contrasts visibly with the neighboring vegetation, to medium-stature rainforest that is not strikingly different in appearance from the vegetation growing in other soils.

Serpentine Plant Life of Western North America

Serpentine plant life varies dramatically across western North America from north to south and, to a lesser extent, from the coast inland. At the latitudinal extremes in Alaska and Baja California, it follows patterns seen in other climatically harsh parts of the world (as discussed in chapter 10), but the species composition is not very distinctive and there are few endemics. In between, in Washington, Oregon, and especially in the California Floristic Province, lies a great diversity of distinctive serpentine vegetation types and endemic species. This chapter outlines the coarse patterns of variation in vegetation structure and endemic species richness across this region, as a prelude to chapter 12, which describes specific serpentine vegetation types in detail. Little has been published about the serpentine vegetation of Alaska and the Yukon. The Serpentine Slide Research Natural Area in central Alaska was described by Juday (1992) as having a mixture of white spruce (Picea glauca) and paper birch (Betula papyrifera) with Rosa acicularis, Juniperus communis, and Vaccinium uliginosum in the understory. Several herbs are shared with Swedish serpentines (e.g., Campanula rotundifolia, Minuartia rubella, Rumex acetosa, Saxifraga oppositifolia, Silene acaulis); several others showed northern range extensions on serpentine (see chapter 9). The ultramafic vegetation of Golden Mountain in southeast Alaska was described by Alexander et al. (1989) as alpine meadow containing forbs, graminoids, and low shrubs, with a transition through low shrubs and stunted lodgepole pines (Pinus contorta) down to spruce (Picea sitchensis)–hemlock (mainly Tsuga mertensiana) forest, with shrubs and some cedar (Chamaecyparis nootkatensis). The forest to alpine transition was lower on serpentine than on other soils. No serpentine endemic species are known from this region. From south–central British Columbia to central Oregon, serpentine has been described by Kruckeberg (1969, 1992) as supporting open stands of various conifers, which are either a subset of the species occurring in adjacent denser forests on other soils or represent elevational or geographic range shifts. Understories are sparse and may include graminoids, perennial forbs, and shrubs. On rocky ridgetops and at higher elevations and latitudes, these conifer plant communities give way gradually to alpine tundra.

Synthesis and Future Directions

Ultramafic rocks come from deep within the earth. Most rocks on the surface of the earth are quite different from them. Unique rocks make unique soils and support special plants. Exploring the links and interactions among these unique rocks, soils, and vegetation is an interdisciplinary endeavor that has been accomplished by experts in three areas. It has helped elucidate serpentine rock–soil–plant relationships and provide a rationale for the unusual soil properties and vegetation associated with ultramafic rocks. Examples from arctic tundra to temperate rainforest and hot desert in western North America provide a framework for the investigation of serpentine geoecosystems around the world. The unusual character of most serpentine vegetation is readily apparent even to an untrained eye. Although a vast number of rock and soil types make up the earth’s surface, few have as dramatic and visible effects on ecosystems as do ultramafic, or serpentine materials. Most ultramafic rocks in western North America have been derived from the mantle of earth via ocean crust. Magnesium is highly concentrated in the mantle and calcium, potassium, and phosphorous are relatively low. Calcium and potassium are further depleted from peridotite in the partial melting of ultramafic rock at the base of the ocean crust. As oceanic plates drift from spreading centers, most of the ocean crust is subducted and returns to the mantle (chapter 2). Only relatively small fragments of ocean crust are added to the continents. Because eukaryotic organisms, from protozoa to plants and animals, have evolved on continental crust, they are adapted to soils with higher concentrations of calcium, potassium, and phosphorus (elements with higher concentrations in continental crust than in ultramafic rocks from the base of the ocean crust) and much lower concentrations of magnesium. Having evolved on continents, plants depend on relatively high ratios of calcium and potassium to magnesium, elements that they use for a wide range of physiological functions. Although there has been a long history of evolutionary adaptation to the chemistry of the continental crust, special adaptations have allowed some plants to colonize the atypical conditions of serpentine.

Serpentine Vegetation of Western North America

As discussed in chapter 11, the general patterning of vegetation on serpentine up and down the western North American continent is relatively straightforward. However, many of the distinctive nuances relating to the structure and composition of the vegetation, particularly in comparison to adjacent nonserpentine vegetation have yet to be described. In this chapter we use vegetation as a tool to describe the variation of biotic diversity on serpentine throughout western North America. Vegetation is valuable in this regard because, by describing it, one assembles the information on all plants growing in different patterns in a landscape. This chapter expands on some of the concepts mentioned in chapter 11 and addresses some of the specific questions of interest to ecologists and biologists regarding the influence of serpentine on groups of plant species, using examples from western North America. Western North America provides an excellent template for understanding general questions about serpentine effects on species and vegetation. The broad latitudinal distribution and the local topographic and geologic diversity of serpentine exposures throughout this area produce an array of gradients of temperature, moisture, soil development, disturbance patterns, and day length to produce multiple ecological gradients operating at multiple scales. Also, within western North America a wide number of species from many different genera and families are influenced by serpentine. Vegetation classification is a tool used for several purposes, including efficient communication, data reduction and synthesis, interpretation, and land management and planning. Classifications provide one way of summarizing our knowledge of vegetation patterns. Although there are many different classification concepts, all classifications require the identification of a set of discrete vegetation classes. The fundamental unit of these discrete classes that is identifiable in the field is the stand. A stand is defined by two main unifying characteristics (CNPS 2003): 1. It has compositional integrity. Throughout the site, the combination of plant species is similar. The stand is differentiated from adjacent stands by a shift in plant species composition that may be abrupt or indistinct. That shift relates to a concomitant shift in certain ecological features such as temperature, moisture, or soil fertility that maintain control over the plant species composition.