Non-serpentine Soils Research Articles

Occurrence of heavy metal‐resistance in microflora from serpentine soil of Andaman

Serpentine soils collected from Saddle Hills, Chidyatapu and Rutland of Andaman Islands, India were analyzed for physico-chemical and microbiological characteristics and compared with those from adjacent non-serpentine localities. The serpentine soils contained high levels of nickel (1740.0-8033.4 mg/kg dry soil), cobalt (93.2-533.4 mg/kg dry soil) and chromium (302.9-4437.0 mg/kg dry soil), in addition to 62-152 g of iron and 37-60 g of magnesium per kg dry soil. Characteristically the serpentine soils showed low microbial density (6.2-11.3 x 10(6) colony forming unit/g soil) and activity (1.7-3.5 microg fluorescein/g dry soil/h) than non-serpentine outcrops. Serpentine microbial population was dominated by bacteria which represented 5.12 to 9.5 x 10(6) cfu/g of soil, while the fungal population ranged from 0.17 to 3.21 x 10(6) cfu/g of soil. A total of 342 (200 from serpentine and 142 from non-serpentine soils) isolates were compared for Ni, Co and Cr resistance. Serpentine microflora was in general, highly resistant than non-serpentine ones and showed a metal-resistance profile of Cr > Ni > Co. Amongst the serpentine isolates, 8 and 11 bacteria tolerated > 12.0 mM Ni and > 16.0 mM Cr respectively, while 6 fungal isolates showed a minimum inhibitory concentration (MIC) value > 8.0 mM Co. These 25 serpentine strains also showed co-resistance to Cu, Zn and Mn but were sensitive to Hg and Cd. The selected bacterial isolates were resistant to ampicillin, penicillin G and polymyxin B, whereas fungal strains showed resistance to amphotericin B, nystatin and fusidic acid.

Microbial community composition on native and drastically disturbed serpentine soils

During construction of roads, entire hillsides can be cut away, dramatically disturbing the ecosystem. Microbial communities play important, but poorly understood roles in revegetating roadcuts because of the many functions they perform in nutrient cycling, plant symbioses, decomposition, and other ecosystem processes. Our objective was to determine relationships among microbial community composition, soil chemistry, and disturbance on a serpentine soil disturbed by a roadcut and then partially revegetated. We hypothesized that the adjacent undisturbed serpentine soil would have a different microbial community composition from barren and revegetated sections of the roadcut and that undisturbed soils would have the greatest microbial biomass and diversity. We measured phospholipid fatty acids (PLFA) and soil nutrient concentrations on barren and revegetated sections of the roadcut and on adjacent undisturbed serpentine and nonserpentine soils. Most roadcut samples had soil chemistry similar to the serpentine reference soil. The microbial biomass and diversity of barren sites was lower than that of revegetated or the serpentine reference site. The nonserpentine reference site had significantly ( P≤0.05) greater microbial biomass than serpentine or disturbed sites but significantly lower relative proportions of actinomycetes, and slow growth biomarkers. The Barren site had the lowest microbial biomass and a significantly ( P≤0.05) greater proportion of that biomass was fungi. Barren, revegetated, and serpentine sites all had dissimilar microbial community composition. The composition of the revegetated communities, however, was intermediate between the serpentine reference and barren soils, suggesting that community composition of revegetated soils is approaching that of an undisturbed site with similar soil chemistry.

Comparison of ectomycorrhizas of Quercus garryana (Fagaceae) on serpentine and non‐serpentine soils in southwestern Oregon

The diversity of ectomycorrhizal communities associated with Quercus garryana on and off serpentine soils was compared and related to landscape-level diversity. Serpentine soils are high in magnesium, iron, and heavy metals and low in fertility. In plant communities on serpentine soils, a high proportion of flowering plant species are endemic. At three sites with paired serpentine and nonserpentine soils in southwestern Oregon, we sampled Q. garryana roots and categorized ectomycorrhizas by morphotyping and by restriction fragment length patterns. Ectomycorrhizas were abundant at all sites; no single fungal species dominated in the ectomycorrhizas. Of 74 fungal species characterized by morphotype and pattern of restriction fragment length polymorphisms, 46 occurred on serpentine soils, and 32 were unique to serpentine soil. These species are potentially endemic to serpentine soil. Similarities in species composition between paired serpentine and nonserpentine soils were not significantly lower than among three serpentine sites or among three nonserpentine sites. We conclude that mycorrhizal communities associated with oaks on serpentine soil do not differ in species richness or species evenness from those on neighboring nonserpentine soil.

Species Richness, Abundance, and Composition of Ground-Dwelling Ants in Northern California Grasslands: Role of Plants, Soil, and Grazing

We examined the role of cattle grazing, plants, and soil attributes on species richness, abundance, and composition of ground-dwelling ants in northern California serpentine and nonserpentine grasslands. In addition, we analyzed the relationship between three numerically dominant ant species and overall ant species richness and abundance. We used pitfall traps to collect worker ants at 80 sites over a 2-wk period in May 2002. Twenty species of ants were identified from a total of 5,149 worker ants; 80% of all individuals belonged to three dominant species: Messor andrei (Mayr), Pheidole californica Mayr, and Solenopsis xyloni McCook. Ant species richness was negatively affected by grazing on nonserpentine soils only. In general, soil chemistry and texture formed the most consistent associations with the ant community. Plants were less important than soil attributes in explaining variation in overall ant species richness and abundance, but the abundance of the three dominant ant species was significantly correlated with plant biomass or plant richness. Based on logistic regression analysis, the presence or absence of each dominant ant species was negatively correlated with the abundance of the other two dominants. However, the three numerically dominant ant species did not correlate with overall ant species richness or abundance.

QTL mapping for a trade-off between leaf and bud production in a recombinant inbred population of Microseris douglasii and M. bigelovii (Asteraceae, Lactuceae): a potential preadaptation for the colonization of serpentine soils.

The different response to growth on serpentine soil is a major autecological difference between the annual asteracean species Microseris douglasii and M. bigelovii, with nearly non-overlapping distribution ranges in California. Early flowering and seed set is regarded as a crucial character contributing to escape drought and thus is strongly correlated with survival and reproductive success on serpentine as naturally toxic soil. M. bigelovii (strain C94) from non-serpentine soil produces more leaves at the expense of bud production in the first growing phase than M. douglasii (B14) from serpentine soil. A QTL mapping study for this trade-off and for other growth-related traits was performed after six generations of inbreeding (F7) from a single interspecific hybrid between B14 and C94 on plants that were grown on serpentine and alternatively on normal potting soil. The trade-off is mainly correlated with markers on one map region on linkage group 03a (lg03a) with major phenotypic effects (phenotypic variance explained [PVE] = 18.8 - 31.7 %). Plants with the M. douglasii allele in QTL-B1 (QTL-NL1) produce more buds but fewer leaves in the first 119 days on both soil types. Three modifier QTL could be mapped for bud and leaf production. In one modifier (QTL-B2 = QTL-NL4) the M. douglasii allele is again associated with more buds but fewer leaves. QTL mapped for bud set in the F6 co-localize with QTL-B1 (major QTL) and QTL-B3. Two additional QTL for leaf length and red coloration of leaves could be mapped to one map region on lg03a. Co-localization of the two QTL loci with major phenotypic effects on bud and leaf production strongly suggests that a major genetic locus controls the trade-off between the two adaptive traits. The importance of mutational changes in major genes for the adaptation to stressful environments is discussed.

Chromium Geochemistry of Serpentine Soils

Serpentine soils derived from the weathering of ultramafic rocks, mainly ophiolitic serpentinites, are typically characterized by Cr concentrations in excess of 200 mg kg-1, comparatively higher than non-serpentine soils. We review the chemistry of Cr in serpentine soils and their protoliths, focusing on serpentine soils collected from New Caledonia, Oregon, and California. Overall, serpentine soils are slightly acidic (average pH of ∼6), contain a variety Fe(III) oxides (magnetite and hematite), Fe(III) (oxy)hydroxides, phyllosilicates (serpentine and chlorite), and clays (smectites and vermiculites), and contain concentrations of Cr (> 200 mg kg-1), Ni (> 1,000 mg kg-1), and Mn (> 200 mg kg-1) exceeding values of non-serpentine soils. Although Cr concentrations in serpentine soils have been reported as high as 6 wt% in New Caledonia, Cr values in New Caledonia, Oregon, and California serpentine soils evaluated in this study range from 827 to 9,528 mg kg-1. Chromium(III) is the only valence state observed in the serpentine soil solids; however, Cr(VI) has been identified in New Caledonia and California serpentine soil solutions at concentrations below 30 μM. The enrichment and range of Cr concentrations in serpentine soils are directly related to the presence of Cr-spinels, specifically chromite and Cr-magnetite. These phases are resistant to weathering and are preserved in the soil environment; however, oxidation of Cr(III) from Cr-spinels by high-valent Mn oxides, or other strong oxidants, is a potential source of Cr(VI) identified in serpentine soil solutions. Due to the weathering resistant nature of the Cr-spinels, Cr-bearing silicates including clay minerals, Cr-chlorite, Cr-garnet, Cr-mica, and Cr-epidote are more viable sources of Cr identified in vegetation, soil extractions, soil solutions, and related waters.

Ecological Heterogeneity in the Effects of Grazing and Fire on Grassland Diversity

Abstract: Grazing and fire and are major forces shaping patterns of native and exotic species diversity in many grasslands, yet both of these disturbances have notoriously variable effects. Few studies have examined how landscape‐level heterogeneity in grassland characteristics, such as soil‐based variation in biomass and species composition, may contribute to variation in the effects of fire or grazing. We studied the effects of livestock grazing and fire in a mosaic of serpentine and nonserpentine soils in California, where most grasslands are dominated by exotic annuals and serpentine soil is the major refuge for native grassland species. We predicted that the effects of disturbance would be proportional to productivity and therefore would be greater on nonserpentine than serpentine soils. We measured species composition at 80–100 grazed or ungrazed sites for 2 years before ( 1998–1999 ) and 2 years after ( 2000–2001 ) an autumn wildfire. Both disturbances increased total species richness on both soils. However, fire enhanced total and exotic species richness more on nonserpentine soils and enhanced native species richness more on serpentine soils. Grazing increased native species richness on serpentine soils but not on nonserpentine soils. These soil‐disturbance interactions suggest that the use of fire and grazing to manage native species diversity in wildlands must be done with careful attention to background ecological heterogeneity.

ROADLESS HABITATS AS REFUGES FOR NATIVE GRASSLANDS: INTERACTIONS WITH SOIL, ASPECT, AND GRAZING

The idea that roadless habitats act as refuges for native-plant diversity against exotic-plant invasion has seldom been tested. We examined the effect of distance from roads and its interactions with soil type, aspect, and livestock grazing on native- and exotic-plant diversity in a 130 000-ha inland California (USA) foothill grassland landscape. During spring 2000 and 2001, we measured the numbers of and cover by native and exotic plant species in 92 sites stratified by distance from roads (10 m, 100 m, and >1000 m), soil type (nonserpentine and serpentine), and aspect (cool, warm, and neutral slopes). In nonserpentine grasslands, native cover was greatest in sites >1000 m from roads (23%) and least in sites 10 m from roads (9%), and the percentage of species that were native was significantly greatest in sites >1000 m from roads (44%) and least in those 10 m from roads (32%). In addition, the most distant sites had the largest number of native grass species and the fewest exotic forb species. In serpentine grasslands there was no significant effect of distance from roads on the numbers of and cover by native and exotic species. On both soils, two exotic species (Centaurea solstitialis and Aegilops triuncialis) were at their lowest frequencies, while a native bunchgrass, Nassella pulchra, was at its highest frequency, in sites >1000 m from roads. On nonserpentine soils only, the exotics, Convolvulus arvensis and Polypogon monspeliensis, were at their lowest frequency, while a native bunchgrass, Poa secunda, was at its highest frequency in the most distant sites. Native species were more abundant on serpentine than nonserpentine soils; on serpentine, natives were more abundant on slopes than flat sites, while on nonserpentine, natives were least abundant on warm, south-facing slopes. Grazing, soil type, and aspect all significantly interacted in their effects on native and exotic richness and cover. Grazing negatively affected the number of native grass species, but not the number of native forb species on nonserpentine, and positively affected the number of native forb species, but not the number of native grass species on serpentine. Roadless areas are significant refuges for native species. However, to protect these habitats from the continued threat of invasion, land managers should consider means of preventing construction of new roads, limiting off-highway vehicle access into grasslands with low road densities, identifying a regime of livestock grazing that favors the persistence of natives over the spread of exotics, and monitoring recreational trails and grazing allotments within roadless areas to detect and eradicate new infestations. Corresponding Editor: C. C. Horvitz.

Nucleolytic activities and appearance of a new DNase in relation to nickel and manganese accumulation in Alyssum murale

Summary Serpentine and non-serpentine plants of Alyssum murale, a nickel (Ni) accumulator plant, from North Greece, were studied in order to examine: (1) The ability of natural plants to accumulate metals; (2) the ability of their seedlings to tolerate increasing concentrations of Ni 2+ or Mn 2+ (0, 0.16, 0.32, 0.5 and 1 mmol/L), when grown in nutrient solution; (3) the activities and electrophoretic patterns of root and shoot DNases and RNases under the above conditions. Measurements of metal concentrations in serpentine and non-serpentine natural plants and the respective soils revealed: (1) Very low calcium (Ca)/magnesium (Mg) (∼0.16) ratio and high concentration of Ni in serpentine soil; (2) very high Ca/Mg (∼17) ratio and high concentration of manganese (Mn) in non-serpentine soil; (3) the ability of serpentine natural plants to accumulate Ni and the inability of plants of both serpentine and non-serpentine populations to accumulate Mn. A. murale plants grown in nutrient solution with increasing Ni 2+ or Mn 2+ concentrations showed a negative correlation between the Ni 2+ or Mn 2+ concentrations in the nutrient solution, and the chlorophyll concentration, shoot and especially root length. The accumulation of Ni 2+ or Mn 2+ in the plant showed a positive correlation with increasing Ni 2+ or Mn 2+ concentrations in the nutrient solution. Application of 0.5 mmol/L Ni 2+ or Mn 2+ resulted in the inhibition of DNase activities and the appearance of a new DNase form, in both root and shoot detected by electrophoresis in active ssDNA polyacrylamide gel. The new gel-extracted DNase showed nicking action against plasmid DNA and has been characterised as an endo-DNase. In contrast, electrophoretic patterns and RNase activities were unaffected. According to our studies on growth, both serpentine and non-serpentine plants of A. murale have a constitutive ability to tolerate and accumulate Ni 2+ or Mn 2+ ; they have similar DNase and RNase electrophoretic patterns and show a new DNase form under Ni 2+ or Mn 2+ stress. This is the first report on the response of nucleolytic enzymes under metallic elements hyperaccumulation.

GRAZING AND SUBSTRATE INTERACT TO AFFECT NATIVE VS. EXOTIC DIVERSITY IN ROADSIDE GRASSLANDS

We compared the native and exotic species composition of ungrazed roadside verges with that of adjacent grazed interiors in the grasslands of California's inner northern coast range (Napa and Lake Counties). We sampled 72 pairs of verge and interior quadrats at five sites representative of the region's grasslands, on both fertile (loam) and infertile (serpentine) soils, avoiding all obvious forms of roadside physical disturbance. We found that, on serpentine soils, ungrazed verges had a higher proportion of exotic species than grazed interiors; on nonserpentine soils, the reverse was true. Within serpentine soils, native species were more prevalent in quadrats with lower biomass; within nonserpentine, natives were more prevalent in quadrats receiving less radiation. Overall, the total species diversity was higher in grazed interiors than on ungrazed verges, regardless of the fertility of the substrate. Our results indicate that the ecological role of roadside verges depends on the interactive effects of community composition and history, environmental gradients, and land use practices that characterize a region.

Diversity of Cenococcum geophilum isolates from serpentine and non-serpentine soils

Serpentine soils are characterized by a disproportionate level of Mg in relation to Ca and often contain phytotoxic levels of available Ni. Both of these factors may represent stresses to plants and fungi colonizing these soils. Ectomycorrhizal fungi play important roles in tree biology, and ecotypic adaptation in these fungi may be critical to the success of trees on serpentine soils. A collection of Cenococcum geophilum isolates was obtained from serpentine and non-serpentine soils by trapping isolates on the roots of Virginia pine (Pinus virginiana) seedlings. Restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer region of ribosomal repeat exhibited certain common fragments among isolates and other fragments that varied in length. Additional polymorphic markers were obtained from PCR-amplified (β-tubulin gene fragments. UPGMA analysis of the RFLP data indicated that, with one possible exception, the serpentine isolates of C. geophilum are genetically more similar to each other than they are to the isolates from local or distant non-serpentine sites. AFLP analyses, sampling a greater number of loci across the genome, provided an even more distinct separation of the serpentine isolates from non-serpentine isolates. All serpentine isolates lacked a group I intron frequently found within the 18S ribosomal RNA gene in isolates of this species. The genetic divergence between serpentine and non-serpentine isolates may reflect adaptation to serpentine soil factors.

Diversity of Cenococcum geophilum Isolates from Serpentine and Non-Serpentine Soils

Serpentine soils are characterized by a disproportionate level of Mg in relation to Ca and often contain phytotoxic levels of available Ni. Both of these factors may represent stresses to plants and fungi colonizing these soils. Ectomycorrhizal fungi play important roles in tree biology, and ecotypic adaptation in these fungi may be critical to the success of trees on serpentine soils. A collection of Cenococcum geophilum isolates was obtained from serpentine and non-serpentine soils by trapping isolates on the roots of Virginia pine (Pinus virginiana) seedlings. Restriction fragment length polymorphism (RFLP) analysis of the internal transcribed spacer region of ribosomal repeat exhibited certain common fragments among isolates and other fragments that varied in length. Additional polymorphic markers were obtained from PCR-amplified (β-tubulin gene fragments. UPGMA analysis of the RFLP data indicated that, with one possible exception, the serpentine isolates of C. geophilum are genetically more similar to each other than they are to the isolates from local or distant non-serpentine sites. AFLP analyses, sampling a greater number of loci across the genome, provided an even more distinct separation of the serpentine isolates from non-serpentine isolates. All serpentine isolates lacked a group I intron frequently found within the 18S ribosomal RNA gene in isolates of this species. The genetic divergence between serpentine and non-serpentine isolates may reflect adaptation to serpentine soil factors.

Habitat patchiness promotes invasion by alien grasses on serpentine soil

Serpentine soils are considerably less invaded by alien species than nonserpentine soils in California’s North Coast Ranges. However, alien species are significantly more prevalent on small patches of serpentine (<5 ha) than in the interiors (>100 m from edges) of very large ones (>1 km2). We studied reasons for this pattern, focusing on the Mediterranean annual grasses Avena fatua L. and Bromus hordeaceus L. Using field transects, we found that both Avena and Bromus were more common at the edges of large patches than in large-patch interiors, even though soils from edges were not significantly different from soils in interiors. Using a growth experiment, we found that soils from small patches did not support better growth of either grass than soils from large-patch interiors. We conclude that the observed pattern is probably caused by small patches and large-patch edges receiving a higher flow of propagules from the nonserpentine matrix, and not by differences in habitat suitability. In both species, populations from small serpentine patches outperformed nonserpentine populations when grown on small-patch soil. This suggests that small serpentine patches may promote the evolution of serpentine-tolerant ecotypes of these alien grasses.

Population and subspecific genetic differentiation in the foxtail pine (Pinus balfouriana).

We performed an allozyme survey of genetic differentiation in Pinus balfouriana, a subalpine conifer endemic to California that is comprised of two allopatric subspecies, one in the Klamath Mountains and the other in the southern Sierra Nevada. Although the two subspecies are morphologically distinct and gene flow between them is virtually nonexistent, we observed much higher levels of differentiation among populations within a subspecies than between the two subspecies. Differentiation is particularly strong in the Klamath populations (multilocus FST = 0.242), which are small, isolated, and ecologically marginal. We attribute this strong differentiation to the mountain island effect, in which populations restricted to high elevations become isolated from each other on different mountains separated by unsuitable intervening habitat, with consequent reduced gene flow allowing populations to evolve independently. Populations of P. balfouriana in the Klamath region only exist scattered on the few highest ridges and peaks that rise above 2,000 m, which defines the lower limit of the species elevational distribution. This pattern of distribution has allowed genetic drift and allelic sorting through historical events to produce strong population-level differentiation, which was likely in place before the two subspecies were geographically separated. Because P. balfouriana occurs on both serpentine soils and nonserpentine soils in the Klamath Mountains, we tested for genetic differentiation between populations growing on serpentine versus nonserpentine soils and our results were equivocal. Our data, combined with several other studies of conifers, show that the mountain island effect can produce significant genetic differentiation in conifers whose life-history traits of widely dispersed pollen, long generation times, and high outcrossing rates would lead us to predict a more homogenous population genetic structure.

POPULATION AND SUBSPECIFIC GENETIC DIFFERENTIATION IN THE FOXTAIL PINE (PINUS BALFOURIANA)

We performed an allozyme survey of genetic differentiation in Pinus balfouriana, a subalpine conifer endemic to California that is comprised of two allopatric subspecies, one in the Klamath Mountains and the other in the southern Sierra Nevada. Although the two subspecies are morphologically distinct and gene flow between them is virtually nonexistent, we observed much higher levels of differentiation among populations within a subspecies than between the two subspecies. Differentiation is particularly strong in the Klamath populations (multilocus FST = 0.242), which are small, isolated, and ecologically marginal. We attribute this strong differentiation to the mountain island effect, in which populations restricted to high elevations become isolated from each other on different mountains separated by unsuitable intervening habitat, with consequent reduced gene flow allowing populations to evolve independently. Populations of P. balfouriana in the Klamath region only exist scattered on the few highest ridges and peaks that rise above 2000 m, which defines the lower limit of the species elevational distribution. This pattern of distribution has allowed genetic drift and allelic sorting through historical events to produce strong population-level differentiation, which was likely in place before the two subspecies were geographically separated. Because P. balfouriana occurs on both serpentine soils and nonserpentine soils in the Klamath Mountains, we tested for genetic differentiation between populations growing on serpentine versus nonserpentine soils and our results were equivocal. Our data, combined with several other studies of conifers, show that the mountain island effect can produce significant genetic differentiation in conifers whose life-history traits of widely dispersed pollen, long generation times, and high outcrossing rates would lead us to predict a more homogenous population genetic structure.Corresponding Editor: M. Dudash

Nickel hyperaccumulation by Thlaspi montanum var. montanum (Brassicaceae): a constitutive trait

Adaptations to particular stresses may occur only in populations experiencing those stresses or may be widespread within a species. Nickel hyperaccumulation is viewed as an adaptation to high-Ni (serpentine) soils, but few studies have determined if hyperaccumulation ability is restricted to populations from high-Ni soils or if it is a constitutive trait found in populations on both high- and low-Ni soils. We compared mineral element concentrations of Thlaspi montanum var. montanum plants grown on normal and high-Ni greenhouse soils to address this question. Seed sources were from four populations (two serpentine, two non-serpentine) in Oregon and northern California, USA. Plants from all populations were able to hyperaccumulate Ni, showing Ni hyperaccumulation to be a constitutive trait in this species. Populations differed in their ability to extract some elements (e.g., Ca, Mg, P) from greenhouse soils. We noted a negative correlation between tissue concentrations of Ni and Zn. We suggest that the ability to hyperaccumulate Ni has adaptive value to populations growing on non- serpentine soil. This adaptive value may be a consequence of metal-based plant defense against herbivores/pathogens, metal- based interference against neighboring plant species, or an efficient nutrient scavenging system. We suggest that the Ni hyperaccumulation ability of T. montanum var. montanum may be an inadvertent consequence of an efficient nutrient (possibly Zn or Ca) uptake system.

How Natural Habitat Patchiness Affects the Distribution of Diversity in Californian Serpentine Chaparral

Components of diversity in the woody plant community were compared among three sets of sites in the Coast Ranges of Northern California: 24 small patches (0.5–3 ha) of serpentine soil, found in four sets of 5–7 patches; 24 equivalently spaced sampling sites within four large (6–55 km2) continuous areas of serpentine; and 24 sites on the nonserpentine soils adjacent to the small patches. On patchy compared with continuous serpentine, alpha diversity (local) was 32% lower, gamma diversity (total) was 17% higher, and beta diversity (differentiation in species composition among sites) was 72% higher. Of the increased beta diversity on patches, most (62%) occurred at the “local” scale of patches 50–3200 m apart, and only 10% occurred at the scale of clusters of patches 16–45 km apart. Complementarity, an alternative measure of beta diversity, showed the same patterns. Woody plants on nonserpentine soils showed diversity patterns similar to those on patchy serpentine, i.e., lower alpha and higher beta and gamma diversity relative to continuous serpentine. Nonserpentine plants showed a stronger response to environmental gradients than did serpentine plants. For the woody plant community. on serpentine soils, the natural large-scale patchiness of the habitat leads to lower local diversity but higher differentiation and regional diversity. The increased regional diversity appears to be almost entirely the result of edge effects, rather than of “patchy coexistence” as described by metacommunity models.

HOW NATURAL HABITAT PATCHINESS AFFECTS THE DISTRIBUTION OF DIVERSITY IN CALIFORNIAN SERPENTINE CHAPARRAL

Components of diversity in the woody plant community were compared among three sets of sites in the Coast Ranges of Northern California: 24 small patches (0.5–3 ha) of serpentine soil, found in four sets of 5–7 patches; 24 equivalently spaced sampling sites within four large (6–55 km2) continuous areas of serpentine; and 24 sites on the nonserpentine soils adjacent to the small patches. On patchy compared with continuous serpentine, alpha diversity (local) was 32% lower, gamma diversity (total) was 17% higher, and beta diversity (differentiation in species composition among sites) was 72% higher. Of the increased beta diversity on patches, most (62%) occurred at the “local” scale of patches 50–3200 m apart, and only 10% occurred at the scale of clusters of patches 16–45 km apart. Complementarity, an alternative measure of beta diversity, showed the same patterns. Woody plants on nonserpentine soils showed diversity patterns similar to those on patchy serpentine, i.e., lower alpha and higher beta and gamma diversity relative to continuous serpentine. Nonserpentine plants showed a stronger response to environmental gradients than did serpentine plants. For the woody plant community. on serpentine soils, the natural large-scale patchiness of the habitat leads to lower local diversity but higher differentiation and regional diversity. The increased regional diversity appears to be almost entirely the result of edge effects, rather than of “patchy coexistence” as described by metacommunity models.

A comparison of ant assemblages (Hymenoptera, Formicidae) on serpentine and non-serpentine soils in northern California

Summary In northern California, ant assemblages in 8 sites in serpentine chaparral habitat were compared with those occurring in 8 chaparral sites on adjacent non-serpentine soils. A total of 27 species of ants was found: 22 species were collected in non-serpentine chaparral and 20 species in serpentine chaparral. Seven species were collected exclusively in non-serpentine, and 5 species were found only in serpentine habitats. A Formica species, conspecific with or closely related to F. xerophila, was found only in serpentine chaparral. Subsequent collections suggest that in northern California, this species is confined to serpentine outcrops. Two other species significantly differed in frequency of occurrence in each habit: Camponotus hyatti, C. cf. vicinus. Five species showed marginal significant differences in their relative abundance between habitats: Camponotus hyatti, C. cf. vicinus, Formica moki, Prenolepis imparis, Leptothorax nevadensis, Stenamma diecki.

Serpentine and non-serpentine Silene dioica plants do not differ in nickel tolerance

Serpentine soils are hostile to plant life. They are dry, contain high concentrations of nickel and have an unfavorable calcium/magnesium ratio. The dioecious plant Silene dioica (L.) Clairv. (Caryophyllaceae) is the most common herb on serpentine soils in the Swedish mountains. It also commonly grows on non-serpentine soils in the subalpine and coastal area. I have compared the germination frequency, plant establishment and growth of serpentine and subalpine non-serpentine populations in serpentine soil under greenhouse conditions. Further more I have studied the specific effect of nickel on root and shoot growth of serpentine and non-serpentine plants from the subalpine and coastal area in solutions with different concentrations of nickel. Plants from serpentine and non-serpentine populations grew well and in a similar fashion in serpentine soil. Moreover, S. dioica plants, irrespective of original habitat, tolerated enhanced concentrations of nickel when grown in solutions. An analysis of metal content in serpentine plants from natural populations shows that S. dioica has a higher nickel concentration in the roots than in the shoots. The growth studies show that S. dioica is constitutively adapted to serpentine, and that all populations have the genetic and ecological tolerance to grow on serpentine.