Are flowers physiological sinks or faucets? Costs and correlates of water use by flowers of Polemonium viscosum

Water loss through inflorescences may place extreme demands on plant water status in arid environments. Here we examine how corolla size, a trait known to influence pollination success, affects the water cost of flowering in the alpine skypilot, Polemonium viscosum. In a potometry experiment, water uptake rates of inflorescences were monitored during bud expansion and anthesis. Corolla volume of fully expanded flowers predicted water uptake during bud expansion (R ²=0.61, P=0.0375) and corolla surface area predicted water uptake during anthesis (R ²=0.59, P=0.044). To probe mechanisms underlying the relationship between corolla size and water uptake, cell dimensions and densities were measured in several regions of fully expanded corollas. Corolla length was positively correlated with cell length in the middle of the corolla tube and cell diameter in the corolla lobe (Pearson's r from 0.26–0.33, n=86, P ≤ 0.05). Cell density was negatively correlated with cell dimensions in the upper corolla tube and lobe (Pearson's r from –0.39 to –0.42, P ≤ 0.0015). These findings suggest that more water may be required to maintain turgor in large corollas in part because their tissues have lower cell wall densities. The carbon cost of water use by flowers was assessed in krummholz and tundra habitats for P. viscosum flowering, respectively, during dry and wet portions of the growing season. For plants in full flower, average leaf water potentials were significantly more negative (P=0.0079) at mid-day in the krummholz (June) than in the tundra (July), but were similar before dawn (P=0.631). Photosynthetic rate at the time of flowering declined significantly with increasing corolla size in the krummholz (P=0.0376), but was unrelated to corolla size on the tundra (P>0.72). Plants losing water through large corollas may close leaf stomata to maintain turgor. If photosynthesis limits growth in this perennial species, then the water cost of producing large flowers should exacerbate the cost of reproduction under dry conditions. Such factors could select for flowers with smaller corollas in the krummholz, countering pollinator-mediated selection and helping maintain genetic variation in corolla size components of P. viscosum. Received: 5 May 1998 / Accepted: 2 October 1998     

MEASURING POLLINATOR-MEDIATED SELECTION ON MORPHOMETRIC FLORAL TRAITS: BUMBLEBEES AND THE ALPINE SKY PILOT,POLEMONIUM VISCOSUM

Sweet-flowered plants of Polemonium viscosum in Colorado are visited by a fly-dominated pollinator fauna at timberline (krummholz), but almost exclusively by bumblebees in higher-elevation tundra habitats. Significant increases in flower size and height are associated with increasing elevation along this habitat gradient. This paper presents the results of an experiment designed to test whether bumblebees exert sufficient selection on morphometric floral phenotypes to account for the clinal shifts seen in natural populations. Two populations of sweet-flowered plants of krummholz origin were established: one randomly pollinated, the other solely bumblebee-pollinated. I tested the effects of two independent axes of floral variation, obtained by principal-components analysis, on mean seed set per flower of plants in each population. PC1, with strong correlations to corolla diameter, corolla length, and stem height, explained a significant amount of variance in seed set for bumblebee-pollinated plants but had no bearing on that of randomly pollinated plants. PC2, with strong correlation to flower number, did not influence seed set in either population. Bumblebee behavior was correlated with variation in PC1 scores of the selected population, yielding positive directional selection on morphometric floral traits associated with PC1. Selection coefficients for PC1, corolla length, corolla diameter, and inflorescence height were estimated, respectively, as 0.11, 0.09, 0.07, and 0.06 (P < 0.025 in all cases). These results support the hypothesis that pollinator-mediated selection can bring about changes in floral form, and can explain shifts in floral morphology of P. viscosum along natural habitat gradients.     

Inbreeding effects on mating system traits for two species of Lupinus (Leguminosae)

The consequences of inbreeding for reproductive traits were investigated for two closely related annual lupines that differ in their mating system. Lupinus bicolor (Leguminosae) is a primarily selling species while Lupinus nanus outcrosses at intermediate rates. A controlled crossing program was used for each species to produce selfed and outcrossed progeny. These progeny were then grown in a greenhouse and scored for the date of first flower, flower morphology, and autofertility. Selfed progeny of L. bicolor produced significantly smaller flowers but did not differ from outcrossed progeny for the remaining traits. Selfed progeny of L. nanus produced flowers that significantly differed in shape and had fewer ovules than the flowers of outcrossed progeny. Selfed progeny of L. nanus also had significantly lower rates of autofertility in comparison to outcrossed progeny. The significant effects of inbreeding on these mating system traits may indicate the presence of directional dominance at the loci underlying these characters. The consequences of these direct effects of inbreeding on reproductive traits for plants growing in natural populations may include nonadaptive changes in the outcrossing rate between generations.     

COVARIATION OF SELFING RATES WITH PARENTAL GENE FIXATION INDICES WITHIN POPULATIONS OF MIMULUS GUTTATUS

Wright's gene fixation index F and two single-locus effective selfing rates—the selfing rate at loci with fixed alleles, and the selfing rate at loci without fixed alleles—were estimated in five populations of Mimulus guttatus. These two effective selfing rates describe the inbreeding observed at a single locus when both uniparental and biparental inbreeding are practiced. Estimates were made using progeny arrays assayed for six allozyme loci and two morphological loci exhibiting dominance. The average of the two selfing rates computed for subpopulations (ca. 10 m diameter) ranged from 24% to 59%, with a mean of 37%. When computed for populations (ca. 1 km diameter), average selfing rates were about 10% higher. In four populations, the selfing rate at loci with fixed alleles was higher than the selfing rate at loci without fixed alleles. Thus, the covariance of selfing with parental gene fixation was positive. In one of the populations, estimates for individual plants sampled along a transect gave positive correlations for selfing rates and for gene-fixation indices between adjacent plants. A highly positive correlation between selfing rate and gene fixation of individual plants was also observed. In another population, the covariance of selfing with gene fixation was higher for a locus causing leaf spots than for allozyme loci. This covariance is partially caused by 1) variation in homozygosity among neighborhoods and 2) biparental inbreeding within neighborhoods. The consequences of this covariance are discussed.     

DOWN THE TUBE: POLLINATORS, PREDATORS, AND THE EVOLUTION OF FLOWER SHAPE IN THE ALPINE SKYPILOT, POLEMONIUM VISCOSUM

Abstract We address how a conflict between pollinator attraction and avoidance of flower predation influences the evolution of flower shape in Polemonium viscosum. Flower shape in P. viscosum is the product of an isometric relationship between genetically correlated (r_A= 0.70) corolla flare and length. Bumblebee pollinators preferentially visit flowers that are more flared and have longer tubes, selecting for a funnel‐shaped corolla. However, flower shape also influences nectar‐foraging ants that sever the style at its point of attachment to the ovary. Surveys of ant damage show that plants having flowers with flared, short corollas are most vulnerable to ant predation. Consistent with this result, the ratio of corolla length to flare is significantly greater in a krummholz (high predation risk) population than in a tundra (low predation risk) population. To explicitly test whether the evolution of a better defended flower would exact a cost in pollination, we created tubular flowers by constricting the corolla during development. Performance of tubular flowers and natural controls was compared for defensive and attractive functions. In choice trials, ants entered control flowers significantly more often than tubular ones, confirming that the evolution of tubular flowers would reduce the risk of predation. However, in a bumblebee‐pollinated population, tubular flowers received significantly less pollen and set fewer seeds than controls. A fitness model incorporating these data predicts that in the absence of the genetic correlation between corolla length and flare, intermittent selection for defense could allow tubular flowers to spread in the krummholz population. However, in the tundra, where bumblebees account for nearly all pollination, the model predicts that tubular flowers should always confer a fitness disadvantage.     

Anti-mite activities of Clerodendrum viscosum Ventenat (Verbenaceae) extracts on tea red spider mite,Oligonychus coffeae Nietner (Acarina: Tetranychidae)

Acaricidal and ovicidal activities of Clerodendrum viscosum Ventenat (Verbenaceae), a common weed of India, were investigated on tea red spider mite, Oligonychus coffeae Nietner (Acarina: Tetranychidae). Different solvent extracts (water, methanol, acetone and petroleum ether) of C. viscosum at different concentrations (1, 2, 4 and 8%) were used. These solvent extracts exhibited mortality of O. coffeae in the range of 40–90% in water, 67–97% in petroleum ether, 50–80% in acetone and 43–87% in methanol extract. Depending on LC₅₀ values, the relative toxicity was found to be significantly highest against petroleum ether extracts and lowest in water extracts. Acetone extract of C.viscosum recorded maximum ovicidal activity followed by petroleum ether, methanol and the less by water extracts. In the field trials, mite population were significantly lower (P < 0.05) on plots sprayed with different of C. viscosum extracts than the control and at par with chemical acaricide and neem biopesticide. No phytotoxic effect (score, 0–5% and grade 1) was observed in the field from tea bushes sprayed with different doses of extracts of C. viscosum. Made tea samples were taint free. Organoleptic test revealed leaf infusions and liquor strength as good, scoring 6.5–7.0 on a 10-point scale. Availability and distribution of this weed (C. viscosum) in and around tea growing areas of sub-Himalayan region, along with its processing for the feasibility of including C.visosum extracts in the current IPM programme are discussed.     

Natural selection of UDP genotypes in an experimental population of Lolium perenne (Poaceae)

The mating system determines the range of genotypes on which selection will act. Ultimately, the population will contain only those genotypes that can survive in the current environment. This study was conducted to determine the extent to which selection affects genotype at four enzyme loci in Lolium perenne. Starch gel electrophoresis was used to determine genotype at the phosphoglucomutase, 6-phosphogluconate dehydrogenase, phosphoglucose isomerase, and UDP-glucose pyrophosphorylase loci. Genotypes of progeny arrays were used to infer maternal genotype in a field-grown population of plants. A mating system analysis was performed on maternal and progeny plants of the field population and also on a population of plants, from the same seed stock, grown in a greenhouse environment. Allelic frequencies differed among populations at the Udp locus. Results indicate that high mortality in the field strongly favored one allele. Assumptions of the mating system model are examined and used to interpret the observed differentiation among populations.     

Effects of water stress on leaf growth in tall fescue, Italian ryegrass and their hybrid: rheological properties of expansion zones of leaves, measured on growing and killed tissue

In Expt 1, plants of tall fescue (Festuca arundinacea Schreb.), Italian ryegrass (Lolium multiflorum Lam.) and their F1 hybrid were grown in soil-based compost in a controlled environment, and subjected to full or partial irrigation for 20 d. In Expt 2, plants of the parent species were grown in nutrient solution in the same environment and subjected to osmotic stress (0.76 MPa) for 2 d. In both experiments, distribution of growth in the leaf growing zone (at the base of the growing leaf) was determined, and elastic and plastic compliances were measured on methanol-killed samples of growing zone and of mature lamina using an extensiometer. In Expt 2 plastic compliance coefficient of extension, extensibility, and hydraulic conductance were calculated from changes in leaf extension rate occasioned by imposing linear stress. 'Plastic and elastic compliances of growing zones were 10-20 times greater than those of mature laminae. In both species, drought reduced (a) leaf extension rate, (b) the length of the growing zone, the height of maximum growth, (d) the plastic compliance of whole bases (Expt 1), and (e) hydraulic conductance. The elastic compliance of whole leaf bases was unaffected by drought, but when expressed per unit length of growing zone was increased by drought. Killing with methanol reduced the plastic compliance of leaf bases in control plants, but not in droughted plants.F. arundinacea differed from L. multiflorum in having (a) a lower leaf extension rate (although drought reduced extension by the same proportion in both species), (b) a longer growing zone in droughted plants in Expt 2, a lower elastic and plastic compliance of whole killed leaf bases and laminae, (d) slightly higher plastic compliance in attached growing leaves, and (e) lower plastic compliance per unit length of growing zone in attached leaves. The hybrid was generally intermediate between the parents. the results are discussed in relation to methodology and to crop improvement.Key words: Extensibility, extension coefficient, hydraulic conductance, elastic compliance, plastic compliance, leaf growth, leaf extension rate.      

RATES OF FLORAL EVOLUTION: ADAPTATION TO BUMBLEBEE POLLINATION IN AN ALPINE WILDFLOWER,POLEMONIUM VISCOSUM

Animal pollinators are thought to shape floral evolution, yet the tempo of this process has seldom been measured. I used the prediction equation of quantitative genetics, R = h²S , to predict the rate at which a change in pollinator abundance may have caused divergence in floral morphology of the alpine skypilot, Polemonium viscosum. A selection experiment determined the rate at which such divergence can actually proceed. Corolla flare in this species increases by 12% from populations pollinated by a wide assemblage of insect visitors to those pollinated only by bumblebees. To simulate the evolutionary process giving rise to this change, I used a pollinator selection experiment. Plants with broad flowers set significantly more seeds than plants with narrow flowers under bumblebee pollination but had equivalent fecundity when visited by other insects or hand-pollinated. Bumblebee-mediated selection for broad corolla flare intensified from 0.07 at seed set to 0.17 at progeny establishment. Maternal parent-offspring regression yielded a confidence interval of 0.22–1.00 for trait heritability. Given these parameter estimates, the prediction equation shows that broadly flared flowers of bumblebee-pollinated P. viscosum could have evolved from narrower ones in a single generation. This prediction is matched by an observed 9% increase in offspring corolla flare after a single bout of bumblebee-mediated selection, relative to offspring of unselected controls. Findings show that plant populations can adapt rapidly to abrupt changes in pollinator assemblages.     

POPULATION STRUCTURE AND GENETIC DIFFERENTIATION IN NATIVE AND INTRODUCED POPULATIONS OF DESCHAMPSIA CAESPITOSA (POACEAE) IN THE COLORADO ALPINE

Deschampsia caespitosa is a widespread grass common in moist areas of the alpine tundra of the Rocky Mountains. Enzyme electrophoresis was used to examine population genetic structure along two soil moisture gradients in Rocky Mountain National Park, Colorado. Introduced plants used in a revegetation project were also sampled at one of the sites. At both sites, there were significant differences among subpopulations in allele frequencies, but these differences were distributed in a patchy fashion and were not correlated with the apparent soil moisture gradients. The degree of genetic subdivision differed between the two sites. At one site, gene flow appeared to be high and differences in allele frequencies are attributed to selection in a mosaic environment. At the other site, gene flow appeared more restricted and differences in allele frequencies between subpopulations are attributed to selection and limited gene flow acting simultaneously. Overall, 15% of the genetic variability is between subpopulations and gene flow is high, even between subpopulations separated by up to 1.5 km, but local conditions can apparently limit gene flow and increase the degree of genetic subdivision. The mean genetic distance between introduced plants and the native subpopulations was significantly higher than the mean genetic distance between all other subpopulations. Despite the high gene flow apparent in alpine tundra subpopulations of Deschampsia caespitosa, significant genetic structuring of these subpopulations has developed.     

Different combinations of morpho‐physiological traits are responsible for tolerance to drought in wild tomatoes Solanum chilense and Solanum peruvianum

Herbaceous species can modify leaf structure during the growing season in response to drought stress and water loss. Evolution can select combinations of traits in plants for efficient water use in restricted environments. We investigated plant traits that mediate adaptation and acclimation to water stress in two herbaceous drought‐tolerant species. Anatomical, morphological and physiological traits related to stems and leaves were examined under optimal watering (OW) and a long period of restricted watering (RW) in 11 accessions from three Solanaceae species (Solanum chilense, S. peruvianum and S. lycopersicum). The relationships between these traits were tested using linear regression and PCA. There were significant differences in anatomical traits between the species under both OW and RW, where leaf area correlated with stem diameter. Proline and total carbohydrates accumulated highly in S. chilense and S. peruvianum, respectively, and these osmolytes were strongly correlated with increased osmotic potential. Stomatal density varied between species but not between acclimation treatments, while stomatal rate was significantly higher in wild tomatoes. There was a strong positive relationship between stem growth rate and a group of traits together expressed as total stomatal number. Total stomata is described by integration of leaf area, stomatal density, height and internode length. It is proposed that constitutive adaptations and modifications through acclimation that mediate RW play an important role in tolerance to drought stress in herbaceous plants. The capacity for growth under drought stress was not associated with any single combination of traits in wild tomatoes, since the two species differed in relative levels of expression of various phenotypic traits.     

Edaphic microsatellite DNA divergence in wild emmer wheat, Triticum dicoccoides, at a microsite: Tabigha, Israel

Twenty eight microsatellite markers were used to analyze genetic divergence in tandem dinucleotide repeated DNA regions between two edaphic subpopulations of Triticum dicoccoides growing on the contrasting terra rossa and basalt soilsfrom a microsite at Tabigha, north of the Sea of Galilee, Israel. The terra rossa soil niche was drier and more stressful than the basalt throughout the growing season (November to May). Significant microsatellite divergence in allele distribution, repeat length, genetic diversity, and linkage disequilibria were found between emmer wheat from the two soil types over two short transects of 100 m each. Soil-specific and -unique alleles and linkage disequilibria were observed in the terra rossa and basalt subpopulations. A permutation test showed that the effects of random genetic drift were very low for the significant genetic diversity at microsatellite loci between the two subpopulations, suggesting that an adaptive molecular pattern derived by edaphic selection may act upon variation of the microsatellites. Received: 4 February 2000 / Accepted: 31 March 2000<@head-com-p1a.lf>Communicated by H.F. Linskens     

EVIDENCE OF PARTIAL APOMIXIS IN ANTENNARIA MEDIA (ASTERACEAE: INULEAE) DETECTED BY THE SEGREGATION OF GENETIC MARKERS

The interplant variation in sexual and asexual reproduction in an Oregon population of the alpine perennial Antennaria media was investigated. Four polymorphic loci were assayed by enzyme electrophoresis of the progeny of 72 families from two subpopulations of A. media. The population was divided into two spatially distinct subpopulations. A multilocus model, incorporating a mixture of apomixis and random outcrossing, was used to estimate the mating system of pistillate plants both on the population and individual levels with statistical significance of the estimates based on bootstrap methods. The population contained a mixture of sexual individuals, partial apomicts, and obligate apomicts. The first subpopulation contained individuals that were partially apomictic and presumably produced both reduced and unreduced embryo sacs. There was a conspicuous difference in the breeding system composition between the two subpopulations. The first subpopulation had a “female” biased gender ratio and contained mostly obligate apomicts, some partial apomicts, and some outcrossing amphimicts. The second subpopulation, which had a nearly balanced gender ratio, contained mostly amphimicts, some obligate apomicts, but no facultative apomicts. This is the first study to document partial apomixis in individual plants by the use of genetic markers.     

Bumble bee behavior and selection on flower size in the sky pilot,Polemonium viscosum

Summary In alpine Polemonium viscosum, plants having sweet-scented flowers are primarily pollinated by queens of the bumble bee species, Bombus kirbyellus. In this paper we ask whether two aspects of the pollination effectiveness of bumble bees, visitation rate and pollination efficiency, vary significantly with flower size in sweet-flowered P. viscosum.(i) Bumble bees visited plants with large flowers on 80–90% of encounters, but visited those with smaller flowers on only 49% of encounters. (ii) However, the gain in pollination that large-flowered plants obtained via increased visitation was countered in part because bumble bees deposited fewer outcross pollen grains per visit on stigmas of large flowers than on those of small ones. When both visitation rate and pollination efficiency are taken into account, the predicted value of a single bumble bee encounter declines from 1.06 seeds for flowers larger than 18 mm in diameter to 0.55 seeds for flowers smaller than 12 mm in diameter. Our results suggest that bumble bee pollinators of P. viscosum prefer flower morphologies that are poorly suited for precise pollination. Such behavioral complexities are likely to place constraints on the evolution of optimal floral design.     

Structural and functional changes in Nothofagus pumilio forests along an altitudinal gradient in Tierra del Fuego,Argentina

Abstract. Structural (density, height, basal area, above‐ground tree biomass, leaf area index) and functional (leaf phenology, growth rate, fine litter fall, leaf decomposition) traits were quantified in four mature forests of Nothofagus pumilio (lenga) along an altitudinal sequence in Tierra del Fuego, Argentina. Three erect forest stands at 220, 440 and 540m and a krummholz stand at 640 m a.s.l. were selected. Along the altitudinal sequence, stem density increased while DBH, height, biomass, leaf‐size and growth period, mean growth rate and decay rate decreased. Dead stems increased and basal area and fine‐litter fall decreased with an increase in elevation among erect forests, but these trends inverted at krummholz. We suggest that krummholz is not only a morphological response to the adverse climate but is also a life form with functional advantages.     

Lotus corniculatus L.: Morphological and cytological analysis of regenerants from three sources of tissue and selected progeny

Regenerants from three types of tissue, leaf explants (132 plants), leaf protoplasts (68 plants) and cotyledonary protoplasts (119 plants) of L. corniculatus cv Leo differed both morphologically and cytologically from control plants grown from seed. Four categories of chromosome number were found. The frequency and type of variation found in the chromosome numbers of regenerants reflected the method of plant regeneration.Regenerants with both normal and abnormal numbers of chromosomes produced progeny which were cytologically normal and showed only minor morphological changes when compared with control plants.     

Dry matter production, population structure and environmental conditions of the spring ephemeralErythronium japonicum growing in various habitats differing in sunlight exposure in cool temperate Japan

Phenology, dry matter production, population structure and environmental conditions were examined inErythronium japonicum Decne plants growing on the floor of a deciduous broad-leavedQuercus mongolica forest (Q.m. stand), an evergreen coniferousCryptomeria japonica plantation (C. j. stand) and bare ground left for 3 years after the clearing of a forest composed of youngQ. mongolica andPinus densiflora trees (bare stand) in the cool temperate zone of Japan. The average population density of the plants growing at theQ.m. stand was much higher than that observed at the bare stand, whereas the average number of flowering plants at the former stand was less than half of that at the latter. The population density and number of flowering plants growing at theC. j. stand were both less than 30% of those at theQ. m. stand. The number of seedlings at theQ. m. stand was much more than that at the bare andC. j. stands. Their survivorship rate over 1 year at the former stand also seems to be significantly higher than those at the other stands. Their aboveground and belowground parts at the bare stand were exposed to more severe heat and water stress than those at the other two stands. The net production per leaf area of the plants growing at theQ. m. stand was two and six times larger than those at the bare andC. j. stands, respectively. The plants at the bare stand did not use the available solar radiation as efficiently for dry matter production through photosynthesis as those growing at theQ. m. stand, whereas those at theC. j. stand are strongly restricted in their photosynthetic process by the significantly limited light condition on the floor of the evergreen coniferous plantation. The differences in the number of plants reaching sexual maturity, the density and structure of the population and the net production between their three habitats are discussed here from the standpoint of differences in environmental conditions.     

Genetic polymorphism in the GOT and GDH loci of the scotch pine seed progeny in the area of action of nitrogen-containing emissions from the chemical complex

The variability in four GOT and GDH loci of the seed progeny (embryos) of three Pinus sylvestris L. subpopulations, differentially exposed to the action of emissions of a large chemical complex producing nitrogen fertilizers, has been studied for four years. A trend toward a decrease in the heterozygosity and an increase in the frequency of cases with significant deviations of the observed genotype distribution from the theoretically expected one were observed in the progeny of plants from a degrading and digressing subpopulation in an area of acute action of aeropollutants (0.3–2 km).     

Diversity Assessment of an Endemic <i>Carpinus oblongifolia</i> (Betulaceae) Using Specific-Locus Amplified Fragment Sequencing and Implications for Conservation

Carpinus oblongifolia is an endemic species and the extant wild populations show a fragmentation distribution in the Baohua Mountain of Jiangsu Province in eastern China. Understanding of genetic diversity plays an important role in C. oblongifolia survival and sustainable development. The wild C. oblongifolia population was artificially divided into four subpopulations according to the microhabitats, and another two subpopulations were constructed by progeny seedlings cultivated with the mature seeds. Then, the leaf buds of 80 individuals from six subpopulations were sampled to develop single nucleotide polymorphisms (SNPs) using specific-locus amplified fragment sequencing (SLAF-seq). Based on these SNPs, we aimed to characterize the genetic diversity and population structure of C. oblongifolia and provide an illumination and reference for effective management of such a small endemic population. The level of genetic diversity was low at the species level, and the progeny subpopulations had a relatively higher genetic diversity than the wild subpopulations. This may be attributed to a high gene flow and an excess heterozygosity to reduce the threat of genetic drift-based hazards. Moreover, the progeny subpopulations had the ability to form new clusters and a great contribution to the genetic structure variation of C. oblongifolia. These results will assist with the development of conservation and management strategies, such as properly evacuating competitive trees to provide more chance for pollen and seed flow in situ conservation, and establishing sufficient seedling plantlets under laboratory conditions for reintroduction to enlarge the effective population size.     

Pikas (Ochotona princeps : Lagomorpha) as allogenic engineers in an alpine ecosystem

Pikas (Ochotona princeps: Lagomorpha) build caches of vegetation (“haypiles”), which serve as a food source during winter in alpine and subalpine habitats. Haypiles appear to degrade over time and form patches of nutrient-rich soils in barren talus and scree areas. We sampled soils underneath and next to haypiles, and plants growing on and near haypiles in an alpine cirque in northwestern Wyoming, USA, to determine the effects of pika food caches on N, C, and C/N ratios in soils and plants. We found that (1) haypile soils had significantly higher carbon and nitrogen levels and lower C/N ratios than both adjacent soils and soils in the general study area, (2) two of three plant species tested (Polemonium viscosum and Oxyria digyna) had significantly higher levels of tissue percent N when growing on haypile soils, and (3) total standing plant biomass at the study site increased with soil percent N suggesting that vegetation was nitrogen limited. Pikas may therefore function as allogenic ecosystem engineers by modulating nutrient availability to plants. Received: 5 July 1997 / Accepted: 30 November 1997