11 research outputs found
Influence of Temperature on the Tensile Strength of Spider Silk (Araneus gemmoides)
No full textTemperature ranges between day and night in southern California can be as great as 30°C and may influence vital functioning of ectothermic organisms. Arachnids produce silks from a pair of spinnerets in their abdomen and rely on variance in protein composition to make different types of silks. Temperature may influence tensile strength of filaments. We tested the effects of temperature on tensile strength of dragline silk of five specimens of Araneus gemmoides (orb-weaver) which were collected from Malibu Creek State Park in the Santa Monica Mountains of southern California, under five temperature conditions. Each specimen was placed in a 0.0283 m3 mesh enclosure and allowed 24- hours to acclimate to a temperature increase of 5°C. Photoperiods were set at 12-hour intervals for light and dark to simulate natural conditions. We then removed a single thread of dragline silk and measured tensile strength using an mechanical testing device (Instron 5544-A). We found that dragline silk is typically composed of two monofilaments wrapped together at points and thus quantified transverse area of both monofilaments. This structure may explain the reason why variability around mean values was similar for the plot of stress at break versus temperature. After running a one way ANOVA statistical analysis for repeated measures, we found that at 10°C both the Young’s Modulus and stress at break were significantly greater (P\u3c0.05) than values obtained at 15°C. Additionally, mass of spider seems to correlate with greater tensile strength (R2=0.52) suggesting that larger spiders produce stronger silk. Currently, biomaterial engineers are attempting to exploit the incredible properties of silk for production of fiber materials. Therefore, understanding how Araneus gemmoides is influenced by temperature offers insight into the optimal temperature for harvesting silk
Foliar Water Uptake and Resurrection: Mechanisms of Drought Tolerance in Eight Species of Ferns in the Santa Monica Mountains
No full textIn a region where drought is severe, ecological surveys provide insight into the adaptations of organisms living on the edge of survival. In this study, the mechanisms of drought tolerance for eight species of ferns in the Santa Monica Mountains were assessed with a focus on foliar water uptake and resurrection strategies. We find that species are significantly different (P \u3c 0.001) in their ability to absorb water through leaves (assessed gravimetrically) and correlate this to minimum seasonal water potential and hydrophobicity of leaf surfaces. Secondly, we irrigated Pentagramma triangularis in the field and tracked chloroplast recovery. We found possible evidence of embolism reversal. Taken together, this study explored the methods of survival of the most ancient family of vascular plants
Post-fire Recovery of Juglans californica in Sycamore Canyon: Vessel Length, Shading, Water Use Efficiency and Water Status
No full textIn April 2013, Sycamore Canyon experienced a major wildfire. This study investigates post-fire recovery of two types of resprouts, basal and epicormic, and compares multiple parameters to mature unburned Juglans californica. In this study, we investigate the influence of time of day on the post-fire water potential of mature unburned plants versus burned Juglans californica epicormic and basal resprouts. One way ANOVA test reveals
Torii and Water: A Gateway to Shinto
No full textWater symbolizes purity in the Shinto religion and thus holds utmost importance as a method of religious purification. Additionally, scholars and worshippers recognize the role of torii as gateways to the kami, or deities of nature. However, there has not been a documented survey of the relationship between torii and their placement in water, a relationship we feel is significant in understanding Shintoism. We intend to bridge this gap in scholarship by displaying the prevalence of torii placed in or right next to water. We will explore torii from various parts of the world as well as different time periods in history. By looking at various torii that are located in water, such as the Itsukushima, Meoto Iwa, Oarai Ibaraki, Shirahige Jinja, and Astuta shrines, we hope to display a significant link between the placement of torii and water as the torii is leading to the highest purity in the spiritual world
Post-fire Recovery of Juglans californica in Sycamore Canyon: Water Potential and Site Characterization
No full textOur study focused on post-fire recovery in the California Black Walnut, Juglans californica. Our study was conducted Sycamore Canyon, an area of the Santa Monica Mountain Range recently damaged by the April 2013 fires. Part of our study focused on water potential and water stress among J. californica; we examined differences in the water potentials of mature, unburned trees and resprouts which have grown since the fires in April. We found that mature trees have a significantly higher water potential than sprouts, either epicormic or basal, which indicates that they are better equipped to handle water stress. We also found that water potential among basal sprouts is higher than water potential among epicormic sprouts. Additionally, we characterized individual trees along a gradient in the canyon. Plant distance from ocean, basal health, and epicormic sprouting were measured. We found that a correlation did indeed exist between epicormic sprouting and the distance of the plant from the ocean, however there were no significant correlations between basal health and distance from ocean
Comparative Study of the Mechanical Strength in Two Species of Ferns: Polystichum munitum and Pteridium aquilinum
No full textA comparative study of the mechanical strength in two species of ferns, the winter deciduous Pteridium aquilinum and the evergreen Polystichum munitum, was done. The mechanical strength of the leaf and stipe were used as a means for comparison. Additional data such as specific leaf mass (g/cm2) were also collected. The first hypothesis was that the evergreen fern would have higher leaf mechanical strength, while the second hypothesis was that there would be no difference in the mechanical strength of the stipe. The mechanical strength of the stipe was compared through the Modulus of Elasticity (MOE), while the leaf tensile strength was contrasted through the Modulus (Automatic) – both quantities having been determined with the Instron. The former comparison yielded a P-value of 0.1299 (P\u3e0.05) for an unpaired t-test for equal variance, and the latter yielded
Comparative Foliar Water Uptake and Leaf Hydrophobicity among Eight Species of California Ferns
No full textIn 2014, Southern California experienced the worst drought in the last 1,200 years. Recent tree ring analysis and climate models suggest that this event may be the front end of a “mega-drought” in the southwestern United Sates. Ferns might be particularly vulnerable. In a region where drought is severe, ecological surveys provide insight into the adaptations of organisms living on the edge of survival. In this study, the mechanisms of drought tolerance for eight species of ferns in the Santa Monica Mountains are assessed with a focus on foliar water uptake and resurrection strategies. We find that species are significantly different (P \u3c 0.001) in their ability to absorb water through leaves and correlate this to minimum seasonal water potential and hydrophobicity of leaf surface. Secondly, we irrigate Pentagramma triangularis in the field and track chloroplast recovery. We find possible evidence of embolism reversal. Taken together, this study explores the methods of survival of the most ancient family of vascular plants
Comparative Foliar Water Uptake and Leaf Hydrophobicity in Island versus Mainland Ferns
No full textIn 2014, Southern California experienced the worst drought in the last 1,200 years. In this study, the mechanisms of drought tolerance for eight species of ferns in the Santa Monica Mountains were assessed with a focus on foliar water uptake and hydrophobicity of frond (leaf) surfaces. We measured gravimetric foliar water uptake and angle of contact for a drop of water on a frond. Seasonal shifts were tracked as a method of following drought response patterns.
Fog is becoming more important due to limited ground water. Fog is far more common on Santa Cruz Island off the coast of California than on the mainland mountains such as the coastal Santa Monica Mountains. Thus a comparison of island versus mainland ferns might illuminate the adaptability of ferns to fog and provides insight into the issue of increasing global temperatures and subsequent fog decrease
Novel Seed Germination in Response to California’s Historic Drought May Deplete Soil Seed Banks
No full textWe observed novel seed germination, without a fire cue, in an obligate seeding species of chaparral (Ceanothus megacarpus) during historic drought in California (2014). We hypothesized that premature germination was promoted by drought-induced canopy dieback among adults that allowed high radiation loads to reach normally shaded soils, cracking seed coats, facilitating water uptake. We hypothesized that because premature seed germination was late in the season (April, when December is typical) roots would not have time to penetrate deep moisture resources before the onset of summer drought, leading to excessive mortality and eventual depletion of soil seed banks. We tested these hypotheses by setting up 67 permanent quadrats (1 m2), at four study sites, varying between a mean of 7 to 10 seedlings per m2, and monitored a total of 576 seedlings, recording mortality every two weeks, from May 2014 to January 2015. We used an infrared thermometer to measure surface soil temperatures below the dead canopy of adults, a dewpoint hygrometer to estimate soil water potentials at 10 cm and 20 cm depths (n = 67), and excavated roots of dead and alive seedlings (n = 12) in late June to estimate maximum rooting depth. Surface soil temperatures at all four study sites approached 70 C. Seed germination trials in the laboratory resulted in \u3e 98% germination at 70 C for 1 h, much higher than controls (~20%). Unpaired Student’s t-test (n = 67) showed the number of seedlings per unit area was significantly higher on trails than off trails where canopy gaps were more prominent. Both findings were consistent with our initial hypothesis. Seedling survival corresponded to maximum rooting depth. Dead seedlings had roots \u3c 20 cm deep whereas surviving seedlings had roots \u3e 20 cm deep, in correspondence with mean soil water potentials of -30 MPa at 10 cm depth, a value more negative than critical levels for hydraulic dysfunction (-11 MPa for C. megacarpus seedlings). By March 2015, total survival rate of the 576 monitored seedlings was only 2.6%, a value significantly lower than the survival rate reported for C. megacarpus seedlings (literature values range between 55-63%). We conclude that novel seed germination due to historic drought in California will not compensate for adult mortality in C. megacarpus but will exacerbate mortality through depletion of the seed bank, causing future shifts in plant community structure
Seasonal changes in tissue water relations for eight species of ferns during historic drought in California
No full textCalifornia experienced unprecedented drought between 2013 and 2015. During this period we compared seasonal changes in tissue water relations among eight fern species in the Santa Monica Mountains of southern California. Our objective was to elucidate differential mechanisms of drought survival and physiological performance during extreme water deficits.
We monitored seasonal changes in water potential (Ψmd) and dark-adapted chlorophyll fluorescence (Fv/Fm), assessed seasonal changes in tissue water relations including osmotic potential at saturation and the turgor loss point (Ψπ, sat and Ψπ, tlp), measured xylem-specific and leaf-specific hydraulic conductivity (Ks and Kl), and estimated, for two evergreen species, vulnerability of stem xylem to water stress-induced embolism (water potential at 50% loss hydraulic conductivity, Y50).
Although species grew within one watershed, they were spatially separated, occupying narrow microsites and displaying differences in water utilization. Among eight species possessing four life history types, three evergreen ferns displayed the greatest disparity in seasonal dehydration, with riparian species maintaining seasonal water potentials above -2 MPa while an upland species repeatedly declined below -8 MPa. Consistent with this disparity, Ψ50 for riparian ferns were -2.5 MPa compared to -4.3 MPa for the upland species.
Observed differences in physiological performance among eight fern species reflected niche segregation in water utilization and habitat preference associated with distinct life history traits. We predict differential survival among fern species as future drought events in California intensify, with desiccation-tolerant resurrection ferns being the most resistant and evergreen dehydration-tolerant ferns the most vulnerable
