12 research outputs found

    The Effect of Freezing Conditions on Xylem Diameter of Malosma laurina and Umbellularia californica in the Santa Monica Mountains

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    Temperature variations in the Santa Monica Mountains are drastic at times, which may be affecting the local plants. To determine the repercussions of these variations in temperature, we measured the xylem diameters of freezing and non-freezing Malosma laurina and Umbellularia californica. U. californica was chosen because it has a large xylem diameter, yet is known to survive freezing conditions. We thought that this plant could provide the most significant results to prove or disprove our hypothesis. M. laurina was chosen because it is abundant in the Santa Monica Mountains and has different physical dimensions than U. californica. Smaller xylem diameters may affect water transport , possibly resulting in physically smaller plant sizes. Natural selection may be acting on these species in the Santa Monica Mountains, eliminating plants with larger xylem diameters in freezing areas. We hypothesize that M. laurina and U. californica in freezing zones will have smaller xylem diameters compared to those in non-freezing zones. We collected samples of M. laurina and U. californica from freezing and non-freezing sites located in Tapia Park and Solstice park in the Santa Monica Mountains and on Pepperdine University’s Malibu Campus. We then prepared slides of the plants’ stems and measured the diameters of the xylems. Using Kaleidagraph, we statistically analyzed our data and found the average values for each plant; freezing M. laurina had an average xylem diameter of 33.3 μm, non-freezing M. laurina had an average xylem diameter of 48.7 μm, freezing U. californica had an average xylem diameter of 33.4 μm, and non-freezing U. californica had an average xylem diameter of 53.8 μm. These results indicate significance as revealed by a p value \u3c0.05

    Correlation Between Freezing Sites and Xylem Vessel Diameter for Three Chaparral Species of the Santa Monica Mountains

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    Coastal exposures of the Santa Monica Mountains rarely experience freezing temperatures (0 °C) because of the ameliorating effects of the Pacific Ocean and seawater’s specific heat capacity. In contrast, inland sites of the Santa Monica Mountains frequently experience winter temperatures below -10 °C. This temperature gradient, from coast to inland, may be a major determinate of species distribution patterns. To investigate possible mechanisms by which freezing impacts chaparral distribution patterns, we examined xylem vessel diameter and vessel length of three chaparral species growing at inland freezing sites versus coastal nonfreezing sites (Malosma laurina, Umbellularia californica, and Ceanothus megacarpus). It has been established that vessel size influences freezing-induced embolism and the blockage of xylem water transport from soil to leaves. However, it is not known if this “size effect” is primarily due to vessel diameter, vessel length, or both. We initially hypothesized that matched species-pairs at non-freezing sites would have both longer and wider vessels than at freezing sites. We determined maximum vessel length by injecting air into stems at decreasing segment lengths and mean vessel diameters by using an ocular micrometer in conjunction with a light microscope. Sample sizes were six for each species pairs. For all three species, mean vessel diameters were narrower at freezing than non-freezing sites (P \u3c 0.05) ranging between 13 µm mean differences for C. megacarpus to 20.4 µm mean differences for U. californica. In contrast, we found no significant difference in vessel lengths for any of the species-pairs (P \u3e 0.05). We conclude that reduction in vessel diameter is more significant than reduction in vessel length for protection from freezing-induced embolism of stem xylem. Furthermore, limits in the genetic plasticity of some species to reduce vessel diameter may preclude their survival at freezing sites

    Extensive Dieback in Malosma laurina in Coastal Exposures of the Santa Monica Mountains Associated with Unprecedented Drought in California

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    Throughout coastal exposures of the Santa Monica Mountains (SMM) there is a recent emergence of widespread dieback in Laurel Sumac (Malosma laurina). M. laurina is a keystone species of chaparral that dominates the SMM. A significant trait of M. laurina is an extensive root system exceeding 12 m in depth. We hypothesized that M. laurina was weakened by unprecedented drought in California (2013-2015) and predisposed to fungal pathogens. An initial study conducted in the summer of 2015 revealed all stem samples taken from dieback adult M. laurina plants were infected with Botryosphaeria dothidea, while zero stem samples taken from healthy adult plants contained the fungus. A survey of dieback in M. laurina was undertaken at 10 microsites along coastal exposures of the SMM between elevations between 60 to 300 m. Plants were scored on a scale of 1 to 5 based on the percentage of dieback a plant was experiencing, and for each of the microsites surveyed, the % adult mortality and canopy dieback did not differ significantly among the microsites. Mean score values for the 10 microsites were 1.19 for dieback plants compared to 5.0 for control plants; these predominantly healthy sites and plants possessed greater access to water. Sample sizes (n) at each microsite varied between 30 and 90 plants. From these results, it is clear that the M. laurina dieback is extensive, but may partially recover if the events surrounding El Niño, specifically rainfall, materialize this coming winter

    Drought-Induced Fungal Infection Causes Severe Dieback in Malosma laurina in the Santa Monica Mountains

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    The current unprecedented drought in California has reached maximums may predisposes plants to fungal infection. Dieback shrubs have shown external wounds, known as cankers, which signals the plant’s immune response to infection. The invading fungus enters through this wound; once inside, it travels through the xylem, thus blocking water transport from the soil to the leaves and thus decreasing photosynthetic rate. Our hypothesis was that photosynthetic rates in Malosma laurina will be high in healthy control resprouts, intermediate in young dieback resprouts, and low in old dieback resprouts with cankers. M. laurina, a chaparral shrub, was used because it is drought-tolerant, has deep roots, has a 99% success rate of resprouting after fires, is co-dominant with other chaparral shrub species, and is a keystone species. To test this hypothesis, a chaparral shrub, M. laurina, was monitored for photosynthesis, transpiration, water potential, conductance, electron transport rate, and ΦPSII using the LI-6400XT Portable Photosynthesis System. Study sites include next to the Theme Tower and at Drescher campus. We found that the control for both adults and resprouts had significantly higher photosynthetic rates than dieback plants. We also discovered that the fungus infecting the local shrubs is Botryosphaeria dothidea. From this, we can conclude that the fungus B. dothidea is causing dieback and thus lowering photosynthesis for infected shrubs. B. dothidea is able to infect the shrubs and cause devastation because the limited water access as a result of the drought causes the plants to be more susceptible to fungal infection

    Possible Fungal Infection Leading to Malosma laurina Dieback

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    There is a significant and apparent dieback of Malosma laurina in the Santa Monica Mountains, some which is found near Pepperdine University. Other areas near Pepperdine show a flourishing growth of M. laurina and our objective was to determine why this difference in M. laurina health exists. We initially hypothesized that in addition to water stress, the unhealthy M. laurina was effected by a pathogen. Under further inspection, the unhealthy plants contained hyphae in some of their xylem vessels, while the healthy ones did not. We sought to determine whether the existence of hyphae in the unhealthy plant’s xylem affected its ability to transport water by measuring the conductance (Kh) of both sick and healthy M. laurina. We created an apparatus that measured water flow through a stem when a known hydrostatic pressure was applied. We also used a vacuum to remove embolism from the stem samples to determine whether the decrease in conductance could be attributed to embolism due to cavitation, or xylem obstruction due to hyphae. Our results showed that the conductance, both pre vacuum and post vacuum, was significantly higher in the healthy M. laurina than in the unhealthy M. laurina. This fact, along with the non significant percent embolism values between the healthy and unhealthy plants demonstrates that there is another factor causing decreased xylem flow in the unhealthy M. laurina samples other than embolism due to cavitation. This conclusion supports our hypothesis that a fungus is involved in the apparent M. laurina dieback

    Resistance to Xylem Cavitation in Evergreen Ferns Correlates with Seasonal Dehydration Levels, Not Mechanical Strength

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    Ferns in the Santa Monica Mountains of southern California display a range of responses to severe drought. In this study, we further characterized the traits that may contribute to fern survival in a mediterranean-type climate. Due to anatomical differences between ferns and angiosperms, we predicted that ferns would exhibit no correlation between stipe mechanical strength and vulnerability to water stress-induced cavitation of stipe xylem. However, we predicted that ferns would show a correlation between seasonal water stress (minimum water potential) and cavitation resistance. Our results support these hypotheses; however, we must increase our sample size of evergreen fern species in order to confirm the relationship between minimum seasonal water potential and vulnerability to cavitation of stipe xylem

    Maximum Photosynthetic Rates Correspond to Life History Type among Eight Fern Species in the Santa Monica Mountains

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    The Santa Monica Mountains of southern California are characterized by a Mediterranean-type climate consisting of hot, dry summers and mild, wet winters. The flora must withstand 6-9 months without rainfall and is most frequently dominated by evergreen, sclerophyllous chaparral. However, various species of ferns are often in the understory of chaparral shrubs. These ferns follow one of four unique life history types relative to frond persistence: evergreen, summer/winter deciduous, or resurrection (desiccation tolerant). The objective of this study was to determine which factors (life history type, microsite, and seasonal activity) might link to maximum photosynthetic performance. Photosynthetic rates were lowest for evergreen species and highest for desiccation-tolerant resurrection plants. Summer and winter deciduous species were intermediate. After comparing maximum photosynthetic performance among our eight species to thirteen fern traits, only Modulus of Elasticity (MOE) had a correlation coefficient approaching significance (r2 = 0.44). Consistent with this observation, maximum stomatal conductance to water vapor diffusion was strongly correlated with MOE (r2 = 0.82). It appears that maximum photosynthetic rates in the eight species examined primarily correlate with frond persistence during summer drought/winter freezing and microsite preference for riparian habitats

    Seasonal changes in tissue water relations for eight species of ferns during historic drought in California

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    California 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

    Weekly Fluctuations in Nonjudging Predict Borderline Personality Disorder Feature Expression in Women

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    OBJECTIVES: Borderline personality disorder (BPD) features have been linked to deficits in mindfulness, or nonjudgmental attention to present-moment stimuli. However, no previous work has examined the role of fluctuations in mindfulness over time in predicting BPD features. The present study examines the impact of both between-person differences and within-person changes in mindfulness. DESIGN: 40 women recruited to achieve a flat distribution of BPD features completed 4 weekly assessments of mindfulness (Five Facet Mindfulness Questionnaire; FFMQ) and BPD features. Multilevel models predicted each outcome from both 1) a person’s average levels of each facet and 2) weekly deviations from a person’s average for each facet. RESULTS: Average acting with awareness, nonjudging, and nonreactivity predicted lower BPD features at the between-person level, and weekly deviations above one’s average (i.e., higher-than-usual) nonjudging predicted lower BPD feature expression at the within-person level. CONCLUSIONS: Within-person fluctuations in the nonjudging facet of mindfulness may be relevant to the daily expression of BPD features over and above dispositional mindfulness
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