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Thomas E. Marler

Four phytophagous insects are among the major threats to Cycas micronesica K.D. Hill on Guam, and the temporal comparisons of infestation levels may inform horticultural and conservation decisions. Incidence of Aulacaspis yasumatsui Takagi, Erechthias Meyrick sp., Chilades pandava Horsfield, and Dihammus marianarum Aurivillius infestations on Cycas micronesica plants were recorded every 6 months from 2004 to 2013 to determine if the incidence of A. yasumatsui was related to patterns of the other three insects. Dihammus marianarum infestations reached ephemeral maximum and minimum levels ≈2 years after A. yasumatsui infestations reached maximum and minimum levels. Erechthias sp. infestations disappeared in early 2006 when Cycas micronesica leaves were being killed by acute A. yasumatsui infestations. Erechthias sp. infestations increased thereafter as A. yasumatsui incidence declined in response to biological control. Chilades pandava infestations appeared to increase and decrease inversely with A. yasumatsui infestations throughout the years. Aulacaspis yasumatsui may be indirectly affecting D. marianarum damage by direct control of changes in overall tree health. Aulacaspis yasumatsui may be indirectly influencing Erechthias sp. through direct control over leaf longevity. The C. pandava and A. yasumatsui populations appear to exhibit direct competition with inverse patterns of incidence.

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Thomas E. Marler

Split-root techniques were used to determine if Cycas edentata seedling roots possessed identity recognition capabilities. One compartment of the split-root containers contained a competing half-sibling seedling, and the second compartment contained one of four treatments. When the second compartment contained a half-sibling or C. edentata seedling from the same habitat, root growth did not differ between compartments. When the second compartment contained a C. edentata seedling from a habitat 130 km away or a C. nitida seedling, root dry weight and root length were increased above that of compartments with half-siblings. Whole plant growth also increased in seedlings that experienced competition with the conspecific plant from a distant habitat or from a different species. The results validated the ability of Cycas edentata roots to recognize and then use a plastic response to neighbor root identity. In horticultural settings, planting cycad plants where neighbors are close relatives may reduce plant growth, and planting to ensure neighbors are not close relatives may increase plant growth.

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Thomas E. Marler

Cycas micronesica is an arborescent cycad with sclerophyllous, long-lived compound leaves that are produced in synchronized pulses. The photosynthetic characteristics of leaves in two sequential cohorts of ≈2 and ≈11 months after leaf expansion were determined in this study. Fluorescence yield following 30-min of light exclusion or from leaves engaged in photosynthesis under ambient light was measured throughout several 24-h periods to determine maximum quantum efficiency of PSII photochemistry and quantum efficiency under ambient light. Maximum quantum efficiency was similar for the two cohorts throughout the nocturnal period. Maximum quantum efficiency and quantum efficiency under ambient light declined following exposure to daily direct sun but recovered quickly each afternoon. This daily decline was greater for the older cohort than the younger cohort. Net carbon dioxide assimilation (Pn) was also determined using gas exchange, and light saturated Pn of the older cohort was 75% to 85% of that for the younger cohort during the daily maximum at late morning. Pn of the older cohort increased more slowly in the morning and declined more rapidly in the afternoon than did Pn of the younger cohort. Apparent quantum yield determined by gas exchange was similar for the two cohorts in the absence of extended sun exposure. However, this characteristic declined during midday, and the decline was greater for the older cohort. These results indicate that photosynthetic capacity of older C. micronesica leaf cohorts remains high, and these older leaves may substantially contribute to the plant's overall carbon economy. However, the number of hours during the day in which these older leaves reach their photosynthetic capacity is less than for the younger leaves.

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Thomas E. Marler

Salinity effects on growth and net gas exchange of carambola (Averrhoa carambola L.) examined in were greenhouse culture with ten-month-old seedlings in perlite: peat: sand: pine bark chip medium in 5.1 liter (21 cm top dia.) containers. Treatments of 0.05, 5.1, 9.5, or 13.9 dS·m-1 were obtained by dissolving ca. 0, 2.5, 5.0, or 7.5 g of dehydrated sea salt per liter of rain water and delivered from elevated tanks by gravity to dribble ring emitters in containers via polyethylene and q icro tubing. All plants except control plants received 5.1 dS·m-1 beginning 25 Nov., and concentration was gradually increased for the two highest salinity levels until reaching 9.5 dS·m-1 on 3 Dec. and 13.9 dS·m-1 on 7 Dec. Plants were watered twice weekly until 1 March 1990. Stomatal conductance was determined (LI-COR 1600 steady-state diffusion porometer) on 7 day intervals beginning 24 Nov. Growth was determined as leaf area (LI-COR 3000 area meter), plant dry weight, and trunk diameter. Stomatal conductance declined in all salinity levels to 50% or less of controls by day 12, with a gradual further decline thereafter. Leaf area, plant dry weight, and trunk diameter declined linearly with increased salinity.

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Thomas E. Marler

An aeroponics system was used to determine root growth of Citrus aurantifolia Swingle following removal from containers. Rooted cuttings were planted in 0.46-liter containers in a 1 sand: 1 perlite medium, and watered daily and fertilized with a complete nutrient solution weekly. The plants were grown in the containers until root growth had filled the container volume. A sample of plants was removed from the bench after 86, 146, or 210 days in container production. Plants were bare-rooted and the existing root system dyed with methylene blue, and placed in the aeroponics system. The plants were maintained in the aeroponics system for 50 days, then were harvested and the roots separated into pre-existing roots and new roots. Two dimensional area and dry weight of roots were measured. Relative new root growth of plants that were maintained 210 days in the containers was less than that of plants that were removed from containers earlier. The data indicate that maintaining plants in containers for extended periods of time may reduce root regeneration following removal from containers.

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Thomas E. Marler

Large stem cuttings were removed from Cycas micronesica K.D. Hill trees and used for asexual propagation to more fully understand resource factors that influence adventitious root formation success. Healthy source trees had received insecticide protection from ubiquitous Aulacaspsis yasumatsui Takagi infestations and unhealthy source trees had suffered from chronic A. yasumatsui infestations. Nonstructural carbohydrates were quantified from stem tissues at the base of each 1-m cutting, and induction of adventitious roots was attempted using field soil as the medium. Carbohydrate concentrations were increased in healthy, protected tree cuttings above those in unhealthy, infested tree cuttings. The relative increase was greatest in the hexoses, intermediate in sucrose, and least in starch. The total nonstructural carbohydrate concentration in cuttings of infested trees was 54% of that of protected trees, and the sugar/starch quotient of infested trees exceeded that of protected trees. Asexual propagation success was 30% for the unhealthy tree cuttings and 100% for the healthy tree cuttings. These manipulative experiments confirm that chronic A. yasumatsui herbivory of C. micronesica trees reduces stem carbohydrates and decreases asexual propagation success. The results indicate that the use of large cuttings from unhealthy C. micronesica trees to rescue tree populations from construction sites is not a wise conservation decision in habitats where A. yasumatsui herbivory has been uncontrolled. Protocols for future rescue operations designed to transplant C. micronesica trees from construction sites may be improved by this new knowledge.

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Thomas E. Marler

‘Sunrise’ and ‘Tainung 2’ papaya seedlings were subjected to 3 weeks of ambient winds in Guam during five experiments, and growth responses of roots, leaves, and stems were quantified to compare speed and extent of the plasticity among the organs. The cultivars responded similarly with 1 week eliciting stem growth responses and 2 weeks eliciting root responses. The timeframe of these studies was sufficient to enable adaptive responses in all three organs. Wind reduced stem and leaf expansion rate but not root extension rate, providing one example of how the form of response differed among the organs. A dose–effect was evident among the experiments with magnitude of response increasing with mean ambient wind speed. Asymmetric stem diameter and root tip density were examples of adaptive responses to directional wind load. These data on young papaya plants may be used to inform field experiments aiming to determine how chronic winds influence long-term growth and fitness.

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Thomas E. Marler

A container study and a hydroponics study were conducted to determine gas-exchange and ion content of `Cariflora' papaya plants as influenced by a combination of salinity and flooding. Plants grown in nutrient solution were subjected to 1 or 8 dS·m–1 as salinity treatments and 6.54, 3.62, or 0.92 mg oxygen/liter as the flooding treatments. Plants in the container study were subjected to 0, 4, or 8 dS·m–1 as salinity treatments, and half of the plants in each salinity level were flooded. Leaf gas-exchange began to decline by day 1 in all plants receiving flooding, and was zero by day 5. In contrast, gas-exchange of plants experiencing salinity began a slow decline after 5 to 7 days. Stomatal conductance of salinized plants was 25% to 33% of the control plants in the container study after 39 days. No interaction occurred between flooding and salinity treatments since the stomatal response to flooding was so rapid across all levels of salinity. Roots and stems played a major role in storing Na+ and Cl in salinized plants. For example, stems contained more than two times the dry weight concentration of both ions as did leaves. Older leaves accumulated more Na+ and Cl than did younger leaves. Flooding decreased Na+ and Cl accumulation in roots, stems, and leaves in all salinized plants.