Thomas Marler
University of Guam, WPTRC, Faculty Member
Translocation of endangered plant species and facilitating in situ regeneration require knowledge of the factors that define suitable habitat characteristics. Four approaches were employed to define how antecedent and contemporary plant... more
Translocation of endangered plant species and facilitating in situ regeneration require knowledge of the factors that define suitable habitat characteristics. Four approaches were employed to define how antecedent and contemporary plant identity influenced Cycas seedling growth and survival in Guam, Yap, and the Philippines. Cycas micronesica K.D. Hill or Cycas nitida K.D. Hill & A. Lindstr. seedlings growing beneath the canopy of the maternal parent tree reached 100% mortality in 4 to 8 year. Cycas micronesica seedlings planted beneath a conspecific male adult tree reached 68% mortality in two years while seedlings planted away from a conspecific individual exhibited 100% survival. Cycas micronesica seedlings planted beneath monostands of invasive Leucaena leucocephala (Lam.) de Wit or Vitex parviflora Juss. reached 40% mortality in two years while seedlings planted in adjacent native forest cover exhibited 100% survival. Cycas micronesica seedlings planted in soil conditioned for ...
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Research Interests: Biology and Thermogenesis
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Research Interests: Biology and Dry Weight
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Tang, William, Xu, Guang, Marler, Thomas, Khuraijam, Jibankumar Singh, Singh, Rita, Lindström, Anders J., Radha, P., Rich, Stephen, Nguyen, Khang Sinh, Skelley, Paul (2020): Beetles (Coleoptera) in cones of cycads (Cycadales) of the... more
Tang, William, Xu, Guang, Marler, Thomas, Khuraijam, Jibankumar Singh, Singh, Rita, Lindström, Anders J., Radha, P., Rich, Stephen, Nguyen, Khang Sinh, Skelley, Paul (2020): Beetles (Coleoptera) in cones of cycads (Cycadales) of the northern hemisphere: diversity and evolution. Insecta Mundi 2020 (781): 1-19, DOI: http://doi.org/10.5281/zenodo.5757989
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The invasion of numerous countries by the armored scale Aulacaspis yasumatsui Takagi has caused widespread mortality of host Cycas species. Few studies have looked at reproductive biology responses of host plants to the herbivore. This... more
The invasion of numerous countries by the armored scale Aulacaspis yasumatsui Takagi has caused widespread mortality of host Cycas species. Few studies have looked at reproductive biology responses of host plants to the herbivore. This study was conducted to determine the influence of direct Cycas seed integument infestation of A. yasumatsui on germination and seedling performance. An observational study in a Tinian ex situ Cycas micronesica K.D. Hill garden revealed that germination percentage was reduced two-thirds by heavy pre-harvest integument infestation, and more than half of the seedlings from infested seeds died in the nursery. Multi-year mortality of plants was six times greater for plants from habitats with infested seeds than for plants from minimally infested habitats. Stem height of nine-year-old plants from habitats with infested seeds was 64% of that of plants from habitats with un-infested seeds. A controlled study in a Philippine ex situ C. micronesica and Cycas ed...
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The literature containing which chemical elements are found in cycad leaves was reviewed to determine the range in values of concentrations reported for essential and beneficial elements. We found 46 of the 358 described cycad species had... more
The literature containing which chemical elements are found in cycad leaves was reviewed to determine the range in values of concentrations reported for essential and beneficial elements. We found 46 of the 358 described cycad species had at least one element reported to date. The only genus that was missing from the data was Microcycas. Many of the species reports contained concentrations of one to several macronutrients and no other elements. The cycad leaves contained greater nitrogen and phosphorus concentrations than the reported means for plants throughout the world. Magnesium was identified as the macronutrient that has been least studied. Only 14 of the species were represented by data from in situ locations, with most of the data obtained from managed plants in botanic gardens. Leaf element concentrations were influenced by biotic factors such as plant size, leaf age, and leaflet position on the rachis. Leaf element concentrations were influenced by environmental factors su...
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Improved horticultural practices may help to reduce demand for wild cycads threatened by unsustainable collection. We determined the influences of leaf retention with or without anti-transpirants on the success and speed of adventitious... more
Improved horticultural practices may help to reduce demand for wild cycads threatened by unsustainable collection. We determined the influences of leaf retention with or without anti-transpirants on the success and speed of adventitious root development of Zamia furfuracea L.f. and Zamia integrifolia L.f. stem cuttings. Root formation success for both species was greater than 95%. The experimental treatments did not influence the percentage success or the speed of root development for Z. furfuracea or Z. integrifolia. The ending dry weights of the stems, leaves, and roots were also not influenced by the experimental treatments. Our results indicated that adventitious root formation on stem cuttings of these two Zamia species was highly successful with or without retained leaves, and horticultural application of transpiration-reducing products on retained leaves did not improve success. Our findings add to the growing body of evidence that show how the horticulture nursery industry c...
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Methods in sunfleck research commonly employ the use of experimental leaves which were constructed in homogeneous light. These experimental organs may behave unnaturally when they are challenged with fluctuating light. Photosynthetic... more
Methods in sunfleck research commonly employ the use of experimental leaves which were constructed in homogeneous light. These experimental organs may behave unnaturally when they are challenged with fluctuating light. Photosynthetic responses to heterogeneous light and leaf macronutrient relations were determined for Cycas micronesica, Glycine max, and Zea mays leaves that were grown in homogeneous shade, heterogeneous shade, or full sun. The speed of priming where one light fleck increased the photosynthesis during a subsequent light fleck was greatest for the leaves grown in heterogeneous shade. The rate of induction and the ultimate steady-state photosynthesis were greater for the leaves that were grown in heterogeneous shade versus the leaves grown in homogeneous shade. The leaf mass per area, macronutrient concentration, and macronutrient stoichiometry were also influenced by the shade treatments. The amplitude and direction in which the three developmental light treatments in...
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Island invasions may cause severe changes in biodiversity, but the factors that influence these changes are not well understood. We established 120 plots in Cycas micronesica habitats throughout Guam in 2005 following the invasion of the... more
Island invasions may cause severe changes in biodiversity, but the factors that influence these changes are not well understood. We established 120 plots in Cycas micronesica habitats throughout Guam in 2005 following the invasion of the armored scale Aulacaspis yasumatsui, then observed plant mortality through 2020. We used transects in Yap as benchmarks, as the Yap C. micronesica population is not threatened. The initial Guam plots contained about 1600 seedlings, 1160 juveniles, and 1240 mature plants per ha. Seedling mortality was 100% by 2006, juvenile mortality was 100% by 2014, and the 2020 census revealed 96% mortality of the plant population. Localities in western Guam and isolated forest fragments exhibited the greatest mortality, with 100% extirpation from two fragmented western localities. The juvenile and mature trees in Yap were unchanged from 2010 to 2018, but the seedling count was heterogeneous among the years. Constrained recruitment from seedlings to juveniles expl...
Research Interests: Diversity, Biology, Ecology, Biodiversity, Population, and 3 moreTransect, Threatened Species, and Juvenile
Stem respiration is influenced by the vertical location of tree stems, but the influence of vertical location on stem respiration in a representative cycad species has not been determined. We quantified the influence of vertical strata on... more
Stem respiration is influenced by the vertical location of tree stems, but the influence of vertical location on stem respiration in a representative cycad species has not been determined. We quantified the influence of vertical strata on stem carbon dioxide efflux (Es) for six arborescent Cycas L. species to characterize this component of stem respiration and ecosystem carbon cycling. The influence of strata on Es was remarkably consistent among the species, with a stable baseline flux characterizing the full mid-strata of the pachycaulous stems and an increase in Es at the lowest and highest strata. The mid-strata flux ranged from 1.8 μmol·m−2·s−1 for Cycas micronesica K.D. Hill to 3.5 μmol·m−2·s−1 for Cycas revoluta Thunb. For all species, Es increased about 30% at the lowest stratum and about 80% at the highest stratum. A significant quadratic model adequately described the Es patterns for all six species. The increase of Es at the lowest stratum was consistent with the influenc...
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Premise of research. The armored scale Aulacaspis yasumatsui Takagi has invaded numerous geographic regions to devastate cultivated populations of Cycas L. and the native population of Cycas micronesica K.D. Hill on the islands of Guam... more
Premise of research. The armored scale Aulacaspis yasumatsui Takagi has invaded numerous geographic regions to devastate cultivated populations of Cycas L. and the native population of Cycas micronesica K.D. Hill on the islands of Guam and Rota. Questions remain as to how this small hemipteran insect can so rapidly kill a large cycad tree. One possibility is depletion of nonstructural carbohydrates (NSCs) until the storage pool can no longer sustain plant viability. Methodology. We infested Cycas revoluta Thunberg plants with A. yasumatsui and harvested whole plants periodically until plant mortality at week 60. Harvested plants were separated into leaves, stems, and roots, and tissue was frozen and then lyophilized. The dry mass of each organ was measured, and then fructose, glucose, maltose, starch, and sucrose were quantified. Concentration and total pool size within each organ were calculated for each NSC. Pivotal results. Concentration and total pool of all five NSCs were greatest in stems. Concentrations exhibited linear or quadratic declines with time of infestation for all NSCs and organs, with the exception of glucose in stems and maltose in leaves. The total pool of all five NSCs declined linearly or quadratically in all three organs, with the exception of maltose in leaves. Initial plant dry mass of 152 g was 23% NSC, and ending plant dry mass of 59 g was 26% NSC. Carbohydrate stoichiometry shifted in favor of sugars over starch, and sugar stoichiometry shifted in favor of hexoses over disaccharides as time of infestation progressed. Conclusions. These results are consistent with carbohydrate depletion as the mechanism that explains rapid Cycas tree mortality during chronic A. yasumatsui infestation. This is the first demonstration of stress-induced expenditures of carbohydrates by cycads.
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The direct role of physical dormancy in delaying germination of Serianthes grandiflora Bentham, Serianthes kanehirae Fosberg, and Serianthes nelsonii Merrill seeds has not been adequately studied, nor has the role of temperature on... more
The direct role of physical dormancy in delaying germination of Serianthes grandiflora Bentham, Serianthes kanehirae Fosberg, and Serianthes nelsonii Merrill seeds has not been adequately studied, nor has the role of temperature on germination behaviors. Imbibition testing indicated seeds with scarified testa absorbed water for the duration of a 24 h imbibition period, but seeds with an intact testa stopped absorbing water after 1 h. The behavior of S. nelsonii seeds most closely matched those of S. kanehirae, with the pattern of water absorption for S. grandiflora seeds deviating from that for the other species. Scarified seeds germinated readily, with initial germination occurring by 50 h for S. nelsonii and 90 hr for the other species, and maximum germination of 80% to 90% occurring by 60 h for S. nelsonii and 100 h for the other species. Predicted optimum temperature based on a fitted quadratic model was 26 °C for S. nelsonii, 23 °C for S. grandiflora, and 22 °C for S. kanehirae...
Research Interests: Chemistry, Biology, Medicine, Seed dormancy, Plants, and 4 moreRespiration, Germination, Seedling, and Dormancy
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We compiled Red List data from all listed cycad taxa to determine the current status of the world's most threatened plant group. Each Red List threat category had different proportions of genera, and the genera comprised different... more
We compiled Red List data from all listed cycad taxa to determine the current status of the world's most threatened plant group. Each Red List threat category had different proportions of genera, and the genera comprised different proportions of threat categories. Each Red List threat category consisted of different proportions of Red List criteria. Each genus was composed of different proportions of Red List criteria, and every genus was represented by different proportions of listed versus non-listed species. Differences among the genera and categories were substantial, revealing no canonical characteristics that define the members of this plant group. Species that are missing from the Red List or Data Deficient deserve high priority for completion of assessment and listing. Cycas is the genus that may change the most as taxonomy and Red List threat assessments continue to be modified. Distinctive overviews of the Red List data such as this one provide a unique snapshot of the...
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The United States is currently home to five native cycad species. We provide a discussion on these five cycad species to illuminate how evolutionary and geopolitical processes influence phytogeography and published checklists of... more
The United States is currently home to five native cycad species. We provide a discussion on these five cycad species to illuminate how evolutionary and geopolitical processes influence phytogeography and published checklists of threatened plants. The number of threatened species in need of protection within any given country is a product of speciation that is contingent with evolutionary processes. However, this number may change instantaneously along with shifting of geopolitical boundaries brought about by armed conflict between rival states and multilateral negotiations. There are five contemporary cycad species within the United States, and the various historical bilateral and multilateral agreements that have generated this list are reviewed. Three of these five cycad species are threatened and in need of urgent protection. A discussion on the history of United States cycads as a microcosm of worldwide conservation issues is presented, with a focus on how federal conservation ...
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Aulacaspis yasumatsui Takagi invaded Guam in 2003 and caused the widespread mortality of the indigenous Cycas micronesica K.D. Hill population. The regeneration of the surviving tree population continues to be constrained 20 years later,... more
Aulacaspis yasumatsui Takagi invaded Guam in 2003 and caused the widespread mortality of the indigenous Cycas micronesica K.D. Hill population. The regeneration of the surviving tree population continues to be constrained 20 years later, and a look at the changes in megastrobili traits may inform future conservation management decisions concerning regeneration. We quantified megastrobilus reproductive effort and output from 2001 to 2022 to address this need. The reproductive effort of each megastrobilus was immediately reduced by the invasion, as the number of megasporophylls declined by 29%, and the number of ovules declined by 73% in 2006. Reproductive output was also damaged, as the percent seed set declined by 56% and the number of seeds per strobilus declined by 88%. These fecundity metrics have shown few signs of recovery through 2022. Our results reveal that chronic A. yasumatsui infestations, combined with other invasive herbivore threats, have damaged the host C. micronesic...
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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... more
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....
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The pachycaulous stem of cycad plants enables the storage of abundant nonstructural carbohydrates. Cycas revoluta Thunb. and Zamia furfuracea L.f. stems were analyzed for starch and 15 sugars to determine carbohydrate richness. All 15... more
The pachycaulous stem of cycad plants enables the storage of abundant nonstructural carbohydrates. Cycas revoluta Thunb. and Zamia furfuracea L.f. stems were analyzed for starch and 15 sugars to determine carbohydrate richness. All 15 sugars were detected in both species. The tetrasaccharide stachyose and the disaccharide sucrose comprised most of the sugar content. Total sugar content of these cycad stems was 330 to 360 mg·g−1 and was similar to starch content. The stems of these two species were composed of 64% to 79% nonstructural carbohydrates. The cycad stem is ideally designed to store and mobilize nonstructural carbohydrates to support sink activity when needed, and stachyose may play a prominent functional role.
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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... more
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 con...
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Container-grown papaya plants were subjected to a slow drying cycle by replenishing a portion of the mean daily water loss. When light-saturated net CO2 assimilation (A) of stressed plants was ≈70% of well-watered plants, sun–cloud... more
Container-grown papaya plants were subjected to a slow drying cycle by replenishing a portion of the mean daily water loss. When light-saturated net CO2 assimilation (A) of stressed plants was ≈70% of well-watered plants, sun–cloud transitions were simulated by placing shadecloth between a lamp and the leaf cuvette. The cuvette was initially positioned to receive photosynthetic photon flux (PPF) of ≈1600 μmol–m–2–s–1. The shadecloth was placed over the cuvette for a 3-min period (250 μmol–m–2–s–1), then removed. Gas-exchange responses were recorded for another 3 min of high light. Within 20 sec of initiating low light on well-watered plants, A was <50% of the high-light value. Stomatal conductance (gs) of these plants began to decline by 60 sec and slowly declined to <90% of the high-light value. Both A and gs recovered to the original values by ≈2 min following return to the high-light conditions. For stressed plants, the decline of gs under low light began earlier and was of...
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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... more
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% ...
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Two studies were conducted with `Known You 1' and `Sunrise' papaya seedlings to determine the combined influence of wind and drought stress on growth. For each study, 4-week-old nursery plants were transplanted into 2.6-L... more
Two studies were conducted with `Known You 1' and `Sunrise' papaya seedlings to determine the combined influence of wind and drought stress on growth. For each study, 4-week-old nursery plants were transplanted into 2.6-L containers and placed in a protected site with rain exclusion provided by polypropylene cover. Industrial fans were used to provide unidirectional wind of ≈2 m/s for 12 hours per day to half of the plants; the remaining half of the plants received no wind. One half of the plants for each cultivar and wind combination were designated as well-watered and received daily irrigation. The remaining half of the plants were designated as drought-stressed and received 25% to 50% of the water applied to the well-watered plants. Plants were grown for 3 weeks under these experimental conditions. There were no interactions between the drought and wind main effects. The reduction in height, trunk cross-sectional area, total plant dry weight, and relative growth rate belo...
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The influence of plant size on recovery following defoliation of `Tainung 1' papaya was used to study the role of respiratory sink size relative to photosynthetic surface area and the carbohydrate pool size available for... more
The influence of plant size on recovery following defoliation of `Tainung 1' papaya was used to study the role of respiratory sink size relative to photosynthetic surface area and the carbohydrate pool size available for remobilization. Defoliated (D) plants at three different ages: oldest, 24 weeks posttransplant (PT), supporting ≈8 weeks of fruit set; intermediate, 10 weeks PT, ≈2 weeks from initial flowering; and youngest, 4 weeks PT, were compared to an equal number of control plants. The oldest plants abscised all fruit <5.5 cm in diameter as a result of defoliation. Increase in stem height and basal circumference ceased on all plants and increase in fruit circumference ceased on the oldest plants following defoliation. Increase in stem height of D plants began again 3 weeks postdefoliation (PD) and returned to that of control plants by 6 weeks PD. Increase in basal circumference of D plants began again 6 weeks PD. Root density was observed on observation windows, and fi...
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The frequency of tropical cyclones is a major factor affecting the vegetation of the Mariana Islands, where these storms are called typhoons. An average of about one typhoon per year has passed within ≈100 km of Guam during the past 50... more
The frequency of tropical cyclones is a major factor affecting the vegetation of the Mariana Islands, where these storms are called typhoons. An average of about one typhoon per year has passed within ≈100 km of Guam during the past 50 years. The physiognomy of Guam's natural and urban forests is largely determined by these typhoons. The impact of each typhoon is determined by a long list of interacting factors such as species characteristics; environmental and horticultural conditions preceding the typhoon; the intensity, direction, and duration of winds; the amount of rainfall associated with the typhoon; and the environmental and horticultural conditions following the disturbance. Many species survive typhoons by reducing aerodynamic drag of the canopy by abscising inexpensive leaves or breakage of small stems which results in an intact major structural framework. Speed of recovery for nonlethal damage following disturbance depends on nonlimiting conditions during recovery. T...
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Trade winds are a widespread horticultural consideration throughout the tropics. Growth and productivity of most horticultural crops are not optimal on sites that are exposed to these chronic, unidirectional winds. We conducted four... more
Trade winds are a widespread horticultural consideration throughout the tropics. Growth and productivity of most horticultural crops are not optimal on sites that are exposed to these chronic, unidirectional winds. We conducted four container studies on an exposed site, using clear plastic or screening material to provide three levels of wind exposure: 0%, 36%, or 100%. Two studies were conducted with direct-seeding, such that seedling emergence and early growth were determined for 7 weeks. Two studies were conducted using 8-week-old nursery plants that had been grown in a protected nursery. These plants were transplanted to the experimental site and grown for 6 weeks. Cultivars were `Known You 1', `Sunrise', and `Tainung 2'. Full exposure to wind reduced height up to 32%, increased root: canopy ratio up to 36% and exhibited no influence or slightly reduced stem cross-sectional area when compared with full protection from wind. Net carbon dioxide assimilation (Pn) was me...
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Trade winds occur throughout the year and drought occurs seasonally in many papaya (Carica papaya L.) production regions. We conducted four studies with `Known You 1' and `Sunrise' papaya seedlings to determine the combined... more
Trade winds occur throughout the year and drought occurs seasonally in many papaya (Carica papaya L.) production regions. We conducted four studies with `Known You 1' and `Sunrise' papaya seedlings to determine the combined influence of wind and water deficit on growth. We conducted three additional experiments to determine plant response to wind within a continuous dose range of 0 to 2.5 m·s–1. The main effects of wind and irrigation significantly reduced most response variables, such as dry weight components, leaf area, and height. However, the two factors acted independently of each other for every measure of plant growth. Thus, there was no departure from simple effects of an additive model for each main factor. The relationship between plant growth and wind between 0 and 2.5 m·s–1 could be described by a quadratic model. Results indicate that the influence of wind on plant growth cannot be studied without controlling or quantifying soil moisture among treatment groups. ...
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Field-grown `Red Lady' papaya (Carica papaya L.) plants were used to measure foliar gas-exchange responses to rapid changes in irradiance levels to determine if papaya stomata are able to track simulated sun-to-cloud cover... more
Field-grown `Red Lady' papaya (Carica papaya L.) plants were used to measure foliar gas-exchange responses to rapid changes in irradiance levels to determine if papaya stomata are able to track simulated sun-to-cloud cover transitions. Natural sunlight and neutral shade cloth placed over the leaf were used to provide high photosynthetic photon flux (PPF) of about 2000 μmol·m-2·s-1 until leaves reached steady state within the cuvette, followed by three minutes with low PPF of about 325 μmol·m-2·s-1, and a return to PPF of about 2000 μmol·m-2·s-1. Net CO2 assimilation (A) declined from an initial 20 μmol·m-2·s-1 to about 9 μmol·m-2·s-1 within 20 seconds of initiating low PPF, and remained fairly stable for the duration of the three minutes of low PPF. Stomatal conductance (gs) declined within 60 seconds of initiating low PPF, from 385 to about 340 μmol·m-2·s-1 during the three minutes duration of low PPF. Following the return to high PPF, A rapidly increased to about 18 μmol·m-2·s...
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Trends in published cycad research within various fields of study were determined using proceedings from international conferences on cycad biology and Google Scholar to access the primary literature. Both search methods indicated that... more
Trends in published cycad research within various fields of study were determined using proceedings from international conferences on cycad biology and Google Scholar to access the primary literature. Both search methods indicated that phylogeny, systematics and ecology are strongly represented in recent cycad literature, while there is a need for more research in horticulture and pathology, reviews and clarification of correspondence between current and discontinued species designations.
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Plant leaf litter decomposition is directly influenced by the identity of the source plants and the leaf age. Defoliation of forests by tropical cyclones (TC) transfers copious amounts of high-quality green leaf litter to soils. We used a... more
Plant leaf litter decomposition is directly influenced by the identity of the source plants and the leaf age. Defoliation of forests by tropical cyclones (TC) transfers copious amounts of high-quality green leaf litter to soils. We used a soil amendment approach with the incubated buried bag method to compare carbon (C) and nitrogen (N) mineralization dynamics of green and senesced leaf litter from cycad Cycas micronesica and angiosperm Morinda citrifolia trees on the island of Guam. Soil priming increased the decomposition of pre-existing organic C, and were greater for green leaf litter additions than senesced leaf litter additions. Available N content increased by day 14 and remained elevated for the entire 117-d incubation for soils amended with green M. citrifolia litter. In contrast, available N content increased above those in control soils by day 90 and above those in soils amended with senesced litter by day 117 for green C. micronesica litter. The net N mineralization rate...
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Exposure to environmental toxins may be partly responsible for mammal neurodegenerative disorders. Consumption of seeds from Guam’s cycad tree has been linked to the disorder known as amyotrophic lateral sclerosis-parkinsonism dementia... more
Exposure to environmental toxins may be partly responsible for mammal neurodegenerative disorders. Consumption of seeds from Guam’s cycad tree has been linked to the disorder known as amyotrophic lateral sclerosis-parkinsonism dementia complex (ALS-PDC). The unambiguous identification of causal agents of ALS-PDC has been elusive. We have examined the levels of eight metals and metalloids in cycad seeds as a function of the ambient shade in which the plants were grown. Of these metals, the data strongly suggest that aluminum (Al) and selenium (Se) are present in washed flour prepared from southern Guam’s cycad seed tissues at elevated levels, especially when the trees are grown in shade. Previous authors have speculated that Al and Se are involved in various ALS outcomes, and our results support this interpretation.
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Soils from the rhizosphere of perennial plants accumulate microorganisms that influence the growth of other plants. This microorganism biodiversity may be exploited by using these soils as an inoculum in new planting sites. Soils... more
Soils from the rhizosphere of perennial plants accumulate microorganisms that influence the growth of other plants. This microorganism biodiversity may be exploited by using these soils as an inoculum in new planting sites. Soils collected from the rhizosphere of mature Serianthes trees were subjected to treatments designed to reduce or increase microorganism populations, then were used in a series of five studies to grow Serianthes plants in container culture. Serianthes kanehirae and Serianthes grandiflora stem growth was 14–19% greater, leaf nitrogen was 40–46% greater, leaf phosphorus was 50–86% greater, and leaf potassium was 28–43% greater when grown in soils from Serianthes rhizosphere than in soils away from a Serianthes tree. Treating the Serianthes rhizosphere soils with sterilization or propiconazole fungicide reduced stem growth of S. grandiflora, S. kanehirae, and Serianthes nelsonii plants by 16–47% below that of untreated soils. The sterilization and fungicide treatme...
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The genus Serianthes has not received adequate research attention, leaving large gaps in the knowledge required to inform conservation decisions. For example, nutrient management protocols are not understood due to lack of research.... more
The genus Serianthes has not received adequate research attention, leaving large gaps in the knowledge required to inform conservation decisions. For example, nutrient management protocols are not understood due to lack of research. Serianthes grandiflora, Serianthes kanehirae, and Serianthes nelsonii plants were grown in container culture to determine the influence of increasing edaphic nitrogen (N), phosphorus (P), or potassium (K) content on stem growth and leaf nutrient relations. Addition of N alone increased leaf N, stimulated stem height and diameter growth, increased leaf number, and reduced leaf tissue concentrations of most nutrients including P and K. Addition of K alone increased leaf K, did not influence stem growth, did not reduce N or P concentration, but caused substantial changes in leaf tissue stoichiometry. Addition of P alone increased leaf P, did not influence stem growth, did not reduce leaf N or K concentration, and exerted minimal influence on concentrations ...
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Trees contribute to ecosystem nutrient cycling through the amount, timing, and composition of litterfall. Understanding the nature of this contribution from endangered tree species may aid in species and habitat recovery efforts.... more
Trees contribute to ecosystem nutrient cycling through the amount, timing, and composition of litterfall. Understanding the nature of this contribution from endangered tree species may aid in species and habitat recovery efforts. Serianthes nelsonii is an endangered tree species from the Mariana Islands, and little is known about litterfall dynamics. The timing of leaf, fruit, and stem litterfall was determined to more fully understand the return of nutrients via litter. The total annual litterfall was 272.8 g·m−2, with 45% represented by leaves, 48% represented by stems, and 7% represented by fruits. Stem litterfall weight contrasted more from month to month than the other organs, and leaf litterfall exhibited the most even distribution throughout the year. The timing of fruit and stem litterfall was influenced by the timing of extreme wind events. Leaf litter contributed nutrients in the following order: carbon > calcium > nitrogen > potassium > magnesium > iron >...
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A laboratory exercise is outlined in which breath is used as the source for elevating CO2. Single-plant enclosures are constructed by placing containers with stem cuttings within clear bags for maintaining high humidity during root... more
A laboratory exercise is outlined in which breath is used as the source for elevating CO2. Single-plant enclosures are constructed by placing containers with stem cuttings within clear bags for maintaining high humidity during root initiation. These enclosures provide a restricted atmosphere in which elevated CO2 is adequately confined. The materials are inexpensive and readily available. The procedure is rapid, with results obtained in as few as 7 days. The increase in canopy and/or root growth as a result of elevated CO2 may be observed visually by younger audiences, or may be measured and analyzed in a manner dependent on the age group. The exercise generates an abundance of discussion and may be used to lead into many lectures on plant physiology, horticultural crop production, or global concepts of CO2 and the plant kingdom.
Research Interests:
Cycas micronesica K.D. Hill trees on the island of Yap were used to determine the influence of position along the leaf rachis on macro- and micro-nutrient concentrations and how leaf age affected the results. The outcomes revealed... more
Cycas micronesica K.D. Hill trees on the island of Yap were used to determine the influence of position along the leaf rachis on macro- and micro-nutrient concentrations and how leaf age affected the results. The outcomes revealed improvements to sampling protocols for future cycad leaf research. The concentration of every element except carbon and copper was influenced by leaflet position along the rachis. Most elements exhibited similar patterns for the oldest and youngest leaves on a tree, but the influence of position along the rachis for nitrogen, phosphorus, calcium, zinc, and boron was highly contrasting for old versus young leaves. The elements with the greatest variability along the rachis were potassium, phosphorus, manganese, and zinc, with the difference in basal and terminal leaflets as great as four-fold. Sampling leaflets at one position on a cycad leaf may generate inaccurate elemental concentration results for most essential nutrients other than carbon and copper. W...
Research Interests:
The need for improved knowledge on conservation and management of cycad species has generated recent interest in compiling a database on leaf nutrient concentrations. However, the sampling protocols have not been consistent among reports... more
The need for improved knowledge on conservation and management of cycad species has generated recent interest in compiling a database on leaf nutrient concentrations. However, the sampling protocols have not been consistent among reports and the influences of some plant and habitat traits on the plasticity of cycad leaf nutrient concentrations has not been adequately determined. We used Cycas micronesica K.D. Hill trees to determine the role of incident light level and leaf age on leaflet content of 11 essential elements. Shade leaves exhibited increased mass-based concentration for nitrogen, phosphorus, and potassium above that of sun leaves. Shade leaves exhibited decreased area-based concentration for all of the macro- and micronutrients below that of sun leaves. Mass-based concentration of nitrogen, phosphorus, and potassium decreased with leaf age, and that of calcium, magnesium, iron, manganese, and zinc increased with leaf age. These findings indicate the relative leaf age an...
Growth and leaf gas-exchange responses of carambola (Averrhoa carambola L.) seedlings to wind or seismic stress were studied under glasshouse conditions. Forty days of twice daily seismic stress applied for 10 seconds consistently reduced... more
Growth and leaf gas-exchange responses of carambola (Averrhoa carambola L.) seedlings to wind or seismic stress were studied under glasshouse conditions. Forty days of twice daily seismic stress applied for 10 seconds consistently reduced carambola height, leaf area, dry weight, relative growth rate, and leaf-area ratio, but increased trunk cross-sectional area compared with plants receiving no seismic stress. Fifty-one days of wind load reduced plant height, leaf area, dry weight, trunk cross-sectional area, net assimilation rate, relative growth rate, leaf-area ratio, and stomatal conductance compared with plants receiving no wind stress. Morphological appearance was similar for plants receiving wind or seismic stress. Net CO2 assimilation of carambola leaflets was reduced by 30 minutes of wind load for up to 6 hours following the stress. Results suggest that wind may reduce carambola growth at least partially by influencing leaf gas exchange or by the mechanical stress associated...