Cycas micronesica Stem Carbohydrates Decline Following Leaf and Male Cone Growth Events

Abstract

The growth of synchronized leaf flushes or male cones on Cycas trees is an ephemeral event, and non-structural carbohydrates (NSCs) are likely deployed from stem and root storage tissues to support their construction. The relationships among various stem NSCs and these rapid growth events have not been studied to date. Monosaccharides, disaccharides, and starch were quantified in Cycas micronesica stem tissue prior to and immediately after the growth of leaf flushes or male cones to determine the influences on the concentration of these carbohydrates. The pre-existing leaves were removed from half of the plants to determine if the elimination of this carbon source would influence the NSC behaviors. Starch and sucrose dominated the NSC profiles, and these two NSCs declined following cone or new leaf growth. Removal of pre-existing leaves generated a greater decline in starch and sucrose for cone growth, and a greater decline in sucrose, but not starch following new leaf growth than in control trees with no leaf removal. The initial differences in starch and sucrose among cortex, vascular, and pith tissues disappeared as the concentrations declined in all three tissue categories to reach similar post-growth concentrations among the stem tissue categories. The fructose, glucose, and maltose behaviors were not consistent, and their concentrations were low such that their influence on the total NSC behaviors was minimal. These results provided indirect evidence that stem NSCs were mobilized to support ephemeral male cone and new leaf growth for this arborescent cycad. Growth of female strobili is slow and lengthy, so we did not include female trees in this study. The contributions of stem NSCs to female strobili growth remain to be studied with alternative methods.

Aulacaspis yasumatsui Invasion Reduced Cycas micronesica Microstrobilus Size and Pollinator Brood Site Competence

“…We have shown that decreases in starch and sugars in Cycas organs accompany scale-induced plant mortality [21]. We have also shown that starch and sucrose concentrations decline in Cycas stems during the production of microstrobili [22]. Therefore, the chronic infestations of this armored scale likely place the mature plants in a chronic status of limited nonstructural resources, forcing microstrobilus time-size tradeoff decisions by male trees that may be expressed as less frequent or smaller reproductive organs within an optimal-allocation model; see [23].…”

Aulacaspis yasumatsui Delivers a Blow to International Cycad Horticulture

“…Howard et al [3] were the first to determine the efficacy of imidacloprid for controlling A. yasumatsui, and this systemic insecticide may require the least amount of labor for chemical control of the scale. This systemic insecticide has been used for A. yasumatsui control on C. micronesica to enable in situ research on horticultural and physiological questions [55,56,91,98].…”

Reproductive phases coincide with changes in morphology and photosynthetic physiology in an endangered cycad species

“…This ancient plant group is threatened by many anthropogenic factors, including habitat destruction, illegal poaching and climate change ( Donaldson, 2003 ). Conservation agencies and practitioners around the world have been working toward restoring and protecting many cycad species from extinction through effective preservation of genetic variation ( Griffith et al, 2015 ), habitat restoration and identification of areas suitable for reintroductions ( Swart et al, 2018 ) and characterization of growth and reproductive biology ( Negrón-Ortiz et al, 1996 ; Krieg et al, 2017 ; Lazcano and Ackerman, 2018 ; Marler and Cruz, 2020 ). Studies of endangered cycad species have shown changes in vegetative growth and morphological traits are correlated with reproductive events ( Clark and Clark, 1988 ) and population persistence in the wild ( Raimondo and Donaldson, 2003 ).…”

“…Thermogenesis in cycads is sustained by converting stored carbon sources, such as starches into usable sugars ( Tang, 1987 ). Moreover, recent work has shown that the timing of leaf production and reproductive events in Cycas micronesica may be particularly driven by depletion in non-structural carbohydrate (NSC) concentrations needed to construct vegetative and reproductive structures ( Marler and Cruz, 2020 ). Despite the evidence for reproductive events being dependent on vegetative changes and carbon storage, the extent to which fertile individuals modulate photosynthetic carbon gain and which underlying traits best explain shifts in plant photosynthetic carbon gain remains unexplored in cycads.…”

“…Among the competing processes an organism must balance, the construction of reproductive structures has been shown to be particularly costly with respect to carbon and nitrogen resources. In addition to the conversion of stored starch to sugars ( Tang, 1987 ; Marler and Cruz, 2020 ), studies have shown that plants can increase photosynthesis during reproduction ( Gifford and Evans, 1981 ; Lehtila and Syrjanen, 1995 ; Laporte and Delph, 1996 ; Obeso, 2002 ; Raven and Griffiths, 2015 ). This increase in whole-plant photosynthetic output can be achieved in two, non-mutually exclusive ways, and has not been explored in cycads.…”