Abstract
Essential nutrients and metals have been quantified in stems of many tree species to understand the role of stems as storage and source organs. Little is known about stored stem resources of cycad tree species. Cycas micronesica tissue was collected from apical and basal axial regions of stems; and pith, vascular, and cortex tissues were separated into three radial regions. Leaves were also sampled to provide a comparison to stems. Minerals and metals were quantified in all tissues. Minerals and metals varied greatly among the six stem sections. Phosphorus varied more among the three radial sections than the other macronutrients, and zinc and nickel varied more than the other micronutrients. Stem carbon was less than and stem calcium was greater than expected, based on what is currently known tree stem concentrations in the literature. Elemental concentrations were generally greater than those previously reported for coniferous gymnosperm trees. Moreover, the stem concentrations were high in relation to leaf concentrations, when compared to published angiosperm and conifer data. The results indicated that the addition of more cycad species to the literature will improve our understanding of gymnosperm versus angiosperm stem nutrient relations, and that the non-woody cycad stem contains copious essential plant nutrients that can be mobilized and deployed to sinks when needed.
Highlights
The study of biogeochemistry requires valuations of allocation, resorption, sequestration, and translocation of minerals and metals among all plant organs [1,2,3]
The pachycaulous cycad stem is comprised of persistent peripheral cortex and central pith tissues, and these two radial sections are separated by concentric vascular cylinders
The results indicated that stems of this arborescent cycad species contain greater concentrations of macronutrients than those of other gymnosperms that have been studied [11]
Summary
The study of biogeochemistry requires valuations of allocation, resorption, sequestration, and translocation of minerals and metals among all plant organs [1,2,3]. This elemental composition of various tissues within a plant is referred to as the ionome [4,5]. The component of the ionome that has been most studied is the essential nutrient composition of the active photosynthetic leaf [6]. Leaf concentrations of essential minerals exceed those of woody stems, and the outer active annulus of stems contains greater concentrations than the inner core [7,10,11,12,13,14]. Gymnosperms as a group contain less nutrients in stems than angiosperms [11]
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