Abstract
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 such as incident light and soil nutrient concentrations within the root zone. These influential factors were missing from many of the reports, rendering the results ambiguous and comparisons among studies difficult. Future research should include the addition of more taxa, more in situ locations, the influence of season, and the influence of herbivory to more fully understand leaf nutrition for cycads.
Highlights
Effective horticultural management of economic crops or threatened plant taxa requires an adequate understanding of essential nutrient accumulation, partitioning among organs, and remobilization prior to organ senescence
The aim of our review is to report which taxonomic groups have been most studied, to compile a listing of the published chemical element concentration data for cycad leaves, and to establish protocols for continued research to ensure the results are comparable among the various laboratories that contribute to the agenda in the future
Differences in C. micronesica leaf element concentrations were reported between homogeneous shade conditions supplied by commercial shadecloth and heterogeneous shade conditions supplied by wood slats [17]
Summary
Effective horticultural management of economic crops or threatened plant taxa requires an adequate understanding of essential nutrient accumulation, partitioning among organs, and remobilization prior to organ senescence. These biological phenomena influence many issues such as attractiveness to herbivores, the speed of litter decomposition, and soil changes within the zone of root proliferation and leaf litterfall. The aim of our review is to report which taxonomic groups have been most studied, to compile a listing of the published chemical element concentration data for cycad leaves, and to establish protocols for continued research to ensure the results are comparable among the various laboratories that contribute to the agenda in the future. We conclude with a discussion of possible future research directions with the hope of inspiring more demanding protocols to better meet horticulture and conservation goals
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