Publishing trends for the Cycadales, the most threatened plant group

Chemical Element Concentrations of Cycad Leaves: Do We Know Enough?

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.

Leaf nutrients of two Cycas L. species contrast among in situ and ex situ locations

An understanding of leaf nutrient relations is required for tree conservation and horticulture success.  The study of cycad leaf nutrient dynamics has expanded in recent years, but direct comparisons among reports remains equivocal due to varying sampling protocols.  We used Cycas micronesica K.D. Hill and Cycas nongnoochiae K.D. Hill trees to determine the influence on leaf nutrient concentrations of in situ versus ex situ locations and orientation of leaves within the tree canopy.  Nitrogen, phosphorus, and potassium concentrations of leaves from ex situ plants exceeded those from in situ plants, and the differences were not explained by soil nutrient differences.  Calcium concentrations of leaves varied among the site pairs, with differences primarily explained by soil calcium.  Magnesium concentrations of leaves were not different among all location pairs even though soil magnesium concentrations varied among the sites more than any of the other elements.  Differences in leaf macronutrient concentrations among four C. micronesica provenances were minimal when grown in a common garden.  Lateral orientation of leaves did not influence any of the essential elements for either of the species.  These findings indicate that the lateral orientation of cycad leaves does not influence leaf nutrient concentrations, leaf nutrient relations of cycad plants in managed ex situ settings do not align with leaf nutrient relations in habitat, and these differences are not explained by soil nutrition for most elements.  We suggest that leaf nutrient concentrations should be determined in all niche habitats within the geographic range of a cycad species in order to fully understand the leaf physiology of each species. 

Inserting cycads into global nutrient relations data sets

Global research agendas on plant nutrient relations attempt to illuminate biotic and abiotic factors that mediate nutrient relations. We contend that cycad species are not adequately represented in these global agendas. Little is known about how various cycad traits such as phylogenetics, growth form, latitudinal range, or ecological niche influence concentration, stoichiometry, and resorption dynamics of leaf nutrients. The addition of cycad species data to the global research dataset will address a critical knowledge gap and benefit global research needs to improve our systemic understanding of biotic and abiotic influences on plant nutrition.