Methods in studying cycad leaf nutrition found to be inconsistent and incomplete

January 21, 2021

Collective research to date regarding nutrients found in the leaves of contemporary cycad species has been inconsistent as far as data collection and narrow in scope, according to a University of Guam-led literature review published on Nov. 19 in Horticulturae journal.

Understanding nutrient accumulation within cycads is essential to effective horticultural management, and more importantly, conservation of this plant group, which is highly prized within the horticulture trade and also threatened worldwide.

"Cycads comprise the most threatened group of plants worldwide, but they are also one of the least studied plant groups," said Benjamin Deloso, a cycad specialist with the University of Guam and lead author of the study. "Most of the disciplines of cycad research are only now accumulating enough peer-reviewed literature to enable organized global reviews, such as this one."

The effort to compile and summarize peer-reviewed literature on the subject was undertaken by scientists from Guam, Florida, the Philippines, Thailand, and the Micronesian Island of Yap -- each of whom also co-authored some of the articles cited in the review.

They concluded that in order to draw more reliable comparisons among studies of cycad leaf nutrition, future research should include: Furthermore, the sampling and analytical methods were highly disparate among the studies.

"One of our main points was that the protocols for sampling leaf tissue to determine nutrient concentrations of cycad leaves have not been homogeneous among the various research agendas," Deloso said. "This compromised our ability to unequivocally determine any canonical trends in the results."

Discoveries based on data review

Despite the disparities in research methods, the review of published research revealed that cycad leaf nitrogen and phosphorus concentrations exceeded the global mean for these elements in all seed-bearing plants. According to the authors, the cyanobacteria endosymbionts that inhabit cycad roots provide additional nitrogen for the cycad to exploit. These cyanobacterial endosymbionts are absent from many other plant groups, which may help explain these findings.

Deloso said the findings of this first-ever literature review on the topic of leaf nutrition in cycads are key moving forward with cycad research.

"Among my co-authors were the world's three leading authorities for Guam's native cycad, Cycas micronesica. This tree is one of the many endangered cycad species, and these experts are crucial sources of knowledge to inform future conservation decisions," he said.

University of Guam

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