Nong, Junqing, Ruijing Xu, Songpo Wei, Shaohui Fan, Quan Qiu, Yiju Li, and Guanglu Liu. "Geographical variation and the role of climate and soil on phenotypic traits of Calamus rhabdocladus across provenances in China." BMC Plant Biology 25, no. 1 (2025): 365.

 What They Did

The researchers collected samples of Calamus rhabdocladus, a woody vine in the palm family, from ten locations across China. They measured 15 plant traits and examined how they correlated with climate and soil conditions, as well as the degree to which each trait varied among locations. They found that the dry weight of the leaves, stems, and roots, as well as the volume of the flagellum (a whiplike climbing structure) varied the most, suggesting that the plant adapts to its environment by adjusting the relative growth of the different organs.

Plants from areas with lower temperatures had more root growth. Because lower temperatures can limit the growth rate of above-ground plant parts, the plant may need to put more resources into root growth as a survival adaptation. The chlorophyll content was higher in areas with more precipitation, possibly as an adaptation to the lower light conditions associated with rain.

In areas with more organic material in the soil, the specific leaf area (one-side area of leaf / leaf dry weight) was larger, suggesting a faster growth rate. The flagellum, however, was smaller, possibly because the plant has less need to climb over other plants when soil fertility is high. Higher soil nitrogen content was correlated with higher dry matter percentages in the above-ground parts of the plant, perhaps because the availability of nutrients provides an opportunity for the plant to generate additional tissue. Overall, however, the climate variables affected the differences in plant traits more than the soil variables did.

 

Further Exploration

In this paper, the researchers used two measures to compare the degree of variation in each plant trait: coefficient of variation and plasticity index. The coefficient of variation is equal to the standard deviation of each trait divided by its mean, times 100%. The plasticity index is the difference between the largest and smallest value for each trait, divided by the largest value. The difference in the kind of information you get from these two measures isn’t immediately obvious to me.

It seems like the plasticity index is only concerned with the total magnitude of variation observed; it doesn’t matter how many individuals are closer to the largest or smallest values, just how large the difference is. If there was no variation, the plasticity index would be zero, and the larger the difference gets, the closer the value gets to 1. Since we’re dividing by the largest value, the plasticity index won’t get any larger than 1.

The coefficient of variation, however, does depend on the total amount of variation. If all values are the same, the coefficient of variation is zero, just like the plasticity index would be. But if there’s enough variation, the standard deviation can be greater than the mean, so the coefficient of variation doesn’t have the upper limit that the plasticity index has. My vague sense is that the plasticity index references how much variation is possible, and the coefficient of variation references how often variation occurs, but that’s a rabbit hole for another day!

Image credit: Obsidian Soul

https://commons.wikimedia.org/wiki/File:Daemonorops_mollis_(rattan_palm)_-_Bukidnon_Philippines.jpg

Note: This plant is in the same genus as the one described in the paper, but it's a different species. I couldn't find a Creative Commons image of the correct species.