The longer a rhizome grows, the more expensive it is to build, report Dinesh Thakur and Zuzana Münzbergová in the Annals of Botany. However, they also find that it’s not just length that alters the relationship between length and cost. Both the cultivation climate and origin climate also make a difference.
Plants don’t just grow from seeds. They can also clone themselves by reproducing vegetatively, and rhizomes can be a tool for this. Rhizomes are often confused with roots. They’re stems that run horizontally underground. They can drop roots or push up new shoots. These new shoots and roots are genetically identical to the parent plant but, if the rhizome gets cut, they can work as a new independent plant.
As a plant grows, it has to decide how to allocate its resources to various organs. However, it’s not clear how expensive it is for plants to grow rhizomes. To measure the cost, Thakur and Münzbergová examined the length of the rhizome per unit dry mass investment [i.e. specific rhizome length (SRzL = rhizome length/dry mass)]. What they wanted to know was: when rhizome lengths increase does it get easier or more difficult for a plant to add extra rhizome length?
The botanists gathered data from 275 genotypes of Festuca rubra, also known as Creeping Red Fescue. They grew the grass under four different climate conditions to measure the effect of various conditions on growth.
“Our analyses show that scaling relationships for the functional traits that primarily influence plant vegetative spread have a scaling exponent greater than 1 in all the cultivation climates,” write Thakur and Münzbergová in their article. “Thus, changes in rhizome length fail to keep pace with increasing mass. This indicates that either bulk rhizome tissue density or thickness (or both) increase as rhizome length increases (causing decreased SRzL).”
“While many current studies are dealing with the benefits of clonal growth, more studies (such as this one) are needed to shed light on clonal growth costs. It can be expected that as with above-ground plant organs, the patterns observed in this study may also hold true for other species that reproduce mainly clonally. Nevertheless, this needs to be tested in diverse species occurring in different ecoregions.”
READ THE ARTICLE
Thakur, D. and Münzbergová, Z. (2022) “Rhizome trait scaling relationships are modulated by growth conditions and are linked to plant fitness,” Annals of Botany, 129(5), https://doi.org/10.1093/aob/mcac023
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