ITHACA, N.Y. -- Add this universal truth to biology textbooks: the mass of a plant's leaves and stems is proportionally scaled to that of its roots in a mathematically predictable way, regardless of species or habitat. In other words, biologists can now reasonably estimate how much biomass is underground just by looking at the stems and leaves above ground.

Up to now, plant biologists could only theorize about the ways stem and leaf biomass relate to root biomass across the vast spectrum of land plants. Researchers from Cornell University and the University of Arizona spent two years poring over data for a vast array of plants -- from weeds to bushes to trees -- in order to derive mass-proportional relations among major plant parts.

This evidence now provides environmental researchers with clues to how much carbon is stored in plants below as well as above ground. "Global climate modelers now can reasonably estimate how much carbon is sequestered in plants on a worldwide basis," says Karl J. Niklas, Cornell's Liberty Hyde Bailey Professor of Plant Biology, whose article appears in the latest issue of Science (Feb. 22). The article, "Global Allocation Rules for Patterns of Biomass Partitioning in Seed Plants," is co-authored by Brian J. Enquist, a University of Arizona assistant professor of ecology and evolutionary biology.

The scientists wanted to know if there were observable, universal patterns of biomass storage across all plant species in different habitats, and they wanted to know if such patterns could be predicted. "Yes and yes," says Niklas. "These patterns can be found in any terrestrial plant, whether you are talking about bamboo, or palm trees, or pine trees or bushes. The same pattern can be found across the whole spectrum of plants on land." Using a mathematically based research method called allometry, which studies the relative growth rates and proportions of different-size parts of organisms, Niklas and Enquist developed biophysical models that would link data on hundreds of specific plants. They studied plant species differing radically in overall size (from giant oak trees to some of the smallest flowering plants such as mouse-ear cress) and found that the proportions of leaf, stem, and root biomass remain, on average, constant.

Enquist's part of the research was supported by the National Science Foundation and Niklas' portion was supported by New York State Hatch grant funds.

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