Plants live, die according to their size

Plants self-regulate their populations to maintain stability and optimize their lives, with the lengths of their lives directly related to their mass, a recent study has found. Further, a single scaling power for lifespan holds true across the entire spectrum of plants, from single-celled phototrophs to giant redwoods.

Scientists have long known that animals’ lifespans are closely scaled to the species’ body size, with elephants living longer than mice. But while plant biologists have predicted such a connection in plants, a full study has never been performed until now.

Researchers Núria Marbà, Carlos Duarte and Susana Agustí at the Mediterranan Institute for Advanced Studies—a joint institute between the CSIC (Spanish Council for Scientific Research) and the University of the Balearic Islands in Esporles, Spain—have recently examined more than 1,000 reports of plant birth and mortality rates across a wide spectrum of species, discovering that the connection holds with extreme precision.

The researchers found that both population mortality rates and population birth rates of all plant species scale as the –¼ power of plant mass. In other words, the smaller a plant, the higher its mortality and birth rates, meaning the shorter its lifespan. Hence, plant lifespan scales as almost exactly the ¼ power of plant mass.

“The functioning of biological systems depends to a large extent on their metabolism, i.e., on how they process energy and materials, such as light, water, and nutrients,” Marbà explained to PhysOrg.com. “Small plants require fewer resources per unit of time than large ones, and, therefore, they are able to turn over the individuals of their populations faster than large plants. As plant size increases, more resources and time are needed to produce a fully grown individual, and thus their lifespan increases, resulting in small plants having shorter life spans than larger ones.”

An interesting aspect of these relationships is that mortality and birth rates are nearly identical within a species, keeping the population extremely stable. Nature has additional reasons for this perfect balance, too, which include stabilizing carbon cycling, optimizing plant life histories, and stabilizing the ecosystems the plants inhabit. The scientists suggest that, to achieve this balance, plant mortality rates have evolved to match the birth rates.

The group also investigated whether temperature entered the equation. According to the metabolic theory of ecology, metabolic rates (which determine lifespan) should be temperature-dependent. However, the researchers found that, unlike animals, plants’ mortality and birth rates are independent of temperature, or at least within the variation of their data. This finding contrasts with previous evidence that mortality rates of phytoplankton, macroalgae, and land plants increase with increasing temperature when the response of single species to temperature is examined. The researchers explain that resolving this issue could have a fundamental impact on predictions of global warming.

“Plant metabolism increases with increasing temperature, and, thus, plant life span and birth and mortality rates are expected to increase with temperature as well,” explained Marbà. “Hence, global warming may have consequences for the stability of plant populations. If temperature increases mortality and birth rates equally, plant populations will turn over faster but they would remain stable. Otherwise, plant populations will decline. In any case, a faster plant turnover, coupled with higher metabolic rates of decomposing microorganims with warming, may lead to a reduction in the CO₂ sink capacity of vegetation.”

Despite the delicate balance between mortality and birth rates, the actual mechanisms governing plant life and death are still unclear to biologists. Most certainly, controls include an assortment of metabolic processes interacting at all levels, from molecular to organismal, and include respiration, reproduction, cellular damage, and structural imbalances. Because plants, unlike animals, retain their reproductive capacity throughout their lives, evolution might put greater selective pressure on plants’ lifespans. The researchers plan to continue investigating how these processes combine to influence plant life histories.

Citation: Marbà, Núria, Duarte, Carlos M., and Agustí, Susana. “Allometric scaling of plant life history.” Proceedings of the National Academy of Sciences, October 2, 2007, vol. 104, no. 40, 15777-15780.

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Related stories:

Vine invasion? Ecologist looks at coexistence of trees and lianas
Among the hundreds of species of woody vines that University of Wisconsin–Milwaukee ecologist Stefan Schnitzer has encountered in the tropical forests of Panama, the largest has a stalk nearly 20 inches in circumference.
Global Warming Linked to Caribou-Calf Mortality
Fewer caribou calves are being born and more of them are dying in West Greenland as a result of a warming climate, according to Eric Post, a Penn State associate professor of biology. Post, who believes that caribou may serve as an indicator species for climate changes including global warming, based his conclusions on data showing that the timing of peak food availability no longer corresponds to the timing of caribou births.
Insecticide combo delivers knockout punch
A cocktail of insecticides containing a plant protein and a common insecticide may be more lethal to crop pests than either ingredient used alone, according to biologists. The one-two punch also inhibits the insects' growth rate and reduces their chance of developing resistance.
India caught in catastrophic smoking epidemic
India is in the midst of a catastrophic epidemic of smoking deaths, which is expected to cause about one million (10 lakh) deaths a year during the 2010s – including one in five of all male deaths and one in 20 of all female deaths at ages 30-69. On average, male bidi smokers lose about six years of life, female bidi smokers lose about eight years and male cigarette smokers lose about ten years.
Study shows genetically engineered corn could affect aquatic ecosystems
A study by an Indiana University environmental science professor and several colleagues suggests a widely planted variety of genetically engineered corn has the potential to harm aquatic ecosystems. The study is being published online this week by the journal Proceedings of the National Academies of Sciences.
A study proposes a new universal rule to explain the equilibrium of plant populations
A study financed by the BBVA Foundation and conducted by scientists Carlos Duarte, Nuria Agustì and Nuria Marbà from the Mediterranean Institute for Advanced Studies (CSIC – University of the Balearic Islands) has allowed the first-time formulation of a universal rule that explains the equilibrium of plant communities, showing how plants assure the survival of their species whether their lives last a day or are prolonged over centuries.
Ethanol vehicles pose a significant risk to human health, study finds
Ethanol is widely touted as an eco-friendly, clean-burning fuel. But if every vehicle in the United States ran on fuel made primarily from ethanol instead of pure gasoline, the number of respiratory-related deaths and hospitalizations would likely increase, according to a new study by Stanford University atmospheric scientist Mark Z. Jacobson. His findings are published in the April 18 online edition of the journal Environmental Science & Technology.
Gene that governs toxin production in deadly mold found
For the growing number of people with diminished immune systems - cancer patients, transplant recipients, those with HIV/AIDS - infection by a ubiquitous mold known as Aspergillus fumigatus can be a death sentence.

News discussion:

General Science news