January 1, 2014
Plants Develop Competitive Strategies In Extreme Desert Environments
redOrbit Staff & Wire Reports - Your Universe Online
Plants in extreme desert environments develop effective strategies to compete for the area’s limited resources, according to new research out of the University of Arizona published in the American Journal of Botany.
Although deserts are often thought of as barren, inhospitable places, numerous plants and animals have adapted to this harsh environment, where they are often forced to compete with rivals for scarce resources such as water.
In natural environments, water availability is typically stochastic, with some years and localities receiving lots of rain, while other areas and times remain dry. During dry years, plants that are more efficient with water use often are the most successful. But this comes at a price, with efficient plants struggling more against faster-growing plants during wetter years.
In deserts, where variable weather is common, plant community patterns can change between wet and dry years, with high densities and a diversity of plants in wet years, and a reduction in both quantity and number of species in dry years.
The University of Arizona researchers investigated the effect those variables – competition and water usage – have on plant communities in the Sonoran Desert.
Jennifer Gremer and colleagues looked at three native, widespread and abundant plants that utilize different strategies to survive in this variable desert environment by occupying different positions on a trade-off spectrum between relative growth rate and water use efficiency.
The researchers interpreted how well the plants responded to different conditions, such as high and low water availability and competition, by measuring plant biomass of shoots, stems, and roots.
The results revealed that all species did better in wet environments when grown alone. However, water availability had additional effects when competition was included, with faster growth rate species less affected by competition in wet environments, and more efficient species less affected in dry environments.
"These observed effects explain the patterns seen in long-term data and are counterintuitive to many readers because some plants might actually do better when conditions are not optimal," said Gremer.
However, in most settings of this research, the intermediate species had the largest overall competitive effect, and also had the highest level of intraspecific competitiveness.
This suggests a reason why the intermediate species does not competitively exclude other species, the researchers said.
The study’s results confirmed that some plants are better at competing in wet environments, while others are better in dry environments. The researchers were able to successfully predict this pattern by looking at important characteristics – water use efficiency and growth rate – to determine how the plants would react to limited resources.
"A major challenge in ecology is to find traits or characteristics that can be used as indicators to predict how plants will respond without having to study each and every individual species,” Gremer said. “In our system, we have had remarkable success at doing that."
However, these traits may not be the most important factors in all systems, she added.
Additional understanding of how these traits mediate competition under different conditions, for both native and non-native plants, is important considering the threats of climate change and invasive species.
"We need to understand the role of competition and water availability in long-term patterns of diversity in our system," Gremer said. "This has implications for understanding responses to climate change and predicting what these communities will look like in the future."
The researchers noted that with the onset of climate change, the deserts are getting hotter and drier, and have been a focus of global change models.
"The Sonoran Desert has already begun to exhibit such changes," Gremer said. "Specifically, the composition of plant communities has changed over the last 30 years, with species that have high water-use efficiency becoming more common and species with high relative growth rates declining."