Why some grasses got better photosynthesis

Brown University News: Even on the evolutionary time scale of tens of millions of years there is such a thing as being in the right shape at the right time. An anatomical difference in the ability to seize the moment, according to a study led by Brown University biologists, explains why more species in one broad group, or clade, of grasses evolved a more efficient means of photosynthesis than species in another clade.

Biologists refer to the grasses that have evolved this better means of making their food in warm, sunny, and dry conditions with the designation “C4.” Grasses without that trait are labeled “C3.” What scientists had already known is that while all of the grasses in the BEP and PACMAD clades have the basic metabolic infrastructure to become C4 grasses, the species that have actually done so are entirely in the PACMAD clade. A four-nation group of scientists wondered why that disparity exists.

To find out, Brown postdoctoral researcher and lead author Pascal-Antoine Christin spent two years closely examining the cellular anatomy of 157 living species of BEP and PACMAD grasses. Using genetic data, the team also organized the species into their evolutionary tree, which they then used to infer the anatomical traits of ancestral grasses that no longer exist today, a common analytical technique known as ancestral state reconstruction. That allowed them to consider how anatomical differences likely evolved among species over time.

…Erika Edwards“Now that we have this increasingly detailed bird’s-eye view, we can start to become a more predictive science. ... In terms of genetic engineering we’re going to be able to provide some useful information to people who want to improve species, such as important crops.”

“Now that we have this increasingly detailed bird’s-eye view, we can start to become a more predictive science. ... In terms of genetic engineering we’re going to be able to provide some useful information to people who want to improve species, such as important crops.” Credit: Mike Cohea/Brown UniversityIn C4 plants, such an anatomical arrangement facilitates a more efficient transfer and processing of CO2 in the bundle sheath cells when CO2 is in relatively short supply. When temperatures get hot or plants become stressed, they stop taking in as much CO2, creating just such a shortage within the leaf…

A grassland in Canastra, Brazil, shot by BDG2007, Wikimedia Commons via Flickr, under the Creative Commons Attribution-Share Alike 2.0 Generic license

Invasive plant species may harm native grasslands by changing soil composition

Newswise: The future landscape of the American Midwest could look a lot like the past—covered in native grasslands rather than agricultural crops. This is not a return to the past, however, but a future that could depend on grasslands for biofuels, grazing systems, carbon sequestration, and other ecosystem services. A major threat to this ecosystem is an old one—weeds and their influence on the soil.

According to a study in the journal Invasive Plant Science and Management, when invasive plants spread, they can leave behind a “legacy” of alteration in the native soil. Even after an invading species has been controlled, its effects can inhibit the regrowth of native plant species. The causes of this process are still being investigated and may involve changes in soil food webs, soil microbial communities, and mutualistic fungi.

In the study, researchers tested soil conditions for changes in composition after three growth cycles of invasive plant species. Researchers looked for changes in colonization rates, diversity, and composition of arbuscular-mycorrhizal fungi (AMF).

Three exotic plant species—crested wheatgrass, smooth brome, and leafy spurge—were tested in a glasshouse experiment. These plants, all characterized as strong invaders, were grown in native soil collected from North Dakota grasslands. Native species, including western wheatgrass, little bluestem, and blue gramma, were also grown, and after three growth cycles, soil composition was compared among these treatments....

Grasslands in Inner Mongolia, shot by Shizhao, Wikimedia Commons, under the Creative Commons Attribution-Share Alike 3.0 Unported license

Tracking invasive cheatgrass role in larger, more frequent Western fires

PhysOrg: New research that relied in part on satellite images suggests that cheatgrass, an invasive species brought west by settlers in the 1800s, is one cause for the larger, hotter and more frequent range fires experienced recently in the Great Basin of the American West. The arid region covers about 230,000 square miles (600,000 km) over much of Nevada and parts of Utah, Colorado, Idaho, California and Oregon.

Bethany Bradley, a biogeographer at the University of Massachusetts Amherst, brought her expertise in remote sensing and spatial analysis to the study, which was led by fire expert Jennifer Balch of Penn State University.

Bradley used data from NASA's Moderate Resolution Imaging Spectoradiometer from 2000 to 2009 to detect burned areas to create the first land cover map for the Great Basin area. With it, the two researchers and their colleagues combined data sets, matched fire dates and perimeters with land cover data to reach their conclusions, reported in the current online edition of Global Change Biology.

Bradley, Balch and colleagues say that over the past 10 years, cheatgrass fueled most of the largest fires, influencing 39 of the largest 50. Also, fires in grass-covered lands were on average significantly larger than the average fire size on lands dominated by other types of vegetation such as pinyon-juniper, montane shrubland and cultivated areas. Data also suggest that cheatgrass plays a role in more frequent fires.

"From 2000 to 2009, cheatgrass burned twice as much as any other vegetation," Balch says. "Although this result has been suspected by managers for decades," the authors note, "this study is the first to document recent cheatgrass-driven fire regimes at a regional scale."...

A 2007 fire outside San Diego, US Navy photograph