Twiglet: Abscission; abscisic acid


Topical for this time of year (in the northern hemisphere at least), abscission referes to the rejection of plant organs, such as leaves in the autumn.

This occurs at an abscission zone, where hydrolytic enzymes reduce cell adhension. The process can be promoted by abscisic acid and inhibited by respiratory poisons, and is controlled in nature by the proportions and gradients of auxin and ethylene. Other hormones may be involved.

Abscisic acid is a terpenoid compound that is one of the five major plant horones. Althought it is synthesised in the chloroplasts, it occurs throughout the plant body and is particularly concentrated in the leaves, fruits and seeds.

It has a powerful grown inhibiting properties generally and also promotes leaf abscission and the senescence of plants and/or their organs, and induces the closing of the stomata and dormancy in seeds and buds.

Its effect is antagonistic to the plant growth hormones, and it is thought to act by inhibiting the synthesis of protein and nucleic acids.

Source: Oxford Dictionary of Plant Sciences

Forest fire emissions ‘poisoning Arctic environment’


Forest fires and straw and stubble burning in North America and Eastern Europe are leading to record-high concentrations of the environmental toxin PCB over the Arctic island of Svalbard, a report warns.

Take Cover library imageOver the past decades, persistent organic pollutants (POPs) have been found in large concentrations in Arctic areas.

These substances accumulate in living organisms and are enriched throughout the food chain.

Polychlorinated biphenyl (PCB) is one of the most important environmental toxins of this type.

“We wanted to draw attention to the causes of the environmental impact in the Arctic and trace the sources of the problem,” said Sabine Eckhardt, a researcher at the Norwegian Institute for Air Research (NILU).

When biomass from trees and dead grass and leaves catches fire, it releases both PCB and other environmental toxins and creates yet another source of PCB emissions.

In 2004 and 2006, big fires ravaged these areas. About 5.8m hectares of coniferous forest burned down in North America, while Eastern Europe experienced extensive emissions from agriculture due to straw and stubble burning.

Several weeks later, the researchers found record-high values of PCB in the atmosphere above Svalbard.

“As far as we know, this is the first study that shows a connection between the burning of biomass and PCB concentrations in the atmosphere far away,” said Sabine Eckhardt.

“With a climate that is constantly changing, we expect the extent of such fires to increase.

“In such case, it also means that the fires may represent an increasing environmental problem in the Arctic.

“That in turn will reduce the effect of the international agreements that aim to reduce emissions of these environmental toxins,’ said Ms Eckhardt.

PCB is a group of synthetically-produced persistent toxic compounds., and can be stored in the fatty parts of the organism and accumulates in the food chain.

Humans, fatty fish and carnivores (such as polar bears) can therefore accumulate concentrations in their bodies that are so high that they are poisoned.

As the primary emissions of organic environmental toxins are reduced, the researchers believe that fires caused by climate change will become more important.

They point to the fact that there has been little focus on the significance of burning biomass, and the potential consequences of this for the Arctic environment.

“For the first time, we have proved that burning biomass is also an important source of persistent organic pollutants in polar areas,” Ms Eckhardt observed.

“This can be of great importance to international agreements that aim to protect the environment in Arctic areas.”

Source: The Research Council of Norway

Date: 31/05/2010

Satellite to spy on tree munching bugs


More than 150 years after tamarisk, a small Eurasian tree, started taking over river banks in south-western US, saltcedar leaf beetles were unleashed to defoliate the “exotic invader”, says a press release from the University of Utah.

Now, researchers from the university say it is feasible to use satellite data to monitor the extent of the beetle’s attack on tamarisk, and whether use of the beetles may backfire with unintended environmental consequences.

“We don’t have any idea of the long-term impacts of using the beetles; their release may have unexpected repercussions,” says Philip Dennison, an assistant professor of geography and the study’s lead author.

“The impact of this defoliation is largely unknown,” adds co-author Kevin Hultine, a research assistant professor of biology.

“The net impact of controlling tamarisk could be positive or negative.

“We would like on-the-ground scientists and managers to understand and think about the long-term impact – what are these riparian [riverbank] areas going to look like 15 years from now, and how can we can maintain ecosystems,” Professor Hultine observes.

The findings, carried out by a team of researchers from the University of Utah and the US Geological Survey (USGS), are expected to be pubished online in the journal Remote Sensing of Environment.

Source: University of Utah press release

Date: 09/03/2009

Top five invasive threats to US southern forests


Apologies that this post refers to information issued in a press release by the US Forest Service back in January, but it contains interesting data and links that could be of use to people – Take Cover team.

US Forest Service Southern Research Station (SRS) ecologist Jim Miller, considered to be one of the foremost authorities on non-native plants in the  southern US, has identified the five invasive plant species he believes pose the biggest threats to southern forest ecosystems in 2009.

“Cogongrass, tallowtree, and Japanese climbing fern are among the fastest moving and most destructive non-native plant species facing many southern landowners this year,” Dr Miller warned.

“Rounding out the top five invasive species that I’m very concerned about would be tree-of-heaven and non-native privets.

“While our forests are besieged by numerous invasive plants, these and other non-native species present serious financial and ecological threats to the South and its forests.”

Non-native species often out-compete native forest plants and may degrade forest productivity, wildlife habitat, recreational values, and water quality.

Invasive species also greatly increase expenses as public and private land managers work to combat their spread and deal with their effects (such as increased wildfire risk and severity).

Non-native plants can be introduced and spread by wildlife or through other natural means.

Humans also spread invasive species by planting them in their gardens and yards and as a result of seeds hitchhiking on clothes.

Additionally, tractors and mowers used in multiple locations without being cleaned often spread the plants.

In an effort to inform forest managers, landowners, and others about where the most threatening invasive plants are in the South, Dr Miller collaborated with SRS Forest Inventory and Analysis (FIA) scientists to develop maps showing the spread, county-by-county, across the south-east of more than 30 of the most serious non-native plant species.

The invasive plant data were collected on FIA plots throughout the southern US in co-operation with state forestry agencies.

In partnership with the University of Georgia’s Center for Invasive Species Science and Ecosystem Health, SRS researchers recently posted the maps and occupation levels online.

Dr Miller hopes government agencies, forest managers, natural resource professionals, landowners, students, and others will use the information to help combat the spread of non-native plant species in southern forest and grassland ecosystems.

Source: US Forest Service press release

Date: 12/01/2009

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