Many scientists studying the effects of increased CO₂ on farming
have predicted higher crop yields, because plants would be able to convert more
of the gas into sugars by photosynthesis. “People foresee an Eden-like scenario
where conditions are lush,” says Lewis Ziska, a plant physiologist at the US
Department of Agriculture’s Climate Stress Laboratory in Beltsville, Maryland.
His team, however, has looked at the effects of elevated CO₂ on
weeds.

The researchers grew three types of weed in greenhouses, some in air
containing current atmospheric levels of CO₂, others in air containing
twice as much of the gas. They then sprayed the weeds with the recommended doses
of glyphosate, which is marketed by the agrochemicals giant Monsanto.

All three weed types stopped growing in the greenhouses with today’s CO
₂ levels. But in the CO₂-rich atmosphere, the growth of only
one—redroot pigweed (Amaranthus retroflexus)—was completely
suppressed. Lamb’s-quarters (Chenopodium album) and quackgrass (Agropyron
repens) continued to grow, although at reduced rates.

The two weeds that resisted the herbicide are “C3” plants. The biochemical
pathways these plants use for photosynthesis become much more efficient when
more CO₂ is available.

Levels of CO₂ are expected to double within 50 years, and Ziska
suspects this may force farmers to seek alternatives to chemical herbicides.
“You can kill these weeds by adding higher concentrations of herbicide, but this
is expensive,” he says.

HEROIN addicts may one day be treated with a polymer implant instead of
taking a daily dose of the heroin substitute methadone. Researchers at Johns
Hopkins School of Medicine in Baltimore have developed a button-sized implant
that releases a steady stream of hydromorphone for up to three months (
Journal of Substance Abuse Treatment, vol 14, p 535). Hydromorphone, like
methadone, blocks opiate receptors in the brain that bind to heroin, eliminating
cravings and withdrawal symptoms.

Heroin addicts have to take a dose every of methadone day—and
increasingly they are being forced to travel to clinics to prevent the growth of
an underground trade in the drug. The implanted polymer releases a steady stream
of hydromorphone, which is as effective at blocking opiate receptors as
methadone, over one to three months.

The implant should increase the number of people successfully completing
heroin therapy. “The primary reason for patients wanting to get out of methadone
treatment is the inconvenience,” says George Bigelow, director of the
behavioural pharmacology research division at Johns Hopkins.

The implant will also cut the cost of treating addicts. This is between
$3500 and $4500 a year, though methadone makes up only 7 per cent
of the total.

However, the researchers do not recommend the implant for people who need
counselling, such as those beginning treatment. Counselling is often coupled
with the daily dose of the substitute drug, and such addicts might relapse
without it.

Heroin addicts may have to wait several years for the implant. The
researchers are first considering using the implant to relieve the pain of
cancer before they study it in heroin addicts.