Rain forest mechanism helps plants survive, brings on rains

ENVIRONMENT
Amazon rain forests appear to have evolved an intricate system of nourishing themselves during dry months that may actually trigger the onset of the wet season. A study led by Ranga Myneni of Boston University's department of geography and environment revealed a 25 percent increase in leaf concentration during dry seasons -- suggesting that vegetation takes advantage of the increased sunlight during those months while drawing on water deep within the soil to increase photosynthesis. "Our finding is similar to the discovery of a large green continent, nearly a third the size of South America, appearing and disappearing each year," said Myneni, whose research was based on NASA satellite images taken over a five-year period. Plants appear to "anticipate" the dry season by furnishing new leaves about a month in advance and later seem to initiate wet seasons through transpiration, the process by which water contained inside leaves escapes into the atmosphere. "It is not surprising that the vegetation" in the Amazon "has evolved in harmony with the land and atmosphere," Myneni said. "If we clear a substantial portion of the forest, we could disrupt the atmosphere and weather in ways we do not know."

BOTTOM LINE: Amazon forests appear to compensate for lack of rain during dry seasons by increasing leaf concentrations to capture sunlight and tapping into water in the soil to carry out photosynthesis. The process seems to trigger the start of the wet season.

CAUTIONS: The authors acknowledge the need for further testing of changes in leaf concentration. Large numbers of leaf measurements such as those provided by the satellite data are difficult to come by, in part because of cost and site accessibility.

WHAT'S NEXT: Myneni plans to study tropical forests in Africa and Asia to learn if they display similar patterns to those observed in the Amazon.

WHERE TO FIND IT: Proceedings of the National Academy of Science, March 20.

AMI ALBERNAZ

PROSTATE CANCER
Obese men are more likely to die from the disease
Obese men diagnosed with prostate cancer are at a higher risk of dying than normal-weight men also diagnosed with the disease, a new study finds. A group of researchers led by Alan Kristal from the University of Washington and the Fred Hutchinson Cancer Research Center in Seattle looked at how obesity affected mortality risk in men diagnosed with prostate cancer. The researchers found out clinical details such as height, weight, smoking habits, diet, and severity of prostate cancer in 752 men between the ages of 40 and 64. They followed the participants for an average of 10 years recording deaths and cases where disease had spread. They found that of the 50 men who died from prostate cancer during the study period, 34 were overweight. Researchers calculated that the risk of death for obese men diagnosed with prostate cancer was 2.6 times higher than normal-weight ones also diagnosed with the disease. Researchers also found that risk of the cancer spreading was 3.6 times higher in obese men.

BOTTOM LINE: "We now have one more reason for men to maintain normal weight," said Kristal. "If an obese man diagnosed with prostate cancer decides to lose weight, he might reduce the risk of death from the disease."

CAUTION: The study looks at a younger age group of men while prostate cancer is more prevalent in an older age group. The number of deaths from prostate cancer in the study group was also small, and more studies like this are necessary to establish an unquestionable link between obesity and higher death risk in prostate cancer patients.

WHAT'S NEXT: In the last decade death from prostate cancer has dropped by 35 percent in the United States for reasons that are still unclear. At the same time obesity has been on the rise. Kristal is now looking at how much mortality from prostate cancer would have dropped if obesity had not increased.

WHERE TO FIND IT: Cancer, March 15.

SENA DESAI GOPAL