Tropes

ScienceDaily_2013 10664.txt

#Contribution of particulate matter from air pollution to forest declineair pollution is related to forest decline and also appears to attack the protecting wax on tree leaves and needles. Bonn University scientists have discovered now a responsible mechanism: particulate matter salt compounds that become deliquescent because of humidity and form a wick-like structure that removes water from leaves and promotes dehydration. These results are published in Environmental Pollution. Nature conservationists call it lingering illness and the latest report on the North-Rhine Westphalian forest conditions confirms ongoing damage. Bonn University scientists have shown now that salt deposits on leaves may decrease the drought tolerance of trees thereby contributing to forest decline. Our study reveals that so-called wax degradation on pine needles may develop from deposited particulate matter says Dr. JÃ rgen Burkhardt from the Institute of Crop science and Resource Conservation. Wax helps to protect leaves and needles from water loss. It has long been known that air pollutants accelerate wax ageing and that wax degradation is closely related to forest damage. Wax degradation was addressed by many studies in the 1980s and 90s but sound explanations for both the degradation mechanism and the high correlation with forest damage have yet been missing Dr. Burkhardt reports. Previous approaches assumed chemical reactions for wax degradation whereas the present study reveals physical reasons. The deposition of hygroscopic salts is capable of decreasing the drought tolerance of trees co-author Shyam Pariyar says. Accelerated dehydration of needles treated with salt solutionsthe scientists sprayed salt solutions on Scots pine needles and recorded their weight loss after abscission. The needles treated with salt solutions dried out significantly faster than the untreated control needles. Using an electron microscope the scientists observed the salts becoming deliquescent and moving into the stomata of the needles. Stomata are used tiny pores by plants to take up carbon dioxide for photosynthesis and release water vapor and oxygen. The deliquescent salts form very thin liquid connections between the surface and interior of the needle and water is removed from the needles by these wick-like structures. Because the plants are unable to counteract this removal of water the plants dehydrate more rapidly. Therefore polluted air containing large amounts of particulate matter may directly reduce the drought tolerance of trees. Simultaneously the deliquescent salts make wax appear degraded. This newly described mechanism was considered not in earlier explanations of Central European forest decline states Dr. Burkhardt. Conceivable aggravation of forest decline by climate changea new type of electron microscope enabled the observation of particle deliquescence and dynamics under changing air humidity. In addition a long-lasting scientific paradigm had excluded any aqueous movement into the stomata and only recently had Bonn University scientists confirmed its existence. Recently regional forest damage has been reported in the western USA and other parts of the world. A relationship with increasing climate change-type drought has been proposed but the newly discovered mechanism involving particulate matter might contribute to the regional forest damage. Particularly because air concentrations of hygroscopic particles have increased largely within the last decades says Dr. Burkhardt. The study was funded by the Deutsche Forschungsgemeinschaft and the European union (project ÃLAIRE. Story Source: The above story is provided based on materials by Universitã¤t Bonn. Note: Materials may be edited for content and length. Journal Reference e

< Back - Next >