In addition to causing significant damage to human health, air pollution also hides the growth of trees, one of the very elements they can to mitigate this typically urban environmental problem.
Researchers at the University of Sao Paulo (USP) in Brazil have have shown that atmospheric pollutants limit tree growth and the ecosystem services provided by trees, such as polluting by absorption aerobic metals in their cortex, assimilating CO2, reducing heat phenomenon of the island with the diminishing of the solar radiation, the mitigation of the rainwater drainage and humidity control.
The study was supported by the São Paulo FAPESP Research Foundation. The results were published in the journal Science of the overall environment.
"We found that in years where particle levels in the atmosphere were higher, for example, trees grew less, as a result of which they later began to provide ecosystem services that play an important role in reducing urban pollution and mitigating or adapting the city to climate change, "said Giuliano Maselli Locosselli, post-doctoral researcher at the Institute of Biological Sciences of the University of Sao Paulo (IB-USP) with a scholarship from FAPESP and the first author of the study.
Using Tipuana tipuana (Tipuana tipu) as a standard, also known as rose or tipu, a tall tree with a large dome and a ubiquitous in the city, the researchers measured the impact of air pollution and weather on tree growth in São Paulo. They sampled specimens of 41 tipuanas aged 36 on average and located at different distances from the Capuava industrial area of Mauá, city borough metropolitan area. Capuava is one of the most industrialized areas in the region, with oil refineries, cement factories and fertilizers factories, as well as the heavy traffic of trucks and cars.
Samples were obtained from the tree growth rings using an instrument called pressure boosting jet, which has a hollow drill and is which are designed to extract a cylindrical portion of wooden web from live tree across its radius with relatively small damage to the plant. All samples were taken at chest height, approximately 1.3 m from the chest surface soil.
By analyzing the chemical composition of the crust and its size growth rings, researchers were able to measure fluctuations in the air levels of contamination based on the different chemical elements to which it is applied the trees were exposed during their development and the appreciation of the way they were factor has affected the growth of trees.
"Tipuana is an excellent marker that clearly represents the levels atmospheric pollution by heavy metals and other chemical elements in the city, "said Locosselli.
Metals and other chemicals suspended in the air are absorbed by bark. The particles are deposited on the leaves, increasing them temperature and reduction of light output for photosynthesis. Development rings show how pollution has affected the life of plant year by year. Thicker rings show years of intense growth and lower levels of pollution, while the thinnest rings show the opposite.
Analysis of growth rings showed that these types were made faster the warmest parts of Capuava with higher levels of phosphorus in the air. Phosphorus is a well-known macronutrient for plants and forms the basis for it their energy metabolism through photosynthesis and respiration.
On the other hand, trees close to traffic and exposed to high levels from aluminum, barium and zinc related to car use components (such as tires, brake linings and clutch plates) appear less development over time.
Particles with a diameter of up to 10 micrometers (PM10) emitted by factories and plants reduced the average tree growth by much to 37%.
Trees exposed directly to high levels of pollution by the the factories in the region grew less in terms of the growth of the trunk diameter throughout their lifetime from plants exposed to medium and low levels " Locosselli said. "Under normal growth conditions, a tipuana breast height may reach 1 meter. "
The time series for PM10 levels in Capuava for a period of 20 years was received from São Paulo State Environmental Company (CETESB) and compared with the results of the cortical and leaf analysis.
The researchers found that PM10 levels accounted for 41% of the annuals variability in tree growth rates, with higher levels of pollution during the course dry months (April-September) reducing growth.
"Diameter increases very quickly when the tree grows normally but it changes a bit when growth is slow, "said Locosselli The size of ecosystem services provided by a tall tree can be 70 times larger than for a small tree. "
Effects on Trees
According to the authors of the study, heavy metals and particles affects the growth of trees by changing the optical properties of the leaf surfaces. As mentioned, these pollutants increase temperatures and decrease the availability of light for photosynthesis. They can also reduce gas exchange due to accumulation in stomata leaves (resources that open and close to allow for carbon dioxide uptake and oxygen release).
"We plan to try to find out if pollution also affects it longevity of these trees. Because pollution limits the various physiological systems, preventing plant growth, probably also are more vulnerable to results that lead to aging, "said Marcos Buckeridge, a professor at IB-USP and principal investigator for the research program.
Urban pollution is likely to cause damage to other species in the same family as a tipuana found in Sao Paulo, such as chicken (Caesalpinia pluviosa) and iron (C. leiostachya).
"Measures to reduce air pollution, such as promoting the use of biofuels, transport electrification and material development reduction of heavy metal emissions, could enhance its maintenance these trees and the ecosystem services they provide, "said Buckeridge.