As well as causing significant damage to human health, air pollution also inhibits tree growth, one element that is very capable attenuate this typical urban environment problem.
Researchers at the University of São Paulo (USP) in Brazil have it shows that atmospheric pollutants limit the growth of trees and ecosystems services provided by trees, such as filtering pollution by absorbing metal air on the skin, absorbs CO2, reduces heat effect of the island by depleting solar radiation, reducing stormwater runoff, and controlling humidity.
This research was supported by the FAPESP São Paulo Research Foundation. The results have been published in the journal Total Environmental Sciences.
"We found that in the years when the levels of particles in the atmosphere were higher, for example, trees grew less. As a result, they start later in their lives to provide ecosystem services that play an important role in reducing urban pollution and reducing or adapting cities to climate change, "said Giuliano Maselli Locosselli, a postdoctoral researcher at the University of Bioscience Institute in São Paulo. (IB-USP) with a scholarship from FAPESP and the first study author.
Uses as a tipuana tree model (Tipuana hokey), also known as rosewood or hokey, tall tree with a large canopy and spread Everywhere in the city, researchers measured the impact of air pollution and weather on tree growth in São Paulo. They analyzed the sample 41 tipuanas average 36 and are located at different distances from the Capuava industrial area in Mauá, a municipality in Brazil metropolitan area. Capuava is one of the most developed districts in the region, with oil refineries, cement plants and fertilizers factories, as well as heavy truck and car traffic.
Samples were taken from tree growth rings using instruments called the Pressler increase borer, which has hollow and medium auger bits designed to extract cylindrical parts from wood tissue from life the tree along its fingers with a relatively small injury to the plant. All samples were taken at breast height, about 1.3 m from topsoil.
By analyzing skin chemical composition and size growth rings, the researchers were able to measure variations in the air pollution levels based on various chemical elements that are the cause trees open during their development and estimate how this happened factors that affect tree growth.
"Tipuana is a very good marker that clearly represents the level air pollution by heavy metals and other chemical elements in Indonesia city, "Locosselli said.
Metals and other chemicals suspended in the air are absorbed by skin. Particulate material is deposited on the leaves, increasing them temperature and reduce the light supply for photosynthesis.
Growth rings show how pollution has affected plant life in years year. Thicker rings indicate years of strong growth and lower levels pollution, while thinner rings show the opposite. Growth ring analysis shows that this tipuana grows faster warm parts of Capuava with higher levels of phosphorus in the air. Phosphorus is a macronutrient known for plants and acts as a basis their energy metabolism through photosynthesis and respiration.
On the other hand, the trees are close to traffic and exposed to high levels from aluminum, barium and zinc related to automotive use fewer parts (such as tires, brake linings and clutch plates) are displayed growth over time.
Particulate material with a diameter of up to 10 micrometers (PM10) plants emitted and plants reduce tree growth rates 37%.
"Trees are exposed to high levels of pollution directly from factories in the area grew less in terms of developing stem diameter throughout their lives than plants exposed to the middle and low levels, " Locosselli said. "Under normal growth conditions, tipuana diameter at breast height can reach 1 meter. "
The time series for PM10 levels in Capuava over a period of 20 years is obtained from the São Paulo State Environmental Company (CETESB) and compared with the results of analysis of bark and leaves.
The researchers found PM10 levels to account for 41% of interannuals variability in tree growth rates, with higher levels of pollution during The driest month (April-September) reduces growth rates.
"Diameter increases very quickly when a tree grows normally but it changes a little when the growth rate is slow, "said Locosselli." That the amount of ecosystem services provided by tall trees can be 70 times larger than small trees. "
Effects on trees
According to the study authors, heavy metals and particulates Material affects the growth of trees by changing the optical properties of leaves surface. As mentioned, these pollutants raise temperatures and reduce light availability for photosynthesis. They can also reduce gas exchange because it accumulates on the leaf stomata (pores that open and close to allow carbon dioxide intake and release of oxygen).
"We plan to try to find out whether pollution also affects the longevity of these trees. Given that pollution limits various things physiological system, inhibits plant growth, maybe also makes it they are more susceptible to the effects that lead to aging, "Marcos said Buckeridge, a professor at IB-USP and principal researcher for research project.
Urban pollution may also damage other similar species family as tipuana found in São Paulo, like partridgewood (Caesalpinia pluviosa) and ironwood (C. leiostachya).
"Measures to reduce air pollution, such as encouraging the use of biofuels, electrification of transportation and development of materials for reduce heavy metal emissions, can improve maintenance these trees and the ecosystem services they provide, "Buckeridge said.