Air pollution affects tree growth in São Paulo – Eurasia Review



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In addition to causing significant harm to human health, air pollution
also retard the growth of trees, one of the elements that can
mitigate this typically urban environmental problem.

Researchers from the University of São Paulo (USP) in Brazil have
showed that air pollutants limit tree growth and the ecosystem
services provided by trees, such as filtering pollution by absorbing
metals suspended in the air in their bark, badimilating CO2, reducing heat
effect of the island by attenuating solar radiation, by attenuating rainwater
runoff and control of moisture.

The study was funded by the São Paulo Research Foundation, FAPESP. The results were published in the journal Total environmental science.

"We found that in years when particulate levels in the atmosphere were higher, for example, trees grew less. As a result, they began later in life to provide ecosystem services that play an important role in reducing urban pollution and mitigating or adapting the city to climate change, "he said. Giuliano Maselli Locosselli, postdoctoral researcher at the Institute of Bioscience of the University of São Paulo. (IB-USP) with a scholarship from FAPESP and first author of the study.

Using as a model the Tipuana tree (Tipuana tipu), also called
rosewood or tipu, a large tree with a large canopy and
ubiquitous in the city, researchers have measured the impact of air
pollution and weather on tree growth in São Paulo. They badyzed samples
of 41 Tipuanas aged 36 on average and located at different distances
from the Capuava Industrial Zone to Mauá, a municipality of the
Metropolitan area. Capuava is one of the most industrialized districts
in the region, with oil refineries, cement plants and fertilizers
factories, as well as the circulation of heavy trucks and cars.

Samples were collected from tree growth rings using an instrument
called Driller Pressler increment, which has a hollow wick and is
designed to extract a cylindrical section of wood cloth from a living
tree in all its radius with relatively minor damage to the plant.
All samples were taken at bad height, approximately 1.3 m from the
topsoil.

By badyzing the chemical composition of the bark and the size of
the growth rings, the researchers were able to measure changes in the air
levels of pollution based on the various chemical elements to which the
the trees were exposed during their development and estimate how
factor influencing tree growth.

"The tipuana is an excellent marker that clearly represents the levels
air pollution by heavy metals and other chemical elements in the
city, "said Locosselli.

The metals and other chemicals suspended in the air are absorbed by
bark. The particles settle on the leaves, which increases their
temperature and reducing the light input for photosynthesis. Growth
the rings indicate how pollution affected plant year life in
year. Thicker rings indicate years of vigorous growth and lower levels
pollution, while thinner rings indicate the opposite.

The growth ring badysis showed that these tipuanas were growing faster
the hottest parts of Capuava with higher levels of phosphorus in the air.
Phosphorus is a macronutrient known to plants and serves as a basis for
their energy metabolism via photosynthesis and respiration.

In contrast, trees close to the circulation and exposed to high levels
of aluminum, barium and zinc badociated with the wearing of motor vehicles
parts (such as tires, brake linings and clutch disks) display less
growth over time.

Particles with a diameter up to 10 micrometers (PM10)
emitted by plants and plants reduced the average growth of trees
like 37%.

"Trees exposed directly to high pollution levels in the
factories in the area have grown less in terms of trunk diameter
throughout their life as plants exposed to medium and low levels,
Locosselli said. "Under normal growing conditions, a tipuana
The diameter at bad height can reach 1 meter.

The time series for PM10 levels at Capuava over a 20-year period were
obtained from the State Environmental Society of São Paulo State (CETESB)
and compared to the results of the badysis of the bark and leaves.

The researchers found that PM10 levels accounted for 41% of interannual consumption.
variability in the rate of tree growth, with higher levels of pollution during the
the driest months (April-September) reducing the growth rate.

"The diameter increases very rapidly when the tree grows normally
but change little when the growth rate is slow, "said Locosselli. "The
the magnitude of the ecosystem services provided by a large tree can be 70
times bigger than for a small tree. "

Effects on trees

According to the study's authors, heavy metals and suspended particles
the material influences tree growth by modifying the optical properties of the leaf
surfaces. As mentioned, these pollutants raise the temperature and reduce
the availability of light for photosynthesis. They can also reduce gases
the exchange due to an accumulation on the stomata of the leaves (pores that open and close
allow the absorption of carbon dioxide and the release of oxygen).

"We plan to try to find out if the pollution is also affecting the
the longevity of these trees. Since pollution restricts various
physiological systems, hindering the growth of plants, it is probably also
more vulnerable to the effects leading to senescence, "said Marcos
Buckeridge, professor at the IB-USP and principal investigator of
research project.

Urban pollution probably also damages other species in the same
family like tipuana found in São Paulo, like partridge wood (Caesalpinia
pluviosa) and ironwood (C. leiostachya).

"Measures to reduce air pollution, such as promoting the use of biofuels,
the electrification of transport and the development of materials allowing
reduce heavy metal emissions, could improve the maintenance of
these trees and the ecosystem services they provide, "said Buckeridge.

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