Abstract
Megapolis such as Mexico City, have atmospheric pollutants that interact with the humidity and solar radiation. The topography of this city promotes air stagnation, generating atmospheric pollutants and episodes of acid rain, a phenomenon well recorded since the end of the 1980s. However, little we know about how urban trees respond to acid rain in the city. Here we present how simulated acid rain causes anatomical and changes in photosynthetic pigments in two of the most abundant urban trees in Mexico City: Liquidambar styraciflua L. and Fraxinus uhdei (Wenz.) Lingelsh. We first described the leaf anatomy of both species. Then, we used one-year-old trees sprayed with sulfuric acid solutions at pH 2.5 and 3.8, and evaluated visible leaf damage, anatomical alterations, and chlorophyll contents. In both species, the pH 2.5 caused cuticle alterations and areas of total tissue destruction. L. styraciflua showed greater sensitivity, but we discuss some of the tolerance mechanisms. Finally, acid rain also reduced the chlorophyll contents. These results contribute toward a catalogue of urban tree species to describe pollution-induced damages, and the identification of tolerant species useful for short- and mid-term detection of environmental crisis, in cities with similar environmental conditions and urban tree composition.
Highlights
Cities and industrial centers are the source of atmospheric pollutants, which in turn can originate other pollutants through the action of light, temperature, or humidity
This work aims to describe for the first time the damage that acid rain causes, at lab-simulated pH values like those reported in Mexico City during the wet season, in order to determine leaf morphological and anatomical changes, as well as chlorophyll content, in two frequent tree species
This research shows for the first time the impact of acid rain levels reported for Mexico City on on the anatomy of two abundant tree species
Summary
Cities and industrial centers are the source of atmospheric pollutants, which in turn can originate other pollutants through the action of light, temperature, or humidity An example of this is the acid deposition, which is the accumulation of strong acids and oxides from the atmosphere in the form of rain, snow, gas, or particulates that originate primarily from human activities [1,2]. These substances arise mainly from sulfur sources from the combustion of fossil fuels and the processing of metallic minerals. Because of the presence of these acids, acid rain possesses elevated levels of hydrogen ions giving way to pH values below 5.6 [1,2]
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