BP #4: Urban Soil

Urban Soil: Like a New York City Apartment, It Is Cruddy and Hard to come by

Finally we reach the end. This will be the final bit of fun we have for these topics, and it will end with dirt—just like everything eventually does, anyway. Well, not dirt exclusively, but any type of soil: sand, silt, clay, et cetera. Plants are entirely reliant on soils (well, most are, anyway; and that depends on your definition of ‘plant’), because they are the substrate in which plants are grown. Not only do plants rely on soils for life, but they also rely on the composition of those soils, such as what type of soil it is, what nutrients the soil contains, what other organisms live in those soils, and much more. Going even farther, plants have a large impact on the soils in which they are grown, too; they can even change the chemistry of soils (Khalid et al. 2007; Angers & Caron 1998). Soils in urban areas are rather poor: nutrient poor and poor in that they are normally heavily contaminated. Another thing regarding soils and plants in the city is that most of the available space in cities are dedicated to humans, whether that space is used as roads, sidewalks, buildings, etc. So plants are working hard to fit into these spaces that they can occupy; but once they’ve done that, they must contend with soils that are terrible for growing anything other than trash piles. It is true: city life is tough. But plants seem to be ever so resilient in dealing with these issues. I mean, they have been around for millions of years, and they have suffered through terrible mass extinctions; not much should destroy them completely—well, we hope that we won’t destroy them, at least.

‘So, what about urban soil is so bad?’, one might ask. It is a reasonable question, and there are tons of answers. First off, city soils tend to be incredibly dirty—I say this tongue-in-cheek, because that is obvious; I mean, it isn’t called dirt for no reason—or polluted, rather. Most urban soils are covered with pollution, whether it be plastic, paper, or what have you. This much is obvious, but one thing that is not as obvious is that they contain heavy metal pollutants such as lead, copper, cadmium, cobalt, zinc, etc. (Wilcke et al. 1998; Jim et al. 1998). Many of these metals, such as mercury and lead, are incredibly poisonous to many animals, and they are also not good for plants (Patra & Sharma 2000). These pollutants likely originate from industrial waste, leaded gas, oil from cars, and so on, but trash and heavy metals are not the only pollutants; there is also agricultural pollution from pesticides, sewage from agriculture and even humans, and so much more. If you think about it, urban soils are really quite disgusting. But that isn’t even all of the story. Adding to pollution, urban soils are rough and coarse: they are littered with stones, brick fragments, and building debris (Jim 1998). Do you think that’s the whole of it? Surely there can’t be more things wrong with urban soils, can there? Well, unfortunately there is. In addition to all of the pollution and the coarseness, they also have terrible infiltration rates due to compaction of the soil (Gregory et al. 2006). What does this mean? It means that water cannot easily penetrate the soil due to the fact that it has lost its permeability from being compact. This leads to less water seeping into the soil, and thus less water for plants to take in. I hope this has driven one idea into your head: city soils suck (See Figure 1 for some of the typical characteristics of urban soil and Figure 2 for a picture of some urban soil with different pollutants highlighted). I mean, they really suck. They are just (seemingly) unusable for anything other than as a receptacle for even more garbage—well, that and more space for even more buildings that we apparently need.

Figure 1: This shows a few of the typical characteristics of urban soils.

Figure 2: this shows some urban soil with different pollutants in it.

So, one might wonder how these soils affect plant growth. Well, it really depends on the plant; they are incredibly variable in their tolerances to all types of soils and levels of pollution (I mean, some plants live in sandy deserts; if that fact isn’t telling, I don’t know what is): some do really well in urban soils, and some fair incredibly poorly (Sainz et al. 1998), and this all depends on the type of plant and the soil components—and the symbionts of the plants, of course. Generally, though, it seems that plants do not enjoy urban soils, but some have no choice—think city parks where populations of plants and animals become separated from their original population due to increased urbanization. Despite all of this, some plants can and do thrive in these terrible soils; many fast-growing plants alter polluted soils to the point that they help in soil remediation by sequestering metals (McIntyre 2003), absorbing them, or translocating them (Krumins et al. 2015). This has been a proposed, and executed, method of remediating soils in a cost-effective manner, and it could be used heavily in the future to rid urban soils of many pollutants. Plants are truly astounding, aren’t they? To be able to adapt to the most hostile conditions is truly awe-inspiring. It makes you ask, aloud, “How did they do it?!?”, as if they are magicians putting on a street show. 

So we have learned throughout these past four blogs that plants have to contend with some pretty tough conditions that we impose on them due to our continuing urbanization. Some of these conditions are a byproduct of the materials we utilize in urban areas, such as asphalt and concrete contributing to the urban heat island effect or the materials that leak into the soil as product of industry. And some conditions are because of how cities affect other organisms that pants utilize for pollination, reproduction, and the uptake of nutrients. And some conditions even come from other plants, such as the introduction of invasive species through importation, leading to global biotic homogenization. We, as contributors to these problems, must take responsibility for our actions; we must work with one another to come up with solutions to these problems and to combat the ill effects of urbanization. Some problems may never be solved, but there are many others that can be, and through research and implementation of the knowledge gained from said research, we can indeed help the group of organisms to which we owe our lives.

Works Cited

Angers, Denis A., and Jean Caron. "Plant-induced changes in soil structure: processes and feedbacks." Plant-induced soil changes: processes and feedbacks. Springer Netherlands, 1998. 55-72.

Gregory, Justin H., et al. "Effect of urban soil compaction on infiltration rate." Journal of soil and water conservation 61.3 (2006): 117-124.

Jim, C. Y. "Urban soil characteristics and limitations for landscape planting in Hong Kong." Landscape and Urban Planning 40.4 (1998): 235-249.

Khalid, M., N. Soleman, and D. L. Jones. "Grassland plants affect dissolved organic carbon and nitrogen dynamics in soil." Soil Biology and Biochemistry 39.1 (2007): 378-381.

Krumins, Jennifer Adams, Nina M. Goodey, and Frank Gallagher. "Plant–soil interactions in metal contaminated soils." Soil Biology and Biochemistry 80 (2015): 224-231.

McIntyre, Terry. "Phytoremediation of heavy metals from soils." Phytoremediation. Springer Berlin Heidelberg, 2003. 97-123.

Patra, Manomita, and Archana Sharma. "Mercury toxicity in plants." The Botanical Review 66.3 (2000): 379-422.

Sainz, M. J., M. T. Taboada-Castro, and A. Vilarino. "Growth, mineral nutrition and mycorrhizal colonization of red clover and cucumber plants grown in a soil amended with composted urban wastes." Plant and soil 205.1 (1998): 85-92.

Wilcke, Wolfgang, et al. "Urban soil contamination in Bangkok: heavy metal and aluminium partitioning in topsoils." Geoderma 86.3 (1998): 211-228.

Figure Credits

Figure 1 Credit: https://www.slideshare.net/watershedprotection/planting-trees-in-urban-areas-presentation

Figure 2 Credit: https://www.soils.org/discover-soils/story/studying-urban-soil-processes-natural-laboratory-setting