Enhanced drought resistance of vegetation growth in cities due to urban heat, CO2 domes and O3 troughs

Authors: FU, PENG - University Of Illinois; HU, LEIQIU - University Of Alabama; Ainsworth, Elizabeth - Lisa; TAI, XIAONAN - New Jersey Institute Of Technology; MYINT, SOE - Arizona State University; ZHAN, WENFENG - Nanjing University; BLAKELY, BETHANY - University Of Illinois; Bernacchi, Carl

Submitted to: Environmental Research Letters
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/18/2021
Publication Date: 12/6/2021
Citation: Fu, P., Hu, L., Ainsworth, E.A., Tai, X., Myint, S.W., Zhan, W., Blakely, B.J., Bernacchi, C.J. 2021. Enhanced drought resistance of vegetation growth in cities due to urban heat, CO2 domes and O3 troughs. Environmental Research Letters. 16(12). Article 124052. https://doi.org/10.1088/1748-9326/ac3b17.
DOI: https://doi.org/10.1088/1748-9326/ac3b17

Interpretive Summary: It is critical to understand how plants respond to their environment because of their role in earths climate system and our dependence on them for food, fiber, lumber, etc. Global change is changing the growth environment of plants faster than any time in history, causing uncertainty in how plants will continue to grow into the future. Many manipulative experiments, where the growth environment is changed to reflect global chance scenarios, have been performed to assess how plants will grow in the future, but these have limitations, particularly in the number of global change treatments that can be imposed on the plants. This experiment uses a gradient between rural and urban environments as a proxy for global changes, with urban areas generally having higher CO2, warmer temperatures, and lower ozone, a damaging gas to plants than plants growing in rural environments. The results show that the plants in urban environments are more resistant to drought, particularly due to the higher CO2 and temperature, as well as lower ozone, of these environments. These results show the impact of competing global change factors on plants at a larger scale than can be done through manipulative experiments and helps reduce uncertainty in understanding the role of plants with global changes.

Technical Abstract: Sustained increase in atmospheric CO2 is strongly coupled with rising temperature and persistent droughts. While elevated CO2 promotes photosynthesis and growth of vegetation, drier and warmer climate tends to negate this benefit, complicating the prediction of future terrestrial carbon dynamics. Manipulative studies such as Free Air CO2 Enrichment experiments have been useful to study the interaction effect of global change factors on vegetation growth; however, their results do not easily transfer to natural ecosystems partly due to their short-duration nature and limited consideration of climatic gradients and potential confounding factors, such as O3. Urban environments serve as a useful small-scale analogy of future climate. Here, we develop a data driven approach using urban environments as test beds for revealing the interactive effect of changing temperature and CO2 on vegetation response to drought. Using 75 urban-rural paired plots from three climate zones over the conterminous United States, we found vegetation in urban areas exhibited a much stronger resistance to drought than in rural areas and the enhanced drought resistance was attributed to rising temperature and CO2 and reduced O3 concentration in cities. Particularly, the controlling factor responsible for urban-rural differences in drought resistance of vegetation varies across climate regions, such as surface O3 gradients in the arid climate, and surface CO2 and O3 gradients in the temperate and continental climates. Thus, our study provides a more general assessment of the impacts of competing factors on vegetation growth at a large scale, and ultimately, helps reduce uncertainties in understanding terrestrial carbon dynamics.