Photosynthesis and isoprene emission from trees along an urban–rural gradient in Texas

• Published in: Global change biology Vol. 21; no. 11; pp. 4221 - 4236
• Main Authors: Lahr, Eleanor C, Schade, Gunnar W, Crossett, Caitlin C, Watson, Matthew R
• Format: Journal Article
• Language: English
• Published: England Blackwell Science 01.11.2015; Blackwell Publishing Ltd
• Subjects: Agriculture; biosphere-atmosphere interactions; Butadienes - metabolism; Carbon dioxide; Cities; Climate Change; Environment; environmental factors; gas exchange; Greenhouse gases; growing season; heat tolerance; Hemiterpenes - metabolism; Hot Temperature; isoprene; leaves; Liquidambar - metabolism; Liquidambar styraciflua; Pentanes - metabolism; Photosynthesis; physiological response; Plant Leaves - metabolism; post oak; Quercus - metabolism; Quercus stellata; spring; stomatal conductance; summer; sweet gum; temperature; Texas; Trees; Trees - metabolism; Urban areas; VOC; volatile organic compound; Texas; ASW, USA, Texas; biosphere-atmosphere interactions; carbon dioxide; sweet gum; temperature; Liquidambar styraciflua; VOC; volatile organic compound; Quercus stellata; post oak
• DOI: 10.1111/gcb.13010
• ISSN: 1354-1013

Isoprene emission is an important mechanism for improving the thermotolerance of plant photosystems as temperatures increase. In this study, we measured photosynthesis and isoprene emission in trees along an urban–rural gradient that serves as a proxy for climate change, to understand daily and seasonal responses to changes in temperature and other environmental variables. Leaf‐level gas exchange and basal isoprene emission of post oak (Quercus stellata) and sweet gum (Liquidambar styraciflua) were recorded at regular intervals over an entire growing season at urban, suburban, and rural sites in eastern Texas. In addition, the temperature and atmospheric carbon dioxide concentration experienced by leaves were experimentally manipulated in spring, early summer, and late summer. We found that trees experienced lower stomatal conductance and photosynthesis and higher isoprene emission, at the urban and suburban sites compared to the rural site. Path analysis indicated a daily positive effect of isoprene emission on photosynthesis, but unexpectedly, higher isoprene emission from urban trees was not associated with improved photosynthesis as temperatures increased during the growing season. Furthermore, urban trees experienced relatively higher isoprene emission at high CO₂ concentrations, while isoprene emission was suppressed at the other sites. These results suggest that isoprene emission may be less beneficial in urban, and potentially future, environmental conditions, particularly if higher temperatures override the suppressive effects of high CO₂ on isoprene emission. These are important considerations for modeling future biosphere–atmosphere interactions and for understanding tree physiological responses to climate change.