© 1996 Heron Publishing—Victoria, Canada
Isoprene emission, photosynthesis, and growth in sweetgum (Liquidambar styraciflua) seedlings exposed to short- and long-term drying cycles
Chengwei Fang (1), Russell K. Monson (2) and Ellis B. Cowling (1)
1. Department of Forestry, North Carolina State University, Raleigh, NC 27695, USA / 2. Department of Environmental, Population and Organismic Biology, University of Colorado, Boulder, CO 80309, USA / Received January 5, 1995
Summary
Isoprene emissions were studied in one-year old sweetgum (Liquidambar styraciflua L.) seedlings during nine drying–rewatering cycles extending over five months. Each drying cycle lasted to the point of leaf
wilting. Growth was essentially stopped in response to the first drying cycle, though seedling survival and capacity to recover
turgor on rewatering remained high throughout the entire nine cycles. Photosynthetic rates of leaves were inhibited by the
drying treatments. Under severe drought, isoprene emission rates of leaves were also inhibited, though isoprene emission was
generally less sensitive to drought than photosynthesis. The lower drought sensitivity of isoprene emission compared with
photosynthesis resulted in a higher percentage of fixed carbon lost as isoprene as seedlings became more stressed. During
the recovery phase of the drying–rewatering cycles, isoprene emission rates in several seedlings were higher than in well-watered
control seedlings. Following the ninth drying–rewatering cycle, sustained daily watering resulted in recovery of isoprene
emission rates to control values within four days. Photosynthetic rates only recovered to 50% of control values after seven
days. We conclude that the mechanisms regulating photosynthetic rate and isoprene emission rate are differentially influenced
by limited water supplies. The results are consistent with past studies that predict a protective role for isoprene emission
during stress, particularly protection from excessive leaf temperatures during drought.
Keywords:
drought, isoprene synthase, survival, thermoprotection.
