Isoprene emission, photosynthesis, and growth in sweetgum (Liquidambar styraciflua) seedlings exposed to short- and long-term drying cycles

Abstract

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.

A model of isoprene emission based on energetic requirements for isoprene synthesis and leaf photosynthetic properties for Liquidambar and Quercus

“…Present models also do not simulate the emission under stress conditions in a satisfactory manner, e.g. isoprene emission declines in water-stressed leaves (Tingey, Evans & Gumpertz 1981;Fang, Monson & Cowling 1996;Lerdau, Guenther & Monson 1997;Steinbrecher et al 1997), but the empirical emission models lack a means for describing these shifts. For accurate prediction of isoprene emission rates (I), a reliable simulation of stress periods is critical, because many important emitting plants function for long periods at suboptimal environmental conditions.…”

“…There is ample evidence of correlations between I and leaf carbon dioxide assimilation rates (A, Harley et al 1994;Litvak et al 1996) and of co-ordinated changes in isoprene emission and photosynthesis during stress periods Fang et al 1996). Since detailed information is available on the mechanisms of environmental and physiological controls (e.g.…”

“…Steinbrecher et al 1997), but the empirical emission models lack a means for describing these shifts. For accurate prediction of isoprene emission rates (I), a reliable simulation of stress periods is critical, because many important emitting plants function for long periods at suboptimal environmental conditions.There is ample evidence of correlations between I and leaf carbon dioxide assimilation rates Litvak et al 1996) and of co-ordinated changes in isoprene emission and photosynthesis during stress periods Fang et al 1996). Since detailed information is available on the mechanisms of environmental and physiological controls (e.g.…”

Knocking Down of Isoprene Emission Modifies the Lipid Matrix of Thylakoid Membranes and Influences the Chloroplast Ultrastructure in Poplar

“…It has been proposed that leaf isoprene emission is an important adaptation for plants, conferring tolerance to different environmental constraints (Vickers et al, 2009;Loreto and Schnitzler, 2010;Loreto and Fineschi, 2014). However, biogenic isoprene emission represents a nontrivial carbon loss in plants, particularly under stress conditions (Fang et al, 1996;Brilli et al, 2007;Teuber et al, 2008;Ghirardo et al, 2014), and the reason(s) why plants emit isoprene are still ambiguous, and the true role of isoprene emission remains elusive. Different approaches and techniques have been used to determine whether and how the cost of this expensive carbon emission is matched by the accomplishment of the physiological function in planta.…”

Scaling Isoprene Fluxes from Leaves to Canopies: Test Cases over a Boreal Aspen and a Mixed Species Temperate Forest

“…Under normal growing conditions plants release 1%-2% of carbon fixed by photosynthesis to the atmosphere as isoprene (Monson and Fall 1989;Sharkey et al 1991;Harley et al 1995). Under moderate water deficits this percentage can exceed 10%, as a result of foliage warming and reductions in net photosynthesis (Fang et al 1996).…”