Isoprene emission and photosynthesis during heatwaves and drought in black locust
Extreme weather conditions like heatwaves and drought can substantially affect tree physiology and the emissions of isoprene. To date, however, there is only limited understanding of isoprene emission patterns during prolonged heat stress and next to no data on emission patterns during coupled h...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-08-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/3649/2017/bg-14-3649-2017.pdf |
| Summary: | Extreme weather conditions like heatwaves and drought can substantially
affect tree physiology and the emissions of isoprene. To date, however, there
is only limited understanding of isoprene emission patterns during prolonged
heat stress and next to no data on emission patterns during coupled
heat–drought stress or during post-stress recovery. We studied gas exchange
and isoprene emissions of black locust trees under episodic heat stress and
in combination with drought. Heatwaves were simulated in a controlled
greenhouse facility by exposing trees to outside temperatures
+10 °C, and trees in the heat–drought treatment were supplied with half of the irrigation water given to
heat and control trees. Leaf gas exchange of isoprene, CO<sub>2</sub> and H<sub>2</sub>O
was quantified using self-constructed, automatically operating chambers,
which were permanently installed on leaves (<i>n</i> = 3 per treatment). Heat and
combined heat–drought stress resulted in a sharp decline of net
photosynthesis (<i>A</i><sub>net</sub>) and stomatal conductance. Simultaneously,
isoprene emissions increased 6- to 8-fold in the heat and heat–drought
treatment, which resulted in a carbon loss that was equivalent to 12 and
20 % of assimilated carbon at the time of measurement. Once temperature
stress was released at the end of two 15-day-long heatwaves, stomatal
conductance remained reduced, while isoprene emissions and <i>A</i><sub>net</sub>
recovered quickly to values of the control trees. Further, we found that
isoprene emissions covaried with <i>A</i><sub>net</sub> during nonstress
conditions, while during the heatwaves, isoprene emissions were not related
to <i>A</i><sub>net</sub> but to light and temperature. Under standard air
temperature and light conditions (here 30 °C and photosynthetically
active radiation of 500 µmol m<sup>−2</sup> s<sup>−1</sup>), isoprene
emissions of the heat trees were by 45 % and the heat–drought trees were
by 27 % lower than in control trees. Moreover, temperature response
curves showed that not only the isoprene emission factor changed during both
heat and heat–drought stress, but also the shape of the response. Because
introducing a simple treatment-specific correction factor could not reproduce
stress-induced isoprene emissions, different parameterizations of light and
temperature functions are needed to describe tree isoprene emissions under
heat and combined heat–drought stress. In order to increase the accuracy of
predictions of isoprene emissions in response to climate extremes, such
individual stress parameterizations should be introduced to current BVOC
models. |
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| ISSN: | 1726-4170 1726-4189 |