Mesophyll conductance measured at the whole-tree canopy level does not respond to elevated temperature
Abstract
Mesophyll conductance (gmes) plays a central role in the regulation of plant-atmospheric exchange of carbon and water from the leaf up to the whole canopy. Nonetheless, most commonly available techniques for measuring gmes are still costly and/or time-consuming and thus are usually limited to the leaf level. Hence, we lack a holistic understanding of how gmes scales to the canopy level. Here, for the first time, we present measurements of whole-tree canopy gmes, calculated from concurrent measurements of whole-tree discrimination against 13C (Δ13C) and whole-tree gas-exchange measured over the course of one day. We measured gmes, photosynthesis (A), transpiration (E) and phloem carbon isotopic composition (δ13Cphloem) once a month over one growing season (October-April) in large, field-grown Eucalyptus tereticornis trees. Six trees were exposed to ambient and six to warmed air-temperature (3 ˚ C above ambient). Our results showed that at the canopy level, gmes strongly limits A and that this limitation is greater in spring and autumn than in the peak of the growing season. Warming did not increase gmes at the canopy level, in agreement with leaf-level measurements on the same trees. Lack of a significant effect of warming on both leaf- and canopy-level gmes contrasts with most leaf-level observations from previous studies. Finally, we suggest that δ13Cphloem serves as a good proxy of canopy-integrated gmes and, once calibrated, for whole-tree water-use efficiency.
- Publication:
-
EGU General Assembly Conference Abstracts
- Pub Date:
- April 2019
- Bibcode:
- 2019EGUGA..2113063G