Field integration of shoot gas-exchange and leaf chlorophyll fluorescence measurements to study the long-term regulation of photosynthesis in situ

Jaakko Oivukkamäki; Juho Aalto; Erhard E Pfündel; Manqing Tian; Chao Zhang; Steffen Grebe; Yann Salmon; Teemu Hölttä; Albert Porcar-Castell

doi:10.1093/treephys/tpae162

Field integration of shoot gas-exchange and leaf chlorophyll fluorescence measurements to study the long-term regulation of photosynthesis in situ

Tree Physiol. 2024 Dec 11:tpae162. doi: 10.1093/treephys/tpae162. Online ahead of print.

Authors

Jaakko Oivukkamäki¹, Juho Aalto², Erhard E Pfündel³, Manqing Tian², Chao Zhang¹, Steffen Grebe¹, Yann Salmon², Teemu Hölttä², Albert Porcar-Castell¹

Affiliations

¹ Optics of Photosynthesis Laboratory, Institute for Atmospheric and Earth System Research (INAR)/Forest Sciences, Viikki Plant Science Center, University of Helsinki, Helsinki, FI 00014, Finland.
² Institute for Atmospheric and Earth System Research (INAR)/Forest Sciences, University of Helsinki, Helsinki, FI 00014, Finland.
³ Heinz Walz GmbH, Eichenring 6, D-91090 Effeltrich, Germany.

PMID: 39660997
DOI: 10.1093/treephys/tpae162

Abstract

Understanding the diurnal and seasonal regulation of photosynthesis is an essential step to quantify and model the impact of the environment on plant function. Although the dynamics of photosynthesis have been widely investigated in terms of CO2 exchange measurements, a more comprehensive view can be obtained when combining gas-exchange and chlorophyll fluorescence (ChlF). Until now, integrated measurements of gas-exchange and ChlF have been restricted to short-term analysis using portable IRGA systems that include a fluorometer module. In this communication we provide a first-time demonstration of long-term, in situ, and combined measurements of photosynthetic gas-exchange and ChlF. We do so by integrating a new miniature PAM-fluorometer into an existing system of automated chambers to track photosynthetic gas-exchange of leaves and shoots in situ. The setup is used to track the dynamics of the light and carbon reactions of photosynthesis at a 20-minute resolution in leaves of silver birch (Betula pendula Roth) during summertime. The potential of the method is illustrated using the ratio between electron transport and net assimilation (ETR/ANET), which reflects the internal electron use efficiency of photosynthesis. The setup successfully captured the diurnal patterns in the ETR/ANET during summertime, including a large increase in noon ETR/ANET in response to a period of high temperatures and relatively low soil moisture, pointing to a drastic decrease in electron use efficiency. The observations emphasize the value of combined and long-term in situ measurements of ChlF and gas-exchange, opening new opportunities to investigate, model and quantify the regulation of photosynthesis in situ and the connection between ChlF and photosynthetic gas-exchange. The next steps, potential and limitations of the approach are discussed.

Keywords: Betula pendula; Alternative energy sinks; Electron transport rate; Field measurements; Micro-pam; Pulse-amplitude modulation (pam); Silver birch.