Tree ring isotope composition to inform models assessing the sentitivity of the forest carbon budget to increased atmospheric CO2 and climate change

2022 Fiscal Year Annual Research Report

• Project Area: Digital biosphere: integrated biospheric science for mitigating global environment change
• Project/Area Number: 22H05725
• Research Institution: Kyoto University
• Principal Investigator: EPRON Daniel 京都大学, 農学研究科, 教授 (60844305)
• Project Period (FY): 2022-06-16 – 2024-03-31
• Keywords: tree ring / cellulose / isotopes / climate change

Outline of Annual Research Achievements

During the fiscal year R4, we successfully sampled wood cores from 14 trees in November in the Kiryu experimental watershed when tree growth and cellulose deposit have ceased. Annual tree rings were cut and cellulose were extracted in February and March. Duplicate samples (1592) were weighed in silver capsules and were analysed by isotope ratio mass spectrometry from July 2023 to February 2024.
During the fiscal year R4, we have also reanalysed the 20-year series of canopy CO2 and H2O fluxes measured by eddy covariance and calculated evapotranspiration, canopy photosynthesis and stand-level water use efficiency. We started to collect samples of sap wood in March to ascertain the relation between xylem water and source water (soil and rainwater).

Current Status of Research Progress

3: Progress in research has been slightly delayed.

Reason

Because the delivery of experimental consumables was delayed due to reduced supply, we were not able to start measuring the isotope composition of the tree ring cellulose during the fiscal year R4. We were able to do it in the next fiscal year (R5) and we successfully completed the work.

Strategy for Future Research Activity

Tree ring isotope composition will be measured on all rings cut from wood cores collected on 14 trees in the Kiryu experimental watershed. We will collect samples of sap wood monthly to ascertain the relation between xylem water and source water (soil and rainwater). Water samples will be analysed for 18O and 2H with a cavity ring-down spectrometer. From May to August (growing season) we will sample leaves and branches and extracted their water monthly. We will also sample atmospheric water and soil water at the same time. We will characterise leaf water enrichment above source water and test several models able to predict the observed enrichment.