Investigation of the Past Climate and the Physiological Response of Trees in a Tropical Rainforest and a Tropical Seasonal Forest Based on the Stable Isotope Composition of the Tree Rings

Kasetsart University, Thailand

Forest Research Institute Malaysia, Malaysia

FY 2014-2017 Grant-in-Aid for Scientific Research (KAKENHI)

YOSHIFUJI, Natsuko

The radial profile of the carbon and oxygen stable isotope composition (SIC) in tree rings is expected to provide information on the past climate and leaf gas exchange in trees because the carbohydrate SIC reflects the meteorological conditions and intrinsic water use efficiency during photosynthetic assimilation. However, the degree of correlation between the observed SIC profile in tree rings and the past climate and intrinsic water use efficiency is not completely understood due to the effects of post-photosynthetic processes, such as the time lag between photosynthetic assimilation and wood formation and the mixing of sugars during phloem transport.

The objective of this study was to clarify the degree of correlation between the high-resolution radial SIC profiles in the tree rings of two types of tropical trees (evergreen tree species in a tropical rainforest and a deciduous tree species in a tropical seasonal forest in Southeast Asia) and meteorological data and intrinsic water use efficiency estimates based on ecosystem water and carbon flux measurements obtained from an in situ flux tower.

We conducted the following investigations at a tropical seasonal forest site [teak (Tectona grandis) plantation] in Thailand and a tropical rainforest site in Malaysia:
1) Analyzed and dated the radial SIC profiles in tree rings at a high resolution and investigated the intra- and inter-annual variations of SIC.
2) Investigated the relationship between the SIC profiles in the tree rings and both meteorological data and intrinsic water use efficiency estimates based on ecosystem water and carbon flux measurements obtained from an in situ flux tower.

No annual tree rings were visible in the evergreen trees growing in the tropical rainforest site (Fig.), so we determined the boundaries of the annual tree rings and dated the SIC profiles through comparison with the expected SIC fluctuations as a result of rainfall fluctuations. By contrast, annual tree rings were visible in the deciduous trees growing in the seasonal forest site, allowing us to date their SIC profiles at the intra-annual level by sampling microcores of the outer xylem at weekly intervals and observing these under a microscope to determine tree-ring formation.
In the tropical rainforest site, the relationship between the carbon SIC profile in the tree rings and soil moisture was different from the relationship between the intrinsic water use efficiency estimated from flux-tower measurement data and soil moisture probably due to the temporal and spatial differences in the information derived from the tree-ring SIC data and the flux-tower observation data and the effects of post-photosynthetic processes on the carbon SIC profile in the tree rings. In the seasonal forest site, the carbon SIC profile in the tree rings reflected the volumetric soil moisture content averaged over a longer period than the carbon SIC profile in the leaves, possibly because stem wood was formed from a mixture of sugars obtained from pools in the leaves and stem wood.

Fig. Cross-sections of an evergreen tree from the tropical rainforest site with no visible tree rings (left) and a deciduous tree from the tropical seasonal forest site with visible tree rings (right)

The findings of this study will assist further investigations on the interpretation of SIC profiles in tree rings and will help us to extract information about the past climate and leaf gas exchange of trees.

Konishi Y, Hayazaki H, Matsuo N, Yoshifuji N, Takanashi S, Fujiwara T, Tanaka N, Igarashi Y, Tantasirin C, 2017. The effect of annual precipitation on the tree ring width and carbon isotope composition of a deciduous teak (Tectona grandis L. f.) in northern Thailand. Chubu Forestry Research 65: 43-46 (In Japanese)

Matsuo N, Ochiai T, Umemura T, Kamakura M, Yoshifuji N, Tantasirin C, Tanaka N, Tanaka K, 2017. The effect of irrigation on leaf water use efficiency of a deciduous teak (Tectona grandis L. f.) in northern Thailand. Chubu Forestry Research 65: 51-54 (In Japanese)