Variations and influential factors of the seed oxygen isotope ratios across 42 forest plant species

Oxygen isotope ratios ( 18 O/ 16 O, hereafter δ 18 O) of plant tissues are widely used for various purposes, including paleoclimatic reconstruction, identification of the geographical origin of plant-based products, and understanding plant water use. On the other hand, δ 18 O values of seeds have been rarely measured. We measured the δ 18 O values of whole seed testas of 42 forest plant species at a single location to clarify the variation in δ 18 O values of seeds among species and its influential factors for exploring how they can be used. The maximum interspecific difference in δ 18 O values of seeds was 16.7‰, which is comparable to the values reported in those of plant tissues collected worldwide. This large variation is influenced by the climate and life form. Precipitation during the month of seed maturation and one to two months beforehand had a negative effect on the δ 18 O values of seeds. The δ 18 O values of seeds varied among life forms, that is, canopy and subcanopy trees > shrubs ≥ lianas. This may reflect vertical differences in water uptake or transpiration due to variations in root depth or plant height. Our results demonstrate that the δ 18 O values of seeds of wild plants contain detectable climatic and ecological signals, particularly those related to precipitation and life forms. These findings suggest that the δ 18 O values of seeds provide a useful basis for future studies aiming to reconstruct past environmental conditions and investigate water use during seed production.