Temporal variation in δ¹³C, wood density and microfibril angle in variously irrigated Eucalyptus nitens

Wood can serve as a record of past climate, recording tree responses to changing conditions. It is also valuable in understanding tree responses to environment to optimise forest management. Stable carbon isotope ratios (δ¹³C), wood density and microfibril angle (MFA) are potentially useful wood property parameters for these purposes. The goal of this study was to understand how δ¹³C varied over time in response to cycles of soil drying and wetting and to variation in temperature in Eucalyptus nitens Deane & Maiden, in concert with wood density and MFA. δ¹³C increases did not necessarily occur when water stress was highest, but, rather, when it was relieved. Our hypothesis is that this was a result of the use of previously fixed carbohydrate reserves when growth and metabolic activity was resumed after a period of dormancy. MFA in particular showed concomitant temporal variation with δ¹³C. A peak in δ¹³C may not coincide temporally with an increase in water stress, but with a decrease, when higher growth rates enable the final incorporation of earlier stored photosynthate into mature wood. This has implications for using δ¹³C as a tool to understand past environmental conditions using radial measurements of wood properties. However, interpreting this data with other wood properties may be helpful for understanding past tree responses.