Chemical isotopes in tree rings can help us learn about past environments, but how can you extract them without interfering with measurements?
Cellulose in tree rings can tell us a lot about past climates and tree physiology. Measuring the stable isotope signatures of carbon and oxygen (stable isotopes are different ‘versions’ of an element that can have more or less mass, but exhibit the same chemical behaviour) in wood is an important method for determining the climate experienced by a tree. But the extraction of cellulose from wood is complicated in conifer species that contain high concentrations of resins, which can interfere with tissue extractions and introduce error into isotope measurements. Typical methods to extract cellulose from conifers for isotope measurements can require toxic chemicals. While acetone has been used as a safer, albeit slower, alternative. it is unknown whether acetone has an adverse effect on the isotope measurements. In a recent article in Tree Physiology, Lin and colleagues sought to develop a faster cellulose extraction method and determine whether acetone was effective in removing resin acids from conifer wood without affecting isotope measurements.
Lin and colleagues were able to show that acetone effectively removed resin acids from wood for five conifer species, without affecting the stable isotope measurements, although it did affect the measurements of oxygen isotopes in Fraser fir. Furthermore, their new method allows for hundreds of samples to be prepared simultaneously, and greatly reduces the required labor. This method will improve the ease with which tree ring isotope data can be collected, which means that greater temporal and spatial resolution for tree ring data in conifers can be obtained.
Why are these findings so important? Tree rings are used to extract data on the environmental conditions that the tree experienced over its life and on how trees respond to climate factors, like precipitation and temperature. As such, larger datasets on tree ring isotopes will give us a better idea of how our climate has already changed and how forests responded to those climate changes. As well, since forests can affect climate, higher spatial resolution in isotope measurements could allow us to look at how the amount of forest cover affected climate in the past. This in turn will allow us to better predict future changes in climate and forest responses to climate change, as we could obtain a deeper understanding of forest-climate feedbacks.
Lin, W., Noormets, A., King, J. S., Sun, G., McNulty, S., & Domec, J.-C. (2016). An extractive removal step optimized for a high-throughput α-cellulose extraction method for δ13C and δ18O stable isotope ratio analysis in conifer tree rings. Tree Physiology. https://doi.org/10.1093/treephys/tpw084