Wood Core Stable Isotopes

Tropical forests represent a large carbon pool storing between 40 – 50% of the terrestrial carbon. Unlike the amazon, where ecosystem exchange measurements of carbon and water are common, measuring these vegetation dynamics in remote locations within the Congo basin remains difficult. Although above ground biomass and carbon cycle dynamics are quantified by regular tree inventories at permanent sampling plots (Kearsley et al. 2012) they provide little information on the temporal dynamics of the carbon and water of African tropical humid forest ecosystems.

However, wood [core] stable isotope analysis can provide a means to overcome these limitations⁠. The combination of dendrochronology and stable isotope composition of carbon and oxygen stored in wood reveals the conditions in which a given tree was growing, and at what rate⁠. As such, the use of dendrochronology and stable isotope wood [core] analysis provides us with the opportunity to quantify long term physiological responses to climate (change), in part sidestepping the need for long-term ecosystem exchange measurements.

A previous position as post-doc within the Congo Basin Integrated Monitoring for FOrest carbon mitigation and biodiversity (COBIMFO) project provided me with privileged access to both wood cores and stem discs collected in humid tropical forest in central DR Congo and stable isotope analyzers. However,  a crucial step in the stable isotope analysis involved getting a cellulose extraction setup running. Here  I provide a short rational to why you would want to use ‘just’ cellulose instead of bulk wood and describe how to create a small ‘budget’ cellulose extraction line. For schematics and cost estimates as well as the associated protocol jump straight to the final paragraph.

Why just cellulose?

Although in literature the use of cellulose in wood core stable isotope analysis isn’t consistent, with several studies using bulk wood instead, it is however advisable. The main reason is decreasing the variability in the measured stable isotope signal. Bulk wood consists of various substances e.g. resins, lignin and cellulose, with some more mobile than others. In addition, all these components have varying quantities of stable isotopes due to different biosynthetic pathways. All these factors could skew the final stable isotope analysis and the final interpretation of the signal.

A comparative study between different purification methods is given by “Cullen and MacFarlane. Comparison of cellulose extraction methods for analysis of stable isotope ratios of carbon and oxygen in plant material Tree Physiol (2005) 25 (5): 563-569 doi:10.1093/treephys/25.5.563″

What you need

This is the list of the things you would need to run a full scale cellulose extraction line (100+ samples). Most ‘wet’ labs will probably be able to cut back on costs as they often stock similar pieces already such as an ultrasonic homogenizer or hot water baths. Some more common items such as chemicals and general lab equipment are not included into the price estimate. All prices are rough estimates as the final price depends on agreements you might have with vendors.

Item Price (euro)
Memmert hot water bath 1500
ISOFLEX tubing (20m) 100
custom glass filter flasks (x100) 1500
glass filter flask holders (teflon) (x5) * 640
NaOH / NaCLO2 / acetic acid  –
ultrasonic homogenizer 2500
beakers / tweezers and general lab equipment  –
Total 6240
* technical drawings can be found here, as well as the protocol (specific for this setup)

 

Technical drawing of the custom Teflon glass filter holders.