Question about radiocarbon :
(1) which tissues (part) should be measured, if I want to know the defoliation effect on current year NSC allocation to growth of trees.
1-year branch (if leaf is OK?), compare treated and un-treated groups; or old branches should also be measured; to compare both old-current year branch and treated and untreated?
(2) What is the difference between dry matter radiocarbon content and extracted mobile sugar-carbon-14 ?
Dear Xiaoyu Wang
Please find the attached files related on your filed of studies.
Thanks,
Ramin Lotfi
You could measure carbon isotope values for subsamples pretreated to alpha-cellulose component of wood material and measure all three isotopes C12, C13 and C14. The variation in C13/C12 ratio is largely related to plant physiological processes (rate of CO2 assimilation rate and conductance), and can be accounted for, ie removed from the variation in the C14 measurements. You might be using C14 as a marker or trace for where sugar-C14 moves to. Regarding (2), wood material will incorporate sugar-C14 from newly fixed carbon (photosynthate or 'sugar') as well as carbon remobilised from other parts of the plant (e.g. from carbohydrate stores) fixed at other times (ie older). Using C14 as a marker will help to investigate the flows and allocation of carbon. Other experimental treatment effects like defoliation might be adequately detectable from variation in the C13/C12 ratio and a knowledge of C3 leaf physiological theory.
1) For labelling note that allocation of photosynthetic products is variable in time. So you either need to have a huge set of seedlings that you treat and label at different times or you have to relabel at regular intervals.
2) You should also note that variation in NSC concentrations is large, My own studies were "less good than they could be" because N should be larger (which would have exlploded our analytical and work force costs. You should find a way that you either have sufficient replications. Mixing samples might be an option. (I suggest to mix always the same trees and use mixed models for analysis),
3) Note also that for the trees I worked with NSC concentrations were pretty stable and not really responsive to defoliation.(I.e. almost everytthing else changed "a lot" and NSC concentrations only a little bit.
I am egocentric enought to add two of my papers here One of them deals directly with the allocation issue and the other one more with NSC concentrations of different parts.
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