has any one seen a change in the abundance of C-13 during the winter and summer season, is it possible to observe relatively high abundance of C-13 in a compound during winter as compared to summers or vice-verse.
This is another good link:
http://www.esrl.noaa.gov/gmd/outreach/isotopes/c13tellsus.html
This depends on what carbon pool you are looking at. Secondary plant metabolites / plant products such as sugar, starch, lipids. leaf waxes are affected by seasonal (or climatic) temperature and humidity changes / differences. Changes in d13C are typically 1 to 2 permil but can be as high as 4 permil. The primary driver for these changes seems to be stomata closure in response to water stress.
It would be something you could easily publish on. I think that some work in papers looking on transport of 13C in plants by Arthur Gessler (e.g. New Phytologist (2001) 150: 653 – 664). I remember other papers by Arthur Gessler on it.
Dear Ramit
in addition to the changes in source (i.e. CO2) delta 13C - as pointed out by Kenneth and Jay there are definitely variations in photosynthetic discrimination as primarily affected by ca/ci. As Wolfram pointed out stomatal conductance but also light availability can affect ci/ca and thus 13C discrimination and consequently d13C of plant organic matter. Stomatal closure decreases ci - anthropomorphically spoken RubisCO can't be that picky anymore and takes relatively more of the heavier isotope - relative 13C abundance in assimilates increases. Low light availability causes Ci to increase - RubisCO can choose - prefers the lighter isotope - and 13C abundance in assimilates decreases. That might explain seasonal differences - however it definitely depends on the system and conditions you are looking at. Another point is post-photosynthetic discrimination that might affect also particular compounds - so starch storage is one important point. Starch is known to be enriched in 13C and compounds produced from storage starch are enriched in 13C consequently. We wrote a tree ring based review recently which gives an overview on possible post-photosynthetic mechanisms affecting delta 13C. (Gessler A, Ferrio JP, Hommel R, Treydte K, Werner RA, Monson RK. 2014. Stable isotopes in tree rings: towards a mechanistic understanding of isotope fractionation and mixing processes from the leaves to the wood. Tree Physiology 34: 796–818.)
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