A dual C-13 and N-15 long term labelling technique to investigate uptake and translocation of C and N in beech (Fagus sylvatica L.)

A continuous dual (CO2)-C-13 and (NH4NO3)-N-15-N-15 labelling experimental set-up is presented that was used to investigate the C and N uptake and allocation within 3-year old beech (Fagus sylvatica L.) during one growing season. The C and N allocation pattern was determined after six, twelve and eighteen weeks of growth. The carbon uptake was distinctly different in the three phases examined: The first six weeks after budbreak were dedicated to leaf growth with a RIS (root to shoot) ratio of 0.14 for the new carbon. The second growth phase showed a balanced RIS ratio of C allocation and after week 13, the root compartment was the main carbon sink (R/S = 6.97). Nitrogen allocation was more basipetal as compared to carbon. In the second growth phase, R/S of N-new was 5.57 but fell to 3.54 for the third growth phase probably due to formation of reserves in buds and stem.