Print PageA 13CO2 canopy pulse labeling experiment was conducted in order to investigate the impact of drought on (i) the time-lag between assimilation and (soil) respiration (ii) the role of leaf mobile and immobile carbon pools for soil respiration on a diurnal time-scale, and (iii) plant carbon allocation. The study was conducted on beech saplings (Fagus sylvatica L.) in a climate chamber with controlled humidity, air temperature and light conditions. By coupling a laser spectrometer to a combined soil/canopy chamber system online real-time measurements of canopy and soil 13CO2 and 12CO2 fluxes could be done independently for each plant component (soil and canopy). Supplementary to the laser spectroscopy measurements, δ13C in plant tissue (bulk, sugar, starch) was also analyzed using isotope ratio mass spectrometry (IRMS).
Results/Conclusions
Drought conditions generally increased carbon residence times within the mobile plant carbon pool by a factor of two and slowed the coupling speed between above- and belowground plant parts significantly (control = 2.73 ± 0.03 h; dry = 6.71 ± 0.66 h). Canopy photosynthesis could be distinguished as the major responsible driver for these changes. Further, drought was also responsible for a higher relative carbon dislocation to the root system as indicated by δ13C measurements of stem and root tissues. Above all, a strong diurnal coupling of leaf metabolism with soil respiration was found for both, control and drought treatments, which was driven by the alternately supply of a leaf mobile and transient immobile carbon pool. The diurnal imprint of leaf metabolism on soil respiration could be reproduced with a simple carbon allocation and growth model simulating carbon metabolism on a whole plant basis.
