Dynamics and allocation of recently photo-assimilated carbon in an Inner Mongolia temperate steppe

Information on carbon (C) dynamics and allocation in plant-soil system is essential for understanding the terrestrial C cycle. Using a C-13 pulse-labeling chamber (I in x I in) technique, we carried out three separate experiments in an Inner Mongolia temperate steppe (Leymus chinensis-Stipa grandis-Cleistogenes squarrosa). The first experiment determined mainly the temporal variation of delta C-13 (parts per thousand) signatures over the chase period of 6-27 July in a fenced site. The second experiment compared the dynamics and allocation of recently assimilated C over 10-20 August between a fenced site and a grazed site. The third experiment measured the effect of N application on assimilated C fluxes over 26 August-4 September in a fenced site. The above- and below-ground partitionings of labeled C-13 were found to vary with site, growth stage and management state. The labeled C-13 in shoots was maximal during the first day after labeling and then declined, whereas it roughly increased in roots. There was the absence of significant variation in Soil delta C-13. In the fenced site, the labeled C-13 partitioning to the shoots accounted for 24.4, 16.8 and 11.1% of initial additions by 10 days after the labelings on 6 July, 10 August and 26 August 2003, respectively. However, the percentage of recently assimilated C partitioning to the roots, about 22-23%, was almost unchanged throughout growing stages. In the grazed site, the labeled C-13 of about 50% was respired, 13% was remained in the shoots, and 37% was translated to the roots; the corresponding percentages, for the fenced site with N, were approximately 60, 20 and 18%, respectively. This study suggests that carbon was rapidly and substantially cycled in the Inner Mongolia temperate steppe by means of photosynthesis and respirations. It appears that the grazing and the N application had significant effects on the dynamics and allocation of recently photo-assimilated C in the plant-soil system. (c) 2006 Elsevier B.V. All rights reserved.