Plant carbon partitioning below ground in the presence of different neighboring species

Knowledge about carbon allocation below ground is necessary to understand soil ecosystem functioning and the global C cycle. It is common knowledge that different plant species coexist in natural and agricultural systems. By using a modified C-13 pulse-chase approach, which enabled us to label individual plants in either mono- or mixed cultures, we investigated the effect of coexistence of different neighboring species on plant carbon partitioning. Maize and faba bean were used as our test plants and isotope pulse labeling was performed twice at 26 and 54 d after emergence. The results showed that a higher proportion of photoassimilates was distributed below ground in maize than in faba bean, resulting in a greater ratio of root to shoot biomass for maize plants during the experiment. The carbon distribution to roots was slightly higher in mixed cultures at 26 d than the counterpart monocultures. The distribution of the plant-assimilated C-13 to soil dissolved organic carbon was also greater in mixed cultures at 26 d relative to the monocultures. The most significant effect of the mixed culturing was a dramatic increase of C-13 incorporation into the soil microbial biomass. These results indicated that the plant carbon allocation below ground was altered in the presence of a different neighboring species. The increase of plant diversity probably enhances the soil microbial activity and hence the turnover of the plant-derived carbon in soil. (C) 2008 Elsevier Ltd. All rights reserved.