Interactive Effects of CO₂ and Nitrogen Resources on Shoot Development of Chenopodium album L. and Amaranthus patulus Bertol.

Abstract

The interactive effects of CO₂ enrichment and nitrogen supply on several attributes of shoot development were examined for two annual weeds, Chenopodium album L. and Amaranthus patulus Bertol., appearing at an early stage of secondary succession. The elevated CO₂ increased the number of branches at high nitrogen levels in C. album and plant height at low nitrogen levels in A. patulus. The larger number of branches may increase the number of potential flowering and fruiting sites. Basal diameter was larger at high nitrogen levels in C. album and at low nitrogen levels in A. patulus. The enlargement of leaf size by CO₂ enrichment required a larger amount of nitrogen in C. album than in A. patulus. These results show that the interactive effects of CO₂ and nitrogen depend on the species-specific nitrogen requirement. In A. patulus, elevated CO₂ and nitrogen supply slightly delayed the beginning of flower bud initiation. The slight delay, however, does not seem to affect the reproductive success of this species considering its reproductive behavior. In addition, there is no morphogenetic effect of CO₂ on leaf initiation per shoot, at least in herbaceous species. The present study suggests that future doubling of CO₂ may not cause the two species to lose their domination potential at an early stage of secondary succession.