Abstract: Plants can adapt to interspecific competition by adjusting their growth behaviors and morphological characteristics at their different growth stages. In this study, a grassland with mixed sowing Avena sativa and Vicia vilosa was established in Qilian mountainous region, aimed to understand the interspecific competitive relationships of the two annual species at their different phonological phases. To evaluate the competitive relationships, the relative yield (RY), relative density (RD), and relative yield total (RYT) of the two species were measured. It was observed that the interspecfic relationships of the two species changed with phenological phase. At seeding stage, there was a strong competition between the two species, manifesting in the mutual limitation of relative number and the slow increase of plant height and leaf number; at tillering stage, the interspecfic competition transformed into interspecfic collaboration, manifesting in the rapid increase of tiller number and leaf number and the increasing RYT; at jointing stage, V. vilosa started to increase its relative number, which limited the development of A. sativa and caused strong intraspecfic competition; at grain-filling stage, the intraspecfic competition transformed into interspecific competition again. Through the adjustment of morphological plasticity at different phonological phases, the two species better responded the transformation of their interspecfic relationship.

Key words: N and P transport, SWAT models, Computer modeling, Remote sensing, GIS