[Effects of simulated nitrogen deposition on competition of weedy species (Echinochloa crusgalli var. mitis L.) and upland rice (Oryza sativa L.) under different air temperatures].

A greenhouse experiment was conducted to study the effects of simulated nitrogen deposition on the growth and competition of C4 weedy species (Echinochloa crusgalli var. mitis L. ) and C3 upland rice (Oryza sativa L.) under day/night temperature of 35 degrees C/25 degrees C and 30 degrees C/20 degrees C. The results showed that under day/night temperature 35 degrees C/25 degrees C, 4.0 g x m(-2) x a(-1) N deposition enhanced the shoot biomass of E. crusgalli and O. sativa by 29.18% and 27.80%, respectively, compared with control. The N and P uptake by E. crusgalli increased by 87.33% and 49.73%, respectively, but no change was found for O. sativa. Under 30 degrees C/20 degrees C, three N depositions (2, 4 and 6 g x m(-1) x a(-1) ) enhanced the shoot biomass, tiller number, and shoot N and P uptake of E. crusgalli by 48.99%, 72.68% and 36.18%, 111.11%, 122.22% and 144.44%, 108.88%, 129.22% and 134.29%, and 16.53%, 65.05% and 22.47%, respectively, but no changes were observed for O. sativa. Nitrogen deposition significantly increased the shoot biomass ratio of E. crusgalli to O. sativa under 30 degrees C/20 degrees C, but had no impact on this ratio under 35 degrees C/25 degrees C. It was suggested that N deposition could enhance the competition of E. crusgalli over O. sativa, especially under lower air temperature.

[Regulation effects of arbuscular mycorrhizal fungi on the interactions between barnyard grass and upland rice under enhanced nitrogen supply].

A pot experiment was conducted to study the regulation effects of arbuscular mycorrhizal fungi (AMF) on the interactions between Echinochloa crus-galli var. mitis L. and Oryza sativa L. under enhanced N supply (4.0 g N x m(-2) x a(-1)). The results showed that under monoculture condition, the AMF colonization on E. crus-galli increased but that on O. sativa decreased. In the treatments with and without AMF inoculation, upland rice biomass and its P and N uptake increased by 42.35% and 13.48%, 4.07% and 2.55%, and 30.35% and 62.09%, respectively, and barnyard grass biomass and its P and N uptake increased by 20.24% and 15.65%, 3.88% and 4.06%, and 15.10% and 30.35%, respectively. Under mixed cropping, the AMF colonization on E. crus-galli increased but that on O. sativa had little change. In the treatments with and without AMF inoculation, the biomass ratio of O. sativa to E. crus-galli decreased, but N uptake ratio changed a little. The P uptake ratio of O. sativa to E. crus-galli increased in treatment without AMF inoculation but decreased in treatment with AMF inoculation. It was suggested that AMF tended to enhance the competition of E. crus-galli to O. sativa under enhanced N supply.