[Effects of Different Rotation Patterns of Oil-Rice on Methane and Nitrous Oxide Emissions in Rice Fields].

A field experiment was carried out to investigate the effects of different rice-rape rotation systems on methane and nitrous oxide emissions, which were measured using the static chamber/gas chromatography method, prediction of their global warming potentials (GWP), and greenhouse gas intensity (GHGI) in paddy fields. The results showed that the average cumulative emissions of CH4from a double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 135.25, 55.64, 5.05, and 1.89 kg ·hm-2, respectively. The CH4 emission during the rice season accounted for 91.8%-98.5% of the annual CH4 emission in different rotation years, and the contents of dissolved organic carbon in paddy soil exhibited a significantly positive correlation with CH4 emission. The CH4 emission in conventional late rice paddy was 18.7% higher than that of hybrid late rice paddy (P<0.05). The average cumulative emissions of N2O from double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 0.94, 0.64, 1.38, and 0.24 kg ·hm-2, respectively. Out of the total annual N2O emission, 57.2% to 70.2% was from the rape field; 17.8% and 30.6% was due to the winter fallow treatments with previous crop type of double corpping rice and single season rice, respectively. There was no significant difference in N2O emission between hybrid rice and conventional rice paddy fields. The GWP of double cropping rice-winter fallow and double cropping rice-rape was higher than that of rice-rape and rice-winter fallow, and the GWP of CH4 in rice season accounted for 71.2% to 90.9% of the annual GWP of rotation. The highest treatment of GHGI was rice-rice-rape, and the treatment of rice-oil and rice-winter slack was lower. According to the comprehensive environmental and economic benefits, the late hybrid rice-rape patterns should be selected to reduce greenhouse gases in multiple cropping rice fields of South China.

[Relationship of histidine auxotrophy of Acidovorax citrulli with pathogenicity].

UNLABELLED: Acidovorax citrulli (Ac) is an important bacterium that occurs in watermelon, melon and other cucurbits. It mainly damages watermelon and melon, and can cause leaf blight, fruit rot, and even mortality. OBJECTIVE: To verify the relationship between defects in the synthesis of histidine and the pathogenicity of Ac. METHODS: We generated a transposon (Tn5) mutant library on the background of strain xjl12 of Ac. Then we used subclone technology to identify the gene. RESULTS: The mutant could not elicit the hypersensitive response (HR) in nonhost tobacco, and its virulence was reduced. It is impaired in hisC, which encodes the protein histidinolphosphate aminotransferase. The other three genes (hisA, hisB and hisD) involved in the process of histidine synthesis were also studied. These mutants could not elicit the hypersensitive response (HR) in nonhost tobacco; their virulence was reduced significantly and disease symptoms caused by mutants were delayed for 48 hours when compared to the wild type strain. By adding exogenous histidine, pathogenicity of the mutants was restored. CONCLUSION: The change of the characteristics of the mutants was directly related to the synthesis of histidine.