[Show abstract][Hide abstract] ABSTRACT: It has been hypothesized that faunal activity in the rhizosphere influences root growth via an auxin-dependent pathway. In this study, two methods were used to adjust nematode and bacterial populations within experimental soils. One is "exclusion", where soil mixed with pig manure was placed in two bags with different mesh sizes (1mm and 5μm diameter), and then surrounded by an outer layer of unamended soil resulting in soil with a greater populations of bacterial-feeding nematodes (1mm) and a control treatment (5μm). The second method is "inoculation", whereby autoclaved soil was inoculated with bacteria (E. coli and Pseudomonas) and Nematodes (Cephalobus and C. elegans). In order to detect the changes in the rice's perception of auxin under different nutrient and auxin conditions in the presence of soil bacterial-feeding nematodes, responses of soil chemistry (NH4+, NO3- and indole acetic acid (IAA)), rice root growth and the expression of an auxin responsive gene GH3-2 were measured. Results showed that, under low soil nutrient conditions (exclusion), low NO3- correlated with increased root branching and IAA correlated with increased root elongation and GH3-2 expression. However, under high soil nutrient conditions (inoculation), a high NH4+ to NO3- ratio promoted an increase in root surface area and there was an additional influence of NH4+ and NO3- on GH3-2 expression. Thus it was concluded that soil bacterial-feeding nematodes influenced soil nutritional status and soil IAA content, promoting root growth via an auxin dependent pathway that was offset by soil nitrogen status.
[Show abstract][Hide abstract] ABSTRACT: The effects of IAA-producing bacteria (Pseudomonas sp. and Burkholderia sp.) and bacterial-feeding nematodes (Cephalobus sp.) on Arabidopsis thaliana (Ecotype, Columbia) root growth were investigated in pots with natural soil under controlled conditions. The soil, nematodes and root morphology of Arabidopsis were analysed at regular intervals. In natural soil, the bacterial-feeding nematodes grazing on bacteria stimulated both the microbial growth and activity and increased the mineral nitrogen and IAA contents. The analysis of the root architecture (total length, the number of tips, average diameter and surface area) of the A. thaliana seedlings revealed a highly branched root system, with longer and thinner roots in the presence of the IAA-producing bacteria and bacterial-feeding nematodes. On the basis of the above findings, it was concluded that the IAA-producing bacteria and bacterial-feeding nematodes improved the root growth of the A. thaliana seedlings in natural soil. The validity of our conclusion may be extended to future applications in agriculture.
Full-text · Article · Sep 2012 · European Journal of Soil Biology
[Show abstract][Hide abstract] ABSTRACT: A field experiment was carried out to investigate the methane emission pattern in a double-rice cropping system under conventional and no tillage in southeast China. The treatments included conventional tillage cultivation in both early rice and late rice (T–T) and conventional tillage in early rice but no-till in late rice (T–NT). The maximum methane emission rate of T–T and T–NT was 21.71 mg m−2 h−1 and 24.70 mg m−2 h−1 in early rice, respectively; and 18.52 mg m−2 h−1 and 7.32 mg m−2 h−1 in late rice, respectively. The seasonal amount of methane emission from the T–T and T–NT was not significantly different in early rice, but significant different (P < 0.05) in late rice, with the values 6.57 g m−2 and 3.04 g m−2, respectively. In comparison with early rice, the seasonal amount methane flux of late rice was reduced by 29% and 68% in the T–T and T–NT, respectively. The decrease of methane emission in the T–NT was attributed to lower dissolved organic carbon (DOC) content and higher soil bulk density. In conclusion, no tillage practice conducted in rice cropping season will markedly decrease methane emission for the rice cropping system.Highlights► No-till reduced methane emission significantly in paddy field. And it did negligibly affect on the methane flux after tillage in the early rice. ► The soil DOC content of no-till was significantly lower than that of the conventional tillage; however, the surface soil (0–10 cm) bulk density was significantly higher than that of the conventional tillage. ► The methane flux of late rice was lower than early rice in both the treatments in this double-rice cropping system. ► The lower DOC content may be another important factor resulting in lower methane emission besides the higher soil bulk density in no-till paddy field.
Full-text · Article · Jun 2011 · Soil and Tillage Research
[Show abstract][Hide abstract] ABSTRACT: A CPE-HPLC (UV) method has been developed for the determination of Prometryne. In this method, non-ionic surfactant Triton X-114 was first used to extract and pre-concentrate Prometryne from water and soil samples. The separation and determination of Prometryne were then carried out in an HPLC-UV system with isocratic elution using a detector set at 254 nm wavelength. The parameters and variables that affected the extraction were also investigated and the optimal conditions were found to be 0.5% of Triton X-114 (w/v), 3% of NaCl (w/v) and heat-assisted at 50 degrees C for 30 min. Using these conditions, the recovery rates of Prometryne ranged from 92.84% to 99.23% in water and 85.48% to 93.67% in soil, respectively, with all the relative standard deviations less than 3.05%. Limit of detection (LOD) and limit of quantification (LOQ) were 3.5 microg L(-1) and 11.0 microg L(-1) in water and 4.0 microg kg(-1) and 13.0 microg kg(-1) in soil, respectively. Thus, we developed a method that has proven to be an efficient, green, rapid and inexpensive approach for extraction and determination of Prometryne from soil samples.