Effects of DD,EDB and PCP upon microorganisms and their activities in soil part I effects on microflora

The extensive use of various insecticides or herbicides makes it desirable to know what influences, if any, such chemicals may exert upon soil microorganisms. The effect of chemicals should be considered not only upon plant pathogenes, but also upon general soil micro-organisms.     

Effects of DD,EDB and PCP upon microorganisms and their activities in soil part II effects on microbial activity

In the previous paper (7), the effect of chemicals upon microbial balance in soil has been reported. Since it is a usual phenomenon that an effect on microbial balance brings about the change of metabolism in soil, experiments were simultanuously conducted on the effect of chemicals upon the microbial activity in soil. It seems that not many reports have been concerned with the above aspects on the new chemicals.     

Microbial communities responsible for the decomposition of rice straw compost in a Japanese rice paddy field determined by phospholipid fatty acid (PLFA) analysis

To identify the microbial communities responsible for the decomposition of rice straw compost in soil during the rice cultivation period, phospholipid fatty acid (PLFA) composition of rice straw compost was determined by periodically sampling the compost from a Japanese rice field under flooded conditions. About 21% of the compost was decomposed within a period of 3 months. The total amount of PLFAs, as an indicator of microbial biomass, was significantly lower under drained conditions than under flooded conditions and was relatively constant during the flooding period. This indicates that the microbial biomass in the compost samples did not increase during the gradual decomposition of rice straw compost under flooded conditions. The proportion of branched-chain PLFAs (biomarker of Grampositive and anaerobic Gram-negative bacteria) slightly decreased during the early period after placement, and increased gradually afterwards. Among the branched-chain PLFAs, i15:0, ail5:0, i16:0 and i17:0 PLFAs predominated and their proportions increased gradually except for i16:0. The proportion of straight mono-unsaturated PLFAs (biomarker of Gramnegative bacteria) was almost constant throughout the period, and 18:1ω9 and 18:1ω7 PLFAs predominated. The proportion of straight poly-unsaturated PLFAs as a biomarker of eukaryotes including fungi was also constant throughout the period, except for a decrease under drained conditions. Straight poly-unsaturated PLFAs consisted mainly of 18:2ω6c PLFA. Therefore, these results suggest that the proportions of Gram-positive and anaerobic Gram-negative bacteria increased during the decomposition of rice straw compost in flooded paddy field. Statistical analyses enabled to divide PLFA patterns of microbiota in the rice straw compost into two groups, one group consisting of rice straw compost samples collected before mid-season drainage and the other of samples collected after mid-season drainage. Small squared distances among samples in cluster analysis indicated that the community structure of microbiota was similar to each other as a whole. These results suggest that the microbial communities changed gradually during the period of placement, and that mid-season drainage may have affected the community structure of microbiota. Principal component analysis of the PLFA composition suggested that the succession of microbiota along with the decomposition in flooded soil was similar between rice straw compost and rice straw and that the changes in the community structure during the decomposition in flooded soil were more conspicuous for rice straw than for rice straw compost.     

Suppressive effect of rice bran incorporation in paddy soil on germination of Monochoria vaginalis and its relationship with electric conductivity

Laboratory experiments were conducted to investigate (1) the effects of the addition of rice (Oryza sativa. L.) bran to paddy soil on the germination of Monochoria vaginalis (Burm. f.) Kunth, and (2) the relationship between the electric conductivity (EC) of the soil solution and germination. Soil samples were collected at 4 sites in Japan. After flooded soils with rice bran had been incubated for 7?d at 30°C, the soil solution was collected using a porous cup and the EC of the soil solution was measured. The amounts of rice bran added to the soil were 0%, 0.3%, 0.6% and 0.9% (weight(w)/w). In the soil solution obtained, seeds of M. vaginalis were incubated for 3?d at 30°C, and the germination percentage was then analyzed. The addition of rice bran suppressed germination, and the degree of suppression increased with increasing content of rice bran. Although the same amount of rice bran was applied to each soil, the degree of growth suppression by rice bran as well as the EC of the soil solution differed among the soils. In each soil, there was a positive correlation between the amount of rice bran and EC, and the degree of growth suppression significantly increased with an increase in EC. When EC was higher than 150?mS?m^?1, seeds of M. vaginalis hardly germinated. There was no significant correlation between the oxidation-reduction potential (Eh) of soil and seed germination, suggesting that EC is a more reliable and convenient indicator than Eh for evaluating the relationship between the addition of organic material and seed germination. In conclusion, the addition of rice bran to soil increases the EC of the soil solution, and EC is one of the factors that suppress the germination of M. vaginalis. The suppressive effect of rice bran on germination is different among soils. This fact is attributed to the difference in EC due to the addition of rice bran. Thus, it is expected that EC can be used as an indicator for determining how much rice bran to add.     

Growth of hydrogenotrophic and acetoclastic methanogens on substrate from rice plant callus cells in anaerobic soil: an estimation to the role of slough-off root cap cells to their growth

Flooded paddy fields are the major anthropogenic sources of methane (CH₄) emission, and organic materials of rice plant origin were estimated to be important as its source. This study used rice (Oryza sativa L. cv, Yukihikari) callus cells as a model material for slough-off root cap cells, and carbon-13 (¹³C)-labelled callus cells were subjected to decomposition in aerobic and anaerobic soil microcosms for 56 days. DNA was extracted from a soil incubated with carbon-12 (¹²C)- and ¹³C-callus cells and subjected to buoyant density gradient centrifugation to identify methanogenic archaeal species that assimilated carbon from the callus cells. ¹³C-labelled 16S rRNA gene (16S rDNA) fragments from methanogenic archaea were not polymerase chain reaction (PCR)-amplified in heavy fractions under aerobic soil conditions, while they were successfully done from day 3 onwards under anaerobic soil conditions. Eighty-four denaturing gradient gel electrophoresis (DGGE) bands in heavy fractions were sequenced, revealing that they were members of Methanosarcina spp. (20 clones), Methanosaeta spp. (18 clones), Methanocella spp. (25 clones), Methanomicrobiales (10 clones), Methanobacterium spp. (7 clones) and Cluster ZC-I (2 clones). They included hydrogenotrophic and acetoclastic methanogens and were phylogenetically different from those residing in rice roots and, presumably, from those assimilating root exudate and mucilage-derived carbon. This study indicates that carbon of slough-off root cap cells propagates specific methanogenic species in rice rhizosphere under anaerobic soil conditions and thus augments the diversity of the total rhizospheric methanogenic community.     

Effect of soil microorganisms on the growth of roots in rice seedlings

Abstract

Root system of rice seedlings grown on nutrient solution inoculated with soil microorganisms were examined morphologically in comparison with those obtained under sterile condition. In the presence of soil microorganisms, primary roots increased in their number and decreased in the total length. Inoculated plants had more secondary roots equipped with tertiary roots. In addition, longer root hairs developed densely on primary and secondary roots of the inoculated seedlings.

Anatomical examination of the primary roots revealed that the number and width of cortical layers, as well as the length and width of the cortical cells, were increased by the effect of microorganisms. Microbial effect on outer morphology of rice roots, consequently, was estimated to have been induced from the alteration in histological and cytological activities including the activation of the periclinal divisions of the epidermal cells, the inactivation of the transverse divisions of the cortical cells and the activation of the elongation of cortical cells.     

Availability of squid viscera meal with cadmium removal treatment as a feed ingredient for fingerling black rockfish Sebastes schlegeli

Two 12-week feeding experiments were conducted to evaluate the nutritional value of squid viscera meal with cadmium removal treatment (dCSVM), which contained 1.5–2.0 mg/kg cadmium, as an alternative protein source to sardine meal in diets for fingerling black rockfish Sebastes schlegeli. Initial mean body weights in experiments 1 and 2 were 23.0 and 6.4 g, and the replacement rates of sardine meal with dCSVM in the test diets were 20–80 % and 30–60 %, respectively. In experiment 1, inclusion of dCSVM at 40 % and higher replacement rates of sardine meal retarded the growth of fish due partly to inferior dCSVM protein digestibility. The cadmium (Cd) concentrations in fish muscle of all treatment groups were below the detection limit (<0.1 mg/dry matter). In experiment 2 using dCSVM containing Cd at a lower level and having a higher protein digestibility than in experiment 1, no significant differences were observed in the growth between the control and 60 % replacement groups, although feed efficiency gradually decreased with the increase of dCSVM inclusion. These results show that dCSVM is safe and useful as an alternative protein source and could replace up to 60 % of sardine meal in fingerling black rockfish diets.     

Effect of water flow on the mobility of the root-knot nematode Meloidogyne incognita in columns filled with glass beads, sand or andisol

In the present study, the migration of nematodes was studied in columns filled with three materials of different textures and chemical properties. The role of soil pores that enable root-knot nematode (Meloidogyne incognita) second stage juveniles (J2) to escape rapid water flow in soil was demonstrated using columns filled with glass beads, sand or andisol that maintained a constant water flow. Under a constant flow flux of 36 cm h⁻¹, living J2, dead J2 or anion bromine tracer (Br⁻) was injected in the middle of the column and then drainage water equivalent to two pore volumes (PV) was collected. The passive transport of the anion tracer in water flow could be explained by a convection dispersion equation. The dead J2 showed a pattern similar to that of Br⁻. However, the living J2 resisted movement in the water flow and remained in the column even at the highest water flow rate of 93.3 cm h⁻¹ in glass beads. The mobility of living J2 was affected by the filling materials; the number of J2 passing through the column was much lower in the andisol-filled column than in the other two columns but the total number of J2 in drainage water was 5% or less of the number injected for all columns. We suggest that J2 were affected not only by soil water flow but also by soil pore structure and have the ability of withstanding or avoiding movement in soil water flow.