Spatial relationships among different forms of soil nutrients in a paddy field

Within-field soil variability has often been reported in Japanese paddy fields. In one of such fields, we examined the relationships of spatial variations among different forms of soil nutrients and their direct influence on rice growth. Samples of surface soils collected from 100 plots (5 x 10 m) in the field were analyzed for the contents of N, P, and K as well as for the total C and clay contents. The values of the coefficient of variation (CV) for the soil properties were relatively high, ranging from 7% (total K) to 33% (inorganic N). More than 60% of the variation was spatially dependent, with ranges of less than 30 m for the contents of inorganic N and clay, 30-40 m for the contents of N (mineralizable and total), P (water-soluble, available, and total), and total C, and more than 60 m for the content of K (water-soluble, exchangeable, and nonexchangeable). These properties were grouped into two types; those significantly correlated either with the total C content (contents of mineralizable N, total N, all P forms, water-soluble K, exchangeable K, and 0.01 M HCl-extractable nonexchangeable K) or with the clay content (contents of fixed Nand NaBPh₄-extractable nonexchangeable K). In a pot experiment in which rice plants were grown in soil from each plot for 50 d, the dry matter weight of shoots exhibited a large variation (CV 12%) and increased significantly with the increase of the level of the components related to the total C content, especially the content of mineralizable N. Significantly positive correlations were also found between the contents of N, P, and K in shoots and the corresponding soil nutrients occurring in a moderately labile form. These soil-plant relationships suggest that site-specific application of organic fertilizers for altering the level of the components related to the total C content in the topsoil could be effective to homogenize rice growth in the paddy field examined.     

Could iron nutrition status be evaluated through photosynthetic pigment changes?

Iron deficiency decreases the amount of photosynthetic pigments in higher plants, and also results in characteristic changes in the relative photosynthetic pigment composition. Iron deficient plants exhibit a relative increase in xanthophylls, largely attributable to pigments within the xanthophyll cycle, violaxanthin, antheraxanthin, and zeaxanthin. Furthermore, the xanthophyll cycle functions in Fe‐deficient plants, but not in other yellow, carotenoid enriched‐materials, such as etiolated or senescing leaves. When Fe‐deficient leaves are illuminated, part of the violaxanthin is converted into antheraxanthin and zeaxanthin. When Fe‐deficient leaves are placed in the dark, the cycle reverts back to violaxanthin. In this paper we present further data on this cycle and discuss the possible relevance of pigment changes as an alternative mechanism for the dissipation of excess energy. The possibility of using characteristic pigment changes as a tool for monitoring Fe status in higher plants is discussed.     

Radiocesium interception potential (RIP) of smectite and kaolin reference minerals containing illite (micaceous mineral) as impurity

Cesium-137 (¹³⁷Cs) is strongly adsorbed on clay minerals, especially on illite. The adsorption of Cs⁺ on reference clay minerals, however, has not been fully investigated in relation to the presence of illite. The objective of this study was to clarify the effect of impurities (i.e., illite and vermiculite), present in reference smectite group minerals and kaolin minerals, on the retention of Cs⁺. The clay mineralogy of the reference minerals was characterized by X-ray diffraction (XRD). The radiocesium interception potential (RIP) was measured as an index of the Cs⁺ retention ability of clays. The content of illite in clay was represented by the total potassium (K) content given that illite is a major source of K in the clay fraction. The content of vermiculite in clay was represented by the Cs fixation capacity induced by Cs saturation followed by heating of samples at 110°C. Metabentonite and beidellite gave extremely high RIP values compared with other smectite group minerals, although a peak for illite (at 1.0 nm) was not observed in XRD analysis. The reference smectite and kaolin minerals showed a range of RIP values, even though their RIP values are theoretically zero. The RIP values had a significant positive correlation with the total K content of all the reference clay minerals (r_s = 0.621*). This indicated that the retention ability for ¹³⁷Cs depended more on the content of illite, as impurity, rather than the type of bulk mineral. Hence, the contribution of illite to the magnitude of the RIP was elucidated by the combination of measurement of total K content and XRD analysis.     

Suspected spontaneous hyperadrenocorticism in a young experimental beagle dog

A 6-month-old female beagle dog, assigned to the low-dose group in a toxicity study, was evaluated for compound toxicity, and spontaneous hyperadrenocorticism was suspected. The animal had an externally apparent distended abdomen on clinical examination upon arrival. Pre-dose clinical pathology showed slightly higher erythroid parameters and stress leukogram on hematology; plasma biochemistry showed higher total protein, gamma-glutamyl transferase, total cholesterol, and triglyceride levels than the reference data. On necropsy, a prominent increase in adipose tissues of the subcutis and abdomen and increased weight of the adrenal gland and liver were observed. Histopathology revealed diffuse hyperplasia of adrenocortical cells in the zona fasciculata and reticularis, cortical atrophy of the thymus, and abundant glycogen accumulation in the hepatocytes. These findings were incidental and not test-substance-related. Electron microscopy of the adrenocortical cells in the zona fasciculata revealed decreased typical translucent lipid droplets, increased electron-dense lipid droplets, and abundant smooth endoplasmic reticulum and lysosomes. Additionally, increased numbers of various sizes and forms of mitochondria with tubular, vesicular, or lamellar cristae compared to that of normal animals were observed. These ultrastructural characteristics of the adrenocortical cells suggested hyperfunction. The pre-dose plasma cortisol levels were slightly higher than those of other females assigned to the toxicity study, while plasma adrenocorticotropic hormone levels were within the normal range. These findings indicate that hyperadrenocorticism is a possible cause of the systemic changes in this case.     

Electrophoretic karyotyping and mapping of pathotype-specific DNA sequences in Japanese isolates of <Emphasis Type="Italic">Verticillium dahliae</Emphasis>

The chromosome number and electrophoretic karyotype of Japanese isolates of Verticillium dahliae were investigated. In a genomic Southern blot analysis of seven isolates probed with a telomere consensus sequence (TTAGGG)₅, 12 or 14 bands were observed. Furthermore, pulsed-field gel electrophoresis (PFGE) of these isolates revealed five or six chromosomal bands. A band (approx. 3.5 Mbp) common to all isolates apparently contained more than two chromosomes. From these results, we concluded that each isolate’s chromosome number is six (an eggplant pathotype isolate) or seven (all isolates of tomato and sweet pepper pathotypes). Although the chromosome sizes differed among isolates, karyotypes were similar within tomato and sweet pepper pathotypes. A small chromosome (approx. 1.8 Mbp) was observed only in the sweet pepper pathotype. Subsequent PFGE-Southern hybridization analyses revealed that the three DNA fragments specific to tomato pathotype are located on the same chromosome. These results suggest that the tomato-pathotype-specific DNA sequences might coexist on one chromosome.     

Overexpression of the LASAP2 gene for secretory acid phosphatase in white lupin improves the phosphorus uptake and growth of tobacco plants

Secretion of acid phosphatase (APase) from the roots to take up phosphorus (P) is a well-known strategy of plants under P-deficient conditions. White lupin, which shows vigorous growth in low-P soils, is noted for its ability to secrete APase under P-deficient conditions. The APase secreted by white lupin roots is stable in soil solution and shows low substrate specificity, suggesting that genetic modification of plants using the APase gene LASAP2 might improve their ability to use organic P. The objective of the present study was to evaluate the potential of LASAP2 transgenic plants to increase organic P utilization. Dry matter production and P accumulation were higher in LASAP2 transgenic tobacco plants grown in gel media containing soluble phytate as the sole P source than in wild-type tobacco plants. Phosphorus uptake by the transgenic plants also increased in soil culture conditions. LASAP2 was apparently more effective in the liberation of organic P, including phytate, in the soil than the native tobacco APase. Thus, the enzymatic stability of LASAP2 in the soil appears to be an important factor for P acquisition.     

Nitrogen immobilization by wood-chip application: Protecting water quality in a northern hardwood forest

Forest harvesting disrupts the nitrogen cycle, which may affect stream water quality by increasing nitrate concentrations, reducing pH and acid neutralizing capacity, and mobilizing aluminum and base cations. We tested the application of wood chips derived from logging slash to increase immobilization of N after harvesting, which should reduce nitrate flux to streams. In August 2004, a stand of northern hardwoods was patch-clearcut in the Catskill Mountains, NY, and four replicates of three treatments were implemented in five 0.2-ha cut patches. Wood chips were applied to the soil surface at a rate equivalent to the amount of slash smaller than eight inches in diameter (1× treatment). A second treatment doubled that rate (2×), and a third treatment received no chips (0×). Additionally, three uncut reference plots were established in nearby forested areas. Ion exchange resin bags and soil KCl-extractions were used to monitor nitrate availability in the upper 5–10 cm of soil approximately every seven weeks, except in winter. Resin bags indicated that the wood chips retained 30% or 42% of the nitrate pulse, while for KCl extracts, the retention rate was 78% or 100% of the difference between 0× and uncut plots. During the fall following harvest, wood-chip treated plots had resin bag soil nitrate concentrations about 25% of those in 0× plots (p = 0.0001). In the first growing season after the cut, nitrate concentrations in wood-chip treated plots for KCl extracts were 13% of those in 0× treatments (p = 0.03) in May and about half those in 0× treatments (p = 0.01) in July for resin bags. During spring snowmelt, however, nitrate concentrations were high and indistinguishable among treatments, including the uncut reference plots for resin bags and below detection limit for KCl extracts. Wood chips incubated in litterbags had an initial C:N of 125:1, which then decreased to 70:1 after one year of field incubation. These changes in C:N values indicate that the wood-chip application can potentially immobilize between 19 and 38 kg N ha⁻¹ in the first year after harvesting, depending on the rate of wood-chip application. Our results suggest that the application of wood chips following harvesting operations can contribute to the protection of water quality and warrant additional research as a new Best Management Practice following cutting in regions that receive elevated levels of atmospheric N deposition.     

Exploring the Socio-Economic Situation of Plantation Villagers: A Case Study in Myanmar Bago Yoma

Since the early 1980s, Myanmar Forest Department has been recruiting shifting cultivators, establishing plantation villages and applying the taungya method in establishing teak plantations. From the beginning, there has been an argument about whether the program is creating ‘forest protective groups’ or ‘forest destructive groups’. A key determinant to that question from the research viewpoint is the socio-economic situation; knowing the present situation of the plantation villagers can help to understand their forest management practices. Interview surveys were carried out in three villages in Bago Yoma, the main region of the special teak plantation program, to examine the current economic benefits to plantation villagers. Questions were designed mainly to explore the incentives for people participation and the socio-economic situations of the plantation villagers. Principal component analysis was used to group landholder types. It was found that local people are willing to participate in the initial establishment of plantations. However, all the incentives relating to plantation projects are temporary, with no long-term consideration for taungya farmers, which jeopardizes the plan to create forest protective groups. It is concluded that the time has come for the Myanmar Forest Department to change its main aim of earning foreign exchange from establishment of teak plantations through the taungya method to redressing deforestation through people participation based on rural socio-economic development.