On the components of soil humic acids VII

The writers already made it clear that by active alumina the humic acids of A- and B-types contained in various soils could be separated into 3 or 4 components (1). And moreover, absorption spectra (2), nitrogen constituents (3) and colloidal nature (4) of them were studied for the purpose of examining their qualities.     

Nutritional Study of Silicon in Graminaceous Crops (Part 1)

Silicon in crop plants has been studied in various ways, for example, in elucidating its effects on phosphorus and nitrogen uptake by roots, or increase of resistance to diseases and insect pests, Graminaceous crops generally contain much more silicon in them than other families of plants, Remarkable effects of silicon application to plants On their growth appear especially in case they have contained about 5 to 10% of silicon before-hand. When silicon content in plants, on the other hand, is quite low, such as less than 0.5% for dry matter, plants show retardation of their grOwth at both vegetative and reproductive stages. It may be deduced that silicon applied to plants might play a role in different ways in cases where they have already had either considerable or quite small amounts of silicon. While the former case has been studied very much, extreme deficiency of silicon in plants has been investigated very little^1)-8). Experiments reported here were designed for elucidating roles of silicon in its defiCient plants and getting information about the essentiality of silicon for them.     

Nutritional Study of Silicon in Graminaceous Crops (Part 2)

It was reported in the previous paper₁₎ that rice plants showed retardation of their vegetative growth and decrease of degree of seed setting when their silicon content was extremely low. It was concluded from these facts that silicon might most probably be essential for rice. But physiological functions or behaviours of silicon in plants should be clarified in order to solve this problem completely. Uptake and disttibution of silicon in rice plants were first investigated here, especially compared with phosphorus. A possibility of using silicon radioactive isotope (₃₁Si) for this kind of experiment was also investigated. Although tracer techniques have been greatly developed in elucidating behaviours or physiological functions of various elements in plants, radioactive silicon isotopes have been used very little in this field of science because of this very short half lives. Recently Rothbuhr and Scott ²⁾ reported having used radioactive silicon isotope for uptake experiments by plants in Harwell, England. Since a nuclear reactor (JRR-I) in the Japanese Atomic Energy Research Institute started to work in 1959, radioactive isotopes which have rather short half lives have become available for plant experiments in Japan. Methods of preparation of ³¹Si for plant experiments were examined and by using ³¹Si it was studied how silicon was absorbed and translocated by rice and wheat under some particular environmental conditions, and also how the uptake and distribution of it in rice plants were affected by various kinds of metabolic inhibitors.     

On the components of soil humic acids (Part iv) on the absorption spectra of the components of B-type humic acid

Introduction

Concerning the A-type humic acid found in different kinds of soil the writers fractionated each of its components and measured its lightabsorbing power and compared the characteristics of those components.     

Hydroxy-Al complexes of montmorillonite and vermiculite and identification of intergrades of montmorillonite-chlorite and vermiculite-chlorite in soils

Much evidence has indicated that the occurrence of montmorillonite and vermiculite containing Al-interlayers is very common in solis, particularly acid soils. Viewed in the light of soil clay minerology, it would be required to investigate the properties of their original minerals. For the latter purpose, the Al-interlayer has been removed prior to the Mg-glycerol,K-saturation and heating tests for identification of montmorillonite and vermiculite. Its removal has been accomplished in sevsral ways; KOH plus KCl (1), NH₄F, KCl plus HCl (2), Na-citrate (3),400C de hydroxylation-NaOH (4) dissolution. Although these methods are effective for the removal of Al-interlayers, they seem drastically to affect the minerals or are time-consuming. Inthe course of the study of hydroxy-Al interlaid complexes of expanding 2:1 layer lattice clay minerals, the authors have noticed the difference between the (001) spacings of hydroxy-Al complexes of montmorillonite and vermiculite; the former exhibited the 20 A basal spacing at room temperature against the 14 A spacing of the latter. This difference might be useful for differentiating montnmorillonite-chlorite intergrades in soils.     

Importance of 2,4-DAPG in the biological control of brown patch by Pseudomonas fluorescens HP72 and newly identified genes involved in 2,4-DAPG biosynthesis

The Pseudomonas fluorescens strain HP72 used as biocontrol agent was isolated from the roots of creeping bentgrass on brown patch-suppressive soil. This strain can suppress brown patch disease caused by Rhizoctonia solani. The analysis of secondary metabolites from strain HP72 revealed that it produced known antifungal compounds, 2,4-diacetylphloroglucinol (2,4-DA-PG), HCN, and a fluorescent siderophore. In the present study, the Tn5inserted mutants of strain HP72, which did not show any antifungal activity, were selected. None of the mutants produced 2,4-DA-PG but they produced a fluorescent siderophore, while some strains produced HCN. Therefore, it is suggested that 2,4-DA-PG plays a major role in the biological control of brown patch disease caused by R. solani. In the genomic region where Tn5 was inserted, two open reading frames (ORFs A and B), which are not included in the 2,4-DAPG gene cluster of HP72, were detected. It was demonstrated that ORFs A and flare involved in the regulation of 2,4-DAPG biosynthesis.     

A seasonal behavior of surface soil moisture condition in a reclaimed tropical peatland

Soil moisture condition is essential to regulate the release of soil carbon from a drained peatland since aerobic microbial activities can be encouraged through oxygen supply associated with dewatering the soil layer while they may be discouraged under too dry conditions. Aiming to characterize the soil moisture condition in a reclaimed tropical peatland, we monitored the volumetric water content at 5?cm depth (θ _5?cm), groundwater level (GWL) and rainfall for 20 months from March 2010 to November 2011 in an oil palm field in Nakhon-Si-Thammarat, Thailand. We also measured the soil water retention curve and the unsaturated hydraulic conductivity (k) for a series of matric potential (h) to simulate the moisture condition monitored in the field by using the Buckingham-Darcy's flux law. During the dry season in 2010, the θ _5?cm consistently stayed lower than 0.35?m³?m^–3 with the GWL lower than a depth of 30?cm. In the transition from the dry season to the rainy season in 2010, the GWL rose to the land surface with peaks and dips across the time for about one month with the θ _5?cm increasing toward saturation. During the rainy season where the GWL stayed near or above the land surface, the θ _5?cm remained the field-saturated value of 0.58?m³?m^–3 on average, less than the laboratory-saturated value of 0.63?m³?m^–3, suggesting the development of a significant amount of entrapped air-phase. Hysteretic behavior in the measured θ _5?cm–GWL relation also supported that the top soil layer refuses to absorb water in wetting processes. The simulated θ _5?cm based on the measured k(h) and soil water retention curves demonstrated that the ease with which the top soil dries during a dry season was due mainly to the low k(h) value in the dried condition, while the slope of the θ(h) curve was so moderate that the soil layer could retain moisture for maintaining liquid water supply to the surface from the dropped GWL. Sensitivity analyses while varying the magnitude of both k(h) and evaporation rate (E) suggested that the k(h) function was more deterministic than the value of E in making the land surface easily dried. As the GWL stayed lower than 30?cm in depth for a total of 187 days out of the year monitored, while surface-ponding conditions took place for 120 days of the year, it was concluded that either the extremely dried condition or the saturated-moisture condition had dominantly occurred in the study site through a year and, thus, there may only be a limited time when soil organic matter near the land surface is in favorable moisture conditions for aerobic decomposition.     

Comparative analysis of the relationship between Cs and K in soil and plant parts toward control of Cs accumulation in rice

The effect of soil exchangeable potassium (K) and cesium (Cs) levels on Cs uptake and accumulation in different parts of rice (Oryza sativa L.) plants were examined using paddy soils with diverse exchangeable K and Cs in pot experiments. Aboveground Cs uptake decreased with higher exchangeable K and was linearly correlated with exchangeable Cs/K ratios, indicating competitive absorption of these elements by roots. Variation in Cs concentration in brown rice among soils was also related to the exchangeable Cs/K ratio. The exchangeable Cs/K ratio was positively reflected in the Cs/K concentration ratio in each plant part, with a specific slope, suggesting that Cs transport was coordinated with K transport and that there were regulated discriminations of Cs against K in the translocation process among parts. The Cs/K ratio was higher in brown rice and dead leaves than in active leaves, stems and husks. The distribution of Cs accumulation in brown rice was 14.5% on average, but it was variable and negatively related to K concentration in the stem. The Cs distribution in aboveground plant parts also decreased with higher K concentration in the root. These results imply the importance of the competitiveness with K in the root absorption and translocation of Cs within the plant. Based on the observed relationship between Cs and K, effective K management and other measures to control Cs accumulation in plant parts are discussed.     

A supernodulating mutant isolated from soybean cultivar enrei

Abstract

Symbiotic nitrogen fixation in nodules of legumes depends on the complex interaction between the legume plant and (Brady)Rhizobium bacteria. Nodule formation and nitrogen fixation are closely regulated by both the host plant and the microsymbiont. Plant mutants with altered symbiotic performance are considered to be useful to gain a better understanding of the plant—microbe interactions in the legume—(Brady)Rhizobium symbiosis (Jacobsen 1984; Carroll et al 1985a, b; Park and Buttery 1988; Duc and Messager 1989; Gremaud and Harper 1989). Recently, Carroll et al. (1985a, b) have isolated the supernodulating mutants of the soybean cv. “Bragg,” which display a very large number of nodules and “nitrate-tolerant-symbiotic” (nts) characteristics. More recently, Gremaud and Harper (1989) have also isolated similar mutants from the soybean cv. “Williams.” These mutants not only provide materials that are useful for investigatings on the interaction in the nodule formation processes but also for agricultural practice. In particular, the nitrate-tolerance of these supernodulating mutants (Carroll et al. 1985b; Gremaud and Harper 1989) is useful for their cultivation in Japan where the level of soil nitrogen in fields is generally high. However, the cultivars previously used for the isolation of these mutants cannot adapt easily in Japanese climate due to different Maturity Group. Therefore, we attempted to isolate mutants with altered symbiotic phenotypes from the soybean cultivar “Enrei,” one of the most common cultivars in Japan.