Influence of sediment phosphorus on utilization efficiency of phosphate fertilizer: a mesocosm study

Influence of initial sediment phosphorus content of the pond sediment on P dose efficiency was examined in a laboratory experiment using four types of sediments collected from ponds located along a nutrient gradient in a sewage‐fed fish farm. Each sediment type (500 g) was dispensed in a glass jar with water and treated with single super phosphate (SSP) treatment at 1.25, 2.5, 5.0 and 10.0 mg L^?1 in triplicate. Determination of orthophosphate (OP) and soluble reactive phosphorus (SRP) in water and available and total P in sediment showed increased response in relation to dose and time. At a given dose, the rate of increase for all species of phosphate in sediment or water was maximum in the case of local pond (LP) soil followed by stocking pond (SP), facultative pond (FP) and anaerobic pond (AP) soil, suggesting that utililization of phosphate fertilizer was much better under oligotrophic conditions than under eutrophic states. The SSP‐induced OP peak at 10 mg L^?1 in LP sediment was similar to that of 5.0 mg L^?1 in AP sediment containing 59% enhanced initial phosphate, implying that fertilizer application can be profitably reduced by 18% in the former without limiting the OP level in the water phase. It is concluded that dosage selection of phosphorus fertilizer in aquaculture ponds should be based on an evaluation of the initial P status of the system.     

Flood vulnerability assessment in the light of rice cultivation characteristics in Mekong River flood plain in Cambodia

More than 2 million hectares of the lower Mekong River flood plain (Cambodian Plain), which extends from southern Cambodia to the border with Vietnam, is cultivated with rice; and more than 60 % of the population in the flood plain are farmers involved in rice cultivation. Rice production in this area is seriously affected by floods almost every year; on the other hand, the farmers need floodwater for their crop fields. Therefore, the farming in this area is about coping with floods, and flood countermeasures should be carefully planned based on good understanding of the livelihood of the farmers. Thus, this study aimed to identify flood-vulnerable rice-growing communities in the Mekong River flood plain in Cambodia. In this research, we proposed a useful methodology to make flood inundation maps by conducting a simple analysis by combining satellite-based digital elevation model (DEM) and river water level data based on the flood characteristics in this area. Then, rice-crop vulnerability maps were derived from previous maps and results from other past researches using the geographical information system (GIS). Comparison among those maps was also conducted to find out the relationship between DEM and people’s lifestyles in this area. This simple, inexpensive methodology was proven useful to understand major crop damage and vulnerability in relation to floods in this area, based on flood characteristics in the Cambodian flood plain. Because the method is a GIS-based approach, it can deliver more accurate results when provided with more accurate data.

     

Isolation and Characterization of Cadmium- and Arsenic-Absorbing Bacteria for Bioremediation

The contamination of hazardous metal(loid) is one of the serious environmental and human health risks. This study isolated a total of 40 cadmium (Cd)- and arsenic (As)-resistant bacterial isolates from coastal sediments by pour plate technique using tryptic soy agar supplemented with Cd or As (50 mg l^?1) for use as metal(loid) bioremediation agents. Out of 40, 4 isolates, RCd3, RCd6, RAs7, and RAs10, showed a relatively higher growth rate in Cd- or As-supplemented culture media which were selected for further study. The selected isolates showed a high minimum inhibitory concentration (60–400 mg l^?1 for Cd and 400–2200 mg l^?1 for As), which demonstrated their remarkable Cd and As resistance capabilities. The metal(loid) removal efficiencies (0.032–0.268 μg Cd h^?1 mg^?1 and 0.0003–0.0172 μg As h^?1 mg^?1 [wet weight cell]) of selected isolates indicated their greater magnitude in absorbing Cd compared to As from water. Phylogenetic analysis of the 16S rDNA sequences revealed that isolates RCd3, RCd6, RAs7, and RAs10 were closely related to Acinetobacter brisouii, Pseudomonas abietaniphila, Exiguobacterium aestuarii, and Planococcus rifietoensis, respectively. Because of high Cd and As resistance and removal efficiency, the selected isolates can survive in a high metal(loid)-contaminated environment and could be a potential tool for bioremediation of high metal(loid)-contaminated effluents to protect the aquatic environment.     

Dynamics of thymocyte-stromal cell interactions visualized by two-photon microscopy

Thymocytes are selected to mature according to their ability to interact with self major histocompatibility complex (MHC)-peptide complexes displayed on the thymic stroma. Using two-photon microscopy, we performed real-time analysis of the cellular contacts made by developing thymocytes undergoing positive selection in a three-dimensional thymic organ culture. A large fraction of thymocytes within these cultures were highly motile. MHC recognition was found to increase the duration of thymocyte-stromal cell interactions and occurred as both long-lived cellular associations displaying stable cell-cell contacts and as shorter, highly dynamic contacts. Our results identify the diversity and dynamics of thymocyte interactions during positive selection.     

Flood vulnerability assessment in the light of rice cultivation characteristics in Mekong River flood plain in Cambodia

Demographic changes, such as aging and depopulation in rural areas, are major reasons for the recent abandonment of the terraced paddy fields in Japan. In addition, the low productivity of terraced paddy fields, due to their small area and the difficulty of using machinery on the plots, further abet this trend. Recent research has shown a growing interest in multifunctional conservation and maintenance of the ecosystem and traditional agro-culture of terraced paddy fields. This paper aims to elaborate on the conservation activities of endangered terraced paddy fields in Japan, by using the case of Shiroyone Senmaida to discuss conservation experience and lessons, and recommend future strategies for adaptive management of the rice terraces under the GIAHS framework, as well as the next necessary steps for research. As an outstanding cultural landscape and tourist attraction in Noto Peninsula, the conservation scheme combining financial support from governmental subsidy, the “owner system” of interaction with urban dwellers, and labor support by conservationist volunteers has contributed to the conservation of traditional farming on Senmaida’s terraced paddy fields. Still, as is the case in other parts of Japan, lack of financial support and an aging farming population threaten conservation of terraced paddy fields in Noto Peninsula.     

CNP Ratio and Dose Regulated Production of Water Chestnut <Emphasis Type="Italic">Trapa</Emphasis>: Social and Environmental Implications

Water chest nut Trapa is a minor fruit crop and potential carbon sequester of atmospheric carbon. Mass production of water chest nut using a vast number of unused small water bodies and derelict waters is a win-win-win-win strategy toward mitigation of global warming, nutritional security, empowerment and resource utilization. Growth performance of Trapa was conducted in small culture units using different CNP ratios (25:02:01; 101:08:01; 290:01:01) at a fixed dose (0.2 kg/tank) of mixed manure with different doses (100, 200, 400, 600 g) of optimal CNP ratio (101:08:01) during the life cycle of Trapa. The total number of fruits and the wet weight of Trapa in different dose treatments ranged from 56 to 192 and from 258 to 379 g/tank. Yield of Trapa remained maximum when CNP ratio was 101:8:1 at 200 g/tank and the dosage was 200 g/tank with the optimal CNP ratio (134 g) and then declined with further rise in fertilizer dose. The proximate analysis of Trapa revealed the highest phosphorus content in all the tissues (fruit, leaf, and root) of Trapa grown in the CNP ratio of 101:08:01. Of the total amount of carbon in Trapa, contribution was maximum by the fruit (38–41%), followed by leaf (27–35%) and root (23–32%) in different ratio treatment. The C content of harvested Trapa grown in different CNP ratios (Table 4) was higher in fruit (38–41%) followed by leaf (27–35%) and root (23–32%) among tissues. The amount of C observed in control (32%) increased by 6% in 25:02:01 (34%) which was higher than remaining two treatments (31%). Dry weight or total carbon content of water chestnut tended to rise with increasing levels of phosphate of water from the dosage of 100 to 200 g with optimal CNP ratio and declined thereafter. A direct relationship between the dry weight or carbon content of Trapa and the total carbon content or phosphate to total carbon ratio of water was established. However, the carbon content remained between 27–32% in all the three tissues of Trapa culture when cultured in different dose treatments. It is reasonable to conclude that water chestnut may be promoted for mass cultivation using the recommended culture protocol that would help trapping atmospheric carbon, provide nutritional security and employment generation and resource utilization.     

Physiological Mechanism and Nutrient Management Strategies for Flood Tolerance in Rice Grown in Lowland Flood Prone Ecosystem

Journal of Crop Science and Biotechnology - In flood-prone areas, rice must have flood tolerance characteristics either through genotypic selections or by nutrient application management...