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1.
Methane is the second most important greenhouse gas which contributes to global warming. As an important source of methane, rice paddy fields contribute an estimated lO% to the global methane emissions (IPCe 1992). Land use and agricultural practices significantly affect atmospheric methane fluxes (Bouwman 1989; Hütsch et al. 1994). Microbial oxidation of atmospheric methane in terrestrial environments is the only known net biological methane sink and the process consumes the equivalent of 1–l0% of the total global emission (Adamsen and King 1993). Methane-oxidizing bacteria (MOB, methanotrophic bacteria) are considered to be obligately or facultatively aerobic respiratory bacteria that can utilize methane as the sole source of carbon and energy for growth (Hanson et al. 1992; Roslev and King 1994). As a result, they are important regulators of atmospheric methane fluxes in nature (Mancinelli 1995). MOB have been isolated from a variety of environments including freshwater lakes, wetlands, and the open ocean (Whittenbury et al. 197Gb; Saralov et al. 1984; Holzapfel-Pschorn et al. 1985; Hanson et al. 1992; Omelchenko et al. 1993; Bowman et al. 1993a; Mancinelli 1995). However, reports on the isolation of MOB from rice paddy fields are limited. More information is needed on the ecology and taxonomy of MOB in paddy fields.  相似文献   

2.
In wetland ecosystems, such as rice fields, methanogenic bacteria (MB) play important roles in global carbon cycling as terminal organic decomposers and in hydrogen cycling as hydrogen consumers, leading to methane production (Jorgensen 1982). In the global atmosphere, concentration of methane has been increasing by about 1% per year (Blake and Rowland 1986; Bouwman 1989; Dlugokensky et al. 1994) and it is considered that 80% is of biological origin (Seiler 1984). The environmental impact of methane on global warming has also been confirmed (Chappellaz et al. 1990). Rice paddy fields contribute to an estimated 10% of the global methane emission (Bouwman 1989; IPCC 1992) and the intensification of paddy cultivation may contribute considerably to the gradual increase of atmospheric methane (Rasmussen and Khalil 1981). From 1970 to 1990, rice production increased by 110% in West Africa (FAO 1970, 1990), as a direct result of encroachment on new lands throughout most of West Africa (Windmeijer and Andriesse 1993; Issaka et al. 1996a, b). In Burkina Faso, about 85% of the rice cultivation areas are lowlands (Sié 1991). In recent years, many studies on methane emission from paddy fields and limited ecological studies on methanogenic populations have been conducted (Schütz et al. 1989; Asakawa and Hayano 1995; Adachi et al. 1996). However, studies on both methane emission and populations of methanogens in African paddy fields are very limited. Garcia et al. (1974) enumerated methanogenic populations in Sénégal rice soils by the most probable number (MPN) method. With the gradual increase in the land area under rice cultivation, more information is needed on methane fluxes, populations, and species of methanogens in paddy fields of West Africa. We reported here the enumeration of methanogenic populations in the soils of lowland paddy fields located in the Sudan and Guinea Savanna zones of Burkina Faso (West Africa) by the MPN method.  相似文献   

3.
Excess nitrate (NO3-) in lakes and streams has deleterious effects for environmental and human health. Nitrate concentrations have become problematic in agricultural watersheds due to increased use of fertilizers and improper management of livestock wastes. Research has indicated that the planting and/or preservation of riparian buffer zones can be an effective means of reducing pollution from agricultural fields (Osborne and Kovacic, 1993; Jordan et al., 1992; Simmons et al., 1992). Biological denitrification is the most desirable means of nitrate attenuation as the microbial conversion of NO3- removes nitrate from the watershed in the form of N gases. Despite the inherent value of biological denitrification, a comprehensive review discussing the role of this process in removing nitrate from riparian zones is lacking. In this paper we examine the results and conclusions of past research on the topic of denitrification in riparian zones and make recommendations for future research in this area. The need for subsurface denitrification assays in riparian zones is emphasized.  相似文献   

4.
Abstract

Green manure legumes are often used to compare biomass production as well as nitrogen-fixing capacity. Mineral deficiency often limits the symbiotic nitrogen fixation of many legumes, thus limiting their productivity despite their high yielding potential (O’Hara et al. 1988; Flis et al. 1993). Leguminous species require large amounts of P for growth, nodulation, and nitrogen fixation. Consequently, they are often unable to grow in acid soils with low available P. The low P availability in tropical acid soils often arises from fixation of P by Al and Fe in soil. Generally, Al and Fe-phosphates are relatively unavailable to plants (McLachlan 1976; Ae et al. 1990).  相似文献   

5.
Under iron deficient conditions, graminaceous plants secrete mugineic acid family phytosiderophores (MAs) from their roots to dissolve sparingly soluble iron compounds in the rhizosphere, and take up iron in the form of an Fe3+-MAs complex (Takagi 1976). A good correlation has been reported between the tolerance of Fe-deficiency and the amount of secreted MAs (Takagi 1993). Therefore, by using the genes involved in MAs biosynthesis, molecular breeding might produce transgenic plants tolerant to Fe-deficiency with a high level of MAs secretion. The biosynthetic pathway of MAs from L-methionine has been clarified (Fig. 1) and the enzymes participating in this process are now being investigated to isolate the genes responsible. Nicotianamine aminotransferase (NAAT) catalyzes the amino group transfer between nicotianamine (NA) and 2-oxoglutaric acid (Fig. 1). In order to purify NAAT, enzyme assay methods for NAAT have been developed and modified (Shojima et al. 1990; Ohata et al. 1993; Kanazawa et al. 1994). Some characteristics of NAAT have been reported using these enzyme assay methods (Kanazawa et al. 1994, 1995). Here, we further investigate some characteristics of this enzyme to improve the enzyme assay method, namely 1) the effect of K+ and Mg2+ on NAAT activity in vitro, and 2) the direct influence of MAs, Fe3+, and Fe2+ on NAAT activity. In addition, based on these results, the induction of enzyme activity by Fe-deficiency and suppression of the activity by Fe-resupply was investigated, by applying the new enzyme assay method.  相似文献   

6.
Extract

Since a rise in atmospheric carbon dioxide (CO2) concentration is expected to lead to global warming, it is important to quantify the global carbon circulation. The CO2 evolution rate from soil has usually been measured by one of three methods: 1) CO2 absorption (Anderson 1982), where the evolved CO2 is absorbed in an alkali solution and the content subsequently determined, 2) closed chamber (Rolston 1986) in which the CO2 evolution rate is calculated from the increase of the CO2 concentration in a closed chamber covering the soil surface, and 3) flow-through chamber (Rolston 1986) in which a fixed rate of ambient air is pumped through an open chamber and the difference in the. CO2 concentration between the inlet and the outlet is measured. Although the CO2 absorption method is very simple in terms of apparatus and procedure, the determined CO2 evolution rate tends to be underestimated in cases where the evolved CO2 is not fully absorbed in the alkali solution (Ewel et al. 1987; Sakamoto and Yoshida 1988), or overestimated in cases where the CO2 concentration in the chamber is too low to stimulate microbial activity (Koizumi et al. 1991; Nakadai et al. 1993), In the closed chamber method, when the gas concentration in the chamber is higher than that of the ambient air, gas diffusion from the soil to the atmosphere is restricted (Denmead 1978). At this point, the flow-through chamber method seems to be most suitable for measuring the CO2 evolution rate, because the rate is determined under nearly natural conditions. However, this method has a disadvantage in that the apparatus is composed of an infra-red CO2 analyzer, air pumps, mass flow meters, a recorder, and other items, which are too large, heavy, and complex to use in the field (Freijer and Bouten 1991). Hence, in spite of the above limitations, most of the studies on CO2 evolution in situ have been carried out using the CO2 absorption method (Kowalenko et al. 1978; Seto et al. 1978a, b; Ewel et al 1981, 1987; Gupta and Singh 1981; Reinke et al. 1981; Edwards and Ros-Todd 1983; Grahammer et al. 1991) or the closed chamber method (Naganawa et al. 1989; Mariko et al. 1994). The flow-through chamber method has been used only at sites where electric power supply and other types of equipment were available (Mathes and Schriefer 1985; Ewel et al. 1987; Nakadai et al. 1993). In the present report a flow-through chamber method using a portable CO2 analyzer system was examined, for the determination of CO2 evolution from soil without an electric power supply or other special equipment.  相似文献   

7.
Abstract

It is generally recognized that the nitrification activity in acid soils is very low. Indeed, nitrification in mineral soils has been found to be negligible at pH values below 5.0 (Dancer et al. 1973; Nyborg and Hoyt 1978). However, it was reported that autotrophic nitrification occurred in some tea soils at pH levels far below 5.0 (Walker and Wickramasinghe 1979; Hayatsu and Kosuge 1993). An acidophilic ammonia-oxidizing bacterium has been recently isolated from strongly acidic tea soils in Japan (Hayatsu 1993). On the other hand, fertilization has-been considered to be an important factor influencing nitrification in agricultural soils. For example, several studies have shown that the addition of ammoniacal fertilizer to soils can lead to the increase of the populations of Nitrosomonas (McLaren 1971; Ardakani et al. 1974). Liming of acidic soils also tends to stimulate the nitrification activity (Dancer et al. 1973; Nyborg and Hoyt 1978). Although nitrification has been studied in a wide variety of agricultural soils, there is little information available on nitrification in tea soils. The effect of fertilization on nitrification in tea soils is poorly documented.  相似文献   

8.
Aluminum (Al) toxicity is a major factor limiting yield production on acid soils (Foy 1983). The initial symptom of Al toxicity in many plants is manifested by the inhibition of root elongation (Ownby and Popham 1990; Llugany et al. 1994; Sasaki et al. 1994; Horst et al. 1997), which occurs during a very short period of time after exposure to Al (Llugany et al. 1994; Staß and Horst 1995). In a large number of recent reports, it was shown that the root apex plays a major role in the Al-sensitivity and response mechanisms (Zhang et al. 1994; Sasaki et al. 1997; Sivaguru and Horst 1998). However, it is interesting to note that stimulatory effects of Al on the growth of plants have also been reported in some studies (Chenery 1955; Konishi et al. 1985; Huang and Bachelard 1993; Osaki et al. 1997). In tea plant (Camellia sinensis L.) a stimulatory effect of Al on the growth was also demonstrated in some experiments, using intact plant (Chenery 1955; Konishi et al. 1985), cultured roots (Tsuji et al. 1994), and pollen tubes (Yokota et al. 1997). The growth of tea roots was typically more stimulated than that of shoots by Al (Konishi et al. 1985). It was assumed that Al effects might be due to the amelioration of phosphorus absorption (Konishi et al. 1985), secretion of malic acid from roots to dissolve aluminum phosphate in the rhizosphere (Jayman and Sivasubramaniam 1975), stimulation of growth of microorganisms on the root surface (Konishi 1990) or replacement of some functions of boron (Konishi 1992; Yokota et al. 1997). However, the stimulatory effects of Al on tea plant growth have not yet been el ucidated.

The formation of callose (1,3-β-glucan) has been reported as a common plant response to a variety of stresses, as well as mechanical, biophysical, chemical, and biological injury (Jaffe and Leopold 1984; Zhang et al. 1994). Increased synthesis of callose has been observed upon exposure to excess amounts of some elements, such as boron (McNairn and Currier 1965), cobalt, nickel, zinc (Peterson and Rauser 1979), and manganese (Wissemeier and Horst} 1987, 1992). Callose synthesis was also induced by Al in the roots of Triticum aestivum (Zhang et al. 1994) and Zea mays (Horst et al. 1997; Sivaguru and Horst 1998), suspension-cultured cells of Glycine max (Staß and Horst 1995), and protoplasts of Avena sativa (Schaeffer and Walton 1990) and Zea mays (Wagatsuma et al. 1995). Induction of callose synthesis in roots seems to be a very rapid physiological indicator of Al-induced injury or genotypical differences in Al sensitivity (Wissemeier and Horst 1992; Zhang et al. 1994; Horst et al. 1997). Nevertheless, Al-induced callose synthesis in tea plant, whose growth is stimulated by suitable Al concentrations, has not been described yet. Therefore, to elucidate the physiological basic effects of Al on tea plant, callose synthesis affected by Al in the root tips of intact plants was analyzed in the present study.  相似文献   

9.
Although zinc (Zn) is an essential element for the growth of higher plants, excess supply may lead to growth inhibition. Symptoms of Zn toxicity are characterized by a reduction in root growth and leaf expansion followed by chlorosis (Mengel and Kirkby 1987), especially root elongation is severely inhibited (Godbold et al. 1983). Due to the increase of input of Zn to farmland by the application of sewage sludge or large amounts of Zn-containing pig manure, Zn toxicity may become an important problem in certain regions (Ruano et al. 1987). In addition, Zn toxicity is also a problem in some acidic soils (Takahashi et al. 1980).

Increasing soil pH by liming is the most effective procedure for decreasing both Zn content and Zn toxicity in plants (White et al. 1979), because Zn solubility decreases 100 times for each unit increase in pH (Neue and Lantin 1994). As an alternative approach, application of large amounts of phosphorus (P) fertilizer was employed to detoxify Zn (Takahashi et al. 1980). However, the mechanisms responsible for the detoxification of the excess Zn by P is remained to be elucidated.

Interactions between Zn and P, which may occur in the rhizosphere and in the uptake and translocation processes, are complex. To separate these factors, in the present study, pollen tubes of tea (Camellia sinensis L.) were used as a model, and the efrect of P on pollen tube growth under Zn toxicity was studied.  相似文献   

10.
The endosperm cell walls of barley are composed largely of a (1→3)(1→4)‐β‐d ‐glucan commonly known simply as β‐d ‐glucan (Wood 2001). There has been much research into the characteristics of barley β‐glucan because of the influence of this polysaccharide on performance of barley in malting and subsequent brewing of beer, and in feed value, especially for young chicks (MacGregor and Fincher 1993). The potential for β‐glucan to develop high viscosity is a problem in these uses, but from the perspective of human nutrition, this characteristic may be an advantage. The glycemic response to oat β‐glucan is inversely related to (log)viscosity (Wood et al 1994a) and there is evidence to suggest that the lowering of serum cholesterol levels associated with oat and barley products (Lupton et al 1994; Wood and Beer 1998) is at least in part due to the β‐glucan (Braaten et al 1994) and probably also its capacity to develop viscosity in the gastrointestinal tract (Haskell et al 1992).  相似文献   

11.
Abstract

In some of the drainage waters in Hachirogata reclaimed land, a very high concentration of inorganic P (up to 2 mg P L-1) has been recently detected (Sato et al. unpublished). The drainage waters flow into the Lake Hachirogata that surrounds the land. Since the lake is also a reservoir, the water circulates through a closed system. Recently, the eutrophication of the lake has been found to be significant (Akita Prefectural Government 1989) and drainage water has been incriminated as one of the P sources of eutrophication. Therefore, it would be important to analyze the mechanisms responsible for the increase of P release from Hachirogata reclaimed land.  相似文献   

12.
In relation to global warming, a great deal of attention has been paid to methane (CH4 ) emission from paddy fields. The amount of CH4 emitted from paddy fields is now estimated to account for about 12% of the total CH4 emission according to Prather et al. (1995). Harvested area of rough rice in Asia covered 1,320,000 km2 in 1990 and 38% of the area was estimated to be maintained under rainfed conditions (IRRI 1991).  相似文献   

13.
High nitrogen (N) input to rivers requires measures for the reduction of diffuse N pollution. Beside the groundwater, artificial subsurface drainage systems are the main pathways of diffuse N input into rivers. Nevertheless, the N discharge via subsurface drainage systems is one of the main missing links for modeling, especially because of the lack of data bases of subsurface drainage areas. We introduce a method to calculate the normally unknown proportions of drained areas in arable lands improving the existing method by Behrendt et al. (2000). The method is applied for the catchment of Middle Mulde river (area: 2,700 km2) in Saxony/Germany. The data records of the mesoscale soil mapping are allocated to the subsurface‐drainage areas digitalized in representative areas using ARC/INFO GIS. In this way, it is possible to establish a differentiated record of the proportion of subsurface‐drainage area of each regional site type. The results were extrapolated to the entire area by transferring the proportions of subsurface‐drainage areas to areas where no information on drainage areas was available. The approach is well‐suited for future model approaches on a regional scale. By creating and integrating new data sets derived from modern GIS operations, the approach reduces the uncertainty of modeling N and water fluxes.  相似文献   

14.
磷素迁移的动力学方程   总被引：1，自引：0，他引：1  
Studies on kinetics of adsorption and release of phosphorus by soil, a new field in soil chemistry, began only over ten years ago (He et al., 1989; Wang and Zhu, 1988; Zhang and Zhang, 1991; Lin, 1989; Lin and Xue, 1989; Jiang, 1993; Xue et al., 1995; Lü et al., 1997). The stress of this field is laid on the speed at which a soil system reaches balance between adsorption and release of phosphorus. Being more close to the field condition and helpful to explain the mechanism of adsorption and release of the phosphorus by the soil, kinetic methods have attracted much attention of the researchers (Aharoni et al., 1991; Griffin and Jurinak, 1974). Different kinetic equations have been used to describe the characteristics of the adsorption and release of phosphorus by the soil (He et al., 1989; Wang and Zhu, 1988; Lü et al., 1997); however, until now which equations are better remains a point of debate. Phosphorus transport in soil is, in fact, a comprehensive process, which includes adsorption, fixation and release of phosphorus by the soil. This study aimed to determine equations useful for describing phosphorus transport process through fitting the phosphorus transport processes in four soils sampled from Shaanxi Province using 17 types of kinetics equations selected.  相似文献   

15.
Recently, in situ hybridization technique targeted to ribosomal RNA (Delong et al. 1989) has been widely used to detect specific microorganisms in various environments such as marine environment (Nishimura 1995), sediments (Spring et al. 1993), inside of organisms (Amann et al. 1991), and soil (Hahn et al. 1992). This technique provides information not only on microscale localization of the microorganisms but also on their metabolic activities in situ. So far, detection by in situ hybridization targeted to ribosomes in soil has been scarcely reported because two problems arise when this method is applied to soil. The first is that cells in natural soils cannot be easily stained because the cellular ribosome content is low in an oligotrophic soil environment. The second is that non-specific binding of the probes to soil particles and autofluorescence of soil components such as organic matter and mineral particles interfere with the signal from the probe specifically hybridized.  相似文献   

16.
Under Zn deficiency, some major deficiency symptoms were observed on rice plants, i.e., reduction of young leaf elongation and development of necrosis on the expanded leaves. To clarify the former phenomena, the physiological role of Zn was studied from the standpoint of protein synthesis (Kitagishi and Obata 1986; Obata et al. 1994, 1996) and metabolism of auxin (Takaki and Arita 1986; Domingo et al. 1992). In contrast, the direct cause of the latter phenomenon has not yet been studied.  相似文献   

17.
Extract

It was reported that flooded rice soil was an important source of atmospheric CH4 (Cicerone and Shetter 1981; Sciler et al. 1984). In flooded rice soils, CH4 is produced under strict anaerobic conditions by methanogenic bacteria (Jones et al. 1987; Jones 1991). Rice plants carry the produced CH4 from anoxic sediment and release it to the atmosphere (Cicerone and Shetter 1981; Nouchi et al. 1990). More than 90% of emitted CH4 is released through rice plants and the emission pattern usually shows large seasonal variations (Cicerone et al. 1983; Sciler et al. 1984; Inubushi et al. 1989). Since the number of methanogens did not change throughout the rice growth season (Schutz et al. 1989; Mayer and Conrad 1990), seasonal variations of CH4 emission could be ascribed to the activities of methanogens and the amount of available substrates. However, the changes in the methanogenic activities in response to available substrates especially in relation to the growth period of rice plants are poorly documented.  相似文献   

18.
Abstract

Soil protease is an important enzyme in the nitrogen cycle which plays an essential role in the growth of various crops. We have attempted to identify a microbial source of soil protease. Selective soil incubation using antibiotics was suitable for a rough estimation of the groups of microorganisms responsible for the production of soil protease (Hayano and Watanabe 1990; Hayano 1993). Enumeration of proteolytic microorganisms in the field and analysis of their protease-producing ability enabled to evaluate the potential of various soil microorganisms for soil protease production (Watanabe and Hayano 1993a; Watanabe et al. 1994). For the accurate estimation of the soil protease source, the characteristics of the soil protease and microbial protease must be compared directly based on enzymatic properties as indices.  相似文献   

19.
In Japan, since about 50% of upland fields are covered with Andosols, in which phosphorus (P) supplied by fertilizer is likely to be immobilized, there is a large accumulation of P in upland soil (Agriculture, Forestry and Fisheries Research Council 1991). However, information on the changes in the availability of accumulated P under long-term field conditions is very limited.

In order to analyze the effect of continuous application of compound fertilizer and farmyard manure on the changes in P compounds and their availability to crop plants in the plow layer of an upland Andosol, a long-term field trial has been carried out in an experimental field of Tokyo University of Agriculture and Technology, Tokyo, Japan since November, 1982. The results obtained in the field trial demonstrated that although crop growth in the plot without P fertilizer application was more reduced than that in the plot with P fertilizer application during each stage of the trial, the differences in crop growth between the plots became attenuate as time passed. These findings suggest that in the plot without P fertilizer application, soil P that accumulated before the start of the trial became available for the growth of crops as time passed (Hirata 1997).

While Truog and Bray No.2 methods have been traditionally used for routine analysis of available soil P in Japan, it has been recently reported that P extraction by these methods led to an overestimation of the amount of available soil P (Kato et al. 1995b). It was reported that the L-value measured by the isotopic dilution method and E-value measured by the isotopic exchange kinetic method were more suitable for estimating the amount of available soil P (Russel et al. 1957; Dalal and Hallsworth 1976; Tran et al. 1988; Kato et al. 1995a, b), and that isotope techniques could become valuable tools for understanding the P dynamics in soil-plant systems (Di et al. 1997).

In the present report, we carried out investigations on P availability in soils taken from plots differing in P fertilizer application in the above trial over a period of 13.5 y by using the 32P isotopic dilution method and the isotopic exchange kinetic method.  相似文献   

20.
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.  相似文献   

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