Adaptation of exotic Azolla to tropical environment of Thailand

There are seven known species of Azolla, two of which have been used in cultivated systems, the tropical speciesA. pinnata, and the temperate speciesA. filiculoides. OnlyA. pinnata is indigenous in Thailand. In this study the two exotic species,A. caroliniana andA. microphylla, were evaluated under the various tropical field conditions in Thailand. When compared with seven selected strains ofA. pinnata under three field conditions,A. caroliniana andA. microphylla were similar to the indigenous species, in terms of growth performance, N₂ fixation, and yield. This study suggests thatA. caroliniana andA. microphylla can be successfully cultivated as a nitrogen fixing green manure for rice production in the tropics.     

Growth and turnover of microbial biomass during the decomposition of organic matter(Polygonum cuspidatum) in vitro

Air-dried fresh and dead specimens ofPolygonum cuspidatum were incubated for 250 days in the laboratory, and the growth and turnover of microbial biomass-C in the organic matter were studied. The biomass-C in the fresh leaf and fresh stem attained maximum levels on day 14 and day 7, respectively, and then settled down to stable levels. In the dead leaf and dead stem, increase in biomass-C ceased by day 4 and the biomass-C levels did not change thereafter. The turnover time of the biomass-C was estimated from the amount of biomass-C and the release rate of CO₂-C. The turnover was rapid in the early period of incubation. Then the turnover time became longer and after incubation for 70 days the values approached those in natural soils (longer than 16 days). During the incubation period, nitrogen was not mineralized in any organic matter. In the dead leaf and dead stem, asymbiotic nitrogen fixation activity increased after incubation for about 40 days and disappeared by the end of the incubation period, whereas nitrogen fixation was hardly detected in the fresh leaf and fresh stem.     

Biology of nitrogen-fixing Rhizobacteria

In non-legumes associative nitrogen-fixing system, several genera of rhizobacteria have been reported. The object of this paper is to summarize the current understanding of how rhizobacteria adhere to the root surface of non-legumes especially rice and other cereal crops. Evidence for involvement of rice lectin in adhesion will be reviewed. An emphasis will be placed on theKlebsiella R15 ammonium assimilation system in free-living state and in associative state with rice seedlings. Nitrogenase and glutamine synthetase (GS) activities of associativeKlebsiella increased significantly in the rhizosphere of rice comparing to the free-living state. In rice, the soluble form of GS specific activity appear to be slightly lower than in rice root in the absence of bacteria. These results suggest that nitrogen-fixing activity has been enhanced during association. The dinitrogen fixed should be changed to amino acids via GS-GOGAT pathway in bacteria. Transfer of fixed nitrogen and assimilation in the rice plant is the problem that needs to be solved in order to improve the efficiency of associative nitrogen fixation.     

Crop uptake and leaching losses of15N labelled fertilizer nitrogen in relation to waterlogging of clay and sandy loam soils

Summary Ammonium nitrate fertilizer, labelled with¹⁵N, was applied in spring to winter wheat growing in undisturbed monoliths of clay and sandy loam soil in lysimeters; the rates of application were respectively 95 and 102 kg N ha⁻¹ in the spring of 1976 and 1975. Crops of winter wheat, oilseed rape, peas and barley grown in the following 5 or 6 years were treated with unlabelled nitrogen fertilizer at rates recommended for maximum yields. During each year of the experiments the lysimeters were divided into treatments which were either freelydrained or subjected to periods of waterlogging. Another labelled nitrogen application was made in 1980 to a separate group of lysimeters with a clay soil and a winter wheat crop to study further the uptake of nitrogen fertilizer in relation to waterlogging. In the first growing season, shoots of the winter wheat at harvest contained 46 and 58% of the fertilizer nitrogen applied to the clay and sandy loam soils respectively. In the following year the crops contained a further 1–2% of the labelled fertilizer, and after 5 and 6 years the total recoveries of labelled fertilizer in the crops were 49 and 62% on the clay and sandy loam soils respectively. In the first winter after the labelled fertilizer was applied, less than 1% of the fertilizer was lost in the drainage water, and only about 2% of the total nitrogen (mainly nitrate) in the drainage water from both soils was derived from the fertilizer. Maximum annual loss occurred the following year but the proportion of tracer nitrogen in drainage was nevertheless smaller. Leaching losses over the 5 and 6 years from the clay and sandy loam soil were respectively 1.3 and 3.9% of the original application. On both soils the percentage of labelled nitrogen to the total crop nitrogen content was greater after a period of winter waterlogging than for freely-drained treatments. This was most marked on the clay soil; evidence points to winter waterlogging promoting denitrification and the consequent loss of soil nitrogen making the crop more dependent on spring fertilizer applications.     

Nitrification and organic nitrogen formation in soils

Summary The formation of mineral nitrogen species and of organic nitrogen was studied in three different types of soils in relation to the application of the nitrification inhibitor nitrapyrin. The results indicate that nitrification brings about a deficit in total mineral nitrogen and a concomitant surplus in non biomass organic nitrogen. This phenomenon increases with increasing levels of applied ammonium nitrogen and soil organic matter. The phenomenon is considered to be due to the reaction of the transient nitrite formed with soil phenolic compounds and appears to be of significance in all soils in which nitrification occurs, even neutral to alkaline and low carbon soils.     

Symbiotic effectiveness of Bradyrhizobium strains isolated from Parasponia and tropical legumes on Parasponia host species

The symbiotic effectiveness of Bradyrhizobium strains isolated from three species of Parasponia and from legumes were compared on Parasponia grown in Leonard-jars. Effectiveness of each symbiotic association was estimated from dry weight and total nitrogen of shoots and nodules of plants grown on medium free of combined nitrogen. Twenty strains isolated from three species of Parasponia were found to vary in their effectiveness on P. andersonii, the least effective fixing one fifth of the nitrogen of the most effective strains. The outcome of the symbiosis was not associated with the host source of the test strain. P. andersonii, P. rugosa and P. rigida responded differently to a selection of seven strains of Parasponia Bradyrhizobium; some strains were either ineffective or fully effective on each host, while others varied in their symbiotic performance. P. andersonii fixed significantly (P < 0.001) larger quantities of nitrogen than either P. rugosa or P. rigida with p. rigida being the least effective. In contrast to Bradyrhizobium strains from Parasponia spp. which formed nodules rapidly (within 11–20 days), nine strains isolated from legumes required between 25 and 74 days to form partially effective nodules. The thre Parasponia species formed relatively large quantities of nodule tissue relative to the amount of nitrogen fixed and shoot dry matter produced. The Bradyrhizobium isolated from Parasponia plants growing in Papua New Guinea soils could be grouped together on the basis of their infection characteristics on Parasponia and legumes.     

The effect of emersion and handling on the nitrogen excretion rates of Clarias gariepinus

African catfish Clarias gariepinus (=119.9&30.6 g) were exposed to periods of emersion (5, 30, 60, 90 and 180 min) and the ammonia and nitrogen excretion rates measured following re-immersion. Immediately following re-immersion (0–30 min), the ammonia excretion and relative ammonia excretion was greatest for the 5-min emersion gro up. Exposure to extended periods of emersion resulted in a decrease in total nitrogen excretion, notably ammonia excretion, although no significant changes were observed in the non-ammonia component of C. gariepinus .     

CORRELATED BIOCHEMICAL AND ULTRASTRUCTURAL CHANGES IN NITROGEN-STARVED EUGLENA GRACILIS1

Growth of Euglena gracilis Z Pringsheim under photoheterotrophic conditions in a nitrogen-deprived medium resulted in progressive loss of chloroplastic material until total bleaching of the cells occurred. Biochemical analysis and ultrastructural observation of the first stages of the starvation process demonstrated an early lag phase (from 0 to 9 h) in which cells increased in size, followed by a period of cell division, apparently supported by the mobilization of some chloroplastic proteins such as the photosynthetic CO₂-fixing enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase. The degradation of the enzyme started after 9 h of starvation and was preceded by a transient concentration of this protein in pyrenoidal structures. Protein nitrogen and photosynthetic pigments as well as number of chloroplasts per cell decreased during proliferation through mere distribution among daughter cells. However, after 24 h, when cell division had almost ceased, there was a slow but steady decline of photosynthetic pigments. This was paralleled by observable ultrastructural changes including progressive loss of chloroplast structure and accumulation of paramylon granules and lipid globules in the cytoplasm. These findings reinforce the role of chloroplastic materials as a nitrogen source during starvation of E. gracilis in a carbon-rich medium. The excess of ribulose-1,5-bisphosphate carboxylase/oxygenase acts as a first reservoir that, once exhausted, is superseded by the generalized disassembly of the photosynthetic structures, if the adverse environment persists more than 24 h.