INHIBITION OF NITRIFICATION BY CLIMAX ECOSYSTEMS. II. ADDITIONAL EVIDENCE AND POSSIBLE ROLE OF TANNINS

The same nine plots were used in this study as in our previous study on inhibition of nitrification (Rice and Pancholy, 1972). These consisted of three stands representing two stages of old field succession and the climax in each of three vegetation types in Oklahoma: tall grass prairie, post oak-blackjack oak forest, and oak-pine forest. Soil samples were analyzed three times during the growing season of 1972 for exchangeable ammonium nitrogen, nitrate, and numbers of Nitrosomonas and Nitrobacter. Results were similar to those obtained during the entire year of 1971. The amount of ammonium nitrogen was lowest in the first successional stage, intermediate in the intermediate successional stage, and highest in the climax. The amount of nitrate was highest in the first successional stage, intermediate in the intermediate successional stage, and lowest in the climax. The numbers of nitrifiers were highest in the first successional stage usually and decreased to a very low number in the climax. These data furnish additional evidence that the nitrifiers are inhibited in the climax so that ammonium nitrogen is not oxidized to nitrate as readily in the climax as in the successional stages. This would aid in the conservation of nitrogen and energy in the climax ecosystem. Some inhibition of nitrification occurred in the intermediate stage of succession also. Previous studies of tannins indicated that these are inhibitory to nitrification, so all important plant species in the intermediate successional stage and the climax were analyzed for total tannin content. A method for extracting and quantifying condensed tannins from soils was developed and the amounts of tannins were determined in each 15-cm level down to 60 cm in the same two plots in each vegetation type. Gallic and ellagic acids, which result from the digestion of hydrolyzable tannins in oak species, were also extracted and quantified in the climax oak-pine forest. All the important herbaceous species, including the grasses, were found to have considerable amounts of condensed tannins. The highest amounts of tannins occurred in the oaks and pine, however. Condensed tannins, hydrolyzable tannins, ellagic acid, gallic acid, digallic acid, and commercial tannic acid (hydrolyzable tannin), in very small concentrations, were all found to completely inhibit nitrification by Nitrosomonas in soil suspensions for 3 weeks, the duration of the tests. Slightly larger concentrations were required to inhibit nitrification by Nitrobacter under similar conditions. The concentrations of tannins, gallic acid, and ellagic acid found in the soil of the research plots were several times higher than the minimum concentrations necessary to completely inhibit nitrification. The inhibition of nitrification was always greater in the climax stand than in the intermediate successional stage in each vegetation type, and the concentration of tannins in the top 15 cm of soil was always higher in the climax stand than in the intermediate successional stage. Moreover, the amounts of tannins calculated to be added to each plot each year are much less than the amounts found in the soil, indicating that the tannins accumulate over a period of time. Thus, it appears that the tannins and tannin derivatives may play a continuous and rather prominent role in the inhibition of nitrification by vegetation.     

IN VITRO ALLELOPATHIC INHIBITION OF NITRIFICATION BY BALSAM POPLAR AND BALSAM FIR

A soil percolation apparatus was used to study the effect of plant extracts on nitrification. Foliar leachates, leaf extracts, and bud extracts of balsam fir (Abies balsamea) and balsam poplar (Populus balsamifera) were added to the ammonium percolation solution. Color tests and quantitative measurement of residual ammonium and formed nitrate were applied. Foliar leachates of balsam fir strongly inhibited nitrification; leachates of balsam poplar were slightly less inhibitory. Balsam fir needle and balsam poplar dormant bud extracts (5% w/v) completely prevented the oxidation of ammonium. The same estracts (2% w/v) still prevented the oxidation of ammonium to nitrate to a large extent. Once again balsam fir extracts inhibited the process more strongly than balsam poplar. No evidence was obtained for the presence of a specific inhibitor of nitrifier microorganisms.     

THE INHIBITION OF CYPRIDINA LUMINESCENCE BY LIGHT

The luminescence of Cypridina luciferin-luciferase solution is inhibited by illumination from a carbon arc of 15,000 foot candles in between 1 and 2 seconds. The blue to violet rays are the effective ones, the limits lying somewhere around 4,600 Å. u. to 3,800 Å. u. The luciferin, not the luciferase, is the substance affected by the light. The effect is partially reversible in the dark. The chemiluminescences obtained by oxidizing phosphorus, lophin, and chlorphenylmagnesium bromide are not inhibited by light under the above conditions.     

INHIBITION BY BACTERIA OF PSEUDOPLASMODIUM FORMATION OF DICTYOSTELIUM DISCOIDEUM

A mutant of Dictyostelium discoideum was isolated, the development of which was normal at 18.5°C but stopped at the aggregate stage when cultured with bacterial associate at 26°C. Probably the bacteria release a factor inhibitory to pseudoplasmodium formation, the inactivation of the inhibitor being temperature-sensitive in this mutant. This bacterial factor is different from the one reported by W eber and R aper (16), judging from the synergism shown by these two types of mutants.
The temperature-shift experiment gave the result that the inhibited developmental step was at about the time of initiation of tip formation. However, once a tip was formed under the permissive conditions, the re-formation of a new tip after removal of the original was not inhibited under the nonpermissive conditions. These results indicate that the bacterial inhibitor acts just before tip formation.     

INHIBITION OF FERN SPORE GERMINATION BY LIPOPHILIC SOLVENTS

Several alcohols and other solvents inhibit germination of spores of the fern, Onoclea sensibilis L. The inhibition is reversible when spores are transferred to solvent-free media. The effectiveness of different solvents, measured by the concentration needed to inhibit germination by 50%, increases with their lipid solubility. The activity of straight-chain alcohols from methanol through n-heptanol is highly correlated with lipid solubility, whereas the correlation is weaker for several other solvents. The results indicate that some lipophilic site in the spore is important in germination.     

双歧杆菌体外对STM拮抗作用的实验研究

研究休外双歧杆菌对鼠伤寒沙门菌的拮抗作用,方法将两歧双歧杆菌ＳＴＭ混合培养。观察ＳＴＭ生长情况。结果ＳＴＭ和Ｂ．ｂｉｆｉｄｕｍ混合培养与ＳＴＭ单独培养对照相比较,菌量明显降低。结论Ｂ．ｂｉｆｉｄｕｍ在体外对ＳＴＭ有拮抗作用。     

REVERSAL OF d-CYCLOSERINE INHIBITION OF BACTERIAL GROWTH BY ALANINE.

Zygmunt, Walter A. (Mead Johnson & Co., Evansville, Ind.). Reversal of d-cycloserine inhibition of bacterial growth by alanine. J. Bacteriol. 84:154-156. 1962.-Reversal of the antibacterial activity of d-4-amino-3-isoxazolidone by alanine in bacterial cultures actively growing on chemically defined media was compared in cultures requiring exogenous alanine and those capable of its synthesis. dl-Alanine was the most effective reversal agent in Pediococcus cerevisiae, an alanine-requiring organism, and d-alanine was effective in Escherichia coli and Staphylococcus aureus, organisms synthesizing alanine. With all three cultures, l-alanine was the least effective reversal agent.     

ALLELOPATHIC INHIBITION OF NITRIFICATION AND NITRIFYING BACTERIA IN A PONDEROSA PINE (PINUS PONDEROSA DOUGL.) COMMUNITY

The dynamics of ponderosa pine (Pinus ponderosa Dougl.) stands in western North Dakota were studied to determine the influence of plant-produced chemicals on nitrification rates and competitive interactions within the stands. Ponderosa pine accounted for more than 98% of all tree and shrub stratum stems in this climax community. Low levels of nitrate-nitrogen relative to ammonium-nitrogen and low numbers of Nitrosomonas and Nitrobacter in the soils indicated that nitrification rates were low. Inhibition of nitrification is often attributed to low soil pH in coniferous forests, but the slightly alkaline soils in this study (pH 7.25–7.75) suggested that another factor caused the low nitrification. Evidence obtained suggested that the reduction in nitrate synthesis was due to the production and subsequent transfer to the soil of secondary plant chemicals that were toxic to Nitrosomonas. Chemical inhibitors of nitrification, including caffeic acid, chlorogenic acid, quercitin, and condensed tannins, were found in extracts from ponderosa pine needles, bark, and A horizon soils. These extracts proved to be toxic to soil suspensions of Nitrosomonas causing reductions of from 68–93% of the control. These findings indicate that climax ponderosa pine communities minimize the conversion of ammonia-nitrogen to nitrate-nitrogen by chemically inhibiting nitrification.