Root Tuberization And Nitrogen Fixation By Pachyrhizus Erosus (L.) A .
ROOT TUBERIZATION AND NITROGEN FIXATIONBY PACHYRHIZUS EROSUS (L.)A THESIS SUBMITTED TO THE GADUATE DIVISION OF THEUNIVERSITY OF HAWAII IN PARTIAL FULFILLMENTOF THE REQUIREMENTS FOR THE DEGREE OFMASTER OF SCIENCEIN AGRONOMYMAY 1979ByPaul Lester WoomerThesis Committee:A. Sheldon Whitney, ChairmanB. Ben BolhoolPeter RotarWallace Sanford
We certify that we have read this thesis and that in our opinion it issatisfactory in scope and quality as a thesis for the degree of Master ofScience in Agronomy.
TABLE OF CONTENTSPageACKNOWLEDGMENTS .4LIST OF TABLES .5LIST OF FIGURES .6LIST OF APPENDICES .8CHAPTER I.INTRODUCTION .9CHAPTER II.LITERATURE REVIEW .12CHAPTER III.THE RHIZOBIUM AFFINITIES OFPACHYRHIZUS EROSUS (L.) .31CHAPTER IV.DIURNAL CHANGES IN SYMBIOTICNITROGENASE ACTIVITY OF THETUBEROUS-ROOTED LEGUMESPACHYRHIZUS EROSUS (L.) ANDPSOPHOCARPUS TETRAGONOLOBUS(L.) DC .42ACCUMULATION AND PARTITIONINGOF DRY MATTER IN PACHYRHIZUSEROSUS (L.) .64CHAPTER VI.THESIS SUMMARY .85CHAPTER VII.LITERATURE CITED .87APPENDICES .93CHAPTER V.
ACKNOWLEDGEMENTSI wish to acknowledge Dr. Karl Stockinger, Dr. PadmanabhanSomasegaran, Tom Ohara, Scott Mawson and Bruce Martin for theirtechnical assistance.Barbara Bird’s computerized literature services and SandraSillapere’s command of the typewriter are greatly appreciated.
LIST OF TABLESTablePage1Designation, source and rating of Rhizobiumstrains tested on P. erosus .342Properties of P. erosus in response to symbioticeffectiveness and nitrogen form .353Regression matrix of plant dry weight andnitrogen parameters .394Regression matrix comparing relative effectivenessand tuberous root characters .405Daily nitrogenase levels of two tuberous-rootedlegume species .496Nitrogenase levels as affected by root and airtemperature .507Specific activity of P. erosus root nodulesas a function of propagule and sampling timeof day .518Components of yield increase of P. erosusas a function of propagule .529Acetylene reduction and root tuberization offield grown P. erosus .5510Effect of prolonged darkness on symbioticnitrogenase activity .5611Ratio of maximum and minimum observed nitrogenaseactivities for some field grown and tuberousrooted legumes .5812Fluctuation in nitrogenase activity for Vignaunguiculata and P. erosus .6213Effects of flower removal upon P. erosus .7814Fresh tuberous root yields after 15 weeks asaffected by inflorescence removal .84
LIST OF FIGURESFigure1PageTuberous root and root nodules of P. erosusa) attachment of large root nodule to root systemb) interior of root nodule, red region is theactive bacteroidal zone .152Diurnal changes in nitrogenase activity offield grown soybeans (Glycine max (L.) Merr.) .243Conflicting reports of diurnal nitrogenaseactivity in Lupinus luteus (L.) .244Diurnal nitrogenase activity of pea (Pisum sativum(L.)) .265Tuberous root size and shape as a function ofRhizobium strain effectiveness .366Vessels and plants for non-destructive acetylenereduction assay in the greenhouse .467P. erosus (Tpe-1) at the time of samplingfor non-destructive acetylene reduction .468Diurnal changes in symbiotic nitrogenanse activityof field grown P. erosus at different stages oftuberous-rootedness .54Field experiment at the NifTAL Project site,P. erosus 5 weeks after emergence, Vignaunguiculata had been recently planted in rowsvacated by the week 3 sampling .6610Dry matter distribution of field grown P. erosusover time follows phasic partitioning .6811Nitrogen accumulation of the components of totalyield over time, podfill is a strong sink foravailable nitrogen .7112Percentage nitrogen in the tissues of plantcomponents over time .7313Rates of nitrogen accumulation and acetylenereduction by field grown P. erosus over time .74Nodule mass (a) and specific nitrogenaseactivity (b) of field grown P. erosusover time .75Spacial displacement of the early root nodulesof P. eruosus by the tuberous root .7691415
FigurePage16Root nodule growth and development of fieldgrown P. erosus .7617Effects of flower removal on field grownP. erosus, flowers removed (left), control(right) .7918Effects of deflowering P. erosus .7919Extremes of tuberous root cracking. a) minorcracking of secondary tuberous rootb) extreme cracking .82Prolific lenticel development on the tuberousroot of deflowered treatment (left), control(right) .8320
LIST OF APPENDICESAppendixPage1Productivity of root crops in Hawaii .932Effects of Rhizobium strain on the componentsof yield and nitrogen content of P. erosus .943Dry matter and nitrogen accumulation forV. unguiculata and P. erosus after 8 weeksof growth in the field .954Nodule mass and specific nitrogenase activityof field grown P. erosus over time .965Effect of ethylene incubation on dry matterproduction of P. erosus using tuberous rootsas propagules .97
CHAPTER IINTRODUCTIONRecently Pachyrhizus erosus (L.) (the Mexican yam bean) has beendescribed as a legume of under-exploited potential in the tropics by theNational Academy of Science (in press).Although root and tuber cropstend not to be agricultural export items (Leslie, 1967), this crop iscurrently exported from Mexico to the United States (Kay, 1973).Earlier reports (Bautista and Cadiz, 1967; Kay, 1973) on the cultureof this crop recommended use of nitrogenous fertilizers and failed tomention that this is a nodulated legume.More recently Marcarian (1978)recognized this as a symbiotic legume and considered the description ofthis crop’s potential to fix nitrogen in the field to be a currentresearch goal.This line of research could reduce the use of costlynitrogenous fertilizers.The tuberous root of P. erosus is edible either raw or cooked.InHawaii it is called the “Chinese potato” or the “chop suey yam” (Ezumah,1970) and is raised on a back yard scale.Determining the yieldpotential, the optimal time to harvest and developing managementtechniques to increase yield and nutritive quality of this crop couldserve to increase production in Hawaii, and potentially develop anagricultural export commodity at a time when production of sugar cane, themajor crop in the islands, is proving unprofitable without subsidy fromthe federal government.Increased production in developing tropical countries of this cropas an export commodity to the more developed countries would have twomajor consequences.countries.Firstly, revenue would be generated in the producingSecondly, just as more protein is needed in the diets ofpeople in the lesser developed countries, so are less calories needed in
the diets of ever fattening affluent populations.If crispy snack foodscan be processed from P. erosus, these would compete directly with farmore fattening substitutes (cookies, potato chips, peanuts, etc.)The intent of this thesis is to describe the sink capacities forassimilate and nitrogen of the various plant organs of P. erosus.Thefollowing investigations were undertaken:1)Rhizobium strain testing, in which 23 strains of varyingeffectiveness were inoculated onto P. erosus grown in sterile,nitrogen free media.Included were treatments receiving chemicalnitrogen and no Rhizobium applied.Across this gradient ofsymbiotic effectiveness dry weights, components of yield andnitrogen contents were compared.2)Diurnal profiles in rates of acetylene reduction(symbiotic nitrogenase activity) for P. erosus at different stagesof root tuberization.3)Seasonal profiles on partitioning of dry matter andnitrogen between plant organs, weekly rates of acetylene reduction,and the effects of pod removal as a sink manipulation promoting roottuberization.Pachyrhizus erosus is one of very few storage organ crops that arecapable of symbiotic nitrogen fixation.Assimilate stored in the tuberousroot may support nitrogen fixation, while at the same time nitrogenrelations and symbiosis may affect root tuberization.If the extent ofdiurnal fluctuation in nitrogenase activity is not altered by increasedroot tuberization then the pattern of nitrogenase activity of tuberous-
rooted legumes is no different than that reported for nodulated legumeswith fibrous roots.It is the intent of this thesis to describe thepotential for root tuberization and nitrogen fixation by P. erosus.
CHAPTER IILITERATURE REVIEWPachyrhizus erosus - Tropical Root CropPachyrhizus erosus (L.) (Mexican yam bean) is one of few leguminous rootcrops.A hairy, twining herb native to Mexico and Central America, P. erosusis also cultivated in S.E. Asia (Purseglove, 1968), China, India (Deshaprabhu,1966), and Hawaii.The lobed, turnip-shaped tuberous root is perennial, butP. erosus is generally cropped as an annual since the tuberous roots becomefibrous with age.The root may be eaten raw, is mildly sweet and very crispy.After eating a sliced section some people unfamiliar with the “chop suey yam”might think this a fruit rather than a root.It is often used as a substitutefor the Chinese water chestnut in oriental cooking.In 1973, Kay estimatedthe annual importation from Mexico to the United States to be 400 tons.Tropical root and tuber crops, owing to their high bulk and relativelylow value, tend not to be international trade items (Leslie, 1967).Evenwithin tropical countries, root crops contribute much less to agriculturalproduction than the acreage would otherwise indicate because root crops areoften grown as a subsistence food and are not marketed.Root and tuber cropstend to be regarded as inferior foods, while cereals are often equated withcivilization and progress.The motto of the United Nations Food andAgriculture Organization is “‘Fiat Panis’ - let there be bread” (Coursey andHaynes, 1970).Because root crops tend to be high in carbohydrates and low in protein,vitamins and fats (Leslie, 1967), this bias is not entirely unjustified.Thecarbohydrate and protein content of P. erosus is even lower than that of yam,taro and sweet potato (Ezumah, 1970).a poor major staple for humans.Thus the roots from P. erosus would be
Additional constraints against expanding production of P. erosus in thetropics are the same as for other root crops.The scale of production tendsto be quite small (Ezumah, 1970) and it is manually harvested (Bautista andCadiz, 1967; Kay, 1973).Mechanical systems of planting and harvesting rootcrops have been developed (Jeffers, 1976) but due to the low value and smallscale of production, initial inputs for increased production should be towardvarietal improvement and expanded use of chemical fertilizers (Johnson, 1967).Production of P. erosus by small farmers is encouraged by severalcultural attributes of this crop.It is adapted to the very humid, hottropics (Rachie and Roberts, 1974), although short term drought resistance isprovided by the tuberous root.Insect and disease problems are infrequent(Bautista and Cadiz, 1967) due in part to the rotenone and pachyrhizid contentof the shoots (Deshaprabhu, 1966).Tolerances to stress and pests allow foradequate yields under low input regimes. A practice easily affordable to smallfarmers raising P. erosus is that of flower and pod removal to promote roottuberization.Various authors report this to be a traditional practice(Deshaprabhu, 1966; Kay, 1973; NAS, in press) yet experimental resultsdescribing the consequences of depodding are not available.The young podsmay be eaten after thorough boiling (Brucher, 1976).Appendix (1) lists the average per acre yield, time to harvest, averageprice and gross return per acre for many root crops produced in Hawaii.Nofigures were available for P. erosus in the Statistics of Hawaiian Agriculturefor 1977, although 11 other root and tuber crops were therein reported.available in Hawaii, P. erosus retails for more than .75 per pound.WhenAssumingcurrent price levels and a potential for export, P. erosus could offer grossreturns comparable to alternative root crops in Hawaii.P. erosus is typical of the major tropical root crops in that it is anodulated legume, receiving benefit of nitrogen fixing Rhizobium bacteria(Figures 1a and 1b).Presently little is known about the Rhizobium
requirement or the potential of P. erosus to supply its nitrogen needs throughsymbiosis in the field (Marcarian, 1978).The role of legumes in farm ecologygoes beyond directly providing nutrition or profit to producers.Through rootnodule symbiosis, legumes act to restore and maintain the nitrogen status ofthe soil.The aerial portion of P. erosus contains much of the total plantnitrogen, and if reincorporated into the soil, would certainly prove ofresidual value.Unfortunately, the shoots of P. erosus are poisonous and unusable as feed toruminant animals.Deshaprabhu (1966) believes that horses accept this as aforage more readily than do cattle.roots are useful as fodder.He also noted that old and non-marketableThe poisonous seeds of P. erosus are used asinsecticides and fish poisons.The stems are said to render a fiber used inFiji to make fish nets (Deshaprabhu, 1966).Despite the undesirability of P.erosus residue as animal food, this crop’s acceptance as a food, the potentialfor export to temperate areas, the ability to fix atmospheric nitrogen, andthe supplemental uses of non-marketable plant parts allow this crop to beconsidered as having under-exploited potential in the tropics.Productivity and Partitioning ofCarbohydrates in Root and Tuber CropsSolar radiation levels determine the rate of dry matter accumulation inplants when other conditions are not limiting.Consequently, time toestablishment of a full canopy after planting determines crop productivity(Loomis and Rapoport, 1976).Haynes et al. (1967) have well correlated theleaf area index and yield for several cultivars of yam (Dioscorea alata (L.)).The authors felt this is particularly significant since leaf area is alterablethrough management practices such as plant spacing, support, irrigation andfertilization.Net assimilation rate was also well correlated with storageorgan yield during early stages of growth in yam; however, at later stages of
storage organ development, the immediate source of dry matter entering thetuber changes from strictly recent assimilate to plant translocate from theshoots (Degras, 1967).This is the onset of the “death by exhaustion” ofthe aerial parts described by Milthorpe (1967).By necessity net productivity does influence yields, but thepartitioning of assimilates between respiration, growth and storage resultin an additional feature, unique to root and tuber crops (Loomis andRapoport, 1976).The extent of root sink strength during the final stagesof plant life greatly influences final yield in sugar beet (Beta vulgaris(L.)) (Das Gupta, 1969), potato (Solanum tuberosum (L.)) and Dahlia sp.(Loomis and Rapoport, 1976).It is not known if storage organs releasegrowth inhibitors that act to mobilize substrate to that organ during latestages of growth (Loomis & Rapoport, 1976).There are two basic patterns of storage organ accumulation, 1)balanced and 2) phasic partitioning.Balanced partitioning as representedin the sugar beet (Beta vulgaris) is relatively insensitive to theenvironment.Concentric cambia are formed early in ontogeny, roots andshoots develop synchronously (Mithorpe, 1967).In phasic partitioningrapid shoot and fibrous root growth precede storage organ initiation.Tuberization may be triggered by some aspect of the environment, followedby rapid predominance of the storage organ as a depository for assimilate(Loomis and Rapoport, 1976).Short days are known to regulate secondarythickening of roots in scarlet runner bean (Phaseolus coccineus (L.)), yam(D. alata), Jerusalem artichoke (Helianthus tuberous (L.)) (Garner andAllard, 1923) and winged bean Psophocarpus tetragonolobus (L.) DC)(Lawhead, 1978).Pachyrhizus erosus (L.) did not tuberize under a 14 hourphotoperiod (Bautista and Cadiz, 1967), while other authors speculate thatinitiation of tuberous-root “bulking” in P. erosus is regulated through thephotoperiod (Ezumah, 1979; Marcarian, 1978).
Torrey (1976) stressed the need of studies concerning hormone flowfrom the shoot to the root under different daylengths since the presence ofcytokinin has been related to early secondary thickening of roots.Trapping of Golgi vesicles by microtubules along the primary xylem has beenshown to be an early state in the secondary root thickening of alfalfa(Medicago sativa (L.)) (Maitra and Deepesh, 1971).In conclusion, both external and internal factors are involved inplant growth and partitioning of assimilate into storage organs.Exactevidence of these factors for Pachyrhizus erosus is not currently availableexcept an indication of a photoperiodic requirement for secondary rootthickening.The Acetylene/Ethylene Assayof Nitrogenase ActivityThe acetylene reduction assay of nitrogen fixation has been shown tobe sensitive, universal, and relatively simple (Hardy et al., 1968).Nitrogenase, the enzyme that reduces atmospheric nitrogen also reducesacetylene to ethylene, cyanide to methane and ammonia, N20 to N2 and water;to mention a few reactions.Using acetylene as a substrate for reductionresults in sensitivity since only two electrons are required for eachethylene molecule produced while atmospheric dinitrogen requires 6 electronsfor complete reduction.The acetylene reduction technique was shown reliable for free livingnitrogen fixing organisms, as well as with the root nodule symbiosis.Acetylene reduction, as measured by gas chromatography, is a less timeconsuming technique than Kjeldahl analysis or15N assayed by massspectrometry.Bergersen (1970) compared rates of acetylene reduction andof soybeans in nitrogen-free media.15N uptakeThe ratio of acetylene reduced to
nitrogen fixed (C2H4:NH3) ranged from 2.7 to 4.2.These observations do notinvalidate the use of acetylene reduction to compare nitrogen fixing systems(nitrogenase enzyme activity); however, this work established that acetylenereduction is a poor quantitative measurement of exact amounts of nitrogenfixed.Mague and Burris (1972) compared rates of acetylene reduction forintact soybean plants, decapitated root systems and detached nodules,finding activity ratios of 100/46/23 respectively.root nodules was shown to decrease activity.Water surfaces on theHardy et al. (1973)comprehensively reported on the use of the acetylene/ethylene assay.Itwas found to have been useful in biochemical and physiological studies ofthe leguminous and non-leguminous symbiosis, soil, marine, rhizosphere,phylloplane and mammalian nitrogen fixing systems within five years of itsdevelopment as a measurement of nitrogenase activity.More recently in situ incubation in acetylene has been used todetermine nitrogenase activity.Fishbeck et al (1973) working with soybeanfound that if the growth media was sufficiently porous, whole plantincubation did not result in significant differences from destructiveincubation of nodulated roots.This in situ technique was used to measurediurnal changes in symbiotic nitrogenase activity.Since then otherauthors (Sinclair et al., 1978) have used the non-destructive acetylenereduction assay to compare acetylene/N2 reduction rations, as well as plantspecies differences in nitrogen fixation.Periodic in situ assay did notdisrupt growth processes of the many forage species that were compared.Ruegg and Alston (1978) used in situ incubation to generate diurnalprofiles of nitrogenase activity for glasshouse grown Medicago truncatula(Gaertn.).Significant diurnal fluctuation was observed over a two daycycle despite incubation in 10% acetylene for 30 or 60 minutes.
Productivity and Partitioningin Symbiotic LegumesUnder ideal field conditions light and temperature levels regulateplant productivity.Wilson et al. (1933) demonstrated that legume growthand symbiotic nitrogen accumulation were increased as the partial pressureof carbon dioxide was raised from .03% to 0.8%.Carbon dioxide is thesubstrate of photosynthetic productivity, just as light is the energysource.This experiment was the first strong indication that assimilatesupply to the root nodules regulate rates of nitrogen fixation and thenumber, size and distribution of the root nodules.comparing15Later researchers,N accumulation of darkened and illuminated symbiotic legumesdemonstrated the importance of light (and therefore recent assimilates) onthe rate of nitrogen fixation (Lindstrom et al., 1952; Virtanen et al.,1955).Bach et al (1958) examined this directly usingphotoperiodnight.1414CO2.During theC accumulated in the root nodules at twice the rate than atThis work demonstrated the need of continued supply of photosynthateto the nodules to maintain maximum rates of nitrogen fixation.Lawrie andWheeler (1973) correlated the rate of acetylene reduction with levels oflabelled photosynthate in pea (Pisum sativum (L.)).the nodules for assimilate was the bacteroidal areas.The main sink withinLater work by thesame authors (Lawrie and Wheeler, 1975) with Vicia faba (L.) detectedthe root nodules within 30 minutes of feeding the shoots14CO2.14C inChing et al(1975) related the decrease in ATP, sucrose, ATP/ADP ratio and nitrogenaseactivity to prolonged darkness for 1 day using 25 day old soybean.Theenergy balance of the nodules was dependent upon arrival of recentphotosynthate.Nitrogenase enzyme activity of temperate legumes is not greatlyaffected by incubation temperatures.Hardy et al (1968) equilibrated andthen incubated nodulated roots of soybean at a range of temperatures.
Between 20o and 30o C there was no temperature effect on acetylenereduction, but a steady decrease was observed when root temperaturesdeclined below 20o C.Temperature strongly affects the supply of carbohydrates to the rootnodules.Michin and Pate (1974) using pea (Pisum sativum) found thathigher night temperatures resulted in a more pronounced decrease in N2fixation during the night.The authors speculated that nodule metabolismcan utilize limited supplies of carbohydrate more efficiently for nitrogenfixation at lowered night temperature, since low night temperature reducesthe rate of respiration more than the rate of nitrogen fixation.In thesame study respiratory output was well correlated with nodule solublecarbohydrate.Reports that changes in the rate of nitrogen fixation are morestrongly correlated with air temperatures than with soil temperaturesimplies that temperature plays an indirect role on nodule function (Magueand Burris, 1972).Sloger et al (1975) found that for field-grown soybeanssoil temperature varied less than nitrogenase activity throughout the day.The effect of air temperatures on the rate of acetylene reductionvaries between hosts and Rhizobium strains.Mes (1959) found thatincreasing day temperatures from approximately 20oC to either 25o or 27oCdecreased nitrogen accumulation in the temperate legumes, Vicia sativa (L.)and Pisum sativum (L.).On the other hand, lowering day temperatures oftropical legumes, Arachis hypogaea and Stizolobium deeringianum Bort.depressed nitrogen accumulation.Similarly, Pate (1962) found that thesymbiosis of Medicago tribuloides (Desr.) was more tolerant of highertemperatures, and that Vicia atropurpurea (Desf.) was more tolerant tolowered temperatures when the two species were compared.In general thesymbiosis of tropical legumes are less sensitive to higher temperatureregimes (27o-35oC) than are the temperate legumes.
Physiological Rhythms inSymbiotic ActivityUsing a split shoot technique with Lupinus augustifolius (L.) in14which one of the shoots was fedCO2 and the other shoot was removed forcollection of exudate, Greig, Pate and Wallace (1962) studied fluctuationsin the amino content and radioactivity of the decapitated stem bleedingsap.The diurnal rhythm of temperature stimulated movement of labeledcarbohydrate from the shoots.Specific activity of the amino fractionincreased over several days, indicating continued radio labeledcarbohydrate supply to the nodules after assimilation of14CO2.maintained in constant temperature and darkness declined in14PlantsCO2 specificactivity over time, translocation of carbohydrates from the shoot could notoffset the depletion of root reserves.In this way both fluctuations oftemperature and exposure to light were shown to stimulate nitrogenfixation.Output of cations and amino compounds in the bleeding sap ofnodulated Pisum arverense exhibited a diurnal rhythm with a maximum nearnoon and a minimum near midnight.one hour of photosynthesis in14Labeled amino acids were recovered afterCO2 (Greig et al, 1962).An endogenous component for rhythmic discharge of amino compounds wasdemonstrated for Lupinus augustifolius (L.) and Pisum arverense (Pate andGreig, 1964).darkness.This occurred for plants under normal light and prolongedThe amplitude of the rhythm was increased by cold nights andwarm days, which acted to time this rhythm.Examination of the ultrastructure and functioning of the transportsystem to and from root nodules of Pisum arverense and Trifolium repens(L.) (Pate et al, 1969) indicated that normal source-sink processes aremaintained with assimilate supply to the nodules, but that amino acid
export from the nodules was associated with active processes.Ultrastructural studies could not clearly define the export mechanism.The differences in nitrogen fixation between fluctuatingtemperature/humidity regimes and constant temperature/humidity conditionswere described by Minchin and Pate (1974) for P. sativum.Acetylenereduction, root respiration and nodule sugars increased during the photoperiod, while nodule soluble nitrogen decreased.The fluctuating environ-ment stimulated overall growth and nitrogen fixation when compared toconstant temperature/humidity.This was due in part to greater rates ofnitrogen fixation under cooler night temperatures, resulting in lessrespiration during the dark period.This study included use of theacetylene reduction assay of nitrogenase activity.When these results werecompared to bleeding sap estimates of the rate of nitrogen fixation, theresults were in conflict.Bleeding sap flux greatly overestimated theextent of diurnal changes in nitrogen fixation because the products ofnitrogen fixation were retained during the night, and not released untilplants were rapidly transpiring during the next photoperiod.In this samestudy, more nitrogen was fixed during the night in the fluctuatingtemperature environment of 18oC day, 12oC night than during the photoperiod.The authors were not certain whether this is an artifact of growth cabinetconditions or if this applies to plants growing in some naturalenvironments.Examples of Diurnal Changesin Nitrogenase ActivityIn most cases where diurnal fluctuation of nitrogenase activity hasbeen observed, the maxima occurs near the period of maximum light intensity(Hardy et al., 1968).This has been demonstrated in the non-legumes AlnusGlutinosa and Myrica gale (Wheeler, 1969), and Casuarina sp. (Bond and
Mackintosh, 1975) as well as for quite a few legumes.Nitrogenase activityof field grown soybeans (Figure 2) consistently showed diurnal changes;however, the extent of these changes varied between two and three-fold(Sloger et al, 1975; Hardy et al, 1968) to five-fold (Mague and Burris,1972).One published report (Ayanaba and Lawson, 1977) claims to havefound no diurnal trend in the field, but when their results are plottedwith other authors a trend does become evident.Some greenhouse (Fishbecket al, 1973) and growth chamber (Mederski and Streeter, 1977) were comparedto bleeding sap estimates of the rate of nitrogen fixation, the resultswere in conflict.Bleeding sap flux greatly overestimated the extent ofdiurnal changes in nitrogen fixation because the products of nitrogenfixation were retained during the night, and not released until plants wererapidly transpiring during the next photoperiod.In this same study, morenitrogen was fixed during the night in the fluctuating temperatureenvironment of 18oC day, 12oC night than during the photoperiod.Theauthors were not certain whether this is an artifact of growth cabinetconditions or if this applies to plants growing in some naturalenvironments.Examples of Diurnal Changesin Nitrogenase ActivityIn most cases where diurnal fluctuation of nitrogenase activity hasbeen observed, the maxima occurs near the period of maximum light intensity(Hardy et al., 1968).This has been demonstrated in the non-legumes AlnusGlutinosa and Myrica gale (Wheeler, 1969), and Casuarina sp. (Bond andMackintosh, 1975) as well as for quite a few legumes.Nitrogenase activityof field-grown soybeans (Figure 2) consistently showed diurnal
Tropical root and tuber crops, owing to their high bulk and relatively low value, tend not to be international trade items (Leslie, 1967). Even within tropical countries, root crops contribute much less to agricultural production than the acreage would otherwise indicate because root crops are often grown as a subsistence food and are not marketed.
Biosynthesis of Fatty Acids / 459 Biosynthesis of Phospholipids / 464 Degradation of Fatty Acids / 466 Biosynthesis of Isoprenoids / 468. 14 NITROGEN METABOLISM 475. Biological Nitrogen Fixation / 475 The Nitrogen Fixation Process / 479 Components of the Nitrogenase System / 480 Symbiotic Nitrogen Fixation / 483 Inorganic Nitrogen Metabolism / 487
Nitrogen Cycle The atmosphere is the largest reservoir of nitrogen on Earth. It consists of 78 percent nitrogen gas. The nitrogen cycle moves nitrogen through abiotic and biotic compo-nents of ecosystems. Absorption of Nitrogen Plants and other producers use nitrogen to synthesize nitrogen-containing organic
Aug 08, 2019 · ) to ammonium, a form of nitrogen that can be utilized by plants (Vessey et al., 2003). Rakash and Rana (2013) reported that the biological nitrogen fixation contributes about 100 million tons of nitrogen for terrestrial ecosystems, 30 to 300 million
1.3.3.3 Nitrogen Oxides Emissions1-2,6-10,15,17-27 - . Oxides of nitrogen (NOx) formed in combustion processes are due either to thermal fixation of atmospheric nitrogen in the combustion air ("thermal NOx"), or to the conversion of chemically bound nitrogen in the fuel ("fuel NOx").The term NOx refers to the composite of nitric oxide (NO) and nitrogen
The ENB 45 Pneumatic Nitrogen Booster provides the capability of boosting remaining lower pressure Nitrogen from supply bottles to the required pressure, up to 4,500 psi. The Nitrogen Booster is driven by compressed air or nitrogen. It cycles automatically to boost low-pressure nitrogen to high pressure.
Operation Open reduction internal fixation Short arm brace for 1st week Active mobilization exercise is allowed if stable fixation External fixation primary cancellous bone graft Indication Unstable fracture with or without articular involvement Comminuted intra-articular fracture External fixation is removed at the end of 3rd weeks. A
7.5 Graphing Square Root and Cube Root Functions 431 Graph square root and cube root functions. Use square root and cube root functions to find real-life quantities, such as the power of a race car in Ex. 48.
ASME A17.1, 2013 NFPA 13, 2013 NFPA 72, 2013 Not a whole lot has changed in the sub-standards. Substantial requirements in the IBC/IFC. International Building Code (IBC) and International Fire Code (IFC) “General” Requirements. Hoistway Enclosures Built as “shafts” using fire barrier construction o 1 hr for 4 stories o 2 hr for 4 or more stories o Additional .
