The interactive effects of phosphorus supply and combined nitrogen (nitrate) on dry matter and nitrogen accumulation by nodulated soybean (Glycine max L. Merr.) plants, and the relative effects of phosphorus supply on nodule number, mass, and function in comparison to host plant growth were used to investigate the role of phosphorus in symbiotic dinitrogen fixation. Mixed positive and negative phosphorus by nitrogen source interactions indicated that severe phosphorus deficiency markedly impaired both host plant growth and symbiotic dinitrogen fixation and that symbiotic dinitrogen fixation has a higher phosphorus requirement for optimal functioning than either host plant growth or nitrate assimilation. In the whole plant phosphorus concentration range of 0.8 to 1.5 grams per kilogram dry weight, plants supplied with 20 millimolar nitrate accumulated significantly more dry matter and nitrogen than symbiotic plants without nitrate. This suggested that the higher phosphorus requirement for symbiotic dinitrogen fixation is internal rather than being associated with differences in the ability of roots in the two nitrogen regimes to absorb phosphorus from the external solution. Increasing the phosphorus concentration in plants solely dependent on dinitrogen fixation resulted in highly significant (P = 0.0001) increases in whole plant nitrogen concentration as well as highly significant increases (P = 0.0001) in whole plant dry matter and nitrogen accumulation. This indicated a greater responsiveness of symbiotic dinitrogen fixation than of host plant growth to improvement in phosphorus nutrition. The large increases in whole plant nitrogen concentration were associated with about 3.5-fold increases in the ratio of nodule mass to whole plant mass and about 2-fold increases in specific acetylene reduction (nitrogenase) activity of the nodules. The large increase in nodule mass (>30-fold) between the 0 and 2.0 millimolar phosphorus levels resulted from 11- and 3-fold increases in nodule number per plant and average mass of individual nodules, respectively. Root mass per plant over the same concentration range increased 3.5-fold. These results indicate that phosphorus has specific roles in nodule initiation, growth, and functioning in addition to its involvement in host plant growth processes.

Investigation of the Role of Phosphorus in Symbiotic Dinitrogen Fixation

Publisher Summary This chapter discusses the role of mycorrhizas in the growth and nutrition of nitrogen-fixing nodulated plants. It reviews some general, well-established principles on mycorrhizal types, morphology, physiology, and function. The interactions between nodular and mycorrhizal endophytes related to the formation and effects of these dual symbioses that greatly enhance the development of the common host plant are discussed. It presents the ecological significance of plants bearing the two types of symbioses, with emphasis on the possibilities of harnessing them to increase crop yield. Mycorrhizal associations play an important role in the growth and nutrition of higher plants. It is recognized that this symbiosis can be harnessed to improve nutrient cycling and crop productivity by reducing industrial fertilizer inputs, thereby conserving and reducing environmental costs. Mycorrhizal infection can help plants to become reestablished in eroded or degraded habitats, to thrive in arid conditions, to deter pathogens, and to cope with various stress situations. The common mycorrhizal types, the vesicular-arbuscular mycorrhizas (VAM), are nearly omnipresent and are studied intensively throughout the world. VAM enhance growth, nodulation, and nitrogen fixation in grain and forage legumes, crops of the greatest interest for food production in the biosphere.

Mycorrhizas and their Significance in Nodulating Nitrogen-Fixing Plants

The influence of P on N2 fixation and dry matter production of young pea (Pisum sativum L. cv. Bodil) plants grown in a soil-sand mixture was investigated in growth cabinet experiments. Nodule dry weight, specific C2H2 reduction and P concentration in shoots responded to P addition before any growth response could be observed. The P concentration in nodules responded only slightly to P addition. A supply of P to P-deficient plants increased both the nodule dry weight, specific C2H2 reduction and P concentration in shoots relatively faster than it increased shoot dry weight and P concentration in nodules. Combined N applied to plants when N2 fixation had commenced, increased shoot dry weight only at the highest P levels. This indicates that the smaller plant growth at the low P levels did not result from N deficiency. The reduced nodulation and N2 fixation in P-deficient plants seem to be caused by impaired shoot metabolism and not by a direct effect of P deficiency of the nodules.

The role of phosphorus in nitrogen fixation by young pea plants (Pisum sativum)

Characterization of the effects of long-term P deficiency and of onset and recovery from P deficiency on bacteroid mass and number per unit nodule mass and energy status of soybean ( Glycine max L. Merr.) nodules was used to investigate the mechanisms by which P deficiency decreases symbiotic N 2 fixation. The continuous P deficiency treatment (0.05 millimolar P) significantly decreased the whole plant dry mass, P, and N by 62, 90, and 78%, respectively, relative to the P-sufficient control (1.0 millimolar) at 44 days after transplanting. Specific nitrogenase activity was decreased an average of 28% over a 16-day experimental period by P deficiency. Whole nodules of P-deficient controls contained 70 to 75% lower ATP concentrations than nodules of P-sufficient controls. Energy charge and ATP concentrations in the bacteroid fraction of nodules were not significantly affected by P treatment. However, ATP and total adenylate concentrations and energy charge in the plant cell fraction of nodules were significantly decreased 91, 62, and 50%, respectively, by the P deficiency treatment. Specific nitrogenase activity, energy charge, and ATP concentration in the plant cell fraction increased to the levels of nonstressed controls within 2, 2, and 4 days, respectively, after alleviation of external P limitation, whereas bacteroid mass per unit nodule mass and bacteroid N concentration did not increase to the level of nonstressed controls until 7 days after alleviation of external P limitation. All of these parameters except bacteroid mass per unit nodule mass decreased to the levels of the P-deficient controls by 11 days after onset of external P limitation. Concentration of ATP in the bacteroid fraction was not significantly affected by alteration in the external P supply. Energy charge in the bacteroid fraction from plants recovering from P deficiency was decreased to a small (10%) but significant extent (P

Energy Status and Functioning of Phosphorus-Deficient Soybean Nodules

This study describes the variation in the mean relative shoot Ca content within the angiosperms at the ordinal level. Data were derived from studies in the literature in which the shoot Ca content of two or more species had been compared, and from a hydroponic experiment in which plants were selected to represent the relative number of species within each angiosperm order. Across all angiosperms, most of the variation in shoot Ca content occurred at and above the level of the order. Relative shoot Ca contents and variances correlated between literature and experimental data. In general, orders of commelinoid monocots had lower Ca contents than other monocot or eudicot orders. These results are used to illustrate how physiological and ecological hypotheses can be formulated using literature data.

Variation in the shoot calcium content of angiosperms

This paper describes the effect of phosphorus on nitrogen concentration and on the total and individual concentrations of the cations calcium, magnesium, potassium, and sodium in the plant tops of 10 tropical legumes and one temperate legume when grown on two soils of different type, a light-textured solodic soil and a gley soil Species used were Phaseolus lathyroides, P atropurpureus, Stylosanthes humilis, Centrosema pubescens, Glycine javanica, Lotononis bainesii, Medicago sativa, Desmodium uncinatum, D intortum, Vigna luteola, and Leucaena leucocephala The nitrogen concentrations in the plant tops were increased by phosphorus supply, and good correlations were established between the nitrogen and phosphorus concentrations in the plant tops When sodium dihydrogen phosphate was used as the source of phosphate, the sodium concentration in V luteola, M sativa, and L bainesii was increased Other species were not affected Increasing phosphate supply as monocalcium phosphate had little effect on plant calcium concentration, but brought about an increase of magnesium in P lathyroides and P atropurpureus In the solodic soil particularly, increases in phosphate supply in most species caused reductions in the potassium concentration, partly compensated by increases in the magnesium and calcium concentrations Concentrations of the cations in the plants reflected the soil exchangeable cation composition Plant species differed in their cation status P atropurpureus and P lathyroides were relatively high in magnesium, L bainesii and D intortum in potassium, V luteola, L bainesii, M sativa, and P lathyroides in sodium, and C pubescens and S humilis in calcium

The effect of phosphorus on the growth and chemical composition of some tropical pasture legumes. II. Nitrogen, calcium, magnesium, potassium, and sodium contents

CS Andrew

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The effect of phosphorus on the growth and chemical composition of some tropical pasture legumes. II. Nitrogen, calcium, magnesium, potassium, and sodium contents