Nitrogen nutrition,photosynthesis and carbon allocation in ectomycorrhizal pine

Summary Studies examined net photosynthesis (Pn) and dry matter production of mycorrhizal and nonmycorrhizalPinus taeda at 6 intervals over a 10-month period. Pn rates of mycorrhizal plants were consistently greater than nonmycorrhizal plants, and at 10 months were 2.1-fold greater. Partitioning of current photosynthate was examined by pulse-labelling with¹⁴CO₂ at each of the six time intervals. Mycorrhizal plants assimilated more¹⁴CO₂, allocated a greater percentage of assimilated¹⁴C to the root systems, and lost a greater percentage of¹⁴C by root respiration than did nonmycorrhizal plants. At 10 months, the quantity of¹⁴CO₂ respired by roots per unit root weight was 3.6-fold greater by mycorrhizal than nonmycorrhizal plants. Although the stimulation of photosynthesis and translocation of current photosynthate to the root system by mycorrhiza formation was consistent with the source-sink concept of sink demand, foliar N and P concentrations were also greater in mycorrhizal plants.Further studies examined Pn and dry matter production ofPinus contorta in response to various combinations of N fertilization (3, 62, 248 ppm), irradiance and mycorrhizal fungi inoculation. At 16 weeks of age, 6 weeks following inoculation with eitherPisolithus tinctorius orSuillus granulatus, Pn rates and biomass were significantly greater in mycorrhizal than nonmycorrhizal plants. Mycorrhizal plants had significantly greater foliar %P, but not %N, than did nonmycorrhizal plants. Fertilization with 62 ppm N resulted in greater mycorrhiza formation than either 3 or 248 ppm. Increased irradiance resulted in increased mycorrhiza formation.     

Efficiency of nitrogen,phosphorus, and potassium use by corn,sunflower, and sugarbeet for the synthesis of organic matter

Summary A three-year experiment was conducted in natural conditions on chernozem soil to examine the efficiency of nitrogen, phosphorus, and potassium use by corn (C₄ type), sunflower and sugarbeet (C₃ type) grown in optimum conditions of mineral nutrition (N₁₀₀P₁₀₀K₁₀₀ kg/ha). Plant materials were analysed for the concentration of nitrogen, phosphorus, and potassium and dry matter mass per individual plant parts and the whole plant.Leaves of different age, of all three plant species, were analysed to find eventual differences in the efficiency of use of nitrogen, phosphorus, and potassium in the synthesis of organic matter depending on leaf age.It was found that corn had the lowest concentration of the elements studied but the highest dry matter mass. In other words, corn was more efficient than sunflower or sugarbeet in the use of these elements for the synthesis of an organic matter unit. Such results were arrived at in both sets of analyses, i.e., the analyses of leaves performed in the course of ontogenetic plant development as well as the analyses of leaves of different age.     

Effects of tannins on growth and digestion in two species of papilionids

The effects of tannins on growth and digestion were compared in two species of swallow-tail caterpillars — Papillio polyxenes, a specialist on Umbelliferae that normally does not encounter tannins in nature, and P. glaucus, a generalist whose hostplant range includes tanniniferous tree species in several families. In one experiment, tannin extracted from Liriodendron tulipifera, a P. glaucus foodplant, was applied to leaves from hostplants on the two species; tannin in the diet caused greater mortality in P. polyxenes but failed to do so in P. glaucus. In a second experiment, tannins did not affect digestion, growth rate or nitrogen utilization in either species over a 24-hour period. These findings are inconsistent with the proposed mechanism of digestibility reduction by tannins and, moreover, demonstrate that some degree of counteradaptation is possible in coevolved species. Tannins may thus possess toxic properties other than digestibility reduction.

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Résumé La comparaison a porté sur les effets des tanins sur la croissance et la digestion de deux espèces, Papilio polyxenes, spécialiste d'Ombellifères qui ne rencontre pas normalement de tanins dans la nature, et P. glaucus, généraliste dont les plantes hôtes comprennent des espèces d'arbres tanifères de plusieurs familles. Dans une expérience, des feuilles de plantes hôtes des deux espèces ont été traitées par du tanin extrait de Liriodendron tulipifera, consommé par P. glaucus; ce tanin dans l'aliment a provoqué une forte mortalité chez P. polyxenes mais a été sans effet sur P. glaucus. Dans une second expérience, les tanins n'ont pas modifié la digestion, le taux de croissance et l'utilisation d'azote par ces espèces pendant une période de 24 heures. Ces résultats ne concordent pas avec les mécanismes de réduction de la digestibilité envisagés pour les tanins, et, par ailleurs, démontrent qu'un certain degré de contreadaptation est possible chez des espèces ayant coévolué. Les tanins peuvent alors posséder quelques propriétés toxiques différentes de la réduction de la digestibilité.

     

Assimilate Conversion in Potato Tubers in Relation to Starch Deposition and Cell Growth

The activity of enzymes involved in the conversion of sucrose to starch together with the distribution of ¹⁴C-labelled photosynthate and ⁴C-sucrose was studied in potato tubers showing a range of growth rates and growth patterns. Within a particular tuber the uptake of ¹⁴C from labelled photosynthate and the conversion to ethanol-insoluble ¹⁴C was greatest in the apical tissue where both the rate of production of new storage cells and starch synthesis were likely to be greatest. Uptake and conversion of ¹⁴C was lowest in the older tissue of the tuber base. Pre-treatment of tubers with gibberellic acid reduced the total input of ¹⁴C from labelled photosynthate, reversed the gradient in ¹⁴C uptake between apical and basal tuber tissue, increased the amount of ¹⁴C per g fresh weight in the basal tissue and decreased the conversion of labelled sugars to starch. For tubers with different growth rates both the total uptake of ¹⁴C from labelled photosynthate and the ratio ethanol-insoluble ¹⁴C/ethanol-soluble ¹⁴C appeared to be correlated with growth rate. In contrast when tubers were fed directly with ¹⁴C-sucrose via the tuber surface, total uptake was independent of growth rate but the correlation between growth rate and the ratio ethanol-insoluble ¹⁴C/ethanol-soluble ¹⁴C persisted. Within a particular tuber there was a decreasing gradient in sucrose synthetase activity between youngest tissue of the tuber apex and the older tissue at the tuber base but there was no clear correlation between mean enzyme activity and tuber growth rate. ADPG-pyrophosphorylase and the ratio ADPG-pyrophosphorylase/starch phosphorylase showed some correlation with tuber growth rate. Starch synthase, starch phosphorylase and UDPG-pyro-phosphorylase activities per g fresh weight of tuber tissue appeared to be relatively constant. The results suggest that the transport of sugar from the phloem sieve tubes to the tuber storage parenchyma cells, in particular the phloem unloading step, and the conversion of sugar into starch are subject to separate regulation in the potato tuber.     

Pertilization and nutrition experiments with conifer seedlings in pots

Summary In conifer fertilization and nutrition experimentsPinus halepensis, P. radiata andP. maritima seedlings were grown in pots, filled with soil derived from mica schist and siliceous tertiary deposits and also in peat substrate in paperpots.Fertilization with P ofP. radiata andP. maritima seedlings growing in soil low in available P and N improved seedling height only in combination with N fertilization and fertilization with alone induced P deficiency symptoms. N fertilization with from 100 to 150 ppm (2.4 to 3.2 g N/kg, respectively) in the soil regardless of the form of N (NH₄ ⁺ or NO₃ ^–) applied in the summer or autumn together with application of 20 ppm P before sowing was the fertilization regime which produced the best seedlings.Fertilization of peat before sowingP. halepensis, P. radiata andP. maritima with omission of one of the nutrients N, P and K resulted in visible symptoms of N, P and K deficiency, respectively, in the seedlings. Comparative chemical analysis of needles from the three kinds of conifer seedlings with deficiency symptoms and healthy ones verified the visual symptoms of N and P deficiency but not so convincingly the K deficiency symptoms.     

Effects of combined nitrogen on anapleurotic carbon assimilation and bleeding sap composition in Phaseolus vulgaris L.

Dwarf french beans, Phaseolus vulgaris L., were grown with or without inoculation with rhizobia (strain 3644), and with or without a combined nitrogen source (nitrate or ammonium ions). The distribution of radioactivity into products of dark ¹⁴CO₂ assimilation was studied in roots or nodules from these plants. A detailed study was also made of the distribution and rates of excretion of nitrogen in xylem bleeding sap in 28 day old plants grown on the various sources of nitrogen. Whereas detached nodules accumulated radioactive glycine, serine and glutamate when incubated with ¹⁴CO₂, bleeding sap from plants root fed ¹⁴CO₂ contained low levels of radioactivity in these compounds but higher levels in allantoin. Chemical analysis showed allantoin to be the major compound transported in the xylem of nodulated plants, whether or not they were fed on combined nitrogen. In contrast uninoculated plants accumulated mainly amino acids in the bleeding sap, the amount and chemical composition of which depended on the combined nitrogen source.Abbreviations PEP phosphoenol pyruvate - OAA oxaloacetate     

Nitrogen fixation, stomatal response and transpiration in Medicago sativa, Trifolium repens and T. subterraneum under water stress and recovery

Stomatal behaviour, transpiration and nitrogen fixation were investigated in Medicago sativa L. (cvs. Tierra de Campos and Aragon, Hidalgo-Maynar 1966), Trifolium repens L. (cv. Aberystwyth S-184) and Trifolium subterraneum L. (cv. Clare) subjected to drought by withholding water and then to three days’ recovery after rewatering. Dawn leaf water potential was measured with pressure chamber, stomatal response with a diffusion porometer and nitrogen fixation by using acetylene reduction technique. At low water potentials, the leaf resistance was higher in Medicago than in Trifolium. As water stress developed all species decreased their transpiration, T. subterraneum being the one most affected by moderate deficits. During water stress ‘Tierra de Campos’ always maintained higher acetylene reduction levels than ‘Aragon’ and the Trifolium species, except for the lowest water potentials. During recovery from water stress only ‘Tierra de Campos’ reached predeficit transpiration rates. In ‘Tierra de Campos’ acetylene reduction recovery after rewatering was more rapid and intense than in ‘Aragon’. It is concluded that, of the plants investigated, ‘Tierra de Campos’ was best adapted to water deficits.     

Growth, nutrition, and nitrogen fixation in grey alder at varied rate of nitrogen addition

Seedlings of grey alder (Alnus incana Moench), nodulated or unnodulated, were investigated at varied relative addition rate of nitrogen. Nitrogen fixation alone, without addition of mineral nitrogen, resulted in an almost optimum nitrogen status but only about half the maximum relative growth rate, probably mainly because of energy costs of nodulation and fixation. The growth deficit due to nodulation was much more than can be explained by the theoretical energy requirement for the amount of nitrogen fixed. Thus, the nitrogen fixation process was not very efficiently used. The nitrogen fixation rate was strongly stimulated by increasing nitrogen addition rate up to high levels. The fixation rate decreased rapidly close to optimum (maximum relative growth rate) and was negligible at maximum growth. A feed-back of mineral nitrogen on photosynthesis increased fixation rate with time, and the relative importance of fixation over mineral nitrogen nutrition increased. However, nitrogen fixation, also at maximum rate, supplied only a small proportion of the nitrogen amount required for maximum growth. The optimum nutrient solutions contained comparatively high nitrogen concentrations to secure free access to nitrogen. The nodules were damaged by this treatment, and it is concluded that the nitrogen additions must be adjusted to the current consumption of the plants to avoid an increased external nitrogen concentration. Strong linear regressions were found between relative growth rate, nitrogen status expressed as percentage content of fresh weight, and relative growth rate in unnodulated seedlings. There was a greater variability in nodulated seedlings than in unnodulated ones, because of the nitrogen fixation. The reactions of unnodulated grey alder were largely the same as previously reported for birch seedlings, but the maximum growth capacity was lower in grey alder. During an initial period of change in the internal nitrogen status, deficiency symptoms appeared, especially in unnodulated seedlings. As in birch, the leaves turned green again at stable nitrogen status, independent of level. The results are in sharp contrast to data from the literature where the external nitrogen concentration was used as the driving variable for the internal nitrogen status. The measured fixation rates for grey alder are much higher than those previously reported. Still, the maximum fixation rate observed is small compared to the total nitrogen uptake rate required for maximum growth, in contrast to reported relationships. These comparisons indicate that increased external nitrogen concentration obscures the real relations between mineral and fixed nitrogen, on one hand because of rapid inhibition of nitrogen fixation and, on the other hand, because of failure to obtain stable optimum nutrition and maximum growth by means of this treatment variable.     

Deep placement: A method of nitrogen fertilizer application compatible with algal nitrogen fixation in wetland rice soils

Summary The effect of different methods of nitrogen fertilizer application on the algal flora and biological nitrogen fixation (Acetylene-reducing activity) in a wetland rice soil was studied in pot and field experiments. Broadcast application of urea inhibited nitrogen fixation and favored the growth of green algae. In contrast, deep placement of urea supergranules (1–2 g urea granules) did not suppress the growth of N₂-fixing blue-green algae and permitted acetylene-reducing activity on the soil surface to continue virtually uninhibited.