INORGANIC NITROGEN NUTRITION OF THE SEEDLINGS OF THE ORCHID,CATTLEYA

When grown in vitro in a medium containing NH₄NO₃ as the sole source of nitrogen, seeds ro the orchid, Cattleya (C. labiata ‘Wonder’ X C. labiata ‘Treasure'), germinated readily and proceeded to form small plantlets. Development of the embryos was accompanied by an increase in their total nitrogen and a decline in the percent dry weight. Growth responses of the seedlings in other ammonium salts like (NH₄)₂SO₄, (NH₄)₂HPO₄, NH₄Cl, ammonium acetate and ammonium oxalate were similar to that in NH₄NO₃. However, when grown in a medium containing NaNO₃, development of the seedlings was drastically inhibited; KNO₃, Ca(NO₃)₂, KNO₂ and NaNO₂ also were poor nitrogen sources. Attempts to grow the seedlings in NaNO₃ by changing the pH or by addition of kinetin, molybdenum or ascorbic acid as supplements were completely unsuccessful. When seedlings growing in NH₄NO₃ for varying periods were transferred to NaNO₃, it was found that those plants allowed to grow for 60 or more days in NH₄NO₃ could resume normal growth thereafter in NaNO₃. Determination of the nitrate reductase activity in seedlings of different ages grown in NaNO₃, after NH₄NO₃, showed that the ability of the seedlings to assimilate inorganic nitrogen was paralleled by the appearance of the enzyme.     

THE EFFECTS OF NITROGEN SUPPLY UPON THE VERTICILLIUM WILT OF ANTIRRHINUM

Isolates of Verticillium albo-atrum, V. dahliae and V. nigrescens grown on media adequately supplied with sodium nitrate induced wilt rather more rapidly in antirrhinum plants growing in soils with a normal and an excessive amount of nitrogen than in plants in nitrogen-deficient soil, though plants became diseased in all soils. Similarly treated isolates of V. nubilum and V. tricorpus induced a greater incidence of wilt in plants in soil supplied with heavy dressings of organic nitrogenous fertilizer than in plants in soil deficient in nitrogen, although V. tricorpus from a medium containing much sodium nitrate, in contrast to V. nubilum , was pathogenic to plants in such deficient soil. The ability of the nitrogen-starved isolates to penetrate the host plant was significantly diminished, and even when wound-inoculated into stems their effect upon the host was much reduced.     

氮肥对覆膜花生固氮活性与产量的影响

不施氮肥花生固氮力为106～146公斤N/顷。施用高量氮肥对花生结瘤不利,用量10、20、40、60公斤NH_4NO_3/亩时,花生固氮率分别降低24、47、67、82%,花生约增产10%,在施低量氮肥(5公斤NH_4NO_3/亩)时不影响花生结瘤,且对花生有增产作用。有机肥对花生结瘤的抑制作用比无机氮肥轻,在2与4吨/亩(0.6％N)用量时,花生固氮作用降低7与23%,花生约增产8.0％     

THE EFFECT OF ADDED NITROGEN ON THE RATE OF DECOMPOSITION OF ORGANIC MATTER

(1) N added to decomposing organic matter often has no effect or a negative effect on microbial activity, at least in the long term. More than 60 papers are cited in support of this statement.
(2) The negative effect of N is mainly found with recalcitrant organic matter with a high C/N ratio (straw, wood, etc.), whereas a positive effect of N is common for easily degradable organic material with low C/N ratio.
(3) The negative effect of N could be explained by: (i) N disturbs the outcome of competition between potent and less potent decomposers; (ii) through 'ammonia metabolite repression', N blocks production of certain enzymes, at least in basidiomycetes, and enhances breakdown of the most available cellulose, whereby recalcitrant lignocellulose accumulates; (iii) amino compounds condense with polyphenols and other decomposition products, forming 'browning precursors' which are toxic or inhibitory.
(4) The effect of adding N may depend on the microflora present.
(5) There are indications that some microorganisms have a 'luxury uptake' of N when it is present in sufficient amounts, thereby delaying N mineralization.
(6) The addition of N seems to increase the formation of water-soluble , brown, recalcitrant compounds, but to decrease the amount of humus formed.     

THE EFFECT OF LIGHT ON THE USE OF THE NITROGEN RESERVES OF GERMINATING SOYBEAN SEEDS

Light affects the mobilization and distribution of several of the storage components of the cotyledons of germinating soybean seeds. The nitrogen content of the cotyledons began to decrease during the first day of germination, continued through day 12 for plants in the light, and day 14 for those in the dark. Cotyledons from both treatments had lost about the same amount of nitrogen by day 14. Plants from both treatments lost about the same amount of dry weight by day 8, but those in the light had taken up nitrogen from the nutrient solution; while those in the dark showed no increase. The plants in the light had higher concentrations of soluble amino nitrogen in the cotyledons than did those in the dark, but the opposite was true for the seedling axis. Aspartate and its amide accounted for half or more of the total free amino acids in all parts of dark-grown plants at 6 and 14 days. In the light-grown plants aspartate and asparagine usually accounted for less than half of the total free amino acids in all plant parts except the cotyledons at 6 and 14 days. Total soluble amino acids were much lower in these plants than those in the dark, excepting the cotyledons.