Reference

Variations of molecular complexes of humic substances as a consequence of acidification with organic acids

Variations of molecular complexes of humic substances as a consequence of acidification with organic acids. Nardi, S.; Dell'Agnola, G.; Albuzio, A. (Ist. Chim. Agrar. Ind. Agrar., Univ. Padova, Padua, Italy). Agrochimica, 30(1-2), 148-59 (Italian) 1986. CODEN: AGRCAX. ISSN: 0002-1857. DOCUMENT TYPE: Journal CA Section: 19 (Fertilizers, Soils, and Plant Nutrition) Humic substances extd. from various soil types were exposed to low pH to simulate the effects of org. acids released by plant roots. Where the pH of the humic substances was lowered to <3.0 with acetic [64-19-7], propionic [79-09-4], or citric acid [77-92-9], the apparent mol. wt. of the humic substances decreased from >100,000 to <5000. Other org. acids, such as malonic [141-82-2], maleic [110-16-7], fumaric [110-17-8], oxalacetic [328-42-7], malic [6915-15-7], succinic [110-15-6], glutamic [110-94-1], glycolic [79-14-1], and glyoxylic acid [298-12-4], provoked a smaller decrease in mol. wt. Mineral acids, alcs., or phenols in solns. of correspondingly low pH had no effect. Acidification of the humic substances was assocd. with the release of metals, esp. Ca, Mg, and Zn, with lesser amts. 79-14-1 and 6915-15-7 which are cas registry numbers of chemicals are mentioned. of Al and Fe. The citric acid-induced decrease in the mol. wt. of humic substances was largely reversible by increasing the pH; although alkalinization also caused respiration of Fe and Zn, the other metal ions were less responsive to increased pH. These data are discussed in relation to the effects of humic substances on ion absorption, transport, and metab. in plants. Humic substances of low mol. wt. may be absorbed by plant roots and hence exert their phsyiol. effects. .

Comparative effects of nitrate and ammonium on growth and metabolism of French bean

Comparative effects of nitrate and ammonium on growth and metabolism of French bean. Chaillou, Sylvain; Morot-Gaudry, Jean Francois; Salsac, Louis; Lesaint, Christiane; Jolivet, Eugene (INAP-G, Paris 75005, Fr.). Physiol. Veg., 679-87 (English) 1986. CODEN: PHYVAP. ISSN: 0031-9368. DOCUMENT TYPE: Journal CA Section: 19 (Fertilizers, Soils, and Plant Nutrition) Bean plants (Phaseolus vulgaris) were grown in a greenhouse with nutrient solns.Some commonly used reagents like 56-45-1 and 57-48-7 are used in this experiment. contg. either NO3- (2 mM) or NH4+ (2 mM) and renewed 3-4 times per h. After 35-45 days, NH4+-fed plants had half the fresh matter of NO3--fed plants. Mineral cation concn. was 30-40% lower and org. acid (malic [110-16-7], malonic [141-82-2], and citric) [77-92-9] concn. was 80-90% lower in NH4+ plants than in NO3- plants. Amino acids (serine [56-45-1], asparagine [70-47-3], and glutamine [56-85-9]) were 3-10-fold higher and carbohydrates (glucose [50-99-7], fructose [57-48-7], sucrose [57-50-1], and starch [9005-25-8]) 1.5-5-fold higher in NH4+ plants than NO3- plants. In general, solute concns. in NH4+ plants were lower than in NO3- plants, but the energetic cost (ATP equiv.) for synthesis of org. acids, amino acids, and free sugars was similar for both N nutrition treatments. The growth deficit in NH4+ plants, which did not appear to be due to pH changes (minimal) in the soln., may be explained by an osmotic handicap in those plants and by perturbations in the chloroplast functioning because of a possible excess of photosynthetic reducing power in the absence of NO3-. Starch accumulation in the leaves of NH4+ plants is an argument for this hypothesis. .