EFFECTS of a SOIL HUMIC COMPOUND on ROOT INITIATION. [ referenced in Visser’ s – Effects of HUMIC SUBSTANCES on BIOLOGICAL AND ENZYMATIC ACTIVITIES in SOIL.] Humic compounds are acidic dark colored and pre-dominantly aromatic substances that occur in soil organic matter in concentrations which range from close to zero to near 10 0 per cent. Because of their exchange capacity and ability to complex metal ions and hydrous oxides, these compounds affect the availability of nutrients to plant roots and biological systems, and also play an important part in the genesis of soil. Little is known about the direct effects of humic compounds, such as those effects caused by uptake by plants and influence on plant metabolism. According to Russian workers (1) small concentrations of humic compounds, that is, up to 60 p. p. m., enhance root development and growth of a number of plants Kristeva(1) believes that these compounds enter the plant during early stages of growth and are supplementary sources of the POLYPHENOLS that serve as RESPIRATORY CATALYSTS. Heavy summer rains may bring concentrations of humic compounds of the order of several thousand p. p. m. into the soil solution. The object of this investigation was to determine the possible influence of these higher concentrations on the initiation of roots. The humic compound used originated from a podzol Bb horizon. Method of extraction purification and drying, as well as a number of physical and chemical characteristics of this organic matter, have been described previously(3). The extracted and purified organic matter was soluble in both alkali and acid, so that, according to the definition accepted in soil science, it was FULVIC ACID. Root initiation was measured as follows(3):cotyledons were removed from 11 day-old bean seedlings ( Phaseolus vulgaris L., C.V. ‘Contender’) which were grown on vermiculite roots and etiolated stem tissues were rejected by trimming 2 in. below the cotyledonary node. The resulting leafy stem cuttings were placed in individual vials, each containing 0.25 ml of 1/40 molar sodium bicarbonate solution either with or without fulvic acid. The cuttings completely absorbed the solutions within 3 to 3.5 h and were then trimmed through the cotyledonary node to leave 2 in. hypocotyls segments which were planted vertically (node end exposed), 1.875 in. deep, in pots of ‘Perlite’ previouslt drenched with nutrient solution. Potted segments were overwrapped by polyethylene and held at 78 degrees F. to develop roots. The segments were removed from the ‘Perlite’ after six days and roots and initials counted under a magnifier-illuminator. Root counts reported here are averages of 22 segments. Root formation was stimulated by fulvic acid concentrations greater than 500 p.p.m. (Fig. 1), reached a maximum at 3,000 p.. p. m. and then remained more or less constant up to 6,000 p. p. m. which was the highest concentration tested. The ph values of the 1/40 molar sodium bicarbonate solutions acid were 7.1, 6.6. and 5.8 respectively. Treatments
with pure 1/40 molar sodium bicarbonate solution (ph 8.4)produced the same root counts as treatments with distilled water.(ph 5.5). The presence of substantial numbers of COOH (the univalent radical COOH, the functional group characteristic of all organic acids)[added], phenolic and alcoholic hydroxyl groups in this fulvic acid(4) suggested that these groups might, at least in part, be responsible for the root initiation properties of fulvic acid. Thus, each of the principal functional groups was blocked selectively by methods described elsewhere(5) These preparations were dissolved in 1/40 molar bicarbonate solution and administered at concentrations of 1,500 p. p. m. Blocking of practically all hydroxyl groups by acetylation reduced root initiation considerably but blocking of COOH groups by esterification had no effect. This suggested that both types of functional groups in the fulvic acid were involved concurrently in reactions which resulted in increased root initiation. A possible explanation for the experimental results lies in the known ability of the fulvic acid to form stable water-soluble complexes with di- and tri-valent metal ions.(4) Thus it is possible that the fulvic acid may aid in the movement of metal ions which can only be transported with difficulty within the plant. Iron is known to be essential to cell division