tailieunhanh - Humic Matter in Soil and the Environment: Principles and Controversies - Chapter 4

GENESIS CÁC VẤN ĐỀ HUlMC 4,1 Đại CHỦ YẾU CỦA HUMIFICATION Quá trình trong đó có vấn đề humic được hình thành đã được gọi là humification, trong đó bao gồm một số các phản ứng sinh hóa. Nó gắn liền với các chu trình hữu cơ và nitơ trong môi trường. Mặc dù một số người có ý kiến rằng các cơ chế để tổng hợp không rõ ràng, một số giả thuyết trong thực tế được trình bày vấn đề hurnic như thế nào được hình thành. Nói chung, những lý thuyết khác nhau trong các nguồn tài liệu gốc. | CHAPTER 4 GENESIS OF HUMIC MATTER MAJOR PATHWAYS OF HUMIFICATION The process by which humic matter is formed has been called humification which involves a number of biochemical reactions. It is closely connected to the organic and nitrogen cycles in the environment. Though some people are of the opinion that the mechanisms for synthesis are not clear a number of hypotheses have in fact been presented on how humic matter is formed. In general these theories differ in the way the sources of original or raw materials are utilized in the synthesis of humic substances. Whereas one group of theories is based on depolymerization of biopolymers causing their direct transformation into humic substances the other group envisages polymerization of small molecules liberated by complete decomposition of the biopolymers in the formation of humic matter. All agree that the materials for formation originate mostly from plant material though in practice animal residue can also be transformed into humic matter. The depolymerization theory called biopolymer degradation by Hedges 1988 assumes that the biopolymers in plants are gradually transformed into humin which eventually will be degraded successively into humic acids and fulvic acids. The lignin theory of Waksman 1932 and its modem version are considered examples of T B X X E K Copyright n 2003 by Marcel Dekker Inc. All Rights Reserved the biopolymer degradation theory. In contrast the polymerization theory claims that the plant biopolymers are decomposed first into their monomers or smaller organic components. Humic substances are then formed by interaction reactions between these small components. This theory assumes fulvic acid to be formed first which by polymerization or condensation can be transformed into humic acids. The polyphenol or phenol quinone and sugar-amine condensation theories belong to the category of the polymerization theory. This second pathway of humification has recently also been called the abiotic .