Molecular Aspects of Humic Substances and Biological Functionality in Soil Ecosystems

The complexity of humic substances and their remarkable properties have attracted and continue to attract the attention of many investigators, bringing over the years new knowledge on their structure, physicochemical and biological properties pointing to the use of these interesting natural compounds in many practical applications. The numerous investigations produced, up to now, controversial results, because of the lack of detailed knowledge on the composition of HS that makes very difficult to identify the relationships between the structure and the activity of these substances. Evidence presented here showed that the effects of HS on plant growth depends on the source, concentration and molecular weight humic fractions and mainly by different chemical compounds contained into them. Humic matter appears also to display an hormone-like activity. It is not clear if this activity is strictly linked to the chemical structure of HS or whether it depends on hormones of microbial origin entrapped into them. In any case, HS exhibit stimulatory effects on plant cell growth and development. In this review, the relationship between humic substances structure, chemical composition and physiological effects on plant growth and metabolism are examined. In particular, the responses of plants to humic substances are described, the regulatory circuits which allow plants to cope with humus are presented, and how the present findings can add new information to the humic substances world, is discussed. Effects of two Lignosulfonate-Humates on Zea mays L. Metabolism A. Ertani, O. Francioso, V. Tugnoli, V. Righi, S. Nardi Department of Agricultural Biotechnology, University of Padova, Agripolis, Viale dell’Università 16, 35020 Legnaro, Italy. Department of Agroenvironmental Sciences and Technologies, University of Bologna, V.le Fanin 40, 40127 Bologna, Italy. Department of Biochemistry “G. Moruzzi”, Via Belmeloro 8/2, 40126, Bologna, Italy. Two lignosulfonate-humates (a and b), derived by an industrial process from lignin, were chemically characterized and their effects on maize plants in terms of growth, nitrogen metabolism and photosynthesis were investigated. The biological effects of lignosulfonatehumates were compared with those induced by a humic acid extracted from leonardite in order to better understand the complexity of their biological effects. Our results displayed that both lignosulfonate-humates (a and b) had a hormone-like activity and increased root and leaf growth. Moreover, all treatments increased the content of chlorophyll, glucose and fructose and enhanced the activity of Rubisco, glutamine-synthetase and glutamate-synthase. The observed intense biological activity indicated that lignosulfonate-humates and leonardite humic acid had a positive role on photosynthetic process of maize plants. In the light of these results, lignosulfonate-humates may be used as biostimulants to increase crop yield.