Invited Speakers

HUMIC SUBSTANCES FROM A POINT OF BIOLOGICAL EVOLUTION AND PLANT PHYSIOLOGY: UNLIKELY, POSSIBLY, POTENTIALLY In spite of growing awareness on potential beneficial effects of humic substances on plants within the last decade, many existing controversies together with significant lack of general scientific evidence still restrict the wide use of the respective products in agricultural practice. The aim of the present talk will be to analyse putative effects of humic substances on plants on the basis of both evolution of plant adaptations to the environment as well as on plant functions, especially, at the level of nutrition and environmental constraints. Emphasis will be given on sorting out these effects and possible mechanisms of action according/in respect to their probability to generate practical benefits of use in agricultural practice. It is evident that plant growth cannot be analysed separately from soil processes, where microbiological activity is a main provider of mineral nutrients for plant needs. In this respect, humic substances, acting through stimulation of certain aspects of soil microbiology, will benefit plants indirectly. Plant hormone-like activity of humic substances is another possibility for consideration, but growth stimulation through exogenous hormones will benefit plant only in the case of optimum mineral nutrient supply. Last but not least, humic substances can increase plant adaptogenic potential, acting as inducers of certain defence responses. However, concept of induced defence implies that some significant part of internal plant resources need to be converted from supporting growth to defence, benefiting plant only in conditions of severe environmental problems.

POTENTIAL OF DISSOLVED ORGANIC MATTER (DOM) TO ASSIST REMEDIATION OF HEAVY METAL POLLUTED SOILS Pollution of soils with heavy metals (HMs), can threaten human health and ecosystem functioning. Therefore, polluted soils must be remediated. Soil washing and phytoextraction seem currently the most attractive remediation methods. Both methods depend on HM solubility (extractability), which can be increased by addition of ligands such as EDTA, NTA and other aminopolycarboxylic acids. As an alternative to these synthetic and environmentally questionable chemicals, the possibility of using naturally occurring dissolved organic matter (DOM) to extract HMs from anthropogenic polluted soils is evaluated in this review based on mainly recently published laboratory studies. DOM isolated or extracted from soils consists of fulvic acid (FA) with some low-molecular-weight-organic-acids (LMWOAs), e.g. citric, oxalic and salicylic acids. In addition to soil DOM, results with other soluble humic substances and LMWOAs will be included.

Jelgavas iela 1

VARIABILITY OF HUMIC ACID PROPERTIES DEPENDING ON THEIR PRECURSOR MATERIAL: A STUDY OF PEAT PROFILES Analysis of variation of peat composition, presence of trace elements in the peat and HSs within peat profiles can give information on the character of transformation of organic matter, important for C biogeochemical cycling, but also about impacts of climate change and human activities. In peat the transformation and decay process of living organic matter (humification) is retarded by the acidic and anaerobic environment, but at the same time the peat can provide information on environmental and paleo-environmental conditions of the past. The aim of the present study is to analyze the elemental and functional composition, spectral characteristics of humic acids isolated from a well characterized raised bog peat profiles to evaluate the impact of the character of humification processes on the peat HA properties.