Ippolito, Francesca (2016) Biochar as a new soil amendment to promote plant growth and disease control. [Tesi di dottorato]

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Biochar as a new soil amendment to promote plant growth and disease control Abstract The utilization of organic amendments has been proposed to decrease the incidence of plant diseases caused by soilborne pathogens. In this thesis, we first reviewed the limited number of studies present in the literature by analysing the different mechanisms proposed to explain biochar disease suppression. A total of 12 papers were included in this analysis with 18 experimental case studies. The effect of biochar amendment was suppressive in 89% and non-significant in the remaining 11%, with few studies reporting a significant increase of disease incidence. Biochar can be effective against both airborne (e.g. Botrytis cinerea, different species of powdery mildew) and soilborne (e.g. Fusarium spp., Phytophthora spp., Rhizoctonia solani) pathogens. Five different mechanisms have been proposed to explain biochar disease suppression: (i) induction of systemic resistance in host plants; (ii) enhanced abundance and activities of beneficial microbes, including mycorrhizal fungi; (iii) modification of soil quality in terms of nutrient availability and abiotic conditions such as liming effect; (iv) direct fungitoxic effect of biochar; (v) sorption of allelopathic, phytotoxic compounds that can directly harm plant roots and thus promote pathogen attacks. Potential side-effects of biochar have been reported, such as the possibility of absorbing agrochemicals such as herbicides, insecticides and fungicides, thus reducing their efficacy. Results from this review demonstrate that biochar amendments have great potential but, until now, not enough studies are available for a widespread adoption of biochar as a soil amendment in today’s agricultural systems. More investigations on the mechanisms underlying biochar disease suppression, as well as long-term field experiments, are needed to make biochar a safe, effective and affordable tool for the control of plant pathogens. In this context, we performed a study with the objective to investigate the effects of the biochemical changes of heated plant tissues on plant and microbial growth. In particular, 48 different organic substrates, including heated and untreated materials, were used. Moreover, plant litter types were characterized by classic proximate chemical analyses and, at molecular level, by solid-state 13C-CPMAS NMR. Fungal growth was consistently higher over untreated plant litter. A dramatic decrease of microbial growth was observed for all species when temperature increased. However, an opposite response of temperature was found on test plant growth. At molecular level, the most significant treatment was at 300°C. It shows a strong degradation of sugars and polysaccharides (O-alkyl-C region) and a contemporary neo-formation of aliphatic and aromatic C compounds. One of the most significant evidence from this study is that the opposite responses of plant and microbial growth can be the result of the balance between the availability of labile organic C sources and the presence of recalcitrant and/or fungitoxic compounds. In addition, on the basis of the existing studies and results obtained with the charred litter, we investigated how biochar affects plant growth and microbial activity. The aims of this study were i) to detect the chemical changes occurring on different feedstocks when pyrolyzed at two specific temperatures (300 °C and 550 °C) by using 13C-CPMAS NMR spectroscopy and ii) to assess how biochar can influence the growth of fungi, bacteria, and crop plants. In particular,12 different organic materials, including pyrolyzed and untreated materials, were used. The experimental design compared the effect of amendments carried out by using biomasses untreated and the derived biochars. We found that undecomposed organic materials may cause a severe inhibition of plant root growth butor , in some cases have a stimulating effect. However the inhibitory effect largely decreased after pyrolyzation. In contrast to the higher plant, fungi and bacteria throve on most of organic materials and showed a steep decline or a complete growth inhibition on biochars obtained at 300°C and 550°C. One of the most significant evidence from this study is that twelve out of fourteen tested microbes, with the exception of two basidiomycetes, showed a remarkably similar pattern of correlation between growth and organic material quality, as defined by 13C CPMAS NMR. An opposite response was observed for the higher plants Lepidium, Lactuca and Lycopersicon in terms of both chemical quality and its correlation with root growth.

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