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Rui Gustavo Santini:
Vineyard soils evaluation. Combining elemental analysis via X-ray fluorescence core scanner and microbial DNA sequencing to assess soil vertical stratification

Date: 31-12-2018    Supervisor: Kurt H. Kjær

Together with environmental features such as climate, latitude and elevation, soil is recognised as a fundamental factor in defining the wine terroir. Soil composition is considered to have a major influence on grapevine vigour, affecting the berries’ quality and, consequently, the wine characteristics. The aim of this thesis is to contribute to understanding soil vertical elemental distribution and the effect of depth on microbial communities’ composition, which are both topics of particular importance for plants that have the potential to develop deep roots, such as grapevines. Along the extension of the entire soil profile, the root system is able to (1) take up available resources; and (2) interact with microorganisms.

To perform the studies presented in this thesis, 19 undisturbed soil cores were retrieved from vineyards in Australia, Spain and Denmark. These soil cores were taken from down to depths of between 2.4 and 6.0 m. Vertical elemental distribution was evaluated through high-resolution X-ray fluorescence (XRF) at the millimetre scale, for scanning of the undisturbed soil cores. For microbial assessment we sub-sampled the soil cores at different depths and sequenced the 16S rRNA gene and the ITS regions for, respectively, prokaryotes (313 samples) and fungi evaluation (63 samples).

The XRF measurements showed important variance of elements along the soil cores, indicating the effects of amendment practices or caused by the natural lithological changes. Microbial communities were shown to vary significantly with depth and geography. While several microbes’ taxa were solely detected in specific soil layers and countries, some prokaryotes appeared as ubiquitous, dwelling in the different soil depths and countries evaluated. Various microorganisms detected along the soil profiles are potential influencers of plant health via microbe-root interactions, including the deep fine roots. Additionally, several bacterial phyla correlated with soil edaphic factors, suggesting a strong effect of soil composition in shaping the microbial communities.

This thesis is part of the MicroWine consortium (www.microwine.eu). The results obtained here, together with the information gathered by the other projects that included microbiological analysis of the vine organs, must and wine, have the potential to expand our knowledge of the relation between soil and wine microorganisms.