Lorenz, Christian (2025) Implementation of Plants Primary Production in Degraded Ecosystems through Plant Growth-Promoting Bacteria (PGPB). [Tesi di dottorato]

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Abstract

Climate change is increasing the pressure of drought and salinity on agriculture posing significant challenges for maintaining crop productivity and achieving global food security. Plant Growth-Promoting Bacteria (PGPB) are increasingly studied as sustainable solution to enhance plants growth and yield through their association with the root system. This thesis evaluates the effectiveness of PGPB as biostimulants across various scales and substrates, integrating laboratory, field, and high-throughput phenotyping experiments. A pilot bibliometric analysis has been conducted to evaluate the state of knowledge and identify gaps in this topic. Based previous documented results, microbial strains that enhance the production for indole-3-acetic acid (IAA) and show the activity of 1-aminocyclopropane-1-carboxylate (ACC) deaminase were tested for application on crops to improve productivity under drought and salinity stress. Preliminary trials in laboratory, which involved inoculating different PGPB consortia on lettuce seeds sown in both sterilized and not-sterilized soils and salinized and non-salinized substrates. Consortia effects arise not only from direct plant-bacteria interactions but also from the ecological interactions between inoculated strains and native soil microbiota. In separate studies carried out in growth chambers, hemp plants were inoculated under progressive decreasing water availability to simulate water stress to test the benefits of PGPB application on plant biomass and physiological attributes. The results indicated that the effects of the inoculation vary significantly between species, even under the same water stress conditions. Further research involved the set-up of outdoor pots and field trials where tomato plants were subjected to water deficit. The aim was to evaluate the effectiveness of the inoculants on overall agronomic productivity, and specifically on the field, plant health using multispectral vegetation indices derived from unmanned aerial vehicle (UAV). In additional experiments, the application of the strains was tested on wheat under two different irrigation regimes by high-throughput phenotyping platforms for monitoring root and shoot growth as well as photochemistry. Finally, in the last experiments strains were isolated in soils of Atacama Desert (Chile) to study their features and suitability for PGP traits. Across these studies, PGPB effects resulted context-dependent. Consistent benefits were observed under water and salt stress and in realistic soils. However, the outcomes on sterilized substrates and in controlled conditions did not reliably translate to larger-scale settings. Field-scale remote sensing techniques were utilized to capture factors impact and aligned well with ground measurements, allowing for early and non-destructive detection of growth within different irrigation regimes. Additionally, extremophile strains sourced from arid and polar environments differentially enhanced the performance of seeds and seedlings, supporting the idea that extreme environments could serve as reservoirs for PGPB. The overall experiments demonstrated that PGPB efficacy results from interactions among strain, plant species, stress, substrate, and inoculation type. These findings support targeted strain selection and emphasize the need for multi-site validation and consortia development to achieve predictable, scalable use in agroecosystems affected by climate change.

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