## 1 Introduction
The RSA refers to the integrated root system topology, the spatial distribution of the primary and lateral roots, and the number and length of various root types. The RSA is modified by PGPR mainly through their ability to interfere with the plant's hormonal balance and processes [32]. The implication of the species-specific production of phytohormones, secondary metabolites, and enzymes leads to changes in the growth rates of the primary roots, the branching of the lateral roots, and the density of the root hairs [32; 33]. In the present context of rising global temperatures, it is useful to study PGPR which also have thermotolerant traits. In the past, several thermotolerant microbial strains were identified [24; 34], including Burkholderia phytofilmans [35]. Paraburkholderia, which is a more recently described new genus that is delineated from Burkholderia, contains many species that assist the plants' growth [36; 37]. _Paraburkholderia phytofilmans_ PsJN is a well-studied model PGPR that is known to induce tolerance to both biotic and abiotic stresses. This beneficial bacterial endophyte is capable of colonizing a wide range of plants including wheat [38], maize [39], grapevines [40], tomatoes [41], and potatoes [35]. Its plant-beneficial effects are attributed to several mechanisms including the production or modulation of plant phytohormones [42], the facilitation of resource acquisition [38], the production of siderophores and secondary metabolites [37], and the induction of systemic resistance (ISR) [43]. PsJN has been used in different plant studies against drought, low temperatures, and salinity [38; 44; 45]. Generally in the root, PsJN has increased the root biomass in maize, potatoes, Brassica and switchgrass, and in the latter two, it also promoted root elongation. It has been shown to increase the number of root hairs in several species including Arabidopsis [46]. To our knowledge, however, only two studies to date have utilized this bacterium to protect against high-temperature stress, and these have focused on the genotypic responses of potatoes [41] as well as the physiological and biochemical changes in tomato aerial tissues [47]. In potatoes [41], PsJN generally increased the root dry weight at the elevated temperatures of 18 potato clones when they were compared to the non-bacterized plants. To our knowledge, the question of the adaptation of the root system architecture to an elevated temperature when the plants are bacterized with PsJN is still open. Quantifying plant growth dynamics requires non-invasive phenotyping on the same plant individuals through time. While multiple approaches exist for the aerial part of the plant, the roots represent a particular challenge due to their hidden nature (inherently, they are in the soil). Earlier investigations of plants' roots and their interactions with microorganisms only utilized destructive measurements or harvest sampling methods (e.g., [48]). Destructive approaches discriminate and fail to capture the diverse growth patterns and dynamics within a plant's ontogeny. To enable an ontogenetic and non-destructive approach, several phenotyping platforms have been employed in plant studies to characterize the root traits [49]. Now, non-invasive, time-resolved phenotyping is becoming more common to the study of plant root-microorganism processes [31; 50]. The root phenotyping pipelines consist of a plant growth system, root imaging, and root trait digitization [51]. A traditional plant cultivation practice to quantify the root growth parameters is the use of a transparent medium such as agar gels [52]. Since manual measurements of the root traits of agar-grown plants are labor- and time-intensive, there is a necessity for increasing the throughput. This is addressed with the use of camera- or scanner-based imaging with varying degrees of automation [52], such as the use of multiple scanners operating in parallel [53; 54] or the use of a shifting camera that is operated by moving stages or a robotic gantry system [55; 56; 57].