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Individual plants vary in their ability to respond to environmental changes. The plastic response of a plant enhances its ability to avoid environmental constraints, and hence supports growth, reproduction, and evolutionary and agricultural success.Major progress in the analysis of above- and belowground processes on individual plants has been made by the application of non-invasive imaging methods including Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET).MRI allows for repetitive measurements of roots growing in soil and facilitates quantification of root system architecture traits in 3D. PET, on the other hand, opens a door to analyze dynamic physiological processes in plants such as long-distance carbon transport in a repeatable manner. Combining MRI with PET enables monitoring of short livedCarbon tracer (11C) allocation along the transport paths (i.e. roots visualized by MRI) into active sink structures.To analyse the link between root-internal C allocation patterns and C metabolism in the rhizosphere, we are combining 11CO2 with stable 13CO2 labelling of plants. Isotope ratio mass spectrometry (IRMS) analyses of rhizosphere soil is applied to link root-internal C allocation patterns with distribution of 13C in the rhizosphere soil. The metabolically active rhizosphere organisms are subsequently identified based on DNA 13C stable isotope probing.In our presentation we will highlight our approaches for gathering quantitative data from both image-based technologies in combination with destructive analysis that provides insights into the functioning and dynamics of C transport processes in the plant-soil system.

In natural ecosystems and low-input agriculture systems often the main source of nitrogen is biological nitrogen fixation by symbiotic coexistence with root colonizing microorganisms such as in root nodules in legumes. In return for this nutrient supply, plants allocate significant amount of photosynthetically fixed carbon (C) belowground, fueling activity and growth of the nodules. However, there is still a lack in understanding how plants modulate carbon allocation to a nodulated root system as a dynamic response to abiotic stimuli. Traditional approaches based on destructive sampling make investigations of localized carbon allocation dynamics difficult. Non-destructive 3D-imaging methods including Magnetic Resonance Imaging (MRI) and Positron Emission Tomography (PET) offers new perspective in analysing belowground processes on individual plants. MRI allows for repetitive measurements and quantification of root system architecture traits nodule structures while growing. PET was employed to follow the spatial distribution of leaf-supplied 11 C tracer to nodules and roots. Using Pisum sativum as model for legumes and applying nitrate as an additional N source we investigated short term C allocation dynamics in the root system. We found that the fraction of 11 C tracer arriving in the most active nodules decreased by almost 40% and remained stable between 16h and 42h after the N application. Our results highlight that the combination of MRI-PET enables deeper insights into short term C dynamics of roots and interactions with colonizing microbes. We expect that this modality has high potential for revealing mechanisms that relate to dynamic fitness traits supporting breedingprograms for future crops.

Legumes associate with root colonizing rhizobia that provide fixed nitrogen to its plant host in exchange for recently fixed carbon. There is a lack in understanding how individual plants modulate carbon allocation to a nodulated root system as a dynamic response to abiotic stimuli. One reason is that most approaches are based on destructive sampling, making quantification of localized carbon allocation dynamics in the root system difficult. We established an experimental workflow for routinely using non-invasive Positron Emission Tomography (PET) to follow the allocation of leaf-supplied 11C tracer towards individual nodules in a three-dimensional (3D) root system of pea (Pisum sativum). Nitrate was used for triggering the shutdown of biological nitrogen fixation (BNF) expected to rapidly affect carbon allocation dynamics in the root-nodule system. This nitrate treatment lead to a reduction of 11C tracer allocation to nodules by 40% – 47% in 5 treated plants while the variation in control plants was less than 11%. The established experimental pipeline enabled for the first time that several plants could consistently be labelled and measured using 11C tracer in a PET approach to quantify C-allocation to individual nodules following a BNF shutdown. This demonstrates the strength of using 11C tracers in a PET approach for non-invasive quantification of dynamic carbon allocation in several growing plants over several days. A major advantage of the approach is the possibility to investigate carbon dynamics in small regions of interest in a 3D system such as nodules in comparison to whole plant development.One sentence summaryPositron Emission Tomography for quantification of carbon allocation dynamics in individual nodules within a 3D root system revealed strong effect of nitrate on carbon allocation.

The digitally generated timemarks from more than 2000 individual detector elements in the pheno PET scanner show individual time offsets. These offsets (or skews) are in the range of ± 1 ns while the actual time resolution of each element is below 250 ps. Thus, the time resolution of the entire system will be highly improved by correcting these offsets. This paper presents a precise correction method based on measurements of the LYSObackground radiation. The Coincidence Resolving Time for the entire scanner could be improved from 1.45 ns to less than 300 ps.

Within the German Plant Phenotyping Network (DPPN), we developed a novel PET scanner based on Philips Digital Photon Counters (DPCs, or dSiPMs = digital Silicon Photomultipliers). The scanner is dedicated for plant research and provides functional information on carbon transport within the plant. To this end the detector ring is oriented horizontally. It provides a Field-of-View of 18 cm dia. and 20 cm in height. The read-out electronics cluster hits from different photodetector pixels when they originate from the same scintillation event. These single events are written via USB 3.0 with up to 300 MB/s to the computer system. Crystal identification, energy discrimination and coincidence detection is realized in software. The spatial resolution in the center Field-of-View (CFOV) could be estimated to approx. 1.6 mm from measurements of a dedicated hot rod phantom. Preliminary sensitivity measurements result in a peak sensitivity of 4.04% (ΔE = 250-750 keV) in the CFOV and a Coincidence Resolving Time of 298 ps could be achieved.

A new kind of a PET-Scanner (PET = positron emission tomography) for plant research is developed asa joint project of the Forschungszentrum Jülich and Philips Digital Photon Counting (PDPC). Thisscanner will utilize digital silicon photomultiplier (dSiPM) for plant phenotyping for the very first time.The goal of this work is to get a further knowledge of the operation of digital silicon photomultiplier.On this account a test-facility for this new photo detectors has been installed at the central instituteof engineering, electronics and analytics (ZEA-2 electronic systems) to determine the usage of thissensors, having regard to use them as scintillation detectors in a PET-Scanner later on.This work has its focus on the development of a fast read-out electronic for the used photo sensorsDPC3200-22-44. As there will be high data rates a fast USB 3.0 interface has been used. All thenecessary processing and data handling has been implemented in a state of the art FPGA.

Non-invasive and rapid determination of plant biomass would be beneficial for a number of research aims. Here, we present a novel device to non-invasively determine plant water content as a proxy for plant biomass. It is based on changes of dielectric properties inside a microwave cavity resonator induced by inserted plant material. The water content of inserted shoots leads to a discrete shift in the centre frequency of the resonator. Calibration measurements with pure water showed good spatial homogeneity in the detection volume of the microwave resonators and clear correlations between water content and centre frequency shift. For cut tomato and tobacco shoots, linear correlations between fresh weight and centre frequency shift were established. These correlations were used to continuously monitor diel growth patterns of intact plants and to determine biomass increase over several days. Interferences from soil and root water were excluded by shielding pots with copper. The presented proof of principle shows that microwave resonators are promising tools to quantitatively detect the water content of plants and to determine plant biomass. As the method is non-invasive, integrative and fast, it provides the opportunity for detailed, dynamic analyses of plant growth, water status and phenotype.