Non-invasive hydrodynamic imaging in plant roots at cellular resolution

A key impediment to studying water-related mechanisms in plants is the inability to non-invasively image water fluxes in cells at high temporal and spatial resolution. Here, we report that Raman microspectroscopy, complemented by hydrodynamic modelling, can achieve this goal - monitoring hydrodynamics within living root tissues at cell- and sub-second-scale resolutions. Raman imaging of water-transporting xylem vessels in Arabidopsis thaliana mutant roots reveals faster xylem water transport in endodermal diffusion barrier mutants. Furthermore, transverse line scans across the root suggest water transported via the root xylem does not re-enter outer root tissues nor the surrounding soil when en-route to shoot tissues if endodermal diffusion barriers are intact, thereby separating ‘two water worlds’.

Quantifying Root Colonization in Arbuscular Mycorrhizas by Image Segmentation and Machine Learning

MotivationArbuscular mycorrhizas are the most widespread plant symbioses and involve the majority of crop plants. The beneficial interaction between plant roots and a group of soil fungi (Glomeromycotina) grants the green host a preferential access to soil mineral nutrients and water, supporting plant health, biomass production and resistance to both abiotic and biotic stresses. The nutritional exchanges at the core of this symbiosis take place inside the living root cells, which are diffusely colonized by specialized fungal structures called arbuscules. For this reason, the vast majority of studies investigating arbuscular mycorrhizas and their applications in agriculture require a precise quantification of the intensity of root colonization. To this aim, several manual methods have been used for decades to estimate the extension of intraradical fungal structures, mostly based on optical microscopy observations and individual assessment of fungal abundance in the root tissues. ResultsHere we propose a novel semi-automated approach to quantify AM colonization based on digital image analysis and compare two methods based on image thresholding and machine learning. Our results indicate in machine learning a very promising tool for accelerating, simplifying and standardizing this critical type of analysis, with a direct potential interest for applicative and basic [email protected]; [email protected]

Characterizing Regenerative Aspects of Living Root Bridges

Living root bridges (LRBs) are functional load-bearing structures grown from Ficus elastica by rural Khasi and Jaintia communities in Meghalaya (India). Formed without contemporary engineering design tools, they are a unique example of vernacular living architecture. The main objective of this study is to investigate to what extent LRBs can be seen as an example of regenerative design. The term "regenerative" describes processes that renew the resources necessary for their function. Whole systems thinking underpins regenerative design, in which the integration of human and non-human systems improves resilience. We adapted the living environments in natural, social, and economic systems (LENSES) framework (living environments in natural, social, and economic systems) to reflect the holistic, integrated systems present in LRBs. The regenerative / sustainable / degenerative scale provided by LENSES Rubrics is applied to 27 focal points in nine flow groups. Twenty-two of these points come from LENSES directly, while five were created by the authors, as advised by the LENSES framework. Our results show 10 focal points in which LRBs are unambiguously regenerative. One focal point is unambiguously sustainable, while 16 are ambiguous, showing regenerative, sustainable, and degenerative aspects. User perspective determines how some focal points are evaluated. The contrast between a local, indigenous perspective and a global, tourism-focused perspective is demonstrated by the results.

Succession between living and dead roots drives the fate of soil carbon pools

<p>There is growing evidence that belowground plant carbon (C) inputs displays a major role for soil organic matter (SOM) dynamics. During the root life-cycle, there is a sequential shift from C inputs from living to dead roots, which might affect the conversion of these specific compound classes to SOM. However, this successional effect has yet not been investigated. In this study, we aimed to evaluate (i) the short-term impacts of living root-derived C on SOM formation and composition and (ii) how the succession between living and dead roots impacts their respective fate in soil. For this purpose, we set up a two-step experiment that simulated the shift between living and dead roots C inputs. In the first step, <em>Eucalyptus</em> spp. plants were cultivated in pots under controlled conditions for 66 days. In order to isolate the living root-derived C, we inserted in each pot 4 cylinders (0.5 cm high, 4.75 cm diameter) capped with a nylon membrane (pore size 5 μm) and filled with soil (clayey Rhodic Ferrasol) at the start of the experiment. Half of the pots were periodically pulse-labeled with <sup>13</sup>C-CO<sub>2</sub> (10 pulses of 10 h, 0.46 g of <sup>13</sup>C plant<sup>-1</sup>), while the remaining ones were used as controls (unlabeled treatments). After 66 days, all pots were harvested, and one cylinder per pot was used to depict the living root effects on SOM pools. Those cylinders were separated in layers according to the distance from the roots (0-4, 4-8, 8-15 and 15-25 mm) and analyzed for organic carbon, nitrogen, as well as δ<sup>13</sup>C. We quantified and characterized the microbial communities using phospholipid fatty acid (PLFA), and extracted the pedogenic oxides (iron and aluminum) to highlight potential alterations in organo-mineral complexes and short-range order phases. Using density/size fractionation, we further gained elemental and isotopic information of specific SOM pools, i.e. particulate, occluded and mineral-associated organic matter. The remaining cylinders were incubated for 84 days in two treatments, with and without dead roots. Heterotrophic respiration rates were measured periodically together with the <sup>13</sup>C enrichment of the CO<sub>2</sub> produced. Carbon derived from living roots was mainly recovered in the first millimeters from the root source, as occluded or mineral-associated SOM. Close to the roots, we detected a shift in the microbial communities and a decrease of organo-mineral complexes and short-range order phases. Carbon derived from living roots was rapidly mineralized and the δ<sup>13</sup>C from the respired CO<sub>2 </sub>returned to natural abundance ranges after 84 days of incubation. The presence of dead roots did not affect the mineralization C derived from living roots. Our work highlights the importance of C inputs from living roots for the formation of SOM. However, the compounds deposited by living roots exhibit also a transient nature which challenges the assumption that living root-derived C is necessarely a precursor of stable SOM formation.</p>

PHOTOGRAMMETRY AS A TOOL FOR LIVING ARCHITECTURE

Living Root Bridges (LRBs), grown by rural Khasi and Jaintia communities in Meghalaya (India), are the best known example of functional living architecture. Over 70 bridges, as well as ladders, pathways and platforms have been grown from a single species (Ficus elastica), using a collection of construction methods in regionally specific environmental conditions. In general, living architecture exhibits geometric complexity for which documentation and representation tools are yet to be established. Photogrammetric surveys provide data-rich point clouds which could be useful for analysis and design specific to living architecture. This study provides the first photogrammetric surveys of LRBs. Useful point clouds were produced for several bridges, as well as joint details. The method is found to have a range of benefits: providing detailed views, showing environmental conditions, and allowing for time analyses. The wider application of photogrammetry to living architecture is discussed, particularly with regards to Baubotanik structures and the improved documentation and representation of LRBs as a unique architectural typology. The need for developing a tool for topological model extraction, and possible methods therein is discussed.