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Plants' roots promote changes in soil structure, forming a strongly-bound soil layer in the surroundings of the root, which is named as rhizosheath. Rhizosheath formation is attributed mainly to the root hairs' presence, that favors the enmeshment of the soil particles around the roots, and the release of mucilage and exudates, which acts as gluing agents of those soil particles. In the present work, we studied the rhizosheath aggregate formation of two Zea mays L. genotypes with contrasting root hair development: a mutant with root hair defective elongation (rth3) and a corresponding wild type (WT). We also tracked the fate of recently-deposited C in the rhizosheath aggregates using two 13CO2 pulse labeling approaches (single vs. multiple pulse labeling). The sampled rhizosheath aggregates were further separated using dry-sieving fractionation into three aggregate size classes: primary small particles and smaller microaggregates (250 µm). We observed that the aggregate size distribution followed the same pattern in both genotypes. This result reinforces the assumption that other soil properties are more important for rhizosheath aggregation than root hair elongation. We observed that the higher potion of the recently-deposited root-derived C (57%) was accumulated in the macroaggregates. Moreover, the multiple pulse labeling approach proportioned a higher 13C enrichment of the rhizosheath aggregates fractions than applying a single pulse. Despite both single and multiple labeling approaches have resulted in a similar distribution of 13C in the rhizosheath aggregates, multiple pulse labeling provided a higher enrichment in the rhizosheath aggregates, which allowed a better separation of significant differences between the genotypes.

Soil organic matter (SOM) originates predominantly from above and belowground OM inputs derived from plants. Although the formation of SOM is well studied, it still remains unclear how the biochemical composition of litter affects the formation of new SOM as well as the degradation of “native” SOM. In the present study we aimed to disentangle the effect of plant litter composition on C transference from different plant tissues into specific SOM fractions and to determine the magnitude of priming effect on native SOC caused by litter amendments. To this end, we individually incubated 13C enriched Eucalyptus spp. major litter types (bark, leaves, twigs and roots) in soil (0–20 cm) of a sandy-clay loam (Haplic Ferralsol - Brazil). Additionally, a soil sample without plant residue addition was incubated as a control. The samples were incubated at 80% of their water-holding capacity at 25 ºC for 200 days. Soil respiration was assessed along the incubation period through headspace gas sampling and 13C/12C–CO2 analysis in a cavity ring-down spectrometer. After the incubation, soil subsamples were physically fractionated using a combined density-particle size separation method. The total C and the δ 13C of each soil organic matter fraction were measured and the litter-C contribution for each SOM fraction was assessed using a two-end member isotope mixing model. The molecular composition of the incubated plant material and SOM fractions were determined by solid-state 13C-CPMAS-NMR spectroscopy. Interestingly, we found no significant differences for total SOM contents among the different treatments. Conversely, incubation without litter amendment (control treatment) resulted in lower total SOM contents, indicating mineralization of “native” SOM along the incubation period. The partitioning of litter-derived C into SOM fractions indicated that leaves litter were preferentially transferred to mineral associated organic matter (MAOM), while roots contributed more to particulate organic matter (POM). Cumulative C-CO2 evolution from the treatments over the incubation period increased in the following order: twigs > leaves > bark > roots > controls. Incubation with twigs, bark and roots significantly increased “native” SOM respiration, while the treatment with leaves addition did not differ from the control. When tracing the source of “native” SOM-derived CO2, we observed a similar amount of C being respired from MAOM, regardless the treatment, while incubation with twigs, bark and roots resulted in higher respiration of “native” SOM-derived C from POM. Our data demonstrates that the biochemical composition of plant litter determines the fate of newly formed organic matter (MAOM or POM) and controls the degradation of “native” SOM. Therefore, plant residues enriched in more easily degradable compounds (leaves) are preferentially transferred to MAOM and causes less native SOC priming. On the other hand, plant residues enriched in structural compounds (twigs, bark and roots), are preferentially respired or allocated into the POM, also resulting in higher priming effect intensity.

The distribution of root system in the soil profile is an important factor for water and nutrient acquisition in planted forests. Harvest residue and litter layer management can alter nutrient availability to the plants, reflecting in shifts of root system distribution in the soil profile. In the present study, we aimed to evaluate the effect of litter layer management in root density and its correlation with depth, soil organic matter (SOM), and soil macro and micronutrients in fast-growing eucalypt plantations. We hypothesized that the presence of litter layer increases root density in the first soil layers while its absence results in higher root density in deeper soil layers. To this end we carried out an experiment in a eucalypt stand (Eucalyptus urophylla x Eucalyptus grandis; 3.3 x 1.82 m spacing; one-year-old trees) in the region of Telêmaco Borba, Paraná – Brazil. The Köppen climate classification is Cfb and the soil is classified as dystrophic Red Latosol. The treatments consisted of presence (+R) or absence (-R) of litter layer. The residue was composed by the previous rotation litter layer that remained in the forest after harvest. The experiment followed a randomized block design, with four replications. Root density (g dm-3) was evaluated in one representative tree per plot at each treatment and replication. We used a 5.3 cm diameter auger to collect root samples from 0-10, 10-20, 20-40 and 40-60 cm depths in seven predefined points in the planting row and interrow. For each sampling point and depth, roots were manually separated, washed to remove soil and other impurities, and subsequently oven dried at 65 °C to determine total dry mass. Additionally, SOM, soil macro and micronutrient contents were analyzed in each soil layer. Pearson’s correlation (α=5%) was performed between root density, depth, SOM, soil macro and micronutrients. Contrary to our hypothesis, the results showed that the presence of litter layer did not impacted root density in the superficial layer (0-20 cm), but resulted in a substantial increase of this trait in deeper soil layers (20-40 cm and 40-60 cm). The increase in root density observed for deeper soil layers was possibly a consequence of the higher nutrient availability favored by the presence of litter layer. The increase of root density in subsurface is important not only to increase tree water and nutrient use efficiency, but also to promote C sequestration in deeper soil layers. Our results highlight the importance of maintaining the litter layer in the field as reasonable strategy for a more sustainable management of fast-growing eucalypt forests.

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, Eucalyptus 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 13C-CO2 (10 pulses of 10 h, 0.46 g of 13C plant-1), 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 δ13C. 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 13C enrichment of the CO2 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 δ13C from the respired CO2 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.

Diabetes Mellitus (DM) is one of the most predominant diseases in the world, causing a high number of deaths. Diabetic foot is one of the main complications observed in diabetic patients, which can lead to the development of ulcers. As the risk of ulceration is directly linked to an increase of the temperature in the plantar region, several studies use thermography as a method for automatic identification of problems in diabetic foot. As the distribution of plantar temperature of diabetic patients do not follow a specific pattern, it is difficult to measure temperature changes and, therefore, there is an interest in the development of methods that allow the detection of these abnormal changes.