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This paper summarized the effects of atmospheric CO2 enrichment on soil microbes and their related factors, including soil microflora, soil respiration, soil microbial biomass, and higher plant-microbe symbiosis. The factors related to soil microbic activity such as litter decomposition, root exudates, soil nutrient availability, nutrient use efficiency and soil fauna were also affected by the CO2 enrichment.
In this paper, three bioassay methods, i.e., relay seeding in agar (RSA), relay seeding in silica (RSS) and seeding in rice root-exudation (SRE), were used to test the allelopathic potential of 8 rice cultivars on the target weed barnyardgrass (Echinochloa crusgalli). The results indicated that RSA was the ideal method for the bioassay, showing the highest efficiency in the evaluation of allelopathic potential. RSS and SRE had a lower efficiency than RSA, but these two methods showed the same tendency in evaluating the allelopathic potential of rice. RSA, the considered best bioassay method in this experiment, was used for 57 allelopathic rice germplasm screening, and 5 of them, i.e., Iguape Cateto, PI312777, Azucena, Taichung Native 1 and IAC25 performed the strongest allelopathic potential in the suppression on barnyardgrass.
By a batch method, this paper studied the effects of different concentration and pH of oxalate, an important root exudate, on the adsorption of acid phosphatase and its activity on < 2 microm colloids of yellow brown soil and latosol, and on minerals goethite and kaolinite. The results showed that the acid phosphatase adsorption by goethite was less affected by the concentration of oxalate; while the adsorbed amount of this enzyme by the other test colloids and kaolinite was sharply decreased with the increasing oxalate concentration (0-5 mmol x L(-1)) first, and then gradually increased to the level equal to or less than the blank, which may be related to the coordination type of oxalate on soil colloids and minerals, and their surface charge change and dissolution. In the systems oxalate existed, the adsorbed amount of acid phosphatase by soil colloids and minerals decreased in order of goethite >> yellow brown soil > kaolinite > latosol. The pH value for the maximum adsorption of acid phosphatase was between the IEP of the enzyme and the PZC of test colloids and minerals. After the enzyme was immobilized on colloids and minerals, the pH of its maximum specific activity had no change, or shifted to a higher value.
Bt toxin Cry1Ac could be introduced into soil by pollen, root exudates, and plant residues. To investigate its toxic effects, the Bt toxin was added into an earthworm-cultured artificial soil, and the survival, growth rate, sperm count, protein content, and activities of acetylcholinesterase (AchE), catalase (CAT), glutathione S-transferase (GST) and cellulase in Eisenia fetida were determined. The results suggested that Bt toxin Cry1Ac had little effects on the biomass and physiological characteristics of E. fetida, with no acute and subchronic toxicity, and was safe for earthworm at field dose level.
This study showed that the amounts of Bt toxin expressed in transgenic Bt cotton leaves and stems (103.5 - 134.1 ng x g(-1)) were rather higher than those expressed in transgenic Bt cotton roots (44.7 - 21.2 ng x g(-1)), indicating that total amount of soil Bt toxin introduced by transgenic Bt cotton could be decreased through treating its above-ground biomass. In comparing with the amount of Bt toxin expressed in transgenic Bt cotton plant, that expressed in its root exudates was rather lower, showing that the effects of plant Bt toxin on soil ecosystem would be limited if other sources of Bt toxin introduced into soil were controlled.
Data were obtained on the dynamics of the abundance of the biocontrol strains of Pseudomonas chlororaphis SPB1217 and Pseudomonas fluorescens SPB2137 with antifungal activity. These strains are able to develop in the rhizosphere of cucumbers grown on mineral substrate under hydroponic conditions in industrial greenhouses. After four weeks of vegetation of plants, the abundance of the inoculated strains was 19-28% of the total bacterial numbers determined by inoculation onto solid medium. The investigated strains spread together with the young, actively growing and exudating roots; they reached a stable level of abundance in deep layers of the greenhouse substrate. A significant difference in the abundance of fungi in the tested variants was observed after 20 days of vegetation: the abundance of fungi in the control was two times higher than in the variant inoculated with strain SPB2137.
The temporal dynamics of partitioning and rhizodeposition of recent photosynthate in wheat (Triticum aestivum) roots were quantified in situ in solution culture. After a 30-min pulse of (14)CO(2) to a single intact leaf, (14)C activities of individual carbon fluxes in the root, including exudation, respiration, and root content, were measured continuously over the next 20 h concurrently with (14)C efflux from the leaf. Immediately after the end of the (14)CO(2) pulse, (14)C activity was detected in the root, the hydroponic solution, and in root respiration. The rate of (14)C exudation from the root was maximal after 2 to 3 h, and declined to one-third of maximum after a further 5 h. Completion of the rapid phase of (14)C efflux from the leaf coincided with peak (14)C exudation rate. Thus, exudation flux is much more rapidly and dynamically coupled to current photosynthesis than has been appreciated. Careful cross-calibration of (14)C counting methods allowed a dynamic (14)C budget to be constructed for the root. Cumulative (14)C exudation after 20 h was around 3% of (14)C fixed in photosynthesis. Partitioning of photosynthate between shoot and root was manipulated by partial defoliation before applying the (14)CO(2) pulse to the remaining intact leaf. Although the rate of photosynthesis was largely unaffected by partial defoliation, the proportion of new photosynthate subsequently partitioned to and exuded from the root was substantially reduced. This clearly indicates that exudation depends more on the rate of carbon import into the root than on the rate of photosynthesis.
This study quantified the concentrations of IgG and IgA in the periapical exudates obtained from 69 single-rooted teeth using enzyme-linked immunosorbent assays, and examined their correlation with clinical findings of the involved teeth. Changes in the levels of these immunoglobulins during root canal treatment were also investigated. The average levels of IgG (85.61 mg/ml) was significantly higher than that of IgA (0.65 mg/ml) (P < 0.001). The exudates from the canals with large lesions (> or = 1 cm in diameter on radiographs) showed significantly higher IgG and IgA levels than small lesions (< 1 cm in diameter) (P < 0.01). The tendency for these to be a decrease in the levels of IgG and IgA was observed following the root canal treatment. These observations suggest that IgG and IgA are involved in the immunopathogenesis of periapical lesions.
This study quantified the concentrations of interleukin-1 alpha (IL-1 alpha) and interleukin-1 beta (IL-1 beta) in the periapical exudates obtained from 69 single-rooted teeth using enzyme-linked immunosorbent assays, and examined their correlation with clinical findings of the involved teeth. Changes in the levels of these factors during root canal treatment were also investigated. The average levels of IL-1 beta (6.57 ng/ml) in periapical exudates were twice that of IL-1 alpha (3.25 ng/ml). The exudates containing pus showed significantly higher IL-1 alpha levels than those from the canals without pus (p < 0.01). The exudates from the canals with small radiolucent areas contained significantly higher IL-1 alpha levels than those from the canals with large radiolucent areas (p < 0.05). The tendency for there to be an increase in the levels of IL-1 alpha and a decrease in the levels of IL-1 beta was observed following root canal treatment. These observations suggest that IL-1 alpha and IL-1 beta are involved in the immunopathogenesis of periapical lesions and that IL-1 alpha and IL-1 beta may play different roles in the healing process of periapical lesions during root canal treatment.
Root traits significantly shape rhizosphere microbiomes, yet their interaction with microbes is often overlooked in plant breeding programs. Here, we propose that selecting modern cultivars based on microbiome interactive trait (MIT), such as root biomass, exudate patterns and the rhizosphere microbiome, can enhance agricultural sustainability by interacting effectively with soil microbiomes, which in turn, promotes plant growth and resistance to stress, thereby reducing reliance on synthetic crop protectants. Through a stepwise selection process (in silico and in vitro) that started with approximately 1000 potato genotypes, we chose 51 potato cultivars based on known phenotypical properties and distinct root exudate patterns. We conducted a greenhouse experiment to evaluate their capacity to interact with the soil microbiome and to assess their MIT scores. Our findings revealed that cultivars significantly influence plant growth, metabolite profiles, and rhizosphere fungal community composition. Moreover, we observed a positive correlation between microbial community diversity and root biomass. Additionally, leaf metabolites were correlated with rhizosphere bacterial composition, supporting the plant holobiont framework. Utilising z-scores, we aggregated all data related to plant growth, metabolomes, and microbiomes, creating a classification of 51 cultivars based on a gradient of MIT scores. By examining the distribution of low, intermediate, and high MIT, we identified a group of 11 potato cultivars suitable for further studies to assess their resilience and productivity under low-input production systems. This study provides an in-depth correlation between microbiome and several plant traits across 51 cultivars, offering tools to facilitate and expedite the incorporation of microbiome traits into breeding goals to support sustainable agriculture.
Topped plants of tomato (Lycopersicon esculentum), cucumber (Cucumis sativus), corn (Zea mays), carrot (Daucus carota), and peanut (Arachis hypogaea) were treated with 0.5 to 50 micromolar Ni (containing (63)Ni) in nutrient solutions. Xylem exudate was collected for 10 hours or, in the case of corn, for 20 hours at 5-hour intervals. Electrophoresis of nutrient solution distributed all Ni cathodically as inorganic Ni(2+). Low concentrations of Ni in tomato exudate migrated anodically, presumably bound to organic anion (carrier). However, this carrier became saturated at about 2 micromolar Ni in exudate, and excess Ni ran cathodically. Most of the Ni in cucumber, corn, carrot, and peanut exudate ran anodically, and its migration rate was identical for all exudates. Peanut root sap contained 14 to 735 micromolar Ni. The anodic Ni carriers in root sap and exudate appear identical. The carrier in root sap became saturated near 100 micromolar Ni, as shown by cathodic streaking of Ni exceeding that concentration. It appears that all five species translocate low concentrations of Ni in the same anionic form.
Aluminum (Al) toxicity and phosphorus (P) deficiency often coexist in acid soils that severely limit crop growth and production, including soybean (Glycine max). Understanding the physiological mechanisms relating to plant Al and P interactions should help facilitate the development of more Al-tolerant and/or P-efficient crops. In this study, both homogeneous and heterogeneous nutrient solution experiments were conducted to study the effects of Al and P interactions on soybean root growth and root organic acid exudation. In the homogenous solution experiments with a uniform Al and P distribution in the bulk solution, P addition significantly increased Al tolerance in four soybean genotypes differing in P efficiency. The two P-efficient genotypes appeared to be more Al tolerant than the two P-inefficient genotypes under these high-P conditions. Analysis of root exudates indicated Al toxicity induced citrate exudation, P deficiency triggered oxalate exudation, and malate release was induced by both treatments. To more closely mimic low-P acid soils where P deficiency and Al toxicity are often much greater in the lower soil horizons, a divided root chamber/nutrient solution approach was employed to impose elevated P conditions in the simulated upper soil horizon, and Al toxicity/P deficiency in the lower horizon. Under these conditions, we found that the two P-efficient genotypes were more Al tolerant during the early stages of the experiment than the P-inefficient lines. Although the same three organic acids were exuded by roots in the divided chamber experiments, their exudation patterns were different from those in the homogeneous solution system. The two P-efficient genotypes secreted more malate from the taproot tip, suggesting that improved P nutrition may enhance exudation of organic acids in the root regions dealing with the greatest Al toxicity, thus enhancing Al tolerance. These findings demonstrate that P efficiency may play a role in Al tolerance in soybean. Phosphorus-efficient genotypes may be able to enhance Al tolerance not only through direct Al-P interactions but also through indirect interactions associated with stimulated exudation of different Al-chelating organic acids in specific roots and root regions.
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Xylem exudates were collected at hourly intervals from short segments which had been excised from two portions of the primary root of corn (Zea mays L.) seedlings and partially immersed in experimental salt solution containing (86)Rb. All segments showed variation in rates of output of both volume and ions for several hours, after which a steady state was attained which persisted for many hours. Apical segments produced little or no exudate for several hours and did not reach a steady state until 18 or more hours after excision. Basal segments produced exudate containing detectable quantities of isotope within an hour and they reached a steady state about 12 hours after excision. During their respective steady states, apical segments produced three times the volume per hour and translocated eight times as much Rb per hour as did basal segments.These differences in the time course of exudation and the large differences in output are interpreted as indicating that two independent systems of ion transport operate simultaneously in intact roots. If this interpretation is correct, then it would appear that one of these systems has a greater potential capacity for ion transport than the other.