Unveiling the variability in cadmium accumulation and tolerance characteristics: a comparative study of Basma and Yunyan 87 tobacco varieties.

Tobacco (Nicotiana tabacum L.) shows promise for remediating Cd-contaminated soil due to its significant Cd accumulation capabilities. Although various tobacco varieties exhibit distinct Cd bioaccumulation capacities, a comprehensive understanding of the underlying mechanisms is lacking. This study, conducted using hydroponics, explores differences in Cd accumulation and tolerance mechanisms between two tobacco varieties, Basma and Yunyan 87. The results showed that Cd stress reduced the dry weight, tolerance index, and root morphology for both varieties. Basma exhibited a relatively smaller decline in these indices compared to Yunyan 87. Moreover, Basma demonstrated a higher Cd bioconcentration factor (BCF), concentration, and accumulated content, signifying its superior tolerance and bioaccumulation capacity to Cd compared to Yunyan 87. The Carbonyl Cyanide3-ChloroPhenylhydrazone (CCCP) addition resulted in reduced Cd accumulation and BCFs in both tobacco species. This effect was more pronounced in Basma, suggesting that Basma relies more on an active transport process than Yunyan 87. This could potentially explain its enhanced bioaccumulation ability. Subcellular Cd distribution analysis revealed Basma's preference for distributing Cd in soluble fractions, while Yunyan 87 favoured the cell wall fractions. Transmission electron microscope showed that Basma's organelles were less damaged than Yunyan 87's under Cd stress, possibly contributing to the superior tolerance of Basma. Therefore, these results provided a theoretical foundation for development of Cd-contaminated soil tobacco remediation technology.

Recent Progress in Metal Oxide-Based Photocatalysts for CO2 Reduction to Solar Fuels: A Review.

One of the challenges in developing practical CO2 photoconversion catalysts is the design of materials with a low cost, high activity and good stability. In this paper, excellent photocatalysts based on TiO2, WO3, ZnO, Cu2O and CeO2 metal oxide materials, which are cost-effective, long-lasting, and easy to fabricate, are evaluated. The characteristics of the nanohybrid catalysts depend greatly on their architecture and design. Thus, we focus on outstanding materials that offer effective and practical solutions. Strategies to improve CO2 conversion efficiency are summarized, including heterojunction, ion doping, defects, sensitization and morphology control, which can inspire the future improvement in photochemistry. The capacity of CO2 adsorption is also pivotal, which varies with the morphological and electronic structures. Forms of 0D, 1D, 2D and 3DOM (zero/one/two-dimensional- and three-dimensional-ordered macroporous, respectively) are involved. Particularly, the several advantages of the 3DOM material make it an excellent candidate material for CO2 conversion. Hence, we explain its preparation method. Based on the discussion, new insights and prospects for designing high-efficient metallic oxide photocatalysts to reduce CO2 emissions are presented.

Effects of CeO2 Nanoparticles on Nutritional Quality of Two Crop Plants, Corn (Zea mays L.) and Soybean (Glycine max L.).

With the widespread applications of manufactured nanoparticles (NPs), there are increasing concerns about their potential adverse effects on the environment and living systems. Many studies demonstrated that NPs could significantly affect the growth and development of crop plants. However, knowledge regarding the impacts of NPs on crop quality is rather limited. In this study, the effects of CeO2 NPs (25, 75, and 225 mg Ce/kg) and CeCl3 (25 mg Ce/kg) on the nutritional components of soil-cultivated corn and soybean plants were evaluated. Both treatments tended to decrease the dry weight of grain per plant, while only 225 mg/kg CeO2 NPs on soybean and CeCl3 on corn showed statistical significance compared with the respective control. CeO2 NPs at 225 mg/kg significantly decreased the content of starch in the corn kernels by 18.2% but increased total phenols in soybean seeds by 18.4%. Neither CeO2 NPs nor CeCl3 significantly affected the contents of minerals in corn kernels except for Zn. However, in the case of soybean, the two treatments tended to decrease the contents of P, Zn, Mn, and Mo but increase the content of S. Overall, the results suggest that CeO2 NPs and Ce3+ ions showed similar but not identical effects on corn and soybean plants. CeO2 NPs affect the nutritional quality of crop plants in a species-dependent manner.

Sulfur enhances cadmium bioaccumulation in Cichorium intybus by altering soil properties, heavy metal availability and microbial community in contaminated alkaline soil.

Cadmium (Cd) contamination seriously threatens the soil health and food safety. Combination of amendment and accumulator plant is a green and effective technique to improve phytoremediation of Cd-contaminated alkaline soil. In this study, a potting experiment was conducted to investigate the effect of sulfur on Cd phytoextraction by Cichorium intybus (chicory). Soil chemical and microbial properties were determined to reveal the mechanism of sulfur-assisting Cd phytoremediation by chicory. Soil pH decreased from 7.77 to the lowest 7.30 with sulfur addition (0.6, 0.9 and 1.2 g kg-1, LS, MS and HS treatment); Electric conductivity, sulfate anion and available cadmium concentration increased gradually with increasing sulfur doses. Cd concentration of shoot and root significantly increased from 1.47 to 4.43 mg kg-1, 6.15 to 20.16 mg kg-1 by sulfur treatment relative to CK, which were attributed to increased available Cd concentration induced by decreased pH. Sulfur treatments significantly increased the Cd bioconcentration factor by 64.1%, 118.6%, 201.0% for shoot, 76.3%, 145.6% and 227.7% for root under LS, MS and HS relative to CK treatment, respectively (P < 0.05). However, only MS treatment significantly improved the Cd removal efficiency by 82.9% in comparison of CK treatment (P < 0.05). Microbial community diversity measured by 16SrRNA showed that Thiobacillus and Actinobacteria were the key and dominant strains of soil microbial communities after sulfur addition, which played a pivotal role in the process of sulfur oxidation involved in decrease of soil pH and the transformation of Cd forms. Correlation analysis and path analysis by structural equation model indicated that soil sulfate anion and Thiobacillus directly affected Cd removal efficiency by chicory in Cd-contaminated alkaline soil. This suggests that combination of sulfur and chicory may provide a way to promote Cd bioaccumulation for phytoremediation of Cd-contaminated alkaline soil.

Combined remediation effects of biochar, zeolite and humus on Cd-contaminated weakly alkaline soils in wheat farmland.

Threats posed by Cd-contaminated arable soils to food security have attracted increasing attention. The combination of organic and inorganic amendments has been extensively applied to immobilize Cd in paddy soils. However, the regulatory mechanism of Cd fractionation under these combined amendments and the effect on wheat Cd accumulation remain unclear in upland soils. In this work, different combinations of organic and inorganic amendments were prepared with biochar, zeolite and humus, and the Cd-immobilization mechanism was also investigated in field experiments. The results demonstrated that the mixture of biochar, zeolite and humus had excellent Cd immobilization performance in highly Cd-contaminated (4.26 ± 1.25 mg kg-1) weakly alkaline soils, resulting in 76.5-84.8% decreases in soil available Cd. The contribution of single components to Cd immobilization in the combined amendment follows the order of humus > biochar > zeolite. The combined amendment converted the acid soluble Cd to the Cd bound to the reducible fraction with higher stability, thereby decreasing Cd bioavailability. The maximum Cd decrease rate in wheat roots, straw and grains could reach 68.2%, 45.0% and 59.3%, respectively, and the Cd content in grains (0.098 mg kg-1) was lower than the food security standards of China (0.1 mg kg-1). Wheat planting for two successive years in a large-scale field further verified the superior Cd immobilization performance and stability of the combined amendment in moderately to slightly Cd-contaminated soil. The present study provides references for the remediation of Cd-contaminated weakly alkaline upland soils and certain guidance for safe food production.

Evaluation of the cadmium phytoextraction potential of tobacco (Nicotiana tabacum) and rhizosphere micro-characteristics under different cadmium levels.

In this study, a field-scale and pot experiment were performed to evaluate the remedial efficiency of Cd contaminated soil by tobacco and explore rhizosphere micro-characteristics under different cadmium levels, respectively. The results indicated that tobacco could remove 12.9 % of Cd from soil within a short growing period of 80 d. The pot experiment revealed that tobacco could tolerate soil Cd concentrations up to 5.8 mg kg-1 and bioaccumulate 68.1 and 40.8 mg kg-1 Cd in shoots and roots, respectively. The high Cd bioaccumulation in tobacco might be attributed to strong acidification in the rhizosphere soil and the increase in Cd bioavailability. Rhizobacteria did not appear to be involved in Cd mobilization. In contrast, tobacco tended to enrich sulfate-reducing bacteria (such as Desulfarculaceae) under high Cd treatment (5.8 mg kg-1) but enrich plant growth-promoting bacteria (such as Bacillus, Dyadobacter, Virgibacillus and Lysobacter) to improve growth under low Cd treatment (0.2 mg kg-1), suggesting that tobacco employed different microbes for responding to Cd stress. Our results demonstrate the advantages of using tobacco for bioremediating Cd contaminated soil and clarify the rhizosphere mechanisms underlying Cd mobilization and tolerance.

Contribution of the flag leaf to lead absorption in wheat grain at the grain-filling stage.

Wheat flag leaf (FL) is one of the primary sources of carbohydrates in grains; however, its role in grain lead (Pb) absorption remains unclear. A field experiment was conducted to assess the relative contribution of the FL to Pb accumulation in wheat grain by two contrasting treatments: without (CK) and with FL removal (FLR) at the grain-filling stage. The Pb concentration in leaves was closely related to leaf strata and decreased from FL to the third leaf. FLR treatment significantly reduced the yield and grain Pb concentration by 2.79% and 11.47%, respectively. The contribution of FL to grain Pb accumulation decreased gradually with the filling process, from 35.08% (at early stage) to 13.94% (at maturity stage). After FLR, the contribution proportion of atmospheric fallout to grain Pb decreased from 69.01% (CK) to 62.43% (FLR). Combined isotope analysis with scanning electron microscopy and energy-dispersive X-ray spectroscopy (SEM-EDS) revealed that the main contribution of FLs to grain Pb originated from Pb fallout in fine atmospheric particles. Therefore, taking measures to reduce the influence of fine atmospheric particles on wheat may be an effective way to control wheat grain Pb contamination.

The use of mercapto-modified palygorskite prevents the bioaccumulation of cadmium in wheat.

In this study, the mechanism by which mercapto-modified palygorskite (MPAL) mediates Cd and Mn absorption by wheat was elucidated. In the aqueous phase, MPAL can react with Cd to form Cd-thiol complexes and CdO and with Mn to form MnO. In the wheat-soil system, 0.1-0.3% MPAL application increased the biomass of wheat by 18.6-29.4% and decreased the Cd concentration in shoots and roots by 19.4-51.8% and 35.9-64%, respectively; however, MPAL application did not decrease the diethylenetriaminepentaacetic acid (DTPA)-extracted Cd concentration in soil, probably because the formed Cd-thiol complexes and CdO could not be taken up by plants but could be extracted by DTPA. MPAL appeared to increase the Mn concentration in plants and the DTPA-extracted Mn concentration in soil, possibly because of the reduction in soil Mn oxides to more soluble Mn(Ⅱ) by the thiol groups in MPAL. MPAL enriched plant growth-promoting rhizobacteria and Cd-immobilizing bacteria and strengthened the sulfate reduction metabolism in rhizosphere soil, which partly contributed to the improvement in plant growth and the reduction in Cd bioaccumulation in wheat. These findings highlight the importance of the thiol group in MPAL and the regulation of the rhizosphere bacterial community in mediating Cd and Mn bioaccumulation in wheat.

Effects of natural vegetative restoration on soil fungal and bacterial communities in bare patches of the southern Taihang Mountains.

Understanding the distribution and composition of soil microbes in bare patches is a critical step to improving ecological remediation. The effects of different vegetative restoration types on soil microbes within semi-arid bare patches remain unclear. Here, we evaluated the distribution of soil fungi and bacteria among different ecological restoration types at the southern Taihang Mountains. Analysis of variance showed that the chemical properties of soil with vegetation cover have higher nutrient quality than those of the exposed soil. The results also suggested that vegetative restoration significantly improved the diversity and the richness of the soil fungal and bacterial communities. Sequencing results showed that Ascomycota and Basidiomycota were the main soil fungal communities, whereas Proteobacteria, Acidobacteria, and Actinobacteria were the main soil bacterial communities. There were significant relationships between the contents of moisture, organic matter and organic carbon and the soil fungal/bacterial communities. Venn and network diagrams indicated that the vegetative restoration types largely influenced the soil fungi and weakly influenced the soil bacteria in the bare patches. This study discusses the importance of vegetative restoration in the ecological remediation of bare patches. These findings provide effective references for soil restorative measures, water conservation, and bare-spot reduction at the southern Taihang Mountains in future.

Removal and tolerance mechanism of Pb by a filamentous fungus: A case study.

Currently, Pb pollution has become a severe environmental problem and filamentous fungi hold a promising potential for the treatment of Pb-containing wastewater. The present study showed that the strain Pleurotus ostreatus ISS-1 had a strong ability to tolerate Pb at high concentration and reached a removal rate of 53.7% in liquid media. Pb was removed by extracellular biosorption, intracellular bioaccumulation by mycelia, or precipitation with extracellular oxalic acids. On the cellular level, Pb was mainly distributed in the cell wall, followed by vacuoles and organelles. Fourier transform infrared spectroscopy (FTIR) analysis indicated that hydroxyl, amides, carboxyl, and sulfhydryl groups provided binding sites for Pb. Furthermore, Pb was found on the cell surface in the form of PbS and PbCO3 through X-ray diffraction (XRD). Intracellular chelates such as thiol compounds and oxalic acid, as well as extracellular oxalic acid, might play an important role in the tolerance of Pb. In addition, isobaric tags for relative and absolute quantitation (iTRAQ) analysis showed that ATP-binding cassette (ABC) transporter, cytochrome P450, peroxisome, and the calcium signaling pathway might participate in both accumulation and detoxification of Pb. These results have successfully provided a basis for further developing Pb polluted water treatment technology by fungi.

Continuing Impacts of Selective Inhibition on Bacterial and Fungal Communities in an Agricultural Soil.

Selective inhibition (SI) has been routinely used to differentiate the contributions of bacteria and fungi to soil ecological processes. SI experiments typically measured rapid responses within hours since the addition of inhibitor, but the long-term effects of selective biocides on microbial community composition and function were largely unknown. In this study, a microcosm experiment was performed with an agricultural soil to explore the effectiveness of two bactericides (bronopol, streptomycin) and two fungicides (cycloheximide, captan), which were applied at two different concentrations (2 and 10 mg g-1). The microcosms were incubated for 6 weeks. A radiolabeled substrate, [1,2,3,4,4a,9a-14C] anthracene, was spiked to all microcosms, and the derived CO2 was monitored during the incubation. The abundance and composition of bacteria and fungi were assessed by qPCR and Miseq sequencing of ribosomal rRNA genes. It was demonstrated that only 2 mg g-1 bronopol and cycloheximide significantly changed the bacteria to fungi ratio without apparent non-target inhibition on the abundances; however, community shifts were observed in all treatments after 6 weeks incubation. The enrichment of specific taxa implicated a selection of resistant or adapted microbes by these biocides. Mineralization of anthracene was continuingly suppressed in all SI microcosms, which may result in biased estimate of bacterial and fungal contributions to pollutant degradation. These findings highlight the risks of long-term application of selective inhibition, and a preliminary assessment of biocide selection and concentration is highly recommended.

Effects of sulfur application on cadmium bioaccumulation in tobacco and its possible mechanisms of rhizospheric microorganisms.

A potting experiment was conducted to investigate the effect of sulfur application on the bioaccumulation by tobacco and its mechanisms of rhizospheric microorganisms. Cadmium content in tobacco was analyzed using atomic absorption spectrometer, while bacterial community and related gene in soil were analyzed via high-throughput sequencing and quantitative PCR techniques, respectively. The obtained results indicated that tobacco had the ability to accumulate cadmium under no sulfur application conditions, with cadmium contents of 35.4, 23.6, and 26.3 mg kg-1 in leaves, stems, and roots, respectively. Under high-sulfur treatment, these values increased to 66.4, 46.1, and 42.6 mg kg-1, respectively, probably due to the increase of the available cadmium content (from 1.1 to 3.3 mg kg-1) in the soil through a decrease of the soil pH value, which was contributed by the sulfur oxidation reaction. dsrA and soxB genes might play an important role in sulfur oxidation, and Thiobacillus sp. was the dominant bacterial genus during the sulfur oxidation process. In addition, sulfur application exerted little effect on the diversity and structure of the soil bacterial community. The combined results indicate that sulfur application is an effective and safe method for Cd phytoextraction by tobacco.

Drivers and assemblies of soil eukaryotic microbes among different soil habitat types in a semi-arid mountain in China.

The effects of environmental and species structure on soil eukaryotic microbes inhabiting semi-arid mountains remain unclear. Furthermore, whether community assembly differs in a variety of soil habitat types, for example, artificial forest, artificial bush, farmland, and natural grassland, is not well understood. Here, we explored species diversity and composition of soil eukaryotic microbes south of the Taihang Mountains (mid-western region of China) using Illumina sequencing of the 18S rRNA gene (V4) region on the MiSeq platform. The results suggest that the forest soil habitat type improved the diversity and abundance of soil eukaryotic microbes that will benefit the restoration of degraded soil. The SAR (Stramenopiles, Alveolates, Rhizaria) supergroup and Metazoa were the dominant soil eukaryotic microbial groups at the phylum level. About 26% of all operational taxonomic units were common among the different soil habitat types. The O-elements, water content, soil organic matter, and elevation significantly influenced the abundance of soil eukaryote communities (P < 0.05). Our findings provide some reference for the effectiveness of local ecological restoration and the establishment of a soil eukaryotic microbe resource databases in a semi-arid area.

Silicon alleviates cadmium toxicity in wheat seedlings (Triticum aestivum L.) by reducing cadmium ion uptake and enhancing antioxidative capacity.

Cadmium (Cd) is a toxic element that poses a great threat to human health, while silicon (Si) is a beneficial element and has been shown to have a mitigation effect on plants under Cd toxicity. However, the mechanisms underlying the role of Si in alleviating Cd toxicity are still poorly understood in wheat. Therefore, growth status, photosynthesis parameters, root morphology, antioxidant system, and Cd2+ uptake and flux under Cd toxicity were studied through hydroponic experiment, aiming to explore the mitigation of Si on Cd toxicity in wheat seedlings. The results showed that Si supply improved plant biomass as well as photosynthetic but had little effects on root morphology of seedlings under Cd stress. Si addition decreased Cd contents both in shoots and roots. In situ measurements of Cd2+ flux showed that Si significantly inhibited the net Cd2+ influx in roots of wheat. Si also mitigated the oxidative stress in wheat leaves by decreasing malondialdialdehyde (MDA) and hydrogen peroxide (H2O2) contents as well as by increasing superoxide dismutase (SOD) and guaiacol peroxidase (POD) activity. Overall, the results revealed that Si could alleviate Cd toxicity in wheat seedlings by improving plant growth and antioxidant capacity and by decreasing Cd uptake and lipid peroxidation.

Alleviatory effect of spent Pleurotus eryngii Quel substrate on replant problem of Rehmannia glutinosa Libosch.

Rehmannia glutinosa Libosch. is a medicinal plant cultivated at a commercial scale in China. However, replanting problems result in a severe decline in both the biomass and quality of its roots, which are of greatest medicinal value. This study attempted to remediate the replant soil using spent Pleurotus eryngii Quel substrate for alleviating this issue, and to investigate the underlying mechanisms. Results showed that R. glutinosa grew successfully in fresh soil and remedial replant soil, while no roots were harvested in the unremedied replant soil. Overall, the nutritional status in the remedial soil was higher than that of the unremedied and fresh soil, while the concentration of allelopathic phenolic acids was lower. When planted in unremedied soil, the growth of five plant pathogens was induced and one beneficial fungus was suppressed. When planted in remedied soil, four out of the five pathogens were suppressed, while two beneficial fungi were identified in the remedial soil. This study suggests that the spent P. eryngii substrate significantly alleviates the replant problem of R. glutinosa, and that the alleviatory function reflects a synergetic effect, including the supplementation of soil nutrition, the degradation of allelochemicals, and the remediation of unbalanced microbial community.

Species diversity and drivers of arbuscular mycorrhizal fungal communities in a semi-arid mountain in China.

Arbuscular mycorrhizal fungi (AMF) play an essential role in complex ecosystems. However, the species diversity and composition of AMF communities remain unclear in semi-arid mountains. Further, it is not well understood if the characteristics of AMF community assemblies differ for different habitat types, e.g., agricultural arable land, artificial forest land, natural grassland, and bush/wood land. Here, using the high-throughput technology by Illumina sequencing on the MiSeq platform, we explored the species diversity and composition of soil AMF communities among different habitat types in a semi-arid mountain (Taihang Mountain, Mid-western region of China). Then, we analyzed the effect of nutrient composition and soil texture on AMF community assembly. Our results showed that members of the Glomus genera were predominated in all soil types. The distance-based redundancy analysis indicated that the content of water, available phosphorus, and available potassium were the most crucial geochemical factors that significantly affected AMF communities (p < 0.05). The analysis of the soil texture confirmed that AMF diversity was negatively correlated with soil clay content. The comparison of AMF diversity among the various habitat types revealed that the artificial forest land had the lowest AMF diversity in comparison with other land types. Our findings suggest that there were differences in species diversity and composition of soil AMF communities among different habitat types. These findings shed new light on the characteristics of community structure and drivers of community assembly in AMF in semi-arid mountains, and point to the potential importance of different habitat types on AMF communities.

Mechanisms of Cd and Cr removal and tolerance by macrofungus Pleurotus ostreatus HAU-2.

Fungi bioaccumulation is a novel and highly promising approach to remediate polluted soil. The present study revealed a high ability to tolerate Cd and Cr in the fungus Pleurotus ostreatus HAU-2. However, high concentrations of Cd and Cr can suppress fungal growth and result in a variation of hypha micromorphology. Batch experiments were performed to investigate Cd and Cr stress effects on the amount of active oxygen in fungi, activity of antioxidant enzyme, as well as the removal efficiency of Cd and Cr. The results revealed that Cd and Cr caused increasing active oxygen and malonaldehyde (MDA) concentrations. Antioxidant enzymes play a central role in removing active oxygen, while glutathione (GSH) aids the Cd detoxification within cells. In fluid culture, fungal removal rates of Cd and Cr ranged from 44.85% to 80.36% and 14.49% to 45.55%, respectively. Intracellular accumulation and extracellular adsorption were the major removal approaches. Bag cultivation testing indicated that the fungus absorbed Cd and Cr contained within soil. In particular, the accumulation ability of Cd (15.6mgkg-1) was higher compared to that of Cr (8.9mgkg-1). These results successfully establish P. ostreatus HAU-2 as promising candidate for the remediation of heavy-metal polluted soils.

Improvement of tolerance to lead by filamentous fungus Pleurotus ostreatus HAU-2 and its oxidative responses.

Wastewater contaminated with heavy metals is a world-wide concern. One biological treatment strategy includes filamentous fungi capable of extracellular adsorption and intracellular bioaccumulation. Here we report that an acclimated strain of filamentous fungus Pleurotus ostreatus HAU-2 can withstand Pb up to 1500 mg L(-1) Pb, conditions in which the wildtype strain cannot grow. The acclimated strain grew in liquid culture under 500 mg L(-1) Pb without significant abnormity in biomass and morphology, and was able to remove significant amounts of heavy metals with rate of 99.1% at 200 mg L(-1) and 63.3% at 1500 mg L(-1). Intracellular bioaccumulation as well as extracellular adsorption both contributed the Pb reduction. Pb induced levels of H2O2, and its concentration reached 72.9-100.9 µmol g(-1) under 200-1000 mg L(-1) Pb. A relatively higher malonaldehyde (MDA) concentration (8.06-7.59 nmol g(-1)) was also observed at 500-1500 mg L(-1) Pb, indicating that Pb exposure resulted in oxidative damage. The fungal cells also defended against the attack of reactive oxygen species by producing antioxidants. Of the three antioxidant enzymes superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), CAT was the most responsive and the maximal enzyme activity was 15.8 U mg(-1) protein. Additionally, glutathione (GSH) might also play a role (3.16-3.21 mg g(-1) protein) in detoxification under relatively low Pb concentration (100-200 mg L(-1)). Our findings suggested that filamentous fungus could be selected for increased tolerance to heavy metals and that CAT and GSH might be important components of this tolerance.

[Correlation of Allelopathy of Rehmannia glutinosa Root Exudates and Their Phenolic Acids Contents].

OBJECTIVE: To study the allelopathic potential of Rehmannia glutinosa root exudates in different growth stages and dynamic change of phenolic acids contents, in order to reveal the correlation between phenolic acids and allelbpathy effect of Rehmannia glutinosa. METHODS: Root exudates of Rehmannia glutinosa in different growth stages were obtained by a new instrument which was used to collect the root exudates of xerophytes. After that, bioassay was applied to estimate allelopathy effect of the root exudates. HPLC was used to determine the contents of five phenolic acids (coumaric acid, 4-hydroxybenzoic acid, vanillic acid, syringic acid and ferulic acid) which were reported to relate to allelopathy effect. Correlation of bioassay data and HPLC data were also analyzed. RESULTS: The germination rate of radish after soaking by root exudates of different growth stages of Rehmannia glutinosa was 97. 89%, 92. 38%, 89. 52%, 85. 71%, 85. 71%, 84. 76% and 83. 81%, respectively, which indicated a decline trend. And significant differences were shown from previous enlargement stage compared with the contrast. The bud length after soaking by root exudates was 5. 68, 5. 76, 5. 91, 5. 65, 5. 41, 5. 28 and 5. 11 cm, separately, which increased slightly before decreasing gradually. Previous enlargement stage was also the initial period when significant differences were shown. Five phenolic acids were detected in root exudates by HPLC, while the change of their contents and the allelopathy effect of root exudates did not perform a similar trend. Correlation analysis indicated the five phenolic acids did not have significant relevance (r = - 0. 666 - 0. 590) with germination rate and bud length of radish except the negative correlation (r = -0. 833, P <0. 05) of syringic acid and bud length. CONCLUSION: Significant allelopathy effect of Rehmannia glutinosa is performed from previous enlargement stage and enhanced with its growth. Syringic acid is a probable dominant allelochemical of Rehmannia glutinosa.