Adaptive response of flavonoids in Robinia pseudoacacia L. affected by the contamination of cadmium and elevated CO(2) to arbuscular mycorrhizal symbiosis.

As a key component in non-enzyme resistance system, flavonoids play a crucial role in the plant growth and defenses, which are significantly affected by biotic and abiotic factors such as fungi, bacteria, viruses, heavy metals, and atmospheric CO2. Arbuscular mycorrhizal fungi (AMF) play an important role in enhancing plant tolerance to adverse environments, which can significantly affect the synthesis of flavonoids by forming mycorrhizal symbionts with plant roots. However, few studies explored the combined effects of AMF, elevated CO2, and heavy metals on flavonoids in plants. Here, we investigated the adaptive response of flavonoids accumulation in Robinia pseudoacacia L. seedlings affected by the contamination of cadmium (Cd) and elevated CO2 to arbuscular mycorrhizal symbiosis. The results showed that G. mosseae decreased (p < 0.05) Cd content in leaves by 62.2% under elevated CO2. Moreover, G. mosseae colonization led to significant decreases in robinin, quercetin, kaempferol and acacetin by 17.4%, 11.1%, 15.5% and 23.1% under elevated CO2 + Cd, respectively. Additionally, G. mosseae down-regulated (p < 0.05) expression levels of phenylalanine ammonia-lyase (PAL) and chalcone synthase (CHS) genes under elevated CO2 + Cd, and CHS and uridine diphosphate flavonoid glucosyltransferase (UFGT) activities decreased (p < 0.05). Quercetin, kaempferol and acacetin showed positive (p < 0.05) correlation with PAL and CHS genes expression and PAL, CHS, and UFGT activities. Cadmium, C/N ratio, carotenoids, leaf biomass, total chlorophyll, P, and starch in leaves and G. mosseae colonization rate in roots influenced (p < 0.05) flavonoids content. Overall, G. mosseae reduced flavonoids synthesis by down-regulating gene expression levels and activities of key enzymes under elevated CO2 + Cd. The results improved our understanding of the regulation of AMF on non-enzymatic resistance of plants grown in heavy metal-contaminated soils under increasing atmospheric CO2 scenarios.

Zhang C ，Jia X ，Zhao Y ，Wang L ，Wang Y ... -  《-》

The combined effects of elevated atmospheric CO(2) and cadmium exposure on flavonoids in the leaves of Robinia pseudoacacia L. seedlings.

Flavonoids participate in several plant processes such as growth and physiological protection in adverse environments. In this study, we investigated the combined effects of eCO2 and cadmium (Cd)-contaminated soils on the total flavonoid and monomer contents in the leaves of Robinia pseudoacacia L. seedlings. Elevated CO2, Cd, and eCO2+ Cd increased the total flavonoids in the leaves relative to the control, and eCO2 mostly increased (p < 0.05) the total flavonoid content under Cd exposure. Elevated CO2 increased (p < 0.05) robinin, rutin, and acacetin contents in the leaves of 45-day seedlings and decreased (p < 0.05) the content of robinin and acacetin at 90 and 135 d under Cd exposure except for robinin at day 45 under Cd1 and acacetin on day 135 under Cd1. Quercetin content decreased (p < 0.05) under the combined conditions relative to Cd alone. Kaempferol in the leaves was only detected under eCO2 on day 135. The responses of total chlorophyll, total soluble sugars, starch, C, N, S, and the C/N ratio in the leaves to eCO2 significantly affected the synthesis of total flavonoids and monomers under Cd exposure. Overall, rutin was more sensitive to eCO2+ Cd than the other flavonoids. Cadmium, CO2, and time had significant interactive effects on the synthesis of flavonoids in the leaves of R. pseudoacacia L. seedlings. Elevated CO2 may improve the protection and defense system of seedlings grown in Cd-contaminated soils by promoting the synthesis of total flavonoids, although robinin, rutin, quercetin, and acacetin yields may reduce with time. Additionally, increased Cd in the leaves suggested that eCO2 could improve the phytoremediation of Cd-contaminated soils.

Zhang C ，Jia X ，Zhao Y ，Wang L ，Cao K ，Zhang N ，Gao Y ，Wang Z ... -  《-》

Effect of arbuscular mycorrhizal fungi in roots on antioxidant enzyme activity in leaves of Robinia pseudoacacia L. seedlings under elevated CO(2) and Cd exposure.

Arbuscular mycorrhizal fungi (AMF) are easily influenced by increasing atmospheric CO2 concentration and heavy metals including cadmium (Cd), which can regulate antioxidant enzyme in host plants. Although the effect of AMF under individual conditions such as elevated CO2 (ECO2) and Cd on antioxidant enzyme in host plants has been reported widely, the effect of AMF under ECO2 + Cd receives little attention. In this study, a pot experiment was conducted to study the effect of AMF community in roots on superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activities in leaves of 135-d Robinia pseudoacacia L. seedlings under ECO2 + Cd. The activities of SOD and CAT increased and POD activity and the richness and diversity of AMF community decreased under ECO2 + Cd relative to Cd alone. The richness and diversity of AMF were negatively related to Cd content in roots and leaves. The richness and OTUs of AMF community positively and AMF gene abundance negatively affected POD activity under the combined treatments. Superoxide dismutase and POD activities were negatively and positively related to Archaeospora and Scutellospora, respectively, under ECO2 + Cd. Cadmium in roots and leaves was negatively and significantly related to Glomus, Scutellospora, and Claroideoglomus abundance under ECO2 + Cd. Overall, AMF diversity and Archaeospora and Scutellospora in roots significantly influenced SOD, POD, and CAT activities. The response of AM symbiosis to ECO2 might regulate antioxidant capacity in host plants upon Cd exposure. Glomus, Scutellospora, and Claroideoglomus might be applied to phytoremediation of Cd-contaminated soils.

Wang L ，Jia X ，Zhao Y ，Zhang C ，Zhao J ... -  《-》

Effects of elevated CO(2) on arbuscular mycorrhizal fungi associated with Robinia pseudoacacia L. grown in cadmium-contaminated soils.

As symbionts capable of reciprocal rewards, arbuscular mycorrhizal fungi (AMF) can alleviate heavy metal toxicity to host plants and are easily influenced by elevated CO2 (ECO2). Although the individual effects of ECO2 and cadmium (Cd) on AMF have been widely reported, the response of AMF to ECO2 + Cd receives little attention. We evaluated the combined effects of ECO2 and Cd on AMF in the rhizosphere soil and roots of Robinia pseudoacacia L. seedlings. Under ECO2 + Cd relative to Cd, AMF gene copies and richness in rhizosphere soils increased (p < 0.05) and the diversity reduced (p < 0.05) at 4.5 mg Cd kg-1 dry soil; whereas root AMF abundance at 4.5 mg Cd kg-1 dry soil and the diversity and richness reduced (p < 0.05). Elevated CO2 caused obvious differences in the dominant genera abundance between rhizosphere soils and roots upon Cd exposure. Responses of C, water-soluble organic nitrogen (WSON), pH, and diethylene triamine penta-acetic acid (DTPA)-Cd in rhizosphere soils and root N to ECO2 shaped dominant genera in Cd-polluted rhizosphere soils. Levels of DTPA-Cd, WSON, C and pH in rhizosphere soils and C/N ratio, N, and Cd in roots to ECO2 affected (p < 0.05) dominant genera in roots under Cd exposure. AMF richness and diversity were lower in roots than in rhizosphere soils. Elevated CO2 altered AMF communities in rhizosphere soils and roots of R. pseudoacacia seedlings exposed to Cd. AMF associated with R. pseudoacacia may be useful/interesting to be used for improving the phytoremediation of Cd under ECO2.

Wang L ，Jia X ，Zhao Y ，Zhang C ，Gao Y ，Li X ，Cao K ，Zhang N ... -  《-》

Elevated CO(2) increases glomalin-related soil protein (GRSP) in the rhizosphere of Robinia pseudoacacia L. seedlings in Pb- and Cd-contaminated soils.

Glomalin-related soil protein (GRSP), which contains glycoproteins produced by arbuscular mycorrhizal fungi (AMF), as well as non-mycorrhizal-related heat-stable proteins, lipids, and humic materials, is generally categorized into two fractions: easily extractable GRSP (EE-GRSP) and total GRSP (T-GRSP). GRSP plays an important role in soil carbon (C) sequestration and can stabilize heavy metals such as lead (Pb), cadmium (Cd), and manganese (Mn). Soil contamination by heavy metals is occurring in conjunction with rising atmospheric CO2 in natural ecosystems due to human activities. However, the response of GRSP to elevated CO2 combined with heavy metal contamination has not been widely reported. Here, we investigated the response of GRSP to elevated CO2 in the rhizosphere of Robinia pseudoacacia L. seedlings in Pb- and Cd-contaminated soils. Elevated CO2 (700 μmol mol-1) significantly increased T- and EE- GRSP concentrations in soils contaminated with Cd, Pb or Cd + Pb. GRSP contributed more carbon to the rhizosphere soil organic carbon pool under elevated CO2 + heavy metals than under ambient CO2. The amount of Cd and Pb bound to GRSP was significantly higher under elevated (compared to ambient) CO2; and elevated CO2 increased the ratio of GRSP-bound Cd and Pb to total Cd and Pb. However, available Cd and Pb in rhizosphere soil under increased elevated CO2 compared to ambient CO2. The combination of both metals and elevated CO2 led to a significant increase in available Pb in rhizosphere soil compared to the Pb treatment alone. In conclusion, increased GRSP produced under elevated CO2 could contribute to sequestration of soil pollutants by adsorption of Cd and Pb.

Jia X ，Zhao Y ，Liu T ，Huang S ，Chang Y ... -  《-》