Accumulation And Transfer Characteristics Of Cadmium In Five Ornamental Grasses And Physiological Metabolism Responses Under Cadmium Stress

With the continuous acceleration of industrial and agricultural modernization,the cadmium（Cd） pollution in soil is becoming increasingly serious.Ornamental grass is a kind of herbaceous plants consisted largely of Poaceae,including Cyperaceae,Typhaceae and other monocotyledonous plants with high ornamental value.Ornamental grasses have the advantages of its beautiful morphology and plentiful color of leaves,deeply loved by people,which is widely used in landscaping and greening.Ornamental grasses generally have well-developed root systems,high biomass,drought and cold resistance,and less pests and diseases.It exhibits strong tolerance in Cd polluted environments,which is an ideal type of soil remediation plant.However,the enrichment and transfer ability of Cd,physiological characteristics and metabolomics of ornamental grasses under Cd stress are currently unclear and require further research.This experiment took five commonly used ornamental grasses（Carex breviculmis,Pennisetum alopecuroides,Andropogon virginicus,Miscanthus sinensis‘Gracillimus’,Muhlenbergia capillaris）as research objects.We conducted research from the aspects of Cd enrichment ability,morphological and physiological characteristics,and metabolomic analysis of P.alopecuroides under Cd stress.The results revealed that:（1）Cd stress reduced the biomass of five ornamental grasses.Under the treatment of 100 mg·L^-1 Cd,the biomass decreased the most in M.capillaris（14.03 g）and the least in P.alopecuroides（5.73 g）;C.breviculmis had the highest accumulation in leaves（435.77μg）,while P.alopecuroides had the highest accumulation in roots（1145.51μg）.The total bioconcentration factors（BCF）of Cd of five ornamental grasses were 0.50～0.90,and the transfer factor（TF）of the five ornamental grasses were 0.03～0.40.Among them,P.alopecuroides had the highest total BCF（0.79）,and the TF was the highest in C.breviculmis（0.33）.This indicated that P.alopecuroides has the strongest Cd enrichment ability,while C.breviculmis has the strongest Cd transfer ability.（2）At the 70th day of Cd stress,the plant height of C.breviculmis,M.sinensis‘Gracillimus’and M.capillaris was decreased significantly;the leaf length of C.breviculmis and M.sinensis‘Gracillimus’was decreased significantly.With the increase of Cd concentration,the root vigor and photosynthetic pigment content decreased,the relative electrical conductivity,malondialdehyde（MDA）content,proline content and peroxidase（POD）activity in leaves and roots of the five ornamental grasses increased.The superoxide dismutase（SOD）activity and catalase（CAT）activity in leaves and roots of C.breviculmis,P.alopecuroides,A.virginicus and M.capillaris increased.The SOD activity in leaves and roots of M.sinensis‘Gracillimus’showed a trend of increasing first and then decreasing,the CAT activity in leaves increased while showed a trend of increasing first and then decreasing in roots of M.sinensis‘Gracillimus’.Principal component analysis indicated that plant height,root to shoot ratio,carotenoid content,MDA content,and Pro content could be used as important indexes of the five ornamental grasses for screening and evaluation under Cd stress.Under the treatment of 100 mg·L^-1Cd,the tolerance was in the order of P.alopecuroides,M.capillaris,M.sinensis‘Gracillimus’,A.virginicus,and C.breviculmis.（3）Cd stress had a significant inhibitory effect on the germination of P.alopecuroides seeds,but the germination rate could still reach over 80%,and the relative cadmium damage rate was within 5%.Under the treatment of 10 mg·L^-1Cd,the fresh and dry weight of P.alopecuroides seedlings were significantly reduced.At this time,the Cd content in the roots exceeds 1 mg·g^-1,and the Cd content in the leaves was 55.91%of the roots.The root-shoot ratio was significantly reduced,which mean Cd has a more severe impact on the root.（4）Under Cd stress,the MDA content,soluble protein content,POD activity,and CAT activity of P.alopecuroides seedlings gradually increased.Metabolomics analysis indicated that,most of the differential amino acids,differential lipids decreased in leaves,while increased in roots.Most of the carbohydrates in leaves and roots decreased under Cd stress,which contribute to the shortened leaf/root length and fresh weight.Metabolic pathway analysis showed that Cd significantly affects 7 and 8 metabolic pathways in leaves and roots.There were 3 common metabolic pathways in roots and leaves,including purine metabolism,aminoacyl-t RNA biosynthesis,cysteine and methionine metabolism.P.alopecuroides adapt to Cd stress by regulating the above metabolic pathways.The results of this study revealed the response mechanism of ornamental grasses to Cd stress,and provided data support and basis for the application of ornamental grasses in the remediation of Cd-contaminated soil,in order to expand plant species for phytoremediation technology of Cd-contaminated soil.