Physiological Responses Of Three Warm-season Turfgrass To Lead Stress

With Eremochloa ophiuroides, Cynodon dactylon(Linn.) Pers. and Zoysia japonica. as material, the effect of different concentration of Pb2+ on theirs seed germination characteristics and vegetative growth of physiological ecological were researched. Its response law and tolerance ability to lead stress were investigated. This study provided the theoretical background for both heavy metal toxicity mechanisms and phytoremediation to heavy metal ground. The results were as follows:(1) With the different concentration of Pb2+ stress (from 0 to 1000 mg/kg), the germination rate of Eremochloa ophiuroides and Cynodon dactylon(Linn.) Pers. increased firstly and then decreased with the addition of the concentration of Pb2+. In the 62.5mg/kg, the germination rate had the maximum. In the 500 mg/kg, Eremochloa ophiuroides was germinating slowly, Cynodon dactylon(Linn.) Pers. still had high germination rate. In the 1000mg/kg, Eremochloa ophiuroides stop germination, the germination rate of Cynodon dactylon(Linn.) Pers. significantly reduced. These showed that low concentrations of Pb2+ stress can increase the germination rate and high concentrations of Pb2+ stress can reduce the germination rate. The germination rate of Zoysia japonica was very low, physiological index cannot be measured.(2) When the Pb2+ concentration was 62.5 mg/kg, the stem-leaf length of Eremochloa ophiuroides were greater than the CK. With the increase of lead concentrations, the root length and the stem-leaf length of Eremochloa ophiuroides both decreased. In the 500mg/kg, seedlings grew poorly, seeding cannot be measured. With the increase of lead concentrations, the root length and the stem-leaf length of Cynodon dactylon(Linn.) Pers. both decreased.In the 1000mg/kg, the root of Cynodon dactylon(Linn.) Pers. was dysplasia. The root growth is more sensitive than the stem-leaf.(3) With the different concentration of Pb2+ stress (from 0 to 1000 mg/kg), the autioxidant enzyme activity, content of malondialdehyde and soluble sugar of Eremochloa ophiuroides and Cynodon dactylon(Linn.) Pers. increased firstly and then decreased at 250mg/kg and 500mg/kg with the addition of the concentration of Pb2+. Leaf chlorophyll a and b content significantly reduced and the content of soluble proteinand significantly increased with the addition of the concentration of Pb2+ among Eremochloa ophiuroides and Cynodon dactylon(Linn.) Pers.. Lead stress resistance of Cynodon dactylon(Linn.) Pers. seedling was higher than Eremochloa ophiuroides.(4)Pot experiment showed that there is a significant decrease of the visual quality and leaf relative water content in the 4000mg/kg comparing with CK among all three turfgrass. Leaf chlorophyll a and b content significantly reduces in the 4000mg/kg comparing with CK among all three turfgrass. The electrolyte leakage in leave gradually rises with the increase of Pb2+ level under Pb2+ treatments among all three turfgrass. In the 4000mg/kg, visual quality of Eremochloa ophiuroides decreased under level 6 at day 30.(5) The antioxidant defense system (dismutase/SOD, superoxide catalase/CAT, peroxidase/POD, polyphenol oxidase/PPO) was greatly activated under the various Pb2+ stress among three turfgrasses species. Under the various Pb2+ treatmens in Eremochloa ophiuroides, the activity of SOD gradually rises and reaches a maximum at day 20 after Pb application, and the activity of CAT at day 5 after Pb2+ treatment is greatly higher than that in control. While the activity of POD increases significantly only under 2000mg/kg and 4000mg/kg Pb2+ treatments and reaches the maximum at day 15 after Pb application. The activity of PPO gradually rises and reaches a maximum at day 20 under the various Pb2+ treatmens. Under the various Pb2+ treatments in Cynodon dactylon(Linn.) Pers., the activity of SOD rises at day 5 after Pb treatment and boosts a maximum at day 25, and the activity of CAT reaches a maximum at day 15 after treatment. While the activity of POD in Pb treatments rises gradually with the accumulation of Pb2+ in soil and reaches a maximum at day 30 in all Pb treatments. The activity of PPO reaches a maximum at day 15 after treatment, then maintained at a high level. The activity of SOD is significantly higher in 4000mg/kg treatment than that in control and reaches a maximum at day 15 after treatment in Zoysia japonica. While the activity of POD reaches a maximum at day 25 after treatment and then drops at day 30, activity of CAT shows a similar trend as that of POD and reaches a maximum at day 15 after treatment. The activity of POD reaches a maximum at day 25 and changed little over time.(6) With the different concentration of Pb2+ stress (from 0 to 4000 mg/kg), the content of soluble sugar, soluble proteinand and free proline of three turfgrass all had significantly increased with the addition of the concentration of Pb2+. The free proline of Cynodon dactylon(Linn.) Pers. was less sensitive.These data implied that that the protection capacity of three enzymes varied among three turfgrass species under lead stress. Combing with the growth effect, we concluded that lead stress resistance from high to low among three turfgrass species is in the following order:Cynodon dactylon(Linn.) Pers.> Zoysia japonica> Eremochloa ophiuroides.