Aluminum Tolerance Physiological Mechanism Of Axonopus Compressus Germplasm Resources

Carpetgrass [Axonopus compressus (Sw.)] wild gennplasm resources are warm-season turfgrass. It is distributed in tropical and subtropical regions, and carpetgrass has abundant genetic diversity. In China, it is mainly distributed in Guangdong, Guangxi, Yunnan,Hainan and Fujian provinces in the acid soil. Aluminum is the main limiting factor of plant growth in the acid soil. Different distribution of the genetic resoures might exist great differences in aluminum resistance. But study of the carpetgrass aluminum resistance mechanism was rarely reported. In the study, 86 varieties of carpetgrass from 5 provinces of China were used to evaluate the aluminum tolerance. And the study researched aluminium growth, nutrient absorption, antioxidant enzyme activity of the system and the secretion of organic acids of aluminum sensitive type and aluminum tolerance type under the stress. This study provided theoretical basis for breeding new varieties of resistance to aluminum lawn grass. The main results are as follows:(1) Evaluation on aluminum tolerance of carpetgrass germplasm resourcesThis study researched the aluminum tolerance by six indicators. Six indicators included total number of secondary branches, relative shoot dry weight, relative root dry weight, total stem length, turf quality and leaf firing percentage, were selected to identify the aluminum tolerance of carpetgrass. The results showed that there were significant (P<0.05) or very significant (P <0.01) correlation between different carpetgrass germplasm after the treatment of 2.1 mM Al. By contrast, the correlation between turf quality and leaf firing percentage was negatively significant. The range of variable coefficient of different indicators was 34.1% -78.6%. The turf quality (34.1%) was minimum and leaf firing percentage (78.6%) was maximum. According to cluster analysis, 86 varieties could be divided into three categories, namely intermediate type, aluminum sensitive type and aluminum tolerance type. And through the result to screen out the carpetgrass represented by S38 and T58 from aluminum sensitive type and aluminum tolerance type separately.(2)Aluminum toxicity effects on Carpetgrass germplasm nutrients absorptionThe study found the different absorption among P, Mg, Ca and K between T58 and S38 in Al stress. Aluminum processing, tolerance germplasm and sensitive resistance germplasm carpetgrass plant P, Mg, Ca and K content have dropped significantly. The ground part of the content of P, Mg, Ca and K respectively decreased by 43.7%, 26.1%,33.2%, 34.7%, root content of P, Mg, Ca and K respectively decreased by 15.4%, 29.9%,36.1%, 29.1%. There were huge differences between the content of P, Mg, Ca and K, in both tolerance germplasm and sensitive resistance germplasm ground parts and root.(3)Under aluminum stress, hematoxylin staining to the apexThe content of carpetgrass root aluminum accumulation was different, hematoxylin staining degree either. Under aluminum stress, the root accumulation of aluminum was greater. The absorbed aluminum in the root was initially accumulated in the root tip. By staining hematoxylin root, the root tip of dyeing showed the deepest degree. The dyeing gradually spreaded from the root top, dyeing degree increased. The recult showed that the aluminum tolerance germplasm under aluminum stress aluminum accumulation quantity and speed were far smaller than aluminum sensitive germplasm.(4 )The secretion of organic acids under aluminum stressAluminum tolerance type T58 and aluminum sensitive type S38 secreted citric acid and malic acid under aluminum stress. There are 6 h lag phase, which belonged to the organic acid secretion mode 2. The results showed that the citric acid and malic acid production of aluminum germplasm sensitive were always greater than aluminum germplasm after the aluminum processing. And there were significant differences between T58 and S38(5 )Aluminum stress under root accumulationUnder aluminum stress, the root aluminum content of T58 and S38 significantly increased (P < 0.05). With aluminium concentration of outside world increasing, plant root aluminum accumulation increased. And S38 increment were significantly higher than that of T58 (P < 0.05). Different concentration of aluminum processing, T58 root aluminium concentrations less than S38. Under aluminum stress, aluminum tolerance type T58 root aluminum accumulation was as 4.4-7.4 times as the control group, aluminum sensitive type S38 root aluminum accumulation was as 4.9-9.17 times as the control group. It showed that carpetgrass increasing the activity of antioxidant enzymes to reduce the stress suffered by aluminum.(6)Acidic soil cultivation effect on Carpetgrass seed source antioxidant systemUnder the condition of aluminum processing, the superoxide dismutase (SOD),peroxidase (POD), malondialdehyde (MDA) content and superoxide anion radical (02-)production rate in both T58 and S38 were increased. The content of SOD of T58 increment amplitude were greater. There were significant differences between T58 and S38(P < 0.05).The study proved that increasing the activity of antioxidant enzymes and toxicity can reduced the damage to carpetgrass.