The Study On The Ecological Stoichiometric Characteristics Of Carbon,Nitrogen,Phosphrous And Potassium Of Azolla

Azolla is a symbiotic organism of ferns and anabaena,which has the characteristics of biological nitrogen fixation and potassium enrichment function.As an important aquatic resource for maintaining ecosystem balance and stability,Azolla plays an important role in ecological agriculture models such as rice-Azolla,rice-Azolla-fish,rice-Azolla-duck,and can be used as feed and green manure.In this study,eight varieties of Azolla are preserved in the National Azolla Germplasm Carp(Fuzhou),namely Azolla filiculoides Lan,Azolla mexicana Presel,Azolla caroliniana Willd,Azolla microphylla Kaulfus,Azolla pinnata var.imbricata,Azolla pinnata var.pinnata R.Brown,Backcrossed Azolla,Hybrid Azolla and Salvinia natan as the control which is based on the non-nitrogen-fixing function.Two kinds of culture methods,Network room soil culture and Greenhouse nutrient solution culture are used to study the biomass,C,N,P and K content and ecological stoichiometry of different growth environments,different growth times and different varieties of Azolla.It provides a scientific basis for the conservation and utilization of germplasm resources of Azolla.At the same time,it provides reference and basic data for the study of ecological stoichiometry of aquatic ecosystems.The main findings are as follows:1)The order of biomass of test varieties is : Azolla mexicanaPresel > Azolla microphylla Kaulfus >Hybrid Azolla>Azolla filiculoides Lan > Backcrossed Azolla > Azolla caroliniana Willd > Azolla pinnata var.imbricata > Azolla pinnata var.pinnata R.Brown > Salvinia natan.The biomass,C,N,P and K contents show that the three genus and the Hybrids Azolla and Backcrossed Azolla produced by them are superior to the nine genus,and the Backcrossed Azolla is optimal.2)Under the condition of Network room soil culture,the biomass,the C content and the P content of 8 varieties of Azolla are higher than that of Greenhouse nutrient solution culture and the P content is lower than Greenhouse nutrient solution culture.Under the two culture conditions,the ecological stoichiometry characteristics of Azolla are different,so it is recommended to keep two culture methods in the culture of Azolla.3)The biomass of Azolla is largest in spring,and smallest in winter.The C content is highest in spring and lowest in autumn.The N content of Azolla is highest in summer and which is lowest in winter.The P content of Azolla is higher in spring and autumn than summer and winter.In practical applications,it is recommended to use Azolla in spring and summer,when the biomass and C,N and P contents are higher.4)In this study,the N:P of Azolla are lower than 14,according to the nutrient limitation law of plant ecological stoichiometry,its growth is mainly restricted by N element.However,due to the strong nitrogenfixation of Azolla,the growth and culture process of Azolla requires more attention to the P element.The Network room soil culture should be supplemented with phosphate fertilizer,and Greenhouse nutrient solution culture should ensure sufficient supply of P element.