Effect Of Light Conditions On Growth Characteristic Of Two Submersed Macrophyte

The recovery of submerged macrophyte in deep lakes is difficult because of low light intensity.Light-compensation technology supply enough light for the submerged macrophyte.However,each submerged macrophyte has its own light intensity,light time and light type for growth.Therefore,it is necessary to determine the lighting conditions of each submerged macrophyte.In this paper,the effects of light intensity,light time and light type on the growth characteristics of submerged macrophytes Vallisneria natans,Elodea nuttallii are studied.Based on the single factor experiments,orthogonal experiment and response surface methodology was employed.The growth indexes,physiological indices and water quality indexes of Vallisneria natans,Elodea nuttallii were determined.The main conclusions of the study are as follows:Vallisneria natans can grow well under the conditions of 5600 lx light intensity,16 h light time and red light.The light intensity had a significant effect on the plant height of Vallisneria natans.The system has highest removal rate for the total nitrogen,nitrate nitrogen and soluble reactive phosphorus under the conditions of 5600 lx light intensity,8h light time and white light.Moreover,the light intensity had a significant effect on the removel of total nitrogen and soluble reactive phosphorus.It is good for the synthesis of photosynthetic pigments under the conditions of 2700 lx light intensity,16 h light time and blue light.Elodea nuttallii can grow well under the conditions of 7000 lx light intensity,12 h light time and red light.The light intensity,light time and light tape had a significant effect on the plant height of Elodea nuttallii.The system has highest removal rate for the total nitrogen and soluble reactive phosphorus under the conditions of 7000 lx light intensity,20 h light time and white light.The light intensity,light time and light tape had a significant effect on the removel of total nitrogen.Using Design-Expert 8.0,the optimal model was obtained.The optimal solution is 6999.99 lx light intensity,19.57 light time and red light.Under this conditions,the four response values of plant height,fresh weight growth rate,TN removal rate and soluble reactive phosphorus removal rate were 66.09 cm,604.11%,63.83%,99%,respectively.In the process of nitrogen removal,the contribution of plant absorption is between 0 and 25.39%.The contribution of other functions,such as the self-purification ability of water and the microorganisms action,is great,have yet to be further researched and studied.The 16 s r DNA Amplicon sequencing studies of the Elodea nuttallii root showned that the mainly nitrifying functional bacteria genera in the system were norank_c__Cyanobacteria,Rhodobacter,Chamaesiphon,Rhizobium,and the main denitrifying functional bacteria were unclassified_f__Comamonadaceae,Rhodobacter,Flavobacterium,Methylotenera.The mainly phosphorus enrichment bacteria genera were unclassified_f__Comamonadaceae.