The Combined Effect Of Light And N, P On Growth And Physiology Of Vallisneria Natans

Light and water N, P are important environmental factors that effect the growth submerged plant in eutrophic water bodies, therefore, to study the combined influences the three factors on growth and physiology of submerged plant is of great significance in providing advances for research practices of the restoration of submerged vegetation in eutrophic water bodies.In this study, Vallisneria natans, the dominant species in submerged vegetation restoration was used as the experimental plant, the combined effects of light and water nutrients N, P on the growth and physiology of Vallisneria natans were studied. The research was divided into three parts: 1. the combined effect of light and N concentration on growth and physiology of Vallisneria natans; 2. the combined effect of light and NH4+-N: NO3--N on growth and physiology of Vallisneria natans; 3. the combined effect of light and N, P on growth and physiology of Vallisneria natans. The research methods and conclusions were as follows:(1) Crossover experiments of 3 levels of light intensity×3N concentration were set, in which high, middle and low light intensity levels were respectively set by 1, 2, 3 layers of light shielding screens, the three N concentrations were set as 2 mg?L-1, 6 mg?L-1 and 12 mg?L-1, NH4+-N:NO3--N of N source is 1:1, the P concentration was 0.5 mg?L-1. The results showed that: the combined effect of light intensity and N concentration is different from the additive effect, there is some interaction. Under high light conditions, when the N concentration attained 12 mg·L-1, the growth of Vallisneria natans was significantly inhibited, specifically the relative growth rate, the growth rate of leaf quantity and plant height were all lower than the 2 mg·L-1 and 6 mg·L-1 groups (P<0.05); under middle and low light conditions, Vallisneria natans showed no significant difference in the three N concentration treatments. And when N concentration was 12 mg·L-1, the SOD enzyme and POD enzyme activities under high light conditions were lower than that under middle and low light conditions (P<0.05).(2) Crossover experiments of 3 levels of light intensity×4 ratios of NH4+-N and NO3--N were set, in which high, middle and low light intensity levels were respectively set by 1,2,3 layer of light shielding screens, NH4+-N: NO3--N were set as 6:6, 6:0, 3:3 and 0:6. The results showed that: Under high light conditions, compared to lower NH4+-N: NO3--N viz. the 3:3, the growth of Vallisneria natans in groups of NH4+-N: NO3--N=6:0 and 6:6 with higher ammonia concentration tend to be inhibited, as the relative growth rate, the growth rate of plant height and root length in 6:0 and 6:6 groups were smaller than in 3:3 groups (P<0.05). But under middle and low light conditions, the result was different, when TN =6 mg?L-1, the growth indexes of Vallisneria natans were not significantly different in different ratios of NH4+-N and NO3—N (P>0.05).(3) Crossover experiments of 2 levels of light intensity×2 N concentrations×2 P concentration were set, in which high, middle and low light intensity levels were respectively set by 1, 3 layer of light shielding screens, the 2 levels of N concentrations were set as 2 mg?L-1 and 6 mg?L-1, and the 2 levels of P concentration were set as 0.05 mg?L-1 and 0.5 mg?L-1. The results showed that, in the three factors of light, N, P, the light play a decisive role on the growth of Vallisneria natans. The high light condition significantly promoted the growth and vegetative propagation of Vallisneria natans, the total biomass, the above ground biomass, the underground biomass and the quantities of new shoots of Vallisneria natans under high light conditions were larger than that under low light conditions. The increase of N, P concentration also could stimulate the growth of Vallisneria natans to a certain extent, but the influences were relatively smaller than that of light. Under high light conditions, either of the two elements N or P be in the low concentration will be the limitation factor to the growth of Vallisneria natans, one in low concentration, the promotion of the growth of Vallisneria natans caused by the increase of the other element would be small.