| Nitrogen is vital for macroalgae and seagrass. However, the nutrient influence on the growth of different species is different in ligotrophic coastal systems or eutrophic areas. The uptake of different 15N uptake rate of Zoster a japonica and Ulva pertusa after three-level light or wave treatment was studied using nitrogen stable isotope tracer technique. The results showed that these two plants had different uptake preference. In addition, nutrient absorption mechanism would vary when light or wave level changed. The main results are summarized as follows:1. The experiment of light effects on nitrogen absorption mechanism1) Under the different light condition, total dry weight of U. pertusa in normal light treatment was significantly higher than that in medium light and low light.2) Under different light level, both N% and δ15N of U. pertusa tissues were not different significantly. But δ15N values of treatment groups were higher than those of the control group after 1 hour isotope processing experiment, among which 815N values increased significantly in 15N labeled ammonium treatment group compared to control group.3) For ammonium treatment group and nitrate treatment group, the 15N absorption values ranked as:normal light>medium light>low light.4) The analysis of different 15N labeled nutrient absorption rate after the impact of the same light level showed that 15N nutrient uptake rate in ammonium treatment group and glycine treatment group were significantly higher than that in nitrate and urea treatment group.2. The experiment of light effects on nutrient absorption mechanism of Z. japonica1) After the different light treatment, biomass and some morphological parameters in Z. japonica changed significantly, and dry weight in normal light treatment was obviously higher than that in medium light and low light. Total dry weight, aboveground dry weight, leaf length, leaf width, rhizome diameter, etc. in the normal light level were significantly higher than those in the other groups respectively, and there were no significant differences in internodal length and root length between different light treatment groups.2) There were no significant differences for δ15N‰ in aboveground or belowground of Z. japonica between different light levels. But δ15N‰ of aboveground part in ammonium treatment group were higher than that in the control group after 1 hour isotope processing experiment, and 815N of belowground were higher than the control group, except glycine treatment group.3) Analysis of the uptake rate of the same nutrient after the different light treatment showed that in the ammonium treatment group and the urea treatment group, 15N nutrient uptake rate of aboveground part and belowground part were highest in medium light level. In nitrate treatment group,15N nutrient uptake rate of aboveground part was extremely low, and the highest value was appeared in low light level.4) The analysis of different 15N labeled nutrient absorption rate after the impact of the same light level showed that 15N nutrient uptake rates of aboveground part and belowground part in ammonium treatment group were significant higher than those in glycine group, and they were both higher than those in nitrate and urea group.5) The comparison of 15N nutrient uptake rate among the Z. japonica aboveground part and belowground part with U. pertusa showed that 15N nutrient uptake rate were higher in U. pertusa in most cases. In addition to aboveground part of Z. japonica,15N nutrient absorption rate was higher in nitrate treatment group.3. The experiment of wave effects on nutrient absorption mechanism of U. pertusa and Z. japonica1) After different wave levels treatment, the biomass for U. pertusa and aboveground and belowground part of Z. japonica did not change significantly in all wave groups, and nor leaf length, leaf width and rhizome diameter of Z. japonica.2) After different wave levels treatment,δ15N values of U. pertusa and underground part of Z. japonica were obviously higher than control group after different nutrient treatment.3) Analysis of the uptake rate of the same nutrient after the different wave treatment showed that 15N glycine absorption rate of U. pertusa in high wave group was lower than that in non-wave group and medium wave group,15N nutrient absorption rate the rest groups of the under different wave levels was not significantly different. The analysis of Z japonica 15N nutrient absorption rate showed that in addition to the urea groups, the rest groups were significantly different in the different waves. For 15N ammonium uptake rate, there was the highest value in high wave level, and for 15N nitrate uptake rate, the highest value appeared in non-wave group. For 15N glycine uptake rate, the values were similar between medium wave group and high wave group, and they were obviously higher than those in low wave group.4) The comparison of 15N nutrient uptake rate among the aboveground and belowground part of Z. japonica with U. pertusa showed that 15N nutrient uptake rate of U. pertusa was higher in many low and medium wave groups, but after high wave treatment,15N nutrient absorption rates of aboveground part for Z. japonica were highest in all isotope treatment groups except nitrate treatment group. |
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