水体氮质量浓度升高对附着藻生长和元素计量特征的影响

Effects of Nitrogen Enrichment on the Growth and Elemental Stoichiometry of Periphyton

附着藻是浅水湖泊重要的初级生产者,水体氮磷质量浓度升高会影响附着藻的生物量和元素计量特征,从而改变牧食螺类的食物数量和质量,进而影响牧食螺类生长及其与沉水植物之间的相互关系。为了探索氮负荷升高对附着藻生物量和质量的影响,基于受控实验研究了水体氮质量浓度升高(总氮2、4、6、8和10 mg·L^(-1);总磷各处理组均为0.1 mg·L^(-1))对附着藻生长和元素计量特征的影响。实验前测定湖水氮、磷本底质量浓度,通过添加配置的营养盐溶液(氮为KNO_3,磷为KH_2PO_4),使其达到实验设计的质量浓度。每3天换1次水以控制营养盐质量浓度。在每个玻璃缸中放置5片聚乙烯附着基用于采集附着藻。实验结束时测定附着藻生物量、氮及磷含量,并计算附着藻的生长率。结果表明:随着氮质量浓度升高,附着藻的生物量和生长率呈先增加后降低趋势,在氮质量浓度为6 mg·L^(-1)时达到最大值。附着藻氮含量和氮磷比随水体氮质量浓度的升高,亦呈现先增加后降低的趋势,氮含量最大值出现在8 mg·L^(-1)处理组,氮磷比最大值出现在6 mg·L^(-1)组。附着藻氮含量与水体氮质量浓度呈显著正相关(r=0.614,P<0.001)。分析认为,附着藻生长率、氮含量及氮磷比在一定范围内随着水体氮质量浓度升高而增加,当氮质量浓度超过一定范围时,三者反而降低。

Periphyton, the primary producer in shallow lakes, plays important roles in energy flow and nutrient cycling. Nitrogen andphosphorus enrichment could affect the biomass and elemental composition of periphyton associated with food quantity and qualityfor freshwater snails, which will change the growth of snails and snail-periphyton interactions. However, the effects of nitrogenenrichment on the biomass and quality of periphyton have not been well addressed? To answer this question, an outdoor experimentwas conducted to examine the effects of nitrogen concentrations on the growth and elemental composition of periphyton, with fivenitrogen levels (total nitrogen concentrations: 2, 4, 6, 8 and 10 mg·L-1; total phosphorus concentrations: 0.1 mg·L-1 for all treatments),which provide basic data for the restoration of submerged macrophytes in subtropical eutrophic lakes. In order to collect theperiphyton five ethylene square slices were submerged into each aquarium. Concentrations of nitrogen and phosphorus were set totargeted values by adding solution of KNO3 and KH2PO4, and the water in each aquarium was replaced every three days.The biomass,nitrogen and phosphorus content of periphyton were measured at the end of experiment. The biomass and growth rate of periphytonshowed unimodal relationships with increasing nitrogen concentration, with the maximum values were recorded at 6 mg·L-1treatment. Periphyton nitrogen content and N/P ratio also exhibited unimodal relationships with nitrogen enrichment, with the peakvalues of periphyton nitrogen content and N/P ratio were observed in 8 mg·L-1 and 6 mg·L-1, respectively. Nitrogen content ofperiphyton was significant correlated with nitrogen concentration in water column (r = 0.614,P < 0.001). The results suggested thatgrowth rate, nitrogen content and N/P ratio of periphyton increased with increasing nitrogen concentration within a certain range.