Effect of increasing nitrogen/phosphorus ratio in loading on the growth of <i>Vallisneria spinulosa</i>

Abstract

磷（P）是水生态系统生产力的限制因子，因此，在水体富营养化治理的过程中，许多地方采取了有效的措施控制流域P的排放；但氮（N）来源复杂，难以有效控制，导致湖泊外源的N：P负荷比日益扩大. 植物的生长需要合适的N：P比，因此，外源N：P负荷比的增加可能会对沉水植物的生长产生影响. 采取控制实验，将刺苦草（Vallisneria spinulosa）栽种于塑料桶中，每隔3 d添加1次N、P营养盐，实验设置5个处理，P外源性负荷量固定为4 mg/（m²·d），N外源性负荷量分别为0、40、80、120、160 mg/（m²·d）. 实验周期为80 d. 结果显示：随着N：P负荷比的增加，刺苦草的叶干重、植株总干重、根干重、叶N及总N含量、叶片数、叶P及总P含量等指标基本保持不变或略有增加，单株总根长、根茎长度、块茎干重和无性系小株数目则呈现下降趋势. 结果表明：随外源N：P负荷比的增加，刺苦草个体生长指标总体呈现不变的趋势，但与种群扩张潜力相关的指标如根茎长度、块茎干重和无性系小株数目等则呈现下降趋势；刺苦草体内累积的N随外源N：P负荷比的增加而增加，但P的累积保持不变. 说明N：P负荷比的增加对刺苦草个体生长影响不大，但对种群扩张不利；刺苦草对P的吸收也并不随N：P比的增加而改变.;Phosphorus (P) is a limiting factor for productivity in aquatic ecosystems. In order to control lake eutrophication, many effective measures are taken to control the P effluent in the basin, but nitrogen (N) is difficult to control due to its complex sources. Thus, the situation of low P but yet high N effluent results in a high ratio of N:P in loading in many lakes. Plants need a suitable N:P ratio to sustain their growth, therefore, the increasing of the N:P ratio in effluents might affect the growth of submerged macrophytes. To acquire an insight into the influence of increasing N:P ratios on the submerged plants, we carried out an outdoor control experiment. Vallisneria spinulosa was planted in plastic buckets with N and P added to the buckets every 3 days. We set up five treatments with an unchanging P loading dose of 4 mg/(m²·d), with a range of nitrogen loading dose including 0, 40, 80, 120 and 160 mg/(m²·d). The experiment lasted for 80 days. Results showed that with an increase of the N:P ratio in the loading, some indicators were nearly stable, such as leaf dry weight, total plant dry weight, leaf N and total N content, leaf number, leaf P and total P content, while some other indicators, such as plant total root length, cloning stem length, stem dry weight and ramet numbers decreaed. The results above revealed that with an increasing N:P ratio in loading, individual growth indicators of V. spinulosa would remain stable or exhibit a minor increase, but that the indicators of population expansion ability, such as cloning stem length, tuber dry weight and ramet numbers, would decline, while the P absorption would not change with increasing N:P ratio in loading.