外源氮磷负荷比增加对刺苦草(Vallisneria spinulosa)生长的影响

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

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/(m^2·d),N外源性负荷量分别为0、40、80、120、160 mg/(m^2·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 sub-merged 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 ever 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 theN：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 in-dicators 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 diy weight and ramet numbers, would decl ine, while the P absorption would not change with in-creasing N： P ratio in loading.