This study examined the ability of acidic and neutral/alkaline fractions of a methanolic extract from giant reed (Arundo donax) and of two of its constituents, gramine and skatole, to inhibit growth of the ichthyotoxic golden alga (Prymnesium parvum) in batch culture. For this study, growth suppression was defined as inhibition of maximum cell density, algicidal activity as early occurrence of negative growth, and algistatic activity as lack of net growth. The acidic fraction did not affect algal growth. The neutral/alkaline fraction showed growth-suppressing and algicidal activities but no signs of algistatic activity – namely, cells in cultures surviving a partial-algicidal exposure concentration (causing transient negative growth) were later able to initiate positive growth but at higher concentrations, algicidal activity was full and irreversible. Gramine suppressed growth more effectively than skatole and at the highest concentration tested, gramine also showed partial-algicidal and algistatic activity. While the partial-algicidal activities of the neutral/alkaline fraction and of gramine were short-lived (≤6 days) and thus may share similar mechanisms, algistatic activity was unique to gramine and persisted for >3 weeks. Given gramine’s reported concentration in the neutral/alkaline fraction, its corresponding level of algicidal activity is much lower than the fraction’s suggesting the latter contains additional potent algicides. Inhibition of maximum cell density by all test compounds was associated with reductions in exponential growth rate, and in the case of the neutral/alkaline fraction and gramine also reductions in early (pre-exponential) growth. These results indicate that giant reed is a potential source of natural products to control golden alga blooms. Giant reed is an invasive species in North America, thus also providing incentive for research into strategies to couple management efforts for both species.

这项研究检查了从巨型芦苇（Arundo donax）的甲醇提取物及其两种成分禾本科和粪臭素的酸性和中性/碱性馏分抑制鱼鳞毒金藻（Prymnesium parvum）生长的能力。）分批培养。对于本研究，生长抑制定义为最大细胞密度的抑制，杀藻活性为负增长的早期出现，抑止活性为缺乏净增长。酸性部分不影响藻类的生长。中性/碱性部分显示出抑制生长和除藻活性，但没有除藻活性的迹象-即，在部分除藻暴露浓度下存活的文化细胞（导致短暂的负增长）后来能够开始正向生长，但在较高浓度下，除藻活动充满并且不可逆转。禾本科植物的生长抑制作用比粪臭素更有效，在最高测试浓度下，禾本科植物也显示出部分杀藻和抑藻活性。虽然中性/​​碱性部分和禾本科植物的部分抗杀虫活性是短暂的（≤6天），因此可能具有相似的机制，但禾本科植物的抑止活性是独特的，持续了超过3周。考虑到格拉明在中性/碱性馏分中所报告的浓度，其相应的杀藻活性水平远低于该馏分的暗示，表明后者含有其他有效的杀藻剂。所有测试化合物对最大细胞密度的抑制与指数生长速率的降低有关，在中性/碱性组分和禾本科植物的情况下，早期（指数前）生长的速率也降低。这些结果表明，巨大的芦苇是控制金藻繁殖的天然产物的潜在来源。巨型芦苇是北美的一种入侵物种，