Plant diversity is a known indicator of healthy ecosystems, therefore understanding interspecific relationships that structure plant communities is critical for invasive species management. A cryptic introduction of invasive macrophyte water chestnut (Trapa bispinosa var. iinumai) into the northeastern United States prompted investigation into potential competitive interactions between it and two common submersed species in the Chesapeake Bay watershed, Vallisneria americana and Hydrilla verticillata. Because the congeneric invader Trapa natans co-occurs in the same watershed with a documented history of negative environmental impacts, it was included for comparison. Reciprocal pairwise competitive effects between water chestnut and resident species were determined by additive reciprocal design, plants were grow in monoculture and biculture under controlled greenhouse conditions for one year. Competitive reciprocal effects between species were evident. Vallisneria americana produced 1.7 X more ramets in monoculture than in combination with Trapa spp. and tuber production was reduced by 37 % in biculture, independent of Trapa competitor. Trapa bispinosa var. iinumai fruit production was reduced by 80 % when grown in biculture with V. americana, and no fruits were produced when grown with H. verticillata. Biculture T. natans fruit production was impacted with less production observed for H. verticillata (54 %) than V. americana (25 %). Trapa bispinosa var. iinumai produced nearly 150 % more biomass in monoculture than T. natans, suggesting increased impacts in species-poor or disturbed areas. Findings suggest established monocultures of V. americana and H. verticillata may be vulnerable to invasion by either species of Trapa, but long-term competitive effects of invasion may not preclude co-existence.

植物多样性是健康生态系统的已知指标，因此了解构成植物群落的种间关系对于入侵物种管理至关重要。侵入性大型植物菱角（Trapa bispinosa var. iinumai）的神秘引入美国东北部促使调查它与切萨皮克湾流域中两种常见的沉水物种，美洲苦豆草和轮状黑藻之间的潜在竞争相互作用。因为同类入侵者Trapa natans共同发生在同一流域，并有记录的负面环境影响历史，因此将其包括在内以进行比较。菱角和常驻物种之间的相互成对竞争效应通过加法互惠设计确定，植物在受控温室条件下以单养和双养方式生长一年。物种之间的竞争互惠效应很明显。Vallisneria americana在单一栽培中比与Trapa spp组合产生的分株多 1.7倍。与Trapa竞争对手无关，双培养中的块茎产量减少了 37% 。Trapa bispinosa var. iinumai水果产量在双培养中减少了 80%V. americana，当与H. verticillata 一起生长时没有产生果实。双培养T. natans果实产量受到影响，观察到的H. verticillata (54 %) 的产量低于V. americana (25 %)。Trapa bispinosa var. iinumai在单一栽培中产生的生物量比T. natans多近 150% ，表明对物种贫乏或受干扰地区的影响增加。研究结果表明，美洲 V.和H. verticillata 的单一栽培可能容易受到Trapa物种的入侵，但入侵的长期竞争效应可能不排除共存。