The invasive tropical tanner grass decreases diversity of the native aquatic macrophyte community at two scales in a subtropical tidal river

ABSTRACT The tropical tanner grass, Urochloa arrecta, is one of the worst aquatic plant invaders in Brazilian freshwater ecosystems. This study aimed to compare beds of macrophytes dominated and without U. arrecta in the Guaraguaçu River, a subtropical tidal river in South Brazil, to analyze effects that this invasive grass has on the biodiversity of native macrophytes at two spatial scales. We compared macrophyte beds dominated by tanner grass to macrophyte beds without, considering species richness, composition, and beta diversity at two scales of variation: among-beds and within-beds. We expected that beds dominated by tanner grass would have lower biodiversity, thus promoting macrophyte biotic homogenization. Our results confirmed our hypotheses, highlighting the lower species richness in beds dominated by tanner grass. Species composition differed among beds. In general, nestedness among beds dominated by U. arrecta was more related to variation in species composition. Beds dominated by tanner grass had lower turnover and higher nestedness within beds. This study indicates a prominent sign of biotic homogenization promoted by U. arrecta, and highlights the degree of biotic homogenization among and within beds.

摘要：直立臂形草（Urochloa arrecta，俗称热带鞣草）是巴西淡水生态系统中危害最为严重的水生入侵植物之一。本研究以巴西南部亚热带潮汐河流瓜拉瓜苏河（Guaraguaçu River）为研究样区，对比了被该入侵草本植物占据与未被其占据的大型水生植物床，旨在分析该入侵物种在两个空间尺度下对本土大型水生植物生物多样性的影响。本研究以床间与床内两个变异尺度为框架，对比了两类植物床的物种丰富度、物种组成及β多样性。我们预设被该入侵草占据的植物床生物多样性更低，进而会引发大型水生植物的生物均质化。研究结果验证了我们的假说：被该入侵草占据的植物床物种丰富度显著更低，且不同植物床的物种组成存在显著差异。总体而言，被Urochloa arrecta占据的植物床间嵌套性与物种组成变异的关联性更强；而此类植物床内部的物种周转更低、嵌套性更高。本研究证实了Urochloa arrecta所引发的生物均质化显著特征，并揭示了植物床间与床内的生物均质化程度。