Effects of grass functional diversity on invasion success by exotic grasses in Cerrado grasslands

Invasive species pose significant challenges to successful restoration efforts worldwide. A strategy to reduce invasions is to establish communities consisting of species with varied ecological strategies. These strategies typically align along the conservative and plant size axes, and more recently, along a below-ground collaboration axis. However, we lack understanding of how the diverse ecological strategies of Cerrado grass species, their combinations and their interactions with soil conditions can mitigate invasions.Here, we investigated how native grass communities composed by species with different ecological strategies affect the invasion success in two soil types of abandoned pastures in the Cerrado. Specifically, we tested the hypothesis that greater above- and below-ground functional diversity reduces exotic species invasion. We also evaluated whether the isolated effects of native species on invasion were positive or negative.We installed an experiment with species richness ranging from zero to eight native grass species. In November 2019, we sowed species combinations to create communities composed by species with different ecological strategies. We quantified the above-ground biomass of exotic species as a measure of invasion. To characterize the species ecological strategies, we measured five functional traits.Functional diversity of maximum height and specific root length (SRL) had the highest predictive power; however, the most parsimonious model included only SRL diversity, which represents the collaboration axis. Native above-ground biomass was also negatively related to exotic species biomass. Furthermore, invasion was greater in less stressful soil conditions but did not interact with diversity. The effect of native species varied from facilitation to competition, with the annual fast-growing native species favouring invasion.Synthesis and applications. Our results show that greater functional diversity of combined above- and below-ground traits reduces invasion success, shedding light on an underexplored role of specific root length diversity. The competitive and facilitative effects of different native species highlight the need for careful selection of the species to be used in restoration programmes. Furthermore, the absence of interaction between diversity and soil types highlights the need for an integrated management of the functional composition and edaphic factors to increase resistance to invasion in these Neotropical grass communities. As especies invasoras representam desafios significativos para os esforcos de restauracao bem-sucedidos em todo o mundo. Uma estrategia para reduzir as invasoes e estabelecer comunidades constituidas por especies com estrategias ecologicas variadas. Essas estrategias normalmente se alinham ao longo dos eixos conservador e de tamanho da planta e, mais recentemente, ao longo de um eixo de colaboracao subterranea. No entanto, falta-nos compreender como as diversas estrategias ecologicas das especies de gramineas do Cerrado, suas combinacoes e suas interacoes com as condicoes do solo podem mitigar as invasoes.Aqui, investigamos como comunidades de gramineas nativas compostas por especies com diferentes estrategias ecologicas afetam o sucesso da invasao em dois tipos de solo em uma pastagem abandonada no Cerrado. Especificamente, testamos a hipotese de que uma maior diversidade funcional acima e abaixo do solo reduz a invasao de especies exoticas. Tambem avaliamos se os efeitos isolados das especies nativas na invasao foram positivos ou negativos.Instalamos um experimento com riqueza de especies variando de zero a oito especies de gramineas nativas. Em novembro de 2019, semeamos combinacoes de especies para criar comunidades compostas por especies com diferentes estrategias ecologicas. Quantificamos a biomassa aerea de especies exoticas como medida de invasao. Para caracterizar as estrategias ecologicas das especies, medimos cinco caracteristicas funcionais.A diversidade funcional de altura maxima e comprimento especifico de raiz (CER) teve o maior poder preditivo, porem, o modelo mais parcimonioso incluiu apenas a diversidade de CER, que esta relacionado com o eixo de colaboracao subterranea. A biomassa nativa acima do solo tambem foi negativamente relacionada com a biomassa de especies exoticas. Alem disso, a invasao foi maior em condicoes de solo menos estressantes, mas nao interagiu com a diversidade. O efeito das especies nativas variou de facilitacao a competicao, com as especies nativas anuais de rapido crescimento favorecendo o sucesso da invasao.Sintese e aplicacoes. Nossos resultados mostram que uma maior diversidade funcional de caracteristicas combinadas acima e abaixo do solo reduz o sucesso da invasao, lancando luz sobre um papel pouco explorado da diversidade de CER. Os efeitos competitivos e facilitadores de diferentes especies nativas destacam a necessidade de uma selecao cuidadosa das especies a serem utilizadas em programas de restauracao. Alem disso, a ausencia de interacao entre diversidade e tipos de solo destaca a necessidade de um manejo integrado da composicao funcional e dos fatores edaficos para aumentar a resistencia a invasao nessas comunidades gramineas neotropicais. Our results show that greater functional diversity of combined above- and below-ground traits reduces invasion success, shedding light on an underexplored role of specific root length diversity. The competitive and facilitative effects of different native species highlight the need for careful selection of the species to be used in restoration programmes. Furthermore, the absence of interaction between diversity and soil types highlights the need for an integrated management of the functional composition and edaphic factors to increase resistance to invasion in these Neotropical grass communities.image