Seasonality increases phylogenetic clustering of neotropical rupestrian communities

Afloramentos rochosos são ecossistemas distribuídos em diversos contextos climáticos, geográficos e geológicos. Suas condições ambientais assemelham-se de forma geral, apontando para um intenso estresse, devido a sua exposição a radiação intensa, ventos fortes, sazonalidade e escassez de substrato. Embora alguns trabalhos mostrem a atuação dos filtros ambientais nas comunidades vegetais desses ecossistemas, nenhum ainda avaliou a estrutura filogenética das mesmas num contexto mais amplo, a fim de verificar como essa estrutura relaciona-se com as características macroclimáticas de precipitação e temperatura. Nosso objetivo foi verificar a relação entre o ambiente e a diversidade taxonômica e estrutura filogenética, bem como a filobetadiversidade de comunidades vegetais sobre afloramentos, ao longo de um gradiente climático e geológico. Para isso, compilamos dados florísticos de 119 áreas. Com suas coordenadas, extraímos as variáveis climáticas do WorldClim 2.0: precipitação anual, temperatura média anual, temperatura máxima, sazonalidade de precipitação e sazonalidade de temperatura. As diferenças taxonômicas entre elas foram verificadas por NMDS e ANOSIM. A diversidade e estrutura filogenética foi quantificada através dos índices PD, MPD, MNTD, sesPD, NRI e NTI, enquanto a filobetadiversidade foi medida por betaNRI e betaNTI. A influência do clima nos índices de estrutura filogenética foi detectada por modelos lineares generalizados (GLM). O agrupamento filogenético entre clados recentes (NTI) aumentou proporcionalmente ao aumento na sazonalidade de precipitação e temperatura, enquanto entre clados basais (NRI) aumentou com a maior temperatura. Atribuímos então um maior estresse ao clima mais sazonal (NTI) das comunidades sobre quartzito da região sudeste, e, no caso de clados mais basais (NRI), às temperaturas mais baixas, mais especificamente dos campos de altitude da região sul. O turnover filogenético foi mais frequente para clados mais recentes (betaNTI), e predominou entre comunidades que habitam rochas diferentes. Alguns pares que não mostraram turnover significativo por betaNRI mostraram por betaNTI. Houve predomínio de agrupamento flogenético, reforçando a importância dos filtros ambientais nessas comunidades, que se intensifica em condições macroclimáticas mais adversas.Rocky outcrops are ecosystems distributed in diverse climatic, geographic ans geological contexts in the Brazilian continent. Its environmental conditions are in general similar, pointing to a strong stress, given their exposure to intense solar radiation, strong winds, seasonality and scarce substrate. Although some works discuss the importance of environmental filters do these ecosystems’ plant communities, no one evaluated their phylogenetic structure in a wide context, in order to verify the relationship among this structure with macroclimatic conditions related to precipitation and temperature. Our goal was to analyze the relationship between climate and taxonomic diversity and phylogenetic structure, as well as the phylogenetic beta diversity (phylogenetic turnover) on rocky outcrops, along a climatic and geological gradient. We compiled floristic data of 119 rock outcrop’s areas. With their coordinates, we extract climatic variables of WorldClim 2.0: annual precipitation, annual mean temperature, maximum temperature, precipitation seasonality an temperature seasonality. Taxonomic differences among areas were verified through NMDS and ANOSIM. Phylogenetic diversity and structure were quantified through the indices PD, MPD, MNTD, sesPD, NRI and NTI, while phylogenetic beta diversity was measured with betaNRI and betaNTI. Generalized linear models (GLM) detected the influence of climate in phylogenetic índices. Phylogenetic clustering among recent clades (NTI) raised with increased precipitation and temperature seasonality, while among basal clades (NRI) it increased with temperature elevation. We linked higher stress to more seasonal climate (according to NTI) in southeastern quartzitic communities, and, to basal clades (NRI), to low temperatures, specifically in southern campos de altitude. Phylogenetic turnover was more common to recnt clades (betaNTI), and predominated among communities from different rocks. Some pares didn’t exhibit significant turnover through betaNRI did to betaNTI. Phylogenetic clustering predominated, reinforcing the importance of enviromental filters in these communities, which intensifies in more adverse macroclimatic conditions.Conselho Nacional de Desenvolvimento Científico e Tecnológic

Arsenic toxicity in Acacia mangium willd. and mimosa Caesalpiniaefolia benth. seedlings

Acacia mangium and Mimosa caesalpiniaefolia are fast-growing woody fabaceous species that might be suitable for phytoremediation of arsenic (As)-contaminated sites. To date, few studies on their tolerance to As toxicity have been published. Therefore, this study assessed As toxicity symptoms in A. mangium and M. caesalpiniaefolia seedlings under As stress in a greenhouse. Seedlings of Acacia mangium and M. caesalpiniaefolia were grown for 120 d in an Oxisol-sand mixture with 0, 50, 100, 200, and 400 mg kg-1 As, in four replications in four randomized blocks. The plants were assessed for visible toxicity symptoms, dry matter production, shoot/root ratio, root anatomy and As uptake. Analyses of variance and regression showed that the growth of A. mangium and M. caesalpiniaefolia was severely hindered by As, with a reduction in dry matter production of more than 80 % at the highest As rate. The root/shoot ratio increased with increasing As rates. At a rate of 400 mg kg-1 As, whitish chlorosis appeared on Mimosa caesalpiniaefolia seedlings. The root anatomy of both species was altered, resulting in cell collapse, death of root buds and accumulation of phenolic compounds. Arsenic concentration was several times greater in roots than in shoots, with more than 150 and 350 mg kg-1 in M. caesalpiniaefolia and A. mangium roots, respectively. These species could be suitable for phytostabilization of As-contaminated sites, but growth-stimulating measures should be used