-(Effects of xylem water transport on CO 2 effl ux of woody tissue in a tropical tree, Amazonas State, Brazil). We assessed the effect of xylem sap fl ux on radial CO 2 effl ux of woody tissue of a tropical trees species growing in the Center of Manaus (Amazonas State, Brazil). An open chamber system was used to constantly measure diurnal changes in CO 2 effl ux over several days. Xylem sap fl ux was monitored additionally. We found a strong relationship between temperature and woody tissue respiration rates during night time. CO 2 effl ux rates were reduced up to 35% during daytime most probably due to vertical water uptake within the tree trunks. The results suggest a distinct daytime depression of the CO 2 effl ux compared with a night time temperature relationship. Xylem sap fl ux appears to be a major infl uence on CO 2 effl ux rates. The reductions in CO 2 effl ux will become most distinct during periods with a high evaporative demand and predictions of CO 2 effl ux by the temperature/fl ux relation are critical during these periods. Key words: daytime depression, sap fl ux, temperature dependency, woody tissue respiration RESUMEN -(Efectos del transporte de agua por el xilema en la afl uencia de CO 2 en el tejido leñoso de un árbol tropical, Estado del Amazonas, Brasil). Evaluamos el efecto del fl ujo de la savia del xilema en la afl uencia del CO 2 radial en tejidos leñosos de una especie de árbol tropical en el centro de Manaos (Amazonas, Brasil). Un sistema de cámara abierta fue usado constantemente para medir cambios diarios en la afl uencia del CO 2 durante varios días. Al mismo tiempo, se midió el fl ujo de la savia del xilema. Encontramos una fuerte relación entre las tazas de temperatura y la respiración del tejido leñoso durante el periodo nocturno. Las tazas de afl uencia de CO 2 se redujeron hasta un 35% durante el día, probablemente debido a la absorción vertical del agua dentro de los troncos. Los resultados sugieren una depresión de la afl uencia del CO 2 específi ca durante el día comparada con la relación de la temperatura durante la noche. El fl ujo de la savia del dilema parece tener una infl uencia más fuerte en las tazas de afl uencia del CO 2 . Las reducciones en la afl uencia del CO 2 serán más marcadas durante periodos con una alta demanda de evaporación y las predicciones de la afl uencia del CO 2 dadas por la relación de temperatura/fl ujo son críticas durante dichos periodos. Palabras-clave: dependencia en la temperatura, depresión diurna, fl ujo de savia, respiración de tejido leñoso 1.
Tropical tree plantations usually consist of a single exotic fast growing species, but recent research describes positive effects on ecosystem functions from mixed tropical tree plantations. In this review, we present the current knowledge of drought resistance of tropical mixed species plantations and summarize preliminary evidence from a tree biodiversity experiment in Panama. Converting mono-specific stands into mixed ones may improve stand stability and might reduce increasing abiotic and biotic disturbances due to climate change. However, little is known about the extent to which tropical tree species or tropical tree communities can resist increasing disturbances in the short term, e.g., water limitations due to increasing dry season intensity or length, or about their resilience after such disturbances and their capacity to adapt to changing conditions in the long term. Studies relating drought resistance and resilience to community diversity are missing. Further, we highlight the urgent need for a multifactorial manipulative throughfall reduction experiment in tropical environments. The outcome of such studies would greatly assist the forestry sector in tropical regions to maintain highly productive and ecologically sound forest plantations in a changing climate.
Bomb-radiocarbon analysis of modern carbon has been applied in many fields of ecology. The method allows determining the residence time of carbon in photosynthetic products and thus all organic matter in ecosystems. The atmospheric 14C signature will soon drop below the prebomb level due to fixation of atmospheric carbon in terrestrial and marine ecosystems and high rates of 14C-free fossil fuel combustion. Hence, the time is running out for bomb-radiocarbon application. Insect collections shelter an immense quantity of specimens stored in alcohol. We show how those specimens can be used for exploring the trophic structure of food webs by comparing their isotopic radiocarbon signature. Arthropods are one the most diverse and numerous groups of animals in many ecosystems. Their involvement in the trophic structure of an ecosystem is often poorly understood, but a good understanding of food web topology is indispensable to investigate and model how structural changes will affect ecosystem functionality (Dunne et al., 2002). The first challenge in analyzing trophic structures of arthropod communities lies in identifying the species and then, in the very labor intensive methods, to study their feeding habits. Recently isotopic methods have been recognized as useful tools to describe the often nontransparent linkages in the trophic levels of food webs. The most recent development was the application bomb radiocarbon by Hyodo et al. (2012) and Hyodo et al. (2015) impressively showing how this method could be applied to analyze the diet age of various invertebrates and even vertebrates. By analyzing the diet age, the study showed how intensively plant-based and detritus-based food webs are connected and how long it takes for carbon to flow through the web from primary producers to the consumers. Up to now applying bomb-radiocarbon in food web studies is the rare exception; however this method has become a standard tool in many other ecological studies looking on residence time of assimilated carbon in biological systems (e.g., Carbone et al., 2013; Muhr et al.,2013)
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