Leaf litter decomposition in Mediterranean streams: microbial processes and responses to drought under current global change scenario

This thesis studied the principal environmental controlling factors and microbial mechanisms involved in leaf litter decomposition in Mediterranean intermittent streams. Additionally, drought disturbance in both Mediterranean intermittent and Atlantic permanent streams was also evaluated. At the Mediterranean intermittent stream leaf litter decomposition varied mainly related to seasonal variations in temperature, conductivity and current velocity. Drought clearly affected microbial assemblages and functioning in these ecosystems although this did not resulted in changes on breakdown rates. In permanent streams drought disturbance also affected microbial activity and structure, reducing breakdown velocity due to emersion of leaves. Microbial communities from nutrient enriched streams were more resistant to drought disturbance. Results suggest that under more extreme environmental variation and dry conditions expected with the global change, microbial decomposers will be severely affected. However consequences in carbon recycling will depend on to the type of drought-related disturbance, interaction with other stressors and previous communities dwelling in.En aquesta tesi s’han estudiat els factors ambientals determinants i els mecanismes microbians involucrats en la descomposició de fullaraca en rius intermitents mediterranis. També s’ha avaluat l’efecte de la sequera en rius intermitents mediterranis i permanents atlàntics. En el riu intermitent mediterrani la descomposició de fullaraca s’ha vist afectada per la variació anual de la temperatura, conductivitat i velocitat de la corrent. La sequera clarament va determinar canvis en els microorganismes descomponedors i el seu funcionament en ambdós tipus de rius, malgrat no sempre va afectar la velocitat de descomposició. Els resultats suggereixen que en condicions extremes de variació ambiental i sequera, esperats pel canvi global, els microorganismes descomponedors de la fullaraca es veuran molt afectats. No obstant, les conseqüències en el reciclatge de carboni dependran del tipus de pertorbació relacionada amb la sequera, de la interacció amb altres impactes i de les comunitats descomponedores prèvies que habiten al riu

Influencia de los factores modeladores sobre el efecto de borde, en un relicto de bosque altoandino en Colombia

La formación de paisajes fragmentados por las actividades humanas, genera ambientes contrastantes (matriz antrópica y bosque), que interactúan entre si a través de un límite o borde. Los ambientes en cercanía a los bordes son en general zonas transicionales donde el microclima, la vegetación y la fauna pueden verse afectados. El grado y tipo de afectación son determinados principalmente por características del paisaje (e.g. historia de uso, tipo de matriz, tipo de bosque y orientación), así como también por las características propias de las especies involucradas. De esta manera, para plantear programas de manejo y conservación en una determinada región, se hace necesario entender el efecto de borde sobre el ambiente y las comunidades biológicas. En la parte alta del municipio de Roncesvalles, Tolima, se realizó un estudio para evaluar el efecto de borde sobre variables microambientales y características de la vegetación, teniendo en cuenta la influencia de algunas de las características del paisaje (fisionomía, ubicación topográfica y orientación). Se eligió un fragmento de bosque altoandino donde se escogieron seis bordes con características de fisionomía, orientación y ubicación topográficas particulares. En cada segmento de borde se tomaron puntos de muestreo cada 10 m, desde 20 ó 30 m en el exterior hasta 60 m en el interior del bosque. En cada punto de muestreo se tomaron variables abióticas (temperatura del aire máxima, mínima y al medio día, temperatura máxima y mínima sobre el suelo y humedad relativa máxima y mínima) y se realizaron parcelas de diferentes tamaños (1 x 1, 2 x 2, 5 x 5 y 25 x 5) para medir las variables bióticas (estructura y composición de la vegetación). En general para todos los bordes la temperatura del aire al medio día y la temperatura máxima sobre el suelo, presentaron una profundidad de influencia del borde (PIB) hasta los 20 m dentro del bosque. Por otro lado, la humedad relativa mínima, temperatura del aire mínima y máxima y temperatura del suelo máxima, presentaron en algunos sitios diferencias con las características internas del bosque o blanco, determinando PIB mayores de 60 m dentro del bosque. La orientación relacionada con la ubicación del borde en el fragmento de bosque, fue el factor modelador que mostró una mayor influencia sobre los valores absolutos de las variables abióticas medidas y ligeramente sobre el efecto de borde de algunas variables. Por otro lado, la estructura de la vegetación presentó una PIB entre 20, 40 y > 60 m hacia el interior del borde, siendo los elementos del sotobosque los que parecieron verse más afectados por la cercanía al borde. La composición no pareció mostrar diferencias marcadas entre borde e interior, aunque en el estrato subarbustivo y arbustivo se alcanzó a detectar una distribución de algunas especies en tres franjas: de 30 m exterior al borde, borde a 20 ó 30 m en el interior y 30 m hacia el interior (incluido blancos). Así, se determinó los estratos regenerativos, como aquellos más amenazados por la influencia de los bordes. En el fragmento de estudio, la fisonomía del borde (abierta y cerrada) y su relación con la intensidad de uso, parecieron ser los aspectos determinantes para la respuesta de la vegetación al borde. A partir de los resultados obtenidos en este estudio, se proponen opciones de manejo para favorecer el mantenimiento y recuperación de la vegetación del fragmento

Microbial decomposition is highly sensitive to leaf litter emersion in a permanent temperate stream

Drought frequency and intensity in some temperate regions are forecasted to increase under the ongoing global change, which might expose permanent streams to intermittence and have severe repercussions on stream communities and ecosystem processes. In this study, we investigated the effect of drought duration on microbial decomposition of Populus nigra leaf litter in a temperate permanent stream (Oliveira, NW Portugal). Specifically, we measured the response of the structural (assemblage composition, bacterial and fungal biomass) and functional (leaf litter decomposition, extracellular enzyme activities (EEA), and fungal sporulation) parameters of fungal and bacterial communities on leaf litter exposed to emersion during different time periods (7, 14 and 21 d). Emersion time affected microbial assemblages and litter decomposition, but the response differed among variables. Leaf decomposition rates and the activity of β-glucosidase, cellobiohydrolase and phosphatase were gradually reduced with increasing emersion time, while β-xylosidase reduction was similar when emersion last for 7 or more days, and the phenol oxidase reduction was similar at 14 and 21 days of leaf emersion. Microbial biomass and fungal sporulation were reduced after 21 days of emersion. The structure of microbial assemblages was affected by the duration of the emersion period. The shifts in fungal assemblages were correlated with a decreased microbial capacity to degrade lignin and hemicellulose in leaf litter exposed to emersion. Additionally, some resilience was observed in leaf litter mass loss, bacterial biomass, some enzyme activities and structure of fungal assemblages. Our study shows that drought can strongly alter structural and functional aspects of microbial decomposers. Therefore, the exposure of leaf litter to increasing emersion periods in temperate streams is expected to affect decomposer communities and overall decomposition of plant material by decelerating carbon cycling in streams.FCT - Fuel Cell Technologies Program (UID/BIA/04050/2013)info:eu-repo/semantics/publishedVersio

Differences in the sensitivity of fungi and bacteria to season and invertebrates affect leaf litter decomposition in a Mediterranean stream

Microorganisms are key drivers of leaf litter decomposition; however, the mechanisms underlying the dynamics of different microbial groups are poorly understood. We investigated the effects of seasonal variation and invertebrates on fungal and bacterial dynamics, and on leaf litter decomposition. We followed the decomposition of Populus nigra litter in a Mediterranean stream through an annual cycle, using fine and coarse mesh bags. Irrespective of the season, microbial decomposition followed two stages. Initially, bacterial contribution to total microbial biomass was higher compared to later stages, and it was related to disaccharide and lignin degradation; in a later stage, bacteria were less important and were associated with hemicellulose and cellulose degradation, while fungi were related to lignin decomposition. The relevance of microbial groups in decomposition differed among seasons: fungi were more important in spring, whereas in summer, water quality changes seemed to favour bacteria and slowed down lignin and hemicellulose degradation. Invertebrates influenced litter-associated microbial assemblages (especially bacteria), stimulated enzyme efficiencies and reduced fungal biomass. We conclude that bacterial and fungal assemblages play distinctive roles in microbial decomposition and differ in their sensitivity to environmental changes, ultimately affecting litter decomposition, which might be particularly relevant in highly seasonal ecosystems, such as intermittent streams.Structure and activity of microbial decomposers are sensitive to environmental variations, which potentially modify the carbon cycle in aquatic environments.Structure and activity of microbial decomposers are sensitive to environmental variations, which potentially modify the carbon cycle in aquatic environments.This work was supported by the Spanish Ministry of Economy and Competitiveness [CGL2008-05618-C02-01/BOS, CGL2011-30151-C02-01 and CGL2014-58760-C3-R projects] and by the Portuguese Foundation for Science and Technology (FCT) through the strategic funding UID/BIA/04050/2013. JMG held a PhD grant (BR) from the University of Girona and SD was supported by FCT (SFRH/BPD/47574/2008 and SFRH/BPD/109842/2015).info:eu-repo/semantics/publishedVersio

FUNDAMENTOS CONSTITUCIONALES DEL DERECHO PROBATORIO

El presente artículo se ocupa de desentrañar los soportes constitucionalesdel derecho probatorio y, por ende, de la prueba jurídica en sus diferentesespecies. Para el efecto comienza por sentar el principio de que laConstitución política es la fuente de todo nuestro derecho objetivo ypositivo.En seguida se precisan las nociones de derecho probatorio, pruebajurídica, prueba jurídica material y sus modalidades ad subtantiam actusy ad probationem, prueba administrativa y prueba judicial. Y con talesconceptos se emprende la búsqueda de las disposiciones constitucionalesque aluden a las mismas para conformar el respectivo inventario.The article concerns with disembowel the constitutional endures ofevidence law and, thus, the juridical evidence in its different species.For this matter the author starts standing the principle according towith the political constitution is the main source of all our objectiveand positive legislation.Subsequently, the author précis the notions of evidence law, thejuridical evidence and its species ad substantiam actus y adprobationem, administrative evidence, and judicial evidence. Withthose concepts the author initiate the search of the differentconstitutional dispositions which focus in the latter making therespective inventory

FUNDAMENTOS CONSTITUCIONALES DEL DERECHO PROBATORIO

El presente artículo se ocupa de desentrañar los soportes constitucionalesdel derecho probatorio y, por ende, de la prueba jurídica en sus diferentesespecies. Para el efecto comienza por sentar el principio de que laConstitución política es la fuente de todo nuestro derecho objetivo ypositivo.En seguida se precisan las nociones de derecho probatorio, pruebajurídica, prueba jurídica material y sus modalidades ad subtantiam actusy ad probationem, prueba administrativa y prueba judicial. Y con talesconceptos se emprende la búsqueda de las disposiciones constitucionalesque aluden a las mismas para conformar el respectivo inventario.The article concerns with disembowel the constitutional endures ofevidence law and, thus, the juridical evidence in its different species.For this matter the author starts standing the principle according towith the political constitution is the main source of all our objectiveand positive legislation.Subsequently, the author précis the notions of evidence law, thejuridical evidence and its species ad substantiam actus y adprobationem, administrative evidence, and judicial evidence. Withthose concepts the author initiate the search of the differentconstitutional dispositions which focus in the latter making therespective inventory

Legacy of summer drought on autumnal leaf litter processing in a temporary mediterranean stream

Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-019-00451-0) contains supplementary material, which is available to authorized usersTemporary Mediterranean streams dry out in summer due to low precipitation and high temperatures, thus affecting biota and ecosystem functioning. The consequences of exposing leaf litter to an extreme summer drought, that is, high solar radiation, low humidity, and high temperatures, were evaluated. It was hypothesised that litter exposure to summer drought conditions in a dry streambed would change litter chemical composition, affecting decomposition and associated benthic communities after autumnal flow resumption. Recently fallen black poplar leaves were enclosed in litterbags and separated into two sets: (1) control leaves, kept air-dry in the dark, and (2) drought leaves, exposed to harsh summer conditions in a simulated dry streambed. Both sets were then immersed in a temporary Mediterranean stream in autumn, and leaf litter decomposition monitored. As expected, summer drought exposure increased nitrogen, total fibre, lignin, and cellulose content in drought leaves. After litterbag immersion, higher cellulose-degrading enzyme activity was observed in drought leaves while lignin-degrading enzyme activity was greater in the control leaves. Fungal and bacterial assemblages clearly differed between treatments. Inter-replicate variability was lower in drought leaves for most of the measured variables, suggesting that drought homogenised decomposer and detritivore communities. Despite these drought-related effects, decomposition rates did not vary, apparently due to counterbalancing effects (that is, drought treatment enhanced recalcitrant compounds and nutrient content in leaf litter) probably related to terrestrial microbial colonisation and photodegradation. Our study demonstrates that summer drought has bottom-up critical legacy effects in temporary Mediterranean streams, affecting the structure and function of decomposer communities.We thank Núria Perujo and Hada Alvarez for their support in laboratory and field work. We also thank Rachel Gough for carefully editing this manuscript. This study was supported by the Spanish Ministry of Economy and Competitiveness (CGL2008-05618-C02-01/BOS, CGL2011-30151-C02-01, CGL2016-76024-R, and RTI2018-097950-B-C21 projects), the European Regional Development Fund—Operational Competitiveness Program (ERDF-COMPETE2020-POCI), and the Portuguese Foundation for Science and Technology-FCT (UID/BIA/04050/2019, PTDC/AACAMB/113746/2009, PTDC/AAC-AMB/117068/2010, PTDC/CTA-AMB/31245/2017). J.M.G. was supported by a PhD grant BR from the University of Girona and the H2020 Marie Skłodowska-Curie actions grant agreement No 706616. S.D. was supported by FCT (SFRH/BPD/47574/2008 and SFRH/BPD/109842/2015)