Effects of Tree Composition and Soil Depth on Structure and Functionality of Belowground Microbial Communities in Temperate European Forests.

Depending on their tree species composition, forests recruit different soil microbial communities. Likewise, the vertical nutrient gradient along soil profiles impacts these communities and their activities. In forest soils, bacteria and fungi commonly compete, coexist, and interact, which is challenging for understanding the complex mechanisms behind microbial structuring. Using amplicon sequencing, we analyzed bacterial and fungal diversity in relation to forest composition and soil depth. Moreover, employing random forest models, we identified microbial indicator taxa of forest plots composed of either deciduous or evergreen trees, or their mixtures, as well as of three soil depths. We expected that forest composition and soil depth affect bacterial and fungal diversity and community structure differently. Indeed, relative abundances of microbial communities changed more across soil depths than in relation to forest composition. The microbial Shannon diversity was particularly affected by soil depth and by the proportion of evergreen trees. Our results also reflected that bacterial communities are primarily shaped by soil depth, while fungi were influenced by forest tree species composition. An increasing proportion of evergreen trees did not provoke differences in main bacterial metabolic functions, e.g., carbon fixation, degradation, or photosynthesis. However, significant responses related to specialized bacterial metabolisms were detected. Saprotrophic, arbuscular mycorrhizal, and plant pathogenic fungi were related to the proportion of evergreen trees, particularly in topsoil. Prominent microbial indicator taxa in the deciduous forests were characterized to be r-strategists, whereas K-strategists dominated evergreen plots. Considering simultaneously forest composition and soil depth to unravel differences in microbial communities, metabolic pathways and functional guilds have the potential to enlighten mechanisms that maintain forest soil functionality and provide resistance against disturbances.

Relative importance of tree species richness, tree functional type, and microenvironment for soil macrofauna communities in European forests.

Soil fauna communities are major drivers of many forest ecosystem processes. Tree species diversity and composition shape soil fauna communities, but their relationships are poorly understood, notably whether or not soil fauna diversity depends on tree species diversity. Here, we characterized soil macrofauna communities from forests composed of either one or three tree species, located in four different climate zones and growing on different soil types. Using multivariate analysis and model averaging we investigated the relative importance of tree species richness, tree functional type (deciduous vs. evergreen), litter quality, microhabitat and microclimatic characteristics as drivers of soil macrofauna community composition and structure. We found that macrofauna communities in mixed forest stands were represented by a higher number of broad taxonomic groups that were more diverse and more evenly represented. We also observed a switch from earthworm-dominated to predator-dominated communities with increasing evergreen proportion in forest stands, which we interpreted as a result of a lower litter quality and a higher forest floor mass. Finally, canopy openness was positively related to detritivore abundance and biomass, leading to higher predator species richness and diversity probably through trophic cascade effects. Interestingly, considering different levels of taxonomic resolution in the analyses highlighted different facets of macrofauna response to tree species richness, likely a result of both different ecological niche range and methodological constraints. Overall, our study supports the positive effects of tree species richness on macrofauna diversity and abundance through multiple changes in resource quality and availability, microhabitat, and microclimate modifications.

Low root functional dispersion enhances functionality of plant growth by influencing bacterial activities in European forest soils.

Current studies show that multispecies forests are beneficial regarding biodiversity and ecosystem functionality. However, there are only little efforts to understand the ecological mechanisms behind these advantages of multispecies forests. Bacteria are among the key plant growth-promoting microorganisms that support tree growth and fitness. Thus, we investigated links between bacterial communities, their functionality and root trait dispersion within four major European forest types comprising multispecies and monospecific plots. Bacterial diversity revealed no major changes across the root functional dispersion gradient. In contrast, predicted gene profiles linked to plant growth activities suggest an increasing bacterial functionality from monospecific to multispecies forest. In multispecies forest plots, the bacterial functionality linked to plant growth activities declined with the increasing functional dispersion of the roots. Our findings indicate that enriched abundant bacterial operational taxonomic units are decoupled from bacterial functionality. We also found direct effects of tree species identity on bacterial community composition but no significant relations with root functional dispersion. Additionally, bacterial network analyses indicated that multispecies forests have a higher complexity in their bacterial communities, which points towards more stable forest systems with greater functionality. We identified a potential of root dispersion to facilitate bacterial interactions and consequently, plant growth activities.

Fungal guilds and soil functionality respond to tree community traits rather than to tree diversity in European forests.

At the global scale, most forest research on biodiversity focuses on aboveground organisms. However, understanding the structural associations between aboveground and belowground communities provides relevant information about important functions linked to biogeochemical cycles. Microorganisms such as soil fungi are known to be closely coupled to the dominant tree vegetation, and we hypothesize that tree traits affect fungal guilds and soil functionality in multiple ways. By analysing fungal diversity of 64 plots from four European forest types using Illumina DNA sequencing, we show that soil fungal communities respond to tree community traits rather than to tree species diversity. To explain changes in fungal community structure and measured soil enzymatic activities, we used a trait-based ecological approach and community-weighted means of tree traits to define 'fast' (acquisitive) versus 'slow' (conservative) tree communities. We found specific tree trait effects on different soil fungal guilds and soil enzymatic activities: tree traits associated with litter and absorptive roots correlated with fungal, especially pathogen diversity, and influenced community composition of soil fungi. Relative abundance of the symbiotrophic and saprotrophic guilds mirrored the litter quality, while the root traits of fast tree communities enhanced symbiotrophic abundance. We found that forest types of higher latitudes, which are dominated by fast tree communities, correlated with high carbon-cycling enzymatic activities. In contrast, Mediterranean forests with slow tree communities showed high enzymatic activities related to nitrogen and phosphorous. Our findings highlight that tree trait effects of either 'fast' or 'slow' tree communities drive different fungal guilds and influence biogeochemical cycles.

A Maize Gene Regulatory Network for Phenolic Metabolism.

The translation of the genotype into phenotype, represented for example by the expression of genes encoding enzymes required for the biosynthesis of phytochemicals that are important for interaction of plants with the environment, is largely carried out by transcription factors (TFs) that recognize specific cis-regulatory elements in the genes that they control. TFs and their target genes are organized in gene regulatory networks (GRNs), and thus uncovering GRN architecture presents an important biological challenge necessary to explain gene regulation. Linking TFs to the genes they control, central to understanding GRNs, can be carried out using gene- or TF-centered approaches. In this study, we employed a gene-centered approach utilizing the yeast one-hybrid assay to generate a network of protein-DNA interactions that participate in the transcriptional control of genes involved in the biosynthesis of maize phenolic compounds including general phenylpropanoids, lignins, and flavonoids. We identified 1100 protein-DNA interactions involving 54 phenolic gene promoters and 568 TFs. A set of 11 TFs recognized 10 or more promoters, suggesting a role in coordinating pathway gene expression. The integration of the gene-centered network with information derived from TF-centered approaches provides a foundation for a phenolics GRN characterized by interlaced feed-forward loops that link developmental regulators with biosynthetic genes.

Evaluación de la producción de ácidos orgánicos por Streptomyces spp. y solubilización de tres fuentes de fósforo por la cepa T3A / Evaluation of organic acid production by Streptomyces spp. and solubilization of three phosphorus sources by strain T3A

Quince aislamientos de actinobacterias solubilizadoras de fósforo obtenidas a partir de suelos de los andes orientales colombianos fueron identificadas por sus características morfológicas y por la secuenciación del gen 16S ADNr. El análisis BLASTN de las 15 secuencias obtenidas mostró que los aislamientos pertenecían al género Streptomyces. Paralelamente, los aislamientos fueron sometidos a la detección de ácidos orgánicos, durante el proceso de solubilización de fósforo con la presencia mayoritaria de los ácidos oxálico, cítrico y glucónico. Dentro de las cepas evaluadas Streptomyces sp. T3A fue seleccionada para ser evaluada bajo diferentes fuentes de fósforo inorgánico debido a los resultados de evaluaciones cualitativas y cuantitativas realizadas previamente, en las cuales mostró una actividad solubilizadora de fósforo significativamente alta. Los resultados evidenciaron la capacidad de ésta actinobacteria para solubilizar diferentes fuentes de fosfatos insolubles con valores de 122 mgP·L-1 paraCa3(PO4)2, 14 mgP·L-1 para AlPO4 y 19,6 mgP·L-1 para roca fosfórica. También los ensayos revelaron que la actividad se mantiene en un rango de pH de 5 a 8 con las mismas fuentes de fosfatos evaluadas. Los resultados presentados contribuyen al avance en la caracterización de estas bacterias como promotoras de crecimiento vegetal con el fin de presentarlos como un recurso clave a nivel de biotecnología agrícola.

Fifteen isolates of Eastern Cordillera of the Colombian Andes were identified by morphological characteristics and 16S rDNA gene sequence. The BLAST analysis of 15 sequences shows that isolates belong to Streptomyes. Also we detected the organic acids in the solubilization process mainly oxalic acid, citric acid and gluconic acid. Streptomyces sp. (T3A) was selected in preliminary qualitative and quantitative assays by the high phosphorus solubilizing activity; in this work we evaluate this strain with different forms of inorganic phosphate. The results evidenced the capacity of this actinobacteria to solubilize phosphorous showed 122 mgP•L-1 Ca3(PO4)2, 14 mgP•L-1 AlPO4 and 19,6 mgP•L-1 for rock phosphate. Also the assays revealed that the activity was maintained between a pH range of 5 to 8 with the same sources of insoluble phosphates evaluated. These results contribute to characterize these strains as plant growth promotion bacteria and as key source in agricultural biotech.

First record of Saprolegnia sp. in an amphibian population in Colombia / Primer registro de Saprolegnia sp. en una población de anfibios en Colombia / Primeiro registro de Saprolegnia sp. numa população de anfíbios na Colômbia

Primer registro de Saprolegnia sp. en una población de anfibios en Colombia. Objetivo. La mayoría de investigaciones en relación al declive de anfibios se han enfocado en la detección del hongo patógeno Batrachochytrium dendrobatidis. Este es el principal patógeno detectado en el mundo. Sin embargo, otras investigaciones han demostrado la presencia de Saprolegnia ferax como un vector mortal en anfibios de Norteamérica. Este trabajo establece una posible transmisión entre especies causada por la presencia de la trucha arcoíris, sugiriendo que el declive de anfibios no solo se atribuye a la presencia de un solo patógeno, sino que puede ser causado por otros patógenos y factores. Materiales y métodos. El estudio revela la presencia de Saprolegnia sp. en la rana de los Andes Atelopus mittermeieri mediante la técnica de impronta con tinción de azul de lactofenol, que permitió la observación de las estructuras típicas de este hongo. Resultados. La importancia de este descubrimiento es la presencia de dos hongos patógenos, B. dendrobatidis y Saprolegnia, afectando simultáneamente una población de anfibios. Este hallazgo enfoca la atención en la eventual presencia de otros microorganismos que podrían estar involucrados individualmente o colectivamente en el declive de especies de anfibios. Conclusiones. Este registro sugiere una posible transmisión entre la trucha arcoiris (Oncorhynchus mykiss), una especie introducida en las montañas de Colombia, que comparte los mismos habitats con diferentes especies de anfibios en el Santuario de Flora y Fauna de Guanentá en el alto río Fonce en la parte media de la Cordillera Oriental de Colombia...

Objective: Most research related to the decline of amphibians has been focused on the detection of the pathogenic fungus Batrachochytrium dendrobatidis. This fungus is the main pathogen detected around the world. However, research has shown the presence of another fungus, Saprolegnia ferax, as a cause of mortality in amphibians in North America. Our study suggests a possible interspecific transmission caused by the presence of rainbow trout; thus, amphibian declines may not be attributable only to the presence of a single pathogen, but to other organisms and factors. Materials and methods. Our study revealed the presence of Saprolegnia sp. in the Andean frog Atelopus mittermeieri using the imprinting technique with lactophenol blue staining, which allowed the typical structures of this fungus to be observed. Results. The importance of this discovery is the presence of two pathogenic fungi, B. dendrobatidis and Saprolegnia, which affecting simultaneously a population of amphibians. This finding brings attention to the eventual presence of other microorganisms that might be involved individually or collectively in the decline of amphibian species. Conclusions. This record suggests a possible transmission between rainbow trout (Oncorhynchus mykiss), an introduced species in the highlands of Colombia, which shares the same habitats with different species of amphibians in the Sanctuary of Flora and Fauna Guanentá in the upper river Fonce in the mid Cordillera Oriental of Colombia...

Primeiro registro de Saprolegnia sp. numa população de anfíbios na Colômbia. Objetivo. A maioria das pesquisas sobre o declínio dos anfíbios tem-se centrado na detecção do fungo patogênico Batrachochytrium dendrobatidis. Este é o principal patógeno encontrado no mundo. No entanto, outros estudos têm demonstrado a presença de Saprolegnia ferax, como vetor mortal de anfíbios de América do Norte. Esta pesquisa estabelece uma possível transmissão entre espécies causada pela presença de truta arco-íris, afirmando que o declínio de anfíbios não só é atribuído à presença de um único patógeno, pudendo ser causado por outros patógenos e fatores. Materiais e métodos. A pesquisa indica a presença de Saprolegnia sp. em rãs dos Andes, Atelopus mittermeieri, pela técnica de impressão com lactofenol-azul-de-algodão, onde observou-se as estruturas típicas deste fungo. Resultados. A importância desta descoberta é a presença de dois fungos (B. dendrobatidis e Saprolegnia) que simultaneamente afetam uma população de anfíbios, concentrando a atenção na presença de outros microorganismos que podem estar envolvidos individualmente ou coletivamente no declínio das espécies de anfíbios. Conclusões. A truta arco-íris (Oncorhynchus mykiss), uma espécie introduzida nas montanhas da Colômbia, que compartilha o mesmo nicho ecológico com Atelopus mittermeieri, no Santuário de Flora e Fauna de Guanentá no Alto Rio Fonce no centro da Cordilheira Oriental da Colômbia, tem sido sugerida por esta pesquisa como o agente transmissor dos fungos as diferentes espécies de anfíbios...