Abstract: Molecular analysis by parallel tandem mass spectrometry (MS/MS) imaging contributes to the in situ characterization of biosynthetic intermediates which is crucial for deciphering the metabolic pathways in living organisms. We report the first use of TOF-SIMS MS/MS imaging for the cellular localization and characterization of biosynthetic intermediates of bioactive γ-lactones rubrynolide and rubrenolide in the Amazonian tree Sextonia rubra (Lauraceae). Five γ-lactones, including previously reported rubrynolide and rubrenolide, were isolated using a conventional approach and their structural characterization and localization at a lateral resolution of ~400 nm was later achieved using TOF-SIMS MS/MS imaging analysis. 2D/3D MS imaging at subcellular level reveals that putative biosynthetic γ-lactones intermediates are localized in the same cell types (ray parenchyma cells and oil cells) as rubrynolide and rubrenolide. Consequently, a revised metabolic pathway of rubrynolide was proposed, which involves the reaction between 2-hydroxysuccinic acid and 3-oxotetradecanoic acid, contrary to previous studies suggesting a single polyketide precursor. Our results provide insights into plant metabolite production in wood tissues and, overall, demonstrate that combining high spatial resolution TOF-SIMS imaging and MS/MS structural characterization offers new opportunities for studying molecular and cellular biochemistry in plants. © 2019, The Author(s).

Abstract: Illicit drug consumption can be estimated from drug target residue (DTR) in wastewater, with the reliability of results being partly linked to DTR stability in the sewage network. However, wastewater temperature and pH drive the stability of molecules and, in this context, tropical conditions must be studied to specify the impact of residence time in the sewage network on DTR degradation. Warmth enhances biotic and abiotic processes such as degradation, leading to a decrease in oxygen content, and consequently, early diagenesis conditions in wastewater. In this study, we conduct laboratory studies under acidic pH and high temperature (30 °C) conditions to determine the degradation half-lives of cocaine (COC), tetrahydrocannabinol, and heroine targets, allowing COC/benzoylecgonine (BZE) ratio variations to be predicted in sewage networks. A rapid COC degradation is observed, as already reported in the literature but without a short-term significant difference between 20 °C and 30 °C. Acidic pH seems to prevent degradation. Thus, theoretically, the use of COC as DTR is only reliable in acidic conditions, with the decrease in COC concentration being 6% at 8 h, but over 40% in other conditions. By contrast, the use of BZE as DTR to estimate COC consumption, which is performed in practice, can be undertaken with the same back-calculation equation as used in temperate countries. However, 11-nor-delta-9-carboxytetrahydrocannabinol stability is more influenced by high temperature: concentration levels after 24 h are 20% lower at 30 °C than at 20 °C, corresponding to a 20% and 40% decrease, respectively. Based on a mean residence time of 8 h, underestimated cannabis consumption is close to 15% in tropical contexts, which is double that of temperate areas. © 2017 Elsevier B.V.

Abstract: The relative contribution of gross primary production and ecosystem respiration to seasonal changes in the net carbon flux of tropical forests remains poorly quantified by both modelling and field studies. We use data assimilation to combine nine ecological time series from an eastern Amazonian forest, with mass balance constraints from an ecosystem carbon cycle model. The resulting analysis quantifies, with uncertainty estimates, the seasonal changes in the net carbon flux of a tropical rainforest which experiences a pronounced dry season. We show that the carbon accumulation in this forest was four times greater in the dry season than in the wet season and that this was accompanied by a 5% increase in the carbon use efficiency. This seasonal response was caused by a dry season increase in gross primary productivity, in response to radiation and a similar magnitude decrease in heterotrophic respiration, in response to drying soils. The analysis also predicts increased carbon allocation to leaves and wood in the wet season, and greater allocation to fine roots in the dry season. This study demonstrates implementation of seasonal variations in parameters better enables models to simulate observed patterns in data. In particular, we highlight the necessity to simulate the seasonal patterns of heterotrophic respiration to accurately simulate the net carbon flux seasonal tropical forest. © 2013 The Authors Global Change Biology Published by John Wiley & Sons Ltd.

Abstract: Over the last decade, distance-based methods have been introduced and then improved in the field of spatial economics to gauge the geographic concentration of activities. There is a growing literature on this theme including new tools, discussions on their specific properties and various applications. However, there is currently no typology of distance-based methods. This paper fills that gap. The proposed classification helps understand all the properties of distance-based methods and proves that they are variations on the same framework. © 2016 Elsevier B.V.

Abstract: Niche theory proposes that species differences underlie both coexistence within communities and the differentiation in species composition among communities via limiting similarity and environmental filtering. However, it has been difficult to extend niche theory to species-rich communities because of the empirical challenge of quantifying niches for many species. This has motivated the development of functional and phylogeny-based approaches in community ecology, which represent two different means of approximating niche attributes. Here, we assess the utility of plant functional traits and phylogenetic relationships in predicting community assembly processes using the largest trait and phylogenetic data base to date for any set of species-rich communities. We measured 17 functional traits for all 4672 individuals of 668 tree species co-occurring in nine tropical rain forest plots in French Guiana. Trait variation was summarized into two ordination axes that reflect species niche overlap. We also generated a dated molecular phylogenetic tree based on DNA sequencing of two plastid loci (rbcL and matK) comprising 97% of the individuals and 91% of the species in the plots. We found that, on average, co-occurring species had greater functional and, to a lesser extent, phylogenetic similarity than expected by chance. We also found that functional traits and their ordination loadings showed significant, albeit weak, phylogenetic signal, suggesting that phylogenetic distance provides pertinent information on niche overlap in tropical tree communities. Synthesis. We provide the most comprehensive examination to date of the relative importance of environmental filtering and limiting similarity in structuring tropical tree communities. Our results confirm that environmental filtering is the overriding influence on community assembly in these species-rich systems. © 2012 The Authors. Journal of Ecology © 2012 British Ecological Society.