Abstract: Ethanol extract of Bagassa guianensis was tested as corrosion inhibitor for zinc in ASTM medium using polarization and electrochemical impedance spectroscopy (EIS). The results obtained show that this plant extract could serve as an effective inhibitor for the corrosion of zinc in sodium chloride media. The extract obtained give inhibition around 85%. Polarization curves show that Bagassa guianensis extract affects the anodic and cathodic reactions and the corrosion potential values were shifted to the positive potentials in the presence of the crude extract in the ASTM medium. The experimental data obtained from EIS method show a frequency distribution and therefore a modelling element with frequency dispersion behavior, a constant phase element (CPE alpha,Q ) has been used. Graphical methods are illustrated by synthetic data to determine the parameter of CPE (alpha, Q). Studies on the phytochemical constituents of thetotal extract were also established. Electrochemical studies, on the chemical families present in the crude extract, were also carried out to find the main constituents responsible for corrosion inhibition properties of the plant extract.

Abstract: A thorough understanding of how tropical forests respond to climate is important to improve ecosystem process models and to reduce uncertainties in current and future global carbon balance calculations. The Amazon rainforest, a major contributor to the global carbon cycle, is subject to strong intra- and interannual variations in climate conditions. Understanding their effect on carbon fluxes between the ecosystem and the atmosphere and on the resulting carbon balance is still incomplete. We examined the long-term (over a 12-year period; 2004–2015) variations in gross primary productivity (GPP), ecosystem respiration (RE) and net ecosystem exchange (NEE) in a tropical rainforest in French Guiana and identified key climatic drivers influencing the changes. The study period was characterized by strong differences in climatic conditions among years, particularly differences in the intensity of the dry and wet seasons, as well as differences in annual carbon fluxes and balance. Annual average GPP varied from 3384.9?g?C?m-2?yr?1 (95% CI [3320.7, 3445.9]) to 4061.2?g?C?m-2?yr?1 (95% CI [3980.1, 4145.0]). RE varied even more than GPP, with a difference of 933.1?C?m-2?yr?1 between the minimum (3020.6?g?C?m-2?yr?1; 95% CI [2889.4, 3051.3]) and maximum (3953.7?g?C?m-2?yr?1; 95% CI [3887.6, 4019.6]) values. Although NEE showed large interannual variability (nine-fold), from ?65.6?g?C?m-2?yr?1 (95% CI [?4.4, ?126.0]) to ?590.5?g?C?m-2 yr?1 (95% CI [?532.3, ?651.6]), the forest remained a carbon sink over the 12-year period. A combination of global radiation (Rg), relative extractable water (REW) and soil temperature (Ts) explained 51% of the daily variations for GPP, 30% for RE and 39% for NEE. Global radiation was always the best predictor of these variations, but soil water content and temperature did also influence carbon fluxes and balance. Seasonally, Rg was the major controlling factor for GPP, RE and NEE during the wet season. During the dry season, variations in carbon fluxes and balance were poorly explained by climate factors. Yet, REW was the key driver of variations in NEE during the dry season. This study highlights that, over the long-term, carbon fluxes and balance in such tropical rainforest ecosystems are largely controlled by both radiation and water limitation. Even though variations in Rg have a greater impact on these fluxes, water limitation during seasonal droughts is enough to reduce ecosystem productivity, respiration and carbon uptake. The reduced precipitation expected in tropical rainforest areas under future climatic conditions will therefore strongly influence carbon fluxes and carbon uptake. This study also highlights the importance for land surface or dynamic global vegetation models to consider the main drivers of carbon fluxes and balance separately for dry and wet seasons.

Abstract: BackgroundMore than a half century ago, Shinozaki et al. (Shinozaki K, Yoda K, Hozumi K, Kira T. 1964a. A quantitative analysis of plant form – the pipe model theory. I. Basic analyses. Japanese Journal of Ecology B: 97–105) proposed an elegant conceptual framework, the pipe model theory (PMT), to interpret the observed linear relationship between the amount of stem tissue and corresponding supported leaves. The PMT brought a satisfactory answer to two vividly debated problems that were unresolved at the moment of its publication: (1) What determines tree form and which rules drive biomass allocation to the foliar versus stem compartments in plants? (2) How can foliar area or mass in an individual plant, in a stand or at even larger scales be estimated? Since its initial formulation, the PMT has been reinterpreted and used in applications, and has undoubtedly become an important milestone in the mathematical interpretation of plant form and functioning.ScopeThis article aims to review the PMT by going back to its initial formulation, stating its explicit and implicit properties and discussing them in the light of current biological knowledge and experimental evidence in order to identify the validity and range of applicability of the theory. We also discuss the use of the theory in tree biomechanics and hydraulics as well as in functional–structural plant modelling.ConclusionsScrutinizing the PMT in the light of modern biological knowledge revealed that most of its properties are not valid as a general rule. The hydraulic framework derived from the PMT has attracted much more attention than its mechanical counterpart and implies that only the conductive portion of a stem cross-section should be proportional to the supported foliage amount rather than the whole of it. The facts that this conductive portion is experimentally difficult to measure and varies with environmental conditions and tree ontogeny might cause the commonly reported non-linear relationships between foliage and stem metrics. Nevertheless, the PMT can still be considered as a portfolio of properties providing a unified framework to integrate and analyse functional–structural relationships.

Abstract: In an inundated Mexican forest, 89 out of 92 myrmecophytic tank bromeliads (Aechmea bracteata) housed an associated ant colony: 13 sheltered Azteca serica, 43 Dolichoderus bispinosus, and 33 Neoponera villosa. Ant presence has a positive impact on the diversity of the aquatic macroinvertebrate communities (n=30 bromeliads studied). A Principal Component Analysis (PCA) showed that the presence and the species of ant are not correlated to bromeliad size, quantity of water, number of wells, filtered organic matter or incident radiation. The PCA and a generalized linear model showed that the presence of Azteca serica differed from the presence of the other two ant species or no ants in its effects on the aquatic invertebrate community (more predators). Therefore, both ant presence and species of ant affect the composition of the aquatic macroinvertebrate communities in the tanks of A. bracteata, likely due to ant deposition of feces and other waste in these tanks. Résumé Dans une forêt inondable du Mexique, sur 92 individus de la broméliacée myrmécophyte Aechmea bracteata, seuls trois étaient dépourvus d’une colonie de fourmis, 13 abritaient Azteca serica, 43 Dolichoderus bispinosus et 33 Neoponera villosa. La présence des fourmis favorise la diversité au sein des communautés aquatiques de macro-invertébrés (30 broméliacées étudiées, index de Shannon, profils de diversité). Une analyse en composantes principales (ACP) montre que la présence de fourmis n’est pas corrélée avec la taille de la plante, la quantité d’eau, le nombre de puits, la quantité de matière organique et la radiation incidente. L’ACP et un modèle mixte généralisé montrent un impact d’Azteca serica (comparé aux autres cas) attribuable à une plus grande quantité de prédateurs (effet top–down). La présence et l’identité des fourmis jouent un rôle sur la composition des communautés de macro-invertébrés aquatiques à travers des interactions directes, les ouvrières évacuant fèces et déchets dans les réservoirs.

Abstract: Wood maturation strains can be estimated from the change in curvature that occurs when a stem grown staked in tilted position is released from the stake.
Trees have a motor system to enable upright growth in the field of gravity. This motor function is taken on by reaction wood, a special kind of wood that typically develops in leaning axes and generates mechanical force during its formation, curving up the stem and counteracting the effect of gravity or other mechanical disturbances. Quantifying the mechanical stress induced in wood during maturation is essential to many areas of research ranging from tree architecture to functional genomics. Here, we present a new method for quantifying wood maturation stress. It consists of tilting a tree, tying it to a stake, letting it grow in tilted position, and recording the change in stem curvature that occurs when the stem is released from the stake. A mechanical model is developed to make explicit the link between the change in curvature, maturation strain and morphological traits of the stem section. A parametric study is conducted to analyse how different parameters influence the change in curvature. This method is applied to the estimation of maturation strain in two different datasets. Results show that the method is able to detect genotypic variations in motor power expression. As predicted by the model, we observe that the change in stem curvature is correlated to stem diameter and diameter growth. In contrast, wood maturation strain is independent from these dimensional effects, and is suitable as an intrinsic parameter characterising the magnitude of the plant’s gravitropic reaction.