Abstract: The influence exerted by tree communities, topography, and soil chemistry on the assembly of macrofungal communities remains poorly understood, especially in highly diverse tropical forests. Here, we used a large dataset that combines inventories of macrofungal Basidiomycetes fruiting bodies, tree species composition, and measurements for 16 soil physicochemical parameters, collected in 34 plots located in four sites of lowland rain forests in French Guiana. Plots were established on three different topographical conditions: hilltop, slope, and seasonally flooded soils. We found hyperdiverse Basidiomycetes communities, mainly comprising members of Agaricales and Polyporales. Phosphorus, clay contents, and base saturation in soils strongly varied across plots and shaped the richness and composition of tree communities. The latter composition explained 23% of the variation in the composition of macrofungal communities, probably through high heterogeneity of the litter chemistry and selective effects of biotic interactions. The high local heterogeneity of habitats influenced the distribution of both macrofungi and trees, as a result of diversed local soil hydromorphic conditions associated with contrasting soil chemistry. This first regional study across habitats of French Guiana forests revealed new niches for macrofungi, such as ectomycorrhizal ones, and illustrates how macrofungi inventories are still paramount to can be to understand the processes at work in the tropics. Abstract in Spanish is available with online material. © 2020 The Association for Tropical Biology and Conservation

Abstract: A hypothetical mechanism for the generation of maturation stress in wood was tested experimentally. The hypothesis was that the maturation stress could partly originate in a physical mechanism related to daily changes in water pressure and associated diurnal strains. The matrix of lignin and hemicellulose, deposited in the cell wall during the night, would be put in compression by the effect of water tension during the next day. The cellulose framework, crystallizing during the day, would be put in tension by the decrease in tension at night and subsequent cell-wall swelling. This was tested on young saplings of sugi and beech. Half of the saplings were submitted to continuous lighting, which canceled diurnal strains. Saplings were tilted 40 degrees, and their uprighting movement was measured. The uprighting movement is directly due to the production of reaction wood and the concomitant development of large longitudinal maturation stress. It occurred in the continuously lighted plants at least as much as in control plants. We conclude that the generation of longitudinal maturation stress in tension or compression wood is not directly related to variations in water pressure and diurnal strains.

Abstract: Rationale: Studies of wetland eco-hydrology in tropical coastal areas are scarce, and the use of water stable isotopes can be of great help. Key constraints for their analysis are (i) the small difference in delta18O values between seawater and old evaporated freshwater, and (ii) the fact that the presence of old brackish water limits the determination of the water origin and dynamic. Methods: The water from tropical storms displays distinctively depleted heavy stable isotopes, in comparison with usual tropical rainfall without strong convective thunderstorms. During tropical storms, such as Hurricane Rafael in mid-October 2012, the rainfall delta18O signal can be decreased by many units. This effect is called an “isotopic spike”, and it could be used as a temporal marker of the water fluxes. Results: Water samples, with delta18O values as low as −8.9/1000, were collected on the islands of Guadeloupe and Saint-Martin during Hurricane Rafael, whereas the usual range of groundwater or mean rainfall delta18O values is around −2.8 +/- 0.5 /1000, as measured from 2009 to 2012. These water “isotopic spikes” allow us to show a surface freshwater uptake by mangrove trees in Guadeloupe, and in Saint-Martin, to calculate the water renewal of the salt ponds and pools. Conclusions: The “isotopic spikes” generated by tropical storms are generally used to track back past storm events, as recorded in trees and stalagmites. Here, the propagation of isotopic spike is followed to improve the understanding of the freshwater circulation and the water dynamic within coastal ecosystems influenced by seawater.

Abstract: Extractives can affect the vibrational properties tan delta (damping coefficient) and E'/rho (specific Young's modulus), but this is highly dependent on species, compounds, and cellular locations. This paper investigates such effects for African Padauk (Pterocarpus soyauxii Taub.), a tropical hardwood with high extractives content and a preferred material for xylophones. Five groups of 26 heartwood specimens with large, yet comparable, ranges in vibrational properties were extracted in different solvents. Changes in vibrational properties were set against yields of extracts and evaluation of their cellular location. Methanol (ME) reached most of the compounds (13%), located about half in lumen and half in cell-wall. Water solubility was extremely low. tan delta and E'/rho were very strongly related (R (2) a parts per thousand yen 0.93), but native wood had abnormally low values of tan delta, while extraction shifted this relation towards higher tan delta values. ME extracted heartwood became in agreement with the average of many species, and close to sapwood. Extractions increased tan delta as much as 60%, irrespective of minute moisture changes or initial properties. Apparent E'/rho was barely changed (+2% to -4%) but, after correcting the mass contribution of extracts, it was in fact slightly reduced (down to -10% for high E'/rho), and increasingly so for specimens with low initial values of E'/rho.

Abstract: The fields of plant water relations and plant biomechanics have traditionally been studied separately even though often the same tissues are responsible for water transport and mechanical support. There is now increasing evidence that hydraulic and mechanical adaptations may influence one another. We studied the changes in the hydraulic and mechanical properties of the wood along lateral roots of two species of buttressed trees. In these roots, the mechanical contstraints quantified by strain measurements are known to decrease distally. Further, we investigated the effect of mechanical loading on the vessel anatomy in these and four other species of tropical trees. We found that as the strain decreased, the wood became progressively less stiff and strong but the conductivity increased exponentially. This was reflected in that adaptations towards re-enforcing mechanically loaded areas resulted in xylem with fewer and smaller vessels. In addition a controlled growth experiment on three tree species showed that drought adaptation may results in plants with stronger and stiffer tissue. Our results indicate that hydraulic and mechanical stress adaptations may be interrelated, and so support recent studied suggesting that physiological responses are complex balances rather than pure optimisations. ©2008 Landes Bioscience.