Roux, O., Le Lann, C., van Alphen, J. J. M., & van Baaren, J. (2010). How does heat shock affect the life history traits of adults and progeny of the aphid parasitoid Aphidius avenae (Hymenoptera: Aphidiidae)? Bull. Entomol. Res., 100(5), 543–549.
Abstract: Because insects are ectotherms, their physiology, behaviour and fitness are influenced by the ambient temperature. Any changes in environmental temperatures may impact the fitness and life history traits of insects and, thus, affect population dynamics. Here, we experimentally tested the impact of heat shock on the fitness and life history traits of adults of the aphid parasitoid Aphidius avenae and on the later repercussions for their progeny. Our results show that short exposure (1h) to an elevated temperature (36 degrees C), which is frequently experienced by parasitoids during the summer, resulted in high mortality rates in a parasitoid population and strongly affected the fitness of survivors by drastically reducing reproductive output and triggering a sex-dependent effect on lifespan. Heat stress resulted in greater longevity in surviving females and in shorter longevity in surviving males in comparison with untreated individuals. Viability and the developmental rates of progeny were also affected in a sex-dependent manner. These results underline the ecological importance of the thermal stress response of parasitoid species, not only for survival, but also for maintaining reproductive activities.
Keywords: developmental rate; fecundity; heat stress; longevity; sex-specific effect; parasitic wasp
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Stahl, C., Burban, B., Bompy, F., Jolin, Z. B., Sermage, J., & Bonal, D. (2010). Seasonal variation in atmospheric relative humidity contributes to explaining seasonal variation in trunk circumference of tropical rain-forest trees in French Guiana. J. Trop. Ecol., 26, 393–405.
Abstract: Large seasonal variation in the rate of change in girth of tropical rain-forest tree species has been described, but its origin is still under debate. We tested whether this variation might be related to variation in atmospheric relative humidity through its influence on bark water content and thickness. Variation in trunk circumference of 182 adult trees was measured about twice a month in an undisturbed tropical rain forest over 18 mo using dendrometers. Furthermore, a laboratory experiment was conducted to test the direct influence of relative air humidity on bark water content and thickness. in the field, most trees displayed highly positive rates of change in girth at the onset of the wet season, while a quarter of the trees displayed negative changes during long dry seasons, whatever their total annual growth. This variation was correlated with environmental conditions, particularly with atmospheric relative humidity. Trees with high bark water content and thickness displayed a stronger decrease in girth during the dry season. in the chamber experiment, desiccation induced a decrease in the diameter of the trunk sections in tandem with a decrease in bark water content. As a result, seasonal variation in the rate of change in girth of tropical rain-forest trees reflects variation in trunk biophysical properties, through the influence of relative humidity on bark properties. but not directly variation in secondary growth.
Keywords: bark; drought; secondary growth; seasonality; tropical rain forest; water
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Paine, C. E. T., Harms, K. E., & Ramos, J. (2009). Supplemental irrigation increases seedling performance and diversity in a tropical forest. J. Trop. Ecol., 25, 171–180.
Abstract: Diversity is positively correlated with water availability at global, continental and regional scales. With the objective of better understanding the mechanisms that drive these relationships. we investigated the degree to which variation in water availability affects the performance (recruitment, growth a rid survival) of juvenile trees. Precipitation was supplemented throughout two dry seasons in a seasonal moist forest in south-eastern Peru. Supplementing precipitation by 160 mm mo(-1), we increased soil moisture by 17%. To generate seedling communities or known species composition, we sowed 3840 seeds of 12 species. We monitored the fates of the 554 seedlings recruited from the sown seeds. as well as 1856 older non-sown seedlings (10 cm <= height < 50 cm), and 2353 saplings (> 1 m tall). Watering significantly enhanced young seedling growth and survival, increasing stern density and diversity. Watering diminished the recruitment of species associated with upland forests, but increased the survival of both upland- and lowland-associated species. Though supplemental watering increased the growth of older seedlings. their density and diversity were unaffected. Sapling performance was insensitive to watering. We infer that variation in dry-season water availability may affect seedling community structure by differentially affecting recruitment and increasing overall survival. These results suggest that differential seedling recruitment and survival may contribute to the observed relationships between water availability, habitat associations and patterns of tree species richness.
Keywords: diversity; Estacion Biologica Los Amigos; habitat filtering; palms; Peru; precipitation; seasonality; seedling recruitment
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Gibernau, M., Orivel, J., Dejean, A., Delabie, J., & Barabe, D. (2008). Flowering as a key factor in ant-Philodendron interactions. J. Trop. Ecol., 24, 689–692.
Keywords: Araceae; domatia; habitat; nest site; non-specific association; Philodendron solimoesense; territoriality
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Baraloto, C., Bonal, D., & Goldberg, D. E. (2006). Differential seedling growth response to soil resource availability among nine neotropical tree species. J. Trop. Ecol., 22, 487–497.
Abstract: Although the potential contribution to tropical tree species coexistence of niche differentiation along light gradients has received much attention, the degree to which species perform differentially along soil resource gradients remains unclear. To examine differential growth response to soil resources, we grew seedlings of nine tropical tree species at 6.0% of full sun for 12 mo in a factorial design of two soil types (clay and white sand), two phosphate fertilization treatments (control and addition of 100 mg P kg(-1)) and two watering treatments (field capacity and water limitation to one-third field capacity). Species differed markedly in biomass growth rate, but this hierarchy was almost completely conserved across all eight treatments. All species grew more slowly in sand than clay soils. and no species grew faster with phosphate additions. Only Eperua grandiflora and E. falcata showed significant growth increases in the absence of water limitation. Faster-growing species were characterized by high specific leaf area, high leaf allocation and high net assimilation rate but not lower root allocation. Slower-growing species exhibited greater plasticity in net assimilation rate. suggesting that tolerance of edaphic stress in these species is related more to stomatal control than to whole-plant carbon allocation. Although relative growth rate for biomass was correlated with both its physiological and morphological components. interspecific differences were best explained by differences in net assimilation rate across six of the eight treatments. A suite of traits including high assimilation and high specific leaf area maintains rapid growth rate of faster-growing species across a wide gradient of soil resources, but the lack of plasticity they exhibit may compromise their survival in the poorest soil environments.
Keywords: biomass allocation; Dicorynia; drought stress; Eperua; French Guiana; Goupia; Jacaranda; plasticity; Qualea; Recordorylon; relative growth rate; Sextonia; soil phosphorus; specific leaf area; Virola
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Epron, D., Bosc, A., Bonal, D., & Freycon, V. (2006). Spatial variation of soil respiration across a topographic gradient in a tropical rain forest in French Guiana. J. Trop. Ecol., 22, 565–574.
Abstract: The objective of this study was to analyse the factors explaining spatial variation in soil respiration over topographic transects in a tropical rain forest of French Guiana. The soil of 30 plots along six transects was characterized. The appearance of the 'dry to the touch' character at a depth of less than 1.2 m was used to discriminate soils exhibiting vertical drainage from soils exhibiting superficial lateral drainage and along with colour and texture, to define five classes from well-drained to strongly hydromorphic soils. Spatial variation in soil respiration was closely related to topographic position and soil type. Increasing soil water content and bulk density and decreasing root biomass and soil carbon content explained most of the decrease in soil respiration from the plateaux (vertically drained hypoferralic acrisol) to the bottomlands (haplic gleysol). These results will help to stratify further field experiments and to identify the underlying determinants of spatial variation in soil respiration to develop mechanistic models of soil respiration.
Keywords: acrisol; carbon balance; carbon flux; gleysol; root biomass
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Bereau, M., Bonal, D., Louisanna, E., & Garbaye, J. (2005). Do mycorrhizas improve tropical tree seedling performance under water stress and low light conditions? A case study with Dicorynia guianensis (Caesalpiniaceae). J. Trop. Ecol., 21, 375–381.
Abstract: We tested the response of seedlings of Diconyina guianensis, a major timber tree species of French Guiana, to mycorrhizal symbiosis and water limitation in a semi-con trolled experiment under natural light conditions. Under well-watered conditions, mycorrhizal colonization resulted in an increase of net photosynthesis, growth and phosphorus uptake. When submitted to water stress, no growth reduction of mycorrhizal seedlings was observed. Mycorrhizal seedlings were more sensitive to drought than non-mycorrhizal ones in terms of carbon assimilation, but not with regard to stomatal closure. In contrast to previous studies on temperate tree seedlings, this result precludes a mycorrhizal effect on the hydraulic properties of this species. Furthermore, our results suggest that below a specific threshold of soil moisture, carbon assimilation of D. guianensis seedlings was decreased by the mycorrhizal symbiosis. This is probably related to the competition between the plant and its host fungus for carbon allocation under low light intensity, even though it did not seem to have a significant effect on mortality in our experiment.
Keywords: French Guiana; leaf gas exchange; mycorrhizal symbiosis; tropical forest; water limitation
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Koponen, P., Nygren, P., Domenach, A. M., Le Roux, C., Saur, E., & Roggy, J. C. (2003). Nodulation and dinitrogen fixation of legume trees in a tropical freshwater swamp forest in French Guiana. J. Trop. Ecol., 19, 655–666.
Abstract: Nodulated legume trees comprised 43% of the stand basal area in the low, most frequently flooded microsites, and 23% in higher, drier microsites in a tropical freshwater swamp forest in French Guiana. Dinitrogen fixation in Pterocarpus officinalis, Hydrochorea corymbosa and Inga pilosula was confirmed by acetylene reduction assay (ARA), presence of leghaemoglobin in nodules and the N-15 natural abundance method. The results for Zygia cataractae were inconclusive but suggested N-2 fixation in drier microsites. Nodulated Inga disticha had a N-15-to-N-14 ratio similar to non-N-2-fixing trees, but ARA indicated nitrogenase activity and leghaemoglobin was present in nodules. All bacterial strains were identified as Bradyrhizobium spp. according to the partial 16S rDNA sequences, and they were infective in vitro in the model species Macroptilium atropurpuretan. About 35-50% of N in the leaves of P. officinalis, H. corymbosa and I. pilosula was fixed from the atmosphere. Dinitrogen fixation was estimated to contribute at least 8-13% and 1728% to whole-canopy N in high and low microsites, respectively. Symbiotic N, fixation appears to provide both a competitive advantage to legume trees under N-limited, flooded conditions and an important N input to neotropical freshwater swamp forests.
Keywords: acetylene reduction assay; Bradyrhizobium; flooding; microtopography; N-15 natural abundance method; 16S rDNA sequencing
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Fonty, E., Molino, J. F., Prevost, M. F., & Sabatier, D. (2011). A new case of neotropical monodominant forest: Spirotropis longifolia (Leguminosae-Papilionoideae) in French Guiana. J. Trop. Ecol., 27(6), 641–644.
Keywords: French Guiana; layering; monodominance; sprouting; supporting strategy; suppressive strategy; tropical rain forests
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Lehnebach, R., Doumerc, L., Clair, B., & Alméras, T. (2020). Mechanical stress in the inner bark of 15 tropical tree species and the relationship with anatomical structure. Bot., 98(1), 1–8.
Abstract: Recent studies have shown that the inner bark is implicated in the postural control of inclined tree stems through the interaction between wood radial growth and tangential expansion of a trellis fiber network in bark. Assessing the taxonomic extent of this mechanism requires a screening of the diversity in bark anatomy and mechanical stress. The mechanical state of bark was measured in 15 tropical tree species from various botanical families on vertical mature trees, and related to the anatomical structure of the bark. Significant tensile or compressive longitudinal stresses were observed in the stems of most species. Tensile longitudinal stress was observed in various botanical families and was always associated with fibers arranged in a trellis-like structure and strong dilatation of rays. The highest tensile stress was recorded in species with gelatinous fibers forming a treillis. Compressive stress was typically associated with a large amount of sclereids in the bark, supporting the differentiation of sclereids as a potential origin of the generation of longitudinal compressive stresses in bark. In species exhibiting both a fibrous trellis structure and a significant amount of sclereids, the sign of longitudinal stress may depend on the balance between these two mechanisms.
Keywords: Bark anatomical structure; Mechanical stress; Sclereids; Secondary phloem; Tree biomechanics; Tropical species
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