Leroy, C., Sejalon-Delmas, N., Jauneau, A., Ruiz-Gonzalez, M. X., Gryta, H., Jargeat, P., et al. (2011). Trophic mediation by a fungus in an ant-plant mutualism. J. Ecol., 99(2), 583–590.
Abstract: 1. Plants often rely on external, mutualistic partners to survive and reproduce in resource-limited environments or for protection from enemies. Such interactions, including mycorrhizal symbioses and ant plant associations, are widespread and play an important role at the ecosystem and community levels. In ant-plant mutualisms, the plants may benefit from both the protection provided by the presence of ants and from the nutrients absorbed from insect debris. However, the role of third partners in plant nutrition, particularly ant-associated fungi, has never before been demonstrated. 2. We investigate this issue in the ant-plant Hirtella physophora. In this model system, Allomerus decemarticulatus ants are involved in two, highly specific interactions: first, with their host plant, and, secondly, with a fungus that they actively manipulate. Moreover, the ants combine both plant trichomes and fungal hyphae to make a trap to capture prey. 3. We empirically demonstrate the existence of a third type of interaction between the fungus and the plant through the use of both experimental enrichments with stable isotopes (N-15) and histological approaches. The fungus growing in the galleries plays a role in providing nutrients to the host plant, in addition to the structural role it plays for the ants. Fungus-facilitated nitrogen uptake occurs mainly in old domatia, where abundant hyphae are in close contact with the plant cells. Whether the fungi inside the domatia and those in the galleries are the same is still uncertain. 4. Synthesis. Together, our results show that a fungal partner in an ant-plant mutualism can benefit the plant by improving its nutrient uptake, and they demonstrate the existence of a true tripartite mutualism in this system. Our results add further evidence to the notion that interpretations of some ant plant symbioses as purely protective mutualisms have overlooked these nutritional aspects.
Keywords: delta N-15; Allomerus decemarticulatus; ant-plant-fungus interactions; Ascomycete; fungal mediation; Hirtella physophora; mutualisms; myrmecophytes; nutrient provisioning; stable isotopes
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Degen, B., Bandou, E., & Caron, H. (2004). Limited pollen dispersal and biparental inbreeding in Symphonia globulifera in French Guiana. Heredity, 93(6), 585–591.
Abstract: In this paper, we report a study of the mating system and gene flow of Symphonia globulifera, a hermaphroditic, mainly bird-pollinated tree species with a large geographic distribution in the tropical Americas and Africa. Using three microsatellites, we analysed 534 seeds of 28 open pollinated families and 164 adults at the experimental site 'Paracou' in French Guiana. We observed, compared to other tropical tree species, relatively high values for the effective number of alleles. Significant spatial genetic structure was detected, with trees at distances up to 150 m more genetically similar than expected at random. We estimated parameters of the mating system and gene flow by using the mixed mating model and the TwoGener approach. The estimated multilocus outcrossing rate, t(m), was 0.920. A significant level of biparental inbreeding and a high proportion of full-sibs were estimated for the 28 seed arrays. We estimated mean pollen dispersal distances between 27 and 53 m according to the dispersal models used. Although the adult population density of S. globulifera in Paracou was relatively high, the joint estimation of pollen dispersal and density of reproductive trees gave effective density estimates of 1.6 and 1.3 trees/ha. The parameters of the mating system and gene flow are discussed in the context of spatial genetic and demographic structures, flowering phenology and pollinator composition and behaviour.
Keywords: gene flow; microsatellites; mixed mating; spatial autocorrelation; tropical tree; twogener
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Nirma, C., Eparvier, V., & Stien, D. (2015). Reactivation of antibiosis in the entomogenous fungus Chrysoporthe sp. SNB-CN74. Journal of Antibiotics, 68(9), 586–590.
Abstract: Chrysoporthe sp. SNB-CN74 was isolated from a Nasutitermes corniger nest, and its ethyl acetate extract was found to exhibit very strong antibacterial activity. Two antibacterial metabolites were isolated, (-)-R-skyrin (2) and (+)-rugulosin A (3). Eventually, the fungus lost its antibiotic potential when subcultured, and the use of yeast extract induced the re-expression of these two antibiotics. Yeast extract possibly activated a cryptic pathway by mimicking the presence of an ecological competitor. © 2015 Japan Antibiotics Research Association All rights reserved.
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Fortunel, C., Garnier, E., Joffre, R., Kazakou, E., Quested, H., Grigulis, K., et al. (2009). Leaf traits capture the effects of land use changes and climate on litter decomposability of grasslands across Europe. Ecology, 90(3), 598–611.
Abstract: Land use and climate changes induce shifts in plant functional diversity and community structure, thereby modifying ecosystem processes. This is particularly true for litter decomposition, an essential process in the biogeochemical cycles of carbon and nutrients. In this study, we asked whether changes in functional traits of living leaves in response to changes in land use and climate were related to rates of litter potential decomposition, hereafter denoted litter decomposability, across a range of 10 contrasting sites. To disentangle the different control factors on litter decomposition, we conducted a microcosm experiment to determine the decomposability under standard conditions of litters collected in herbaceous communities from Europe and Israel. We tested how environmental factors ( disturbance and climate) affected functional traits of living leaves and how these traits then modified litter quality and subsequent litter decomposability. Litter decomposability appeared proximately linked to initial litter quality, with particularly clear negative correlations with lignin-dependent indices ( litter lignin concentration, lignin : nitrogen ratio, and fiber component). Litter quality was directly related to community-weighted mean traits. Lignin-dependent indices of litter quality were positively correlated with community-weighted mean leaf dry matter content (LDMC), and negatively correlated with community-weighted mean leaf nitrogen concentration (LNC). Consequently, litter decomposability was correlated negatively with community-weighted mean LDMC, and positively with community-weighted mean LNC. Environmental factors ( disturbance and climate) influenced community-weighted mean traits. Plant communities experiencing less frequent or less intense disturbance exhibited higher community-weighted mean LDMC, and therefore higher litter lignin content and slower litter decomposability. LDMC therefore appears as a powerful marker of both changes in land use and of the pace of nutrient cycling across 10 contrasting sites.
Keywords: climate; community functional parameters; disturbance; leaf traits; litter decomposability; litter quality
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Coste, S., Baraloto, C., Leroy, C., Marcon, E., Renaud, A., Richardson, A. D., et al. (2010). Assessing foliar chlorophyll contents with the SPAD-502 chlorophyll meter: a calibration test with thirteen tree species of tropical rainforest in French Guiana. Ann. For. Sci., 67(6), 607.
Abstract: Chlorophyll meters such as the SPAD-502 offer a simple, inexpensive and rapid method to estimate foliar chlorophyll content. However, values provided by SPAD-502 are unitless and require empirical calibrations between SPAD units and extracted chlorophyll values. Leaves of 13 tree species from the tropical rain forest in French Guiana were sampled to select the most appropriate calibration model among the often-used linear, polynomial and exponential models, in addition to a novel homographic model that has a natural asymptote. The homographic model best accurately predicted total chlorophyll content (mu g cm(-2)) from SPAD units (R-2 = 0.89). Interspecific differences in the homographic model parameters explain less than 7% of the variation in chlorophyll content in our data set. The utility of the general homographic model for a variety of research and management applications clearly outweighs the slight loss of model accuracy due to the abandon of the species' effect.
Keywords: chlorophyll estimate; model calibration; homographic functions; neotropical trees
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Verryckt, L. T., Van Langenhove, L., Ciais, P., Courtois, E. A., Vicca, S., Peñuelas, J., et al. (2020). Coping with branch excision when measuring leaf net photosynthetic rates in a lowland tropical forest. Biotropica, 52(4), 608–615.
Abstract: Measuring leaf gas exchange from canopy leaves is fundamental for our understanding of photosynthesis and for a realistic representation of carbon uptake in vegetation models. Since canopy leaves are often difficult to reach, especially in tropical forests with emergent trees up to 60 m at remote places, canopy access techniques such as canopy cranes or towers have facilitated photosynthetic measurements. These structures are expensive and therefore not very common. As an alternative, branches are often cut to enable leaf gas exchange measurements. The effect of branch excision on leaf gas exchange rates should be minimized and quantified to evaluate possible bias. We compared light-saturated leaf net photosynthetic rates measured on excised and intact branches. We selected branches positioned at three canopy positions, estimated relative to the top of the canopy: upper sunlit foliage, middle canopy foliage, and lower canopy foliage. We studied the variation of the effects of branch excision and transport among branches at these different heights in the canopy. After excision and transport, light-saturated leaf net photosynthetic rates were close to zero for most leaves due to stomatal closure. However, when the branch had acclimated to its new environmental conditions—which took on average 20 min—light-saturated leaf net photosynthetic rates did not significantly differ between the excised and intact branches. We therefore conclude that branch excision does not affect the measurement of light-saturated leaf net photosynthesis, provided that the branch is recut under water and is allowed sufficient time to acclimate to its new environmental conditions. © 2020 The Association for Tropical Biology and Conservation
Keywords: branch cutting; canopy physiology; French Guiana; gas exchange; photosynthesis; rainforest; stomatal conductance; ecological modeling; environmental conditions; forest canopy; leaf; measurement method; photosynthesis; tree; tropical forest; Gruidae
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Christensen-Dalsgaard, K. K., Fournier, M., Ennos, A. R., & Barfod, A. S. (2007). Changes in vessel anatomy in response to mechanical loading in six species of tropical trees. New Phytol., 176(3), 610–622.
Abstract: It is well known that trees adapt their supportive tissues to changes in loading conditions, yet little is known about how the vascular anatomy is modified in this process. We investigated this by comparing more and less mechanically loaded sections in six species of tropical trees with two different rooting morphologies. We measured the strain, vessel size, frequency and area fraction and from this calculated the specific conductivity, then measured the conductivity, modulus of elasticity and yield stress. The smallest vessels and the lowest vessel frequency were found in the parts of the trees subjected to the greatest stresses or strains. The specific conductivity varied up to two orders of magnitude between mechanically loaded and mechanically unimportant parts of the root system. A trade-off between conductivity and stiffness or strength was revealed, which suggests that anatomical alterations occur in response to mechanical strain. By contrast, between-tree comparisons showed that average anatomical features for the whole tree seemed more closely related to their ecological strategy.
Keywords: hydraulic architecture; hydraulic-mechanical trade-off; mechanical adaptation; rooting morphology; tropical trees; vascular anatomy
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Vantaux, A., Roux, O., Magro, A., Ghomsi, N. T., Gordon, R. D., Dejean, A., et al. (2010). Host-Specific Myrmecophily and Myrmecophagy in the Tropical Coccinellid Diomus thoracicus in French Guiana. Biotropica, 42(5), 622–629.
Abstract: A variety of arthropods, particularly insects, have developed myrmecophilous interactions with ants to gain access to resources and/or for protection. Among these myrmecophiles, only a few examples have been documented in the Coccinellidae, most of them involving species able to feed on ant-tended Hemiptera. We report here a new case of obligate myrmecophily in the coccinellid Diomus thoracicus. Larvae are invariably and exclusively found in the nests of the ant Wasmannia auropunctata and seem to rely on ant brood as their only food source. Not only do ant workers show no aggressiveness toward the D. thoracicus larvae in their behavioral interactions at the colonial level, but also at the species level; while coccinellid adults are always attacked. The integration of the larvae inside of the ant nests is based on their chemical mimicry of the host's cuticular cues. Therefore, given the presence of the D. thoracicus larvae inside of the ant's nest, their predation on Wasmannia brood and their chemical mimicry, this species can be considered a specific parasite of W. auropunctata. Overall, this new case of myrmecophily not only specifically involves a highly invasive ant species, but also provides insights into the evolution of myrmecophily and myrmecophagy in coccinellids.
Keywords: ants; ladybird; mimicry; parasite; Wasmannia auropunctata
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Leguet, A., Gibernau, M., Shintu, L., Caldarelli, S., Moja, S., Baudino, S., et al. (2014). Evidence for early intracellular accumulation of volatile compounds during spadix development in Arum italicum L. and preliminary data on some tropical Aroids. Naturwissenschaften, 101(8), 623–635.
Abstract: Staining and histochemistry of volatile organic compounds (VOCs) were performed at different inflorescence developmental stages on nine aroid species; one temperate, Arum italicum and eight tropical from the genera Caladium, Dieffenbachia and Philodendron. Moreover, a qualitative and quantitative analysis of VOCs constituting the scent of A. italicum, depending on the stage of development of inflorescences was also conducted. In all nine species, vesicles were observed in the conical cells of either the appendix or the stamens (thecae) and the staminodes. VOCs were localised in intracellular vesicles from the early stages of inflorescence development until their release during receptivity of gynoecium. This localisation was observed by the increase of both number and diameter of the vesicles during 1 week before receptivity. Afterwards, vesicles were fewer and smaller but rarely absent. In A. italicum, staining and gas chromatography analyses confirmed that the vesicles contained terpenes. The quantitatively most important ones were the sesquiterpenes, but monoterpenes were not negligible. Indeed, the quantities of terpenes matched the vesicles' size evolution during 1 week. Furthermore, VOCs from different biosynthetic pathways (sesquiterpenes and alkanes) were at their maximum quantity 2 days before gynoecium receptivity (sesquiterpenes and alkanes) or during receptivity (isobutylamine, monoterpenes, skatole and p-cresol). VOCs seemed to be emitted during gynoecium receptivity and/or during thermogenesis, and FADs are accumulated after thermogenesis in the spadix. These complex dynamics of the different VOCs could indicate specialisation of some VOCs and cell machinery to attract pollinators on the one hand and to repulse/protect against phytophagous organisms and pathogens after pollination on the other hand. © 2014 Springer-Verlag Berlin Heidelberg.
Keywords: Araceae; Cytochemistry; Gas chromatography; Nuclear magnetic resonance; Volatile compounds
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Clair, B., Déjardin, A., Pilate, G., & Alméras, T. (2018). Is the G-layer a tertiary cell wall? Frontiers in Plant Science, 9, 623.
Keywords: Flax; G-layer; Gelatinous layer; Maturation stress; Secondary cell wall; Tension wood; Tertiary cell wall
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