Isolation of endophytic bacteria from the medicinal, forestal and ornamental tree Handroanthus impetiginosus.

Plant interactions with endophytic bacteria produce mutual benefits and contribute to environmental sustainability. Handroanthus impetiginosus (Mart. ex DC.) Mattos 'pink lapacho' (syn. Tabebuia impetiginosa, Bignoniaceae) is a medicinal, ornamental and forestal native tree from South and Mesoamerica. Plant growth promoting bacteria (PGPB) isolated from pink lapacho are scarcely described. The aim of this work was to isolate and characterize native endophytic bacteria from pink lapacho. Ten bacterial strains were isolated from leaves and six from roots of naturally growing trees in Luján (Central-Eastern region of Argentina). Endophytes were identified as Bacillus, Paenibacillus, Pseudomonas, Rhizobium, Rummeliibacillus and Methylobacterium genera, according to 16S rRNA gene sequencing and phylogenetic analysis. In the present study, a strain of the Rummelibacillus genus (L14) has been first ever reported as endophyte. This strain was capable of growing in Nfb medium and exhibited zinc solubilization ability. A high percentage of strains showed PGPB traits; namely 88% fixed nitrogen, 63% solubilized zinc, 69% solubilized phosphate and 63% produced indole compounds such as IAA. Most strains were salt tolerant that confer them a potential competitive advantage to survive in saline conditions. To the best of our knowledge, this is the first study reporting an approach to assess the diversity of cultivable endophytic bacteria of H. impetiginosus tree and its plant growth promoting capacity. The knowledge about this kind of associations could contribute to environmental sustainability by developing effective biofertilizers that minimize the use of chemical fertilizers and pesticides.

Photosynthetic plasticity of a tropical tree species, Tabebuia rosea, in response to elevated temperature and [CO2 ].

Atmospheric and climate change will expose tropical forests to conditions they have not experienced in millions of years. To better understand the consequences of this change, we studied photosynthetic acclimation of the neotropical tree species Tabebuia rosea to combined 4°C warming and twice-ambient (800 ppm) CO2 . We measured temperature responses of the maximum rates of ribulose 1,5-bisphosphate carboxylation (VCMax ), photosynthetic electron transport (JMax ), net photosynthesis (PNet ), and stomatal conductance (gs ), and fitted the data using a probabilistic Bayesian approach. To evaluate short-term acclimation plants were then switched between treatment and control conditions and re-measured after 1-2 weeks. Consistent with acclimation, the optimum temperatures (TOpt ) for VCMax , JMax and PNet were 1-5°C higher in treatment than in control plants, while photosynthetic capacity (VCMax , JMax , and PNet at TOpt ) was 8-25% lower. Likewise, moving control plants to treatment conditions moderately increased temperature optima and decreased photosynthetic capacity. Stomatal density and sensitivity to leaf-to-air vapour pressure deficit were not affected by growth conditions, and treatment plants did not exhibit stronger stomatal limitations. Collectively, these results illustrate the strong photosynthetic plasticity of this tropical tree species as even fully developed leaves of saplings transferred to extreme conditions partially acclimated.

Two tropical conifers show strong growth and water-use efficiency responses to altered CO2 concentration.

BACKGROUND AND AIMS: Conifers dominated wet lowland tropical forests 100 million years ago (MYA). With a few exceptions in the Podocarpaceae and Araucariaceae, conifers are now absent from this biome. This shift to angiosperm dominance also coincided with a large decline in atmospheric CO2 concentration (ca). We compared growth and physiological performance of two lowland tropical angiosperms and conifers at ca levels representing pre-industrial (280 ppm), ambient (400 ppm) and Eocene (800 ppm) conditions to explore how differences in ca affect the growth and water-use efficiency (WUE) of seedlings from these groups. METHODS: Two conifers (Araucaria heterophylla and Podocarpus guatemalensis) and two angiosperm trees (Tabebuia rosea and Chrysophyllum cainito) were grown in climate-controlled glasshouses in Panama. Growth, photosynthetic rates, nutrient uptake, and nutrient use and water-use efficiencies were measured. KEY RESULTS: Podocarpus seedlings showed a stronger (66 %) increase in relative growth rate with increasing ca relative to Araucaria (19 %) and the angiosperms (no growth enhancement). The response of Podocarpus is consistent with expectations for species with conservative growth traits and low mesophyll diffusion conductance. While previous work has shown limited stomatal response of conifers to ca, we found that the two conifers had significantly greater increases in leaf and whole-plant WUE than the angiosperms, reflecting increased photosynthetic rate and reduced stomatal conductance. Foliar nitrogen isotope ratios (δ15N) and soil nitrate concentrations indicated a preference in Podocarpus for ammonium over nitrate, which may impact nitrogen uptake relative to nitrate assimilators under high ca SIGNIFICANCE: Podocarps colonized tropical forests after angiosperms achieved dominance and are now restricted to infertile soils. Although limited to a single species, our data suggest that higher ca may have been favourable for podocarp colonization of tropical South America 60 MYA, while plasticity in photosynthetic capacity and WUE may help account for their continued persistence under large changes in ca since the Eocene.

Establecimiento y desarrollo de plántulas de Tabebuia rosea (Bignoniaceae) en una selva subcaducifolia manejada de la costa Pacífica de México / Establishment and development of Tabebuia rosea (Bignoniaceae) seedlings in a semideciduous tropical forest under management, Pacific coast of Mexico

We evaluated the effect of soil "scarification" and vegetation clearing treatments on the natural regeneration and initial development of Tabebuia rosea (Bertold) DC. seedlings in a moderate sized semideciduous tropical forest subjected to wood harvesting on the coast of Jalisco, Mexico. The treatments were applied under "seed" trees, and the number of germinated seedlings and their development were evaluated for nine months. Soil "scarification" promoted seed germination and initial seedling development, while the control of the competing vegetation increased the seedling growth and reduced their mortality. These results should be taken into account for the natural regeneration of this species, after clearing, to improve wood production, and should be incorporated into the silvicultural techniques currently developed in the region.

Evaluamos el efecto de los tratamientos de remoción de suelo y roza de vegetación sobre el establecimiento y desarrollo inicial de la regeneración natural de Tabebuia rosea (Bertold) DC. en una selva mediana subcaducifolia sometida a aprovechamiento maderable en la costa de Jalisco, México. Los tratamientos se aplicaron bajo la copa de árboles “semilleros” y se evaluó el número de plántulas emergidas y su desarrollo durante nueve meses. El tratamiento de remoción de suelo favoreció la emergencia de plántulas y su desarrollo inicial, mientras que el control de la vegetación competidora promovió un mayor crecimiento y menores porcentajes de mortalidad. Estos aspectos deben tomarse en cuenta para la regeneración natural de la especie después de la aplicación de las cortas con fines de aprovechamiento maderable y se sugiere incorporarlos a las técnicas silvícolas que actualmente se desarrollan en la zona.

[Establishment and development of Tabebuia rosea (Bignoniaceae) seedlings in a semideciduous tropical forest under management, Pacific coast of Mexico]. / Establecimiento y desarrollo de plántulas de Tabebuia rosea (Bignoniaceae) en una selva subcaducifolia manejada de la costa Pacífica de México.

We evaluated the effect of soil "scarification" and vegetation clearing treatments on the natural regeneration and initial development of Tabebuia rosea (Bertold) DC. seedlings in a moderate sized semideciduous tropical forest subjected to wood harvesting on the coast of Jalisco, Mexico. The treatments were applied under "seed" trees, and the number of germinated seedlings and their development were evaluated for nine months. Soil "scarification" promoted seed germination and initial seedling development, while the control of the competing vegetation increased the seedling growth and reduced their mortality. These results should be taken into account for the natural regeneration of this species, after clearing, to improve wood production, and should be incorporated into the silvicultural techniques currently developed in the region.

Density-dependent shoot-borer herbivory increases the age of first reproduction and mortality of neotropical tree saplings.

Shoot herbivory by the sapling specialist shoot-borer Cromarcha stroudagnesia (Lepidoptera, Pyralidae, Chrysauginae) is shown to have large direct and indirect effects on the rates of height increment and mortality of saplings of its host tree, Tabebuia ochracea (Bignoniaceae), in the secondary successional tropical dry forests of the Area de Conservación Guanacaste, Costa Rica. Experiments and field observations over 3-4 years show a substantial reduction in sapling height increments due to C. stroudagnesia herbivory, of equivalent magnitude to the difference in height increments between undamaged saplings in canopy gaps and full understorey shade. Extrapolating this data at average amounts of C. stroudagnesia herbivory increases the duration of the pre-reproductive sapling life stage by about 40% relative to undamaged plants. This is an underestimate, as top shoot herbivory by C. stroudagnesia also increased the probability of canopy gap saplings being overtopped and shaded by surrounding vegetation. Sapling mortality was increased by C. stroudagnesia herbivory, with 11.8% of the most heavily damaged young saplings dying in 3 years while no undamaged saplings died. Cromarcha stroudagnesia herbivory strongly increases with the number of conspecific T. ochracea saplings and the number of conspecific shoots within 50 m of focal saplings. It is therefore likely to disproportionately decrease the number of saplings and rate of recruitment to reproductive age in areas of high conspecific sapling density. These results suggest that sapling herbivory, especially herbivory of terminal meristems, has an important but largely unexplored influence on the population dynamics of tropical tree species. They further demonstrate that sapling herbivory by insects, in addition to the well-studied insect predation and herbivory of seedlings, is likely to influence tree species coexistence in tropical forests.