Acid waters in tank bromeliads: Causes and potential consequences.

PREMISE: The consequences of acidity for plant performance are profound, yet the prevalence and causes of low pH in bromeliad tank water are unknown despite its functional relevance to key members of many neotropical plant communities. METHODS: We investigated tank water pH for eight bromeliad species in the field and for the widely occurring Guzmania monostachia in varying light. We compared pH changes over time between plant and artificial tanks containing a solution combined from several plants. Aquaporin transcripts were measured for field plants at two levels of pH. We investigated relationships between pH, leaf hydraulic conductance, and CO2 concentration in greenhouse plants and tested proton pump activity using a stimulator and inhibitor. RESULTS: Mean tank water pH for the eight species was 4.7 ± 0.06 and was lower for G. monostachia in higher light. The pH of the solution in artificial tanks, unlike in plants, did not decrease over time. Aquaporin transcription was higher for plants with lower pH, but leaf hydraulic conductance did not differ, suggesting that the pH did not influence water uptake. Tank pH and CO2 concentration were inversely related. Fusicoccin enhanced a decrease in tank pH, whereas orthovanadate did not. CONCLUSIONS: Guzmania monostachia acidified its tank water via leaf proton pumps, which appeared responsive to light. Low pH increased aquaporin transcripts but did not influence leaf hydraulic conductance, hence may be more relevant to nutrient uptake.

Open for Bismuth: Main Group Metal-to-Ligand Charge Transfer.

The synthesis, characterization, and photophysical properties of 4- and 6-coordinate Bi3+ coordination complexes are reported. Bi(bzq)3 (1) and [Bi(bzq)2]Br (2) (bzq = benzo[h]quinoline) are synthesized by reaction of 9-Li-bzq with BiCl3 and BiBr3, respectively. Absorption spectroscopy, electrochemistry, and DFT studies suggest that 1 has 42% Bi 6s character in its highest-occupied molecular orbital (HOMO) as a result of six σ* interactions with the bzq ligands. Excitation of 1 at 450 nm results in a broad emission feature at 520 nm, which is rationalized as a metal-to-ligand charge transfer (MLCT) and phosphorescent emission resulting from bismuth-mediated intersystem crossing (ISC) to a triplet excited state. This excited state revealed a 35 µs lifetime and was quenched in the presence of oxygen. These results demonstrate that useful optoelectronic properties of Bi3+ can be accessed through hypercoordination with covalent organobismuth interactions that mimic the electronic structure of lead perovskites.

A tale of two plasticities: leaf hydraulic conductances and related traits diverge for two tropical epiphytes from contrasting light environments.

We compared the effects of different light environments on leaf hydraulic conductance (Kleaf ) for two congeneric epiphytes, the tank bromeliads Guzmania lingulata (L.) Mez and Guzmania monostachia (L.) Rusby ex Mez. They occur sympatrically at the study site, although G. monostachia is both wider ranging and typically found in higher light. We collected plants from two levels of irradiance and measured Kleaf as well as related morphological and anatomical traits. Leaf xylem conductance (Kxy ) was estimated from tracheid dimensions, and leaf conductance outside the xylem (Kox ) was derived from a leaky cable model. For G. monostachia, but not for G. lingulata, Kleaf and Kxy were significantly higher in high light conditions. Under both light conditions, Kxy and Kox were co-limiting for the two species, and all conductances were in the low range for angiosperms. With respect to hydraulic conductances and a number of related anatomical traits, G. monostachia exhibited greater plasticity than did G. lingulata, which responded to high light chiefly by reducing leaf size. The positive plasticity of leaf hydraulic traits in varying light environments in G. monostachia contrasted with negative plasticity in leaf size for G. lingulata, suggesting that G. monostachia may be better able to respond to forest conditions that are likely to be warmer and more disturbed in the future.

Leaf hydraulic conductance for a tank bromeliad: axial and radial pathways for moving and conserving water.

Epiphytic plants in the Bromeliaceae known as tank bromeliads essentially lack stems and absorptive roots and instead take up water from reservoirs formed by their overlapping leaf bases. For such plants, leaf hydraulic conductance is plant hydraulic conductance. Their simple strap-shaped leaves and parallel venation make them suitable for modeling leaf hydraulic conductance based on vasculature and other anatomical and morphological traits. Plants of the tank bromeliad Guzmania lingulata were investigated in a lowland tropical forest in Costa Rica and a shaded glasshouse in Los Angeles, CA, USA. Stomatal conductance to water vapor and leaf anatomical variables related to hydraulic conductance were measured for both groups. Tracheid diameters and numbers of vascular bundles (veins) were used with the Hagen-Poiseuille equation to calculate axial hydraulic conductance. Measurements of leaf hydraulic conductance using the evaporative flux method were also made for glasshouse plants. Values for axial conductance and leaf hydraulic conductance were used in a model based on leaky cable theory to estimate the conductance of the radial pathway from the vein to the leaf surface and to assess the relative contributions of both axial and radial pathways. In keeping with low stomatal conductance, low stomatal density, low vein density, and narrow tracheid diameters, leaf hydraulic conductance for G. lingulata was quite low in comparison with most other angiosperms. Using the predicted axial conductance in the leaky cable model, the radial resistance across the leaf mesophyll was predicted to predominate; lower, more realistic values of axial conductance resulted in predicted radial resistances that were closer to axial resistance in their impact on total leaf resistance. Tracer dyes suggested that water uptake through the tank region of the leaf was not limiting. Both dye movement and the leaky cable model indicated that the leaf blade of G. lingulata was structurally and hydraulically well-suited to conserve water.