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Premise: Barriers at different reproductive stages contribute to reproductive isolation. Self-incompatibility (SI) systems that prevent self-pollination could also act to control interspecific pollination and contribute to reproductive isolation, preventing hybridization. Here we evaluated whether SI contributes to reproductive isolation among four co-occurring Opuntia species that flower at similar times and may hybridize with each other., Methods: We assessed whether Opuntia cantabrigiensis, O. robusta, O. streptacantha, and O. tomentosa, were self-compatible and formed hybrid seeds in five manipulation treatments to achieve self-pollination, intraspecific cross-pollination, open pollination (control), interspecific crosses or apomixis, then recorded flowering phenology and synchrony., Results: All species flowered in the spring with a degree of synchrony, so that two pairs of species were predisposed to interspecific pollination (O. cantabrigiensis with O. robusta, O. streptacantha with O. tomentosa). All species had distinct reproductive systems: Opuntia cantabrigiensis is self-incompatible and did not produce hybrid seeds as an interspecific pollen recipient; O. robusta is a dioecious species, which formed a low proportion of hybrid seeds; O. streptacantha and O. tomentosa are self-compatible and produced hybrid seeds., Conclusions: Opuntia cantabrigiensis had a strong pollen-pistil barrier, likely due to its self-incompatibility. Opuntia robusta, the dioecious species, is an obligate outcrosser and probably partially lost its ability to prevent interspecific pollen germination. Given that the self-compatible species can set hybrid seeds, we conclude that pollen-pistil interaction and high flowering synchrony represent weak barriers; whether reproductive isolation occurs later in their life cycle (e.g., germination or seedling survival) needs to be determined., (© 2024 The Authors. American Journal of Botany published by Wiley Periodicals LLC on behalf of Botanical Society of America.) more...

Premise: Terminal velocity (Vt) is an important factor for the dispersal of biological particles but has scarcely been studied for anemochorous fern spores, and the influence of spore characteristics on Vt has not been evaluated. Here, we measured the Vt of 1234 spores of 18 fern species and two Selaginella microspores using videoimaging analysis and evaluated the effects of mass, size, and ornamentation on Vt., Methods: We designed a sedimentation tower with a graduated microtelescope attached to a high-speed video camera to record falling particles and measure the Vt of fern spores using video-image processing software. Spores were measured for each species and their size correlated with Vt., Results: The Vt of fern spores ranged from 4.7 cm·s -1 (Cyathea costaricensis) to 18.85 cm·s -1 (Acrostichum danaeifolium). The method is accurate and reliable as predicted by Stokes model for glass beads of known density and size. In addition, Vt had a higher correlation coefficient with mass (ρ = 0.72) than size (ρ = 0.20), and ornamental appendages reduced Vt., Conclusions: The reported values of Vt of fern spores are within the range of different biological airborne particles such as moss spores and pollen grains of seed plants. The results showed that spore ornamentation is directly related to Vt rather than spore size and may increase or decrease the drag. This method will aid future aerobiological research on biological particles., (© 2022 Botanical Society of America.) more...

• Premise of the study: Xylem sap osmolality and salinity is a critical unresolved issue in plant function with impacts on transport efficiency, pressure gradients, and living cell turgor pressure, especially for halophytes such as mangrove trees.• Methods: We collected successive xylem vessel sap samples from stems and shoots of Avicennia germinans and Laguncularia racemosa using vacuum and pressure extraction and measured their osmolality. Following a series of extractions with the pressure chamber, we depressurized the shoot and pressurized again after various equilibration periods (minutes to hours) to test for dynamic control of osmolality. Transpiration and final sap osmolality were measured in shoots perfused with deionized water or different seawater dilutions.• Key results: For both species, the sap osmolality values of consecutive samples collected by vacuum extraction were stable and matched those of the initial samples extracted with the pressure chamber. Further extraction of samples with the pressure chamber decreased sap osmolality, suggesting reverse osmosis occurred. However, sap osmolalities increased when longer equilibration periods after sap extraction were allowed. Analysis of expressed sap with HPLC indicated a 1:1 relation between measured osmolality and the osmolality of the inorganic ions in the sap (mainly Na + , K + , and Cl - ), suggesting no contamination by organic compounds. In stems perfused with deionized water, the sap osmolality increased to mimic the native sap osmolality.• Conclusions: Xylem sap osmolality and ionic contents are dynamically adjusted by mangroves and may help modulate turgor pressure, hydraulic conductivity, and water potential, thus being important for mangrove physiology, survival, and distribution., (© 2014 Botanical Society of America, Inc.) more...

The biogeography of plant-animal interactions is a novel topic on which many disciplines converge (e.g., reproductive biology, biogeography, and evolutionary biology). Narrative reviews have indicated that tropical columnar cacti and agaves have highly specialized pollination systems, while extratropical species have generalized systems. However, this dichotomy has never been quantitatively tested. We tested this hypothesis using traditional and phylogenetically informed meta-analysis. Three effect sizes were estimated from the literature: diurnal, nocturnal, and hand cross-pollination (an indicator of pollen limitation). Columnar cactus pollination systems ranged from purely bat-pollinated in the tropics to generalized pollination, with diurnal visitors as effective as nocturnal visitors in extratropical regions; even when phylogenetic relatedness among species is taken into account. Metaregressions identified a latitudinal increase in pollen limitation in columnar cacti, but this increase was not significant after correcting for phylogeny. The currently available data for agaves do not support any latitudinal trend. Nectar production of columnar cacti varied with latitude. Although this variation is positively correlated with pollination by diurnal visitors, it is influenced by phylogeny. The degree of specificity in the pollination systems of columnar cacti is heavily influenced by ecological factors and has a predictable geographic pattern. more...

Columnar cacti have been traditionally classified as crassulacean acid metabolism (CAM) plants, though recent research indicates some cactus seedlings employ the C(3) pathway. To verify this last result, we measured acidity fluctuations for five columnar and one globular cactus species in seedlings from 1 to 48 d old after experimental exposure to 60% and 30% full sunlight, and in adult plants in the field. Using light-response curves of chlorophyll fluorescence, we determined photosynthetic efficiency (ΔF/Fm'), maximum electron transport rate (ETR(max)) and saturating photosynthetically active photon flux density (PPFD(sat)). All seedlings used the CAM pathway from their first day of development, and increases in nocturnal acidity depended on species, light treatment, and age. The CAM pathway was also found in adult plants. Cactus seedlings were able to acclimatize to light conditions by making photochemical adjustments, mainly by modifying the level of light at which photosystem II is saturated (PPFD(sat)). The presence of CAM in the seedlings of columnar cacti increases water-use efficiency and reduces the risk of photoinhibition. This could favor survival in the highly variable light levels characteristic of the desert environments of columnar cacti. more...