Who helps whom? Pollination strategy of Iris tuberosa and its relationship with a sexually deceptive orchid

Identification of characteristic aroma compounds for spicy in Iris lactea var. chinensis

Iris lactea var. chinensis (Fisch.) Koidz has a unique floral fragrance that differs from that of other Iris spp.; however, its characteristic aroma composition remains unknown. This study aimed to identify the floral fragrance components of I. lactea var. chinensis during different flowering stages using headspace solid-phase microextraction in conjunction with gas chromatography mass spectrometry, electronic nose, and sensory evaluation. During the three flowering phases (bud stage, bloom stage, and decay stage), 70 volatile organic compounds (VOCs), including 13 aldehydes, 13 esters, 11 alcohols, 10 alkanes, 8 ketones, 7 terpenes, 7 benzenoids, and 1 nitrogenous compound, were identified. According to principal component analysis, the primary VOCs were (-)-pinene, β-irone, methyl heptenone, phenylethanol, hexanol, and 2-pinene. A comparison of the differential VOCs across the different flowering stages using orthogonal partial least squares discriminant analysis and hierarchical clustering analysis revealed that 3-carene appeared only in the bud stage, whereas hexanol, ethyl caprate, ethyl caproate, linalool, (-)-pinene, and 2-pinene appeared or were present at significantly increased levels during the bloom stage. The phenylethanol, methyl heptenone, 3-methylheptane, and β-irone reached a peak in the decay stage. The odor activity value and sensory evaluation suggested that "spicy" is the most typical odor of I. lactea var. chinensis, mainly due to 2-methoxy-3-sec-butylpyrazine, which is rare in floral fragrances.

Unclusterable, underdispersed arrangement of insect-pollinated plants in pollinator niche space

Pollinators can mediate facilitative or competitive relationships between plant species, but the relative importance of these two conflicting phenomena in shaping community-wide pollinator resource use remains unexplored. This article examines the idea that the arrangement of large samples of plant species in Hutchinsonian pollinator niche space (n-dimensional hypervolume whose axes represent pollinator types) can help to evaluate the comparative importance of facilitation and competition as drivers of pollinator resource use at the community level. Pollinator composition data were gathered for insect-pollinated plants from the Sierra de Cazorla mountains (southeastern Spain), comprising ~95% of widely distributed insect-pollinated species. The following questions were addressed at regional (45 sites, 221 plant species) and local (1 site, 73 plant species) spatial scales: (1) Do plant species clusters occur in pollinator niche space? Four pollinator niche spaces differing in dimensionality were considered, the axes of which were defined by insect orders, families, genera, and species. (2) If all plant species form a single, indivisible cluster, are they overdispersed or underdispersed within the cluster relative to a random arrangement? "Clusterability" tests failed to reject the null hypothesis that there was only one pollinator-defined plant species cluster in pollinator niche space, irrespective of spatial scale, pollinator niche space, or pollinator importance measurement (proportions of pollinator individuals or flowers visited by each pollinator type). Observed means of interspecific dissimilarity in pollinator composition were smaller than randomly simulated values in the order-, family-, and genus-defined pollinator niche spaces. This finding revealed an underdispersed arrangement of plant species in each of these pollinator niche spaces. In the undisturbed montane habitats studied, arrangement of insect-pollinated plant species in the various niche spaces defined by pollinator composition did not support a major role for interspecific competition as a force shaping community-wide pollinator resource use by plants, but rather suggested a situation closer to the facilitation-dominated extreme in a hypothetical competition-facilitation gradient. Results also highlight the importance of investigations on complete or nearly complete insect-pollinated plant communities for suggesting and testing novel hypotheses on the ecology and evolution of plant-pollinator systems.

Pollen viability of Euro-Mediterranean orchids under different storage conditions: The possible effects of climate change

The future impact of climate change and a warmer world is a matter of great concern. We therefore aimed to evaluate the effects of temperature on pollen viability and fruit set of Mediterranean orchids. The in vitro and controlled pollination experiments were performed to evaluate the ability of pollinia stored at lower and higher temperatures to germinate and produce fruits and seeds containing viable embryos. In all of the examined orchids, pollen stored at -20 °C remained fully viable for up to 3 years, reducing its percentage germination from year 4 onwards. Pollinia stored at higher temperatures had a drastic reduction in vitality after 2 days at 41-44 °C, while pollinia stored at 47-50 °C did not show any pollen tube growth. The different levels of pollen viability duration among the examined orchids can be related to their peculiar reproductive biology and pollination ecology. The germinability of pollinia stored at lower temperatures for long periods suggests that orchid pollinia can be conserved ex situ. In contrast, higher temperatures can have harmful effects on the vitality of pollen and consequently on reproductive success of the plants. To our knowledge, this is the first report demonstrating the effects of global change on orchid pollen, and on pollen ability to tolerate, or not, higher air temperatures. Although vegetative reproduction allows orchids to survive a few consecutive warm years, higher temperatures for several consecutive years can have dramatic effects on reproductive success of orchids.

Floral scent in Iris planifolia (Iridaceae) suggests food reward

Iris species can adopt different pollination strategies to attract their pollinators, generalized shelter-mimicking, specialized deceptive sexual-mimicking or food-rewarding. As attractive stimuli, Iris flowers may use their colours, large-size, symmetry, and volatile organic compounds (VOCs). However, relatively few studies investigated Iris floral olfactory cues in the context of plant-visitor/pollinator interactions. In the present study we combined the identification of the floral volatiles of the nectariferous I. planifolia with insects visiting its flowers to gather data on its biology. Floral volatiles were collected in the natural environment by dynamic headspace and analysed by gas chromatography-mass spectrometry (GC-MS). Insect visitors/pollinators were also recorded. The volatile bouquet was aromatic-dominated with 1,4 dimethoxybenzene as major compound. Among the insects visiting its flowers, bumble and honey bees were the most abundant followed by hover flies. Overall, our results suggest that I. planifolia advertises its food reward by an aromatic dominated volatile composition.