Neutral processes contribute to patterns of spatial variation for flower colour in the Mediterranean Iris lutescens (Iridaceae).

BACKGROUND AND AIMS: Flower colour polymorphism in plants has been used as a classic model for understanding the importance of neutral processes vs. natural selection in population differentiation. However, current explanations for the maintenance of flower colour polymorphism mainly rely on balancing selection, while neutral processes have seldom been championed. Iris lutescens (Iridaceae) is a widespread species in the northern Mediterranean basin, which shows a stable and striking purple-yellow flower colour polymorphism. To evaluate the roles of neutral processes in the spatial variation for flower colour in this species, patterns of neutral genetic variation across its distribution range were quantified, and phenotypic differentiation was compared with neutral genetic differentiation. METHODS: Genetic diversity levels and population genetic structure were investigated through the genotyping of a collection of 1120 individuals in 41 populations ranging from Spain to France, using a set of eight newly developed microsatellite markers. In addition, phenotypic differentiation for flower colour was also quantified by counting colour morph frequency in each population, and measuring the reflectance spectra of sampled individuals. KEY RESULTS: Populations in Spain present a sharp colour transition from solely purple to solely yellow. The results provide evidence that genetic drift through limited gene flow is important in the evolution of monomorphic populations. In contrast, most populations in France are polymorphic with both phenotypes, and the colour frequencies vary geographically without any spatial gradients observed. A pattern of isolation by distance is detected in France, and gene flow between adjacent populations seems to be an important factor maintaining populations polymorphic. CONCLUSIONS: Overall, neutral processes contribute to patterns of spatial variation for flower colour in I. lutescens, but it cannot be excluded that natural selection is also operating. An interaction between neutral processes and natural selection is suggested to explain the spatial variation for flower colour in I. lutescens.

Competition, salinity, and clonal growth in native and introduced irises.

PREMISE OF THE STUDY: Iris pseudacorus spread rapidly into North America after introduction from Europe in the 1800s and now co-occurs with native I. hexagona in freshwater Louisiana wetlands. Native irises support and interact with multiple trophic levels, whereas I. pseudacorus is classified an invasive pest because it grows aggressively, reduces biodiversity, and displaces native vegetation. Salinity levels are increasing in coastal wetlands worldwide. We examined how salt-stress affects competitive interactions between these conspecifics. METHODS: We established a three-way full-factorial common-garden experiment that included species (I. pseudacorus, I. hexagona), competition (no competition, intraspecific competition, and interspecific competition), and salinity (0, 4, 8 parts per thousand NaCl), with six replicates per treatment. KEY RESULTS: After 18 mo, Iris pseudacorus produced much more biomass than the native species did (F1, 92 = 71.5, P < 0.0001). Interspecific competition did not affect the introduced iris, but biomass of the native was strongly reduced (competition × species interaction: F2, 95 = 76.7, P = 0.002). Salinity significantly reduced biomass of both species (F2, 92 = 21.8, P < 0.0001), with no species × salinity interaction (F2, 84 = 1.85, P = 0.16). CONCLUSIONS: Our results demonstrate that salt stress strongly reduced clonal reproduction in native and introduced irises; however, the introduced iris had a competitive advantage over the native, regardless of environmental salinity levels. Based on patterns in clonal reproduction, the introduced iris could potentially threaten native iris populations. We are currently investigating seed production and mortality during competition and stress because both clonal and sexual reproduction must be considered when predicting long-term population dynamics.

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

Reproductive success of plants may be affected by interactions with co-flowering species either negatively, through competition for pollinators, or positively, by means of a magnet species effect and floral mimicry. In this study, potential interactions between Iris tuberosa, a rewarding species, and Ophrys fusca, a sexually deceptive orchid, were explored in four populations in southern Italy. In each population plots showing different ratios of the examined species were arranged in the field, and in each plot the number of pollinators and fruit set were assessed. In addition, flower size and floral hydrocarbons produced by the two species were analysed. Morphological and scent data pointed out that flower size and aliphatic compounds did not differ significantly between the two species. Interestingly, both species shared tricosane and 11-nonacosene, electrophysiologically active compounds in the shared dominant pollinator Adrena. We have found that fruit production and number of pollinators in I. tuberosa varied significantly among plots, while percentage of capsules and number of pollinators of O. fusca captured showed no significant differences across plots. These results suggested, that the presence of O. fusca contributes differentially to pollinator attraction, and thus, to total reproductive success of I. tuberosa, according to a different ratio of aggregation. These findings suggest that I. tuberosa profits from the greater abundance of insects attracted by the presence of orchid specimens, and that a sexually deceptive orchid may be a magnet species in pollination strategy.

Are pollinators the agents of selection for the extreme large size and dark color in Oncocyclus irises?

Pollinator-mediated selection is a major evolutionary driver of floral traits; yet, such selection has rarely been tested for floral extreme traits. The Oncocyclus irises have exceptionally large, dark-colored flowers, associated with night-sheltering pollination and heat reward by the dark flowers. We quantified phenotypic selection on stem length, floral size and color in two species of iris (Iris atropurpurea and I. haynei), using an experimental approach. We estimated selection gradients for both flowers open to natural pollination and for flowers receiving supplementary hand pollination, assuming that open-pollinated flowers are affected by all factors that could influence fitness, whereas supplementary pollination removes the possible influence of pollinators. We found evidence for pollinator-mediated selection to increase floral size and stem length in I. atropurpurea, but floral color in this species was not under pollinator-mediated selection. In I. haynei, no pollinator-mediated selection on any of the traits was detected. We conclude that the extreme floral size of I. atropurpurea has probably evolved as a result of pollinator behavior. Lack of such evidence for I. haynei and for the dark floral color in both species suggests that other non-pollinator agents are selecting for these prominent traits, or that phenotypic color variation in these irises is neutral.

Brackish Eutrophic Water Treatment by Iris pseudacorus L.-Planted Microcosms: Physiological Responses of Iris pseudacorus L. to Salinity.

Iris pseudacorus L. has been widely used in aquatic ecosystem to remove nutrient and has achieved positive effects. However, little is known regarding the nutrient-removal performance and physiological responses of I. pseudacorus for brackish eutrophic water treatment due to high nutrients combined with certain salinity levels. In this study, I. pseudacorus-planted microcosms were established to evaluate the capacity of I. pseudacorus to remove excessive nutrients from fresh (salinity 0.05%) and brackish (salinity 0.5%) eutrophic waters. The degradation of total nitrogen and ammonia nitrogen were not affected by 0.5% salinity; 0.5% salinity promoted the degradation of nitrate nitrogen while severely inhibited the degradation of total phosphorus. Additionally, 0.5% salinity was found to induce stress responses quantified by measuring six physiological indexes. Compared to 0.05% salinity, 0.5% salinity resulted in significant decreases in the chlorophyll a, b and total chlorophyll contents of I. pseudacorus which closely related to photosynthesis (p < 0.05). Furthermore, the higher proline, malondialdehyde contents and antioxidant enzyme activities were detected in I. pseudacorus exposed to 0.5% salinity, which provided protection against reactive oxygen species. The results highlight that the cellular stress assays are efficient for monitoring the health of I. pseudacorus in salinity shock-associated constructed wetlands.

Positive effect of the yellow morph on female reproductive success in the flower colour polymorphic Iris lutescens (Iridaceae), a deceptive species.

The deceptive Iris lutescens (Iridaceae) shows a heritable and striking flower colour polymorphism, with both yellow- and purple-flowered individuals growing sympatrically. Deceptive species with flower colour polymorphism are mainly described in the family Orchidaceae and rarely found in other families. To explain the maintenance of flower colour polymorphism in I. lutescens, we investigated female reproductive success in natural populations of southern France, at both population and local scales (within populations). Female reproductive success was positively correlated with yellow morph frequency, at both the population scale and the local scale. Therefore, we failed to observe negative frequency-dependent selection (NFDS), a mechanism commonly invoked to explain flower colour polymorphism in deceptive plant species. Flower size and local flower density could also affect female reproductive success in natural populations. Pollinator behaviour could explain the positive effect of the yellow morph, and our results suggest that flower colour polymorphism might not persist in I. lutescens, but alternative explanations not linked to pollinator behaviour are discussed. In particular, NFDS, although an appealingly simple explanation previously demonstrated in orchids, may not always contribute to maintaining flower colour polymorphism, even in deceptive species.

The endangered Iris atropurpurea (Iridaceae) in Israel: honey-bees, night-sheltering male bees and female solitary bees as pollinators.

BACKGROUND AND AIMS: The coastal plain of Israel hosts the last few remaining populations of the endemic Iris atropurpurea (Iridaceae), a Red List species of high conservation priority. The flowers offer no nectar reward. Here the role of night-sheltering male solitary bees, honey-bees and female solitary bees as pollinators of I. atropurpurea is documented. METHODS: Breeding system, floral longevity, stigma receptivity, visitation rates, pollen loads, pollen deposition and removal and fruit- and seed-set were investigated. KEY RESULTS: The main wild pollinators of this plant are male eucerine bees, and to a lesser extent, but with the potential to transfer pollen, female solitary bees. Honey-bees were found to be frequent diurnal visitors; they removed large quantities of pollen and were as effective as male sheltering bees at pollinating this species. The low density of pollen carried by male solitary bees was attributed to grooming activities, pollen displacement when bees aggregated together in flowers and pollen depletion by honey-bees. In the population free of honey-bee hives, male bees carried significantly more pollen grains on their bodies. Results from pollen analysis and pollen deposited on stigmas suggest that inadequate pollination may be an important factor limiting fruit-set. In the presence of honey-bees, eucerine bees were low removal-low deposition pollinators, whereas honey-bees were high removal-low deposition pollinators, because they removed large amounts into corbiculae and deposited relatively little onto receptive stigmas. CONCLUSIONS: Even though overall, both bee taxa were equally effective pollinators, we suggest that honey-bees have the potential to reduce the amount of pollen available for plant reproduction, and to reduce the amount of resources available to solitary bee communities. The results of this study have potential implications for the conservation of this highly endangered plant species if hives are permitted inside reserves, where the bulk of Oncocyclus iris species are protected.

Influence of earthworm Eisenia fetida on Iris pseudacorus's photosynthetic characteristics, evapotranspiration losses and purifying capacity in constructed wetland systems.

Four constructed wetland systems were studied to investigate the effects of adding Eisenia fetida on the purifying capacity of constructed wetlands. Addition of E. fetida increased the photosynthetic rate (Pn), transpiration rate (Tr) and chlorophyll meter value of leaves of Iris pseudacorus L. in the constructed wetlands by 16, 35 and 7%, respectively. Compared with the substrate only system, evapotranspiration losses were increased by 8, 48 and 56% for the wetland systems with substrate and E. fetida, with substrate and I. pseudacorus, and with substrate, I. pseudacorus and E. fetida, respectively. Addition of E. fetida to the substrate only and substrate and plant wetland systems decreased the substrate bulk density by 3 and 6%, respectively. The addition of E. fetida to the system with substrate and plants increased the removal efficiency of chemical oxygen demand (CODMn), total nitrogen (TN) and total phosphorus by 5, 7 and 22%, respectively. Evapotranspiration losses were significantly positively correlated with the removal efficiency of CODMn (P < 0.01). The significantly negative correlation between the removal efficiency TN and bulk density was found (P < 0.05). Therefore, E. fetida could stimulate I. pseudacorus growth and improve the substrate bulk density in the constructed wetland, resulting in enhanced purifying capacity.

Differential response of the homoploid hybrid species Iris nelsonii (Iridaceae) and its progenitors to abiotic habitat conditions.

PREMISE OF THE STUDY: Homoploid hybrid speciation involves the evolution of reproductive isolation between a hybrid lineage and its progenitors without a change in chromosome number. Ecological divergence presumably plays a large role in the stabilization of hybrid lineages, as all homoploid hybrid species described to date are reported to be ecologically divergent from their progenitors. However, the described ecological divergence in most systems is anecdotal and has not been empirically tested. METHODS: We assessed the vegetative response of Iris nelsonii, a homoploid hybrid species, and its three progenitor species, I. brevicaulis, I. fulva, and I. hexagona, to different abiotic conditions (i.e., varied sunlight availability and flooding conditions) that largely characterize the habitats of these four species in their natural habitats in Louisiana, USA. KEY RESULTS: The species differed in their responses to the water-level treatment for many of the response variables, including rhizome weight, ramet growth, plant height, and two principal components used to characterize the data. The species differed in their response to the light-level treatment for root allocation and the principal component used to characterize plant size. Iris nelsonii significantly differed from its progenitors, including its most closely related progenitor species, in response to many of the treatments. CONCLUSIONS: The differential response to abiotic habitat conditions of I. nelsonii suggests that this species is ecologically divergent from its progenitor species.

Pollinator behaviour and plant speciation: can assortative mating and disruptive selection maintain distinct floral morphs in sympatry?

• Pollinators, as gene flow vectors and selection agents, play a central role in the origin and maintenance of floral variation in natural populations. However, it is debatable whether pollination alone can complete the speciation process in sympatry. • Mating patterns and phenotypic selection on floral traits were characterized over two flowering seasons for sympatric corolla tube length morphs of the hawkmoth-pollinated iris Gladiolus longicollis. A mating model with genetic and spatial-temporal predictors was developed to identify seed paternity. A multivariate analysis was used to estimate selection on correlated floral traits based on maternal and paternal fitness. • Mating patterns among floral morphs were density dependent, resulting in assortative mating at low plant densities, and random mating among morphs at high densities. Weak disruptive selection on tube length was detected in one season for maternal fitness. Plant height was under opposing directional selection for maternal (+) and paternal (-) fitness functions. • These results indicate that G. longicollis morphs will introgress rather than diverge towards speciation. The lack of strong assortative mating, particularly at high densities, is predicted to result in the loss of rare morphs within populations, and indicates that spatial and temporal co-occurrences of floral morphs are evolutionarily unstable.

[Study on pollen viability and stigma receptivity of 5 Iris plants].

OBJECTIVE: To increase the reproduction efficiency of Iris plants. METHOD: Pollen viability, stigmatic receptivity, the color of anther and stigma of 5 Iris plants were observed during blooming. RESULT: 1. The highest pollen viability was in 4 hours after blooming; 2. The stigmatic receptivities of I. sichuanensis, I. leptophylla, I. lactea and I. goniocarpa were strong in 4 hours after blooming, while that of I. lactea var. chinensis was strong in 2 hours after blooming; 3. The color of anther could reflect the pollen viability, but could not indicate the viability level; 4. The stigma color could not reflect the receptivity of stigma. CONCLUSION: The optimum artificial pollination time of these five species were 12:00 -14:00.

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.

Growth responses of eight wetland species to water level fluctuation with different ranges and frequencies.

Fluctuation range and frequency are two important components of water level fluctuation, but their effects on wetland plants have not been evaluated separately. We subjected eight wetland species to a control treatment with static water level and fluctuation treatments with different ranges or frequencies to examine their effects on plant growth. Acorus calamus, Butomus umbellatus and Iris wilsonii showed high survival rates in all treatments with various fluctuation ranges and frequencies. Their survival rates were higher at the medium fluctuation frequency than at the low and high frequencies, suggesting beneficial effects of the medium frequency. In the experiment comparing the fluctuation ranges, A. calamus and I. wilsonii could maintain the capacity for asexual propagation and accumulate higher biomass compared with the control plants, while biomass of the other six species dramatically decreased. In the experiment comparing fluctuation frequency, species with relatively high survival rates (≥ 50%) maintained or increased the capacity of asexual propagation, and A. calamus and I. wilsonii allocated relatively more biomass to roots, which may enhance plant growth and survival. In contrast, these species did not show increased biomass allocation to shoots in response to both fluctuation range and frequency, presumably because shoots are prone to mechanical damage caused by streaming floodwater. Taken together, biomass accumulation in roots rather than in shoots and the ability to asexually propagate are important for the survival of these species during water fluctuation.

The genetic architecture of reproductive isolation in Louisiana irises: flowering phenology.

Despite the potential importance of divergent reproductive phenologies as a barrier to gene flow, we know less about the genetics of this factor than we do about any other isolating barrier. Here, we report on the genetic architecture of divergent flowering phenologies that result in substantial reproductive isolation between the naturally hybridizing plant species Iris fulva and I. brevicaulis. I. fulva initiates and terminates flowering significantly earlier than I. brevicaulis. We examined line crosses of reciprocal F1 and backcross (BC1) hybrids and determined that flowering time was polygenic in nature. We further defined quantitative trait loci (QTL) that affect the initiation of flowering in each of these species. QTL analyses were performed separately for two different growing seasons in the greenhouse, as well as in two field plots where experimental plants were placed into nature. For BCIF hybrids (BC1 toward I. fulva), 14 of 17 detected QTL caused flowering to occur later in the season when I. brevicaulis alleles were present, while the remaining 3 caused flowering to occur earlier. In BCIB hybrids (BC1 toward I. brevicaulis), 11 of 15 detected QTL caused flowering to occur earlier in the season when introgressed I. fulva alleles were present, while the remaining 4 caused flowering to occur later. These ratios are consistent with expectations of selection (as opposed to drift) promoting flowering divergence in the evolutionary history of these species. Furthermore, epistatic interactions among the QTL also reflected the same trends, with the majority of epistatic effects causing later flowering than expected in BCIF hybrids and earlier flowering in BCIB hybrids. Overlapping QTL that influenced flowering time across all four habitat/treatment types were not detected, indicating that increasing the sample size of genotyped plants would likely increase the number of significant QTL found in this study.

Growth, physiological adaptation, and NHX gene expression analysis of Iris halophila under salt stress.

This study investigated the growth, physiological changes, and the transcript levels of NHX1 gene of Iris halophila in response to low NaCl concentration (50 mM) and high NaCl concentration (150 mM). Our results showed that both 50 and 150 mM NaCl had no obvious negative effects on plant growth; what is more, low NaCl concentration (50 mM) increased root length, root fresh weight, and the ratio of root length to leaf length compared with the control group. The malondialdehyde (MDA) contents in leaves and roots of I. halophila had no obvious difference as compared with control. Proline levels of I. halophila exhibited basically an enhancement under salt stress conditions. Particularly at 4 days, the proline contents in leaves reached 1.85 to 2.31-fold higher and the contents in roots reached 1.27 to 1.62-fold higher than that of control at 50 and 150 mM NaCl, respectively. The contents of the soluble sugar in leaves and roots of I. halophila under 150 mM NaCl at 7 days were 32.4 and 98.7% higher than that of control, respectively. The increase rate of K+ contents with the increasing concentration of salt was less than that of Na+ contents, but K+ contents in the seedlings under NaCl stress was still higher than Na+ contents and the ratio of K+ to Na+ was also greater than 1. The transcript levels of IhNHX1 in leaves of I. halophila at 4 and 7 days under 150 mM NaCl were higher than that of control; however, the transcript levels of IhNHX1 in roots had no significant difference compared with the control under low and high salt stress at 1, 4, and 7 days. Therefore, salt tolerance in I. halophila could be partially due to higher proline, soluble sugar, and K+ accumulation.

Effects of microcystin-LR on the tissue growth and physiological responses of the aquatic plant Iris pseudacorus L.

The release of cyanobacterial toxins during algal bloom has adverse effects on aquatic plants and animals. This study aimed to understand the toxic effects and mechanism of microcystin-LR (MC-LR) on the seedling growth and physiological responses of Iris pseudacorus L. (calamus). After a one-month exposure experiment, the growth and development of the calamus leaves were significantly inhibited, and this inhibitory effect was verified to be concentration dependent. Furthermore, the cell membrane system was damaged, and the photosynthesis was also adversely affected by MC-LR. The relative conductivity of the leaves increased from 10.96% to 97.51%, and the total chlorophyll content decreased from 0.89 mg/g to 0.09 mg/g. Notably, the behavior of the roots in the presence of MC-LR was different from that of the leaves. The seedlings needed to absorb more nutrients to maintain the normal growth at low-toxin concentrations, but the high concentration of (over 250 µg/L) MC-LR exceeded the tolerance of plants and inhibited the growth of roots. In addition, MC-LR led to an excessive accumulation of H2O2, and the seedlings enhanced the activities of catalase, peroxidase, and superoxide dismutase to resist oxidative stress. The presence of MC-LR also affected the capacity of the plants to absorb nitrogen and phosphorus. The removal efficiency of NO3--N, the main source of nitrogen, was 63.53% in the presence of 100 µg/L MC-LR. As a result, the pH increased, and the growth of plants was indirectly inhibited. Therefore, the presence of MC-LR could affect the purification efficiency of calamus in eutrophic water. This study provides theoretical support for the selection of plants in the eutrophic water.

[Effect of phytohormones on plant regeneration in callus culture of Iris ensata Thunb].

The effect of phytohormones on plant regeneration in callus culture of Iris ensata Thunb. was studied. 2,4-Dichlorophenoxyacetic acid (2,4-D) proved to be the most convenient auxin for the induction and subculturing of morphogenic callus. Biogenic calluses were induced from isolated embryos at the wax-ripeness stage in MS medium supplemented with 2,4-D (1.0-2.0 mg/l) and kinetin (0.2-0.5 mg/l). Changes in the medium hormonal composition favor the development of adventitious structures. The setting of vegetative bugs took place in the presence of 6-benzylaminopurine, while the development of shoots and root primordia was observed after 2,4-D replacement with indoleacetic acid (2.0 mg/l). The root initiation in regenerating plants required a hormone-free medium. The properties of seedling growth from native regenerating I. ensata were studied. Analysis of the shoot structure demonstrated that in vitro cultured plants are at the juvenile stage.

Effect of plant species compositions on performance of lab-scale constructed wetland through investigating photosynthesis and microbial communities.

This study focused on the effects of plant compositions on removal rates of pollutants in microcosms through investigating rhizosphere microbial populations, photosynthetic efficiency and growth characteristics. Mixed-culture groups improved the removal efficiency of TN and TP significantly but exhibited lower COD removal rates. Total plant biomasses were improved as the species richness increased, but the N/P content in the plants was mainly affected by the type of species. The mixed-culture groups showed lower photosynthesis rates and oxygen supply generated from roots under high irradiation. Microbial communities of the cultured groups in the rhizosphere exhibited significant differences. According to principal component analysis (PCA), the fungi were the typical microbes of SPA, SPAB, and SPABC, resulted in improvement in nutrient accumulation. These results demonstrated that a mixed culture strategy can represent the overyielding of biomass, promote the photo-protection mechanism, and will further increase the removal rates of pollutants in a constructed wetland.

The inhibition and adaptability of four wetland plant species to high concentration of ammonia wastewater and nitrogen removal efficiency in constructed wetlands.

Four plant species, Typha orientalis, Scirpus validus, Canna indica and Iris tectorum were selected to assess their physiological response and effects on nitrogen and COD removal to high total ammoniacal nitrogen (TAN) in constructed wetlands. Results showed that high TAN caused decreased relative growth rate, net photosynthetic rate, and leaf transpiration. C. indica and T. orientalis showed higher TAN adaptability than S. validus and I. tectorum. Below TAN of 200 mg L(-1), growth of C. indica and T. orientalis was less affected or even stimulated at TAN range 100-200 mg L(-1). However, S. validus and I. tectorum was obviously suppressed when TAN was above 100 mg L(-1). High TAN generated obvious oxidative stress showing increased proline and malondialdehyde contents, and superoxide dismutase was inhibited. It indicated that the threshold for plant self-bioremediation against high TAN was 200 mg L(-1). What's more, planted CWs showed higher nitrogen and COD removal. Removal rate of C. indica and T. orientalis was higher than S. validus and I. tectorum.