Role of plant aeration in zonation of Zizania latifolia and Phragmites australis

The emergent plants Phragmites australis (Cav.) Trin. ex Steud and Zizania latifolia (Griseb.) Stapf. are distributed along a gradient of increasing water depth, with P. australis restricted to shallow water and Z. latifolia to deeper water. The lower limits of the two vegetational zones were discussed from the view-point of oxygen supply from aerial shoots. The oxygen influx to the underground organs from aerial shoots is proportional to the gradient between oxygen concentrations in atmosphere and inside the basal stem (C). The proportional constant (Q), called here the ventilation coefficient, expresses the efficiency of the diffusion of oxygen. An attempt was made to measure Q and C. The values of Q for the two species in their dominant niches are higher in Z. latifolia than in P. australis, corresponding to the natural distribution with increasing depths of water. Q in Z. latifolia and P. australis first increased and then decreased. Corresponding to such changes of Q, the oxygen concentration inside the basal stem (C) fell to low values for Z. latifolia at the greatest water-depth. Since in Z. latifolia a low value of C in deeper waters was accompanied by a decline in standing crop of aerial shoots, it was concluded that oxygen is the limiting factor for the distribution of Z. latifolia in the deeper waters.     

Rapid In Vitro Propagation of East Indian Rosewood (Dalbergia latifolia Roxb.) through High Frequency Shoot Proliferation from Cotyledonary Nodes

An efficient protocol is described for large scale in vitro propagation of east Indian rosewood (Dalbergia latifolia Roxb.) using cotyledonary nodes derived from axenic seedlings. Of the four different cytokinins tested, BA was most effective in inducing multiple shoot buds in the explants. High frequency shoot proliferation (93%) coupled with maximum number of shoot formation (10-12 shoots/explant) was recorded on Murashige and Skoog’s medium supplemented with 2.0 mg/l BA. The frequency of shoot proliferation declined at higher levels of cytokinins. Shoot culture was multiplied by subculturing the original cotyledonary node on a fresh shoot multiplication medium each time aHer excising the newly formed shoots. Shoots obtained from each passage were multiplied further as nodal explants and each node produced 3-4 shoots. In two months from a single cotyledonary node, about 90 shoots were obtained. Rooting was induced in 72% of the regenerated shoots on half-strength MS containing IAA, IBA and IPA each at 1.0 mg/l. Rooted plantlets were hardened off and eventually established in soil.     

Oxygen demand and supply in Zizania latifolia and Phragmites australis

The oxygen demand of underground organs in tall emergent plants was assumed to be supplied with the oxygen flux through aerial shoots. Measurements were made of the respiratory activity of underground organs and oxygen flux through aerial shoots in Zizania latifolia (Griseb.) Stapf and Phragmites australis (Cav.) Trin. ex Steud.Oxygen uptake rates of Z. latifolia roots and rhizomes decreased as the supply of oxygen decreased. Phragmites australis, however, did not respond to decreases in the supply of oxygen until the oxygen supply was relatively low. The values for old rhizomes of P. australis were very low. Most of the oxygen flux for P. australis was derived from standing dead shoots. The important role of dead shoots of P. australis in plant aeration is suggested. The degree of sufficiency of oxygen supply for Z. latifolia was 179% in May and 92% in August. The values for P. australis were 45% both in May and August. Furthermore, estimation of mean oxygen concentration of inner underground organs for P. australis showed very low values, 1.6% both in May and August, even in shallow water.     

Analysis of the Complexity and Diversity of mRNAs from Pollen and Shoots of Tradescantia

The mRNAs of the mature pollen grain of Tradescantia paludosa at anesthesia and of vegetative shoots have been compared by analyzing the kinetics of hybridization between homologous and heterologous reactions of cDNA to poly(A)RNA in excess. The mRNAs in pollen can be divided into three abundance classes with complexities of 5.2 × 10⁴, 1.6 × 10⁶, and 2.1 × 10⁷ nucleotides. The three classes are made up of sequences that constitute 15, 60, and 24% of the mRNAs and each sequence is present on an average at 26,000, 3,400, and 100 copies, respectively, per pollen grain. About 20,000 different genes are expressed in pollen as compared to about 30,000 in vegetative shoots. Estimates have been made of pollen mRNA sequences shared with those of shoot tissue and of shoot sequences common to those in pollen.     

Maturation timing of stamens and pistils in the dioecious plant Silene latifolia

The dioecious plant Silene latifolia depends on nocturnal insects for pollination. To increase the chance of cross-pollination, pollen grains seem to be released and stigmas seem to be receptive simultaneously at night. We divided the floral development of S. latifolia into 1–20 stages, and determined the timetables of male and female function. The corolla of both male and female flowers opens at sunset (1900 hours) and closes at sunrise (0900 hours). To investigate the period of the reproductive phase of male and female function, we measured the germination rate on a pollen medium and the pollen germination rate on stigma during the period when stamens and stigmas were viable in the timetable. Male flowers had early- and late-maturing stamens that had the highest pollen viability, germination rate and pollen tube growth at midnight (0000 hours) at 1 day after flowering (DAF) and 0000 hours at 2 DAF. In contrast, female flowers maintained a germination rate of nearly 100 % from 1800 hours at 1 DAF to 1200 hours at 3 DAF. These results suggested that S. latifolia transferred the matured pollen grains from male flowers to female flowers only at night.     

Fine-scale genetic structure of Nothofagus pumilio (lenga) at contrasting elevations of the altitudinal gradient

Montane forests provide the natural framework to test for various ecological settings at distinct elevations as they may affect population demography, which in turn will affect the spatial genetic structure (SGS). We analyzed the fine-scale SGS of Nothofagus pumilio, which dominates mountain areas of Patagonia, in three pairs of sites at contrasting elevations (low- vs. high-elevation). Within a total area of 1 ha fresh leaf tissue from 90 individuals was collected at each of the six studied stands following a spatially explicit sampling design. Population genetic diversity parameters were analyzed for all sampled individuals using five polymorphic isozyme loci, and a subset of 50 individuals per stand were also screened for five microsatellite loci. The SGS was assessed on 50 individuals/stand, using the combined datasets of isozymes and microsatellites. Most low-elevation stands consisted of older individuals with complex age structures and genetically diverse plots. In contrast, high-elevation stands and one post-fire low-elevation population yielded even-aged structures with evidence of growth suppression, and were genetically homogeneous. All stands yielded significant SGS. Similarly to mature stands of the non-sprouter congener Nothofagus dombeyi, multi-age low-altitude N. pumilio yielded significant SGS weakened by competing species of the understory and the formation of seedling banks. Alike the sprouter Nothofagus antarctica, high-altitude stands produced significant SGS as a consequence of occasional seedling establishment reinforced by vegetative spread.     

Ecology of vegetative regeneration after coppicing in macchia stands in central Italy

Vegetative regeneration after coppicing of Quercus ilex, Phillyrea latifolia, and Fraxinus ornus in two macchia stands in the Maremma Nature Park (Grosseto, Italy) has been studied.Observations during the first three years after the cut showed that horizontal space occupation by shoots is rapid (95% of the available space being reoccupied within 3 yrs.) and stool mortality very low. We observed differences among species in resprouting, growth pattern and shoot differentiation. Q. ilex and P. latifolia had a longer budburst period than F. ornus. There were no considerable differences in height growth among the three species in the first year. During the second and third years the height increments decreased. F. ornus average height increments were higher than those of Q. ilex and P. latifolia. These two species produced proleptic flushes from the first year on, while F. ornus only showed spring flush. The examination of proleptic shoots and of summer and autumn rainfall seem to show that the latter control Q. ilex growth and shoot differentiation more than that of other species. Differentiation among shoots of the same stool occurs from the first year onwards and the initial vigour differences amongst shoots remain during the following years. Resprouting, space occupation and shoot differentiation have been discussed in relation to rainfall and temperature.The high stool survival and the strong link between stool vigour parameters before and after coppicing confirm a certain stability in successional dynamics following a single coppicing event.Abbreviations CA Crown Projection Area - DBH Diameter at Breast Height (1.30 m) - F. ornus Fraxinus ornus - G Basal area at Breast Height (1.30 m) - HD Height of the dominant shoot per stool - ND Number of the dominant shoots per stool - P. latifolia Phillyrea latifolia - Q. ilex Quercus ilex     

Asymmetrical conspecific seed-siring advantage between Silene latifolia and S. dioica

Background and Aims

Silene dioica and S. latifolia experience only limited introgression despite overlapping flowering phenologies, geographical distributions, and some pollinator sharing. Conspecific pollen precedence and other reproductive barriers operating between pollination and seed germination may limit hybridization. This study investigates whether barriers at this stage contribute to reproductive isolation between these species and, if so, which mechanisms are responsible.

Methods

Pollen-tube lengths for pollen of both species in styles of both species were compared. Additionally, both species were pollinated with majority S. latifolia and majority S. dioica pollen mixes; then seed set, seed germination rates and hybridity of the resulting seedlings were determined using species-specific molecular markers.

Key Results

The longest pollen tubes were significantly longer for conspecific than heterospecific pollen in both species, indicating conspecific pollen precedence. Seed set but not seed germination was lower for flowers pollinated with pure heterospecific versus pure conspecific pollen. Mixed-species pollinations resulted in disproportionately high representation of nonhybrid offspring for pollinations of S. latifolia but not S. dioica flowers.

Conclusions

The finding of conspecific pollen precedence for pollen-tube growth but not seed siring in S. dioica flowers may be explained by variation in pollen-tube growth rates, either at different locations in the style or between leading and trailing pollen tubes. Additionally, this study finds a barrier to hybridization operating between pollination and seed germination against S. dioica but not S. latifolia pollen. The results are consistent with the underlying cause of this barrier being attrition of S. dioica pollen tubes or reduced success of heterospecifically fertilized ovules, rather than time-variant mechanisms. Post-pollination, pre-germination barriers to hybridization thus play a partial role in limiting introgression between these species.     

Food supplementation affects interactions between a phytoseiid predator and its omnivorous prey

The beneficial effect of food supplements in supporting populations of generalist arthropod predators in agricultural systems has been shown to enhance pest control. When providing additional foods in a crop that is attacked by an omnivorous pest, food supplements may be available to both pest and predator populations resulting in more complex interactions. We assessed the consequences of adding extra food sources to a tritrophic system in the laboratory, consisting of leaf discs of kidney bean plants (Phaseolus vulgaris), western flower thrips Frankliniella occidentalis (Thysanoptera: Thripidae) and the predatory mite Amblydromalus limonicus (Acari: Phytoseiidae). The supplemental food sources tested were cattail pollen, Typha latifolia, dry decapsulated cysts of the brine shrimp, Artemia franciscana (Branchiopoda: Artemiidae) and eggs of the Mediterranean flour moth, Ephestia kuehniella (Lepidoptera: Pyralidae). Larvae of F. occidentalis were observed to feed on all three food sources when applied to bean leaves. The immature development time of F. occidentalis was significantly shorter when T. latifolia pollen was provided compared to bean leaves only and bean leaves supplemented with A. franciscana or E. kuehniella. The predation rate of A. limonicus females on first instars of F. occidentalis decreased with about 30% irrespective of food type supplemented to the leaf discs. The presence of additional foods reduced antipredator behavior of F. occidentalis larvae killing predator eggs. Thrips larvae did not attack eggs of A. limonicus when cattail pollen was added to the leaf discs, whereas 2.5 predator eggs per day were consumed without food supplementation. Leaf damage decreased substantially when Typha pollen was present on the leaf discs. The findings of this study indicate that food supplementation shifts tritrophic interactions both top-down and bottom-up and may affect the outcome of an augmentative biological control program.     

The effect of sewage sludge flooding on growth and morphometric parameters of Phragmites australis (Cav.) Trin. ex Steudel

Phragmites australis is the most frequently used species in constructed wetlands (CW) for dewatering and mineralization of sludge. Such CW create a very hostile environment for plants because their roots are exposed to permanently anaerobic conditions. Our working hypothesis assumed a simple relationship between the success of reed in colonising sludge flood stands and maximalisation of shoot oxygen production and transport to rhizomes and roots. Morphometric parameters and density of common reed shoots growing in reed bed systems inundated with sewage sludge were investigated. It was proved that flooding with sewage sludge significantly influenced characteristics of common reed populations. In comparison with natural stands, on stands treated with sewage sludge, maximal density of shoots was higher, biomass was twice as high, shoot diameter was significantly greater, and leaf weight ratio of an individual shoot was also significantly higher. Tendency to shorten shoots was noted. Growing period was longer for reed shoots treated with sewage sludge than on natural stands.     

Contrasting foliar responses to drought in Quercus ilex and Phillyrea latifolia

Leaf morphology, longevity, and demography were examined in Quercus ilex and Phillyrea latifolia growing in a holm oak forest in Prades mountains (northeast Spain). Four plots (10 × 15 m) of this forest were submitted to an experimental drought during three years (soil moisture was reduced about 15 %). Leaf area, thickness and leaf mass per area ratio (LMA) were measured in sun and shade leaves of both species. Leaf longevity, the mean number of current-year shoots produced per previous-year shoot (Sn/Sn-1), the mean number of current-year leaves per previous-year shoot (Ln/Sn-1), and the percentage of previous-year shoots that developed new ones were measured once a year, just after leaf flushing. LMA and leaf thickness increased since leaf unfolding except in summer periods, when stomatal closure imposed low photosynthetic rates and leaves consumed their reserves. LMA, leaf area, and leaf thickness were higher in Q. ilex than in P. latifolia, but leaf density was higher in the latter species. Drought reduced the leaf thickness and the LMA of both species ca. 2.5 %. Drought also increased leaf shedding up to ca. 20 % in Phillyrea latifolia and decreased it up to ca. 20 % in Q. ilex. In the later species, Sn/Sn-1 decreased by 32 %, Ln/Sn-1 by 41 %, percentage of shoots developed new ones by 26 %, and leaf area by 17 %. Thus the decrease of leaf number and area was stronger in the less drought-resistant Q. ilex, which, under increasingly drier conditions, might lose its current competitive advantage in these Mediterranean holm oak forests.     

The functional response ofTyphlodromus pyri to its prey,Panonychus ulmi: the effect of pollen

We looked at the effect of the presence of pollen (Typha latifolia) on the functional response ofTyphlodromus pyri (Phytoseiidae) toPanonychus ulmi (Tetranychidae) in the laboratory. We found that pollen significantly reduced the predation rate but that the magnitude of the effect was not large. Over the lower range of prey densities the effect appeared to be due to a decrease in search efficiency.     

Seasonal changes in the growth of clones ofTypha latifolia L. in natural conditions

The paper describes in quantitative terms the vegetative spreading of clones ofTypha latifolia in natural conditions. The highest rates of the formation of new shoots during the growing season were recorded in the summer (July to early August) and in the autumn (September to October): this corresponds to the two maxima in the increments in rhizome biomass. The highest rate of expansion was observed in two-year clones in which the annual increment in the colony diameter amounted up to 4 m. The relations between the rhizome and shoot growth in one-year and two-year clones are also discussed and a brief comparison of the results with data found in fully developed stands is included.     

The Significance of Root Starch in Post-fire Shoot Recovery of the Resprouter Stirlingia latifolia R. Br. (Proteaceae)

Stirlingia latifolia, a common shrub of Banksia woodlands ofSW Australia, is a highly successful resprouter species recoveringfrom fire by multiple sprouting of new shoots from its upperroot stock. in comparison with the congeneric fire-sensitive(obligate seeder) species Stirlingia tenuifolia it exhibitsa low shoot:root dry weight ratio and high concentrations ofstored starch in the cortical tissue of its roots. The relationshipbetween root reserves of starch and development of newly sproutingshoot material following fire is examined in S. latifolia afterspring and summer burns. During the initial 2-5 month periodafter fire, levels of stored starch in the roots fall by 50-75%,followed by a slow increase as plants reproduce and the attainmentof pre-fire starch levels by 1·5-2 years after the fire.Starch reserves of roots can be further reduced by shading theregenerating shoots to limit their input of photosynthates andalmost totally eliminated by monthly removal of successive flushesof new shoots over a 10-12 month period. New shoots continueto sprout until all the starch is eliminated. The data are discussedin relation to the fire-induced reproduction of S. latifoliaand its ability to thrive in very frequently burnt habitats.Copyright1993, 1999 Academic Press Fire response, Proteaceae, resprouter, shoot:root ratio, starch storage, Stirlingia latifolia     

An analysis of the quantity and diversity of messenger RNAs from pollen and shoots of Zea mays

Summary The mRNAs of the mature pollen grain of Zea mays and of vegetative shoots were analyzed by comparing the kinetics of hydridization between homologous and heterologous reactions of cDNA to poly-(A)RNA in excess. The total complexity of pollen poly-(A)RNA i s 2.4×10⁷ nucleotides, whereas in the seedling shoot it is 4.0×10⁷ nucleotides. This corresponds to 24,000 different sequences in pollen and about 31,000 diverse mRNAs in shoots. The mRNAs in pollen can be divided into three abundance classes that constitute 35%, 49% and 15% of the total mRNAs having complexities of 2.1×10⁵, 6.4×10⁶ and 1.8×10⁷ nucleotides, respectively. Estimates have been made of the number of copies of each sequence per pollen grain or shoot cell, and also of the pollen mRNA sequences shared with those of the shoot.     

Linkage Disequilibrium between Allozymes in Natural Populations of Lodgepole Pine

Pairwise linkage disequilibrium values (D) were estimated for 14 allozyme loci in two natural populations of lodgepole pine (Pinus contorta ssp. latifolia). Maternal multilocus genotypes were inferred from samples of (haploid) megagametophytic seed-endosperms. Coupling/repulsion double heterozygotes were distinguished for closely linked pairs of loci. Assays of seven of the loci in seed embryos allowed estimates of D for these loci in the outcross pollen pool (estimates of outcrossing rates indicate no significant departures from random mating in either population). No disequilibrium was observed between unlinked loci in either maternal genotypes or outcross pollen. However, significant disequilibrium was observed within and between gametes for some allelic combinations of four tightly linked loci; the assumption of random association of gamete types within individuals is thus invalid for some loci in lodgepole pine. Possible causes of the observed D were examined using the noncentrality parameter of the general noncentral chi square distribution. We concluded, from estimates of population size, linkage and measurements of population substructure, that neither drift nor population subdivision was responsible for the significant values of D which were observed and that epistatic selection was the most likely cause of the disequilibrium observed.     

Effects of stand size on pollination in temperate populations of the mangrove Avicennia marina

Populations of the mangrove Avicennia marina in the Sydney region exist as stands of varying size, reflecting both natural and anthropogenic fragmentation. We hypothesised that, as observed in many terrestrial forests, small stands (<100 plants) would experience lower pollinator densities and altered pollinator behaviour and visitation and, in consequence, would display reduced pollen deposition as compared with large stands (>10,000 plants). Nevertheless, we recognise that such predictions may be overly simplistic because within this region A. marina attracts a diversity of flower visitors, but its only significant pollinator is the exotic honeybee Apis mellifera. Moreover, it is unclear how readily A. mellifera moves among groups of plants within different mangrove stands of varying sizes separated either by water or urban habitat matrix. Our detailed surveys within pairs of large and small stands in two locations support the predictions that pollinator density and pollen deposition are reduced or altered within small stands. Within small stands honeybee abundance and pollen deposition were on average reduced significantly by 84 and 61 %, respectively. Moreover, within small stands there was a non-significant 12 % increase in the mean time that honeybees spent foraging on individual plants and hence potentially depositing self pollen. Taken together, our data indicate that fragmentation affects the performance of A. mellifera as a pollinator of A. marina and reduce pollinator abundance, leading to pollen limitation in small as compared to large stands, which may negatively affect reproductive output.     

High Rates of Gene Flow by Pollen and Seed in Oak Populations across Europe

Gene flow is a key factor in the evolution of species, influencing effective population size, hybridisation and local adaptation. We analysed local gene flow in eight stands of white oak (mostly Quercus petraea and Q. robur, but also Q. pubescens and Q. faginea) distributed across Europe.Adult trees within a given area in each stand were exhaustively sampled (range [239, 754], mean 423), mapped, and acorns were collected ([17,147], 51) from several mother trees ([3], [47], 23). Seedlings ([65,387], 178) were harvested and geo-referenced in six of the eight stands. Genetic information was obtained from screening distinct molecular markers spread across the genome, genotyping each tree, acorn or seedling. All samples were thus genotyped at 5–8 nuclear microsatellite loci. Fathers/parents were assigned to acorns and seedlings using likelihood methods. Mating success of male and female parents, pollen and seed dispersal curves, and also hybridisation rates were estimated in each stand and compared on a continental scale.On average, the percentage of the wind-borne pollen from outside the stand was 60%, with large variation among stands (21–88%). Mean seed immigration into the stand was 40%, a high value for oaks that are generally considered to have limited seed dispersal. However, this estimate varied greatly among stands (20–66%). Gene flow was mostly intraspecific, with large variation, as some trees and stands showed particularly high rates of hybridisation.Our results show that mating success was unevenly distributed among trees. The high levels of gene flow suggest that geographically remote oak stands are unlikely to be genetically isolated, questioning the static definition of gene reserves and seed stands.     

Cytology of five species of subfamily Papaveroideae from the Western Himalayas

During the present course, population-based meiotic studies were carried out on five species of subfamily Papaveroideae from selected localities of Kashmir and Himachal Pradesh in the Western Himalayas (India). Varied intraspecific chromosome counts were reported for the first time in Argemone mexicana and Meconopsis latifolia, both existing on 2n?=?2x?=?14. The x?=?7, confirmed for the first time from the newly found diploid cytotype, is suggested to be the primary chromosomal basic number for the Meconopsis. Furthermore, meiotic course was noted to be normal in Argemone ochroleuca, it varied from normal to abnormal in the populations of A. mexicana and Papaver dubium whereas it was invariably found to be abnormal in all the populations of Meconopsis aculeata and M. latifolia. These anomalous taxa were marked with meiotic abnormalities in the form of cytomixis, chromosomal stickiness, unoriented bivalents, formation of laggards and bridges resulting in abnormal microsporogenesis, and production of heterogeneous-sized fertile pollen grains along with reduced pollen fertility.     

Analysis of pollen proteins of Typha species in relation to identification of hybrids

Hybridization studies have been carried out with Typha angustifolia, T. latifolia, T. shuttleworthii and T. minima. All combinations, except those with T. minima, were successful. The hybrid $\text{T. latifolia (♀) × T. angustifolia (♂)}$ has been obtained after 5 attempts involving hundreds of pollinations. The pollen proteins of the parental as well as the F₁ generation have been examined by isoelectrofocusing (IEF). The proteins from each species and each hybrid form displayed a distinct and constant pattern. The pollen protein profile thus represents a new, quite easily accessible character by which F₁ hybrids between the species studied can be unequivocally identified, whereas the morphological criteria described in the literature to distinguish intermediate forms is insufficient for this purpose.