Density and distribution of seeds in bottom sediments in Zostera marina beds in Ago Bay,central Japan

The density of Zostera marina L. seeds in bottom sediments was examined to study the reproductive patterns of the Z. marina population in Ago Bay, Mie Prefecture, central Japan.Seeds and seed coats were numerous in Tategami, where the annual type of Z. marina grows. In contrast, seeds were scarce in Hamajima, where the perennial type of Z. marina grows. Bottom sediment was sampled with sediment cores at Tategami in November 2004 and March 2005 to examine density and depth distribution of the seeds. Seeds were found as deep as 8 cm, but no deeper. On the other hand, empty seed coats were found as deep as 16 cm in both months. In the upper layers of the sediment to a depth of 8 cm, the average number of seed coats was 7960 ± 2997 m⁻² in November and 16,318 ± 2922 m⁻² in March. Deeper than 8 cm, the number of seed coats gradually decreased owing to decomposition, and none was found below 16 cm. We used the density of reproductive shoots and number of seeds per spadix in Tategami to estimate the fate of seeds and seed coats of the annual type of Z. marina in bottom sediments: out of the 6000 seeds m⁻² produced annually, 72% disappears from the stand and 28% is buried locally. The density and distribution of Z. marina seeds are among the most important factors in maintenance and propagation of the annual population at Tategami.     

Interactive effects of salinity and water depth on the growth of Melaleuca ericifolia Sm. (Swamp paperbark) seedlings

Melaleuca ericifolia Sm. (Swamp paperbark) is a common tree species in freshwater and brackish wetlands in southern and eastern Australia. The survival of this species in many wetlands is now threatened by increased salinity and inappropriate water regimes. We examined the response of 5-month-old M. ericifolia seedlings to three water depths (exposed, waterlogged and submerged) at three salinities (2, 49 and 60 dS m⁻¹). Increasing water depth at the lowest salinity did not affect survival, but strongly inhibited seedling growth. Total biomass, leaf area and maximum root length were highest in exposed plants, intermediate in waterlogged plants and lowest in submerged plants. Although completely submerged plants survived for 10 weeks at the lowest salinity, they demonstrated negative growth rates and were unable to extend their shoots above the water surface. At the higher salinities, M. ericifolia seedlings were intolerant of waterlogging and submergence: all plants died after 9 weeks at 60 dS m⁻¹. Soil salinities increased over time, and by Week 10, exceeded external water column salinities in both the exposed and waterlogged treatments. In exposed sediment, ∼90% of plants survived for 10 weeks at 60 dS m⁻¹ even though soil salinities reached ∼76 dS m⁻¹. No mortality occurred in the exposed plants at 49 dS m⁻¹, and small but positive relative growth rates were recorded at Week 10. We conclude that at low salinities M. ericifolia seedlings are highly tolerant of sediment waterlogging, but are unlikely to tolerate prolonged submergence. However, at the higher salinities, M. ericifolia seedlings are intolerant of waterlogging and submergence and died rapidly after 5 weeks exposure to this combination of environmental stressors. This research demonstrates that salinity may restrict the range of water regimes tolerated by aquatic plants.     

Trace amounts of nickel in belowground rhizomes of Vaccinium myrtillus L. decrease anthocyanin concentrations in aerial shoots without water stress

Nickel (Ni) may impair plant water balance through detrimental effects on the belowground level. Bilberry (Vaccinium myrtillus L.) plants were grown in a mesic heath forest-type soil and subjected to Ni sulphate (NiSO₄·6H₂O) concentrations of 0, 10, 50, 100 and 500 mg m⁻² during an entire growing season in northern Finland (65°N). Biomass of belowground rhizomes, and tissue water content (TWC) and anthocyanin concentrations of aerial shoots were determined from mature plants in order to study rhizospheric Ni stress, and its possible long-distance effects on aerial shoots. As the major proportion of biomass of bilberry is invested in belowground parts, it was hypothesised that Ni-induced rhizospheric disturbance causes water stress in aerial shoots and increases their anthocyanin concentrations for osmotic regulation. Uptake of Ni from the soil to the rhizome and aerial shoots was measured with X-ray fluorescence spectrometry. Ni concentrations in the soil and rhizome exhibited a dose–response relationship, but the concentrations in the rhizome were about 10-fold lower (<3 mg Ni kg⁻¹) than those in the soil (<30 mg Ni kg⁻¹). Translocation of Ni from the rhizome to aerial shoots did not occur, as Ni concentrations in shoots remained at 1 mg Ni kg⁻¹. Although Ni concentrations in the rhizome were below the threshold values of Ni toxicity (i.e. 10–50 mg Ni kg⁻¹), Ni decreased the rhizome biomass. Anthocyanins decreased in aerial shoots along with the Ni accumulation in the rhizome, while TWC was unaffected. The result suggests that anthocyanins are not involved in osmotic regulation under Ni stress, since anthocyanins in aerial shoots responded to the Ni concentrations in the rhizome despite the lack of water stress.     

The seed ecology of an ornamental wattle in South Africa — Why has Acacia elata not invaded a greater area?

Australian Acacia species introduced to South Africa as ornamentals have notably smaller invasive ranges than those introduced for forestry or dune stabilization. We asked whether the relatively small invasive extent of Acacia elata, a species used widely for ornamental purposes, is due to low rates of reproduction. Age at reproductive maturity, seed dispersal, annual seed production, seed bank dynamics and seed germination and viability were assessed at five sites in the Western Cape. Results indicate that A. elata has similar traits to other invasive Australia Acacia species: annual seed input into the leaf litter was high (up to 5000 seeds m^− 2); large seed banks develop (> 20,000 seeds m^− 2) in established stands; seed germinability is high (> 90%); seeds accumulate mostly in the top soil layers but can infiltrate to depths of 40 cm; and seed germination appears to be stimulated by fire. However the age at the onset of reproduction (~ 4 years) is longer than most widespread invaders (~ 3 years) and dispersal is fairly limited (seeds fell up to distances of 6 m from the parent canopy; the highest density of seed rain was found directly under the canopy with over 20% of seeds falling directly under the terminal branches). We suggest that the current limited distribution of invasive A. elata populations is the result of the relatively small size of initial populations (cf. large plantations and widespread plantings for forestry and dune stabilization species), the species' apparent lack of secondary dispersal vectors, and the planting of trees in gardens and urban settings offer limited opportunities for recruitment, proliferation and spread. The species is, however, increasing in abundance and range. We propose methods to improve management of invasions of the species. Management to reduce seed production of this species through classical biological control, as has been achieved for other Australian Acacia species in South Africa, should be prioritised.     

Role of iron plaque in Cd uptake by and translocation within rice (Oryza sativa L.) seedlings grown in solution culture

A hydroponics culture experiment was conducted to investigate the effect of iron plaque on Cd uptake by and translocation within rice seedlings grown under controlled growth chamber conditions. Rice seedlings were pre-cultivated for 43 days and then transferred to nutrient solution containing six levels of Fe (0, 10, 30, 50, 80 and 100 mg L⁻¹) for 6 days to induce different amounts of iron plaque on the root surfaces. Seedlings were then exposed to solution containing three levels of Cd (0, 0.1 and 1.0 mg L⁻¹) for 4 days. In order to differentiate the uptake capability of Cd by roots with or without iron plaque, root tips (white root part without iron plaque) and middle root parts (with iron plaque) of pre-cultivated seedlings treated with 0, 30 and 50 mg L⁻¹ Fe were exposed to ¹⁰⁹Cd for 24 h. Reddish iron plaque gradually became visible on the surface of rice roots but the visual symptoms of the iron plaque on the roots differed among treatments. In general, the reddish color of the iron plaque became darker with increasing Fe supply, and the iron plaque was more homogeneously distributed all along the roots. The Fe concentrations increased significantly with increasing Fe supply regardless of Cd additions. The Cd concentrations in dithionite–citrate–bicarbonate (DCB)-extracts and in shoots and roots were significantly affected by Cd and Fe supply in the nutrient solution. The Cd concentrations increased significantly with increasing Cd supply in the solution and were undetectable when no Cd was added. The Cd concentrations in DCB-extracts with Fe supplied tended to be higher than that at Fe₀ at Cd_0.1, and at Cd_1.0, DCB-Cd with Fe supplied was significantly lower. Cd concentrations in roots and shoots decreased with increasing Fe supply at both Cd additions. The proportion of Cd in DCB-extracts was significantly lower than in roots or shoots. Compared to the control seedlings without Fe supply, the radioactivity of ¹⁰⁹Cd in shoots of seedlings treated with Fe decreased when root tips were exposed to ¹⁰⁹Cd and did not change significantly when middle parts of roots were exposed. Our results suggest that root tissue rather than iron plaque on the root surface is a barrier to Cd uptake and translocation within rice plants, and the uptake and translocation of Cd appear to be related to Fe nutritional levels in the plants.     

The seed bank in a subtropical freshwater marsh: implications for wetland restoration

Seed bank samples were collected from Huli Marsh, a subtropical shallow water mountainous marsh in Hunan Province, South China. Core samples were divided into upper and lower layers (each 5 cm in depth) and allowed to germinate in three water levels (0, 5 and 10 cm) over a 4-month period. A total of 51 species germinated and the mean density was 9211 ± 7188 seedlings m⁻². In the top 5 cm 41 species and 5747 ± 5111 seedlings m⁻² germinated, whereas 40 species and 3464 ± 3363 seedlings m⁻² did so from 5–10 cm. Germinated seedling density was significantly higher in the upper layer, largely due to differences in eight species. With increasing experimental water depth, less seedlings germinated: respectively, 9788 ± 7157 m⁻², 2050 ± 2412 m⁻² and 1978 ± 2616 m⁻², of 44, 21 and 19 species, submerged under 0, 5 or 10 cm. Seven species could emerge only in 0 water level. Vallisneria natans occurred only in 5 cm water, whereas Ottelia alismoides occurred in 10 cm water. In the vegetation survey of the marsh, 25 species were recorded, which was less than half of the species recorded in the seed bank. The top 10 dominants in the standing vegetation, accounting for 89% of vegetation abundance, represented only 10% in the seed bank. Twenty germinated species that also occurred in the standing vegetation accounted for 56% of the total seed bank. Our observed number of species germinating from a Chinese wetland seed bank is within the range observed elsewhere in the northern hemisphere (15–113 species).     

Sea buckthorn (Hippophae rhamnoides L.) vegetative parts as an unconventional source of lipophilic antioxidants

The profile of lipophilic antioxidants in different vegetative parts (leaves, shoots, buds and berries) was studied in sea buckthorn (Hippophae rhamnoides L.) male and female plants collected in the end of spring. Five lipophilic compounds, i.e. three tocopherol homologues (α, β and γ), plastochromanol-8 and β-carotene, were identified in each vegetative part of male and female sea buckthorn plants at the following concentrations: 7.25–35.41, 0.21–2.43, 0.41–1.51, 0.19–1.79 and 4.43–24.57 mg/100 g dry weight basis. Additionally, significant amounts of α-tocotrienol (1.99 mg/100 g dry weight basis) were detected in buds. The α-tocopherol and β-carotene were predominant lipophilic antioxidants in each vegetative part, accounting for 78.3–97.0% of identified compounds. The greatest amounts of lipophilic antioxidants were found in leaves, especially of female plants. Nevertheless, apart from leaves, also shoots of plants of both sexes seem to be a good source of α-tocopherol and β-carotene.     

In vitro propagation of ginger (Zingiber officinale Rosco)

An efficient and promising protocol for in vitro propagation of Zingiber officinale Rosco using sprouting buds was established. Sprouting buds were sterilized and cultured onto MS medium supplemented with different growth regulators. Augmentation of MS-medium with 4.5 mg/l BAP recorded the highest percentage of shootlets multiplication. Shootlets were highly rooted on half strength of B₅ medium supplemented with 1.0 mg/l NAA. The maximum percentage of acclimatization, hardening and rhizomes production of in vitro derived plants in greenhouse was 80–100%.     

In vitro cultures of Silybum marianum and silymarin accumulation

In this study, a protocol for initiation of callus and shoot cultures from leaves and shoot tips explants of different silybium genotypes collected from different locations in Egypt was established. Callus cultures were initiated from leaves explants and exposed to different concentrations of the precursor (coniferyl alcohol). Shoot cultures were initiated from shoot tips explants. Moreover, the produced plants of the different Silybium shoots as well as intact plants were subjected to protein screening using SDS–PAGE analysis.Results obtained revealed that the optimum medium for growth and maintenance of friable callus was MS medium supplemented with 0.25 mg L⁻¹ 2,4-Dichlorophenoxy acetic acid (2,4-D) + 0.25 mg L⁻¹ Kinetin (Kin). The best medium for proliferation of high number of shoots was MS-medium with 0.25 mg L⁻¹ each of Benzyl Adinine (BA) and Naphthalene Acetic Acid (NAA). Coniferyl alcohol in concentration of 30 μM caused an increase in accumulation of silymarin contents in most callus cultures. SDS–PAGE of different Silybium shoots revealed that the protein profiles of 100% of in vitro produced plantlets similar to their control.     

Lantana camara and the fruit- and seed-damaging fly,Ophiomyia lantanae (Agromyzidae): Seed predator,recruitment promoter or dispersal disrupter?

The seed damaging fly, Ophiomyia lantanae is a widespread agent that infests the fruits and seeds of Lantana camara. Its effectiveness in reducing seed dispersal or seedling recruitment has not been comprehensively tested. We determined the effects of O. lantanae damage on fruit removal rates of L. camara in a field study. We also investigated recruitment responses (seed germination in growth cabinets and seedling emergence in pot trials) of two common L. camara biotypes, pink and pink-edged red (PER) to O. lantanae damage. We found that fewer damaged fruits were removed than undamaged fruits, suggesting that frugivores select against damaged fruit. In all recruitment experiments, the responses to damage were biotype dependent. In germination experiments, these differential responses were primarily due to significantly reduced germination of damaged PER seeds. Seedling emergence from pots of the PER biotype was also lower in damaged seeds (27.5%) than undamaged seeds (56.1%). In contrast, emergence increased with seed damage in the pink biotype, from 28.2 to 41.1%. O. lantanae damage significantly reduced seed mass only in the smaller seeded PER biotype. In the larger seeded pink biotype, it may have promoted seedling emergence by interfering with dormancy mechanisms. We also examined in situ seed banks at L. camara populations prior to peak seed production. Mean viable seed densities ranged from 78.6 to 402.8 seeds m⁻². Of these, non-dormant seeds comprised 24.6 to 98.2 seeds m⁻², suggesting that recruitment is unlikely to be seed limited. We conclude that while O. lantanae influences recruitment and dispersal processes, the magnitude of the responses measured are unlikely to greatly influence plant densities in south-east Queensland infestations.     

Dynamic response of woody vegetation on fencing protection in semi-arid areas; Case study: Pilot exclosure on the Firmihin Plateau,Socotra Island

Woody vegetation dynamics and Dracaena cinnabari regeneration have been studied for five years in the conditions of Socotra Island. Woody plants were measured regularly inside and outside the exclosure area, and the growth and survival of D. cinnabari seedlings were observed. In the exclosure of about 1000 m² a total of 49 species were identified, including 23 endemics, growing in the average density of 3.82 specimens per m². The fenced area was overgrown relatively rapidly by dense grass cover – reaching approx. 2.7 t/ha. Species growth dynamics inside and outside the exclosure shows that grazing had a marked impact, leading to the elimination of trees and shrubs. All grazed species grew noticeably in the exclosure, in the average of 50 cm in 5 years. D. cinnabari as the dominant flagship species of Socotra has been studied with regards to regeneration dynamics. Observations indicate that probability of its seedlings survival increases with their age. No seedlings germinated from the seeds sown in the experiment, however, outplanted seedlings performed relatively well. Field observations show that D. cinnabari seed germination is triggered when the seed reaches a protected micro-habitat with a developed humus layer and high relative humidity in the soil lasts for at least two days.     

Dynamics of Typha latifolia L. populations in treatment wetlands in Estonia

The aim of this paper is to evaluate and compare broadleaved cattail (Typha latifolia L.) biomass production and the nitrogen (N) and phosphorus (P) content in phytomass in three treatment wetland systems and to propose suitable areas for treatment wetlands in Estonia for raw material production. The biomass samples (roots/rhizomes, shoots with leaves and spadixes) and litter were collected from 1 m × 1 m plots—15 plots in the Tänassilma semi-natural wetland, 15 plots in the Põltsamaa free water surface (FWS) constructed wetland (CW), and 10 plots in the Häädemeeste FWS CW. The average aboveground biomass of T. latifolia varied from 0.37 to 1.76 kg DW m^?2 in autumn and from 0.33 to 1.38 kg DW m^?2 in winter. The greatest average nitrogen (22,950 mg N kg^?1) concentration was found in spadixes in 2002, and the phosphorus (6500 mg P kg^?1) concentration was measured in roots–rhizomes in 2003. Average standing stock of nitrogen and phosphorus was higher in aboveground than belowground phytomass. In FWS CWs with high hydraulic and nutrient loadings, however, the harvesting of aboveground biomass is not an effective means for the removal of nutrients. Cattail biomass is a valuable insulation material, whereas the fibre from spadixes mixed with clay gives elasticity to clay plasters. According to our estimates, about 5412 km² could be used for Typha cultivation in Estonia.     

Analysis of the relationship between photosynthetic photon flux density and natural Taxus baccata seedlings occurrence

The aim of the present work was to analyse the relationship of seedlings and saplings of Taxus baccata to the photosynthetic photon flux density (PPFD) reaching the forest floor under natural conditions. Two permanent plots, subdivided into 1 × 1 m square plots, were established in a naturally regenerating population of T. baccata formed during last decades in the Kórnik Arboretum, Poland. All seedlings in every 1 × 1 m plots were counted. Relative PPFD was measured for every plot at the canopy height of the yew seedlings. The dependence of seedling density upon PPFD was examined. We found, that the frequency of the smallest seedlings (to 6.0 cm tall) was highest in the most shaded plots and decreased in plots with increasing PPFD. Thus, the youngest yew seedlings can germinate and grow in very shady conditions. However, the older seedlings (6.1–25.0 and 25.1–100.0 classes) were observed most frequently in 2–7% PPFD. The small numbers of older, taller seedlings in deep shade likely indicate a higher mortality rate of seedlings less than 6 cm in height without promotion to the next height class. Probably the low value of PPFD under the canopy of the stand significantly reduces the competition of other plants with the youngest yew seedlings. At higher light levels they may not be able to compete with more light-demanding plants, such as herbs and seedlings of broad-leaved trees. The seedlings of the second (6.1–25.0 cm) and third (25.1–100.0 cm) height classes were observed most frequently in the plots with 2–7% PPFD (Fig. 1b and c).     

In vitro regeneration of Hypoxis colchicifolia plantlets

Corms of Hypoxis species are heavily traded for use in traditional medicine in southern Africa. High demand has increased unsustainable harvesting from the wild, diminishing natural populations. Micropropagation of Hypoxis colchicifolia was investigated as a means of mass producing plants for both commercialization and re-establishment in the wild. Various plant organs were tested as explant sources and decontamination optimized for each explant type. Seeds failed to germinate in vitro, and inflorescence peduncles, leaves (young and mature) turned brown and did not respond in culture. Only 6% of corm explants produced callus and shoots. Flower buds responded best, with multiple shoots initiated from explants either directly from meristemoids or indirectly via callus. The problem of browning due to phenolic exudation was solved by including polyvinylpyrrolidone (PVP) in the culture medium when required. Common pathogens were partially controlled by washing affected explants in benomyl solutions. Rooting and corm induction were successful, and plantlets could be stored at low temperature (10 °C) prior to acclimatization with no adverse effects. In planting trials with 5-month-old and 21-month-old plants regenerated using the improved protocols, flowering percentage, corm and leaf size were increased significantly in plants grown in pots compared to those grown in the field over a 28 month period.     

Heavy metal bioaccumulation by the organs of Phragmites australis (common reed) and their potential use as contamination indicators

The concentrations of heavy metals in the roots, rhizomes, stems and leaves of the aquatic macrophyte Phragmites australis (common reed), and in the corresponding water and sediment samples from the mouth area of the Imera Meridionale River (Sicily, Italy), were investigated to ascertain whether plant organs are characterized by differential accumulation, and to test the suitability of the various organs for heavy metal biomonitoring of water and soil. Heavy metals considered were Cd, Cr, Cu, Hg, Mn, Ni, Pb, Zn. Results showed that belowground organs were the primary areas of metal accumulation. In particular, metal concentrations in plant organs decreased in the order of root > rhizome ≥ leaf > stem. All four organs showed significant differences in concentration for Cr, Hg, Mn, Zn, thus suggesting low mobility from roots to rhizomes and to aboveground organs. Although the organs followed different decreasing trends of metal concentration, the trend Mn > Zn > Pb > Cu was found in each plant organ. Mn showed the highest concentrations in all organs whereas the lowest concentrations regarded Cd and Cr in the belowground and aboveground organs, respectively. The toxic threshold was exceeded by Cr in roots, rhizomes and leaves, Mn in roots and leaves, Ni in roots. The highest average concentrations were found as follows: Cd, Hg, Pb, Zn in root, Cr, Mn, Ni in sediment, Cu in water. Positive linear relationships were found between heavy metal concentrations in all plant organs and those in water and sediment, thus indicating the potential use of such organs for pollution monitoring of water and sediment. Advantages of using plant species as biomonitors, especially Phragmites australis, were also discussed.     

Multiple regeneration pathways in Spathoglottis plicata Blume — A study in vitro

Asymbiotic germination of immature seeds (embryos), and mature seeds and micropropagation of Spathoglottis plicata were described. Effects of three nutrition media namely, Murashige & Skoog (MS); Phytamax (PM); and Phyto-Technology orchid seed sowing medium (P₇₂₃), two carbon sources such as glucose and sucrose at 2–3% (w/v), two plant growth regulators such as 6-benzylaminopurine (BAP; 0.5–3.0 mg l^− 1) and α-naphthalene acetic acid (NAA; 0.5–2.0 mg l^− 1) and peptone (2.0 g l^− 1) were examined on seed germination, early protocorm development and micropropagation. The maximum germination of mature seeds (95%) was recorded in PM medium supplemented with 2% (w/v) sucrose + 2.0 g l^− 1 peptone. For germination of embryos P₇₂₃ medium supplemented with 1.0 mg l^− 1 BAP proved best. Multiple shoot buds or protocorm-like bodies (PLBs) were produced from stem segments of in vitro raised seedlings. Both direct organogenesis and embryogenesis were observed and the morphogenetic response was initiated by different concentrations and combinations of PGRs. The optimum PGR combination for maximal PLB regeneration was 1.0 mg l^− 1 NAA + 2.5 mg l^− 1 BAP, while 1.0 mg l^− 1 NAA + 1.0 mg l^− 1 BAP for shoot bud development. Strong and stout root system was induced in half strength PM medium supplemented with 0.5 mg l^− 1 IAA. The well-rooted plantlets were transferred to pots containing a potting mixture composed of saw dust, coconut coir, humus, and coal pieces at 1:1:1:2 (w/w) with 80% survival in outside environment and flowered after two years of transfer.     

Uptake and allocation of 13C by Enhalus acoroides at sites differing in light availability

Carbon fixation and allocation were studied using ¹³C incubation and leaf marking techniques in mature monospecific stands of Enhalus acoroides L.f. Royle in August 1998 and January 1999 in Banten Bay, Indonesia. The highest rate of ¹³C uptake (>0.008 g ¹³C g C⁻¹ d⁻¹) was found in the middle to distal parts of leaves of E. acoroides. Young and senescing leaves numbers had lower ¹³C incorporation compared to mature leaves. The incorporation of ¹³C by epiphytes on the leaves was higher than that of the leaves themselves (>0.01 g ¹³C g C⁻¹ d⁻¹). The results showed that turbidity of the water influenced the leaf growth, productivity and Relative Growth Rate of E. acoroides, which were lower at Kepuh Island, the more turbid site. However, at Kepuh Island, where the water column was turbid, the plant could still harvest sufficient light for an uptake rate of ¹³C, higher than the uptake rates at Kubur and Panjang Islands, stations with a much more transparent water column (on average 0.0047 g ¹³C g C⁻¹ d⁻¹ at Kepuh Island, versus 0.0045 g ¹³C g C⁻¹ d⁻¹ at Panjang Island and 0.0034 g ¹³C g C⁻¹ d⁻¹ at Kubur Island). There was evidence that ¹³C was exported from the incubated shoots to the roots and rhizomes and to neighboring shoots of E. acoroides in clear water, but not in turbid water. We suggest that single shoots of E. acoroides are able to grow in turbid water under low light conditions. They assimilate sufficient carbon for their own maintenance but are not able to export to neighboring plant parts.     

Gibberellic acid mediated induction of salt tolerance in wheat plants: Growth,ionic partitioning,photosynthesis, yield and hormonal homeostasis

In order to elucidate the GA₃-priming-induced physiochemical changes responsible for induction of salt tolerance in wheat, the primed and non-primed seeds of two spring wheat (Triticum aestivum L.) cultivars, namely, MH-97 (salt intolerant) and Inqlab-91 (salt tolerant) were sown in a field treated with 15 dS m⁻¹ NaCl salinity. Although all the three concentrations (100, 150 and 200 mg L⁻¹) of GA₃ were effective in improving grain yield in both cultivars, the effect of 150 mg L⁻¹ GA₃ was much pronounced particularly in the salt intolerant cultivar when under salt stress. Seed priming with GA₃ altered the pattern of accumulation of different ions between shoots and roots in the adult plants of wheat under saline conditions. Treatment with GA₃ (150 mg L⁻¹) decreased Na⁺ concentrations both in the shoots and roots and increased Ca²⁺ and K⁺ concentrations in the roots of both wheat cultivars. GA₃-priming did not show consistent effect on gaseous exchange characteristics and the concentrations of auxins in the salt stressed plants of both wheat cultivars. However, all concentrations of GA₃ reduced leaf free ABA levels in the salt intolerant, while reverse was true in the salt tolerant cultivar under saline conditions. Priming with GA₃ (150 mg L⁻¹) was very effective in enhancing salicylic acid (SA) concentration in both wheat cultivars when under salt stress. Treatment with GA₃ (100–150 mg L⁻¹) lowered leaf free putrescine (Put) and spermidine (Spd) concentrations in the plants of both wheat cultivars. The decrease in polyamines (Put and Spd) and ABA concentrations in the salt stressed plants of the salt intolerant cultivar treated with GA₃ suggested that these plants might have faced less stress compared with control. Thus, physiologically, GA₃-priming-induced increase in grain yield was attributed to the GA₃-priming-induced modulation of ions uptake and partitioning (within shoots and roots) and hormones homeostasis under saline conditions.     

Patch dynamics of the Mediterranean seagrass Posidonia oceanica: Implications for recolonisation process

Patch dynamics of the Mediterranean slow-growing seagrass Posidonia oceanica was studied in two shallow sites (3–10 m) of the Balearic Archipelago (Spain) through repeated censuses (1–2 year⁻¹). In the sheltered site of Es Port Bay (Cabrera Island), initial patch density (October 2001) was low: 0.05 patches m⁻², and the patch size (number of shoots) distribution was bimodal: most of the patches had less than 6 shoots or between 20 and 50 shoots. Mean patch recruitment in Es Port Bay (0.006 ± 0.002 patches m⁻² year⁻¹) exceeded mean patch loss (0.001 ± 0.001 patches m⁻² year⁻¹), yielding positive net patch recruitment (0.004 ± 0.003 patches m⁻² year⁻¹) and a slightly increased patch density 3 years later (July 2004, 0.06 patches m⁻²). In the exposed site of S’Estanyol, the initial patch density was higher (1.38 patches m⁻², August 2003), and patch size frequency decreased exponentially with size. Patch recruitment (0.26 patches m⁻² year⁻¹) and loss (0.24 patches m⁻² year⁻¹) were high, yielding a slightly increased patch density in the area 1 year later (October 2004, 1.40 patches m⁻²). Most recruited patches consisted of rooting vegetative fragments of 1–2 shoots. Seedling recruitment was observed in Summer 2004 at both sites. Episodic, seedling recruitment comprised 30% and 25% of total patch recruitment in Es Port Bay and S’Estanyol, respectively. Patch survival increased with patch size and no direct removal was observed among patches of 5 shoots or more. Most patches grew along the study, shifting patch distribution towards larger sizes. Within the size range studied (1–150 shoots), absolute shoot recruitment (shoots year⁻¹) increased linearly with patch size (R² = 0.64, p < 4 × 10⁻⁵, N = 125), while specific shoot recruitment was constant (about 0.25 ± 0.05 year⁻¹), although its variance was large for small patches. Given the slow growth rate and the high survival of patches with 5 or more shoots, even the low patch recruitment rates reported here could play a significant role in the colonisation process of P. oceanica.