Interspecific effects on plant size inequality: evidence from a temperate savanna community

The influences of intraspecific competition on plant size inequality have been well documented, but interspecific effects on this topic remain little understood. Here we examined the effects of canopy shading and fine roots of the trees (Elaeagnus angustifolia) on size inequality of the grasses (Achnatherum splendens) in a temperate savanna community in northwest China. Three study plots of 400 m² were divided into 4-m² quadrats, within each of which (1) canopy shading was quantified by modeling cumulative direct solar radiation (CDSR) and (2) the root effect was quantified using an empirical relationship between tree fine root density (TFRD) and relative distance to tree bases. Morphological traits were measured to represent grass size. Redundancy analysis (RDA) was conducted to examine the relative influences of grass density, CDSR and TFRD on the coefficient of variation of grass size. Results showed that no significant correlation occurred between grass density and grass size inequality. Both CDSR and TFRD had significant negative correlations with grass size inequality, suggesting that canopy shading and the presence of fine roots of trees can, respectively, increase and reduce grass size inequality. Canopy shading and TFRD played competitive roles in determining grass size inequality, where the root effect was a stronger factor than canopy shading. The tree effects can substantially alter the intensity of water stress. In response, size inequality of the grasses could be influenced through size-specific growth/mortality and slowed size divergence. These mechanisms could operate together in the savanna community.     

On the detection of dynamic responses in a drought-perturbed tropical rainforest in Borneo

The dynamics of aseasonal lowland dipterocarp forest in Borneo is influenced by perturbation from droughts. These events might be increasing in frequency and intensity in the future. This paper describes drought-affected dynamics between 1986 and 2001 in Sabah, Malaysia, and considers how it is possible, reliably and accurately, to measure both coarse- and fine-scale responses of the forest. Some fundamental concerns about methodology and data analysis emerge. In two plots forming 8 ha, mortality, recruitment, and stem growth rates of trees ≥10 cm gbh (girth at breast height) were measured in a ‘pre-drought’ period (1986–1996), and in a period (1996–2001) including the 1997–1998 ENSO-drought. For 2.56 ha of subplots, mortality and growth rates of small trees (10–<50 cm gbh) were found also for two sub-periods (1996–1999, 1999–2001). A total of c. 19 K trees were recorded. Mortality rate increased by 25% while both recruitment and relative growth rates increased by 12% for all trees at the coarse scale. For small trees, at the fine scale, mortality increased by 6% and 9% from pre-drought to drought and on to ‘post-drought’ sub-periods. Relative growth rates correspondingly decreased by 38% and increased by 98%. Tree size and topography interacted in a complex manner with between-plot differences. The forest appears to have been sustained by off-setting elevated tree mortality by highly resilient stem growth. This last is seen as the key integrating tree variable which links the external driver (drought causing water stress) and population dynamics recorded as mortality and recruitment. Suitably sound measurements of stem girth, leading to valid growth rates, are needed to understand and model tree dynamic responses to perturbations. The proportion of sound data, however, is in part determined by the drought itself. Electronic supplementary material  The online version of this article (doi:) contains supplementary material, which is available to authorized users.     

Slashing Phragmites (Phragmites australis) prior to planting does not promote native vegetation establishment

Phragmites or Common Reed (Phragmites australis) is a tall rhizomatous cosmopolitan grass. While native to Australia, it can be invasive in wetlands, forming dense monocultures and reducing their ecological integrity. We assessed the potential for the cutting of Phragmites reeds prior to planting to promote the establishment of indigenous shrubs that might ultimately outcompete Phragmites. We established ten 5 m × 5 m quadrats in an area dominated by Phragmites, brush‐cut the reeds to ground level in five of them and left five uncut as controls. Within each quadrat, we planted 20 plants (~40 cm tall) of each of five indigenous shrub species, unguarded (4 plants/m²). We surveyed the plants one month after planting and annually for the following four years for survival, height and browsing damage. Browsing damage to plants was common (>50%) and unaffected by cutting. After four years, overall plant survival rates were ~25% and mean plant heights for the five shrub species ranged between 120 and 174 cm. Cutting of Phragmites had no positive effect on plant survival or height. In fact, two Melaleuca species grew taller in the uncut quadrats. Cutting of Phragmites reed beds prior to planting is unlikely to promote the establishment of woody plantings. However, planting within established Phragmites with or without prior brush‐cutting is worthy of further trialling as a potential tool for reinstating native diversity at Phragmites‐dominated sites.     

Isolation,callus formation and plantlet regeneration from mesophyll protoplasts of <Emphasis Type="Italic">Tylophora indica</Emphasis> (Burm. f.) Merrill: an important medicinal plant

Protoplast culture and plant regeneration of an important medicinal plant Tylophora indica were achieved through callus regeneration. Protoplasts were isolated from leaf mesophyll cells and cultured at a density of 5 × 10⁵ protoplasts per gram fresh weight, which is required for the highest frequency of protoplast division (33.7%) and plating efficiency (9.3%). The first division was observed 2 d after plating and the second division after 4 d. Culture medium consists of Murashige and Skoog (MS) liquid medium with 4 μM 2,4-D, 0.4 M mannitol and 3% (w/v) sucrose with pH adjusted to 5.8. After 45 d of culture at 25°C in the dark, protoplasts formed colonies consisting of about 100 cells. The protoplast-derived microcalli were visible to the naked eye within 60 d of culture and reached a size of 0.2–0.4 mm in diameter after 90 d. Calli of 0.2–0.4-mm size were transferred to MS medium supplemented with 2,4-D (4 μM), 3% (w/v) sucrose and 0.8% (w/v) agar, formed friable organogenic calli (7-8 mm size) after 8 wk under incubation in normal light period supplemented with 200 μmol m⁻² S⁻¹ of day light fluorescent illumination. The calli were transferred to MS medium supplemented with thidiazuron (TDZ) (1–7 μM) and naphthalene acetic acid (NAA) (0.2–0.4 μM) for regeneration. The calli developed shoot buds after 3–4 wk, and the frequencies of calli-forming shoots varied from 5% to 44%. Optimum shoot regeneration occurred on MS medium supplemented with 5 μM TDZ and 0.4 μM NAA. On this medium, 44% cultures responded with an average number of 12 shoots per callus. Whole plants were recovered following rooting of shoots in 1/2 MS medium supplemented with 3 μM indole 3-butyric acid.     

Responses of CO2 Exchange and Primary Production of the Ecosystem Components to Environmental Changes in a Mountain Peatland

The complexity of natural ecological systems presents challenges for predicting the impact of global environmental changes on ecosystem structure and function. Grouping of plants into functional types, that is, groups of species sharing traits that govern their mechanisms of response to environmental perturbations, reduce the complexity of species diversity to a few key plant types for better understanding of ecosystem responses. Chambers were used to measure CO₂ exchange in grass and moss growing together in a mountain peatland in southern Germany to assess variations in their response to environmental changes and how they influence ecosystem CO₂ exchange. Parameter fits and comparison for net ecosystem exchange (NEE) in two ecosystem components were conducted using an empirical hyperbolic light response model. Annual green biomass production was 320 and 210 g dwt m ⁻², whereas mean maximum NEE was –10.0 and –5.0 μmol m ⁻² s ⁻¹ for grass and moss, respectively. Grass exhibited higher light use efficiency (α) and maximum gross primary production [(β+γ)₂₀₀₀]. Leaf area index explained 93% of light use and 83% of overall production by the grass. Peat temperature at 10-cm depth explained more than 80% of the fluctuations in ecosystem respiration (R _eco). Compared to grass, moss NEE was more sensitive to ground water level (GWL) draw-down and hence could be more vulnerable to changes in precipitation that result in GWL decline and may be potentially replaced by grass and other vegetation that are less sensitive. Author’s Contribution  Werner Borken conceived the study. Ai Nishiwaki, Margerete Wartinger, G. Lischeid and Zaman Hussain conducted measurements. Jan Muhr helped with the methodologies and result discussion. Dennis O. Otieno designed and conducted measurements and wrote the paper.     

Effect of competition intensity on recruitment of palatable and unpalatable grasses

In this study, we made an attempt to reveal how competition intensity from established plants impacts on palatable and unpalatable grass seedlings recruitment, in a natural mesic grassland of central Argentina. Our objective was to assess the seedling recruitment of a palatable species (Chascolytrum subaristatum) and an unpalatable species (Nassella trichotoma) in microsites differing in competition intensity from established plants. Identity (C. subaristatum and N. trichotoma) and defoliation severity were used as surrogate for competition intensity. In March 2017, we permanently marked established individuals of N. trichotoma and C. subaristatum and placed two circular plots adjacent to each individual. In one plot we added seeds of N. trichotoma and in the other seeds of C. subaristatum. After seeding, established plants were randomly assigned to one of three level of defoliation: without defoliation, low defoliation severity and high defoliation severity. From April to November 2017 (i.e. over a complete annual growing cycle), we measured seedling density, recruitment and growth. Our results supported the hypothesis that seedlings of palatable grasses are more competitive than seedlings of unpalatable grasses. Seedling of the palatable grass C. subaristatum recruited successfully regardless the intensity of competition from established plants, whereas seedlings of the unpalatable grass N. trichotoma recruited better under low competitive pressure from established plants. Our results suggest that the availability of microsites with low competitive pressure from the established vegetation, created by selective grazing of palatable grasses, promotes the recruitment of unpalatable grass seedlings. This mechanism may contribute to the species replacement process commonly observed in heavy grazed grasslands.     

The relative importance of above- versus belowground competition for tree growth during early succession of a tropical moist forest

Competition between neighboring plants plays a major role in the population dynamics of tree species in the early phases of humid tropical forest succession. We evaluated the relative importance of above- versus below-ground competition during the first years of old-field succession on soil with low fertility in Southern Mexico, using the premise that competition for light is size-asymmetric, unlike competition for nutrients. Plant growth is thus expected to be disproportionally impeded by larger neighbors. We studied how growth and survival of 3.5–5.5 m tall saplings of Cecropia peltata and Trichospermum mexicanum, two pioneer species that dominate the secondary forests in the study region, varied with the abundance and size of neighboring trees in 1–2 year old secondary vegetation. We found that local neighborhood basal area varied 10-fold (3 to 30 cm² m^-2) and explained most of the variation in diameter and height growth of the target saplings. Most growth variables were strongly affected by the neighbors bigger than the focal trees with no significant additive effect of the smaller neighbors, indicating asymmetric competition. Smaller neighbors did have a small but significant additive effect on the diameter growth of Cecropia saplings and stem slenderness of Trichospermum saplings. We conclude that competition for light was more important than belowground competition in this initial phase of moist tropical forest successional, despite the low soil fertility.     

Diversity of understory plants in undisturbed and disturbed tropical lowland forests of Little Andaman Island, India

Species richness and density of understory plants were investigated in eight 1 ha plots, distributed one each in undisturbed and disturbed tropical evergreen, semi-evergreen, deciduous and littoral forests of Little Andaman island, India, which falls under one of the eight hottest hotspots of Biodiversity in the world viz. the Indo-Burma. One hundred 1 m⁻² quadrats were established in each 1 ha plot, in which all the understory plants (that include herbs, undershrubs, shrubs and herbaceous climbers) were enumerated. The total density of understory plants was 6,812 individuals (851 ha⁻¹) and species richness was 108 species, representing 104 genera and 50 families. Across the four forest types and eight study plots, the species richness ranged from 10 to 39 species ha⁻¹. All the disturbed sites harbored greater number of species than their undisturbed counterparts. Herbs dominated by species (63%) and density (4,259 individuals). The grass Eragrostis tenella (1,860 individuals; IVI 40), the invasive climber Mikania cordata (803; IVI 20) and the shrub Anaxagorea luzonensis (481; IVI 17.5) were the most abundant species. Poaceae, Asteraceae, Acanthaceae, Orchidaceae and Euphorbiaceae constituted the species-rich families represented by 6 species each. The species-area curves attained an asymptote at 0.8 ha level except in sites DD and DL, indicating 1 ha plot is not sufficient to capture all the understory species in disturbed forests. The alien weeds formed about one-fourth of the species richness (31 species; 28%) and density (1,926 individuals; 28.3%) in the study sites, indicating the extent of weed invasion and the attention required for effective conservation of the native biodiversity of the fragile island forest ecosystem.     

Fumonisins in Maize in Relation to Climate,Planting Time and Hybrids in Two Agroecological Zones in Zambia

Field experiments in the high rainfall zone (HRZ) and the medium rainfall zone (MRZ) in Zambia were designed to determine the natural occurrence of fumonisins (FB_1–2) in Zambian maize hybrids, accumulation of FB_1–2 resulting from artificial inoculation with Fusarium verticillioides and effects of climate and planting time on FB_1–2 in maize. Combined FB_1–2 concentrations varied from 0 to 13,050 ng/g, with an overall mean of 666 ng/g. Maize from the HRZ had low incidences of FB_1–2-positive samples (mean 41%) which contained FB_1–2 below 500 ng/g. In the MRZ, higher incidences (mean 97%) and concentrations (40% of samples >1,000 ng/g) were recorded in two out of three years. There was no correlation between mean location FB_1–2 concentrations in individual years and precipitation, number of rain days or monthly precipitation. Postponing the planting time with 10 or 20 days did not significantly affect FB_1–2 concentration, but it reduced the yields in some years.     

Macrotermes mounds as sites for tree regeneration in a Sudanian woodland (Burkina Faso)

The importance of mounds created by Macrotermes subhyalinus as safe site for tree regeneration was analysed in a savannah woodland of Burkina Faso. Plantlets (height <1.5 m) were sampled and followed over an year in 72 × 4 m² quadrats located on M. subhyalinus mounds and adjacent areas. The mechanisms of regeneration and plantlet mortality were also determined. We identified three regeneration mechanisms: seedlings regenerated by seed (abundant on mounds), sprouts (abundant on adjacent areas) and root suckers (a rare case on both sites). A total of 37 species representing 17 families and 30 genera were found on all quadrats, of which 29 species were found on termite mounds and 22 species on adjacent areas. Species richness and density of plantlets at the 4 m² scale were higher on mounds than in the adjacent area (P < 0.05). Among plantlet categories, seedling density was significantly different among microhabitats (P < 0.001) and across sampling periods (P < 0.01) and, the majority of plantlet individuals appeared within the 0–25 cm height class. The mortality of plantlets and particularly seedling mortality differed significantly between microhabitats (P < 0.01) and between periods (P < 0.01), whereas more than half the variation in the death of Acacia erythrocalyx seedlings (the most abundant species) were related to the density of the live seedlings of the same species (P < 0.001). The observed mortality rate was way below 50%; plantlet density remained higher on mound during sampling periods as compared to the adjacent area. It can thus be concluded that Macrotermes termite mounds are favourable sites for the recruitments of woody plants in savannah woodlands.     

Deschampsia antarctica Desv. primary photochemistry performs differently in plants grown in the field and laboratory

Primary photochemistry of photosystem II (F _v/F _m) of the Antarctic hair grass Deschampsia antarctica growing in the field (Robert Island, Maritime Antarctic) and in the laboratory was studied. Laboratory plants were grown at a photosynthetic photon flux density (PPFD) of 180 μmol m⁻² s⁻¹ and an optimal temperature (13 ± 1.5°C) for net photosynthesis. Subsequently, two groups of plants were exposed to low temperature (4 ± 1.5°C day/night) under two levels of PPFD (180 and 800 μmol m⁻² s⁻¹) and a control group was kept at 13 ± 1.5°C and PPFD of 800 μmol m⁻² s⁻¹. Chlorophyll fluorescence was measured during several days in field plants and weekly in the laboratory plants. Statistically significant differences were found in F _v/F _m (=0.75–0.83), F ₀ and F _m values of field plants over the measurement period between days with contrasting irradiances and temperature levels, suggesting that plants in the field show high photosynthetic efficiency. Laboratory plants under controlled conditions and exposed to low temperature under two light conditions showed significantly lower F _v/F _m and F _m. Moreover, they presented significantly less chlorophyll and carotenoid content than field plants. The differences in the performance of the photosynthetic apparatus between field- and laboratory-grown plants indicate that measurements performed in ex situ plants should be interpreted with caution.     

Bioremediation of Fungicides by Spent Mushroom Substrate and Its Associated Microflora

Experiments were conducted both under in vitro and in situ conditions to determine the biodegradation potential of button mushroom spent substrate (SMS) and its dominating microbes (fungi and bacteria) for carbendazim and mancozeb, the commonly used agricultural fungicides. During 6 days of incubation at 30 ± 2°C under broth culture conditions, highest degradation of carbendazim (17.45%) was recorded with B-1 bacterial isolate, while highest degradation of mancozeb (18.05%) was recorded with Trichoderma sp. In fungicide pre-mixed sterilized SMS, highest degradation of carbendazim (100.00–66.50 μg g⁻¹) was recorded with mixed inoculum of Trichoderma sp. and Aspergillus sp., whereas highest degradation of mancozeb (100.00–50.50 μg g⁻¹) was with mixed inoculum of Trichoderma sp., Aspergillus sp. and B–I bacterial isolate in 15 days of incubation at 30 ± 2°C. All these microbes both individually as well as in different combinations grew well and produced extracellular lignolytic enzymes on SMS, which helped in fungicides degradation. Under in situ conditions, among three different proportions of SMS (10, 20 and 30%, w/w) mixed with fungicide pre-mixed soil (100 μg g⁻¹ of soil), the degradation of carbendazim was highest in 30% SMS treatment, while for mancozeb it was in 20% SMS treatment. The residue levels of both fungicides decreased to half of their initial concentration after 1 month of SMS mixing.     

Influence of intraspecific interaction and substrate type on initial growth and establishment of Hydrilla verticillata

Both substrate type and plant–plant interaction can greatly influence the growth and establishment of plants. In order to assist the re-vegetation of submerged macrophytes, the growth of Hydrilla verticillata with increasing equi-distance neighboring plant density on two substrate types (sediment and sand, representing high- and low-nutrient level, respectively) was assessed in monoculture stands. The results showed that substrate type greatly changed the biomass allocation patterns of the target plants, with a smaller root mass ratio on sediment compared to sand (0.70 vs. 3.11%). However, interaction between substrate type and neighboring density was observed. At low density, growth on sediment greatly increased plant height (43.90 vs. 22.10 cm), leaf biomass (216.63 vs. 68.41 mg), and total biomass (298.39 vs. 121.77 mg) when compared to growth on sand. However, at high density, no significant effect of the substrate type was found in those parameters. On sediment, high neighboring density greatly decreased the height, root number, total root length, root mass, and total biomass, implying large intraspecific plant–plant competition. However, such competition can be greatly reduced in infertile environments. Therefore, when the plants were grown on sand, neighboring density showed little effect on the height (22.10–26.53 cm), total root length (21.34–40.50 cm), and root biomass (3.14–6.27 mg). Total biomass and root number significantly increased by 50% and 115%, respectively, at high density compared to low density on sand, suggesting that facilitation rather than competition was occurring. Therefore, plant–plant interaction can vary from competition in fertile environments to facilitation in infertile environments. In summary, neighboring density should be manipulated according to the environmental nutrient level, so as to reduce intraspecific competition or increase intraspecific facilitation, and finally enhance the initial growth and establishment of H. verticillata in re-vegetation activities.     

Population dynamics of the mushroom coral Heliofungia?actiniformis in the Spermonde Archipelago, South Sulawesi, Indonesia

The fungiid Heliofungia actiniformis is one of the most popular coral species in the Indonesian aquarium trade, yet information on the biology of this species is limited. H. actiniformis growth rates, population size–frequency distributions and the seasonality of recruitment rates were measured at three replicate sites in the Spermonde Archipelago, South Sulawesi. Growth and population models were applied to estimate coral ages, mortality rates and the size of maximum yield. Growth decreased linearly with polyp size. High numbers of attached polyps budded from clusters of stalks attached to the reef, with each cluster originating from the settlement of a sexually produced larva. Neither the settlement of sexual recruits, nor their asexual budding, showed seasonality. The overall population structure reflected the high mortality rates of young, attached polyps (Z = 0.5–0.6 yr⁻¹), and the much lower mortalities of free-living individuals (Z = 0.05–0.08 yr⁻¹). There were no statistically significant differences in overall mortality rates and the age–frequency distributions of polyps aged 0–15 years between the sites. Differences in the abundance of large H. actiniformis polyps at the three replicate sites were correlated with percent cover of coral rubble. The application of the Beverton and Holt model revealed the highest biomass per H. actiniformis recruit was 12 cm, corresponding to a polyp age of 20 years.     

Efficacy of entomopathogenic nematodes against the tomato leafminer <Emphasis Type="Italic">Tuta absoluta</Emphasis> in laboratory and greenhouse conditions

The tomato leafminer, Tuta absoluta (Meyrick) (Lepidoptera: Gelechiidae) is an important pest of tomato crops in South America and it has recently arrived in Europe affecting tomato plantations. The susceptibility of T. absoluta larvae and pupae to three species of entomopathogenic nematodes (Steinernema carpocapsae, Steinernema feltiae and Heterorhabditis bacteriophora) was examined under laboratory conditions. Leaf bioassays were conducted to evaluate the nematode’s capability to reach the larvae and kill them within the galleries. The efficacy of the three nematode species after foliar application to potted tomato plants was evaluated under greenhouse conditions. High larval mortality (78.6–100%) and low pupae mortality (<10%) was determined in laboratory experiments. In the leaf bioassay a high level of larval parasitation (77.1–91.7%) was recorded revealing the nematode’s capacity to kill the larvae inside the galleries. In the pot experiments nematode treatment reduced insect infection of tomato plants by 87–95%. The results demonstrate the suitability of entomopathogenic nematodes for controlling T. absoluta.     

The heat is on: frequent high intensity fire in bracken (<Emphasis Type="Italic">Pteridium aquilinum</Emphasis>) drives mortality of the sprouting tree <Emphasis Type="Italic">Protea</Emphasis><Emphasis Type="Italic">caffra</Emphasis> in temperate grasslands

We examined the effect of fire frequency and intensity on a Protea caffra tree population in the temperate montane grasslands of north-western KwaZulu-Natal, South Africa. We assessed the effect of fire by comparing the population structure of the resprouter P. caffra in discrete bracken (Pteridium aquilinum) patches with that in the surrounding grassland matrix. Fuel biomass did not differ between grassland and bracken, but bracken fuel was significantly drier than grass. Above-ground fire temperatures and fireline intensity, measured by P. caffra char height, were significantly higher in the bracken habitat. Forty-two percent of the P. caffra population in grassland and in bracken persisted by coppice resprouts, having lost their original stem to fire damage. Exposure to higher intensity bracken fire suppressed P. caffra regeneration and caused greater adult mortality compared with trees in grassland. Consequently, the P. caffra population in bracken was skewed towards old age with most trees severely fire damaged. The high incidence of small trees in grassland indicates that a regular fire interval of 2–3 years does not negatively affect regeneration of P. caffra. However, in bracken patches regular high intensity fires cause high mortality among all P. caffra size classes and will ultimately result in local extinction. Bracken thus has the potential to significantly alter tree–grass interactions in these montane grasslands.     

Photosynthetic CO2 affinity of the aquatic carnivorous plant Utricularia australis (Lentibulariaceae) and its investment in carnivory

Aquatic carnivorous plants usually grow in shallow dystrophic waters poor in inorganic N and P. Utricularia australis was chosen as a model plant for its prolific distribution and great ecological plasticity. The photosynthetic CO₂ compensation point and factors associated with investment in carnivory and capture of prey were measured in 17 U. australis micropopulations in Třeboň basin, Czech Republic, together with water chemistry factors at these sites differing greatly in their trophic level, water hardness, and prey availability. Apical shoot growth rate was estimated at some oligotrophic sites. The micropopulations differed greatly in the proportion of traps with animal prey (2.7–70%, mean 26%), trap proportion to total biomass (1.4–42%, mean 26%), mean trap biomass (0.7–63 μg trap⁻¹, mean 19 μg), and maximum trap size (1–3 mm, mean 2.0 mm). CO₂ compensation points ranged from 0.7 to 6.1 μM (mean 2.6 μM). A weak HCO₃ ⁻ use (compensation point 0.51 mM) was found in plants growing in alkaline water. Trap biomass proportion did not correlate significantly with prey capture and CO₂ compensation points with ambient [CO₂]. A very rapid apical growth (2.5–4.2 new nodes day⁻¹) occurred in sand pits. Thus, HCO₃ ⁻ use in U. australis can be induced by growing at very high pH. CO₂ compensation points resembled those known in other aquatic non-carnivorous plants. They did not reflect carnivory. In spite of very rapid apical shoot growth, the relative growth rate of U. australis can be zero in oligotrophic habitats without prey.     

Seasonal Pattern of Reproduction Of Hizikia Fusiformis (Sargassaceae, Phaeophyta) from Nanao Island, Shantou, China

The maturation pattern of sexual reproduction in Hizikia fusiformis (Harvey) Okamura (Sargassaceae, Phaeaophyta) was examined in 2003 at Yunao Bay, Nanao Island, Shantou, China. Maturation began in mid-April (seawater temperature 19–21 ^∘C), reached the peak in mid-May (maturation rate ca. 70%, and seawater temperature 23.5–25 ^∘C) and finished in late-June (seawater temperature 27.5–30 ^∘C). The Hizikia plants continued to gain the length from the beginning of maturation season to reach a maximum mean length of 34.8 cm in mid-May, after which the mean length was reduced drastically due to the senescence and rupture of the larger plants in size. The major portion of the mature plants belonged to the larger plants between April and May, but to the smaller ones in June. It is suggested that the plant must achieve a critical size before reproductive maturation occurred. There was a positive relationship between the number of receptacles (NR), as well as the reproductive allocation (RA), and the plant size of Hizikia population, with the recorded maximum values of NR and RA being 1220 and 64.3% respectively, for a single plant.     

Yield improvement through female homosexual hybrids and sex genetics of sweet gourd (<Emphasis Type="Italic">Momordica cochinchinensis</Emphasis> Spreng.)

The present research aimed to evaluate the effect of silver nitrate (AgNO₃) on sex modification in sweet gourd (Momordica cochinchinensis Spreng.), and to explore the possibility of sexual crossing between two genetically female plants. Spray applications of AgNO₃ on 30 days’ old female plants induced hermaphrodite flowers. Male plants were insensitive to the AgNO₃ sprays. Application of 500 mg/l AgNO₃ on female plants produced the maximum proportion of induced hermaphrodite flowers. Hermaphrodite flowers appeared 17–21 days after AgNO₃ spray and continued up to 8–17 days, depending upon the concentration of AgNO₃. Pollen grain viability of induced hermaphrodite flowers (93.5%) was similar to pollen grain viability of normal male (95.0%) flowers. Because of higher fruit weight, progenies from female homosexual cross recorded higher yield. The hybrids from such crosses produced only female plants while the hybrids between female and normal male segregated into male and female in an equal proportion, indicating that sex in sweet gourd is controlled by a single factor, male being heterozygous and female being homozygous recessive. Through this technique, elite characters of female genotypes could be combined into a single plant.