Leaf production,reproductive patterns,field germination and seedling survival in Chamaedorea bartlingiana,a dioecious understory palm

Summary Chamaedorea bartlingiana is a dioecious palm that grows in the cloud forest understories of the Venezuelan Andes. Age and sexual differences in phenology and reproductive patterns were studied in labelled individuals of all age categories. This species has long-lived leaves and low leaf production, both characteristic of understory plants. Growth rates are lower in juveniles than in adults and in females than in males, as in other palms. Male and female individuals show different reproductive patterns. Male inflorescences are always produced at the same rate and the probability of surviving until anthesis is constant. Females produce reproductive buds at the same rate as males, but these buds have a 35% probability of becoming a ripe infrutescence if the plant has infrutescences already growing, and 70% if it does not. This pattern and the slow growth of inflorescences (1 year for males from bud to flowers, 2 years for females from bud to ripe fruits) cause a pluriannual reproductive pattern at the population level. Field germination does not follow this pattern, but shows one annual peak probably related to environmental conditions.     

Two new secondary metabolites isolated from Avena sativa L. (Oat) seedlings and their effects on osteoblast differentiation

Seedlings of natural crops are valuable sources of pharmacologically active phytochemicals. In this study, we aimed to identify new active secondary metabolites in Avena sativa L. (oat) seedlings. Two new compounds, avenafuranol (1) and diosgenoside (2), along with eight known compounds (3–10) were isolated from the A. sativa L. seedlings. Their chemical structures were elucidated via 1D and 2D NMR spectroscopy, high-resolution ESIMS, IR spectroscopy, optical rotation analysis, and comparisons with the reported literature. The effect of each isolated compound on alkaline phosphatase (ALP) activity for osteoblast differentiation induced by bone morphogenetic protein-2 (BMP-2) was investigated using the C2C12 immortal mouse myoblast cell line. Compounds 1, 4, 6, 8, and 9 induced dose-dependent increases in ALP expression relative to ALP expression in cells treated with only BMP-2, and no cytotoxicity was observed. These results suggest that A. sativa L. seedlings are a natural source of compounds that may be useful for preventing bone disorders.     

Effect of GA3 and 2,4-D foliar application on the anatomy of date palm (Phoenix dactylifera L.) seedling leaf

Two concentrations (10-5M and 10-3M) of both GA3 and 2,4-D were used as foliar spray to evaluate the response of date palm (Phoenix dactylifera L.) cv. Khedri seedlings. They affected some of the anatomical characteristics of the first leaf emerging after the beginning of the spray. The high concentration of GA3 increased the size of the midrib and its vascular bundle numbers. Both low and high concentrations of 2,4-D inhibited the formation of the midrib. 2,4-D in both low and high concentrations decreased the number of vessels in both protoxylem and metaxylem and also decreased their diameters, where as GA3 in low and high concentrations have less effect on the number of vessels and its diameters. GA3 in high concentration increased the number of vascular bundles in 1mm long of the leaf blade, while 2,4-D in low and high concentrations decreased their numbers. 10-3M of 2,4-D increased the size and layers of special hypodermal cells.     

Artificial sowing of endangered dry grassland species into disused basalt quarries

Steppe-like dry (semi) natural grasslands are valuable and endangered habitats in central Europe. In the study area (the ?eské st?edoho?í Hills, Czech Republic), they occur in fragments on southern slopes of volcanic hills, often in the vicinity of quarries, which are numerous there. We performed sowing experiments and observed seedling recruitment of six species, typical for the dry grasslands, in 9 basalt quarries located in 3 different climatic regions over 3 yr. The sowing experiments were established in young successional stages, 5–12 yr after quarrying was stopped. The objectives of the experiments were to evaluate: (i) if seedling recruitment and survival of the target species are possible regarding different climatic regions and (ii) what is the influence of weather fluctuations among years on seedling survival. Seedlings of all studied species were able to recruit and survive in the early successional stages at least in some quarries. The species, except one, showed significant differences in recruitment among the climatic regions, with the best recruitment and survival in the driest and warmest region. Seedlings of two species did not recruit in the wettest and coldest region. All species survived in the driest and warmest region, while only one did so in the coldest and wettest region. Different weather conditions in the studied years significantly influenced recruitment of two species. The number of localities (floristic records) of particular species in the regions was the best predictor of species germination and survival. Thus a traditional floristic survey may help to predict success of species in restoration projects. It emerged that artificial sowing can be considered in restoration programs as a way of contributing to restoration of dry grasslands in disused quarries.     

Changes in structure of savanna woodlands in northern Botswana following the impacts of elephants and fire

Fluctuations in densities of woody plant species were monitored in plots within three northern Botswana woodland types subjected to elephant damage and burning. Woodlands dominated by Baikiaea plurijuga and Colophospermum mopane sustained significant changes occurring on an annual basis, whereas Acacia erioloba plots maintained a typical structure. The structure of A. erioloba woodlands appeared to be influenced by factors other than elephants and the occurrence of fire. Woodlands dominated by C. mopane plants were subjected to obtrusive elephant damage, although the densities of tall trees remained largely unchanged. The effects of fire were most prominent in B. plurijuga woodlands. Tree densities declined consistently and plants of lower height classes, such as shrubs and seedlings increased in densities in areas subjected to a high occurrence of fire.     

Regeneration strategies of tree species in the laurel forest of Tenerife (The Canary Islands)

The laurel-forest of the Canary Islands is a montane cloud-forest. In order to gain some knowledge on the processes that maintain tree species diversity, we conducted an analysis of three different laurel-forest plots of the Anaga massif (Tenerife), varying in canopy composition but growing under similar environmental conditions. For each plot we recorded basal area of the canopy trees (h<1.30 m), the density of suckers and seedlings (h>1.30 m), as well as seed-bank composition. The plots have similar regeneration composition, which appears to be independent of differences in canopy composition. Laurus azorica is the most common seedling species, whereas Prunus lusitanica is the most abundant species among suckers and basal shoots. Neither Erica arborea nor Myrica faya, the two main canopy trees in one of the plots, were found in any of the stands as seedlings or suckers, despite their existence as viable seeds in the seed-bank. The regeneration composition and the canopy composition in one of the plots is remarkable different, revealing differents dynamics processes in the three plots. The results suggest the existence of three well-defined ecological groups: pioneer (regeneration primarily by seedlings), non-pioneer (regeneration by seedlings and suckers) and remnant species (regeneration primarily by suckers).These three groups and the effect of small scale disturbances (natural and human-induced), could help to understand the maintenance of tree species richness.     

中亚热带格氏栲天然林幼苗竞争强度研究

采用Hegyi单木竞争指数模型对格氏栲幼苗种内和种间竞争强度进行定量分析.结果表明,格氏栲幼苗种内竞争强度随幼苗高度的增加而逐渐减少.种间竞争强度的顺序为:桂北木姜子＞梨茶＞黄润楠＞毛鳞省藤＞矩圆叶鼠刺＞木荷＞酸味子＞狗骨柴＞少叶黄杞＞山黄皮＞光叶山矾＞沿海紫金牛＞小叶赤楠＞尖叶水丝梨＞赤楠＞草珊瑚＞格氏栲＞丝栗栲＞杜...     

Differential distribution of leaf chemistry in eucalypt seedlings due to variation in whole-plant nutrient availability

We investigated the effects of whole-plant nutrient-availability on the degree of distribution of some plant primary and secondary (nitrogen, fibre, flavonols, gallotannins and cineole) chemicals across young, mature and old leaves of seedlings of Eucalyptus nitens. Four treatments that ranged from low to high nutrient-application rates resulted in mean whole-plant foliar concentrations of 0.63%, 0.85%, 1.11% and 1.82% nitrogen dry matter (N%DM) for treatments A, B, C and D, respectively. Within-plant distribution (across the leaf age profile of young, mature and old leaves within a eucalypt seedling) of N%DM ranged from zero in treatment A to a wide range of distribution in treatment D (low N%DM concentrations in old leaves to high N%DM concentrations in young leaves). Similarly, the distribution of fibre ranged from zero in treatment A to a wide range of distribution in treatment D, but with high concentrations in old leaves and low concentrations in young leaves. In contrast, flavonols (weakly) and gallotannins had a wide range of distribution in treatment A (low concentrations in old leaves to high concentrations in young leaves) but were little or not distributed in the other treatments. Again in contrast, cineole was strongly distributed between old and young leaves (low concentrations in old leaves to high concentrations in young leaves) across all treatments while concentrations in mature leaves reflected one or other leaf age depending on treatment. Protein precipitable phenols in treatments A, B and C were high in young, and low in old leaves; whereas in treatment D they were low and similar between leaves of different ages.     

Predicting Species Response to Disturbance from Size Class Distributions of Adults and Saplings in a Jamaican Tropical Dry Forest

The diversity of tropical dry forests is poorly described and their regeneration ecology not well understood, however they are under severe threat of conversion and degradation. The Hellshire Hills constitute a dry limestone forest reserve on the south coast of Jamaica that is of high conservation value. In order to describe the structure and composition of this forest and assess the extent to which the population structures of its tree species do characterize their regeneration ecologies, pre-disturbance structure, floristics and seedling populations were compared with post-disturbance species responses in twelve 15 m × 15 m permanent sample plots which were laid out in a blocked design in April 1998, giving a total sample area of 0.27 ha. These plots were subjected to disturbance in April 1999 (cutting) with each of four blocks being assigned with two randomly allocated treatment plots (partially and clear cut) and one control plot (uncut). A total of 1278 trees (≥2 cm DBH) and 7863 seedlings and saplings (0–2 mm and 2–20 mm root collar diameter (RCD) respectively), comprising 60 and 52 species, respectively, were sampled in the plots prior to disturbance. The species-area curve for trees reached a maximum at 0.20 ha, and abundance was widely distributed amongst the species (26 had importance values greater than 1%); four species were notably codominant (with importance values between 7 and 8%). The forest stand structure had a reverse J-shaped curve for tree and for seedling/sapling size-class distributions, which indicated that the forest as a whole was probably regenerating adequately. From an analysis based on adult and sapling size-class distributions (SCDs), 21 species with 15 or more individuals were classified into 3 groups. Many of the species (15 of the 21), had flat adult SCDs that deviate from the whole-community reverse J-shaped SCD. However, sapling SCDs for 6 of the 15 species were strongly positive indicating the potential for their populations to be sustained by recruitment from the saplings present. No general association was found between these SCD species groupings and the actual ability of the species to recover from disturbance. Analysis of post-disturbance response revealed that for only 9 of the 21 species did adult SCDs provide adequate prediction, but for an additional 6 of the species information on sapling SCDs improved the accuracy of prediction if the ‘release’ of saplings or smaller individuals predominated recovery. However in this forest, recovery following disturbance which left stem and roots in place is predominantly by coppice regrowth, and there were no significant correlations found between adult SCDs and the species’ ability to coppice.     

Thalassia testudinum seedling responses to changes in salinity and nitrogen levels

The dominant seagrass in Florida Bay, Thalassia testudinum Banks ex König, is a stenohaline species with optimum growth around marine salinity (30-40 PSU). Previous studies have examined the responses of mature short shoots of T. testudinum to environmental stresses. Our goal was to assess responses of seedlings to changes in water chemistry in Florida Bay that might occur as part of the Comprehensive Everglades Restoration Plan (CERP). Specifically, we examined seedling survival, growth, photosynthesis, respiration and osmolality in response to hypo- and hyper-salinity conditions, as well as possible synergistic effects of depleted and elevated ammonium concentrations. The study was conducted in mesocosms on T. testudinum seedlings collected during August 2003 near Florida Bay. Hyper- and hypo-saline conditions were detrimental to the fitness of T. testudinum seedlings. Plants at 0 and 70 PSU exhibited 100% mortality and a significant decrease in survival was observed in the 10, 50 and 60 PSU treatments. Increased levels of ammonium further decreased growth in the lower salinity treatments. Seedlings in 30 and 40 PSU had the greatest growth. Quantum yield and relative electron transport rate, measured using PAM fluorometry, showed a decrease in photosynthetic performance on either side of the 30-40 PSU optimum. Tissue osmolality decreased significantly with decreased salinity but tissue remained consistently hyperosmotic to the media across all salinity treatments. Maintaining negative water potential and allocating more energy to osmoregulation may decrease the productivity of this species in salinity-stress conditions. Our results suggest that the salinity-tolerance limits of this seagrass at the seedling stage are not as broad as those reported for mature plants. Increased fresh water inflow, especially if co-occurring with an increase in water-column ammonium, could negatively affect successful recruitment of T. testudinum seedlings in northern regions of Florida Bay.