Effect of tree species identity and related habitat parameters on understorey bryophytes – interrelationships between bryophyte,soil and tree factors in a 50-year-old experimental forest

Plant and Soil - Overstorey tree species influence both soil properties and microclimate conditions in the forest floor, which in turn can induce changes in ground bryophyte communities. The aim of...     

Effect of competition on the demography of planktonic cladocerans — Daphnia and Diaphanosoma

Summary Isolated and mixed continuous cultures of Daphnia hyalina and Diaphanosoma brachyurum in lake water were maintained under laboratory conditions to elucidate demographic effects of competition. Population dynamics curves were obtained. Interspecific competition was revealed by the decrease in the average density of animals in the mixed versus isolated cultures and by the extinction of one species in the presence of the other. Within the first 50 days either Diaphanosoma (4 cases) or Daphnia (1 case) was the superior competitor, depending on the initial conditions. Further cultivation resulted in the extinction of Diaphanosoma in the mixed cultures. There were no statistically significant differences between the maximum rates of population increase (r _m ) in Daphnia and Diaphanosoma at the concentration of edible algae about 2·10⁵ m³ml^-1(0.293 and 0.286 days^-1, respectively). Time lags for density-dependent parameters of the populations were evaluated by means of rank cross-correlations. Regardless of the species identity the time lags of fecundity, birth rate, and the rate of population growth were significantly higher in the superior competitor. The initial conditions of culturing affected the time lags which in their turn influenced the outcome of the interaction. Enhanced competitive ability due to the maximized time lags in Daphnia was not associated with the loss of population stability. Conversely, it brought about destabilization of Diaphanosoma populations which seemed to be the ultimate cause of its extinction observed in the end of the experiment. Time lag of the population growth rate was well predicted based on the half-sum of time lags in birth and death rates (r²=0.80, P<0.001). Daphnia responded to competition with a sharp shortening of the time lags of fecundity, birth rate, and the population growth rate. It increased clutch size and showed inverse relationship between the fecundity time lag and average fecundity even though it was strongly suppressed by Diaphanosoma. The competitive ability was not related to the percentage of adults in the populations. In contrast to the current belief the major result of interspecific competition in the experiment was not a decrease in the rate of population growth but was a reduction in population time lags.     

Are brood sex ratios adaptive?—The effect of experimentally altered brood sex ratio on nestling growth,mortality and recruitment

Brood sex ratios (BSRs) have often been found to be nonrandom in respect of parental and environmental quality, and many hypotheses suggest that nonrandom sex ratios can be adaptive. To specifically test the adaptive value of biased BSRs, it is crucial to disentangle the consequences of BSR and maternal effects. In multiparous species, this requires cross-fostering experiments where foster parents rear offspring originating from multiple broods, and where the interactive effect of original and manipulated BSR on fitness components is tested. To our knowledge, our study on collared flycatchers (Ficedula albicollis) is the first that meets these requirements. In this species, where BSRs had previously been shown to be related to parental characteristics, we altered the original BSR of the parents shortly after hatching by cross-fostering nestlings among trios of broods and examined the effects on growth, mortality and recruitment of the nestlings. We found that original and experimental BSR, as well as the interaction of the two, were unrelated to the fitness components considered. Nestling growth was related only to background variables, namely brood size and hatching rank. Nestling mortality was related only to hatching asynchrony. Our results therefore do not support that the observed BSRs are adaptive in our study population. However, we cannot exclude the possibility of direct effects of experimentally altered BSRs on parental fitness, which should be evaluated in the future. In addition, studies similar to ours are required on various species to get a clearer picture of the adaptive value of nonrandom BSRs.     

Does sex matter? Gender-specificity and its influence on site-chronologies in the common dioecious shrub Juniperus communis

In recent years an increasing number of studies have shown shrubs to be reliable proxies of environmental conditions in regions where Trees − due to harsh climate conditions − are absent. Although many shrubs are monoecious, some are dioecious, which poses certain questions related to gender-specific growth as observed for trees in previous studies. Here, we address the questions whether dioecious shrubs, similar to trees, show growth differences between male and female plants, and − if so − whether this difference needs to be considered in terms of sample selection. We chose Juniperus communis. L., the most widely distributed woody plant, and a common and well-studied dioecious shrub species in the northern hemisphere, especially in the Boreal, Subarctic tundra and Alpine regions. Our samples were collected from four sites − three from the Ural Mountains and one site from Kirkenes in Norway. To see if there were differences in radial growth between sexes we performed four different analyses. First, we used multivariate explorative statistics to see if there were gender biased sub-populations and generally found no differences. Secondly, to compare growth over the lifetime of shrubs we computed cumulative annual increments of basal area which revealed no gender-specific growth patterns. Thirdly, to test if differences in radial growth between male and female shrubs affect the resulting site-chronology, we compared individual shrub chronologies with the site-chronology and found a significant differentiation between normalized correlations of gender-specific chronologies to the site-chronology. This significant difference was restricted to an overall comparison, but not evident at individual site-level. Lastly, we compared correlations of gender-specific chronologies and a mean site-chronology with monthly climate records to find only very few meaningful differences in their responses. In summary, we could not detect any clear gender-specific growth pattern in Juniperus communis but observed a trend towards more non-climatic signals in female junipers which may affect the resulting site-chronology.     

Effects of climate, tree age, dominance and growth on δ15N in young pinewoods

Needles, annual rings from basal stem discs and bark of three dominant and three suppressed Pinus pinaster from a 12-year-old pine stand (naturally regenerated after a wildfire) were analysed to study the effects of climate, tree age, dominance, and growth on tree δ¹⁵N. Foliar-N concentration in dominant pines (0.780–1.474% N) suggested that soil N availability was sufficient, a circumstance that allowed isotopic discrimination by plants and (greater) differences in δ¹⁵N among trees. The δ¹⁵N decreases in the order wood (−0.20 to +6.12‰), bark (−1.84 to +1.85‰) and needles (−2.13 to +0.77‰). In all trees, before dominance establishment (years 1–8), the N stored in each ring displayed a decreasing δ¹⁵N tendency as the tree grows, which is mainly due to a more “closed” N cycle or an increasing importance of N sources with lower δ¹⁵N. After dominance establishment (years 9–12), wood δ¹⁵N values were higher in suppressed than in dominant trees (2.62 and 1.46‰, respectively; P < 0.01) while the reverse was true for needles and bark; simultaneously, the absolute amount of N stored by suppressed pines in successive rings decreased, suggesting a lower soil N assimilation. These results could be explained by lignification acting as major N source for needles in suppressed pines because products released and reallocated during lignification are ¹⁵N-depleted compared with the source. According to principal component analysis, wood δ¹⁵N appears associated with wood N concentration and precipitation during the growing season, but clearly opposed to age, basal area increment and mean temperature in spring and summer.     

Effect of climate and competition on radial growth of Pinus massoniana and Schima superba in China’s subtropical monsoon mixed forest

Tree growth is affected by many exogenous and endogenous factors, especially climate and competition. To address the issue of how these factors influence tree growth under global warming, dendroclimatology combined with competition analysis was used to examine the radial growth response of two major species – Pinus massoniana and Schima superba in subtropical monsoon mixed forests in southern China. For growth-climate relationship analysis, residual and ARSTAN chronologies of these two species were compared for the response function analysis over the past several decades. In terms of competition analysis, annual basal area increment (BAI) over several time intervals was calculated and linear mixed model techniques were employed. Several distance-independent competition indices were measured, including density (N), basal area (BA), and sum of diameter at breast height (SDBH). For competition trees with greater diameter (GR) than the subject tree, NGR, BAGR, SDBHGR were also calculated. Growth-climate relationship analysis suggested that tree growth varied in response to climate and was mostly correlated with minimum, mean and maximum air temperature as indicated by the adjusted R² value. Summer and winter temperatures had a negative effect on tree growth, while early spring temperature showed positive effects. Competition analysis suggested that subtropical trees had been affected by competition in varying degrees. Trees in the oldest forest had the most competition stress, while trees in younger forests were less affected by competition according to the adjusted R² value. Given that subtropical forests in China have been found to have more smaller trees with recent warming, it is expected that these forests will experience a decreasing effect of competition in near future. This can have profound effects on forest productivity and carbon sequestration potentials in Chinese subtropical forests.     

Effect of distance,aggregation, and habitat on levels of seed predation for two mammal — dispersed neotropical rain forest tree species

The effect of seed aggregation and distance from conspecific trees on seed predation was experimentally examined for two neotropical tree species, Macoubea guianensis (Apocynaceae) and Pouteria sp. (Sapotaceae) in a lowland tropical rain forest in northeastern Peru. Results of these experiments are discussed in the context of the Janzen-Connell model (Janzen 1970; Connell 1971), which predicts decreased seed survival near parent trees due to either density-or distance-responsive mortality, and Howe's model (Howe 1989) which predicts that trees with seeds dispersed in clumps (aggregated) will not suffer density-dependent predation, and will have higher survival of seeds near the parent tree than other trees. We also examined whether predation on seeds of these species was affected by seed placement in or near 30-m-wide strips regenerating after clear-cutting. Both species appeared to be mammal-dispersed but differed in how frugivores handled seeds, seed size, overall fruit crop size, and gemination time. Neither of the two species studied appeared to suffer seed predation in a manner predicted by the Janzen-Connell model, and patterns of seed predation for only one of the species was similar to predictions of Howe's model. For neither species did seed predation along the edge of, or in the center of, regenerating clear cuts differ from predation 15 m into the primary forest. For Pouteria, seed predation in and near regnerating strips was significantly greater than around forest trees, but the opposite pattern held for Macoubea. Overall, seed predation was much greater on Macoubea. The difference in seed predation for these two species was most likely a result of differences in the types of seed predators that attacked these two species.     

Effect of metalaxyl,fosetyl‐al,dimethomorph, cymoxanil on development and control Phytophthora on peach tree in vitro

Four fungicides were evaluated for their effectiveness against Phytophthora diseases of peach trees and their ability to absorbed and translocated by roots of peach tree in laboratory. Meta‐laxyl suppressed the development of P. cactorum and P. citwphthora on segments. Fosetyl‐Al showed variable fungicidal activity against P. cactorum and P. citwphthora. Both dimetho‐morph and cyraoxanil were not effective to inhibit the growth of fungi on segments. Section of tree trunks in 2‐yr‐old GF 677 trees were painted with one of the test fungicides. Strips of bark were removed 10 and 20 days after painting within treated area and inoculated with P. cactorum and P. citwphthora. Generally, the results agree with them obtained with excised stem and excised twig methods. Exception is the dimethomorph that reduced the development of P. cartorum and P. citrophthora. This study indicated that application with metalaxyl to the peach tree appears to be an effective procedure to control Phytophthora diseases on peach trees.     

The effect of temperature on sex ratio in the isopod Porcellionides pruinosus: Environmental sex determination or a by-product of cytoplasmic sex determination?

The sex ratios of the progenies of woodlice Porcellionides pruinosus (Crustacea, Isopoda) raised at different temperatures were studied. Females from three French populations sampled in the wild produced highly female-biased broods at 20°C and male-biased broods above 30°C. The effect of high temperature was not due to selective mortality of females. Sex determination was thus sensitive to temperature in P. pruinosus. We also found an interpopulation variability of sex ratio thermosensitivity and a weak inheritance of male-biased sex ratios at high temperatures. Samples taken from a wild population throughout the year showed that while the thermal conditions required for changes in the sex ratio occurred, there was no significant variation in the sex ratio. On the other hand, almost all the females and many males in the four populations studied harboured intracytoplasmic bacteria. These maternally inherited symbionts belong to the genus Wolbachia and are known to possess a feminizing effect. While in other arthropods Wolbachia are destroyed at high temperatures, the symbionts of P. pruinosus were detected by a PCR procedure whatever the rearing temperatures. In light of these results, we propose that the thermosensitivity of sex determination in P. pruinosus could reflect the removal of the cytoplasmic effect on sex determination rather than environmental sex determination sensu stricto. The reduction in the amount of bacteria (but not their entire elimination), or the inhibition of bacterial metabolism, may be responsible for sex ratio variations relating to temperature. The incomplete inheritance of male-biased sex ratios at high temperatures might reflect a selection of thermo-tolerant bacterial strains.     

Effect of Silt, Water and Periphyton Quality on Survival and Growth of the Mayfly Heptagenia Sulphurea

The herbivorous mayfly Heptagenia sulphurea is characteristic of rivers with stony bottoms. Records from the 20th century showed that this species had disappeared from the Common Meuse in the Netherlands, probably due to river regulation or changes in water quality. A field survey in 2003 showed that H. sulphurea was present in the Geul tributary, approximately 300 m upstream of its confluence with the Common Meuse. H. sulphurea has not recolonized the Common Meuse despite improvements in water quality over the last decades. Concentration of suspended sediments in the River Meuse, however, is still high, much higher than in the beginning of the 20th century. The presence of a silt layer may limit the return of H. sulphurea in this river by reducing availability and quality of its food. The prime objective of this study was to investigate the impact of silt on survival and growth of H. sulphurea in a laboratory experiment. Furthermore, the impact of water and periphyton quality from the Common Meuse on survival and growth of this mayfly was also investigated. Results showed that neither water quality nor cultured periphyton from the Common Meuse reduced survival and growth of H. sulphurea. The presence of a silt layer resulted in a significantly lower growth rate of the mayfly larvae. It is concluded that the silt layer reduces the accessibility of the food. Covering of food is possibly one of the main factors limiting the recolonization of H. sulphurea and probably other benthic grazers in the Common Meuse.     

Inter-colony and sex differences in the effects of parental body condition and foraging effort on the brood growth of Adélie penguins

Among colonies with different foraging distances, central-place-foraging seabirds may change their foraging and reproductive efforts. We compared the body condition, meal frequency, and diving behavior of male and female Adélie penguins at two locations: Dumont d'Urville, where there was little sea ice and they foraged in open waters far from the colony; and Syowa, where there was heavy, fast sea ice and they foraged in ice cracks close to the colony. The parental mass decrease rate during the chick-rearing period was similar between colonies and between sexes. A large individual variation in meal frequency positively affected the brood growth rate, but daily underwater time did not. A weak but significant positive effect of body condition on brood growth rate was found only in males at Syowa. It was suggested that males work with better body condition than females. We propose the hypothesis that the regional difference in the distance to the feeding sites and the sex difference in body energy reserve might constrain the capacity to regulate reproductive effort.     

Effect of pyridine homologues on the basal rate of electron transport and H+/e − ratio in chloroplasts

Low concentrations of hydrophobic pyridine homologues (1 mM) were found to increase the rate of the Hill reaction in chloroplasts without significantly affecting either the steady-state proton uptake or the rate of proton leakage in the dark. By assuming that the organic base can be bound to two types of independent binding sites in the thylakoid membrane with dissociation constantsK ₁ andK ₂ respectively, the kinetic data can be treated quantitatively. The values ofK ₁ andK ₂ determined by the treatment are in the same relative order as the hydrophobicities of the pyridine homologues:K ₁=1.16 mM andK ₂=54 mM for pyridine; 0.6 and 38 mM for 4-picoline; 0.27 and 31 mM for 4-ethylpyridine, 0.10 and 4.2 mM for 4-t-butylpyridine; 0.08 and 3.2 mM for 4-n-butylpyridine. The rates of oxygen generation and proton uptake by illuminated chloroplasts with either ferricyanide or 1,4-benzoquinone as the electron acceptor were also measured in the presence of various pyridine homologues. Low concentration of pyridine homologues were found to decrease the H⁺/e ^– ratio. This last observation seems to substantiate an indirect coupling mechanism between electron transport and proton translocation.Abbreviations Chl chlorophyll - CF₀ - CF₁ the coupling factor complex of chloroplast - FCCP carbonylcyanide-p-trifluoromethoxyphenylhydrazone - DCMU 3-(3,4-dichlorophenyl)-1,1-dimethylurea - Tricine N-tris-(hydroxymethyl)methylglycine     

Effect of peripheral nerve on the neurite growth from retinal explants in culture

The effect of peripheral nerve (PN) on neurite outgrowth from retinal explants of adult hamsters was examined.Cultures of retinal explants,and co-cultures of retinal explants and PN were performed using chick retinal basement memebrane (BM) as substrate.The presence of PN increases the number and length of neurite outgrowth.In addition,a high proportion of neurites situated close to PN tend to grow towards it.Since there was no contact between retinal explants and PN,we suggest that PN might secete diffusible substances to attract the neurites to grow towards it.