发育阶段和海拔对岷江源区陇蜀杜鹃小枝功能性状及生物量分配的影响

本研究分析了岷江源区卡卡山典型高山灌丛植物陇蜀杜鹃不同发育阶段(花芽期和开花期)及不同海拔(3600 m低海拔和3800 m高海拔)下功能小枝和叶片性状的差异,以及空间异质性对花芽期和开花期小枝功能性状相关性及其权衡作用的影响。结果表明: 低海拔同一生长期陇蜀杜鹃小枝长度显著大于高海拔,高海拔开花期小枝的花数量和花质量显著高于低海拔。同一海拔花芽期的小枝质量、叶片数量、总叶质量、总叶面积和总叶柄质量均显著大于开花期,单叶质量和单叶柄质量均显著小于开花期。与花芽期相比,开花期叶生物量占比减少了13%,而小枝质量占比显著增加。小枝的生物量权衡表明,花芽期性状倾向于小枝质量,开花期倾向于总叶质量;花芽期的叶偏好分配于单叶质量,低海拔和高海拔开花期叶片分别偏好分配到单叶柄质量和单叶质量。低海拔开花期小枝质量与总叶面积、总叶质量均为异速生长,单叶柄质量和单叶面积为异速生长。海拔和发育阶段共同影响了陇蜀杜鹃功能小枝和叶片的性状。     

Sapling biomass allocation and growth in the understory of a deciduous hardwood forest

Above- and belowground tissues of co-occurring saplings (0.1-1 m height) of Acer saccharum Marsh. (very shade tolerant), Acer rubrum L. (shade tolerant), Fraxinus americana L. (intermediate shade tolerant), and Prunus serotina Ehrh. (shade intolerant) were harvested from a forest understory to test the hypothesis that the pattern of biomass allocation varied predictably with shade-tolerance rank. The placement and length of branches along the main axis were consistent with the formation of a monolayer of foliage for the tolerant and intermediate species. Other morphological characteristics did not vary predictably with shade-tolerance rank. The maintenance of high specific leaf area (SLA; leaf area/leaf mass) and leaf area ratio (LAR; leaf area/sapling mass) is considered important for growth under extreme shade, yet these traits were not clearly related to the shade-tolerance rank of these species. Fraxinus americana, an intermediate species, had the highest LAR and growth rate in the understory, and with the exception of P. serotina, the very shade-tolerant A. saccharum had the lowest LAR. Prunus serotina maintained a large starch-rich tap root and shoot dieback was common, yielding the largest root/shoot ratio for these species. The observed allocation patterns were not similar to the long-standing expectation for the phenotypic response of juvenile trees to shade, but were consistent with three hypothetical "growth strategies" in the understory: (1) the low SLA and LAR of A. saccharum may provide a measure of defense against herbivores and pathogens and thus promote persistence in the understory, (2) the high SLA for F. americana and high LAR for F. americana and A. rubrum may enable these species to achieve high growth rates in shade, and (3) the large carbohydrate stores of P. serotina may poise this species for opportunistic growth following disturbance. The relative importance of resistance to herbivores and pathogens vs. the maintenance of high growth rates may be important in evaluating the patterns of biomass allocation in the understory.     

Spatial distribution of canopy and subcanopy species along a sloping topography in a cool-temperate conifer-hardwood forest in the snowy region of Japan

The spatial distributions of canopy and subcanopy species (50cm stem length) were investigated within a plot extending from the top of a ridge to the valley bottom in a cool-temperate old-growth mixed forest, dominated by Cryptomeria japonica and Fagus crenata, in the snowy region of Japan. Based on the longitudinal profile of the slope, the study slope was divided into the relatively gentle upper slope position (US), the steep lower slope position (LS), the flat valley bottom (VB) and the boundary zone between the upper and lower slopes (BS). Spatial dispersal and the association patterns of species were analyzed in upperstory (10cm d.b.h) and understory (<10cm d.b.h) layers. Dominant species in the upperstory layer abruptly changed from Cryptomeria to Fagus at the BS site. In contrast, the understory trees of many species, including shade-intolerant and evergreen species, were independent of the location of conspecific upperstory trees or canopy gaps and extended their distributions on and around the BS site. Significant, diverse canopy and subcanopy species occurred at this site in both upperstory and understory layers. On the BS site, which is the lower margin of Cryptomeria-dominated vegetation, there were many medium-sized C.japonica that were killed by uprooting or breaking of the stems as a result of heavy snow pressure. It is suggested that the snow pressure gradient along a slope has a strong influence on community structure and the maintenance of diverse canopy and subcanopy species in this snowy mixed forest.     

Differences in parasite susceptibility and costs of resistance between naturally exposed and unexposed host populations

It is generally assumed that resistance to parasitism entails costs. Consequently, hosts evolving in the absence of parasites are predicted to invest less in costly resistance mechanisms than hosts consistently exposed to parasites. This prediction has, however, rarely been tested in natural populations. We studied the susceptibility of three naïve, three parasitized and one recently isolated Asellus aquaticus isopod populations to an acanthocephalan parasite. We found that parasitized populations, with the exception of the isopod population sympatric with the parasite strain used, were less susceptible to the parasite than the naïve populations. Exposed but uninfected (resistant) isopods from naïve populations, but not from parasitized populations, exhibited greater mortality than controls, implying that resistance entails survival costs primarily for naïve isopods. These results suggest that parasites can drive the evolution of host resistance in the wild, and that co‐existence with parasites may increase the cost‐effectiveness of defence mechanisms.     

Optimal allocation to vegetative and sexual reproduction in plants: the effect of ramet density

Vegetative reproduction is a very common alternative by which plants can contribute to the next generations. There are many considerations predicting which mode of reproduction, vegetative or sexual, should be favored and numerous experimental studies to verify them. However, the results are inconsistent especially when the effect of plant density is considered. I apply here a dynamic optimization model to predict the rate of vegetative and sexual reproduction in plants as a response to changes in the local plant density. The population is assumed to occupy a heterogeneous environment consisting of patches in which growth and reproduction of plants are possible and unfavorable space between them. As the environment is globally stable, the seeds, which can disperse without restriction, exhibit a constant recruitment rate. The ramets are assumed to settle only within the patch of the mother plant. The rate of ramet production effects local density, which in turn determines ramet recruitment. The optimal strategy maximizes the expected lifetime genetic contribution, realized via both vegetative and sexual reproduction. The solutions obtained under these assumptions are dualistic. The model predicts that different approaches applied in studying the effect of ramet density should give opposite outcomes. When the comparison is between patches in natural populations, a positive relationship between relative ramet allocation and density is expected. When the density is experimentally manipulated or its effect is analyzed across different successional stages, a negative relationship should be found. The results seem to be confirmed by empirical studies.     

Stability of salt tolerance at the cell level after regeneration of plants from a salt tolerant tobacco cell line

Plants were regenerated from both the wild type and a stable NaCI-tolerant line of tobacco cells ( Nicotiana tabacum/gossii ). The regeneration process was much more difficult in the case of the NaCI-tolerant line and was only successful in the absence of NaCI. These plants differed morphologically from those regenerated from the wild type cell line, exhibiting abnormally short internodes, small leaves and reduced growth. Cell suspension cultures derived from plants regenerated from the stable NaCI-tolerant line retained a high level of tolerance to salt. The NaCI-concentration required to reduce fresh and dry weight gain by 50% was about twice that observed in the case of the cells obtained from wild type plants.
The results presented here, together with those of Watad et al. (1985), indicate that resistance to salt is operating and stable at the cellular level before and after plant regeneration. When the regenerated plants were grown in increasing levels of salt their growth response was not clearly different from that of the plants regenerated from the wild type cell line. However, the survival of plants on high concentrations of NaCI tended to be higher in the case of plants regenerated from the NaCI-tolerant cell line.     

Seasonal variation in heat shock proteins Hsp70 and Hsp90 expression in an exposed and a shaded habitat of Iris pumila

Seasonal variation in heat shock proteins Hsp70 and Hsp90 expression was studied in the leaves of two naturally growing Iris pumila populations, one inhabiting an open dune site, and the other the understorey of a Pinus silvestris stand. The Hsps were quantified by an immunoblotting procedure. The level of the Hsps was found to vary significantly both across seasons and between habitats. The mean Hsp70 concentration was significantly greater at the open area than in the woodland understorey, reaching its maximum in the summer, especially in plants experiencing full sunlight. Two Hsp90 isoforms, referred to as Hsp90a (86 kDa) and Hsp90b (84 kDa), were detected. At both habitats, the level of Hsp90a was highest in autumn, that of Hsp90b in spring, whereas both of them reached a nadir in summer. Throughout the growing season, the relative abundance of Hsp90b was higher in plants growing under vegetation canopy in comparison to those inhabiting the open dune site. An inverse relationship between the phenotypic variation in specific leaf area and the level of Hsp90b over seasons at both habitats was observed, suggesting the role of this protein in buffering phenotypic variation in the wild.     

The interplay between shifts in biomass allocation and costs of reproduction in four grassland perennials under simulated successional change

When perennial herbs face the risk of being outcompeted in the course of succession, they are hypothesized to either increase their biomass allocation to flowers and seeds or to invest more in vegetative growth. We tested these hypotheses in a 3-year garden experiment with four perennials (Hypochaeris radicata, Cirsium dissectum, Succisa pratensis and Centaurea jacea) by growing them in the midst of a tall tussock-forming grass (Molinia caerulea) that may successionally replace them in their natural habitat. In all species except for the short-lived H. radicata, costs of sexual reproduction were significant over the 3 years, since continuous bud removal enhanced total biomass or rosette number. To mimic succession we added nutrients, which resulted in a tripled grass biomass and higher death rates in the shorter-lived species. The simulated succession resulted also in a number of coupled growth responses in the survivors: enhanced plant size as well as elevated seed production. The latter was partly due to larger plant sizes, but mostly due to higher reproductive allocation, which in turn could be partly explained by lower relative somatic costs and by lower root–shoot ratios in the high-nutrient plots. Our results suggest that perennial plants can increase both their persistence and their colonization ability by simultaneously increasing their vegetative size and reproductive allocation in response to enhanced competition and nutrient influxes. These responses can be very important for the survival of a species in a metapopulation context. Electronic Supplementary Material Supplementary material is available for this article at and is accessible for authorized users.     

Differences in genetic structure and ecological diversity between parental forms and hybrids in a Daphnia species complex

Hybridization is a common phenomenon in Daphnia species complexes. Hybrids often dominate in Daphnia populations; therefore it is worthwhile to look for principal differences between parental and hybrid populations with respect to their genetic structure and clonal differentiation. We studied natural populations of members of the Daphnia galeata/hyalina/cucullata complex in three lakes. In one of these lakes, one parental species (D. galeata) and one hybrid (D. galeata × cucullata) were investigated more intensively. The frequency of sexual reproduction was higher in parental populations, whereas clonal diversity was higher in hybrid populations. Ecological differentiation among clonal groups was more pronounced in the D. galeata × cucullata hybrid compared to D. galeata, whereas selection intensity was weaker. These results are discussed with respect to stability of clonal groups, multiple hybridizations and selective constraints.     

峡谷型喀斯特不同生态系统的土壤微生物数量及生物量特征

采用样地调查与室内分析相结合的方法,研究了峡谷型喀斯特水田、旱地、草地、灌丛、人工林、次生林6种生态系统不同深度土壤微生物数量、微生物生物量特征及其分形关系。结果表明:峡谷型喀斯特不同生态系统的土壤微生物数量及组成不同,微生物数量均以次生林最高,旱地最低,其组成数量均为细菌放线菌真菌,细菌是土壤微生物的主要类群,数量多达26.66×105—71.64×105cfu/g,占全部微生物比例为87.00%—95.50%,其次为放线菌数量,为1.45×105—3.78×105cfu/g,所占比例为4.21%—12.39%,真菌数量最小,为0.07×105—0.23×105cfu/g,所占比例仅为0.24%—0.61%,不足1%。不同生态系统土壤微生物生物量碳(MBC)、氮(MBN)、磷(MBP)的含量不同,次生林MBC与MBN最高,人工林MBP最高,旱地MBC最低,草地MBN与MBP最低;各生态系统均为MBCMBNMBP。不同生态系统的MBC/SOC、MBN/TN、MBP/TP分别为0.44%—0.97%、2.13%—3.13%、1.46%—2.13%,差异不显著;MBC/MBN在3.06—6.54之间,其中次生林极显著高于其他生态系统,其他生态系统差异不显著。不同生态系统土壤微生物数量及生物量均随土层加深而减少,且具有良好分形关系,均达到了极显著水平(P0.01)。探讨土壤微生物活性为提高石灰土土壤肥力、促进喀斯特植被迅速恢复提供依据。     

Reproductive strategy, clonal structure and genetic diversity in populations of the aquatic macrophyte Sparganium emersum in river systems

Many aquatic and riparian plant species are characterized by the ability to reproduce both sexually and asexually. Yet, little is known about how spatial variation in sexual and asexual reproduction affects the genotypic diversity within populations of aquatic and riparian plants. We used six polymorphic microsatellites to examine the genetic diversity within and differentiation among 17 populations (606 individuals) of Sparganium emersum, in two Dutch-German rivers. Our study revealed a striking difference between rivers in the mode of reproduction (sexual vs. asexual) within S. emersum populations. The mode of reproduction was strongly related to locally reigning hydrodynamic conditions. Sexually reproducing populations exhibited a greater number of multilocus genotypes compared to asexual populations. The regional population structure suggested higher levels of gene flow among sexually reproducing populations compared to clonal populations. Gene flow was mainly mediated via hydrochoric dispersal of generative propagules (seeds), impeding genetic differentiation among populations even over river distances up to 50 km. Although evidence for hydrochoric dispersal of vegetative propagules (clonal plant fragments) was found, this mechanism appeared to be relatively less important. Bayesian-based assignment procedures revealed a number of immigrants, originating from outside our study area, suggesting intercatchment plant dispersal, possibly the result of waterfowl-mediated seed dispersal. This study demonstrates how variation in local environmental conditions in river systems, resulting in shifting balances of sexual vs. asexual reproduction within populations, will affect the genotypic diversity within populations. This study furthermore cautions against generalizations about dispersal of riparian plant species in river systems.     

Pollen flow between flowers of the same morph in invasive populations of Oxalis pes-caprae L. in the western Mediterranean region

Oxalis pes-caprae is a tristylous South African geophyte that is invasive in regions with Mediterranean climate. Given the introduction of the short-styled morph only, vegetative reproduction was, until recently, the reproductive mode known for this invaded area. The detection of new floral morphs, fruit and seed production in natural populations of the invaded range, together with the reported weakening in the heteromorphic incompatibility system, raised the question on whether the short-styled flowers are able to exchange pollen among themselves, and if so, which mechanisms account for it. Thus, flower morphometric analysis and field experiments were conducted to assess pollinator visitation rates and pollen flow in three invasive populations. Flower morphological changes suggesting the evolution from tristyly towards semi-homostyly were observed. Moreover, O. pes-caprae flowers were visited by different functional groups of pollinators, mostly hymenopteran. Dye flow experiments revealed that the short-styled flowers were able to successfully exchange pollen among themselves in natural conditions. All of this, together with the weakening of the incompatibility system, constitutes further data that might help to explain the recently reported occurrence of sexual reproduction in this invaded range, which by itself bears important implications for the invasion process of O. pes-caprae.     

间伐对日本落叶松人工林林下更新木本植物组成和生长影响的时间效应

明确间伐对针叶人工林林下更新阔叶木本植物组成和生长影响的时间效应,可为促进人工纯林向针阔混交林转化、进而解决纯林生产与生态功能无法兼顾的问题提供参考。本研究以我国北方重要针叶人工林——日本落叶松人工林为例,比较间伐后短期(1～3年)、中期(4～9年)和长期(>9年)人工林林下更新木本植物组成的差异;并选择具有较高重要值且与落叶松互惠共生的3种更新树种蒙古栎、色木槭、糠椴,分析不同间伐时期人工林内光照(郁闭度)与更新木本植物生长的关系。结果表明: 在间伐样地内更新的阔叶木本植物达46种,不同间伐时期样地内共有且占据优势的乔木树种为色木槭,灌木树种为忍冬和卫矛。随间伐后时间的推移,更新物种数逐渐减少,但乔灌比呈增大的趋势;中性树种占据优势地位。间伐对更新树种生长影响的时间效应受树种耐荫性的影响,糠椴的基径和树高均高于蒙古栎和色木槭。随间伐后时间的延长,糠椴的基径、色木槭的树高对光照响应较敏感,分别倾向于采用“耐荫策略”和“避荫策略”以适应间伐后变化的环境。间伐对日本落叶松人工林林下更新阔叶木本植物组成和生长的影响具有明显的时间效应;在制定以促进人工林林下树种更新为目标的间伐措施时,应该考虑适当延长间伐间隔,从而保证糠椴和色木槭等阔叶树幼苗的生长,使其进入林冠层,促进形成针阔混交林,实现人工林的可持续发展。     

Reproductive allocation and the long-term costs of reproduction in Siparuna grandiflora, a dioecious neo-tropical shrub

1 Using a combination of observational and experimental approaches, both allocation of resources to reproduction (often called the direct cost of reproduction) and the subsequent long-term costs (the indirect, delayed or demographic cost) associated with reproductive allocation to male and female function in Siparuna grandiflora (Siparunaceae), a tropical dioecious shrub, were examined.
2 The objectives were to determine whether females allocate more biomass or nitrogen per reproductive episode than males, and whether there is a long-term cost of reproduction in terms of subsequent growth or reproduction for either sex. If there is no long-term cost of reproduction, then reproduction may be viewed as free in an evolutionary sense.
3 As is generally the case in dioecious species, females allocated more biomass and nitrogen to reproduction than males. Females also showed delayed costs of reproduction in terms of decreased growth and subsequent reproduction, whereas males did not.
4 The lack of measurable delayed costs in males suggests that with the evolution of dioecy, selection has reduced delayed costs of reproduction in S. grandiflora males. In contrast, females that were prevented from reproducing were able to re-allocate resources to growth, and produced more stem length on average than males. This re-allocation response may have evolved to reduce delayed costs of reproduction in females over time frames longer than that considered in the present study.     

Distribution of Daphnia in a trade-off between food and temperature: individual habitat choice and time allocation

1. In a thermally stratified water column with a deep‐water algal maximum, Daphnia face a trade‐off between food (high fecundity) and temperature (fast development). Recent studies showed that Daphnia populations move up and down the entire water column to take advantage of both, but the proportion of time allocated by individuals to the epilimnion, metalimnion and hypolimnion with their specific food and temperature conditions is not yet known. 2. In a system of 1 m deep, vertical perspex tubes, I established three temperature gradients with 2, 5 and 10 °C differences between the surface (epilimnion) and the bottom layer (hypolimnion). Algae were added to the hypolimnion to simulate a deep‐water algal maximum. 3. The migration behaviour of individual neonate and egg‐bearing Daphnia hyalina × galeata was monitored in order to measure the proportions of time the individuals allocated to the different vertical habitats and to assess the frequency of their shifts between epilimnion and hypolimnion. 4. Neonates stayed continuously at the surface, taking advantage of the higher temperature, possibly because feeding was less important for them because of egg yolk reserves. In contrast, egg‐bearing females spent more time feeding in the hypolimnion when the temperature gradient was weak, but also migrated into the epilimnion to take advantage of the higher temperature. In the steepest temperature gradient, the egg‐bearing females either shifted between epilimnion and hypolimnion, or dwelled constantly in the metalimnion with intermediate conditions.     

Brooding crustaceans in a highly fragmented habitat: the genetic structure of Mediterranean marine cave-dwelling mysid populations

Habitat fragmentation and climate change are two major threats on biodiversity. Fragmentation limits the number of patches and their decreased connectivity cannot always maintain populations at dynamic equilibrium. The natural extreme fragmentation of marine cave habitats represents an opportunity to understand how these processes interact. The hypothesis of a low gene flow among populations due to a high level of fragmentation was tested by analysing sequence variation in a fragment of the mitochondrial gene of the cytochrome oxidase subunit I in 170 individuals (23 localities across the NW Mediterranean) of two marine cave-dwelling mysids of the genus Hemimysis. The species Hemimysis margalefi recently replaced its congener Hemimysis speluncola, a species shift that could be related to the warming of the Mediterranean Sea and to differences in their thermal tolerances. There were too few H. speluncola samples to further discuss their genetic structuring, but for H. margalefi, the present study revealed high levels of genetic diversity and genetic structuring, as shown by the eight genetically distinct groups identified. The Croatian group might constitute a sibling species due to a strong divergence (15%). Nevertheless, these groups present reduced but orientated gene flow according to the general circulation in the Mediterranean, and fit a stepping-stone model. At local scale (Marseille area, France), gene flow among caves is dependent on unexpected local hydrodynamic barriers, that determine metapopulation sizes. Through the example of mysid species inhabiting marine caves, the present work confirms the strong influence of habitat disjunction (natural fragmentation) on population structure, and stresses the importance of coastal geomorphological features in inducing complex interactions between the circulation of water masses and the circulation of genes.     

施氮和减水对中亚热带壳斗科三种幼树生物量及其分配的影响

土壤氮素和土壤含水量是森林生态系统中限制植物生长的重要因子。为探讨常绿阔叶树种对模拟氮沉降增加和降水减少的响应,以同质园中自然生长的壳斗科(Fagaceae)丝栗栲(Castanopsis fargesii)、大叶青冈(Cyclobalanopsis jensenniana)和麻栎(Quercus acutissima)五年生幼树为对象,比较了对照(CK)、施氮(+N,施氮60 kg hm~(-2) a~(-1))、减水(-W,减少自然降水的50%)以及施氮和减水(+N-W,施氮60 kg hm~(-2) a~(-1)和减少自然降水的50%)对总生物量、各器官生物量及其生物量分配的影响。研究表明:(1)施氮显著增加了三种幼树的总生物量及各器官生物量(P0.05)。(2)减水未引起三种幼树的总生物量及各器官生物量的显著下降(P0.05)。(3)除麻栎树叶生物量、树枝生物量外,施氮和减水交互作用对三种幼树总生物量及各器官生物量没有明显影响(P0.05)。(4)施氮显著提高了丝栗栲幼树的干重比、大叶青冈幼树的干重比和枝重比(P0.05),降低了大叶青冈的叶重比和根重比(P0.05)。(5)减水导致丝栗栲幼树和麻栎幼树的根重比、麻栎幼树的根冠比显著增加(P0.05),引起丝栗栲幼树的枝重比、麻栎幼树的叶重比、枝重比和干重比显著降低(P0.05)。(6)施氮和减水交互作用显著提高了丝栗栲幼树的根重比(P0.05),降低了麻栎幼树的干重比(P0.05)。