Production of male flowers does not decrease with plant size in insect‐pollinated Sagittaria trifolia,contrary to predictions of size‐dependent sex allocation

Abstract It has been proposed that relative allocation to female function increases with plant size in animal‐pollinated species. Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size‐dependent sex allocation (SDS), throwing doubt on the generalization of SDS. Plant size, phenotypic gender, and flower production were measured in experimental populations of an aquatic, insect‐pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities. The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors. In the high‐density population, 48% of ramets were male without female flowers, but in the low‐density population all ramets were monoecious. We observed allometric growth in reproductive allocation with ramet size, as evident in biomass of reproductive structures and number of flowers. However, within both populations female and male flower production were isometric with ramet size, in contrast to an allometric growth in femaleness as predicted by SDS. Phenotypic gender was not related to ramet size in either population. The results indicated that large plants may increase both female and male function even in animal‐pollinated plants, pointing towards further studies to test the hypothesis of size‐dependent sex allocation using different allocation currencies.     

树干附生尖叶拟船叶藓性比和有性生殖的比例

通过对贵州梵净山树干附生尖叶拟船叶藓的野外调查和室内研究,结果表明,在44个被调查样方共计1320株植株中,尖叶拟船叶藓单株的性比为8♀∶1♂(N=1320),其中25.0%的单株没有进行性表达;其种群的性比为5♀∶1♀♂(雌性种群:混合种群,N=44),没有发现雄性种群;其单株的有性生殖的比例为10.5%,种群的有性生殖比例为9.3%。结果表明尖叶拟船叶藓种群具有明显的雌性偏向,其种群的自然更新更多的是依赖各种营养繁殖。     

Production of male flowers does not decrease with plant size in insect-pollinated Sagittaria trifolia, contrary to predictions of size-dependent sex allocation

It has been proposed that relative allocation to female function increases with plant size in animalpollinated species.Previous investigations in several monoecious Sagittaria species seem to run contrary to the prediction of size-dependent sex allocation (SDS),throwing doubt on the generalization of SDS.Plant size,phenotypic gender,and flower production were measured in experimental populations of an aquatic,insect-pollinated herb Sagittaria trifolia (Alismataceae) under highly different densities.The comparison of ramets produced clonally can reduce confounding effects from genetic and environmental factors.In the high-density population,48％ of ramets were male without female flowers,but in the low-density population all ramets were monoecious.We observed allometric growth in reproductive allocation with ramet size,as evident in biomass of reproductive structures and number of flowers.However,within both populations female and male flower production were isometric with ramet size,in contrast to an allometric growth in femaleness as predicted by SDS.Phenotypic gender was not related to ramet size in either population.The results indicated that large plants may increase both female and male function even in animal-pollinated plants,pointing towards further studies to test the hypothesis of size-dependent sex allocation using different allocation currencies.     

To share or not to share: clonal integration in a submerged macrophyte in response to light stress

The ability of clonal plant species to share resources has been studied in many experiments. The submerged macrophyte Potamogeton perfoliatus produces interconnected ramets within short time intervals and hence may or may not share resources with ramets growing in less favourable microhabitats. From a genet point of view, sharing with ramets growing under less favourable conditions might not be an optimal strategy when photosynthates could be used to establish other ramets growing under more favourable conditions. To analyse the plasticity in clonal integration of P. perfoliatus, we set up a factorial aquaria experiment with unshaded or shaded recipient ramets (offspring), which were connected to or separated from donor ramets (parents). Increased biomass production of offspring in parent–offspring systems compared with severed offspring in both light and shade showed that ramets share resources through clonal integration. The relative translocation to the first- and second-offspring generation was influenced by habitat quality: If first-offspring ramets grew in a shaded microhabitat, second-offspring ramets clearly profited. This may be at least partially because of the fact that resources are shifted from first-offspring to second-offspring ramets, indicating controlled senescence of the first-offspring. This complex sharing behaviour might be relevant when plants produce ramets within a dense patch of macrophytes, where support of a shaded ramet might not pay off.     

Influence of local floral density and sex ratio on pollen receipt and seed output: empirical and experimental results in dichogamous Alstroemeria aurea (Alstroemeriaceae)

Local density and sexual composition are two aspects of floral neighborhoods thought to influence pollination and seed output of recipient plants. I characterized the floral neighborhood of 436 flowering ramets of Alstroemeria aurea, a southern Andean perennial, distributed among three sites. On each ramet, I measured total pollen receipt and seed output. The long-lived, bumblebee-pollinated flowers of A. aurea are synchronously protandrous with a given ramet being either all male or all female and thus incapable of self or geitonogamous pollination at the ramet level. Even though each ramet changes sex over time, A. aurea forms floral neighborhoods that remain stable with respect to density and sex ratio during the span of a focal ramet female phase. Contrary to expectation, under field conditions neither local density nor sexual identity explained significant amounts of variation in pollen receipt. Density of neighboring flowering ramets marginally affected pollen receipt in two of the three populations but in opposite directions. Despite the absence of strong effects of neighborhood sexual composition on pollen receipt, the sexual identity of neighbors affected seed output which suggests effects on the quality of pollination due to changes in patterns of pollen flow. I also compared pollen loads on the stigmas of artificially isolated ramets (6 m) with those on experimental focal ramets surrounded by six close neighbors (20 cm) that were either all male or all female. Here, pollen receipt by focal ramets in all-male neighborhoods was 1.3 times greater than in isolated ramets, and 3.8 times greater than in ramets in all-female neighborhoods. In these artificial neighborhoods, stigmatic pollen deposition increased significantly over time. In nature, rates of bumblebee visits were higher in female-biased (early-flowering) than in male-biased (late-flowering) co-occurring floral patches. Thus, spatio-temporal shifts in visitation frequencies associated with the sexual composition of floral neighborhoods might compensate for spatial variability in pollen availability within populations and explain the discrepancies between empirical and experimental results. Received: 11 June 1996 / Accepted: 24 March 1997     

COMPARISON OF INTRASPECIFIC VARIATIONS IN THE REPRODUCTION AND PHOTOSYNTHESIS OF AN UNDERSTORY HERB,ARNICA CORDIFOLIA

Intraspecific variations in the reproduction of individual ramets and monospecific patches of the understory herb Arnica cordifolia Hook. were compared with variations in photosynthesis and understory light conditions. Ramets and patches were compared from three microhabitats (open, intermediate, and shaded) that differed in daily integrated irradiance. Individual ramets from open microhabitats (> 12 MJ m⁻² d⁻¹) had 23% more total dry wt and produced twice as many seeds, when compared to ramets from shaded locations (< 5 MJ m⁻² d⁻¹). In addition, monospecific patches from open locations were 63% more dense, and estimates of seed and vegetative patch reproductive effort were 4 and 2 times greater, respectively, when compared to shaded plant patches. For all measurements, ramets and patches from intermediate understory locations (6–10 MJ m⁻² d⁻¹) were intermediate in reproductive capacity between those of open and shaded locations. In addition, A. cordifolia seeds from open microhabitats germinated significantly better (45%) than either intermediate or shaded location seeds under high light and only seeds from shaded microhabitats germinated (14%) in the dark. Compared to shaded location plants, the greater total dry weight and seed production of individual ramets and the greater estimated reproductive effort of patches from open locations corresponded to a greater maximum photosynthetic rate (16.9 μmoles m⁻² s⁻¹) and daily carbon gain (12.2 g m⁻² d⁻¹). Possibly, a greater photosynthetic capacity may make more photosynthetic resources available for reproduction by A. cordifolia plants in open locations. Thus, intraspecific variation in physiology may contribute to intraspecific variation in reproduction.     

Effects of light quality and quantity on growth of the clonal plant Eichhornia crassipes

Summary Plant canopy shade reduces photosynthetic photon flux density (PPFD) and ratio of red to far-red light (z). Both effects can cause plants to increase potential for light acquisition through vertical growth and leaf area expansion. Clonal plants such as Eichhornia crassipes might alternatively increase light interception via horizontal growth of stolons or rhizomes and placement of new ramets in less shaded microsites. Effect of simulated canopy shade and component effects of PPFD and z were tested by filtering or adding light uniformly, to a whole group of connected ramets, or locally, to individual ramets within a group. In uniform treatments, low PPFD reduced total growth but low z did not. Low PPFD and low z independently reduced stolon and ramet production and caused etiolation of petioles; effect of low PPFD plus low z on ramet production was greater than that of either factor alone. Lateral clonal growth thus did not seem to be a response to uniform shading; instead, uniformly low PPFD or low z increased partitioning to established ramets. Low z changed partitioning without changing total growth. In local treatments, reduction of growth of individual ramets due to low PPFD and inhibition of new ramet production attributable to spectral composition of light were mitigated when connected ramets were unshaded; plants may respond differently to patchy than to uniform shade.     

分株比例对异质光环境下美丽箬竹克隆系统光合生理的影响

分株数量或生物量比例差异会明显影响克隆系统对资源异质性环境的生态适应性, 地下茎木质化、连接稳固的竹类植物在生长过程中相连克隆分株通常会生活在异质光环境中, 但其叶片光合生理特性对异质光环境的响应及其分株比例效应则未见报道。该研究以地下茎相连的美丽箬竹(Indocalamus decorus)克隆系统为实验材料, 设置2个遮光率(分别为50% ± 5%和75% ± 5%)和3个分株比例(遮光与未遮光分株比例分别为1:3、2:2、3:1)处理, 分株数量为4株。分别测定了遮光处理后30、90、150天遮光和未遮光分株叶片光响应特征、气体交换参数、光合色素含量, 分析了异质光环境下美丽箬竹光合生理的变化规律。结果显示: 分株比例对美丽箬竹光合生理有显著影响, 且其与遮光、处理时间交互作用显著。美丽箬竹克隆系统遮光分株比例越大, 即遮光相对分株数量越多, 其表观量子效率(AQE)、光饱和点、最大净光合速率(P_{n max})、净光合速率(P_n)、气孔导度(G_s)、蒸腾速率(T_r)、水分利用效率越大, 光补偿点、暗呼吸速率越小, 其光合效率越高, 光能利用能力越强, 而与之相连的未遮光分株则相反; 随遮光分株比例的增大, 遮光分株叶片叶绿素a、叶绿素b含量呈先升高而后下降的变化趋势, 类胡萝卜素(Car)含量则持续下降, 而与之相连的未遮光分株叶片光合色素含量则呈下降趋势; 遮光率提高, 相同分株比例美丽箬竹克隆系统遮光分株叶片AQE、P_{n max}、P_n、G_s、胞间CO₂浓度(C_i)和光合色素含量总体升高, 而与之相连的未遮光分株叶片P_{n max}、C_i以及Car含量则总体下降。研究结果表明异质光环境下, 遮光分株光合效率和弱光利用能力明显增强, 而未遮光分株则相反, 克隆系统内分株间发生了明显的克隆分工, 且2:2、3:1分株比例克隆系统较1:3分株比例对异质光环境具有更好的适应能力。美丽箬竹克隆系统可通过差异性调节分株光合生理特性和光合色素含量, 提高遮光分株光能利用和光合效率来适应异质光环境, 以提高克隆系统的适合度。     

扎龙湿地芦苇分株生态可塑性及其对土壤因子的响应

扎龙湿地的芦苇既可形成大面积的单优群落,也可形成不同群落斑块。采用大样本抽样调查与统计分析方法,对湿地内水生生境、湿生生境、旱生生境和盐碱生境芦苇种群分株高度和生物量进行比较。结果表明,6—10月份,4个生境芦苇种群分株高度及生物量均以水生生境最高,盐碱生境最低,水生生境株高为盐碱生境的1.5—2.3倍,分株生物量为2.0—5.1倍,生境间的差异性以及差异序位均相对稳定。4个生境株高生境间变异系数(19.45%—31.56%)均高于生境内变异系数(8.07%—17.61%),分株高度在生境间的可塑性更大;分株生物量中水生生境、湿生生境和盐碱生境3个生境间的变异系数(33.43%—55.61%)均低于生境内变异系数(44.85%—79.82%),分株生物量在生境内的可塑性更大。不同生境条件下芦苇种群分株,在生长和生产上均存在较大的生态可塑性,表现出明显的环境效应,其中土壤含水量是该地区芦苇分株生态可塑性变异的主要驱动因子(R0.80),为正向驱动。     

Effects of soil heterogeneity and clonal integration on Alternanthera philoxeroides populations with a radial ramet aggregation

Some clonal plants can spread their ramet populations radially, and soil heterogeneity and clonal integration may greatly affect the establishment of these types of populations. We constructed Alternanthera philoxeroides populations with a radial ramet aggregation, allowing old ramets of clonal fragments to concentrate in central pots and younger ramets to root in peripheral pots. The peripheral pots were supplemented either with three different levels (high, medium and low) of soil nutrients to simulate a heterogeneous soil environment, or only one medium level of soil nutrients to simulate a homogeneous environment. Stolon connections between the central older ramets and the peripheral younger ramets were left intact or severed to test the effect of clonal integration. The maintenance of stolon connection could induce the division of labor between different‐aged ramets, by increasing the root investment in central ramets and the above‐ground growth in peripheral ramets. The maintenance of stolon connection could improve the growth of the central and peripheral ramets, clonal fragments and even the whole population. However, the positive consequence in peripheral ramets and whole fragments was only detected in the high‐nutrient patch of heterogeneous treatment. In sum, in the population with the radial ramet aggregation, clonal integration can play a key role in the rapid recruitment of young ramets of A. philoxeroides fragments, as well as the expansion of the whole population. The magnitude of clonal integration also became more obvious in the peripheral young ramets and whole fragments that experienced high‐nutrient patches.     

Impact of soil water chemistry on the apparent sex ratio of the flowering ramets of the dioecious plant Myrica gale var. tomentosa

We determined whether the apparent (M/Fl) sex ratio (male ramets/flowering ramets) and apparent reproductive ramet ratio (Fl/Li ratio; flowering ramets/living ramets) in 15 Myrica gale var. tomentosa populations varied with dissolved total nitrogen, dissolved total phosphorus, potassium, magnesium, calcium, or pH in the soil water. Our aim was to define the environmental factors affecting the M/Fl sex ratio and Fl/Li ratio of the populations. We also examined the habitat conditions of these populations by analyzing soil water chemistry and water dynamics. In 2007, 3 of the 15 populations had no females. The remaining 12 had significantly male-biased (M/Fl sex ratio?=?0.59-0.97). Although we could not explain the absence of females by the current potassium levels alone, as potassium increased, so did the M/Fl sex ratio. As nitrogen increased and potassium decreased, Fl/Li ratio decreased. Our soil water chemistry analyses suggested that the potassium supply by soil surface erosion from flooding and the inflow of anthropogenic nitrogen were the important factors influencing the M/Fl sex ratio and Fl/Li ratio. Nitrogen management would be important in one of the endangered populations where inflow of nitrogen was the highest among 15 habitats.     

Ramet dynamics in a centrifugally expanding clonal sedge: a matrix analysis

Carex humilis is a clonal sedge that can form distinct rings of densely aggregated ramets. We hypothesize that rings form because both production of new ramets and ramet dispersal are positively correlated to ramet size. This would lead to an overrepresentation of fast-moving and large ramets with high ramet production at the periphery, whereas slow-moving and small ramets with low ramet production would mainly be found in the interior of rings. We use matrix models to analyse how ramet populations both at the periphery and in the interior develop in the absence of ramet dispersal. We found that the stable size class distributions of ramets predicted by the models were not different from the distributions found in the field. Also, the asymptotic ramet population growth rates (λ₁) were the same. Hence, we conclude that rings would form even in the absence of a link between ramet dispersal and ramet production. Further analysis of the matrix models showed that the ramet population increases at the periphery but decreases in the interior of rings because medium and large ramets produce fewer large ramets in the interior than at the periphery. We also found that the temporal variance in λ₁ and transitions rates during the four study years was much higher at the periphery than in the interior. Our results suggest that rings may form because C. humilis ramets use below-ground resources from a much larger area than the one covered by the shoots. As the clone grows larger, the soil volume available to the ramets in the interior decreases because their access to soil outside the ring is cut-off by the ramets at the periphery. Ramet density in the interior is therefore decreasing.     

Clonal integration affects growth and sediment properties of the first ramet generation,but not later ramet generations under severe light stress

克隆整合影响严重光胁迫下第一分株世代的生长和沉积物特征但不影响 后续分株世代的生长和沉积物特征 克隆整合通过缓冲环境压力和提高资源获取效率使克隆植物受益。然而,在一个克隆系统中,受益于克隆整合的连接分株世代的数量很少受到关注。我们进行了一个盆栽实验来评估沉水植物苦草 (Vallisneria natans)克隆系统内的生理整合程度,该克隆系统由一个母株和3个依次连接的后代分株组成。 母株生长在正常光照下,而后代分株被严重遮荫。母株与后代分株间的匍匐茎被切断或保持连接,但3个后代分株之间的连接仍然存在。与遮荫的后代分株连接时,苦草未遮荫的母株的光合能力显著增强,但其生物量积累大大减少。克隆整合显著增加了第一分株世代(相邻分株)的生物量积累和土壤的碳氮可用性、胞外酶活性和微生物生物量,但没有增加后续分株世代的这些特征。我们的结果表明,在严重光胁迫下,来自苦草母株的支持可能仅限于克隆系统中相邻的后代分株,这暗示着一个分株世代的效应。我们的结果有助于更好地理解克隆植物的层次结构和分段化。这些发现表明克隆整合程度在分株种群的生态相互作用中起着至关重要的作用。     

High levels of inter-ramet water translocation in two rhizomatous Carex species,as quantified by deuterium labelling

We studied water trnaslocation between interconnected mother and daughter ramets in two rhizomatous Carex species, using a newly developed quantitative method based on deuterium tracing. Under homogeneous conditions, in which both ramets were subjected either to wet or dry soil, little water was exchanged between the ramets. When the ramet pair was exposed to a heterogeneous water supply, water translocation became unidirectional and strongly increased to a level at which 30–60% of the water acquired by the wet ramet was exported towards the dry ramet. The quantity of water translocated was unrelated to the difference in water potential between the ramets, but highly correlated to the difference in leaf area. In both species, the transpiration of the entire plant was similar under heterogeneous and homogeneous wet conditions. This was a direct result of an increase in water uptake by the wet ramet in response to the dry conditions experienced by the interconnected ramet. In C. hirta, the costs and benefits of integration in terms of ramet biomass paralleled the responses of water consumption. This species achieved a similar whole-plant biomass in heterogeneous and homogeneous wet treatments, and water translocation was equally effective in the acropetal and basipetal directions. In C. flacca, responses of biomass and water consumption did not match and, under some conditions, water translocation imposed costs rather than benefits to the plants of this species. It is concluded that enhanced resource acquisition by donor ramets may be of critical importance for the net benefits of physiological integration in clonal plants.     

Lion (Panthera leo) demographics in the south-western Kgalagadi Transfrontier Park

Changes in demographic features of the lion population in the south-western Kgalagadi Transfrontier Park cause conservation concern. The ratio between adult males and females changed from 1♂:2♀ to 1♂:1♀ over a 32-year period (1977–2010). This is atypical for undisturbed lion populations. We evaluated mechanisms that on their own or together could explain the trend by using both a discrete- and continuous-time capture–recapture model to analyse 2 years of individual-based observation data (May 2013–June 2015). Although most vital rates were within expected parameters, shifts in the sex structure remained similar to that reported for sub-adults previously. The population comprised of 26.9% cubs and juveniles (<2 years), 14.2% sub-adults (2–4 years) and 59% adults (>4 years). Litters had equal sex ratios at first detection. Birth rates were lower (0.44 cubs per female per year) than between 1998 and 2001 (0.69 cubs per female per year). The continuous model indicated a higher survival effect for female cubs, while both models showed higher survival rates/effects for sub-adult and adult females relative to males. However, the sex ratio for sub-adults was male-biased. The shift in demographic signals may associate with changes in age-related immigration rates of sub-adult males.     

Morphological and Physiological Acclimation Responses to Contrasting Light and Water Regimes in <Emphasis Type="Italic">Primula sieboldii</Emphasis>

The effects of the availability of light (high, medium and low) and soil water (wet and dry) on morphological and physiological traits responsible for whole plant carbon gain and ramet biomass accumulation were examined in a splitter-type clonal herbaceous species Primula sieboldii, a spring plant inhabiting broad range of light environments including open grassland and oak forest understory. Growth experiments were conducted for three genets originated from natural microhabitats differing in light and soil water availability. Ramets of a genet from high light and wet microhabitat, which were grown in low light (relative photon flux density: R-PPFD of 5%) showed 41% less light-saturated photosynthetic rate, 50% less dark respiration rate and earlier defoliation than the ramets in high light (R-PPFD of 61%). The estimation of daily photosynthesis revealed that the light acclimation response in leaf gas exchange contributes to efficient carbon gain of whole plants, irrespective of experimental light conditions. Water stress increased root weight ratio, decreased ramet leaf area, petiole length and photosynthetic capacity. These morphological effects of water stress were larger in high and medium light regimes than in low light regime. The consequence of the above responses was recognized in the relative growth rate of the ramets. The relative growth rate of the ramets in high light with wet regime was four-fold of that in low light plus wet regime, and was 1.5-fold of that in high light plus dry regime. However, even in low light and/or dry regimes, ramets kept positive relative growth rates and produced gemma successfully. We could not detect significant variation in growth responses among genets. The high photosynthetic plasticity revealed in the present study should enable Primula sieboldii to inhabit in a broad range of light and soil water availability.     

Habitat and sex specific differences in the dioecious weed Acetosella vulgaris (Polygonaceae)

Abstract Patterns of resource allocation, numbers of reproductive structures and sex ratios of flowering populations of the dioecious weed Acetosella vulgaris (Fourr.) were examined in the Kosciuszko alpine region of Australia. Specifically, the sex‐specific response of ramets was compared between a disturbed alpine habitat, in which weeds such as A. vulgaris are common (disturbed roadside/path‐edge), and a native alpine habitat in which weeds appear to have a limited capacity to germinate, grow and reproduce (undisturbed tall alpine herbfield). The disturbed habitat was generally more favourable for growth of A. vulgaris. Ramets of both sexes had greater total and vegetative biomass than ramets in native habitats. Although reproductive biomass was also greater in disturbed habitats, females had less reproductive biomass than males, which was not as predicted. Reproductive effort was not affected by habitat or gender. The disturbed habitat also favoured increased numbers of inflorescences per ramet and flowers per ramet, as expected. Whereas the gender of the ramet also influenced numbers of reproductive structures, again, this was not as predicted. Females had more flowers per ramet and more flowers per inflorescence than males. This may be because of factors associated with wind pollination. Females were taller in native habitats but there was no difference between the sexes in disturbed habitats. Sex ratios varied from all male populations to nearly all female populations among the 25 sites sampled irrespective of habitat. Factors such as time since last disturbance may have contributed to variation in the sex ratios of alpine populations of A. vulgaris in Australia.     

Clonal integration ameliorates the carbon accumulation capacity of a stoloniferous herb,Glechoma longituba,growing in heterogenous light conditions by facilitating nitrogen assimilation in the rhizosphere

Background and Aims Enhanced availability of photosynthates increases nitrogen (N) mineralization and nitrification in the rhizosphere via rhizodeposition from plant roots. Under heterogeneous light conditions, photosynthates supplied by exposed ramets may promote N assimilation in the rhizosphere of shaded, connected ramets. This study was conducted to test this hypothesis.Methods Clonal fragments of the stoloniferous herb Glechoma longituba with two successive ramets were selected. Mother ramets were subjected to full sunlight and offspring ramets were subjected to 80 % shading, and the stolon between the two successive ramets was either severed or left intact. Measurements were taken of photosynthetic and growth parameters. The turnover of available soil N was determined together with the compostion of the rhizosphere microbial community.Key Results The microbial community composition in the rhizosphere of shaded offspring ramets was significantly altered by clonal integration. Positive effects of clonal integration were observed on NAGase activity, net soil N mineralization rate and net soil N nitrification rate. Increased leaf N and chlorophyll content as well as leaf N allocation to the photosynthetic machinery improved the photosynthetic capability of shaded offspring ramets when the stolon was left intact. Clonal integration improved the growth performance of shaded, connected offspring ramets and whole clonal fragments without any cost to the exposed mother ramets.Conclusions Considerable differences in microbial community composition caused by clonal integration may facilitate N assimilation in the rhizosphere of shaded offspring ramets. Increased N content in the photosynthetic machinery may allow pre-acclimation to high light conditions for shaded offspring ramets, thus promoting opportunistic light capture. In accordance with the theory of the division of labour, it is suggested that clonal integration may ameliorate the carbon assimilation capacity of clonal plants, thus improving their fitness in temporally and spatially heterogeneous habitats.     

光强对比度对大米草克隆整合作用的影响

通过温室控制试验,分析不同光强及光强对比度处理下克隆植物大米草生长性状的差异,研究同质异质光强条件下克隆整合对大米草响应遮阴能力的修饰作用.结果表明： 在同质条件下,大米草在无遮阴(高光强：温室内自然光照强度)条件下的生物量显著大于中度遮阴(中光强：光照强度为高光强的70%)和深度遮阴(低光强：光照强度为高光强的30%).在低对比度异质性光强条件下(分株对的一个分株不遮阴,另一个分株中度遮阴),大米草遮阴分株的叶片数、根长和生物量均显著高于同质中度遮阴处理,而无遮阴分株各生长指标与同质无遮阴处理相比均无显著差异.因此,在低对比度异质性光强下,大米草受体(遮阴)分株通过克隆整合显著受益;同时,对供体(非遮阴)分株没有显著的耗损.然而,在高对比度处理下(分株对的一个分株不遮阴,另一个分株深度遮阴),克隆整合对受体(遮阴)分株的效应不显著.大米草的克隆整合并不随着光强对比度的增加而增加.在自然生境中度遮阴情况下,克隆整合可以提高大米草的生长和克隆繁殖能力,但在深度遮阴情况下,克隆整合对大米草适应性的作用可能很小.     

Sex expression and sex dimorphism in sporophytic populations of the desert moss Syntrichia caninervis

Ten sporophytic populations of Syntrichiacaninervis contained an average of 22 individualscm^–2, with a sex ratio of 7.9 Female:1 Male: 3.1 Nonexpressing(N = 300). In each of the populations, female individuals outnumberedmale individuals. A representative population size of 50 × 25cm was estimated to contain 27,250 organically distinct individualplants. Given the wide disparity in reproductive investment in this dioeciousspecies, sex-specific traits were investigated at the level of the individualinbiomass, total stem length, number of ramets, number of branches, length ofannual growth interval, length of longest ramet, age, number of inflorescences,number of ramets expressing sex, and consecutive seasons of sex expression. Theonly significant sex dimorphism recorded was in consecutive seasons of sexexpression, with nonsporophytic female individuals exhibiting a higherfrequencythan males. However, nonexpressing individuals had lower biomass, shorter totalstem length, fewer branches, and shorter ramets than males and females, andfewer ramets than female individuals. When the biomass of female and maleindividuals was controlled for inflorescence number, no significant differencesbetween the sexes in biomass were found. There appears to be a threshold sizefor sex expression, with all individuals above 2.0 mg dry weightexpressing sex (N = 108). Biomass and total stem length are strongpositive correlates (r = 0.88), and individual biomass is a betterpredictor of the number of inflorescences produced per individual than is stemlength (r = 0.85 vs. r = 0.69, respectively). Independent of stemlength, individual biomass had a positive and significant relationship withinflorescence number; however, independent of individual biomass, stem lengthwas not associated with inflorescence number. Overall sex expression was 0.74(individual level) and 0.65 (ramet level). The functional sex ratio wasassessedat the inflorescence level, and ranged from 9.7:1, to14.9:1 over the most recent four years. Fertilization frequencywas 0.69 (individual level) and 0.34 (perichaetial level). Over the last threeyears, 63% of all fertilized perichaetia resulted in an abortivesporophyte.