Phenological responses to temperature of an annual and a perennial Lesquerella species

BACKGROUND AND AIMS: The annual Lesquerella fendleri, native to the south-western desert of United States and Mexico, and the perennial L. mendocina, native to Argentina, may have potential as new crops for cold-arid environments. The introduction of a new crop requires an understanding of environmental influences on growth and development, particularly temperature, which has been recognized as the main factor affecting the rate of development in crops. The objective of this study was to examine differences in the phenology of L. fendleri and L. mendocina and in the response to temperature in both vegetative and reproductive phases. METHODS: Plants of each species were grown at a range of constant temperatures under controlled conditions and developmental responses were analysed and quantified. KEY RESULTS: The rate of development of L. fendleri increased linearly with temperature in the phase from emergence (EM) to floral bud appearance (FBA) over the range 9-20 degrees C, and for the phase from FBA to first flower open (FL) over the range 9-24 degrees C. In contrast, the rate of development of L. mendocina was insensitive to temperature during the phase EM to FBA. In the phase FBA to FL, L. mendocina had a lower sensitivity to temperature than L. fendleri. In addition, L. fendleri exhibited a quantitative response to supra-optimal temperatures (reducing rate of development with further increases in temperature) whereas L. mendocina showed a qualitative response, with development ceasing to progress at temperatures above the optimum. CONCLUSIONS: This differential behaviour at high temperatures could explain the biennial habit found for L. mendocina sown during late spring under field conditions, whereas it behaves as an annual when sown in autumn-winter. The possibility is discussed of using this information for establishing the coincidence of critical stages with environmental conditions that can limit potential and actual yield through agronomic practices.     

沙质草地不同生活史植物的生物量分配对氮素和水分添加的响应

以氮素和水分(冬季增雪和夏季增雨)为控制因子, 开展相关田间控制实验, 分析不同功能群(以生活史为划分依据)尺度和群落尺度植物生物量分配格局对氮素和水分的响应, 得出以下结论: 1)一年生植物的繁殖生物量比重明显高于多年生植物, 而多年生植物种的叶/地上生物量比值显著高于一年生植物; 2)一年生植物对氮素和水分添加的响应剧烈, 氮添加耦合夏季增雨、氮添加耦合冬季增雪显著增加了一年生植物的繁殖生物量比重和叶生物量比重。多年生植物对氮素和水分添加的响应不敏感, 表现为多年生植物的各器官生物量分配格局对氮素添加和水分添加的响应不明显。3)氮素添加和水分处理改变了群落尺度生物量分配格局: 氮素添加耦合冬季增雪处理降低了群落植物的繁殖生物量比重和茎生物量比重, 提高了群落植物的叶生物量比重。4)冬季增雪和夏季增雨与氮素添加的交互作用对群落生物量分配格局的改变不同。夏季增雨耦合氮素添加处理下群落的茎生物量比重显著提高, 群落茎生物量分配的改变引起群落的垂直结构发生改变。冬季增雪氮素处理下群落的叶生物量比重增加, 但茎生物量比重增加不明显。冬季增雪也改变了群落的结构和功能。     

Seasonal dynamics of biomass and nitrogen in canopies of Solidago altissima and effects of a yearly mowing treatment

Seasonal dynamics of biomass and nitrogen allocation in ramets of the clonal perennial Solidago altissima in response to yearly mowing were assessed in a field experiment. Final biomass of all component organs of the ramets was lower in mown than in unmown plots. Except for a negative effect on rhizome nitrogen concentration, mowing did not influence tissue nitrogen concentrations but, as a consequence of the reduced biomass accumulation, pools of standing-crop nitrogen were reduced in all organs. At all times during the annual stand development, the nitrogen concentration in the leaf canopies declined exponentially from the top downwards. The gradient of this decline was most marked at the beginning of the season and then became less apparent. In the mature stands, the area-based nitrogen contents of `upper-canopy' leaves (receiving > 50 % of incoming light), for a given light availability, on average were greater in mown than in unmown plots. About half of the nitrogen still remaining in pre-senescent leaves sampled in July was re-absorbed before leaf death. Nevertheless, the decreases in the absolute leaf- and stem-nitrogen pools per ramet during reproductive growth were much lower than the concomitant nitrogen gains of the developing inflorescences, implying that more than half of the nitrogen allocated to reproductive structures was taken up from the soil. On the other hand, there was evidence for nitrogen re-allocation from old to new leaves during vegetative growth which apparently enabled individual ramets to maintain an exponential nitrogen profile even during the phase of rapid leaf production in spring, thus using nitrogen efficiently.     

Metabolism of Hydroxy Fatty Acids in Developing Seeds in the Genera Lesquerella (Brassicaceae) and Linum (Linaceae)

Members of the genus Lesquerella produce seed oil that contains a high proportion of hydroxy fatty acids (HFAs). There are three groups of Lesquerella species that are distinguished by their most abundant seed oil fatty acid: lesquerolic acid (20:1OH; e.g. Lesquerella fendleri), densipolic acid (18:2OH; e.g. Lesquerella kathryn), and auricolic acid (20:2OH; e.g. Lesquerella auriculata). To investigate the biochemistry of HFA production in Lesquerella species, the conversion of putative radiolabeled intermediates of HFA biosynthesis, including 18:1, 20:1,18:1OH, 18:2OH, and 20:1OH, was examined in developing embryos of L. fendleri, L.kathryn, and L. auriculata. The results are consistent with (a) 18:1OH formation by hydroxylation of 18:1, (b) elongation and desaturation of 18:1OH to produce 20:1OH and 18:2OH, respectively, and (c) desaturation of 20:1OH to produce 20:2OH. The desaturation of 20:1OH was also found to occur in developing embryos of high, but not low, linolenic acid flax. This suggests that the desaturation is catalyzed by the extraplastidial linoleate desaturase. Confirming this suggestion, it was notable that 18:1OH and 18:2OH were found in low and high linolenic flax (Linum usitatissimum) seeds, respectively, at levels of 0.2 to 1%.     

种子异型植物异子蓬的生殖分配和结实格局

选择能产生异型果实和种子的一年生盐生植物异子蓬(Suaeda aralocaspica)为研究对象, 研究其生殖分配和结实格局。结果表明, 异子蓬具有较高的生殖分配和规律性的“谨慎型”结实格局。异子蓬的生殖分配高达56%。在资源充裕时, 该植物对扁圆形棕色种子(采取机会主义的萌发策略)的投资多于双凸镜形黑色种子(采取谨慎的萌发策略)的投资。异子蓬的花序类型为二歧聚伞花序, 单个果序含果实(种子)的数目为1-15个, 最多可分为4级。果序内果实的分布具有一定的规律: 第一级1个果实, 第二级2个, 第三级4个, 第四级8个。异子蓬优先将资源供给黑色种子的果实, 利用不同类型种子的发育顺序, 首先保证黑色种子的产出。具有较高的生殖分配和采取“谨慎”的生殖策略是异子蓬与其所处盐漠环境长期适应的结果。     

Mineral allocation to reproduction in Sorhum bicolor and Sorghum halepense in relation to parental nutrient supply

Summary This experiment investigated the effect of parental nutrient shortage on the allocation of five nutrients to seeds and rhizomes in Sorghum halepense, a perennial, noxious weed, and to seeds in Sorghum bicolor, an annual, cultivated species. Plants from both species were grown from seeds and supplied with fertilizer at three concentrations. The allocation of biomass and nutrients (N, P, K, Ca and Mg) to reproductive and vegetative parts was determined. Relative biomass allocation to reproduction (either sexual or vegetative) remained constant in S. halepense in spite of large differences in total plant weight. In S. bicolor, however, biomass allocation to sexual reproductive structures decreased significantly with decreasing nutrient supply. Individual seed weight was not modified by parental nutrient supply in S. halepense, but it increased with decreasing nutrient availability in S. bicolor. Important differences in mineral allocation to seeds were found between the two species. While S. bicolor seeds were largely buffered from the differences in parental nutrient status, concentration of nutrients in S. halepense seeds decreased significantly with decreasing supply for all the nutrients analyzed except Ca. However, mineral nutrient concentration in S. halepense rhizomes remained remarkably constant despite differences in the external supply, evincing the priority given to vegetative reproduction at the expense of sexual reproduction. Overall, the pattern of nutrient allocation in S. bicolor seeds under different nutrient supply resembled the pattern observed in S. halepense rhizomes, but it had little resemblance to the pattern of nutrient allocation in S. halepense seeds. The results are discussed in terms of differences and similarities in the reproductive strategy of these two species.     

结果初期黄冠梨对春施15N-尿素的吸收、分配与利用

以3年生黄冠梨为材料,探讨了早春施用¹⁵N尿素后,树体在萌芽期-新梢缓慢生长期和新梢缓慢生长期-果实成熟期对氮素的吸收、分配与利用特性。结果表明: 梨树在萌芽期-新梢缓慢生长期主要以新梢和叶片等营养器官生长为核心;在新梢缓慢生长期-果实成熟期则以根系等贮藏器官生长为主,果实产量品质形成为辅,且树体尤其是贮藏器官的生物量成倍增加。由于各器官尤其是新梢和叶片生长旺盛、新梢缓慢生长期吸收的标记氮量相对较多,各器官吸收的肥料氮(Ndff)值相对较高;果实成熟期除粗根外各器官的Ndff值均低于新梢缓慢生长期。萌芽期到新梢缓慢生长期吸收的标记氮主要分配在新梢和叶片营养器官中,新梢缓慢生长期到果实成熟期吸收的标记氮则主要分配在贮藏器官中;整个生育期间,植株吸收的标记氮在贮藏器官中分配率最高,营养器官次之,生殖器官中分配率最低。3年生梨树从萌芽期-新梢缓慢生长期、新梢缓慢生长期-果实成熟期吸收的肥料氮分别占当年总吸氮量的31.1%和21.0%,而两个时期内吸收的土壤氮占比分别达68.9%和79.0%。     

Significance of the simultaneous growth of vegetative and reproductive organs in the prostrate annual Chamaesyce maculata (L.) Small (Euphorbiaceae)

To elucidate the significance of the simultaneous growth of vegetative and reproductive organs in the prostrate annual Chamaesyce maculata (L.) Small (Euphorbiaceae) from the standpoint of meristem allocation, we investigated plant architecture, meristem allocation, and the spatial and temporal patterns in vegetative growth and reproduction in the reproductive stage. The numbers of secondary and tertiary shoots successively increased by branching in the reproductive stage, and the sum of shoot length was greater in secondary shoots than in primary shoots. The specific shoot length (shoot length per shoot biomass) was greater in lateral shoots than in primary shoots, indicating efficient lateral shoot elongation. The internode length was shorter in secondary shoots than in primary shoots, increasing the number of nodes per shoot length in secondary shoots. Many nodes on a shoot generated two meristems, one of which committed to a flower and one to a lateral shoot. The number of reproductive meristems was greatest in tertiary shoots, and 96% of total reproductive meristems on shoots were generated in lateral shoots. On almost all nodes, the reproductive meristem developed into a flower, and 95–98% of the flowers produced a fruit. Therefore, vegetative growth by branching in the reproductive stage contributed to the increase in reproductive outputs. From the standpoint of meristem allocation, the simultaneous growth of vegetative and reproductive organs in prostrate plant species might be important for increasing the number of growth and reproductive meristems, resulting in the increase in reproductive outputs.     

扰动环境中不同刈割方式柠条营养生长补偿的影响

 柠条（Caragana korshinskii）在地上组织破坏后进行补偿性生长,这是重复利用柠条资源的基础,但对 柠条不同刈割方式下营养生长补偿的模式有待探讨。该文通过5种刈割方式：去除主枝长的30%（30%RSL） 、去除主枝长的60%（60%RSL）、去除分枝数的25%（25%RSN）、去除分枝数的50%（50%RSN）和去除分枝 数的100%（100%RSN）来研究柠条的营养生长补偿。结果表明：刈割处理的柠条生物量当年发生了超补偿 ,当年生枝数/枝、当年生枝长、当年生枝生物量/枝、当年生枝生物量/株比对照高。对照、30%RSL和 60%RSL 处理未长出基梢。 100%RSN处理的基梢数/刈割枝、基梢长、单个基梢平均生物量显著高于25%RSN 和50%RSN处理,基梢生物量/株随刈割去除生物量的增加而增加。100%RSN 处理未结果,其它处理果实产量 表现出超补偿或精确补偿。对照处理营养生长和生殖生长均低,其它处理当年生枝生物量与果实产量成显 著负相关。从整个生长季节来看,营养生长主要集中在果实成熟之前。我们认为,100%RSN处理是柠条地上 组织破坏后尽快恢复的合理方式,其当年生生物量远高于其它处理。顶端优势的破坏促使休眠芽的萌发, 根冠比的改变使地上组织获得较多养分和水分,根系储存的碳水化合物的供应是促使刈割柠条营养生长超 补偿的的可能机制,而减少生殖生长对资源的消耗,是100%RSN处理地上生物量尽快恢复的另一重要因素 。     

新疆郁金香营养生长、个体大小和开花次序对繁殖分配的影响

植物有性繁殖与资源分配的关系研究对于揭示植物生活史特征及繁育系统进化具有重要意义。新疆郁金香(Tulipa sinkiangensis)是新疆天山北坡荒漠带特有的一种多年生早春短命植物。在自然生境中,该物种仅以有性繁殖产生后代,每株能产生1-8朵花,且不同植株上的花数及果实数以及花序不同位置上的花与果实大小明显不同。本文通过对新疆郁金香有性繁殖与营养生长及植株大小的关系以及花序中不同位置花及果实间的资源分配研究,旨在揭示营养生长、个体大小及开花次序对其繁殖分配的影响。结果表明:在开花和果实成熟阶段,新疆郁金香植株分配给营养器官(鳞茎和地上营养器官)与繁殖器官的资源间均存在极显著的负相关关系(P<0.01),说明其植株的营养生长与生殖生长间存在权衡关系。多花是新疆郁金香的一个稳定性状,其植株上花数目、花生物量、果实生物量和种子数量与植株生物量间均呈极显著的正相关关系(P<0.01),说明新疆郁金香植株的繁殖分配存在大小依赖性。在具2-5朵花的新疆郁金香植株中,花序内各花的生物量、花粉数和胚珠数、结实率、果实生物量、结籽数、结籽率及种子百粒重按其开花顺序依次递减,说明花序内各花和果实的资源分配符合资源竞争假说。植株通过减少晚发育的花或果实获得的资源来保障早发育的花或果实获得较多的资源,从而达到繁殖成功。     

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.     

Uptake and allocation of carbon and nitrogen in Vicia narbonensis plants with increased seed sink strength achieved by seed-specific expression of an amino acid permease

Over-expressing an amino acid permease in Vicia narbonensis seeds increases sink strength for N that is evident from the higher seed protein content and seed weight. Here, the effect of increased seed sink strength of line AAP-12 on growth, development, and on whole plant carbon and nitrogen uptake and partitioning is analysed. AAP-12 plants have a prolonged growth period. Accumulation and partitioning of dry matter and N in leaves, stems, and pods are higher whereas remobilization to the seeds is delayed, indicating that the switch from growth to reserve allocation and remobilization is delayed. Measuring uptake and allocation of (15)N-ammonia applied via the roots revealed a higher and longer label uptake period during maturation. Measuring whole plant carbon fixation and allocation after (13)C labelling shows higher levels at maturation, particularly in seeds, indicating higher seed sink strength for C and increased allocation into maturing seeds. Levels of cytokinins were dramatically increased in AAP-12 seeds indicating its role in nitrogen-mediated growth stimulation. AAP-12 seeds have higher natural abundances for (13)C indicating increased C fixation via PEP carboxylase in order to meet the higher demand of carbon acceptors for amino acid synthesis. In summary, increased seed sink strength for N in AAP-12 stimulates seed growth, but also that of vegetative organs, which finally leads to a higher ratio of vegetative to seed biomass at maturity and thus a lower harvest index. Therefore, the increased N uptake due to higher seed demand of AAP-12 is partly compensated by growth stimulation of vegetative organs.     

Competition between Lolium perenne and Digitaria sanguinalis: Ecological consequences for harbouring an endosymbiotic fungus

Abstract. This study examined the influence of the fungal endophyte Neotyphodium lolii on the competitive interactions between its perennial, cool season host, Lolium perenne (perennial ryegrass), and a warm season, annual grass, Digitaria sanguinalis (large crabgrass), in densely planted stands (>1000 plant.m^?2) in the glasshouse. Endophyte infection had little or no effect on L. perenne tiller production, above‐ or below‐ground biomass or root: shoot ratio in monoculture. However, endophyte infection significantly reduced L. perenne tiller production and above‐ground biomass in mixtures with D. sanguinalis. Conversely, D. sanguinalis had significantly higher above‐ground biomass and yielded more seed (g) when competing with endophyte infected L. perenne. An apparent trade‐off between allocation of resources to reproductive vs root tissues was observed in D. sanguinalis– root: shoot ratio was significantly lower when competing with endophyte infected L. perenne. Results indicate negative ecological consequences for harbouring the fungal endophyte when competing with the fast growing annual grass in newly established stands. These findings underscore the existence of a physiological cost of harbouring the fungal endophyte which is often overlooked.     

Optimization of Plant Root: Shoot Ratios and Internal Nitrogen Concentration

A general theoretical approach is developed to analyze the morphologicaland physiological responses of plants to nitrogen availability.The optimal leaf-nitrogen concentration and corresponding optimalroot: shoot ratio which maximize relative growth rate are foundquantitatively as a function of root—specific activitywhich is assumed to be a function of soil nitrogen availability.The cost of increasing tissue nitrogen concentration is foundto be primarily related to an increase in allocation to roots.Predictions of the analysis are consistent with previous theoriesand general empirical findings, suggesting that plants respondoptimally to soil nitrogen. Relative growth rate is predictedto be a nearly linear function of whole-plant nitrogen concentrationand shoot fraction is a monotonically increasing function oftissue nitrogen concentration when plants respond optimallyto soil nitrogen availability. Plant growth, root:shoot ratios, biomass allocation, nitrogen productivity, optimization     

A Model Allocating Growth Among Leaf Proteins, Shoot Structure, and Root Biomass to Produce Balanced Activity

A model is developed that considers the allocation of carbonand nitrogen substrates to a protein compartment in the shoots,shoot structural components, and root biomass. Inclusion ofa shoot-protein compartment allows variation in shoot-specificactivity to be modelled as a function of leaf nitrogen concentration.Allocation to the biomass compartments is controlled by twopartitioning variables that are defined by explicitly usingthe balanced activity hypothesis. The model produces balancedactivity where the shoot-specific activity, as well as rootand shoot biomass, vary in response to the above-ground (lightand CO₂) and below-ground (nitrogen) environments. The predictedpatterns of both root: shoot ratio and leaf nitrogen concentrationin response to environmental resource availability are qualitativelyconsistent with general trends observed in plants. Biomass allocation, plant growth, modelling, leaf nitrogen, root: shoot ratio, balanced activity     

Capture and allocation of nitrogen byQuercus douglasii seedlings in competition with annual and perennial grasses

Summary The spatial overlap of woody plant root systems and that of annual or perennial grasses promotes competition for soil-derived resources. In this study we examined competition for soil nitrogen between blue oak seedlings and either the annual grassBromus mollis or the perennial grassStipa pulchra under controlled outdoor conditions. Short-term nitrogen competition was quantified by injecting¹⁵N at 30 cm depth in a plane horizontal to oak seedling roots and that of their neighbors, and calculating¹⁵N uptake rates, pool sizes and¹⁵N allocation patterns 24 h after labelling. Simultaneously, integrative nitrogen competition was quantified by examining total nitrogen capture, total nitrogen pools and total nitrogen allocation.Stipa neighbors reduced inorganic soil nitrogen content to a greater extent than didBromus plants. Blue oak seedlings responded to lower soil nitrogen content by allocating lower amounts of nitrogen per unit of biomass producing higher root length densities and reducing the nitrogen content of root tissue. In addition, blue oak seedlings growing with the perennial grass exhibited greater rates of¹⁵N uptake, on a root mass basis, compensating for higher soil nitrogen competition inStipa neighborhoods. Our findings suggest that while oak seedlings have lower rates of nitrogen capture than herbaceous neighbors, oak seedlings exhibit significant changes in nitrogen allocation and nitrogen uptake rates which may offset the competitive effect annual or perennial grasses have on soil nitrogen content.     

Micrometeorological measurements over 3 years reveal differences in N2O emissions between annual and perennial crops

Perennial crops can deliver a wide range of ecosystem services compared to annual crops. Some of these benefits are achieved by lengthening the growing season, which increases the period of crop water and nutrient uptake, pointing to a potential role for perennial systems to mitigate soil nitrous oxide (N₂O) emissions. Employing a micrometeorological method, we tested this hypothesis in a 3‐year field experiment with a perennial grass‐legume mixture and an annual corn monoculture. Given that N₂O emissions are strongly dependent on the method of fertilizer application, two manure application options commonly used by farmers for each crop were studied: injection vs. broadcast application for the perennial; fall vs. spring application for the annual. Across the 3 years, lower N₂O emissions (P < 0.001) were measured for the perennial compared to the annual crop, even though annual N₂O emissions increased tenfold for the perennial after ploughing. The percentage of N₂O lost per unit of fertilizer applied was 3.7, 3.1 and 1.3 times higher for the annual for each consecutive year. Differences in soil organic matter due to the contrasting root systems of these crops are probably a major factor behind the N₂O reduction. We found that a specific manure management practice can lead to increases or reductions in annual N₂O emissions depending on environmental variables. The number of freeze‐thaw cycles during winter and the amount of rainfall after fertilization in spring were key factors. Therefore, general manure management recommendations should be avoided because interannual weather variability has the potential to determine if a specific practice is beneficial or detrimental. The lower N₂O emissions of perennial crops deserve further research attention and must be considered in future land‐use decisions. Increasing the proportion of perennial crops in agricultural landscapes may provide an overlooked opportunity to regulate N₂O emissions.     

Effect of protection on the nutrient concentration and uptake of some Mediterranean desert annuals

The present study includes an evaluation of the effect of protection of a grazing ecosystem on the nutrient concentration and uptake in the organs of four annual species of non-saline depressions in the western Mediterranean regionof Egypt.The concentration of macro- and micronutrients in different organs became lower due to the increase in biomass of individuals with protection. The maximum uptake of nutrients occurred during the early vegetative stage, except for a few cases in which the uptake in some species reached two peaks, one in the early vegetative stage and the other in the reproductive stage.The efficiency of the selected annual species in uptaking and accumulating nutrients was compared with rates of uptake of nutrients and amounts of nutrients accumulated in tissues of two species representing other life forms. The annuals and perennial herbs (ephemeroids) are in general more efficient in uptaking and accumulating nutrients in their tissues than perennial shrubs.     

Construction of the cybrid transplastomic Brassica napus plants containing Lesquerella fendleri chloroplasts

Transferring of Lesquerella fendleri genetically transformed plastids to Brassica napus plants has been performed with the somatic hybridization method. The plastome of the previously engineered transplastomic L. fendleri plants contained the aadA16gfp selective marker gene conferring spectinomycin/streptomycin resistance and green fluorescence under UV light. The protoplasts of B. napus chlorophyll-deficient plants were fused with gamma-irradiated protoplasts of L. fendleri transplastomic plants. A total of 59 green hybrid colonies have been isolated followed by spectinomycin/streptomycin selection. Shoot regeneration has been observed for two cell lines. Morphologically normal plants have been regenerated for one of them. PCR and isozyme analyses showed that the plants were transplastomic cybrids containing B. napus nuclei and L. fendleri transformed chloroplasts.     

Size-dependent resource allocation among vegetative propagules and male and female functions in the forest herb Laportea bulbifera

Reproductive resource investment among vegetative propagules and male and female sexual function and their size-dependence were investigated in a perennial forest herb, Laportea bulbifera . A theoretical model based on fitness gain curves predicts that optimal investments in three reproductive modes will increase with plant size if fitness returns in all three modes increase but become saturated with investment. In a field population, large plants of L. bulbifera produced both male and female inflorescences with propagules, while small plants produced only vegetative propagules. Biomass of propagules, male inflorescences, and infructescences with achenes were all positively correlated with plant size. The increase in investment with plant size was larger for propagule production than for sexual reproduction. The relationship between propagule biomass and plant size was constant irrespective of year, while the relationship between the biomass of sexual reproductive organs and plant size differed between two successive years. Annual change of individual sex expression was investigated for 25 transplanted plants. Although each plant changed its sex expression variously among male, female and bisexual from year to year, 23 out of 25 plants produced both male and female inflorescences in at least one year. The number of viable (germinated and survived) offspring from seeds was not significantly different from the number from propagules. The production cost of a propagule was higher than that of a seed. Resource allocation theory does not seem to be applicable to size-dependent resource allocation, especially the allocation between seeds and propagules in this species.