Seedlings of the semi-shrub Artemisia ordosica are resistant to moderate wind denudation and sand burial in Mu Us sandland, China

Sand movement is a common stress for plants in dune ecosystems. Seedlings in such an environment often experience various degrees of denudation or burial. A field experiment was conducted with Artemisia ordosica, a dominant semi-shrub species in Mu Us sandland, China, to test seedling survival and growth under different degrees of denudation and burial. Seedlings from two cohorts with height of 5.0 ± 0.02 cm (S1) and 9.3 ± 0.09 cm (S2) were selected and randomly subjected to three denudation treatments (2.5, 5, and 10 cm), five burial treatments (2.5, 5, 7.5, 10, and 15 cm), or a control. S2 seedlings had a higher survivorship than S1 seedlings, especially under severe denudation (10 cm) and complete burial (5 cm in S1; 10 cm in S2). Seedling survivorship was unaffected by moderate burial (<5 cm in S1; <10 cm in S2) or denudation (<10 cm), but it was significantly reduced under complete burial or severe denudation. Seedling growth in leaf area, height, and biomass only declined in severe denudation or complete burial. Seedling burial led to higher biomass investment in shoots, while the reverse was the case in denudation. The results indicate A. ordosica is highly tolerant to moderate burial and denudation, showing adaptive responses that likely increase survival. Differences in responses between seedling cohorts suggest that large seedling size is beneficial for successful establishment in sandy environments and measures to prevent severe denudation and burial of recently germinated seedlings are necessary in attempts to restore steppe vegetations.     

Costs of reproduction as related to the timing of phenological phases in the dioecious Shrub Pistacia lentiscus L

Females of woody dioecious species usually devote more resources to reproduction than males. This may lead to a decrease in female survival and growth. The costs of reproduction, however, can be lightened through a number of mechanisms, as for example avoiding the temporal coincidence of reproduction and vegetative growth. The aim of this study was to evaluate whether males and females of P. lentiscus differ in the timing of their vegetative growth, and to assess whether the sequencing of vegetative growth and reproduction reduces reproductive costs. We monitored phenology in males and females. We also compared male and female allocation of nutrients and biomass in the branch, and the developmental stability of the growing shoots. We did this both prior to and at the end of the fruiting period. Males and females showed similar vegetative and flowering phenologies. Males invested more biomass in flowering, but the sexes showed equal vegetative biomass and nutrient content prior to the fruiting period. In female branches, no trade-off was found between fruit load and current-year vegetative growth. In P. lentiscus, avoiding the overlap of flowering, vegetative growth and fruiting probably contributes to reduce the immediate costs of reproductive efforts, both in males and females.     

LIFETIME BIOMASS PARTITIONING AND YIELD COMPONENT RELATIONSHIPS IN THE HIGHBUSH BLUEBERRY,VACCINIUM CORYMBOSUM L. (ERICACEAE)

The proportion of annual biomass production allocated to various vegetative and reproductive tissues was measured in differently aged individuals of Vaccinium corymbosum from native populations in southern Michigan. The relationship between age and allocation was determined and a lifetime pattern of biomass partitioning was developed. The proportion of biomass allocated to reproduction was higher than many have predicted for woody species, and the relationship between age and reproductive effort did not conform to optimality models. In addition, reproductive performance was not affected by previous growth or reproduction. The basis of this complex reproductive behavior was examined by quantifying the relationships among components of reproduction. In general, yield components behaved independently within a season. A high potential reproductive effort coupled with yield component independence may be an adaptation to fluctuating environments.     

Interactions in the patterns of vegetative growth and reproduction in woody dioecious plants

Summary Interactions between vegetative growth and reproduction were evaluated in Peumus boldus, Lithraea caustica and Laretia acaulis, three woody dioecious species in central Chile. Phenological observations were made periodically on marked branches of male and female plants, and biomass allocation (dry weight) to vegetative and reproductive tissues was measured. The magnitude of flowering was evaluated in groups of plants in three successive seasons. The patterns of activities are species- and sex-dependent, and cycles of 2–4 years have been established. Branches that produce flowers either do not grow or grow less than branches without flowers, and males and females have differential resource allocation: male branches attain higher biomass values. Groups of plants show seasonal behavior that suggest synchrony in their reproductive activities.     

不同生境自交植物黄花大苞姜生殖分配的研究

为了探讨自交植物黄花大苞姜(Caulokaempferia coenobialis)对石壁附生这一特殊生境的生态适应,对其不同物候期和不同生境的生殖分配进行了对比研究。结果表明,在生殖生长过程中,黄花大苞姜种群用于营养生长的生物量分配占有绝对优势,而用于生殖的生物量分配比例较小(<13%)。在黄花大苞姜各构件的生物量分配中,根茎和叶的比重较大(24.22%~43.25%)。在光线较弱生境中的种群,为了提高资源获取能力,黄花大苞姜分配到叶的比重明显高于光线较强的种群,而分配给根茎的比例却明显低于光线较强的种群。随着物候期的推移,黄花大苞姜生殖分配的比例不断增加,到果期达到最大值。不同种群间和年度间黄花大苞姜分配给生殖构件的比例没有显著差异,推测其生殖分配可能受遗传因素控制。个体大小与根茎生物量呈极显著线性函数同速生长,而与生殖分配在云天海种群没有表现出相关性,在上坪和天堂顶种群表现为同速生长关系,但决定系数小于40%。因此,黄花大苞姜能有效调节其在不同生境的生物量分配以适应石壁附生的特殊生境,在光线较弱的种群提高叶的生物量分配并降低根茎的生物量分配以提高资源的获取能力。整体上投资到营养构件的生物量占比高达87%以上,生殖构件在居群间和年度间均保持稳定。这种繁殖策略,一方面较高的营养构件投资可以获得更多的资源,另一方面稳定的生殖投资可以保证种群的延续,各构件相互协调以更好适应石壁这一资源匮乏的生境。     

Cost and probability of flowering at the shoot level in relation to variability in shoot size within the crown of Vaccinium hirtum (Ericaceae)

Size-related variation in the cost and probability of flowering among shoots within a crown of Vaccinium hirtum was investigated to clarify patterns and regulation of flowering at the shoot-module level, below the level of the individual. The apices of previous-year shoots differentiated into current-year shoots vegetatively (vegetative branches) or became reproductive by developing inflorescences (reproductive branches). Length growth and fate of current-year shoots were determined, and the future potential for reproduction was estimated using a matrix model of shoot dynamics. Reproductive branches had fewer current-year shoots and shorter total shoot lengths and thus had a reduced potential for reproduction compared with vegetative branches, indicating the cost of flowering at the shoot level. This cost of flowering was higher in longer shoots. The probability of the initiation of flowering in a shoot increased with increasing shoot length in shorter shoots, reached a maximum in medium-sized shoots, and decreased in longer shoots. The size-related changes in the probability of flowering at the shoot level can be largely explained by the size-dependent changes in shoot-level resource availability and cost of flowering.     

Reproductive allocation in hermaphrodite and female plants of Sidalcea oregana SSP. spicata (Malvaceae) using four currencies

Reproductive allocation was investigated in female and hermaphrodite plants of gynodioecious Sidalcea oregana ssp. spicata. Total reproductive investment and partitioning of that investment was documented at the level of whole plants in terms of four ecologically relevant currencies: biomass, nitrogen, phosphorus, and potassium. Nutrient augmentations in the field confirmed that nutrients were limiting plant vegetative growth and propensity to flower; thus the use of these nutrients as currency was appropriate. Once the effects of plant size were removed, the sex morphs allocated similar total amounts of biomass, nitrogen, phosphorus, and potassium to reproduction, but partitioned those differentially. For any given individual size, females allocated larger proportions of their reproductive resource budgets to seeds. Hermaphrodites' reproductive investment in pollen and flowers was allocated at the expense of allocation to seeds. These data are relevant to the evolution of gynodioecy from hermaphroditism and support the hypothesis that females reallocate resources not spent on pollen to seeds.     

Effects of sand burial on survival, growth, gas exchange and biomass allocation of Ulmus pumila seedlings in the Hunshandak Sandland, China

BACKGROUND AND AIMS: In the last decade, the number of young plants of Ulmus pumila in the Hunshandak Sandland has decreased sharply because of severe sand burial, and their ecological protective function has been weakened. In order to develop an understanding of the tolerance of U. pumila to sand burial and to suggest reasonable measures to protect the sparse-elm-grassland ecosystem, the effects of burial on the survival, growth, photosynthesis and biomass allocation in U. pumila were studied. METHODS: Seedlings were buried at five different depths in pot experiments: no burial (control), partial burial (33 % and 67 % stem height), and complete burial (100 % and 133 % stem height). Growth analyses and measurements of photosynthesis were carried after the plants had been uncovered. KEY RESULTS: All the plants survived partial burial, but about 30 % and 80 % of the seedlings died as a result of the 100 % and 133 % sand burial treatments, respectively. The numbers of newly produced leaves and branches, and the height of the stems of the seedlings in the 33 % and 67 % burial treatments during the period of the experiment were significantly greater than those in the control. Furthermore, net photosynthetic rate, transpiration rate and water use efficiency were also elevated by the partial burial, but not affected by burial time. This might be attributed to the increased root length, which improved water acquisition. The biomass and biomass allocation of the seedlings were significantly changed by the burial treatments and burial times. The biomass was enhanced by partial burial but was reduced by complete burial at each burial time. However, the biomass allocation was not significantly changed by the 33 % and 67 % sand burial treatments 2 or 4 weeks following the burial. CONCLUSIONS: Ulmus pumila was shown to be tolerant to partial sand burial, but must be protected from complete burial.     

Resource allocation patterns of two California-Sonoran desert ephemerals

Summary The patterns of allocation of structural and nonstructural carbon were followed in the co-occurring desert ephemerals Plantago insularis and Camissonia boothii. Patterns of biomass distribution were determined from material harvested at biweekly intervals as were levels of nonstructural sugar and starch. Seasonal patterns of growth and reproduction differed markedly with Plantago allocating significantly more structural and nonstructural carbon to reproduction early in the season. Plantago completed its life cycle in less than 60 days but Camissonia continued both vegetative and reproductive growth to over 100 days. The longer growing season of Camissonia was possible because more energy was allocated to vegetative tissues and storage presumably as investment toward longer life and higher levels of reproduction.     

SEXUAL DIMORPHISM IN BIOMASS ALLOCATION AND CLONAL GROWTH OF XANTHOXYLUM AMERICANUM

Reproduction can have a high resource cost. It has been suggested that greater investments in sexual reproduction by female dioecious plants leads to a lower rate of vegetative growth in females than in males. In this study, we investigated sexual dimorphism in biomass allocation and genet growth of the dioecious clonal shrub, northern prickly ash (Xanthoxylum americanum). The allocation of biomass over the course of one growing season to reproductive tissue, leaves, and growth of aboveground first-year wood, was compared in 18 clones growing in fields and six clones in woods in southeastern Wisconsin during 1985 and 1986. In addition, the number of shoots per clone, and weight of nonfirst-year wood (accumulated biomass) above- and below-ground were estimated. In open field sites, male clones allocated more biomass to new wood and less to reproduction than females, although males allocated more to flowers alone. Accordingly, male clones had significantly more shoots and more accumulated biomass both above- and below-ground than female clones. In the woods, where fruit set was near zero, there were few significant differences between male and female clones in either biomass allocation or accumulated biomass. These results support the hypothesis that the high resource investment in fruit production by females reduces their vegetative growth relative to males.     

Effects of burial in sand on the growth and reproduction of Cakile edentula

Studies were conducted to examine the effects of sand burial on the growth and reproduction of Cakile edentula under controlled greenhouse conditions Sand burial enhanced both the vegetative growth and reproduction of plants Within one week after burial, plants showed a significant increase in the length of the internode just below the current sand surface This response was not mediated by the dark conditions imposed by sand burial About two weeks after burial, adventitious roots grew upwards into the deposited sand Plants buried in washed sand did not differ in their dry weight whereas those buried in unwashed sand were significantly taller, produced greater biomass and larger number of seeds per plant than control However, the mean mass per fruit and per seed were not altered The frequency distribution of fruit and seed was only slightly modified by the burial treatments     

Reproductive allocation and costs in gynodioecious Leucopogon melaleucoides (Ericaceae): implications for the evolution of gender dimorphism

In dioecious species, females typically allocate more resources to reproduction and incur greater costs of reproduction than males. In gynodioecious species, sex-based differences in reproductive allocation (RA) and costs have been less studied. Such knowledge, however, is relevant to address how females establish and increase in frequency in populations. We examine RA and reproductive costs by comparing fruit set, the proportion of biomass allocated to reproduction, and the responses of fruit set and vegetative growth to shoot defoliation in females and hermaphrodites in gynodioecious Leucopogon melaleucoides. Relative to hermaphrodites, females exhibited a two-fold fruit set advantage. Female fruit set increased proportionately with flower number, but hermaphrodite fruit set was reduced on plants with more flowers. Sex-based differences in allocation to other traits were small. Thus, female RA at flowering was similar to hermaphrodite RA, but was 1.4-fold greater at fruiting. Relative to controls, defoliation reduced fruit set and the percentage of shoots that produced new vegetative growth similarly in both sexes. However, females had a lower proportion of shoots with new growth overall. Further, defoliation on females reduced the dry mass of new growth by 44% compared with controls, whereas hermaphrodites were not affected. These results indicate a trade-off between reproduction and vegetative growth, and greater female costs of reproduction, particularly under resource-limiting conditions. In the absence of compensatory traits to offset higher female reproductive costs, such trade-offs have the potential to retard the spread of females in gynodioecious populations.     

Costs of reproduction in life history of a perennial plant <Emphasis Type="Italic">Carex secalina</Emphasis>

We tested a hypothesis based on life history theory that examines reproductive costs incurred by individuals in consecutive years of their life. A multi-year dataset of resource allocation to vegetative and reproductive structures was analysed in Carex secalina — a perennial, monoecious sedge, reproducing only sexually. In a four-year garden experiment, we assessed above-ground biomass at the end of each season and reproductive allocation expressed as the total length of male and female spikes. The study was aimed at determining how size and age of a plant relates to its reproduction, and how the rate of reproduction affects the year-toyear biomass change in Carex secalina. We observed that after each reproductive episode, individuals had significantly smaller sizes and produced a lower number of generative tillers. The total production of reproductive structures decreased significantly with age in all populations. Moreover, the decrease in plant biomass was greater when more reproductive structures were produced in a previous year, which indicates that the plants incur costs of reproduction in terms of above-ground biomass production.     

Seasonal control over allocation to reproduction in a tussock-forming and a rhizomatous species of Eriophorum in central Alaska

Summary The evergreen tussock-forming Eriophorum vaginatum revealed consistently earlier (c. 1 moth) phenology and greater biomass per tiller than the summergreen rhizomatous E. scheuchzeri in all four components measured (vegetative and reproductive shoots and stems) under the same climatic regime in central Alaska over one growing season. Greatest allocation to vegetative shoot growth occurred in mid-summer in both species. The tussock growth form of E. vaginatum raised shoot meristems 25–30 cm above the soil surface, where temperatures were warmer, permitting shoot growth to begin earlier in spring and continue longer in autumn than in E. scheuchzeri. Consequently, E. vaginatum was able to allocate reserves to reproductive tillers primarily in autumn and early spring, times when minimal reserves were required for vegetative growth. By contrast, the rhizomatous E. scheuchzeri had a more constrained growing season, and allocation to reproduction coincided with allocation to vegetative growth. For this reason, reserves were drawn down more fully in mid-summer in E. scheuchzeri than in E. vaginatum. The more conservative use of nutrient stores in E. vaginatum may relate to its great longevity, reduced allocation to reproduction (including low seedling recruitment), and relatively stable habitats. The mid-seasonal pulse of allocation to reproduction in E. scheuchzeri appears viable only in relatively fertile disturbed sites, where the soil nutrient supply is sufficient to support simultaneous allocation to vegetative growth and reproduction.     

Some effects of soil-moisture availability on above-ground production and reproductive allocation in Larrea tridentata (DC) Cov

Summary Data from the US/IBP Desert Biome validation studies indicate that above-ground production and biomass allocated to reproduction in Larrea tridentata vary from one year to another depending upon the timing and extent of soil-moisture availability. In an attempt to verify these observations and determine to what extent water availability can affect total aboveground production and reproductive allocation in this widely distributed warm desert shrub, a series of soil-moisture augmentation experiments were conducted. High levels of soil moisture had a greater effect on reproductive allocation than on total above-ground production. Enhanced soil moisture during the period of active growth increased total above-ground production and reduced the percentage of biomass allocated to reproduction. Enhanced soil moisture during the normal periods of little or no growth did not increase total above-ground production.     

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.     

展毛翠雀花期繁殖特征和生物量分配对放牧的响应

生物量分配影响植物生长和繁殖,是植物生活史研究的重要内容。为了了解植物生活史性状对放牧的响应,该研究以青藏高原高寒草甸毒杂草展毛翠雀为对象,分析了放牧干扰对展毛翠雀的花期繁殖分配和性分配的影响。结果表明:放牧显著降低了展毛翠雀的总生物量、个体大小和繁殖投入; 放牧未改变展毛翠雀的营养部分与繁殖部分的等速生长关系,但显著增加了繁殖部分的生物量分配和总花数; 展毛翠雀的个体大小与总花数呈显著的正相关关系,但与性分配呈显著的负相关关系; 展毛翠雀的总花数与单花大小、单花的花瓣比例均表现出负相关关系,表明总花数与单花大小之间、总花数与单花的花瓣比例之间均存在权衡。因此,在放牧条件下,展毛翠雀的繁殖分配和性分配均表现出显著的可塑性。     

Patterns of vegetative growth and reproduction in relation to branch orders: the plant as a spatially structured population

The patterns of vegetative growth and reproduction in relation to orders of terminal branches were examined in the evergreen woody plant, Eurya japonica. The branch order number was determined centrifugally. The trunk was given order number 1; branches issuing directly from the trunk were order 2; branches growing on order 2 branches were order 3, and so on. The results of this study show the differential patterns of vegetative growth and reproduction in relation to the branch orders. Lower-order shoots of terminal branches grew more, but produced few flowers. On the other hand, for the higher-order terminal branches, shoot growth was very limited but flowering was more intense. The results show that a tree can be interpreted not as a mere population of equivalent modules but as a spatially structured population. Thus, it is essential to consider the position of modules within the branch system when patterns of vegetative growth and reproduction are examined. It is hypothesized that the difference in the opportunity cost in relation to the branch orders is the main cause of the spatial structure for patterns of vegetative growth and reproduction. Furthermore, for same-order terminal branches, current-year shoot elongation was independent of flowering intensity. These results suggest that this species only invests resources in reproduction that are surplus to its requirements for the functions associated with survival, such as growth and/or storage. Received: 22 July 1999 / Accepted: 12 January 2000     

Effects of parasitic castration on plant resource allocation

It has been proposed that host castration is a parasite strategy to reallocate host resources from reproductive to vegetative functions to increase parasite fitness. Since resource partitioning between reproduction and vegetative growth can affect host life-history traits, parasite effects on resource allocation can affect both plant fitness and host-parasite coevolution. Field and greenhouse experiments were used to investigate the effects of host castration by the fungus Atkinsonella hypoxylon on the resource allocation and architecture of the grass Danthonia spicata. The results indicate that non-infected D. spicata can reallocate resources from reproduction to vegetative growth when resource allocation to reproduction is prevented. However, I found no evidence that fungal castration causes reallocation of resources from host reproduction to vegetative growth. Instead, infection reduces host biomass and the fungus directly utilizes resources that would have been used for host reproduction for its own reproduction. Received: 25 March 1999 / Accepted: 24 October 1999     

两种生境中薇甘菊种群的生物量生殖分配

于2004年薇甘菊（Mikania micrantha）生殖阶段的现蕾期至种子成熟期,从种群和构件水平上研究了两种生境（林窗和开阔地）中薇甘菊种群的生物量生殖分配。结果表明,在生殖生长过程中,两种生境中的种群用于营养生长的生物量分配均占有绝对优势,而生殖生长的波动相对较大。花序的生物量分配（RA）总体上均呈现由低到高的变化趋势。在不同时期,林窗薇甘菊种群的营养枝生物量分配均小于开阔地,而除了种子形成期和种子成熟期以外的其它各个时期,林窗中生殖枝的生物量分配均大于开阔地,林窗中花序的生物量分配均显著大于开阔地。表明薇甘菊能有效权衡其在不同生境中的繁殖策略,开阔地中的薇甘菊种群的繁殖策略倾向于克隆繁殖,而林窗生境中薇甘菊种群则相对更倾向于有性生殖。