GERMINATION ECOPHYSIOLOGY OF HYDROPHYLLUM APPENDICULATUM,A MESIC FOREST BIENNIAL

In north central Kentucky, seeds of the mesic forest biennial Hydrophyllum appendiculatum Michx., are innately dormant at maturity in June. Under natural and simulated seasonal temperature changes, dormancy break occurred in two stages. Root dormancy was broken by high summer temperatures, and shoot dormancy was broken by low winter temperatures. Consequently, roots emerged from seeds during autumn, and cotyledons emerged the following spring. A 90-day warm (30/15 C) stratification treatment broke root dormancy, but the roots emerged only after transfer to lower temperatures. After the warm stratification treatment, roots emerged from 93, 73, 6 and 9% of the seeds incubated at 5, 15/6, 20/10 and 30/15 C (12/12 hr), respectively. Zero, 28, 56 and 84 days of cold (5 C) stratification of seeds with emerged roots resulted in 9, 21, 49 and 82% cotyledon emergence, respectively, at 20/10 C. Thus, H. appendiculatum exhibits a type of morpho-physiological dormancy known as epicotyl dormancy. Although many seeds germinate the first year, others remain dormant and germinate in successive years until the fourth season after ripening.     

GERMINATION ECOPHYSIOLOGY OF THE WOODLAND HERB OSMORHIZA LONGISTYLIS (UMBELLIFERAE)

Osmorhiza longistylis is an herbaceous perennial that grows in woodlands of eastern and central North America. In northcentral Kentucky seeds ripen in early to mid July, and dispersal begins in September and October. Although most of the seeds are shed during late autumn and winter, some remain on the dead shoots for up to 18 months. Seeds are dormant at maturity due to an underdeveloped embryo. Embryos grew at low (5 C) temperatures, but only after seeds were given a period of warm (30/15 C) stratification. With an increase in the length of the warm treatment, there was an increase in the number of embryos that grew to full length during a 12-wk period at 5 C and an increase in the percentage of seeds that germinated. Seeds given 12 wk of warm stratification required more than 8 wk at 5 C to overcome dormancy. Embryos in freshly-matured seeds averaged 0.60 mm long, but those in seeds given 12 wk warm plus 12 wk cold stratification averaged 8.86 mm. Lengths of embryos of seeds kept moist at 30/15 and 5 C for 24 wk averaged 0.63 and 0.89 mm, respectively. Regardless of age and dispersal time, imbibed seeds must be exposed to high (i.e., summer or autumn) and then to low (i.e., winter) temperatures before they will germinate. Consequently, germination occurs only in spring.     

REPRODUCTIVE ECOLOGY OF JEFFERSONIA DIPHYLLA (BERBERIDACEAE)

The reproductive ecology of Jeffersonia diphylla (L.) Pers. (Berberidaceae) was investigated by studying its breeding system, ovule production, seed set, seed dispersal by ants and seed predation by rodents. This species flowers early in the spring and is facultatively autogamous. In a typical year fruit and seed set is high (90%), however, freezing temperatures from late spring frosts in 1983 and 1985 resulted in low fruit set (7% and 20%, respectively), and reduced seed set in those flowers that produced fruit. No differences in seed set between selfed and outcrossed flowers were observed over a two-yr period (1983–84). Ovule number per capsule increased with plant size as measured by leaf number. Seed set and seed wt were unaffected by leaf number unless leaves were removed after flowering was initiated. Jeffersonia diphylla is myrmecochorous. Ants removed seeds faster when seeds were placed in areas where J. diphylla plants were absent, suggesting that dispersal within J. diphylla populations is ant limited. Moreover, fresh (1 day old) seeds were removed by ants faster than 3 day old seeds. Seed predation by rodents prior to dehiscence from capsules is heavy in large populations (85–90%), and apparently negligible in small populations. Predation of seeds that are released from capsules is heavy (approx. 66%), particularly at night. Overall, seed predators consume about 96% of the seed crop in well established populations, but probably much less in small young populations. Hence, seedling recruitment is likely to be higher in small populations, whereas ramet production from rhizomes is the primary mode of propagation in large ones. The evolution of autogamy, early flowering, and myrmecochory are discussed in light of the results of this study.     

GERMINATION ECOPHYSIOLOGY OF HERBACEOUS PLANT SPECIES IN A TEMPERATE REGION

Germination phenology data have been collected from 75 winter annuals, 49 summer annuals, 28 monocarpic perennials, and 122 polycarpic perennials, and experimental investigations of dormancy breaking and germination requirements have been conducted on 56 winter annuals, 32 summer annuals, 18 monocarpic perennials, and 73 polycarpic perennials. The purpose of these studies was to determine if there are correlations between the dormancy breaking and germination requirements of seeds and the germination phenology, life cycle type, habitat requirements, range of geographical distribution, and phylogenetic relationships of the species. Germination phenology is highly correlated with the responses of seeds to the yearly temperature cycle. Species with winter and summer annual life cycles have predictable germination characteristics, but monocarpic and polycarpic perennials do not. Several dormancy types may be found in a given habitat, and narrowly endemic and widely-distributed species in the same genus may have similar germination characteristics. Within some families there is a tendency for a particular type of seed-temperature response to be very important, but frequently this is related to the predominance of a given life cycle type in the family.     

FACTORS AFFECTING GERMINATION IN GREENHOUSE-PRODUCED SEEDS OF OXALIS CORNICULATA,A PERENNIAL WEED

A study was conducted to investigate the physiological responses of greenhouse-produced Oxalis corniculata seeds to light, temperature, moist heat treatment, aging, and season of production. Fresh seeds exhibited over 90% germination and required low levels of light (5 μmol m^-2 s^-1, 400–700 nm) to germinate. Seeds germinated over a broad, yet seasonally-dependent range of incubation temperatures. Seeds produced in winter had the narrowest temperature range of germination (15 to 25 C) and the lowest germination percent (44% at 2 wk) at optimum temperature (17 C); seeds produced in summer had the widest temperature range of germination (10 to 30 C) and the highest germination percent (93% at 2 wk) at optimum temperature (17 C). Incubation at non-optimum temperatures between 5 and 40 C suppressed or slowed the rate of germination until seeds were placed at optimum temperature, where full germination subsequently occurred. Moist heat treatment at temperatures over 40 C resulted in varying degrees of inhibition of subsequent germination. When seeds were stored dry in laboratory conditions, three of four seed lots examined retained over 80% germination capacity until ca. 8 months; 50% capacity remained after ca. 15 months. These results indicate that the seasonal temperature and daylength effects on maternal plants in the greenhouse environment are major determinants of seed germination characteristics of O. corniculata.     

内生真菌侵染对黑麦草种子萌发、幼苗生长及渗透胁迫抗性的影响

 以含有内生真菌的黑麦草(Lolium perenne L.)种子为材料,采用4 ℃冰箱内和20 ℃培养箱内保存18个月的方式分别构建内生真菌侵染（EI）和内生真菌非侵染（EF）的黑麦草种群,通过比较EI和EF种群在正常条件下（对照）和渗透胁迫条件下种子发芽、幼苗生长等方面的差异,探讨内生真菌对其宿主植物的直接和间接影响。结果表明：在对照和胁迫条件下,EI种子的发芽势及发芽率均明显高于EF种子,而在重度胁迫下EI植株的叶延伸速率、根系总长度高于EF植株。内生真菌对宿主植物分蘖数和生物量的变化没有促进作用,但     

林线树种太白红杉种子萌发的生理生态特性

 太白红杉(Larix chinensis)是太白山的高山林线树种。通过在人工气候室内的试验,研究了太白红杉种子在6种不同的光照与温度组合处理条件下的萌发特性。结果表明：在恒温和变温两种条件下,交替光照对于种子吸胀后的脱落酸（ABA）和赤霉素 (GA)有刺激作用。在恒温条件下,持续光照对于种子吸胀后的生长素 (IAA)有刺激作用,而变温条件下交替光照对生长素有刺激作用。细胞分裂素（CTK）的变化情况与IAA相反。光照条件相同时,恒温条件下的植物激素含量要高于变温条件下的含量,说明恒温对于各种激素有刺激作用。在25 ℃环境下种子的萌发率高于在12 ℃环境下的萌发率,说明温度对于种子的萌发有重要作用。太白红杉种子的萌发受交替光照（12 h光照/12 h黑暗）的刺激;恒温（25 ℃）条件下的种子萌发率高于变温（12 ℃/25 ℃）条件下的种子萌发率。实验结果反映了内源激素在太白红杉种子萌发过程中起着重要作用。     

内生真菌侵染对黑麦草种子萌发、幼苗生长及渗透胁迫抗性的影响

以含有内生真菌的黑麦草(Lolium perenne L.)种子为材料,采用4 ℃冰箱内和20 ℃培养箱内保存18个月的方式分别构建内生真菌侵染（EI）和内生真菌非侵染（EF）的黑麦草种群,通过比较EI和EF种群在正常条件下（对照）和渗透胁迫条件下种子发芽、幼苗生长等方面的差异,探讨内生真菌对其宿主植物的直接和间接影响。结果表明：在对照和胁迫条件下,EI种子的发芽势及发芽率均明显高于EF种子,而在重度胁迫下EI植株的叶延伸速率、根系总长度高于EF植株。内生真菌对宿主植物分蘖数和生物量的变化没有促进作用,但     

GERMINATION ECOPHYSIOLOGY OF ARENARIA GLABRA,A WINTER ANNUAL OF SANDSTONE AND GRANITE OUTCROPS OF SOUTHEASTERN UNITED STATES

The germination ecophysiology of Arenaria glabra Michx., a characteristic winter annual plant species of granite and sandstone outcrops of southeastern United States, was investigated. Seeds germinate in early autumn, plants overwinter in the rosette stage and then flower, set seeds, and die in late spring; seeds are dispersed soon after maturity. Eighty-five to 90% of freshly-matured seeds were innately dormant, and the other 10–15% germinated only at temperatures lower than those that occur in the habitat at the time of seed dispersal in June. During the summer after-ripening period, seeds stored dry under ambient laboratory conditions exhibited progressive increases in rates and total percentages of germination, a widening of the temperature range for germination, and a loss of the light requirement. At a 14-hr daily photoperiod, seeds kept on continuously moist soil germinated to 83% at simulated July and August temperatures during July and August, and the remainder germinated at September temperatures in September. On the other hand, seeds subjected to alternate wetting and drying during July and August germinated to only 9% during those 2 months, and the remainder germinated after the soil was kept continuously moist, beginning on 1 September, at simulated habitat temperatures during September and October. Thus, the timing of germination of A. glabra in the field is controlled by an interplay of the seeds' physiological state with the dynamics of temperature and soil moisture conditions.     

雄蕊合生植物半边莲的花部综合征与繁育系统

 为了解花内雄蕊合生结构的繁殖适应意义, 初步研究了雄蕊合生植物半边莲(Lobelia chinensis)的花部综合征、传粉特性和繁育系统。半边莲花大且鲜艳, 花瓣中下部弯折并合生成背部有裂缝的不封闭的花冠筒。5雄蕊的花药紧密合生成花药筒, 花丝中上半部也合生在一起, 只有花丝基部分离插生于花冠筒上。柱头被包裹在花药筒内。半边莲单花寿命可达5 d左右。雄性先熟, 柱头在伸出花药筒之后才具活性。花的主要访问者为蚂蚁、食蚜蝇和苍蝇类等小型昆虫。半边莲单花花粉数约为(5 200±130)粒、胚珠数约为(55±6)颗, 花粉胚珠比为94.54, 应属于兼性自交繁育系统, 但异交指数和其它特征都显示其以异交为主, 部分自交亲和。套袋和人工授粉实验发现, 半边莲不存在无融合生殖与自发自交, 但自交亲和性高。雄蕊合生(尤其是花药的合生)能把花药中的花粉聚拢在一起在传粉者的一次访问中就被同时带出, 与同样具有较低花粉胚珠比的花粉聚联(Pollen aggregation)传粉过程近似。半边莲的雄蕊合生结构(花药合生成筒、花丝上部也合生)可能与一些特定的花部特征, 如花被合生成未完全封闭的筒、雌雄异熟以及低花粉胚珠比等联系在一起, 形成了适应小型传粉者的“花部综合征”     

GERMINATION OF LIGHT-INHIBITED SEED OF NEMOPHILA INSIGNIS

Germination of Nemophila insignis seed is inhibited by light over a wide range of temperatures. At low temperatures the light intensity required for inhibition is higher. At 25 C there is little germination (in darkness as well as in light); at 27.5 C germination is inhibited altogether. Virtually complete germination in light is obtained when the endosperm directly covering the radicle is removed. This operation also improves germination in darkness at 25 C. Mechanical scarification performed elsewhere in the seed is without effect. As with Phacelia tanacetifolia, Nemophila seed apparently fails to germinate in light because the endosperm restrains the expansive growth of the embryo. The embryo of dark-imbibed seed develops a force which enables it to overcome the physical resistance of the endosperm. Light inhibits the process which leads to generation of “expansive force.” Gibberellic acid at 5 × 10^–4 m stimulates germination in light and in the dark. Abscisic acid at 10^-4 m inhibits germination; at 10^-6 m it inhibits only root growth. The inhibition of germination or root growth caused by abscisic acid cannot be reversed by gibberellic acid. Eighty per cent oxygen under certain conditions promotes germination. The rate of O₂ uptake is enhanced in oxygen-enriched atmosphere; however, there is no corresponding increase in the rate of CO₂ output. Thus high oxygen tension enhances an oxidative process other than respiration. This reaction is favorable to seed germination.     

杭州石荠种子萌发的生理生态学研究

本文研究了我国特有的、分布区极狭窄的１年生草本植物——杭州石荠（Ｍｏｓｌａｈａｎｇｃｈｏｗｅｎ－ｓｉｓ）种子萌发的生理生态学特性。结果表明：杭州石荠种子冬天休眠,早春开始萌发;萌发的温度范围是１０～３５℃,２０℃时萌发率最高,因此其萌发的季节仅限于春季;变温处理的萌发率不高于恒温处理;全日照和黑暗条件使萌发率比最适条件的萌发率降低３６％;水选上层种子的萌发率仅为７％,水选下层种子萌发率可达６０％,但水选下层种子在全部种子中仅占３２．６％,说明种子质量差可能是其萌发率低的重要原因。萌发率与千粒重、气介容重及电导率有显著相关;与母株生境也有一定关系,４０％日照下母株所产种子的平均萌发率为２４．６％,４０％日照以下母株所产种子的萌发率降低;不同地区种群种子萌发率均低于３５％。种子萌发率低是杭州石荠各个种群存在的共同问题。     

暖温带落叶阔叶林冠层对降水的分配作用

 对1996年生长季节中两种落叶阔叶林冠层对降水的分配各分量的测定和分析表明：降水在辽东栎林冠层中的分配为：干流量S,66.7mm;透流量T,539.3mm;截留量I,117.6mm;分别占同期降水量的9.2％、74.5％和16.3％。混交林对降水的分配为：干流量S,32.8mm(4.5％);透流量T;555.9mm(76.8％);截留量I,134.9mm(18.6％)。各分量与降水特性的多元回归的结果表明：干流量S与降水量P和前24小时降水量P1之间呈显著正相关关系;透流量T与降水量P和最大雨强M正相关显著。     

SEASONAL ALTERATION OF PHOTOSYNTHETIC UNIT SIZES IN THREE HERB LAYER COMPONENTS OF A DECIDUOUS FOREST COMMUNITY

The pigment content and photosynthetic unit size of three herbs on the floor of a mature yellow oak (Quercus meuhlenbergii) forest were measured during most of the growing season. Two species, dutchman's breeches (Dicentra cucullaria) and Virginia bluebell (Mertensia virginica) are spring ephemerals, while Hepatica acutiloba has a semi-evergreen habit. Although pigment composition changed in Dicentra, photosynthetic unit size only varied slightly. Mertensia was nearly invariant in pigment composition, but unit size was modified as the growing season progressed. The semi-evergreen herb, Hepatica, underwent a remarkable alteration in pigment content, photosynthetic unit size, and number following overstory leaf expansion. The results indicate that an alteration of photosynthetic unit size is possible in fully expanded leaves of two forest floor herbs.     

AN ECOLOGICAL COMPARISON OF UPLAND DECIDUOUS AND EVERGREEN FORESTS OF CENTRAL TEXAS

Scrub evergreen forests cover most of the cedar breaks region of the Edwards Plateau of central Texas; however, limited strips of deciduous forests are found on north-facing slopes just below the limestone caprock. Dominant species occurring in the deciduous forests in descending order of importance include Quercus texana, Q. glaucoides, Juniperus ashei, Diospyros texana, Prunus serotina, Aesculus pavia, Juglans nigra, and Fraxinus texensis. Nineteen woody species were found in the deciduous forests. Forty-eight percent of the species were exclusive to the deciduous forest community. The deciduous forests had a statistically greater number of species/stand and a higher density. The deciduous species found in the strip forests had combined relative density, dominance and importance values of 59, 93 and 72%, respectively. Dominants in the evergreen forest were J. ashei and D. texana, which had relative density, dominance, and importance values totaling 90, 97 and 93%, respectively. Total dominance was the same for both communities; however, J. ashei dominance was 20 times higher in the evergreen forests. Soils of the deciduous forests were significantly deeper and rockier. Also, these soils had higher organic contents and water retention capacities. The potential field capacity (PFC) was 3.47 times higher for the deciduous forest soils resulting in a 2.36-fold increase in the water availability index (WAI). Factors regulating distribution and composition of the deciduous forest communities appear to be insolation and PFC, resulting in part from differences in topographic position.     

GENETIC COMPARISONS OF SEED BANK AND SEEDLING POPULATIONS OF A PERENNIAL DESERT MUSTARD,LESQUERELLA FENDLERI

Soil seed banks may accumulate and store seed genotypes produced over many seasons. If germination and establishment of these soil seeds are influenced by seed genotypes, then seed bank and seedling populations may differ genetically. I compared the genetic structure of dormant but viable soil seeds of the desert mustard Lesquerella fendleri with the genetic structure of Lesquerella seedlings at the Sevilleta Long-Term Ecological Research Site. In 1991 and 1992, soil seeds and seedlings were mapped and genetically analyzed using starch gel electrophoresis. When data from all loci were lumped, there were highly significant differences in allele frequencies between soil seeds and seedlings at the population level (all plots) in both years, in all subpopulation (adjacent plots) comparisons in 1991, and three of five subpopulations in 1992. Differences at some individual loci were also detected in one or both years. Analysis of data pooled across both years revealed highly significant differences in the distribution of multilocus soil seed and seedling heterozygosity, but no significant differences in mean heterozygosity. F_st values showed small but statistically significant genetic differentiation within soil seeds and seedlings in both years. F_st values also showed significant genetic differentiation between these two groups at three of seven loci in 1991, and at one locus in 1992. Soil seeds and seedlings showed a general pattern of decreasing genetic relationship with distance, as estimated by the coefficient of coancestry analyses. In 1991, seedlings were roughly twice as genetically related to each other than were soil seeds at fine spatial scales (0–0.25 and 0.25–0.50 m). This study suggests that Lesquerella seedlings in this system represent a nonrandom genetic subset of the underlying Lesquerella seed bank. Such temporal genetic change may be an important yet frequently overlooked mechanism for generating population genetic structure.