Factors affecting leaf morphology: a case study of Ranunculus natans C. A. Mey. (Ranunculaceae) in the arid zone of northwest China

In order to examine the role of environmental factors affecting foliar morphology, we performed a case study of leaf morphological variation of Ranunculus natans found in the arid zone of northwest China. We found that foliar phenotypic variation differed significantly between populations. We described substantial positive correlations between altitude and leaf area (LA) as well as leaf perimeter (LP), and also between longitude and number of teeth, along with dissection index (DI). The pH, conductivity, and salinity of the environment caused a significant decrease in both LA and LP. Ranked in terms of their impacts on leaf morphology, the six selected factors were: altitude > pH > conductivity > salinity > longitude > latitude. We found that foliar morphological variations are functional responses to water-quantity factors (e.g., altitude and longitude at regional scales) and water-availability relation factors (e.g., pH, conductivity, and salinity at local scales), rather than to temperature-relation factors (latitude). Therefore, altitude and longitude, along with pH, conductivity, and salinity, are the main factors that significantly influence foliar morphology in the arid zone of China. We found that main factors played major roles in plant phenotypic plasticity in a complex ecosystem, although different combinations and interactions of environmental and geographical factors in each local environment may obscure the general trends in trait changes along environmental gradients.

Altitudinal differences in the leaf fitness of juvenile and mature alpine spruce trees (Picea crassifolia)

In many plant species, leaf morphology varies with altitude, an effect that has been attributed to temperature. It remains uncertain whether such a trend applies equally to juvenile and mature trees across altitudinal gradients in semi-arid mountain regions. We examined altitude-related differences in a variety of needle characteristics of juvenile (2-m tall) and mature (5-m tall) alpine spruce (Picea crassifolia Kom.) trees growing at altitudes between 2501 and 3450 m in the Qilian Mountains of northwest China. We found that stable carbon isotope composition (delta C-13), area- and mass-based leaf nitrogen concentration (N-a, N-m), number of stomata per gram of nitrogen (St/N), number of stomata per unit leaf mass (St/LM), projected leaf area per 100 needles (LA) and leaf mass per unit area (LMA) varied nonlinearly with altitude for both juvenile and mature trees, with a relationship reversal point at about 3 100 m. Stomatal density (SD) of juvenile trees remained unchanged with altitude, whereas SD and stomatal number per unit length (SNL) of mature spruce initially increased with altitude, but subsequently decreased. Although several measured indices were generally found to be higher in mature trees than in juvenile trees, N-m, leaf carbon concentration (C.), leaf water concentration. (LWC), St/N, LA and St/LM showed inconsistent differences between trees of different ages along the altitudinal gradient. In both juvenile and mature trees, VC correlated significantly with LMA, N-m, N-a, SNL, St/LM and St/N. Stomatal density, LWC and LA were only significantly correlated with delta C-13 in mature trees. These findings suggest that there are distinct ecophysiological differences between the needles of juvenile and mature trees that determine their response to changes in altitude in semi-arid mountainous regions. Variations in the fitness of forests of different ages may have important implications for modeling forest responses to changes in environmental conditions, such as predicted future temperature increases in high attitude areas associated with climate change.

中国卧龙自然保护区不同海拔川滇高山栎(Quercus aquifolioides)群体的遗传变异

海拔梯度造成的环境异质性，如崎岖的地形、复杂的植被结构以及花期延迟等可能会极大地影响到物种的形态和遗传变异格局。理解物种形态和遗传变异的海拔格局对于物种多样性的管理和保护是非常重要的。尽管植物群体遗传学是一个飞速发展的研究领域，然而与海拔相关的形态变异、遗传变异及群体间遗传差异的研究却很少。到目前为止，还不清楚遗传变异与海拔之间是否必然的相关性。 川滇高山栎是一种重要的生态和经济型树种，广泛分布于中国西南的四川、西藏、贵州和云南省的高海拔地区，在保持水土、调节气候方面起着十分重要的作用。尽管主要受阳光限制而仅分布于阳坡，但其海拔梯度范围较大，表明川滇高山栎对不同的环境具有很强的适应性。本文通过叶型及生理响应、微卫星分子标记和扩增性片段长度多态性方法，试图探索川滇高山栎叶沿海拔梯度的形态和生理响应及其沿海拔梯度的遗传变异格局，为川滇高山栎的保护和利用提供进一步的遗传学理论依据和技术指导。 对叶形、含氮量及碳同位素的试验结果表明，平均比叶面积、气孔密度、气孔长度和气孔指数等气孔参数随海拔的升高呈非线性变化。在海拔大于2800 m时，川滇高山栎的比叶面积、气孔长度和气孔指数都随海拔升高而降低，但是在海拔小于2800 m时，这些指标都随海拔的升高而增大。相对而言，单位叶面积的含氮量和碳同位素则表现出相反的变化模式。另外，比叶面积是决定碳同位素沿海拔梯度变化的最重要参数。本研究结果表明，海拔2800 m附近是川滇高山栎生长和发育的最适地带，在这里生长的植物叶片厚度更薄、气孔更大、叶碳同位素值更小。 利用六对微卫星引物对五个不同海拔川滇高山栎群体遗传多样性进行研究，结果表明，群体内表现出较高的遗传多样性，平均每位点等位基因数11.33个，平均期望杂合度达0.820。群体间差异较小，分化仅为6.6％。聚类分析也并没有显示出明显的海拔格局。然而低频率等位基因却与海拔呈显著性正相关(R2=0.97, P < 0.01)，表明在高海拔处，川滇高山栎以更多的稀有基因来适应恶劣的环境条件。本试验结果表明由海拔梯度形成的选择性压力对川滇高山栎群体的遗传变异影响并不明显。 为了进一步探讨川滇高山栎群体遗传变异与海拔之间的相互关系，我们还对其进行了扩增性片段长度多态性分析。结果表明：(1)随海拔的升高(从群体WL2到群体WL5)，群体内遗传变异降低，而群体间遗传差异增加；(2)低海拔群体WL1表现出最低的遗传变异性(HE = 0.181)，同时与其余四个群体间呈现出最大的遗传差异性(平均FST = 0.0596)；(3)在除去低海拔群体WL1后，Mantel检测表明群体间遗传距离与海拔距离之间表现出正相关性。另外，研究结果还表明，遗传变异受生境条件(过度的湿热环境)及人为干扰(火烧、砍伐和放牧)的影响，这一点至少在低海拔群体WL1上发生了作用。 通过叶形态、生理及DNA分子水平的研究，结果表明叶形态特征和碳同位素与海拔紧密相关，与海拔之间呈非线性变化，海拔2,800 m附近是川滇高山栎生长和发育的最适地带。海拔梯度在一定程度上会影响到川滇高山栎群体的遗传变异结构，但在这样一个狭窄的地理分布区域里，这种影响并不足以导致群体间较大的遗传分化。同时生境条件及人为干扰也是影响遗传变异的限制性因子，不容忽视。 Altitudinal gradients impose heterogeneous environmental conditions, such as rugged topography, a complex pattern of vegetation and flowering delay, and they likely furthermore markedly affect the morphological and genetic variation pattern of a species. Understanding altitudinal pattern of morphological and genetic variation at a species is important for the management and conservation of species diversity. Although plant population genetics is a fast growing field of research, there are only few recent investigations, which analyzed the genetic differentiation and changes of intra-population variation along altitudinal gradients. At present, it is still unclear whether there are some common patterns of morphological and genetic variation with altitude. Quercus aquifolioides Rehder & E.H. Wilson, which is an important ecological and economical endemic woody plant species, is widely distributed in the Yunnan and Sichuan provinces, Southwest China. Its large range of habitat across different altitudes implies strong adaptation to different environments, although it is mainly restricted to sunny, south facing slopes. It plays a very important role in preventing soil erosion, soil water loss and regulating climate, as well as in retaining ecological stability. In this paper, we tried to understand the altitudinal pattern of morphological and genetic variation along altitudinal gradients through the experiments of leaf morphological and physiological responses, microsatellite analysis and AFLP markers. In leaf morphological and physiological responses experiment, we measured leaf morphology, nitrogen content and carbon isotope composition (as an indicator of water use efficiency) of Q. aquifolioides along an altitudinal gradient. We found that these leaf morphological and physiological responses to altitudinal gradients were non-linear with increasing altitude. Specific leaf area, stomatal length and index increased with increasing altitude below 2,800 m, but decreased with increasing altitude above 2,800 m. In contrast, leaf nitrogen content per unit area and carbon isotope composition showed opposite change patterns. Specific leaf area seemed to be the most important parameter that determined the carbon isotope composition along the altitudinal gradient. Our results suggest that near 2,800 m in altitude could be the optimum zone for growth and development of Q. aquifolioides, and highlight the importance of the influence of altitude in research on plant physiological ecology. Genetic variation and differentiation were investigated among five natural populations of Q. aquifolioides occurring along an altitudinal gradient that varied from 2,000 to 3,600 m above sea level in the Wolong Natural Reserve of China, by analyzing variation at six microsatellite loci. The results showed that the populations were characterized by relatively high intra-population variation with the average number of alleles equaling 11.33 per locus and the average expected heterozygosity (HE) being 0.779. The amount of genetic variation varied only little among populations, which suggests that the influence of altitude factors on microsatellite variation is limited. However, there is a significantly positive correlation between altitude and the number of low-frequency alleles (R2=0.97, P < 0.01), which indicates that Q. aquifolioides from high altitudes has more unique variation, possibly enabling adaptation to severe conditions. F statistics showed the presence of a slight deficiency of heterozygosity (FIS=0.136) and a low level of differentiation among populations (FST=0.066). The result of the cluster analysis demonstrates that the grouping of populations does not correspond to the altitude of the populations. Based on the available data, it is likely that the selective forces related to altitude are not strong enough to significantly differentiate the populations of Q. aquifolioides in terms of microsatellite variation. To further elucidate genetic variation pattern of Q. aquifolioides populations under sub-alpine environments, genetic variation and differentiation were investigated along altitudinal gradients using AFLP markers. The altitudinal populations with an average altitude interval of 400 m, i.e. WL1, WL2, WL3, WL4 and WL5, correspond to the altitudes 2,000, 2,400, 2,800, 3,200 and 3,600 m, respectively. Our results were as follows: (i) decreasing genetic variation (ranging from 0.253 to 0.210) and increasing genetic differentiation with altitude were obtained from the WL2 to the WL5 population; (ii) the WL1 population showed the lowest genetic variation (HE = 0.181) and the highest genetic differentiation (average FST = 0.0596) with the other four populations; (iii) the positive correlation was obtained using Mantel tests between genetic and altitude distances except for the WL1 population. Our results suggest that altitudinal gradients may have influenced the genetic variation pattern of Q. aquifolioides populations to some extent. In addition, habitat environments (unfavorable wet and hot conditions) and human disturbances (burning, grazing and felling) were possible influencing factors, especially to the low-altitude WL1 population. The present study shows that there were close correlations between morphological features and carbon isotope composition in our data. This indicates that a coordinated plant response modified these parameters simultaneously across different altitudes. Around 2,800 m altitude there seems to be an optimum zone for growth and development of Q. aquifolioides, as indicated by thinner leaves, larger stomata and more negative d13C values. All available evidence indicates altitudinal gradients may have influenced the genetic variation pattern of Q. aquifolioides to some extent. Decreasing genetic variation and increasing genetic differentiation with altitude was obtained except for the WL1 population. And the environment of habitats and human disturbances were also contributing factors, which impact genetic variation pattern, especially to the low-altitude WL1 population.

岷江冷杉林群落几种树苗对光强的响应与适应

在青藏高原东部的亚高山针叶林区，如何尽快恢复这一生态脆弱地区的植被，改变生态环境恶化的趋势，是一个十分重要的课题。光一直被认为是植物种间相互替代，尤其是森林演替过程中植物相互替代或植被恢复中的关键环境要素之一。植物能否适应林冠下或林窗中异质的、或多变的光照条件，对其在林中的生存、分布、更新以及森林动态都是非常重要的。 本文以青藏高原东部亚高山针叶林的主要森林类型——岷江冷杉林群落的几种树苗为研究对象，采用实验生态学、生理及生物化学等方法，通过模拟针叶林不同大小林窗内光照强度的变化，在中国科学院茂县生态站内采用遮荫处理设置6个光照梯度（100、55、40、25、15与7%全光照），来研究具有不同喜光特性的植物对光强的响应与适应机制，其研究结果可为揭示亚高山针叶林的演替规律、以及人工林下幼苗的存活与定居提供科学依据，也能为苗木的生产与管理提供科学指导，尤其是对针阔树种在不同光强下的响应与适应的比较研究，能为如何将阔叶树种整合到人工针叶林中提供新的思路。 光强对植物生长的影响 光强对植物的生长具有重要作用，不同植物在各自适宜的光强梯度下才能生长良好。通过一个野外盆栽实验，来研究不同光强对植物生长的影响（第三章）。主要研究结果如下，低光强下植物株高/茎生物量增加，说明植物会将生物量更多用于高生长，以便有效地拦截光资源；在强光下，植物将生物量更多地向根部分配，使得植物在强光下能够吸收更多的水分，而避免干旱胁迫。 在第一个生长季节，以相对生长速率（RGR）表示，红桦和青榨槭在100%全光照下RGR最大，粗枝云杉在55%最大，岷江冷杉在25-40%下较好；然而，在第二个生长季节，2种阔叶树的相对生长速率（RGR）的适宜光强则变为25-55%，云杉为55-100%，而冷杉为25-100%。可见，从第一年到第二年，2种阔叶树苗更适宜在部分荫蔽的条件下生长；而2种针叶树苗对光的需求则逐渐增加，这可能是增加对根生物量相对投资的结果，因为以这种方式，强光下生长的针叶树幼苗更能保持其内部水分平衡，其生长不会因干旱胁迫而受到严重影响。另外，严重遮荫会引起冷杉幼苗死亡。 植物对光强的生理适应 植物可以通过自身形态和生理特征的调整，来发展不同的光能利用策略从而能够在林中共存。通过一个野外盆栽实验，研究了不同光强下生长的几种树苗的生理特征（第四章）对不同光强的响应与适应。结果显示：强光下，粗枝云杉和红桦的光合能力增加，而岷江冷杉和青榨槭在中度遮荫（25-55%）的条件下光合能力最大。植物叶氮和叶绿素含量增高，而光补偿点和暗呼吸速率降低，这些都是植物对低光环境的适应性反应；而强光下植物叶片和栅栏组织变厚，是对强光的一种保护性反应。 植物对光的可塑性反应 不同植物会表现出对光适应有利的生理和形态可塑性反应。本文对第三章、第四章的实验数据进行可塑性指数分析，来研究植物对光强的表型可塑性反应（第五章）。结果显示，生理特征调整是植物对不同光环境的主要适应途径。红桦和青榨槭的可塑性指数平均值要大于粗枝云杉和岷江冷杉，充分表明这2种阔叶树在生理和形态上较强的可塑性更有利于对光环境的适应，而具有比耐荫树种更强的适应能力。另外，2种针叶树相比，云杉的适应性更强。本研究结果支持树种的生理生态特性决定了其演替状况和生境选择的假说。 植物的光抑制与防御 当植物叶片吸收了过多光能，会发生光抑制现象。植物对光抑制的敏感性及防御能力对其生长具有重要意义。本文通过两个野外盆栽实验，研究了生长在强光下（第六章）和变化光强下（第八章）植物的光抑制现象及其防御策略。结果表明，在强光下或从遮荫状态转入强光下，植物都会发生光抑制，其对光抑制的敏感性与植物的耐荫性（或喜光）和演替状态有密切联系。长期生长在强光下的植物受到光抑制是可恢复的，而当处于荫蔽环境的植物突然暴露于强光下时，受到的光抑制不能完全恢复，可能是（部分）光合机构受到破坏的缘故。粗枝云杉和青榨槭防御光抑制伤害的能力较强，热耗散是其防御光抑制的主要途径。长期的强光作用能使岷江冷杉和红桦发生严重光抑制，甚至光伤害，而红桦能够通过“凋落老叶，萌发新叶”的途径来适应新的强光环境。 How to restore the vegetation of subalpine coniferous forest in eastern Qinghai-Tibet Plateau, and change the trend of ecological deterioration is a very important issue. Acclimation of tree seedlings to different and varing light environment affects to a great extent the successful regeneration and establishment of subalpine coniferous forests in southwestern China’s montane forest areas, because the ability to respond to such changing resource are commonly assumed to be critical to plant success, and have a growth advantage than others. In this paper, several species seedlings in Abies faxoniana community were chosed to study the response and adaptation to light intensity and the interspecific differences of adaptability in six shaded sheds (100, 55, 40, 25, 15 and 7% of full sunlight) in the Maoxian Ecological Station of Chinese Academy of Sciences. Our results could provide a strong theoretical evidence for understanding the forest succession laws of subalpine coniferous forests, and the survival and settlement of seedlings under plantations, and provide scientific direction for the production and management of seedlings, especially the comparative studies of the acclimation to light between the conifer and broadleaf trees could provide new ideas for how to integrate the broad-leaved trees into the artificial coniferous forest. Growth under different light intensity Light intensity plays an important role on plant growth. One field experiments was conducted to study the growth of tree seedlings of Picea asperata, Abies faxoniana, Betula albo-sinensis and Acer davidii under different light intensities. The results showed that plants under low light environment could increase the specific stem length (stem length/ stem dry mass), in order to effectively intercept light resources, while biomass greater allocation to the roots, could make plants under high light environment absorb more water, and avoid drought stress. During the first growing season, the relative growth rates (RGRs) of Betula albo-sinensis and Acer davidii had the greatest values under the 100% of full light, for 55% of Picea asperata, and for 25-40% of Abies faxoniana. However, in the second growing season the the relative growth rates of the two broad-leaved trees changed and were appropriate for 25-55% of full light, for 55-100% of spruce, and for 25-100% of fir. Thus, from the first year to the second year, two broad-leaved seedlings maybe more suitable to partly shading environment, and two coniferous seedlings would have an increase in light demand, which may be an increased root biomass investment. Because in this way, seedlings grown under high light could better maintain their internal water balance, and thus its growth would not be seriously affected by drought stress. In addition, serious shading would cause fir seedlings to die. Acclimation of physiology to light Plants could coexist in forest ecosystem by forming different strategies of light use. One field experiments was conducted to study the acclimation of tree seedlings to different light intensity of Picea asperata, Abies faxoniana, Betula albo-sinensis and Acer davidii. The results showed that the photosynthetic capacity of Picea asperata and Betula albo-sinensis exhibited a general tendency of increase with more light availability; but for Abies faxoniana and Acer davidii seedlings, their highest values of the same parameters were found under intermediate light regime (i.e. 25-55% of PFD relative to full sunlight). Plants under low light environment could increase the specific stem length (stem length/ stem dry mass), in order to effectively intercept light resources. Leaf nitrogen and chlorophyll content increased, while dark respiration rate and light compensation points decreased, all of which were adaptive response to the low light environment. On the contrary, plants under high light environment had the thicken leaves and palisade tissue, which was a protective response to high light. Phenotypic plasticity to light Phenotypic plasticity can be exhibited in morphological and physiological processes. Physiological characteristical adjustment is the main for plant adaptation to different light environment.The means of plasticity indexes for Betula albo-sinensis and Acer davidii seelings were greater than Picea asperata and Abies faxoniana, amplied that the two broad-leaved trees were much more adaptable to the environment. In addition, spruce had the higher adaptablity than fir. The findings supported the hypothesis that the ecological characteristics of the species determined the biological status and its biological habitat selection. Photoinhibition and photoprotection to light Compared with conifer, broad-leaved trees could better change leaf morphology and adjust biomass allocation to adapt to changing light environment. However, excess light can photoinhibit photosynthesis and may lead to photooxidative destruction of the photosynthetic appatus. Two field experiments were conducted to study the photoinhibition of photosynthesis. The results showed that when plants grown under high light environment or plants transferred from low to high irradiance, the four tree seedlings would undergo a period of photoinhibition. In four species, photoinhibited leaves could recover to initial photosynthetic rates when they were long-term planted under high light environment. However, when plants were suddenly exposed to high irradiance, this photoinhibition could not be reversible, may be the photosynthesis apparatus were (or partly) photooxidatively destructed.

Photosynthesis of Saussurea superba and Gentiana straminea is not reduced after long-term enhancement of UV-B radiation

Experiments were conducted in an alpine Kobresia humilis meadow near Haibei Alpine Meadow Ecosystem Research Station (37degrees29'-37degrees45'N, 101degrees12'-101degrees33'E; altitude 3200 m). Effects of enhanced ultraviolet-B (UV-B) radiation on photosynthesis of the alpine plants of Saussurea superba and Gentiana straminea were investigated. Both species were exposed to a UV-B-BE density at 15.80 kJ m(-2) per day, simulating nearly 14% ozone (O-3) reduction during the plant growing season. Neither photosynthetic CO2 uptake rate nor photosynthetic O-2 evolution rate were decreased after a long period of enhanced UV-B radiation treatment. On the contrary, there was a tendency to increase of both parameters in both species. The photosynthetic pigments were also increased, when expressed on a leaf area basis. UV-B absorbing compounds, detected by the absorbance values at 300 mm, had a tendency to increase in both species after enhanced UV-B radiation. After long-term exposure of plants to enhanced UV-B radiation, leaf morphology was also affected. Leaf thickness in both S. superba and G. straminea were increased significantly (P < 0.001). This supports our hypothesis that the increase of leaf thickness in both species after long-term exposure of enhanced UV-B radiation could compensate for the photodestruction of photosynthetic pigments when light passes through the leaf. Therefore, photosynthesis is not reduced in either species when expressed on leaf area basis. (C) 2003 Elsevier B.V. All rights reserved.

COMPARISON OF MASTICATORY MORPHOLOGY BETWEEN RHINOPITHECUS-BIETI AND R-ROXELLANA

The masticatory apparatus for two endemic species of golden monkey in China, Rhinopithecus bieti and Rhinopithecus roxellana, were compared with those of macaques, Macaca and leaf monkeys, Presbytis. Multivariate analyses demonstrated that the two golden monkey species are distinct. Interspecies allometric analyses revealed that golden monkeys differ in their masticatory apparatus from both macaques and leaf monkeys. The prominent symphysial fusion, corpus, and sagittal condylar dimension of R. roxellana may produce efficient biting force on the incisal and posterior canine teeth, with the heavy reaction force barn on the temporomandibular joint. However, the well-developed bizygamatic width and mandibular height in R. bieti suggest that posterior canine function is similarly prominent in R. roxellana, while incisal function is not. (C) 1995 Wiley-Liss, Inc.

Linear energy transfer dependence of the effects of carbon ion beams on adventitious shoot regeneration from in vitro leaf explants of Saintpaulia ionahta

Purpose: To determine the effects of carbon ion beams with five different linear energy transfer (LET) values on adventitious shoots from in vitro leaf explants of Saintpaulia ionahta Mauve cultivar with regard to tissue increase, shoots differentiation and morphology changes in the shoots. Materials and methods: In vitro leaf explant samples were irradiated with carbon ion beams with LET values in the range of 31 similar to 151 keV/mu m or 8 MeV of X-rays (LET 0.2 keV/mu m) at different doses. Fresh weight increase, surviving fraction and percentage of the explants with regenerated malformed shoots in all the irradiated leaf explants were statistically analysed. Results: The fresh weight increase (FWI) and surviving fraction (SF) decreased dramatically with increasing LET at the same doses. In addition, malformed shoots, including curliness, carnification, nicks and chlorophyll deficiency, occurred in both carbon ion beam and X-ray irradiations. The induction frequency with the former, however, was far more than that with the X-rays. Conclusions: This work demonstrated the LET dependence of the relative biological effectiveness (RBE) of tissue culture of Saintpaulia ionahta according to 50% FWI and 50% SF. After irradiating leaf explants with 5 Gy of a 221 MeV carbon ion beam having a LET value of 96 keV/mu m throughout the sample, a chlorophyll-deficient (CD) mutant, which could transmit the character of chlorophyll deficiency to its progeny through three continuous tissue culture cycles, and plantlets with other malformations were obtained.

Effects of ion beam irradiation on adventitious shoot regeneration from in vitro leaf explants of Saintpaulia ionahta

The effects of 960 MeV carbon ion beam and 8 MeV X-ray irradiation on adventitious shoots from in vitro leaf explants of two different Saintpaulia ionahta (Mauve and Indikon) cultivars were studied with regard to tissue increase, shoots differentiation and morphology changes in the shoots. The experimental results showed that the survival fraction of shoot formation for the Mauve and Indikon irradiated with the carbon ion beam at 20 Gy were 0.715 and 0.600, respectively, while those for both the cultivars exposed to the Xray irradiation at the same dose were 1.000. Relative biological effectiveness (RBE) of Mauve with respect to X-ray was about two. Secondly, the percentage of regenerating explants with malformed shoots in all Mauve regenerating explants irradiated with carbon ion beam at 20 Gy accounted for 49.6%, while that irradiated with the same dose of X-ray irradiation was only 4.7%; as for Saintpatdia ionahta Indikon irradiated with 20 Gy carbon ion beam, the percentage was 43.3%, which was higher than that of X-ray irradiation. Last, many chlorophyll deficient and other varieties of mutants were obtained in this study. Based on the results above, it can be concluded that the effect of mutation induction by carbon ion beam irradiation on the leaf explants of Saintpaulia ionahta is better than that by X-ray irradiation; and the optimal mutagenic dose varies from 20 Gy to 25 Gy for carbon ion beam irradiation.

Seed germination and seedling morphology of the seagrass, Halophila engelmannii (Hydrocharitaceae)

Seeds of Halophila engelmannii Aschers., that were collected in Redfish Bay, Texas, at weekly intervals from mid-May to mid-June 1986, began to germinate 3–4 weeks after collection. Most of the collections subsequently showed an increase in the rate of germination under increased light intensity and all had a stoppage of germination after transfer to darkness, indicating a light requirement to break endogenous seed dormancy. During the 5 weeks after seeds germinated, seedlings in soil culture produced a rosette of six leaves before the appearance of a rhizome bud in the axil of the third leaf. The first node of the rhizome produced a root and an upright shoot with a pseudowhorl of three to five leaves.