THE EFFECT OF SUCROSE SPRAYING ON SYMPTOMS CAUSED BY BEET YELLOWS VIRUS IN SUGAR BEET

When leaves of sugar-beet plants infected with beet yellows virus were sprayed daily with 10% sucrose solution, yellowing symptoms were intensified. When glasshouse plants were shaded so that the light intensity was reduced to less than half of full daylight, yellowing symptoms were suppressed more completely on un-sprayed than on sprayed plants. Spraying with 2–5 % sucrose solution had similar, but slightly smaller effects.
Spraying with sucrose solution increased the carbohydrate content of the leaves, and the effects on symptom intensity and carbohydrate content were closely correlated. The regression coefficients of symptom score on total sugar content were nearly the same for shaded and unshaded plants. As the severity of symptoms was increased by supplying carbohydrate without change in the light conditions, it is concluded that light intensity affects symptom expression by varying the carbohydrate content of the leaves through its influence on photosynthesis.
Sucrose spraying increased the yield of roots of healthy and infected plants, and most of the increase was sucrose. This shows that sprayed sugar was translocated to the roots from the leaves of both healthy and infected plants.
Measurements of changes in carbohydrate content between evening and morning samplings confirmed that movement of carbohydrate out of infected leaves is not stopped by infection.     

根茎型植物扁秆荆三棱对光照强度和养分水平的生长响应及资源分配策略

自然界中光照和养分因子常存在时空变化,对植物造成选择压力。克隆植物可通过克隆生长和生物量分配的可塑性来适应环境变化。尽管一些研究关注了克隆植物对光照和养分因子的生长响应,但尚未深入全面了解克隆植物对光照和养分资源投资的分配策略。以根茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis)为研究对象,在温室实验中,将其独立分株种植于由2种光照强度(光照和遮阴)和4种养分水平(对照、低养分、中养分和高养分)交叉组成的8种处理组合中,研究了光照和养分对其生长繁殖及资源贮存策略的影响。结果表明,扁秆荆三棱的生长、无性繁殖及资源贮存性状均受到光照强度的显著影响,在遮阴条件下各生长繁殖性状指标被抑制。且构件的数目、长度等特征对养分差异的可塑性响应先于其生物量积累特征。在光照条件下,高养分处理的总生物量、叶片数、总根茎分株数、长根茎分株数、总根茎长、芽长度、芽数量等指标大于其他养分处理,而在遮阴条件下,其在不同养分处理间无显著差异,表明光照条件可影响养分对扁秆荆三棱可塑性的作用,且高营养水平不能补偿由于光照不足而导致的生长能力下降。光照强度显著影响了总根茎、总球茎及大、中、小球茎的生物量分配,遮阴条件下,总生物量减少了对地下部分根茎和球茎的分配,并将有限的生物量优先分配给小球茎。总根茎的生物量分配未对养分发生可塑性反应,而随着养分增加,总球茎分配下降,说明在养分受限的环境中球茎的贮存功能可缓冲资源缺乏对植物生长的影响。在相同条件下,根茎生物量对长根茎的分配显著大于短根茎,以保持较高的繁殖能力;而总球茎对有分株球茎的生物量分配小于无分株球茎,表明扁秆荆三棱总球茎对贮存功能的分配优先于繁殖功能。研究为进一步理解根茎型克隆植物对光强及基质养分环境变化的生态适应提供了依据。     

光照强度和基质养分对匍匐茎草本金戴戴克隆生长和克隆形态的影响

在深度遮光(光照强度为高光条件的6.25%,约为自然光照的5.3%)或低养分条件下,金戴戴(Halerpestes ruthenica Ovcz.)生物量、初级分株叶面积、分株总数、匍匐茎总数和总长度均显著减小,而比节间长和比叶柄长显著增加.在低养分条件下,金戴戴匍匐茎平均节间长显著增加,而匍匐茎分枝强度和分株数显著减小.这些结果与克隆植物觅食模型相符合,表明当生长于异质性生境中,金戴戴可能通过以克隆生长和克隆形态的可塑性实现的觅养行为来增加对养分资源的摄取.在深度遮光条件下,金戴戴平均间隔子长度(即平均节间长和平均叶柄长)均显著减小.这一结果与以往实验中匍匐茎草本间隔子对中度和轻度遮光(光照强度为高光条件的13%～75%,>10%的自然光照)的反应不同.这表明,在深度遮光条件下匍匐茎克隆植物可能不发生通过间隔子可塑性实现的觅光行为.光照强度和基质养分条件的交互作用对许多性状如总生物量、匍匐茎总数和总长度、二级和三级分株数、分株总数、初级分株叶面积以及分枝强度均有十分显著的效应.在高光条件下,基质养分对这些性状有十分显著的影响;而在低光条件下,基质养分条件对这些性状不产生影响或影响较小.这表明,光照强度影响金戴戴对基质养分的可塑性反应.在深度遮光或低养分条件下,金戴戴可能通过减小匍匐茎节间粗度(增加比节间长)来增加或维持其相对长度,从而更有机会逃离资源丰度低的斑块.     

光照强度和基质养分对匍匐茎草本金戴戴克隆生长和克隆形态的影响

在深度遮光 (光照强度为高光条件的 6 .2 5% ,约为自然光照的 5.3% )或低养分条件下 ,金戴戴 (HalerpestesruthenicaOvcz.)生物量、初级分株叶面积、分株总数、匍匐茎总数和总长度均显著减小 ,而比节间长和比叶柄长显著增加。在低养分条件下 ,金戴戴匍匐茎平均节间长显著增加 ,而匍匐茎分枝强度和分株数显著减小。这些结果与克隆植物觅食模型相符合 ,表明当生长于异质性生境中 ,金戴戴可能通过以克隆生长和克隆形态的可塑性实现的觅养行为来增加对养分资源的摄取。在深度遮光条件下 ,金戴戴平均间隔子长度 (即平均节间长和平均叶柄长 )均显著减小。这一结果与以往实验中匍匐茎草本间隔子对中度和轻度遮光 (光照强度为高光条件的 1 3%～ 75% ,>1 0 %的自然光照 )的反应不同。这表明 ,在深度遮光条件下匍匐茎克隆植物可能不发生通过间隔子可塑性实现的觅光行为。光照强度和基质养分条件的交互作用对许多性状如总生物量、匍匐茎总数和总长度、二级和三级分株数、分株总数、初级分株叶面积以及分枝强度均有十分显著的效应。在高光条件下 ,基质养分对这些性状有十分显著的影响 ;而在低光条件下 ,基质养分条件对这些性状不产生影响或影响较小。这表明 ,光照强度影响金戴戴对基质养分的可塑性反应。在深度遮光     

长期弱光对苦草幼苗生长发育的影响

用遮光法研究弱光(5%、1%、0.5%、0.1%全光照)对苦草幼苗生长发育的影响,统计了苦草的生物学参数,测定了叶片叶绿素荧光参数。结果表明:1)0.1%组无新株萌发,随着实验时间的延长其余组新株萌发逐渐被抑制。2)随着实验时间增加和光照强度降低,老株叶片形成受到的抑制程度呈增大趋势;前20d时新株叶片形成未被抑制,但随着实验时间延长显著被抑制。3)老株、新株的叶宽均受到显著抑制。4)老株叶片的伸长显著被抑制,且随着光强降低叶片伸长的幅度呈显著降低趋势;前20天时新株叶长被促进,随着实验时间延长叶片伸长显著被抑制。5)随实验天数的增加,老株叶片光化学最大量子产量(Fv/Fm)呈显著降低趋势,第80天时相对电子传递速率(rETR)和非光化学淬灭(NPQ)显著降低。6)新、老植株根、茎、叶的鲜重均显著低于对照,且随着光照强度降低老株的茎重/株重和根重/株重呈增加趋势,而叶重/株重呈显著的降低趋势。第80天时苦草植株仍具有一定的光合能力,地下茎的生物量比例较高,因此,≤1%全光照下苦草植株具有较强的耐受能力。     

Uptake and transport of lead by perennial ryegrass from flowing solution culture with a controlled concentration of lead

Summary Perennial ryegrass was grown in flowing solution culture in a glasshouse, and during February lead was added to the nutrient solution and held at a constant concentration; uptake and transport of lead were followed in conditions of low intensity daylight or higher intensity artificial light. Uptake of lead by the roots was most rapid during the first 4 days after addition to the nutrient solution. After this time there was a steady increase in uptake per g dry weight of root with plants grown in artificial light having a much higher rate of uptake than plants grown in daylight. Roots always contained more lead than the corresponding shoots and concentration was always greater in the roots than in the shoots. The concentration in both roots and shoots increased with time but that in plants grown in artificial light was higher than that in plants grown in daylight. Two phases of uptake were identified, an initial rapid phase which is probably an exchange phenomenon, and a slow sustained phase which may be under metabolic control. A lower proportion of the total lead taken up remained in the roots of plants grown in artificial light than in those grown in daylight. This difference may have resulted from differences in (i) the production of organic carriers and/or (ii) transpiration. re]19750930     

Differences between maize and wheat in growth-related nutrient demand and uptake of potassium and phosphorus at suboptimal root zone temperatures

The effects of low root zone temperatures (RZT) on nutrient demand for growth and the capacity for nutrient acquisition were compared in maize and wheat growing in nutrient solution. To differentiate between direct temperature effects on nutrient uptake and indirect effects via an altered ratio of shoot to root growth, the plants were grown with their shoot base including apical shoot meristem either within the root zone (low SB), i.e. at RZT (12°, 16°, or 20°C) or, above the root zone (high SB), i.e. at uniformly high air temperature (20°/16° day/night).At low SB, suboptimal RZT reduced shoot growth more than root growth in wheat, whereas the opposite was true in maize. However, in both species the shoot growth rate per unit weight of roots, which was taken as parameter for the shoot demand for mineral nutrients per unit of roots, decreased at low RZT. Accordingly, the concentrations of potassium (K) and phosphorus (P) remained constant or even increased at low RZT despite reduced uptake rates.At high SB, shoot growth at low RZT in both species was higher than at low SB, whereas root growth was not increased. At high SB, the shoot demand per unit of roots was similar for all RZT in wheat, but increased with decreasing RZT in maize. Uptake rates of K at high SB and low RZT adapted to shoot demand within four days, and were even higher in maize than in wheat. Uptake rates of P adapted more slowly to shoot demand in both species, resulting in reduced concentrations of P in the shoot, particularly in maize.In conclusion, the two species did not markedly differ in their physiological capacity for uptake of K and P at low RZT. However, maize had a lower ability than wheat to adapt morphologically to suboptimal RZT by increasing biomass allocation towards the roots. This may cause a greater susceptibility of maize to nutrient deficiency, particularly if the temperatures around the shoot base are high and uptake is limited by nutrient transport processes in the soil towards the roots.     

GROWTH AND MORPHOLOGY OF YOUNG GAMETOPHYTES OF PORPHYRA ABBOTTAE (RHODOPHYTA): EFFECTS OF ENVIRONMENTAL FACTORS IN CULTURE1

Growth, blade shape and blade thickness of young gametophytes of Porphyra abbottae Krishnamurthy cultured from conchospores were determined at various combinations of temperature (8, 10, 12° C), photon flux density (17.5, 70, 140 μmol·m-^?2·S^?1), nutrient concentration (5, 25, 50, 100% f medium) and water motion (0, 50, 100, 150 rpm). Growth (as surface area) was light-saturated at 70 μmol· m^?2· S^?1, light-inhabited at 140 μmol·m^?2· S^?1, and nutrient-saturated an 25% f medium. Temperature had no significant effect on growth. Water motion and nutrients had an interactive effect on growth, with water motion having the greatest effect at the lowest nutrient concentrations. Water motion enhanced growth even at saturating nutrient concentrations. Blade length / width ratio was greater in low light (2.5) than in saturating light (1.9); with increasing water motion the ratio increased from 1.2 to 2.4. Blade thickness (53-88 μm) was greatest at the highest nutrient concentrations and at the lowest water motion levels. Temperature and light did not have a consistent effect on blade thickness.     

Energy metabolism of Plantago major ssp. major as dependent on the supply of mineral nutrients

Plantago major L. ssp. major , a grassland species from a relatively nutrient-rich habitat, was grown in nutrient-rich and nutrient-poor culture solutions. Half of the plants were transferred from high to low or from low to high nutrient conditions. The rate of dry matter accumulation in both shoots and roots decreased slowly upon transfer of plants to low nutrient conditions and the shoot to root ratio was unaffected. The rate of structural growth of both roots and shoots increased upon transfer from low to high nutrient conditions and the shoot to root ratio, if calculated from non-structural-carbohydrate-free dry weights, increased.
Photosynthesis was largely independent of the nutrient supply. Root respiration, particularly the activity of the alternative oxidative pathway, decreased with increasing age. This decrease was ascribed to a decreased shoot to root ratio, which reduced the relative amount of carbohydrates translocated to the roots and thus the amount available for the alternative pathway. It is calculated that in young as well as in old plants grown in full nutrient solution 48% of the daily produced photosynthates was translocated to the roots.
This is at variance with data on P. lanceolata , where a decreasing proportion of the daily produced photosynthates was translocated to the roots when the plants grew older. It is concluded that shoot growth plus shoot respiration consumed a constant amount of the daily produced photosynthates in P. major and that the rest was left for translocation. It is further calculated that in P. major plants grown in full nutrient solution c . 25% and c . 2% of the daily produced photosynthates in young and old plants, respectively, was respired in a way that is not involved in production of energy that is utilized in growth and maintenance ('inefficient root respiration').
The results are discussed in comparison with those of P. lanceolata , a species from a relatively nutrient-poor habitat.     

The relative importance of carbohydrate and nitrogen for the resprouting ability of Quercus crispula seedlings

BACKGROUND AND AIMS: Plants need some kind of stored resources to resprout after shoot destruction. The aim of this study was to determine the relative importance of carbohydrate and nitrogen (N) storage levels for their ability to resprout. METHODS: A shoot clipping experiment was conducted on Quercus crispula seedlings, which were grown in a factorial experimental design, with two light levels (40% and 3% of full light) and three nutrient concentrations (low, medium and high). KEY RESULTS: At the time of shoot clipping (the end of spring leaf expansion), seedlings exposed to 40% light had an average total non-structural carbohydrate (TNC) concentration of 17.0% in their roots compared with 4.9% in the roots of seedlings exposed to 3% light, and the average amount of TNC (TNC pools) in the roots was 203.8 mg and 20.0 mg at 40% light and 3% light, respectively. In contrast, root N concentration averaged 2.3% in the 3% light treatment compared with 1.2% in the 40% light treatment, and it increased with successive rises in nutrient concentrations at both light levels. Regardless of the nutrient status, at the 40% light level >80% of the seedlings resprouted after shoot clipping. Few seedlings, however, resprouted at the 3% light level, particularly in the medium- and high-nutrient treatments. Furthermore, both root TNC concentrations and TNC pools decreased after resprouting, but the amount of root N remained constant. CONCLUSIONS: These results suggest that carbohydrate storage has a stronger influence on resprouting in Quercus crispula than N storage. However, the size of the resprouting shoot was positively correlated with the amount of both N and TNC in roots. The level of N storage is, therefore, also important for the growth of resprouting shoots.     

生长环境光强对夏蜡梅子叶显微形态结构和光合参数的影响

夏蜡梅子叶在一年生幼苗的成苗和生长过程中具有重要作用。为了解夏蜡梅子叶的光适应能力和机制,采用不同层数遮阳网遮光的方式,研究四种生长环境光强(4%、22%、50%和100%全光照)对夏蜡梅子叶显微形态结构和光合参数的影响。结果表明,随着生长环境光强的减弱,夏蜡梅子叶光饱和点(LSP)、光补偿点(LCP)、叶片厚度降低,叶绿素含量升高。在50%全光照下,子叶结构发育完全,细胞排列紧密,维管组织发达,最大净光合速率(Pmax)和暗呼吸速率最高(Rd);而低于22%全光照下子叶趋向于阴生叶结构。因此,夏蜡梅子叶具有较强的耐荫能力。     

Competitive ability of two Brassica varieties in relation to biomass allocation and morphological plasticity under varying nutrient availability

Green cabbage (Brassica campestris, leafy variety) and turnip (Brassica campestris var. rapifera, rooty variety) were grown in both monocultures and mixtures at three nutrient levels to investigate their responses to nutrient availability with respect to biomass allocation, morphological plasticity and competitive ability. Their allocation parameters and leaf morphological traits were affected by both nutrient availability and developmental stage. Both of the varieties had a smaller biomass allocation to leaf blades, but a greater allocation to petioles at high nutrient levels. Root:shoot ratio (RSR) of green cabbage decreased with increasing nutrient availability, whereas that of turnip increased. Turnip had a smaller leaf blade weight ratio (LBWR) than cabbage, being compensated for by larger leaf area ratio (LAR) and specific leaf area (SLA). Leaf area ratio and SLA of both the varieties increased with increasing nutrient availability as did their mean dry weights. The mean dry weight of turnip was slightly greater than that of green cabbage in their respective monocultures, while that of green cabbage was greater than that of turnip in their 1:1 mixture. Therefore, green cabbage, having inherently greater biomass allocation to leaves, was generally more competitive than turnip with more biomass allocation to roots, especially at higher nutrient levels. However, within a variety, morphological plasticity (variation in LAR and SLA) was more important than the plasticity in biomass allocation (e.g. variation in RSR and LBWR) in determining competitive ability. The implication of our results is that competition models based on biomass allocation pattern alone may fail to predict competitive outcomes and that such models should also take morphological plasticity into full account.     

The modular character of growth in Nicotiana tabacum plants under steady-state nutrition

The impact of different plant growth rates on biomass allocation and growth distribution in tobacco was studied on the whole plant, total leaf area and single leaf level. On the whole plant level, constant relationships were found between the total leaf area and the biomass allocation to leaves and the nonphotosynthetic organs (roots and stem) independent from the overall growth rate and the nutrient addition rate to the plants. On the level of total leaf area, plants grown at lower nutrient supply reached a distinct distribution of leaf area later than those grown at higher nutrient supply, but the normalized distribution of leaf area along the stem at a certain plant size did not differ between plants growing at different nutrient supply and growth rates. On the leaf blade level, growth rates declined, initially linearly, from the leaf base to the leaf tip. Distinct gradients within the side veins were not observed, but the growth rates of the side veins were closely correlated to the adjacent mid-vein segments. These gradients flattened with increasing size of the leaf. The modular character of growth in tobacco is discussed in the context of basic growth analysis and as a framework for physiological, cytological, biochemical, and molecular studies in growing plants.Key words: Nicotiana tabacum, whole plant, total leaf area, leaf growth, growth rate, biomass.      

Comparative accumulation of manganese and boron in barley tissues

Summary The uptake of Mn and B by barley plants was studied in a 5-week period in growth chambers. Fluorescent light was provided with an intensity of 3200 foot-candles in a 12-hour day length and the entire plants were grown at temperatures of 10°, 15°, or 20°C. The root medium consisted of a base nutrient solution in which Mn or B was added in the following concentrations: 0, 0.1, 0.5, 2.0, and 5.0 ppm. Five plants were grown in volumes of 20 liters of solution. At the end of the growth period the shoots and roots were analyzed for Mn and B. The Mn content of the roots increased with temperature and with the Mn concentration of the external solution while the B content remained virtually static regardless of temperature or solution concentration. The shoots were divided into young, mature, and old leaves. The Mn and B content of the old leaves showed increases which varied both with temperature and concentration. Similar results were obtained with young and mature leaves. The failure of B to accumulate in the roots was discussed. It was suggested that boric acid, with a very low degree of dissociation, is present largely in a molecular form and does not participate in the customary metabolic activity connected with ion uptake and accumulation in roots.     

Do large‐seeded herbs have a small range size? The seed mass–distribution range trade‐off hypothesis

We aimed to introduce and test the “seed mass–distribution range trade‐off” hypothesis, that is, that range size is negatively related to seed mass due to the generally better dispersal ability of smaller seeds. Studying the effects of environmental factors on the seed mass and range size of species, we also aimed to identify habitats where species may be at risk and need extra conservation effort to avoid local extinctions. We collected data for seed mass, global range size, and indicators for environmental factors of the habitat for 1,600 species of the Pannonian Ecoregion (Central Europe) from the literature. We tested the relationship between species’ seed mass, range size, and indicator values for soil moisture, light intensity, and nutrient supply. We found that seed mass is negatively correlated with range size; thus, a seed mass–distribution range trade‐off was validated based on the studied large species pool. We found increasing seed mass with decreasing light intensity and increasing nutrient availability, but decreasing seed mass with increasing soil moisture. Range size increased with increasing soil moisture and nutrient supply, but decreased with increasing light intensity. Our results supported the hypothesis that there is a trade‐off between seed mass and distribution range. We found that species of habitats characterized by low soil moisture and nutrient values but high light intensity values have small range size. This emphasizes that species of dry, infertile habitats, such as dry grasslands, could be more vulnerable to habitat fragmentation or degradation than species of wet and fertile habitats. The remarkably high number of species and the use of global distribution range in our study support our understanding of global biogeographic processes and patterns that are essential in defining conservation priorities.     

PHYSIOLOGICAL AND ULTRASTRUCTURAL RESPONSES OF CYCLOTELLA MENEGHINIANA (BACILLARIOPHYTA) TO LIGHT INTENSITY AND NUTRIENT LIMITATION1

Photosynthetic characteristics and chloroplast ultrastructure of Cyclotella meneghiniana Kütz. were quantified while the organism was simultaneously adjusting to light and nutrient stress. Cells were grown in batch culture at either low or high light intensity on medium with a nitrogen/phosphorus molar ratio of 2:1 as a control, or with nitrogen or phosphorus deleted from the medium to create nutrient deficiencies. Analysis of variance indicated that light intensity, nutrient deficiency and duration of nutrient deficiency all had significant effects on cell growth, chlorophyll (Chl) concentration/cell, cellular fluorescence capacity (CFC), chloroplast volume and thylakoid surface density. Because interactions existed among nutrient deficiency, extent of nutrient deficiency, and light intensity, all three must be considered together in order to describe accurately the physiology and chloroplast ultrastructure of the diatom. Significant correlations were found between the Chl/cell or CFC/cell and chloroplast volume and thylakoid surface density. Through an increase in Chi concentration, chloroplast volume and thylakoid surface density, the cells successfully adapted to the conditions of low light intensity even while under nutrient stress. In contrast, less Chl/cell, smaller chloroplast volume and less thylakoid surface density were found at high light intensity.     

遮阴对地枫皮幼苗生长和生物量分配的影响

为了解光照强度对地枫皮(Illicium difengpi)幼苗生长和生物量分配的影响,对不同等级幼苗在不同遮阴处理下的形态和生物量变化进行了研究。结果表明,遮阴处理下幼苗的株高、冠宽和平均单叶面积均显著高于对照,同时比叶面积均随光强增大而显著降低。除I级苗50%遮阴处理外,全光处理下各等级幼苗的根长均显著高于遮阴处理。随着光照强度的增加,各等级幼苗的根生物量比与根冠比显著增加,叶生物量比显著减少;不同等级幼苗对强光和弱光环境均表现出较强的适应性,但以50%遮阴处理的总生物量最大,全光和85%遮阴处理均较小。遮阴处理的幼苗个体大小与其初始大小呈正相关,其中II级苗与I级苗差别较小,III级苗生长较差。在人工育苗条件下I级苗数量不到10%,较差的种苗质量叠加喀斯特山顶恶劣环境,可能是导致野外幼苗更新限制的重要原因。因此在野外回归和人工栽培过程中宜选用I、II级种苗,光强控制在透光率50%为宜。     

Effects of light and nutrient availability on dry matter and N allocation in six successional grassland species

Summary Recent discussions on determinants of competitive success during succession require the study of the combined effect of light and nutrient availability on growth and allocation. These effects can be used to predict the outcome of competition at changing resource availabilities. This work is part of a study on the successional sequence in permanent grassland starting after fertilizer application is stopped, but with continued mowing, in order to restore former species-rich communities. This yields a successional sequence which proceeds from grasslands with a high nutrient availability and a closed canopy, to grasslands with a low nutrient availability and an open canopy. If allocation is related to competitive ability, species from the productive stages would be expected to allocate more biomass and nitrogen to leaves, which could make them better competitors for light, while species from the unproductive stages would allocate more biomass to roots, which could make them better nutrient competitors. This study reports on growth, specific leaf area (SLA), vertical display of leaves, and allocation of biomass and nitrogen of six grassland species from this successional sequence at 16 combinations of light and nutrient supply. Species from the poorer successional stages reached a lower final dry weight than species from the richer stages, over all treatment combinations. The experimental design made it possible to test for unique effects of the resource ratio effect of light and nutrients on allocation characteristics. This resource-ratio effect was defined as the ratio light intensity/(light intensity + nutrient supply rate), using standardized levels for the treatments. The within-species variation (plasticity) in both allocation of dry matter and nitrogen was linearly related to this resource-ratio effect. Some interspecific differences in this relationship were found which could be related to the position of the species along the successional gradient. However, the range of plasticity in allocation pattern expressed within each species was much larger than the differences between species. It was concluded that allocation differences between these grassland species are relatively unimportant, given the large amount of plasticity in these traits. Interspecific differences in SLA and vertical stature seemed to be more important in explaining the position of species along the successional gradient.     

Interaction between Light Intensity and NaCl Salinity and Their Effects on Growth, CO(2) Assimilation, and Photosynthate Conversion in Young Broad Beans

Seedings of Vicia faba were grown for four weeks at two different light intensities (55 and 105 watts per square meter) in a saline (50 millimolar NaCl) and nonsaline nutrient solution. NaCl salinity depressed growth and restricted protein formation, CO₂ assimilation, and especially the incorporation of photosynthates into the lipid fraction. Conversion of photosynthates in leaves was much more affected by salinity than was photosynthate turnover in roots. The detrimental effect of NaCl salinity on growth, protein formation, and CO₂ assimilation was greater under low than under high light conditions. Plants of the high light intensity treatment were more capable of excluding Na⁺ and Cl⁻ and accumulating nutrient cation species (Ca²⁺, K⁺, Mg²⁺) than plants grown under low light intensity. It is suggested that the improved ionic status provided better conditions for protein synthesis, CO₂ assimilation, and especially for the conversion of photosynthates into lipids.     

Physical conditions of propagation media and their influence on the rooting of cuttings

Summary The formation and subsequent growth of roots by cuttings of poinsettia, hydrangea, rose and azalea in various propagation media, Jiffy-7, Jiffy-9 and Grodan under different conditions of aeration was investigated. The interrelationships of the effects of air content of the media, temperature and light intensity on the rooting of poinsettia cuttings was also studied.With low air contents (0 cm moisture tension) in the propagation media the formation and growth of roots was strongly inhibited. The rooting performance of rose appeared to be less affected by the poor aeration. Increasing air content improved rooting but best results were obtained at moisture tensions of 4 to 8 cm. Rooting seems to be better correlated with oxygen diffusion rate (ODR) than with air content.For poinsettia cuttings the optimum temperature for rooting was 24 to 28°C. At low temperatures rooting was delayed while at higher temperatures it was almost completely inhibited. Callus formation increased with temperature but decreased with increasing moisture tension. Conditions which induced large callus formation inhibited root formation.High light intensity during rooting reduced overall rooting performance and the inhibition was most pronounced in conjunction with high moisture tensions.Report No. 255.