The ultrastructure of Spirulina platensis in relation to temperature and light intensity

The ultrastructure of Spirulina platensis, a cyanobacterium with a helical morphology, has been studied in relation to temperature and light intensity. An increase in temperature gives rise to a more tightly coiled trichome, an increase in sheath material formation and a decrease in cyanophycin (above 17°C) and polyglucan (above 20°C) granule concentration. An increase in light intensity leads to an increase in gas vesicle concentration while the phycobilisome content decreases. Furthermore, cylindrical bodies have been observed with a somewhat different ultrastructure from those found in other species of cyanobacteria. The occurrence, size and ultrastructure of polyhedral bodies, photosynthetic lamellae, mesosomes, lipid deposits and an unknown kidney-shaped inclusion in relation to temperature and light intensity are described.     

Growth responses of rice seedlings to triacontanol in light and dark

Triacontanol, a 30-carbon primary alcohol, applied in nutrient culture solutions to rice (Oryza sativa L.) seedlings at 2.3×10^-8 M (10 g/l), caused an increase in dry weight and leaf area of the whole plants. The response could be observed as early as 3 h of treatment. It was observed at relatively high and low light intensities as well as in the dark where control plants lost but triacontanol-treated plants gained in dry weight. The dry weight gain in the dark was, however, eliminated by removing CO₂ from the atmosphere. Triacontanol-treated plants also increased their content of Kjeldahl-N and contained 30% more total N per plant than controls after 6 h in the dark.     

Photosynthesis and root growth in Spartina alterniflora in relation to root zone aeration

Spartina alterniflora Lois. is a dominant species growing in intermediate and saline marshes of the US Gulf coast and Atlantic coastal marshes. S. alterniflora plants were subjected to a range of soil redox potential (Eh) conditions representing a well aerated to reduced conditions in a rhizotron system under controlled environmental conditions. The low soil Eh resulted in inhibition of root elongation shortly after treatment initiation. Root elongation was reduced as soil Eh approached values below ca. +350 mV. Substantial decrease in root elongation was noted when soil Eh fell below +200 mV. Generally, net photosynthetic rate (PN) decreased as soil Eh was reduced, with substantial reductions in PN found when Eh approached negative values. Average PN was reduced to 87, 64, and 44% of control under +340, +245, and -180 mV treatments, respectively. The reductions in root elongation and PN in response to low soil Eh indicated the adverse effects of low soil Eh on plant functioning and the need for periods of soil aeration that allow plants to resume normal functioning. Thus periods of drainage allowing soil aeration during the growing season appear to be critical to S. alterniflora by providing favorable conditions for root growth and gas exchange with important implications for plant carbon fixation. This revised version was published online in June 2006 with corrections to the Cover Date.     

Photosynthesis and root growth in Spartina alterniflora in relation to root zone aeration

Spartina alterniflora Lois. is a dominant species growing in intermediate and saline marshes of the US Gulf coast and Atlantic coastal marshes. S. alterniflora plants were subjected to a range of soil redox potential (Eh) conditions representing a well aerated to reduced conditions in a rhizotron system under controlled environmental conditions. The low soil Eh resulted in inhibition of root elongation shortly after treatment initiation. Root elongation was reduced as soil Eh approached values below ca. +350 mV. Substantial decrease in root elongation was noted when soil Eh fell below +200 mV. Generally, net photosynthetic rate (PN) decreased as soil Eh was reduced, with substantial reductions in PN found when Eh approached negative values. Average PN was reduced to 87, 64, and 44% of control under +340, +245, and -180 mV treatments, respectively. The reductions in root elongation and PN in response to low soil Eh indicated the adverse effects of low soil Eh on plant functioning and the need for periods of soil aeration that allow plants to resume normal functioning. Thus periods of drainage allowing soil aeration during the growing season appear to be critical to S. alterniflora by providing favorable conditions for root growth and gas exchange with important implications for plant carbon fixation.     

Growth rate of four freshwater algae in relation to light and temperature

Four algae of freshwater phytoplankton were studied in monospecific culture: Chlorella vulgaris, Fragilaria crotonensis, Staurastrum pingue and Synechocystis minima. Experiments were performed to determine the growth rate over a wide range of light intensities (5–800 µE m^–2 s^–1, 15/9 light/dark photoperiod) and temperatures (10–35 °C). The results provide a set of parameters (particularly the maximal growth rate associated to optimal conditions of light and temperature) for a three-equation model used to described the growth rate response of a non-nutrient-limited culture.     

Flowering responses to light and temperature

Light and temperature signals are the most important environmental cues regulating plant growth and development. Plants have evolved various strategies to prepare for, and adapt to environmental changes. Plants integrate environmental cues with endogenous signals to regulate various physiological processes, including flowering time. There are at least five distinct pathways controlling flowering in the model plant Arabidopsis thaliana: the photoperiod pathway, the vernalization/thermosensory pathway, the autonomous floral initiation, the gibberellins pathway, and the age pathway. The photoperiod and temperature/vernalization pathways mainly perceive external signals from the environment, while the autonomous and age pathways transmit endogenous cues within plants. In many plant species, floral transition is precisely controlled by light signals(photoperiod) and temperature to optimize seed production in specific environments. The molecular mechanisms by which light and temperature control flowering responses have been revealed using forward and reverse genetic approaches. Here we focus on the recent advances in research on flowering responses to light and temperature.     

Regulation of root anaerobiosis and carbon translocation by light and root aeration in Isoetes alpinus

The activity of alcohol dehydrogenase (ADH) was measured in corms and roots of the submerged freshwater macrophyte Isoetes alpinus Kirk. growing in situ, and related to its capacity for internal oxygen transport and to carbohydrate translocation. ADH activity was present in roots but not corms at uniform activity (0.15–0.35 × 10^?6 mol g^?1 fresh weight s^?1) over the entire plant depth range (3–7 m depth), and was intermediate to that developed in excised roots after 1‐week exposure to either dissolved oxygen at air‐saturation or to anoxia. Responses of photosynthesis and root oxygen release to light intensity confirmed that shoot‐to‐root oxygen transport saturated at similar light intensities to photosynthetic oxygen evolution, but was positive in the dark and at irradiances below the compensation point for photosynthesis, due to contributions to transport by oxygen diffusion from the external medium. Transport of ¹⁴C‐labelled photo‐assimilates to roots nevertheless ceased when intact plants were exposed to a combination of leaf darkness and root external anoxia, even when high ¹⁴C concentrations were present in shoots, but remained high when the roots were provided with external oxygen. The lack of any control over permeability of the root surface to gases in this species suggested that ADH activity and reduced translocation is most likely caused by development of hypoxic tissues in the apical tissue. These results suggest that reductions in ambient light intensity may have indirect effects on I. alpinus viability by increasing the degree of root hypoxia and impairing carbon partitioning.     

Growth responses to arbuscular mycorrhizae by rain forest seedlings vary with light intensity and tree species

Light intensity and root colonization by arbuscular mycorrhizal (AM) fungi are considered important factors affecting the performance of rain forest plants, yet few studies have examined how these two factors interact. Whether AM colonization promoted growth or caused shifts in biomass allocation in seedlings of four species of Australian rain forest tree (Flindersia brayleana, Acmena resa, Cryptocarya mackinnoniana and Cryptocarya angulata), grown in a glasshouse under light conditions that mimicked the shaded understory (3% PAR) and small light gaps (10% PAR), was examined. Seedlings were grown in sterilized field soil and either inoculated with AM fungi or provided sterile inoculum. Four major findings emerged. First, in all species, seedlings grown in small gap light intensities were larger than seedlings grown in understory light intensities. Second, when seedling biomass was included as a covariate, variation in light intensity was associated with significant shifts in biomass allocation. In all species, leaf area ratio was lower at 10% PAR than at 3% PAR, while root-to-shoot ratio showed the opposite pattern in one of the four species (C. mackinonniana). Third, although percentage root length colonized by AM fungi was greater at 10% PAR than 3% PAR in all species, this difference could be accounted for by variation in seedling size in all species except C. angulata. Fourth, growth and biomass allocation responses to AM colonization varied with light intensity and plant species. AM colonization promoted growth in both light regimes only in F. brayleana, while it had no effect on growth in C. mackinnoniana and C. angulata in either light regime and promoted growth only under high light in A. resa. AM colonization had no effect on leaf area ratio or root-to-shoot ratio in any of the species, and significantly altered specific root length in only one of the four species (C. mackinnoniana). These findings suggest that rain forest seedlings are highly variable in their growth responses to AM colonization and that some of this variability is related to the light intensity of the environment. Given that seedlings may spend many years in the shaded understory, these differences among species could have important effects on long-term seedling performance and seedling community dynamics.     

Soil aeration in relation to soil physical properties, nitrogen availability, and root characteristics within an arctic watershed

The seasonal change in soil oxygen availability was determined in several habitats along a topographic moisture gradient in an arctic watershed. The effect of changes in soil aeration on soil chemical and plant properties was examined by comparison of the driest (tussocks) and wettest (wet sedge tundra) sites along this gradient. Spatial variability and seasonal change in soil oxygen availability was closely linked to the hydrologic regime and the thickness of the organic soil horizon. The greatest extension of the aerobic soil layer was found beneath well-drained tussocks, while less than 10% of the unfrozen soil layer is aerated in flooded wet sedge tundra. Intertussock areas and watertracks (channels of water drainage) have intermediate levels of aeration. In tussock tundra, soil oxygen diffusion is restricted in the mineral soil layer below the organic horizon due to reduced pore space. Organic matter constituents and their change with depth were similar beneath tussocks and in wet sedge tundra, indicating that factors other than soil aeration (e.g. low soil temperatures, short growing season) are the primary controls on decomposition in these two arctic tundra systems. NH₄ ⁺, the dominant form of inorganic N, was more available in wet sedge tundra than in tussock tundra. At both sites, extractable and soil solution NO₃ ^- concentrations increased 4 to 8 fold in the second part of the growing season, indicating increased nitrifier activity with improved soil oxygen availability. Although soils thawed as deep as 60 cm, approx. 90% of the root biomass was concentrated within 20 cm of the surface. Despite the anaerobic soil environment in wet sedge tundra, the dominant species there, Eriophorum angustifolium, reached slightly greater rooting depths than E. vaginatum, whose roots grow in the elevated, aerobic portion of tussocks. E. angustifolium had a root porosity of 31%, within the range found for wetland species, while roots of E. vaginatum had a porosity close to 12%. Rhizome porosity were low in both species (11%).     

虾池常见微藻的光照强度、温度和盐度适应性

通过Smith生态位宽度指数和Pianka生态位重叠指数分析了虾池常见微藻种群(啮蚀隐藻、新月菱形藻、微绿球藻和蛋白核小球藻)在光照强度、温度和盐度资源上的生态位宽度和生态位重叠特征.结果表明:新月菱形藻和蛋白核小球藻具有较大的生态位宽度值,啮蚀隐藻和微绿球藻的生态位宽度值则相对较小.蛋白核小球藻和微绿球藻在光照强度、温度和盐度资源上的生态位重叠值均为最大,啮蚀隐藻在各资源与其他微藻的重叠值最小.新月菱形藻与蛋白核小球藻适应光照强度的范围较广.当水温达16.9℃,可定向培育新月菱形藻;当水温达25℃,可定向培育新月菱形藻和啮蚀隐藻;当水温达30℃时,可定向培育新月菱形藻、蛋白核小球藻和微绿球藻.养殖水体盐度处于9～26,可引入蛋白核小球藻与微绿球藻;处于9～17.5,应引入啮蚀隐藻;高盐水体,应引入新月菱形藻.蛋白核小球藻和微绿球藻在光照强度、温度和盐度资源上的生态位重叠值均为最大,因此微藻定向培育,不可同时引入蛋白核小球藻与微绿球藻.     

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。     

Influence of soil water conditions on growth and root porosity of rice

Summary The influence of different depths of submergence (6±1 and 3±1 cm) and moisture tensions (0, 20, 60, 350, 500 and 1000 millibar) of lateritic sandy loam soil on root porosity and growth parameters of rice, variety IR8 was studied at two different growth phases under controlled greenhouse conditions. Best rice growth occurred at 3±1 cm submergence and it significantly reduced with the increase of soil moisture tension. Unlike other growth parameters, root length increased as the soil moisture tension was raised. The development of pore spaces in rice roots decreased significantly with the increase in soil moisture tension. However, higher root porosity was observed under greater depths of submergence. Irrespective of soil water condition, the number and dry weight of the root system showed significant positive correlation with root porosity. Oxygen diffusion rate in soil, which increased with the increasing moisture tension, was significantly and inversely related with the porosity of rice root. Contribution from the Agricultural Engineering Department, Indian Institute of Technology, Kharagpur, West Bengal, India.