Effects of irradiance, temperature, and nutrients on growth dynamics of seagrasses: A review

Productivity of seagrasses can be controlled by physiological processes, as well as various biotic and abiotic factors that influence plant metabolism. Light, temperature, and inorganic nutrients affect biochemical processes of organisms, and are considered as major factors controlling seagrass growth. Minimum light requirements for seagrass growth vary among species due to unique physiological and morphological adaptations of each species, and within species due to photo-acclimation to local light regimes. Seagrasses can enhance light harvesting efficiencies through photo-acclimation during low light conditions, and thus plants growing near their depth limit may have higher photosynthetic efficiencies. Annual temperatures, which are highly predictable in aquatic systems, play an important role in controlling site specific seasonal seagrass growth. Furthermore, both thermal adaptation and thermal tolerance contribute greatly to seagrass global distributions. The optimal growth temperature for temperate species range between 11.5 °C and 26 °C, whereas the optimal growth temperature for tropical/subtropical species is between 23 °C and 32 °C. However, productivity in persistent seagrasses is likely controlled by nutrient availability, including both water column and sediment nutrients. It has been demonstrated that seagrasses can assimilate nutrients through both leaf and root tissues, often with equal uptake contributions from water column and sediment nutrients. Seagrasses use HCO₃⁻ inefficiently as a carbon source, thus photosynthesis is not always saturated with respect to DIC at natural seawater concentrations leading to carbon limitation for seagrass growth. Our understanding of growth dynamics in seagrasses, as it relates to main environmental factors such as light, temperature, and nutrient availability, is critical for effective conservation and management of seagrass habitats.     

Life cycle of Egeria densa planch., an aquatic plant naturalized in Japan

The ecophysiological life cycle of Egeria densa Planch., in a lotic irrigation ditch was evaluated. Phenological and quantitative measurements were made from August 1984 to July 1985. Lateral shoots with roots developed and elongated to the surface of the water when the bottom-water temperature increased above c. 15°C. Root crown developed simultaneously as the plant biomass increased. Dense shoot crown was formed under the water surface after the shoot reached the water surface. Plant biomass had two maxima in August and December-January. The bimodal curve in plant biomass was caused by the difference of growth attributed to the winter-type and summer-type plants. Relative growth rate, in length, of summer-type plants occurred at an optimum temperature of 20.7°C in culture. The seasonal activity of photosynthesis and respiration was measured in March, August and December. The optimum temperature of net photosynthesis of the summer-type plants reached a high 35°C similar to that of the C₄ plant. The compensation for light intensity at 35°C was 340 lux. Each photosynthesis-temperature curve suggested that Egeria had the ability to adapt to the seasonal changes in temperature in the natural habitat. The maximum starch concentrations reached 25.4% in the leaf and 22.6% in the stem in December. The shortage in the balance of organic matter for overwintering was found to be maintained by stored starch in the leaf and the stem.     

Acclimation of Photosynthesis and Dark Respiration of a Submersed Angiosperm beneath Ice in a Temperate Lake

Ceratophyllum demersum L. remained physiologically active beneath ice of a southeastern Michigan lake. The effect of seasonally low photosynthetic photon flux density (PPFD) and cold but nonfreezing temperature on whole-plant physiology was studied. Net photosynthesis was measured at six temperatures and 12 PPFDs. Net photosynthesis, soluble protein concentration, ribulose-1,5-bisphosphate carboxylase/oxygenase (Rubisco) protein concentration, and Rubisco activity of winter plants were 32, 31, 33, and 70% lower, respectively, than those of plants collected in the summer. Optimum temperatures for net photosynthesis of winter and summer plants were 5 and 30[deg]C, respectively. Dark respiration of winter plants was up to 313% greater than that of summer plants. Reduced Rubisco activity and increased dark respiration interacted to reduce net photosynthesis. Interaction of reduced net photosynthesis and increased dark respiration increased CO2 and light compensation points and the light saturation point of winter plants. Growth of C. demersum was limited by the ambient phosphorus concentration of lake water during summer. Apical stem segments of winter-collected plants had 54 and 35% more phosphorus and nitrogen, respectively, than summer-collected plants. Physiologically active perennation beneath ice enabled C. demersum to accumulate phosphorus during the winter when it was most abundant. Partial uncoupling of phosphorus acquisition from utilization may reduce phosphorus limitation upon growth during the summer when phosphorus concentration is seasonally the lowest.     

The temperature and pH properties of the extracellular hemicellulose-Degrading enzymes of aureobasidium pullulans NRRL Y 2311-1

Aureobasidium pullulans grown on arabinoxylan accumulates β-xylanase, p-nitrophenyl xylosidase, - -arabinofuranosidase and acetyl esterase activity in the culture fluid. The pH and temperature optima of these arabinoxylan-degrading enzymes were determined. The temperature optima of β-xylanase and p-nitrophenyl xylosidase were between 45 and 50°C whereas the optima for acetyl esterase and - -arabinofuranosidase were 55 and 60°C, respectively. β-xylanase, p-nitrophenyl xylosidase and - -arabinofuranosidase were stable over 3 h at 35°C, 35°C and 60°C, respectively, whereas acetyl esterase remained stable at 55°C for h. The enzymes were inactivated at higher temperatures. The pH optima for β-xylanase, p-nitrophenyl xylosidase and - -arabinofuranosidase were pH 4·0, between 4·0 and 7·0 and 5·0, respectively. β-xylanase, p-nitrophenyl xylosidase, - -arabinofuranosidase and acetyl esterase were most stable at pH 5·0 4·0–5·0, 6·0 and 5·0–6·0, respectively. The most suitable conditions for the use of the enzymes together to hydrolyze arabinoxylan would be 35 °C and pH 5.     

Effects of temperature, irradiance, and daylength on the marine diatom Leptocylindrus danicus Cleve. IV. Growth

Growth and dark respiration rates of the marine diatom Leptocylindrus danicus Cleve were measured in axenic batch culture under 49 combinations of temperature (5, 10, 15, 20°C), daylength(15:9, 12:12, 9:15 LD), and irradiance (at least four irradiances per daylength). Cell division rates exhibited a temperature-dependent daylength effect. Optimal temperatures occurred between 15 and 20°C. Both the initial slope () and the growth rate at light saturation (μ_max) were strongly influenced by temperature; increased five-fold and μ_max by an order of magnitude between 5 and 20°C. The compensation irradiance (I_c) was independent of temperature. μ_max was 2.7 div day⁻¹ at 20°C, 2.6 at 15°C, 1.1 at 10°C, and 0.3 at 5 °C. Cells grown under 15:9 and 12:12 LD exhibited similar growth-light curves at 20°C and at 15°C. μ_max of cells grown under 9:15 LD at these temperatures were substantially lower than μ_max under longer daylengths. Growth at 10 and 5°C was independent of daylength.

Dark respiration rates were a linear function of cell division rates at 10, 15, and 20°C, and support the concept that growth rate is dependent on dark respiration rate. These relationships were not influenced by daylength. A detectable relationship between dark respiration and growth at 5°C was not observed.

Photosynthesis and excretion showed temperature-dependent curvilinear relationships with growth rate, reflecting the lower saturation irradiance for growth compared to light saturation of photosynthesis and excretion. The relationship between Chl a-specific photosynthesis and growth was controlled by the C:Chl a ratio, which showed a positive correlation with cell division rate. At 15 and 20°C, light saturation of growth was associated with C:Chl a ratios of 40 to 60; at 5 and 10°C, cells growing at μ_max contained C:Chl a in ratios of 80 to 110.     

Climatic warming changes plant photosynthesis and its temperature dependence in a temperate steppe of northern China

Warming responses of photosynthesis and its temperature dependence in two C₃ grass (Agropyron cristatum, Stipa krylovii), one C₄ grass (Pennisetum centrasiaticum), and two C₃ forb (Artemisia capillaris, Potentilla acaulis) species in a temperate steppe of northern China were investigated in a field experiment. Experimental warming with infrared heater significantly increased daily mean assimilation rate (A) in P. centrasiaticum and A. capillaris by 30 and 43%, respectively, but had no effects on other three species. Seasonal mean A was 13, 15, and 19% higher in the warmed than control plants for P. centrasiaticum, A. capillaries, and S. krylovii, respectively. The mean assimilation rate in A. cristatum and P. acaulis was not impacted by experimental warming. All the five species showed photosynthetic acclimation to temperature. The optimum temperature for photosynthesis (T_opt) and the assimilation rate at T_opt in the five species increased by 0.33–0.78 °C and 4–27%, respectively, under experimental warming. Elevated temperature tended to increase the maximum rate of ribulose-1,5-bisphosphate (RuBP) carboxylation (V_cmax) and the RuBP regeneration capacity (J_max) in the C₃ plants and carboxylation efficiency and the CO₂-saturated photosynthetic rate in the C₄ plant at higher leaf temperature, as well as the optimum temperatures for the four parameters. Our results indicated that photosynthetic responses to warming were species-specific and that most of the species in the temperate steppe of northern China could acclimate to a warmer environment. The changes in the temperature dependence of V_cmax and J_max, as well as the balance of these two processes altered the temperature dependence of photosynthesis under climatic warming.     

Photosynthesis and respiration in bladelets of Ecklonia cava Kjellman (Laminariales, Phaeophyta) in two localities with different temperature conditions

Characteristics of photosynthesis and respiration of bladelets were compared between Ecklonia cava Kjellman sporophytes growing in a warmer temperate locality (Tei, Kochi Pref., southern Japan) and in a cooler temperate locality (Nabeta, Shizuoka Pref., central Japan). Photosynthesis and respiration were measured with a differential gas-volumeter (Productmeter). In photosynthesis-light curves at 20°C, the rate of net photosynthesis was almost the same at light intensities lower than 25 μmol m⁻² s⁻¹ and the light-saturation occurred at 200–400 μmol m⁻²s⁻¹ in plants of both localities. The light-saturated net photosynthetic rates were higher in winter and spring than in summer and autumn in both plants. The optimum temperature for net photosynthesis at 400 μmol m⁻²s⁻¹ was 27°C throughout the year in the Tei plant and 25–27°C in the Nabeta plant. The decrease of net photosynthetic rates in the supraoptimal temperature range up to 29°C was sharper in winter and spring than in summer and autumn in both plants, being smaller in the Tei plant than in the Nabeta plant in all seasons. The dark respiration rate always increased with water temperature rise in both plants. No clear differences were found in the dark respiration rate between Tei and Nabeta plants except that when measured against dry weight, the Tei plant showed a slightly lower rate as compared with the Nabeta plant.     

Acclimation to UV radiation and antioxidative defence in the endemic Antarctic brown macroalga Desmarestia anceps along a depth gradient

The endemic Antarctic brown macroalga Desmarestia anceps colonizes the subtidal between 5 and 30 m in Potter Cove on King George Island (South Shetland Islands, Antarctica). Experiments were conducted to study photosynthetic activities, antioxidative enzymes and UV tolerance of field-grown individuals with respect to the light histories along different subtidal positions. Individuals collected from the upper (5.5 m) and mid-subtidal (9.0 m) are characterized by high maximum electron transport rates (ETRmax) measured by PAM-fluorometry and high activities of superoxide dismutase (SOD) supported by considerable activities of glutathione reductase. Individuals of this species from the upper subtidal are able to tolerate high irradiances of UV-B radiation because its photosynthetic apparatus is putatively well protected by phlorotannins. In contrast, individuals from lower subtidal positions (13.5 and 15.5 m) showed an opposite trend: lower ETRmax and SOD activities as well as a lower UV tolerance of photosynthesis. Moreover, a non-denaturing polyacrylamide gel electrophoresis (native PAGE) of a partially purified crude extract reveals that D. anceps has probably six isoforms of SOD. These intra-specific patterns imply a high phenotypical plasticity of D. anceps with respect to its photosynthesis and photoprotective mechanisms. Overall, photosynthesis, UV tolerance and antioxidative potential are highly regulated in D. anceps corresponding to the respective light regimes along its natural growth sites.     

Physiological ecology of Juniperus virginiana in oldfields

Juniperus virginiana plants grow faster than other associated tree species in abandoned fields. During the summer the needles of the species do not light saturate even at 1,750 E m^-2 s^-1, reach optimum photosynthesis at 20°C, and maintain maximum photosynthesis at-8 to-12 bar twig water potential. In the field, the plants experience pronounced daily changes in water potential. The magnitude of the changes becomes more pronounced later in the summer. Leaves of the mature plants have highest rate of photosynthesis, young trees intermediate, and seedlings lowest. In winter there is a slight shift in optimum temperature for photosynthesis and the plants photosynthesize at 0°C. The rates of photosynthesis are lower in winter than in summer. On sunny days with calm winds, mature individuals and seedlings maintain significantly higher temperatures than air temperature while intermediate plants do not. The latter exhibit a lower photosynthetic rate than both mature plants and seedlings. The trends of photosynthesis, in the 3 size classes, both in winter and summer, correspond to the chlorophyll content of their leaves. It is concluded that J. virginiana grows well in open field habitats because it is a sun-adapted, drought resistant species with a long growing season which includes winter. The species is excluded from mature forests because it is shade-intolerant.     

Growth and photosynthesis of Hydrocotyle ranunculoides L. fil. in Central Europe

Floating Pennywort (Hydrocotyle ranunculoides L. fil.) is a worldwide distributed aquatic plant. The species is native to North America and quite common also in Central and South America. In Europe, Japan and Australia it is known as an alien plant, sometimes causing serious problems for affected ecosystems and human use of water bodies. Starting from Western Europe with an eastwards directed spread, Floating Pennywort was recorded in Germany in 2004 for the first time. Since then, the species spread out and got established in western parts of Central Europe. For a definite prediction of the potential of a further spread, data about biology, in particular growth and photosynthesis are needed. Here, regeneration capacity, growth at different nutrient availabilities and photosynthesis of H. ranunculoides were investigated. In addition biomass samples were taken in the field. Results show an enormous regeneration capacity (e.g., by forming new shoots from small shoot fragments), increasing growth rates under increasing nutrient availability and a maximum increase of biomass reaching 0.132±0.008 g g⁻¹ dw d⁻¹. Dense populations of H. ranunculoides growing in ponds and oxbows were found at high nutrient content of the substrate, the biomass reaching there up to 532.4±14.2 g dw m⁻². Gas exchange analysis showed a physiological optimum of H. ranunculoides CO₂ uptake at temperatures between 25 and 35 °C and high photon flux densities (PPFD) above 800 μmol photons m⁻² s⁻¹. In comparison, native Hydrocotyle vulgaris showed an optimum of net photosynthesis at 20–30 °C and a light saturation of CO₂ gas exchange at 350 μmol photons m⁻² s⁻¹.     

Temperature responses of economically important red algae and their potential for mariculture in Brazilian waters

Data are presented on temperature responses, based onin vitro growth performance, of eight species of colloid-producing red algae; these include the five most important commercial species of agarophytes in South America. The temperature optima do not conform strictly to geographic distribution, and intolerance to high temperature is not the factor that controls the spreading of temperate species ofGracilaria to warmer areas. WithinPterocladia capillacea (Gmelin) Bornet et Thuret, populations from two distinct localities had different responses to temperature optima. Data suggest that the disjunct distribution of this species in the American Atlantic is due to its poor performance at temperatures above 26 °C. The fastest maximum growth rate was observed inHypnea cornuta (Lamouroux) J. Agardh (doubling time 2.8 d), and the slowest inP. capillacea from Cabo Frio (doubling time 50.0 d). All the species studied, including the valuable Chilean and Argentinean species ofGracilaria, could tolerate the temperature regimes of the Brazilian waters.     

两种五倍子蚜虫冬寄主藓类植物的光合特性及其与光照、温度和植物体水分含量变化的关系

使用CI-301PS(CID Inc.USA)对生长于冬季和春季的大羽藓(Thuidium cymbifolium)与垂藓(Chrysocladium retrorsum)的净光合速率(Pn)及其与光照、温度和植物体水分含量的关系进行了研究.结果表明,大羽藓和垂藓的光合能力分别达到141和117μmolCO₂kg^-1·dw·s^-1,光合能力从冬季到春季呈上升趋势.这两种藓类植物的光响应曲线比较相似,光饱和点高达800～900μmol·m^-2s^-1,光补偿点为40～50μmol·m^-2s^-1,光合作用最适温度在春季为25～36℃,而冬季为20～30℃.同时对于低温又具有很强的抗性,在冰点以下的温度条件下(-15～0℃)能够保持一定的净光合.净光合速率的水分响应曲线表明,这两种藓类的最适水分含量为200～300(400)%dw,水分含量降低到150%dw时光合作用开始受到抑制,在40%～50%dw时净光合降低到零或略变为负数.结果表明,大羽藓和垂藓都属于耐干旱、强阳性的藓类,但垂藓在这几个方面略逊于大羽藓.     

Leaf anatomical and photosynthetic acclimation to cool temperature and high light in two winter versus two summer annuals

Acclimation of foliar features to cool temperature and high light was characterized in winter (Spinacia oleracea L. cv. Giant Nobel; Arabidopsis thaliana (L.) Heynhold Col‐0 and ecotypes from Sweden and Italy) versus summer (Helianthus annuus L. cv. Soraya; Cucurbita pepo L. cv. Italian Zucchini Romanesco) annuals. Significant relationships existed among leaf dry mass per area, photosynthesis, leaf thickness and palisade mesophyll thickness. While the acclimatory response of the summer annuals to cool temperature and/or high light levels was limited, the winter annuals increased the number of palisade cell layers, ranging from two layers under moderate light and warm temperature to between four and five layers under cool temperature and high light. A significant relationship was also found between palisade tissue thickness and either cross‐sectional area or number of phloem cells (each normalized by vein density) in minor veins among all four species and growth regimes. The two winter annuals, but not the summer annuals, thus exhibited acclimatory adjustments of minor vein phloem to cool temperature and/or high light, with more numerous and larger phloem cells and a higher maximal photosynthesis rate. The upregulation of photosynthesis in winter annuals in response to low growth temperature may thus depend on not only (1) a greater volume of photosynthesizing palisade tissue but also (2) leaf veins containing additional phloem cells and presumably capable of exporting a greater volume of sugars from the leaves to the rest of the plant.     

Influence of light intensity during growth on photosynthesis and activity of several key photosynthetic enzymes in a C4 plant (Zea mays)

Maize ( Zea mays L. Hybrid Sweet Corn, Royal Crest), a C₄ plant, was grown under different light regimes, after which the rate of photosynthesis and activities of several photosynthetic enzymes (per unit leaf chlorophyll) were measured at different light intensities. Plants were grown outdoors under direct sunlight or 23% of direct sunlight, and in growth chambers at photosynthetic photon flux densities of about 20% and 8% of direct sunlight. The plants grown under direct sunlight had a higher light compensation point than plants grown under lower light. At a light intensity about 25% of direct sunlight, plants from all growth regimes had a similar rate of photosynthesis. Under saturating levels of light the plants grown under direct sunlight had a substantially higher rate of photosynthesis than plants grown under the lower light regimes. The higher photosynthetic capacity in the plants grown under direct sunlight was accompanied by an increased activity of several photosynthetic enzymes and in the amount of the soluble protein in the leaf. Among five photosynthetic enzymes examined, RuBP carboxylase (EC 4.1.1.39) and pyruvate, Pi dikinase (EC 2.7.9.1) were generally just sufficient to account for rates of photosynthesis under saturating light; thus, these may be rate limiting enzymes in C₄ photosynthesis. Pyruvate, Pi dikinase and NADP-malate dehydrogenase (EC 1.1.1.82) were the only enzymes examined which were light activated and increased in activity with increasing light intensity. In the low light grown plants the activity of pyruvate, Pi dikinase closely paralleled the photosynthetic rate measured under different light levels. With the plants grown under direct sunlight, as light intensity was increased the activation of pyruvate, Pi dikinase and NADP⁺-malate dehydrogenase proceeded more rapidly than photosynthesis.     

Production and population ecology ofPhyllospadix iwatensis Makino. II. Comparative studies on leaf characteristics,foliage structure and biomass change in an intertidal and subtidal zone

A seagrass in Japan,Phyllospadix iwatensis Makino, is distributed in the lower intertidal zone and upper subtidal zone making a dense population on the Choshi coast, Japan. IntertidalP. iwatensis is able to receive sufficient light for photosynthesis but experienced severe exposure to the air, which decreased a large amount of aboveground biomass in April to June (i.e. the daytime exposure season). SubtidalP. iwatensis was never exposed throughout the year and the aboveground biomass increased gradually over the daytime exposure season. However, the maximum aboveground biomass and shoot density of the subtidal plant never exceeded that of the intertidal plant. The dense foliage, large aboveground biomass and high shoot density of both intertidal and subtidal plants is likely to be an adaptation to heavy water movement, but the subtidal plants always received insufficient light for photosynthesis as a result of having dense foliage, particularly in turbid water. In choppy and swell sea,P. iwatensis did not seem to be adapted to growing in the subtidal zone where there was shortage of light.     

油页岩废渣地12种木本植物光合作用的季节变化

研究了引种在油页岩工业废渣地12种木本植物冬、夏季光合作用特征,根据此评价引种植物的光合作用效率,测定的主要参数包括净光合速率(P_n)、蒸腾速率(T_r)和气孔导度(G_s)。结果表明:1) 冬、夏季各项测定指标差异很大,P_n、T_r、G_s均是夏季高于冬季,而且,夏季平均P_n、T_r和G_s值要比冬季均值分别高60.9%、77.7%和85.7%,但水分利用效率(WUE)却是冬季高于夏季26.8%~77.2%。2) P_n日变化节律冬、夏季有异,夏季较多的种出现“双峰型”,而冬季较多出现“单峰型”。但也有例外,樟树(Cinnamomum camphora)冬、夏季均出现“单峰”;油榄仁(Terminalia bellirica)、红胶木(Tristania conferta)和柚木(Tectona grandis)冬、夏季均出现“双峰”;海南蒲桃(Syzygium cumini)则冬季为“双峰”,夏季为“单峰”。3) 若某一植物种在冬、夏季都表现出有较高的P_n日均值,相对于另一种植物其中有一季有较高的P_n,说明前者更适应当地环境生长。据此,以冬、夏季P_n日均值的平均值高低排序,评价参试植物在当地自然光照条件下的光合作用效率高低,树种的排序为:大叶相思(Acacia auriculiformis)、油榄仁、铁刀木(Cassia siamea)、云南石梓(Gmelina arborea)、柚木、红胶木、樟树、海南红豆(Ormosia pinnata)、铁冬青(Ilex rotunda)、海南蒲桃、双翼豆(Peltophorum ptetocarpum)和海南翅萍婆(Pterygota alata)。     

新疆准噶尔荒漠短命植物群落特征及其水热适应性

短命植物是一类利用短暂湿季快速生长的特殊植物类群, 包括一年生短命植物和类短命植物。作者在新疆北部准噶尔荒漠的莫索湾地区从2005-2008年进行了连续4年的群落调查研究, 通过25条样线201个样方的调查, 并结合同时段冬春季节的气温、降水资料, 探讨了短命植物对环境水热变化的适应性特征。结果表明: (1) 早春季节, 短命植物在准噶尔荒漠植物群落组成中占据优势地位, 物种数均占调查总物种数的52%左右; (2) 从群落优势种来看, 7种植物标准频度在40%以上, 其中6种是短命植物, 分别是旱麦草(Eremopyrum orientale)、卷果涩芥(Malcolmia scorpioides)、硬萼软紫草(Arnebia decumbens)、狭果鹤虱(Lappula semiglabra)、四齿芥(Tetracme quadricornis)和沙滨藜(Atriplex dimorphostegia); (3) 群落中短命植物萌发的个体数量与前一年冬季温度关系极为密切, 较低的冬季温度更易激发其萌发, 而当年群落外貌特征则更多地依赖于早春季节的降水, 若早春季节温度过低也会影响短命植物的萌发; (4) Shannon-Wiener多样性指数和Pielou均匀度指数年际间变化趋势与同期冬春降水总量变化趋势一致。总之, 温度和降水的不同配置是引起短命植物多样性发生年际变化的主要因素。     

Does irradiance influence the tolerance of marine phytoplankton to high pH?

The effect of irradiance on the tolerance to high pH of the two marine protists Heterocapsa triquetra and Nitzschia navis-varingica were investigated by conducting a series of pH drift experiments. In order to select appropriate levels of irradiance for the pH drift experiments, the photosynthetic activity and the growth rates of the two species were investigated at irradiances from 5 to 250 µmol photons m^-2 s^-1. Irradiances of 20, 35, 80 and 250 µmol photons m^-2 s^-1 were subsequently selected for further studies, because they represented conditions from severely light limited to fully light saturated with respect to photosynthesis and growth. At all four light levels, the pH limits for growth were 9.29-9.42 for H. triquetra and 9.54-9.77 for N. navis-varingica. The pH limit for growth was not positively correlated to irradiance in either of the species. We therefore conclude that low light does not reduce the pH tolerance of the protists studied.     

Solar irradiance level alters the growth of basil (Ocimum basilicum L.) and its content of volatile oils

The experiments were commenced in March 2003 and repeated in June 2003 at Sutton Bonington Campus, the University of Nottingham, UK, to investigate the effect of irradiance on plant growth and volatile oil content and composition in plants of basil. Four levels of irradiance were provided in the glasshouse, i.e. no shade (control), 25, 50 and 75% glasshouse irradiance. It suggested that basil grows well in full sun, however it can tolerate light shade. Heavy shading (75%) to provide a light integral of 5.3 moles m⁻² d⁻¹ resulted in shorter plants, lower weight, smaller leaf area, less shoots and higher specific leaf area, and also strongly reduced the rate of photosynthesis. There was no difference in CO₂ assimilation rate between 24.9 moles m⁻² d⁻¹ light integrals (no shading) and 13.5 moles m⁻² d⁻¹ light integrals (25% shading). Shading effectively reduced leaf temperature when air temperature was less than 30 °C, but heavy shading (75%) could not reduce leaf temperature when air temperature was above 36 °C due to a limitation of free air convection. Consequently, leaf temperature increased. Heavy shading strongly reduced total volatile oil content in fresh leaves, especially in older plants (shading treatment applied at the 3 leaf-pair growth stage). There were three chemical compounds in basil leaves, namely linalool, eugenol and methyl eugenol, influenced by the shading treatments. Linalool and eugenol, which contribute to the characteristic taste of basil, were significantly increased by high daily light integrals, whereas methyleugenol was increased by lower daily light integrals. No differences in the relative content of 1,8-cineole, one of the key aromatic compounds of Ocimum species, were observed.     

湖北九宫山成熟常绿落叶阔叶混交林 3种优势种的邻域效应研究

以最近邻株距离统计研究了湖北九宫山成熟常绿落叶阔叶混交林3种优势种青冈栎(Cyclobalanopsis glauca)、甜槠(Castanopsis eyrei)和短柄枹栎(Quercus serrata var.brevipetiolata)的邻域效应,进而探讨了局域尺度上的竞争/帮促关系与物种共存格局。结果显示,青冈栎、甜槠和短柄枹栎的最近邻株距离不存在下限;青冈栎的胸径大小与其种内最近邻株距离存在正相关(p= 0.029),甜槠的胸径大小与种内、种间最近邻株距离均无相关性(p≥ 0.360),而短柄枹栎的胸径大小与种间最近邻株距离为负相关(p= 0.040);3树种中任意一个的种内与种间最近邻株距离都没有显著差异(p≥ 0.122)。这些结果表明,九宫山成熟常绿落叶阔叶混交林内邻域尺度上的竞争排斥并未充分激化,但是青冈栎的种内竞争仍然在起作用,而甜槠的竞争效应不明显,短柄枹栎则依赖种间帮促甚于相互竞争。同种和异种之间的排斥效果没有差异表明局域尺度的物种共存格局可能出于随机过程而非负密度制约过程。