The Effects of Light and Temperature on Germination and Growth of Luffa aegyptiaca

The effects of light and temperature on the germination and growth of Luffa aegyptiaca were investigated both in the laboratory and in the field. The seeds germinated in both darkness and light but germination was better in the light. At constant temperatures germination was best at 21°C, while alternating temperatures of 21 and 31°C and 15 and 41°C caused higher germination than the most favourable constant temperature. Constant temperatures of 15 and 31°C and alternating temperatures of 21 and 41°C resulted in very low germination, whereas no germination occurred at 41°C and at alternating temperatures of 31 and 41°C. Soil depth caused only a delay in seed germination, as it did not affect the total germination. High temperature and high light intensity resulted in good seedling growth in terms of dry weight, leaf area and relative growth rate. High temperature and low light intensity caused increased plant height and high shoot weight ratio, both of which manifested in seedling etiolation. They also caused high leaf area ratio. Under low temperatures, irrespective of light intensity, growth was generally poor, but it was significantly poorer under low light intensity, which also caused high root weight ratio. High light intensity was principally responsible for high leaf weight ratio. The results help to explain the abundance of the species in newly cleared areas in Lagos and its environs.     

镉胁迫对鸡冠花种子萌发及幼苗生理生化特性的影响

采用水培法和盆栽法测定分析不同浓度Cd(0、50、100、150、200 mg/L)胁迫对鸡冠花种子萌发、幼苗生物量、叶片光合色素、渗透调节物质(可溶性蛋白、可溶性糖、脯氨酸)、丙二醛(MDA)、低分子巯基化合物(GSH、GSSG、Cys、NPT)含量以及抗氧化酶 (SOD、POD、CAT、APX)活性的影响,探讨鸡冠花耐受Cd胁迫的能力及其生理机制,为植物解毒机制提供基础资料。结果显示：(1)鸡冠花种子的发芽势、发芽率和发芽指数在低浓度Cd处理下提高,而活力指数、根长及苗长在各浓度Cd胁迫下均不同程度降低,以上指标均在低浓度(50、100 mg/L)Cd胁迫下受到显著抑制,且根长受抑制程度显著高于苗长;幼苗生物量(整株鲜重、地上部分鲜重及地下部分鲜重)在200 mg/L Cd胁迫时受到显著抑制,较对照分别下降了61.9%、58.4%和72.7%;根冠比及主根长虽未受到显著影响,但总体呈现降低趋势。(2)鸡冠花幼苗叶片叶绿素和类胡萝卜素含量在100~200 mg/L Cd胁迫下均显著降低,叶片可溶性蛋白、可溶性糖和脯氨酸含量在Cd胁迫下总体呈升高趋势,并分别在50、150、200 mg/L时显著升高。(3)鸡冠花幼苗叶片各抗氧化酶活性在Cd胁迫下呈不同变化趋势,POD和APX活性在各浓度Cd胁迫分别增加23.1%~304.2%和160.0%~280.0%;SOD活性在各浓度Cd胁迫均受到抑制,但仅在150 mg/L时显著降低43.2%;CAT活性在50~150 mg/L Cd胁迫下显著增强了46.6%~66.5%,但在200 mg/L Cd胁迫却显著降低59.5%。(4)高浓度(200 mg/L)Cd胁迫下鸡冠花幼苗叶片巯基化合物GSH、GSSG、Cys、NPT含量分别比对照上升了53.2%、164.2%、53.9%和0.79%,而GSH/GSSG比值显著降低。研究发现,鸡冠花种子萌发期和幼苗期对Cd胁迫均具有一定的耐受力,但高浓度Cd胁迫仍致使幼苗部分抗氧化酶活性降低,ROS过量积累,引起膜脂过氧化程度加深,其产物MDA含量逐渐升高;Cd胁迫促进低分子巯基化合物含量呈不同幅度的增加,但GSH/GSSG比值下降,细胞内氧化还原反应(Redox)受到抑制,导致幼苗正常生长代谢受阻,生物量持续降低。     

LIGHT,TEMPERATURE AND SALINITY EFFECTS ON GROWTH,LEAF ANATOMY AND PHOTOSYNTHESIS OF DISTICHLIS SPICATA (L.) GREENE

The effects of light, temperature, and salinity on growth, net CO₂ exchange and leaf anatomy of Distichlis spicata were investigated in controlled environment chambers. When plants were grown at low light, growth rates were significantly reduced by high substrate salinity or low temperature. However, when plants were grown at high light, growth rates were not significantly affected by temperature or salinity. The capacity for high light to overcome depressed growth at high salinity cannot be explained completely by rates of net photosynthesis, since high salinity caused decreases in net photosynthesis at all environmental conditions. This salinity-induced decrease in net photosynthesis was caused largely by stomatal closure, although plants grown at low temperature and low light showed significant increases in internal leaf resistance to CO₂ exchange. Increased salinity resulted in generally thicker leaves with lower stomatal density but no significant differences in the ratio of mesophyll cell surface area to leaf area. Salinity and light during growth did not significantly affect rates of dark respiration. The mechanisms by which Distichlis spicata tolerates salt appear to be closely coulpled to the utilization of light energy. Salt-induced leaf succulence is of questionable importance to gas exchange at high salinity in this C₄ species.     

Salt tolerance in Aster tripolium L. I. The effect of salinity on growth

Abstract A study of the growth of the maritime halophyte Aster tripolium L. has been carried out over a range of salinity treatments. The regression approach to growth analysis using frequent small harvests has been used to allow ‘continuous’ measurement of growth over a period of 36 d. Salinity was applied with the major ions present in ratios typical of those found in seawater. Growth was inhibited in terms of both dry weight production and leaf expansion at salinity levels equivalent to 0.625 strength sea water (full culture solution 300) and above, with the greatest effect being seen in terms of leaf area. Aster tripolium did not show increased succulence at high salinity, leaf fresh weight to dry weight ratio in fact declined, whilst leaf fresh weight per unit area remained constant. It should be noted that the plants exhibit low growth rates due to the low light intensity used.     

Effects of light and temperature on leaf anatomy and photosynthesis in Fragaria vesca

Summary Fragaria vesca, the woodland strawberry, was grown under a series of controlled environments including variations in light intensity, average temperatures, and temperature amplitude around a constant mean. Observations on CO₂ exchange capacities, leaf anatomy, and cell ultrastructure were made for each treatment to determine relationships between these variables. With increasing light intensity, leaf thickness, leaf density, and mesophyll cell surface area and volume per leaf surface area increased. Net photosynthesis (NPS) per leaf weight decreased with increasing light pretreatment while NPS per area increased from low to medium intensity, then decreased at the highest intensity. Depression of photosynthesis at the highest light pretreatment may have been due to massive starch accumulation in the chloroplasts associated with the sodium vapor lamps used. Correlation of all anatomical variables was highly significant with dark respiration and NPS per dry weight but insignificant for NPS per leaf area. In the variable temperature treatments, photosynthetic acclimation occurred with a shift in optimum temperature for NPS in the direction of prevailing growth temperature. Absolute rates were highest at moderate pretreatment temperatures and were reduced by extreme growth temperatures. Thick leaves with low density mesophyll became thinner and more dense with increasing growth temperature corresponding to an increase in maximum net photosynthetic rates. Leaves became thicker and more dense at the highest temperatures, but with an increase in cell damage and indications of changes in metabolic pathways. Highest correlations for gas exchange rates were with specific leaf weight (weight per area). Correlation with other anatomical variables were scattered or insignificant. It was concluded that adaptation to a range of environmental conditions cannot be consistently attributed to changes in mesophyll cell volume or surface area.     

光强对杉木幼苗形态特征和叶片非结构性碳含量的影响

选取南方重要的造林树种杉木(Cunninghamia lanceolata(Lamb.)Hook)幼苗为研究对象,通过搭建遮荫棚设置5个光照强度(分别为自然光照的100%、60%、40%、15%和5%),研究了幼苗在不同光照强度下的生长形态、生物量积累及分配、叶片的非结构性碳含量(NSC)特征。结果显示:(1)叶长、叶宽和叶面积在40%光照强度下最大,而比叶面积和叶片相对含水量随着光照强度的降低呈递增趋势;(2)随着光照强度的降低,杉木幼苗各器官生物量下降,根生物量比和根冠比降低,茎和叶生物量比增加;(3)杉木幼苗在60%光照强度下叶片非结构性碳含量最高,5%光照强度下含量最低;(4)杉木幼苗比叶面积与叶生物量以及与非结构性碳含量之间存在极显著的负相关关系(P0.01),叶生物量与非结构性碳含量之间存在极显著的正相关关系(P0.01)。杉木幼苗能够通过形态学上的可塑性来适应不同的光强环境,提高光竞争能力和生存适合度,但在5%光照强度下,由于较难维持碳收支平衡而不利于其生长和存活。     

披针叶茴香对变化光环境的表型可塑性

植物对变化光环境的表型可塑性大小影响其在林下生境中分布、生长和更新。为探讨披针叶茴香在不同光环境下的整体表型可塑性及其适应机制,采用遮荫试验模拟5种光照条件(100%、52%、33%、15%和6%相对光照强度),研究了不同光环境下披针叶茴香叶片形态、生理、解剖结构、根系形态以及生物量分配等的变化。结果表明:叶生物量在5种光照处理之间差异不显著,但叶面积和比叶面积均随光照强度减弱显著增加。遮荫处理增加了叶绿素a、叶绿素b和类胡萝卜素的含量,但叶绿素a/b比值随光照强度减弱而降低。遮荫降低了非结构性碳水化合物(淀粉和可溶性糖)和可溶性蛋白的含量,增加了叶片氮和磷含量,对叶片氮/磷比影响较小。在52%和33%相对光照处理下,叶片中硝酸盐含量最低,而在100%和6%相对光照处理下硝酸盐积累较多。根生物量、细根和粗根的长度、表面积以及比根长和比根表面积在5种光照处理之间均没有显著差异,根系氮含量在低光环境(15%和6%相对光照处理)中显著降低。随光照强度减弱,披针叶茴香采取保守生存策略,并没有增加叶生物量的分配,而是分配较多的生物量给枝条和树干,储存能量。综合来看,披针叶茴香具有较宽的光生态幅,在6%—100%光照强度下均能正常生长,遮荫有利于披针叶茴香地上和总生物量的积累,52%的相对光照条件下生长最佳。变化光环境下根系性状和整体结构的可塑性相对较低,叶片生理性状的可塑性在披针叶茴香适应光环境变化过程中发挥了主要作用。     

Responses to light changes in tropical deciduous woody seedlings with contrasting growth rates

We evaluated the responses in growth, biomass allocation, photosynthesis and stomatal conductance, to changes in light in woody seedlings from the tropical deciduous forest in Mexico, which shows a highly seasonal rain pattern. We studied ten species, which differed by 30-fold in relative growth rate (RGR). We analyzed plant growth in two contrasting light levels during 52 days and two transfers: from high to low (HL) and from low to high (LH) light intensity, and the respective controls in high (HH) and low (LL) light for another 52 days. The photosynthetic capacity (A _max) and stomatal conductance were measured at the day of the transfer between light conditions and at the end of the experiment. Species with high RGR showed the largest changes in RGR in response to contrasting light conditions (HH/LL ratio), and species with low RGR showed low responses. The fast-growing species were the most plastic, followed by species with intermediate growth rates, with the slow-growing species being the least plastic. Fast-growing species achieved higher maximum photosynthetic capacities (A _max) and stomatal conductance and higher response to light than slow-growing species. Species with high RGR showed a low RGR HH/LH ratio, suggesting a large response of L plants when transfered to H. The RGR of the species were associated with species specific leaf area and with the response in the leaf area, net assimilation rate and leaf weight ratio, suggesting the importance of the leaf area produced and the leaf characteristics rather than root:shoot ratio in determining RGR. Considering that seed germination is expected at the beginning of the rainy period, seedlings of most of the species will experience high-light conditions during its early growth. There are large annual variations in the time required for canopy closure (35–75 days). The influence of these variations may have different effect on the species studied. Species with intermediate growth rate and intermediate response to light changes were less affected by light reduction than fast-growing species. The intermediate-RGR species Caesalpiniaeriostachys is the most abundant and widely distributed species, perhaps this could be in part due to its ability to acclimate to both light increases and decreases. The fast-growing species studied here can be found in open sites in the forest and in areas cleared for pasture growth. These fast-growing species eventually reach the canopy, although this may require several canopy openings during their lives, which implies juvenile shade tolerance. In the tropical deciduous forest juvenile pioneer trees also benefit from the temporary high light available caused by the dry period during the rainy season. The slow-growing species Celaenodendronmexicanum forms small patches of monospecific forest; the adult trees are not completely deciduous, and they retain their old leaves for a long time period before shedding. Thus seedlings of this species may receive lower levels of light, in agreement with its shade tolerance and its lower response to light increases. Received: 14 April 1997 / Accepted: 29 July 1997     

不同光照对望天树种子萌发和幼苗早期生长的影响

在不同光照梯度的人工遮荫和森林生境中,研究了西双版纳季节雨林标志树种望天树的种子萌发和幼苗早期生长特征.结果表明,裸地上的强光照和深度遮荫均不利于望天树种子的萌发,中等程度的遮荫有利于种子萌发.望天树种子萌发率在林窗中央最大,而且萌发迅速,林窗边缘和林下生境不利于种子萌发.幼苗株高、基径和单株叶面积等生长指标均在部分遮荫处理条件下最大;幼苗根冠比在裸地上最高,且随遮荫程度的增加而降低;幼苗比叶面积在一定光照强度范围内随遮荫程度的增加而增大,在3层遮荫最大.除幼苗根冠比以外的其它生长参数均在林窗中央最大.讨论了环境因子(主要是光照强度和光质)对望天树种子萌发和幼苗生长的影响.     

Germination responses of Discopodium penninervium Hochst. to temperature and light

The germination responses of Discopodium penninervium were tested at different constant and alternating temperature regimes as well as under various light conditions both in the laboratory and glasshouse. Seeds incubated at 10, 15, 20, 25 and 30 °C failed to germinate. When the seeds were incubated at alternating temperatures of 20/12 °C and 30/12 °C under continuous light, germination was 89 and 61%, indicating that the species requires alternating temperatures as a cue for germination. However, germination declined as the amplitude of alternating temperatures increased from 8 °C and was completely inhibited at an amplitude of 23 °C, suggesting that the optimum amplitude is around 8 °C. Germination was less than 10% in light and nil in darkness at 20 °C in the laboratory. In contrast, seeds incubated at 20/12 °C germinated to 96 and 86% in light and darkness, respectively. Seeds incubated under leaf shade in the glasshouse failed to germinate whereas those incubated under direct daylight and darkness germinated to 44 and 50%, respectively, 30 days after sowing. When seeds incubated under leaf shade and in darkness were exposed afterwards to light, final percent germination was 83% from seeds incubated initially under direct daylight, 79% from those incubated under leaf shade and 86% from those incubated in darkness. The requirement for alternating temperatures and light rich in red:far red ratio to break the dormancy of seeds of D. penninervium could restrict germination to gaps in the vegetation. The results conform with the ecology of the species.     

光照和氮磷供应比对木荷生长及化学计量特征的影响

光照和养分限制是影响林下植物生长和更新的关键影响因素,以亚热带主要常绿树种木荷（Schima superba）实生幼苗为试验对象,研究了不同光照（全光照、遮阴即45%全光照）和N、P供应比例（5,15,45）对幼苗生长和化学计量特征的影响。结果表明：（1）遮阴不仅严重抑制了木荷各器官和单株生物量积累,更加剧了P限制。尽管N、P添加对木荷生长没有显著促进作用,但N、P供应比例为5时的性状组合更有利于木荷后期生长,但高N、P供应比例可能导致P限制。（2）遮阴下叶N、P含量显著增加,但叶C/N和C/P比显著降低;不同光照处理组中各器官及总N含量均随N、P供应比例增大而显著增加,而C/N比逐渐降低;P的分配格局发生改变,全光照组各器官P含量为茎 > 叶 > 根,遮阴组各器官P含量为根 > 茎 > 叶。（3）随N、P供应比例增加或光照强度降低,木荷均趋向降低根冠比和根质比、增加叶质比或茎质比。（4）木荷生物量与各器官N、P含量、叶质比呈极显著负相关,而与C/N和C/P比及根冠比、茎质比、根质比呈极显著正相关。光强和N、P比例变化均显著影响了木荷幼苗的养分利用特征,因而木荷作为伴生树种优化林分环境对其早期生长具有重要意义。     

Early seedling growth of pine (Pinus densiflora) and oaks (Quercus serrata,Q. mongolica,Q. variabilis) in response to light intensity and soil moisture

In climatic chambers seed germination and seedling growth of Pinus densiflora Sieb. et Zucc., Quercus serrata Thunb., Quercus mongolica Fisch. ex Turcz. and Quercus variablilis Bl. were investigated as functions of light intensity and soil moisture. In Korea these tree species occur widely and form mixed forests with different distributions. Species clearly differed in the pattern of germination and early seedling growth between light and soil treatments. The germination of pine did not differ between the experimental treatments until the breaking of the primary buds. After that, light intensity was the deciding factor for further development. In the most moist treatment (approx. field capacity) growth of the pine seedlings was strongly inhibited. For the three oak species, differences between experimental treatments first occurred after complete formation of primary leaves. Seed development strongly correlated with the weight of the acorn. The large seeded Q. variabilis (acorns with mean weight of 4.7 g) developed faster and reached larger dimensions towards the end of the experiment than Q. mongolica (2.8 g per acorn) and Q. serrata (0.9 g per acorn). Regarding height and biomass growth, the oak species showed a higher shade tolerance than pine. The proleptic shoot growth was clearly influenced by the light intensity. Root formation was favoured by a high exposure to light. In case of the oak species reduction of soil moisture increased the length of primary roots and the number of secondary roots.     

鸡冠花耐热性评价方法研究

以探讨快速鉴定鸡冠花耐热特性的方法和指标为目的,选用6个鸡冠花品种,以30℃为起始温度,每4 h升高5℃,最高处理温度为50℃,分别对种子和10叶龄幼苗进行热胁迫处理,划分了热萎蔫指数,观测了种子发芽率、成苗率、相对电导率、丙二醛（MDA）含量、超氧化物歧化酶（SOD）活性。结果表明,高温下鸡冠花种子的发芽率和成苗率显著降低,鸡冠花幼苗的顶芽是最易受热害部位,热害萎蔫指数4是幼苗恢复极限,在高温胁迫下,幼苗的相对电导率、MDA显著增加,SOD活性为先升高后降低,且45℃高温处理时,相对电导率和MDA增加最快,SOD的活性最高。6个品种的耐热顺序为：世纪绿叶和洋娃娃最强,新象和城堡其次,和服和世纪铜叶最弱。种子发芽率、成苗率、相对电导率、丙二醛含量、超氧化物歧化酶活性均可作为鸡冠花耐热性评价指标。     

Effects of seismic stress on the vegetative growth of Glycine max (L.) Merr. cv. Wells II

Abstract. Vegetative plants of soybean [ Glycine max (L.) Merr. cv. Wells II] grown in a greenhouse and agitated periodically on a gyratory shaker had shorter stems, less leaf area, and lower leaf and plant dry weight than did undisturbed greenhouse-grown (GG) plants after 16 d of treatment. Outdoor-grown (OG) plants, which were subjected to additional environmental stresses including ultraviolet radiation, wind loading, and uncontrolled temperature and humidity fluctuations, were smaller and had less dry weight than GG controls, but growth was not inhibited further by gyratory shaking. Periodic shaking of GG soybeans resulted in the same plant and leaf dry weight as for OG soybeans. Response of GG plants to mechanical stress depended on light intensity, with minimum growth reduction occurring under full light (FL) level, and maximum growth reduction occurring under lower light levels (24–45% FL). Reduction in dry weight gain due to mechanical stress corresponded to a decrease in relative growth rate (RGR). Decreases in net assimilation rate and leaf area ratio contributed equally to the lower RGR of shaken plants, indicating that seismic stress inhibits dry weight accumulation by decreasing both the photosynthetic efficiency and the assimilatory surface of soybean.     

Growth,biomass distribution and CO2 exchange of northern hardwood seedlings in high and low light: relationships with successional status and shade tolerance

The physiology, morphology and growth of first-year Betula papyrifera Marsh., Betula alleghaniensis Britton, Ostrya virginiana (Mill.) K. Koch, Acer saccharum Marsh., and Quercus rubra L. seedlings, which differ widely in reported successional affinity and shade tolerance, were compared in a controlled high-resource environment. Relative to late-successional, shade-tolerant Acer and Ostrya species, early-successional, shade-intolerant Betula species had high relative growth rates (RGR) and high rates of photosynthesis, nitrogen uptake and respiration when grown in high light. Fire-adapted Quercus rubra had intermediate photosynthetic rates, but had the lowest RGR and leaf area ratio and the highest root weight ratio of any species. Interspecific variation in RGR in high light was positively correlated with allocation to leaves and rates of photosynthesis and respiration, and negatively related to seed mass and leaf mass per unit area. Despite higher respiration rates, early-successional Betula papyrifera lost a lower percentage of daily photosynthetic CO₂ gain to respiration than other species in high light. A subset comprised of the three Betulaceae family members was also grown in low light. As in high light, low-light grown Betula species had higher growth rates than tolerant Ostrya virainiana. The rapid growth habit of sarly-successional species in low light was associated with a higher proportion of biomass distributed to leaves, lower leaf mass per unit area, a lower proportion of biomass in roots, and a greater height per unit stem mass. Variation in these traits is discussed in terms of reported species ecologies in a resource availability context.     

Differential salt tolerance of two Artemisia species growing in contrasting coastal habitats

To investigate factors determining the differences in their salt tolerance, growth and germination, experiments were conducted on two plant species belonging to genus Artemisia: Artemisia fukudo Makino, a biennial salt marsh plant and Artemisia stelleriana Bess, a perennial coastal hind dune plant. Growth experiments revealed that salinity (100 and 300 m m NaCl) inhibited the relative growth rate (RGR) in A. stelleriana significantly but not in A. fukudo. These specific differences in salt tolerance were mainly attributed to differential responses of net assimilation rate (NAR). That is, the reduction in RGR in A. stelleriana was mainly due to the reduction in NAR, whereas no significant reduction in NAR was observed in A. fukudo. The reduction in RGR in A. stelleriana in the salt treatment was also attributable to a reduced leaf area ratio (LAR). Specific leaf area (SLA) in the two species decreased in the 300 m m treatment. The decrease in SLA in A. fukudo was, however, compensated for partly by an increase in leaf weight ratio (LWR). Germination experiments also showed that A. fukudo has a higher salt tolerance than does A. stelleriana. These results are consistent with the differences in the salinity conditions between the native habitats of the two species.     

Effects of different treatments of fly ash and mining soil on growth and antioxidant protection of Indian wild rice

The aim of the present study was investigation of the effects of fly ash and mining soil on growth and antioxidant protection of two cultivars of Indian wild rice (Oryza nivara and Oryza rufipogon) for possible phytoremediation and restoration of metal-contaminated site. In this study, Indian wild rice showed significant changes in germination, growth, and biochemical parameters after exposure to different ratio of fly ash and mining soil with garden soil. There was significant reduction of germination, fresh weight, dry weight, leaf chlorophyll content, leaf area, Special Analysis Device Chlorophyll (SPAD) Index, proteins, and activities of antioxidant enzymes in both cultivars of the wild rice grown in 100% fly ash and mining soil compared to the plants grown in 100% garden soil. Results from this study showed that in both cultivars of wild rice, all growth and antioxidant parameters increased when grown in 50% fly ash and mining soil. Taken together, Indian wild rice has the capacity to tolerate 50% of fly ash and mining soil, and can be considered as a good candidate for possible phytoremediation of contaminated soils.     

The Vegetative Growth of Helianthus annuus and Phaseolus vulgaris as Affected by Seasonal Factors in Freetown, Sierra Leone

Sand-culture experiments were carried out in full daylight atsuccessive weekly intervals between March and December 1969,to investigate the effects of seasonal changes in climatic factorson the growth of Helianthus annuus and Phaseolus vulgaris inFreetown. Values for a number of growth parameters were calculatedfrom the dry weights of the leaves, stems, and roots, and fromthe leaf areas. Simultaneously the diurnal changes in climaticfactors were recorded. Multiple regressions linking light, temperature, and relativehumidity with some of the growth parameters were calculated.The total variance accounted for in the regressions of relativegrowth-rate, net assimilation rate, and leaf weight ratio onlight, temperature, and relative humidity ranged from 51 to60 per cent in P. vulgaris. In H. annuus relative humidity wasless important; the percentage proportion of total varianceaccounted for in the regression of leaf weight ratio (and leafarea ratio in both species) on light and temperature was notsignificant. The results showed that H. annuus grew faster than P. vulgaris,but the latter's growth was depressed less by the dull weatherof the rainy season. The relative growth-rates of both specieswere positively dependent on light and temperature while theirnet assimilation rates were negatively dependent on relativehumidity, and their leaf area ratios negatively dependent onlight. All parameters used except leaf area ratio and leaf areato leaf weight ratio showed seasonal variations correspondingto dry and rainy seasons. The initial and final values of leafarea ratio and weight ratios were always different but did notvary in the same direction in both species. The results are discussed in relation to similar work done elsewhere.     

The effects of light and nitrogen on photosynthesis,leaf characteristics,and dry matter allocation in the chaparral shrub,Diplacus aurantiacus

Summary Plants of Diplacus aurantiacus, a successional shrub common in California chaparral, were grown under controlled conditions in which either quantum flux density or nitrogen availability was varied. Photosynthesis and leaf nitrogen content were determined on a leaf area and a leaf weight basis, and whole plant growth was monitored.There was a direct relationship between photosynthesis and leaf nitrogen content on both area and weight bases. Reduced light intensity of the growth environment resulted in reductions in light-saturated photosynthesis and nitrogen content on an area basis, but not on a weight basis. With reduced nitrogen availability, photosynthesis and leaf nitrogen content per unit leaf weight decreased.Resource use efficiency increased as the resource became more limiting. The results are consistent with a model of plant growth in which net carbon gain of the leaf is maximized. Abbreviations. For brevity, the following set of abbreviations is used in presenting and discussing the results. P/area and N/area are, respectively, photosynthesis and leaf nitrogen content per unit leaf area. P/wt and N/wt are the same quantities per unit leaf dry weight. SLW (specific leaf weight) is dry weight per unit leaf area. RGR (relative growth rate) is the relative rate of increase in shoot dry matter per day     

狭叶红景天幼苗对水分及遮阴的生长及生理生化响应

研究植物对水分和遮阴胁迫的响应及其生理机制对制定合理的栽培管理措施十分必要。以红景天属植物为研究对象,设置土壤含水量分别为田间持水量的80%(过湿水分)、70%(正常水分)、60%(轻度干旱)、40%(中度干旱)、20%(重度干旱)5个水分梯度;设置2个遮阴处理,以全光照(遮阴率为0)为对照、黑色遮阴网遮阴(遮阴率为85%),研究狭叶红景天生长及生理生化指标的变化特征。结果表明:在不同水分处理下,与对照相比,叶绿素含量、茎干重和茎重比(SMR)显著增加(P0.05),株高、总生物量、叶面积、叶干重、叶重比(LMR)、比叶面积(SLA)、叶面积比(LAR)和叶面积根干重比(LARMR)增加,根冠比和根重比(RMR)减少;随着干旱程度加剧,丙二醛(MDA)、脯氨酸(Pro)和可溶性糖(Ss)含量增加,超氧化物歧化酶(SOD)活性总体呈先增加后减小的趋势。在遮阴处理下,株高、SMR、SLA、LAR和LARMR显著增加(P0.05),叶绿素SPAD值和叶面积增加,总生物量、根干重、根冠比和LMR显著减少(P0.05),茎干重和叶干重减少,MDA含量显著增加,Pro含量略有下降,Ss含量减少。在水分胁迫下,狭叶红景天中度干旱时通过增加酶活性抵御伤害,重度干旱超过其阈值,SOD活性下降,植物体受到伤害,Ss可能是主要的渗透调节物质。在遮阴处理下,狭叶红景天通过增加SLA避免遮阴伤害。狭叶红景天在受到环境胁迫时会通过形态改变、调节MDA含量、抗氧化酶活性和渗透调节物质来保证自身正常的生长发育。