Effect of naturally changing zooplankton concentrations on feeding rates of two coral species in the Eastern Pacific

Zooplankton concentrations are known to vary by as much as an order of magnitude over a lunar cycle. Here, we conducted an experiment to determine the effect of ambient zooplankton concentrations over a lunar cycle on feeding rates of the corals Pavona gigantea (Verrill) (mounding coral, 3.0 mm diameter polyps) and Pocillopora damicornis (Linnaeus) (branching coral, 1.0 mm diameter polyps) in situ on a shallow reef at Isla Contadora, Gulf of Panamá (Pacific), Panamá. Coral fragments exposed to either enhanced or ambient zooplankton concentrations were allowed to feed for 1 h, collected, and their gut contents dissected. The number of zooplankton captured was counted, feeding rates calculated per cm², and the species composition of captured zooplankton assemblages determined. Although both species captured the same zooplankton assemblage, feeding rates were always significantly higher for P. gigantea than for P. damicornis. Under ambient flow and zooplankton concentrations, feeding rates were highly correlated with zooplankton concentration in the 200-400 μm size class. Under constantly enhanced zooplankton concentrations in the control fragments, feeding rates did not vary significantly over the lunar cycle. As such, coral feeding rates vary not as a result of lunar phase per se, but with changes in zooplankton abundance over the lunar cycle. Coral feeding rates are directly proportional to ambient zooplankton concentrations and may vary by as much as 50% over a lunar cycle, suggesting that corals must cope with major swings in sources of fixed carbon and nutrients over relatively short timescales.     

Motility inOscillatoria salina as affected by different factors

All 3-10-d-old Oscillatoria salina filaments glide with the speed of 323-330 microm/min (BG 11 medium, pH 7.5, 21 +/- 2 degrees C, continuous light intensity of approximately 30 micromol m(-2) s(-1)) in a culture chamber. However, a time bound progressive decrease in gliding speed and in percentage of gliding filaments occurred, depending upon the severity of different stress factors studied, viz. water stress (2-8% agarized media, liquid media with 0.2-1 mol/L NaCl, blot-dryness of filaments for > or = 5 min), temperature shock (5, 40 degrees C for > or = 5 min; 35 degrees C for > or = 15 min), darkness and low light intensity (2, 10 micromol m(-2) s(-1)), UV exposure (0.96-3.84 kJ/m2), pH extremes (< or = 6.5 and > or = 9.5), lack of all nutrients from liquid medium (double distilled water), presence of 'heavy' metals (1, 25 ppm Fe, Cu, Zn, Ni, Co, Hg) or organic substances in liquid medium (25, 250 ppm 2,4-D, captan, urea, DDT, thiourea). This feature of the alga (i.e. reduction in speed and percentage of gliding filaments depending upon severity of stress conditions) may thus be suggested to be used in assessing water quality.     

The ontogeny of physiological response to light intensity in early stage spiny lobster (Jasus edwardsii) larvae

Early stage phyllosoma larvae of the spiny rock lobster Jasus edwardsii were examined for swimming speed, feeding, oxygen consumption and nitrogen excretion as instantaneous performance indicators when exposed to different irradiance levels. Swimming speed was measured in recently hatched Stage I larvae while all other parameters were measured in larvae from hatch to mid-Stage V. The swimming speed of recently hatched Stage I phyllosoma increased logarithmically between light intensities of 2.9 x 10(14) and 1.8 x 10(16) quanta s(-1) cm(-2) indicating that, within this range, swimming activity was only suppressed at the lowest irradiance level. Larvae examined under dark (no light) conditions showed lower feed intake, oxygen consumption and nitrogen excretion than larvae under low (7.7 x 10(12) q s(-1) cm(-2)) and high (3.9 x 10(14) q s(-1) cm(-2)) light intensities, and this was a consistent pattern observed throughout development from hatch to Stage V. There was no difference in feeding, oxygen consumption and nitrogen excretion between larvae exposed to low and high light intensities. However, from mid-Stage I to mid-Stage V, the metabolic feeding efficiency (feed intake:oxygen consumption ratio) was consistently higher in larvae exposed to low light intensity than in phyllosoma assessed in the dark and under high irradiance. A light intensity of about 7.7 x 10(12) quanta s(-1) cm(-2) and no higher than 3.9 x 10(14) quanta s(-1) cm(-2) is recommended to stimulate feeding and optimise metabolic feeding efficiency in early larval stages of J. edwardsii.     

持续低温弱光对黄瓜叶片气体交换、叶绿素荧光猝灭和吸收光能分配的影响

持续常温弱光(25℃/18℃,l00umol m-2 s-1)、低温弱光(12℃/12℃,100 umol m-2 s-1和7℃/7℃,l00μmolm-2s-1)均导致黄瓜生长减慢或停滞、叶绿素含量、气孔导度和净光合速率、光合电子传递速率下降以及胞间CO2浓度上升.常温弱光和12℃弱光处理对光系统II的最大光化学效率Fv/Fm无显著影响,而7℃弱光处理导致Fv/Fm的可逆性下降.常温弱光和7℃、12℃弱光处理均导致了光化学反应速率的降低以及天线热耗散和反应中心过剩能量的增加.在胁迫后,12℃弱光0比7℃弱光更有利于植株光合功能的恢复.     

Survival and motility of diatoms<Emphasis Type="Italic">Navicula grimmei</Emphasis> and<Emphasis Type="Italic">Nitzschia palea</Emphasis> affected by some physical and chemical factors

Navicula grimmei and Nitzschia palea occurring almost equally in a mixed population on department moist garden soil surface when maintained in fresh supernatant (of soil-water medium) at pH 7.0, temperature of 26 +/- 1 degree C and under continuous light (intensity of approximately equal to 30 micromol m(-2) s(-1)) in a culture chamber exhibited a similar cell survival period (of 28 d) and percentage (at the beginning 100 % and mid of survival period 65 %) and stop gliding 11 d prior to cell death (with gliding speed reduced in both from 204-330 microm/min at the beginning to 82.5-99 microm/min at the mid of gliding period) irrespective of their size differences. However, a sharp fall in the cell gliding period, gliding cell percentage and speed occurred at various levels (different from cell survival period and percentage) in both diatoms in a similar extent under water stress (2, 4 and 6 % agarized supernatant, liquid supernatant with 0.2-1.0 mol/L NaCl, blot-dryness of cells for 5-15 min), pH extreme of liquid supernatant (< or =5.0, > or =9.0), temperature extremes in liquid supernatant (< or =15, > or =40 degrees C), UV exposure (0.96-5.76 kJ/m2), lack of all nutrients from the medium (double distilled water), darkness or low light intensities (2 and 10 micromol m(-2) s(-1)), presence of 'heavy' metals (Ni, Cu, Zn, Co, Fe, Hg; 1-200 ppm), organic substances in liquid supernatant (DDT, captan, urea, 2,4-D, 100-2000 ppm; thiourea, 50-1000 ppm). N. palea sway (turn around at either ends) or not only when gliding but independent of cell gliding speed, which decreased continuously under all conditions.     

Non-invasive monitoring of the light-induced cyclic photosynthetic electron flow during cold hardening in wheat leaves

The effect of irradiance during low temperature hardening was studied in a winter wheat variety. Ten-day-old winter wheat plants were cold-hardened at 5 degrees C for 11 days under light (250 micromol m(-2) S(-1)) or dark (20 micromol m(-2) s(-1)) conditions. The effectiveness of hardening was significantly lower in the dark, in spite of a slight decrease in the Fv/Fm chlorophyll fluorescence induction parameter, indicating the occurrence of photoinhibition during the hardening period in the light. Hardening in the light caused a downshift in the far-red induced AG (afterglow) thermoluminescence band. The faster dark re-reduction of P700+, monitored by 820-nm absorbance, could also be observed in these plants. These results suggest that the induction of cyclic photosynthetic electron flow may also contribute to the advantage of frost hardening under light conditions in wheat plants.     

Energy--dependent bacterivory in Ochromonas minima--a strategy promoting the use of substitutable resources and survival at insufficient light supply

Phagotrophy and competitive ability of the mixotrophic Ochromonas minima were investigated in a three-factorial experiment where light intensity (low: 1.0 micromol m(-2)s(-1) and high: 60 micromol m(-2)s(-1) PPFD), nutrient concentration (ambient: 7.0 micromolNl(-1), 0.11 micromol P l(-1) and enriched: 88 micromol N l(-1), 6.3 micro mol P l(-1)) and DOC supply (without and with enrichment, 250 micromol C l(-1)) were manipulated. Ochromonas minima and bacterial abundance were monitored for 12 days. We found significant and interacting effects of light and nutrients on Ochromonas minima growth rate and abundance. At high light intensity, nutrient enrichment resulted in increased growth rates and population sizes. In contrast, reduced growth rates and population sizes were observed for nutrient enrichment when light intensity was low. Although, Ochromonas minima was able to ingest bacteria under both high and low light conditions, it grew only when light intensity was high. At high light intensity, Ochromonas minima grew exponentially under nutrient conditions that would have been limiting for photoautotrophic microalgae. In non-enriched low light treatments, Ochromonas minima populations survived, probably by using background DOC as an energy source, indicating that this ability can be of relevance for natural systems even when DOC concentrations are relatively low. When competing with photoautotrophic microalgae, the ability to grow under severe nutrient limitation and to survive under light limitation should be advantageous for Ochromonas minima.     

钝顶螺旋藻在不同光照条件下的放氧特性

钝顶螺旋藻在持续照光和中等频率 (0.01~20 Hz) 的光/暗交替照光下的放氧特性对光生物反应器的设计和操作具有重要意义。构建了一套可实现光/暗交替的光生物反应器系统对此进行研究,结果显示：根据与放氧速率的关系,可以将光强分为4个区：光限制区 (0~335 μmol/(m2·s)),过渡区 (335~875 μmol/(m2·s)),光饱和区 (875~2 775 μmol/(m2·s)) 以及光抑制区 (2 775 μmol/(m2·s)以上)。提高光/暗频率能否提高微藻光合速率取决于所采用的光强和     

Photoinhibition, bleaching susceptibility and mortality in two scleractinian corals, Platygyra ryukyuensis and Stylophora pistillata, in response to thermal and light stresses

In the present study, we examined the effect of thermal stress on the photoinhibitory light threshold in a bleaching susceptible (Stylophora pistillata) and a bleaching resistant (Platygyra ryukyuensis) coral. Four light (0, 110, 520, 1015 micromol quantam(-2)s(-1)) and three temperature (26, 32 and 34 degrees C) conditions were used over a 3-h period, followed by 24- and 48-h recovery periods at approximately 21 degrees C under dim light. Dynamic photoinhibition could be detected in both P. ryukyuensis and S. pistillata under 520 and 1015 micromol quantam(-2)s(-1) at 26 degrees C and under 110 micromol quantam(-2)s(-1) at 32 degrees C only in S. pistillata. Chronic photoinhibition was recorded under 520 and 1015 micromol quantam(-2)s(-1) at 34 degrees C in P. ryukyuensis, and under 1015 micromol quantam(-2)s(-1) at 32 degrees C and under all light levels at 34 degrees C in S. pistillata. These results show that high temperature reduced the threshold light intensity for photoinhibition differently in two corals with different bleaching susceptibilities under thermal stress. No visual paling and mortality in P. ryukyuensis was observed at any treatment, even in chronically photoinhibited specimens, while paling and high mortality of S. pistillata was noted in all treatments, apart from samples at 26 degrees C. These observations suggest a potential role of the host in differential bleaching and mortality determination.     

Phototropins promote plant growth in response to blue light in low light environments

Phototropins (phot1 and phot2) are plant-specific blue light receptors for phototropism, chloroplast movement, leaf expansion, and stomatal opening. All these responses are thought to optimize photosynthesis by helping to capture light energy efficiently, reduce photodamage, and acquire CO2. However, experimental evidence for the promotion of plant growth through phototropins is lacking. Here, we report dramatic phototropin-dependent effects on plant growth. When plants of Arabidopsis thaliana wild type, the phot1 and phot2 mutants, and the phot1 phot2 double mutant were grown under red light, no significant growth differences were observed. However, if a very low intensity of blue light (0.1 micromol m(-2) s(-1)) was superimposed on red light, large increases in fresh weight up to threefold were found in those plants that carried functional PHOT1 genes. When the intensity of blue light was increased to 1 micromol m(-2) s(-1), the growth enhancement was also found in the phot1 single mutant, but not in the double mutant, indicating that phot2 mediated similar responses as phot1 with a lower sensitivity. The effects occurred under low photosynthetically active radiation in particular. The well-known physiological phototropin-mediated responses, including chloroplast movement, stomatal opening, and leaf expansion, in the different lines tested indicated an involvement of these responses in the blue light-induced growth enhancement. We conclude that phototropins promote plant growth by controlling and integrating a variety of responses that optimize photosynthetic performance under low photosynthetically active radiation in the natural environment.     

低温光抑制恢复过程中黄瓜叶片PSⅡ活性及其电子传递对PSⅠ的影响

以“津春4号”黄瓜为试材,通过测定黄瓜叶片叶绿素荧光快速诱导动力学曲线和对820 nm光的吸收曲线,结合叶绿素荧光淬灭分析,研究低温光胁迫(4℃,200 μmol·m-2·s-1)6 h后,黄瓜叶片在常温(25℃)不同光强(0、15、200μmol·m-2·s-1)下PS Ⅰ和PS Ⅱ活性的恢复,以及恢复过程中PS Ⅰ与PS Ⅱ的相互作用.结果表明:低温光胁迫6h后,PS Ⅰ和PS Ⅱ发生不同程度的光抑制.在常温恢复阶段,PS Ⅱ活性快速恢复且对光强不敏感;PS Ⅰ活性在弱光下(15 μmol·m-2·s-1)快速恢复,在较强光(200 μmol·m-2·s-1)下恢复较慢.在低温光抑制恢复过程中,常温下PS Ⅱ活性恢复较快可能导致PS Ⅱ向PS Ⅰ的线性电子传递过快,进而抑制PS Ⅰ的活性恢复.因此,在进行黄瓜抗冷性育种时,不应该仅追求较高的PS Ⅱ抗性和较快的PS Ⅱ恢复速度,还应该注意两个光系统活性的协调.在生产中,应当在低温逆境发生及其之后较长一段时间内采取措施降低叶表面光照强度,以利于对植株光合机构的保护和光合活性的恢复.     

An experimental analysis of the effects of light and zooplankton on coral zonation

Summary In Panamá, vertical zonation of coral species is well marked; branching corals (Pocillopora spp.) predominate in shallow (1–6 m) water while massive forms (Pavona spp.) occupy the deeper (6–10 m) areas of the reef. To test the hypothesis that this zonation represents differential resource utilization (i.e., niche partitioning of food resources), one year manipulative field experiments were conducted at two depths (1 m and 7 m below Mean Lower Sea Level) assessing the relative contribution of light and zooplankton to the nutrition of three Pacific corals: Pocillopora damicornis, Pavona clavus and Pavona gigantea. Also tested were the related hypotheses that (i) energy for the maintenance and growth of corals comes mainly from light, independent of zooplankton supply and (ii) Porter's model, in which coral morphology is a predictor of the phototrophic-heterotrophic capabilities of a particular species. That is, corals with a branching morphology and a small polyp diameter (and short tentacle length) should be primarily phototrophic while those species with larger polyps and/or a massive form should show a greater degree of heterotrophy.The comparison of caged versus control corals indicated that the branching coral, Pocillopora damicornis (polyp diameter — 1 mm) grew independent of zooplankton supply (>95) but was markedly affected by shading. Pavona clavus (massive form with intermediate size polyps — 2 mm) was also negatively affected by shading but this effect was minimized when zooplankton was present. Surprisingly, under ambient light conditions, the growth of this specics was independent of zooplankton (>95); perhaps indicating a facultative reliance on zooplankton especially in shallow water. The third species, Pavona gigan-tea (massive form with largest polyps — 3 mm) was highly dependent on both light and zooplankton and was unable to compensate for the effects of shading by zooplankton feeding. This high dependence on light was unexpected since large polyps, according to Porter's model, would predict a more heterotrophic existence.Under all treatments, in both shallow and deep water, Pocillopora was found to grow more rapidly than either massive species. Thus, this study indicates that zonation on eastern Pacific reefs cannot be explained by depth-related differences in nutritional requirements among the species present. These results do provide the first long-term, experimental field evidence that corals are largely phototrophic organisms. The validity of Porter's model attempting to correlate phototrophic-heterotrophic abilities to morphological characteristics is, at least, partially verified: species with larger tentacles do appear to utilize zooplankton to a greater extent than those species with smaller tentacles. However, the significance of corallum morphology in predicting the mode of nutrient acquisition is unclear. Rather, behavioral patterns (tentacle expansion-contraction cycles) and location on the reef may be more important factors to consider.     

Effects of light and chloramphenicol stress on incorporation of nitrogen into cyanophycin in Synechocystis sp. strain PCC 6308

(1)H NMR spectroscopy was used to compare the uptake of nitrogen into cyanobacterial cyanophycin from two sources: from the breakdown of intracellular proteins and amino acids, and directly from the external growth medium. Cells grown initially in medium containing (14)N-nitrate were transferred to (15)N-nitrate medium in the presence of chloramphenicol in both low (4 microE m(-2) s(-1)) and normal (100 microE m(-2) s(-1)) light, and in low light alone. Cyanophycin was separated from cells and analyzed by (1)H NMR spectroscopy. Cyanophycin is synthesized both from (14)N (degradation of cellular proteins) and from (15)N in the medium, the latter at a faster rate and to a greater extent under all conditions. SDS-PAGE showed that cyanophycin synthesis takes place by addition of monomers to already synthesized polymer.     

Light responses in the green sulfur bacterium Prosthecochloris aestuarii: changes in prosthecae length, ultrastructure, and antenna pigment composition

The morphology (mainly prosthecae length), ultrastructure, and antenna pigment composition of the green sulfur bacterium Prosthecochloris aestuarii changed when grown under different light intensities. At light intensities of 0.5 and 5 micromol quanta m(-2) s(-1), the cells had a star-like morphology. Prosthecae, the characteristic appendages of the genus Prosthecochloris, were 232 nm and 194 nm long, respectively. In contrast, when grown at 100 micromol quanta m(-2) s(-1), these appendages were shorter (98 nm) and the cells appeared more rod-shaped. Transmission electron microscopy revealed a significant decrease in the cell perimeter to area ratio and in the number of chlorosomes per linear microm of membrane as light intensity increased. In addition to these morphological and ultrastructural responses, Prosthecochloris aestuarii exhibited changes in its pigment composition as a function of light regime. Lower specific pigment content and synthesis rates were found in cultures grown at light intensities above 5 micromol quanta m(-2) s(-1). A blue shift in the bacteriochlorophyll (BChl) c Q(y) absorption maximum of up to 17.5 nm was observed under saturating light conditions (100 micromol quanta m(-2) s(-1)). This displacement was accompanied by changes in the composition of BChl c homologs and by a very low carotenoid content. The morphological, ultrastructural and functional changes exhibited by Prosthecochloris aestuarii revealed the strong light-response capacity of this bacterium to both high and low photon-flux densities.     

Photoinhibition induced alterations in energy transfer process in phycobilisomes of PS II in the cyanobacterium, Spirulina platensis

Exposure of algae or plants to irradiance from above the light saturation point of photosynthesis is known as high light stress. This high light stress induces various responses including photoinhibition of the photosynthetic apparatus. The degree of photoinhibition could be clearly determined by measuring the parameters such as absorption and fluorescence of chromoproteins. In cyanobacteria and red algae, most of the photosystem (PS) II associated light harvesting is performed by a membrane attached complex called the phycobilisome (PBS). The effects of high intensity light (1000-4000 micromol photons m(-2) s(-1)) on excitation energy transfer from PBSs to PS II in a cyanobacterium Spirulina platensis were studied by measuring room temperature PC fluorescence emission spectra. High light (3000 micromol photons m(-2) s(-1)) stress had a significant effect on PC fluorescence emission spectra. On the other hand, light stress induced an increase in the ratio of PC fluorescence intensity of PBS indicating that light stress inhibits excitation energy transfer from PBS to PS II. The high light treatment to 3000 micromol photons m(-2) s(-1) caused disappearance of 31.5 kDa linker polypeptide which is known to link PC discs together. In addition we observed the similar decrease in the other polypeptide contents. Our data concludes that the Spirulina cells upon light treatment causes alterations in the phycobiliproteins (PBPs) and affects the energy transfer process within the PBSs.     

Ontogenetic changes in habitat use by whitefish,Coregonus lavaretus

Synopsis The whitefish, Coregonus lavaretus, in the lake Mj?sa exhibited two niche changes during their life cycle. Juveniles (< 25 cm body length) were confined to the shallow (0–30 m) epibenthic zone. Medium sized whitefish (25–35 cm body length) expanded their habitat use to include the deep (30–90 m) epibenthic zone as well as the pelagic zone. From a body length of 35 cm, habitat use was restricted to the deep epibenthic zone. Small fish in the shallow epibenthic zone ate small and medium-sized prey (zooplankton, insect larvae and surface insects). Medium-sized fish in this zone were in addition feeding on the larger amphipod, Pallasea quadrispinosa. In the pelagic zone, the diet of medium-sized whitefish was dominated by zooplankton, although some larger prey like surface insects and age-0 smelt, Osmerus eperlanus, were also eaten. In the deep epibenthic zone, the diet of both medium-sized and large (< 35 cm) whitefish consisted mainly of the large prey P. quadrispinosa.     

Factors contributing to enhanced freezing tolerance in wheat during frost hardening in the light

The interaction between light and temperature during the development of freezing tolerance was studied in winter wheat (Triticum aestivum L. var. Mv Emese). Ten-day-old plants were cold hardened at 5 degrees C for 12 days under normal (250 micromol m(-2)s(-1)) or low light (20 micromol m(-2)s(-1)) conditions. Some of the plants were kept at 20/18 degrees C for 12 days at high light intensity (500 micromol m(-2)s(-1)), which also increased the freezing tolerance of winter wheat. The freezing survival rate, the lipid composition, the antioxidant activity, and the salicylic acid content were investigated during frost hardening. The saturation level of hexadecanoic acid decreased not only in plants hardened at low temperature, but also, to a lesser extent, in plants kept under high light irradiation at normal growth temperature. The greatest induction of the enzymes glutathione reductase (EC 1.6.4.2.) and ascorbate peroxidase (EC 1.11.1.11.) occurred when the cold treatment was carried out in normal light, but high light intensity at normal, non-hardening temperature also increased the activity of these enzymes. The catalase (EC 1.11.1.6.) activity was also higher in plants grown at high light intensity than in the controls. The greatest level of induction in the activity of the guaiacol peroxidase (EC 1.11.1.7.) enzyme occurred under cold conditions with low light. The bound ortho-hydroxy-cinnamic acid increased by up to two orders of magnitude in plants that were cold hardened in normal light. Both high light intensity and low temperature hardening caused an increase in the free and bound salicylic acid content of the leaves. This increase was most pronounced in plants that were cold treated in normal light.     

A TPR-family membrane protein gene is required for light-activated heterotrophic growth of the cyanobacterium Synechocystis sp. PCC 6803

The unicellular cyanobacterium Synechocystis sp. PCC6803 can grow heterotrophically in complete darkness, given that a brief period of illumination is supplemented every day (light-activated heterotrophic growth, LAHG), or under very weak (<0.5 micromol m(-2) s(-1)) but continuous light. By random insertion of the genome with an antibiotic resistance cassette, mutants defective in LAHG were generated. In two identical mutants, sll0886, a tetratricopeptide repeat (TPR)-family membrane protein gene, was disrupted. Targeted insertion of sll0886 and three downstream genes showed that the phenotype was not due to a polar effect. The sll0886 mutant shows normal photoheterotrophic growth when the light intensity is at 2.5 micromol m(-2) s(-1) or above, but no growth at 0.5 micromol m(-2) s(-1). Homologs to sll0886 are also present in cyanobacteria that are not known of LAHG. sll0886 and homologs may be involved in controlling different physiological processes that respond to light of low fluence.     

钾素水平对网纹甜瓜叶片光合特性及叶绿体亚显微结构的影响

在设施基质栽培条件下,研究了营养液中120、240及360 mg·L^-1 3个钾素水平对网纹甜瓜‘甜甜1号’叶片光合特性及叶绿体亚显微结构的影响.结果表明,营养液中钾素水平过低（120 mg·L^-1）或过高（360 mg·L^-1）均导致网纹甜瓜叶片净光合速率下降,使叶绿体片层结构混乱、变形和片层数减少,但对CO₂补偿点（70 μl·L^-1）、饱和CO₂（600 μl·L^-1）、光补偿点（50 μmol·m^-2·s^-1）无显著影响.适宜的钾素水平能显著提高叶片的饱和光强、羧化效率和表观量子效率,3个指标分别为1 200 μmol·m^-2·s^-1、0.1364和0.0237.在试验条件下,提高温室内基质栽培网纹甜瓜叶片光合效率的最适钾素水平为240 mg·L^-1.