Photosynthetic Patterns Research Articles

Hydrilla verticella as a carbon capturing plant

Global warming is a threatening problem to the entire world. As a proactive measure, scientists are developing new techniques to reduce CO2 emission to the atmosphere. Carbon capture and long time storage is a relatively new concept even though it is not economically feasible. Hence scientists have now focused on CO2 capture technology utilising salt water alga. In the present study, CO2 capturing rates of salt water algal plants Ulva fasciata , Caulerpa racemosa , Sargassum cervicone , Chaetomorpha spp , Padina spp , Corallina spp and Gracilaria spp . which are found in the ocean surrounding Sri Lanka were measured. However, it is very difficult to mimic the natural physical conditions inside the laboratory. Therefore an attempt was made to capture CO2 using an aquatic plant found in fresh water. Hydrilla verticella is an aquatic, invasive plant to Sri Lanka with a high growth rate. The CO2 capturing rate of Hydrilla verticella was compared with other salt water algal plants. When carrying out the experiment for salt water algae, the initial pH was reduced to 5 by pumping CO2 in to a fixed volume of salt water and then 30g of the specimen was placed and the variation of pH was measured with time. A Similar procedure was carried out with Hydrilla verticella by pumping CO2 in to distilled water. A control was kept under similar conditions without the specimen for each case. Ulva fasciata showed highest CO2 capture rate and Hydrilla verticella was second best. Hydrilla verticella was chosen as it is easy to manipulate for this study. The graph plotted between pH and time for Hydrilla verticella exhibited a typical photosynthetic pattern found in other plants. In this research, main parameters that have been investigated were on the salinity of the medium and the photoperiod to enhance the CO2 capture rate of Hydrilla verticella . Different salinity levels were obtained by adding different quantities of NaCl (10, 20, 30 ….70 g) in to one liter of distilled water. Results showed that this plant is adaptable to very different levels of salinity but the optimum salinity range is 10-20 gdm-3. Photoperiod was determined by exposing the samples to sun light over varying periods (0, 4, 8, 12 hrs) of time. Results showed that maximum activity was seen when exposed to 12 hrs of sunlight yet it is interesting to note that it can capture CO2 even under very low light intensities; even during night time when other plants respirate. CO2 capturing rate was the highest when the pH of the medium was in between 5-7. The concept of carbon credits came into existence as a result of increasing awareness of the need for controlling green house emissions. There are many companies that cell carbon credit to commercial and individual customer who are interested in lowering their carbon foot print on voluntary basis, hence above technique which is economically feasible can be implemented in order to mitigate global warming by reducing CO2 emission.

Identification of C4 photosynthesis metabolism and regulatory-associated genes in Eleocharis vivipara by SSH

This is the first effort to investigate the candidate genes involved in kranz developmental regulation and C(4) metabolic fluxes in Eleocharis vivipara, which is a leafless freshwater amphibious plant and possesses a distinct culms anatomy structure and photosynthetic pattern in contrasting environments. A terrestrial specific SSH library was constructed to investigate the genes involved in kranz anatomy developmental regulation and C(4) metabolic fluxes. A total of 73 ESTs and 56 unigenes in 384 clones were identified by array hybridization and sequencing. In total, 50 unigenes had homologous genes in the databases of rice and Arabidopsis. The real-time quantitative PCR results showed that most of the genes were accumulated in terrestrial culms and ABA-induced culms. The C(4) marker genes were stably accumulated during the culms development process in terrestrial culms. With respect to C(3) culms, C(4) photosynthesis metabolism consumed much more transporters and translocators related to ion metabolism, organic acids and carbohydrate metabolism, phosphate metabolism, amino acids metabolism, and lipids metabolism. Additionally, ten regulatory genes including five transcription factors, four receptor-like proteins, and one BURP protein were identified. These regulatory genes, which co-accumulated with the culms developmental stages, may play important roles in culms structure developmental regulation, bundle sheath chloroplast maturation, and environmental response. These results shed new light on the C(4) metabolic fluxes, environmental response, and anatomy structure developmental regulation in E. vivipara.

Spatio‐temporal heterogeneity in Arabidopsis thaliana leaves under drought stress

Using chlorophyll (chl) fluorescence imaging, we studied the effect of mild (MiDS), moderate (MoDS) and severe (SDS) drought stress on photosystem II (PSII) photochemistry of 4-week-old Arabidopsis thaliana. Spatio-temporal heterogeneity in all chl fluorescence parameters was maintained throughout water stress. After exposure to drought stress, maximum quantum yield of PSII photochemistry (F(v)/F(m)) and quantum efficiency of PSII photochemistry (Φ(PSΙΙ)) decreased less in the proximal (base) than in the distal (tip) leaf. The chl fluorescence parameter F(v) /F(m) decreased less after MoDS than MiDS. Under MoDS, the antioxidant mechanism of A. thaliana leaves seemed to be sufficient in scavenging reactive oxygen species, as evident by the decreased lipid peroxidation, the more excitation energy dissipated by non-photochemical quenching (NPQ) and decreased excitation pressure (1-q(p)). Arabidopsis leaves appear to function normally under MoDS, but do not seem to have particular metabolic tolerance mechanisms under MiDS and SDS, as revealed by the level of lipid peroxidation and decreased quantum yield for dissipation after down-regulation in PSII (Φ(NPQ)), indicating that energy dissipation by down-regulation did not function and electron transport (ETR) was depressed. The simultaneous increased quantum yield of non-regulated energy dissipation (Φ(NO)) indicated that both the photochemical energy conversion and protective regulatory mechanism were insufficient. The non-uniform photosynthetic pattern under drought stress may reflect different zones of leaf anatomy and mesophyll development. The data demonstrate that the effect of different degrees of drought stress on A. thaliana leaves show spatio-temporal heterogeneity, implying that common single time point or single point leaf analyses are inadequate.

Temporal matching among diurnal photosynthetic patterns within the crown of the evergreen sclerophyll Olea europaea L.

Trees are modular organisms that adjust their within-crown morphology and physiology in response to within-crown light gradients. However, whether within-plant variation represents a strategy for optimizing light absorption has not been formally tested. We investigated the arrangement of the photosynthetic surface throughout one day and its effects on the photosynthetic process, at the most exposed and most sheltered crown layers of a wild olive tree (Olea europaea L.). Similar measurements were made for cuttings taken from this individual and grown in a greenhouse at contrasted irradiance-levels (100 and 20% full sunlight). Diurnal variations in light interception, carbon fixation and carbohydrate accumulation in sun leaves were negatively correlated with those in shade leaves under field conditions when light intensity was not limiting. Despite genetic identity, these complementary patterns were not found in plants grown in the greenhouse. The temporal disparity among crown positions derived from specialization of the photosynthetic behaviour at different functional and spatial scales: architectural structure (crown level) and carbon budget (leaf level). Our results suggest that the profitability of producing a new module may not only respond to construction costs or light availability, but also rely on its spatio-temporal integration within the productive processes at the whole-crown level.

Compensatory growth and photosynthetic responses of Pharbitis purpurea seedlings to clipped cotyledon and second leaf

Leaf tissue damaging to seedlings can limit their subsequent growth, and the effects may be more extensive. Compensatory photosynthesis responses of the remnant cotyledon and primary leaf of Pharbitis purpurea to clipping and the effect of clipping on seedling growth were evaluated in a pot-cultivated experiment. Three treatments were conducted in the experiment, which were clipped cotyledon (CC), clipped second leaf (CL), and control group (CG). The area, thickness, mass, and longevity of the remaining cotyledon of CC exhibited over-compensatory growth. In contrast, seedlings of CC had under-compensatory growth in seedling height, root length, seedling mass, and root to shoot ratio. However, the traits of remnant cotyledon and seedling in CL treatment exhibited equal-compensatory growth. Net photosynthetic rate of the cotyledon of CC was significantly higher than those of CL and CG treatments, and the diurnal changes in photosynthetic rates showed significantly different patterns which were unimodal curve (CC) and bimodal curve (CL and CG), respectively. There was no significant difference between CL and CG treatment. Net photosynthetic rate of the primary leaf of CL was significantly higher than that of CG treatment. However, the photosynthetic rates of primary leaves of CL and CG treatments showed similar photosynthetic patterns characterized by a bimodal curve. P. purpurea seedlings used a compensatory growth strategy in the remaining cotyledon or the primary leaf to resist leaf loss and minimize any adverse effects.

Diurnal pollen tube growth rate is slowed by high temperature in field-grown Gossypium hirsutum pistils

For Gossypium hirsutum pollination, germination, and pollen tube growth must occur in a highly concerted fashion on the day of flowering for fertilization to occur. Because reproductive success could be influenced by the photosynthetic activity of major source leaves, we hypothesized that increased temperatures under field conditions would limit fertilization by inhibiting diurnal pollen tube growth through the style and decreasing subtending leaf photosynthesis. To address this hypothesis, G. hirsutum seeds were sown on different dates to obtain flowers exposed to contrasting ambient temperatures while at the same developmental stage (node 8 above the cotyledons). Collection and measurement were conducted at 06:00, 09:00, 12:00, 15:00, and 18:00 h on August 4 (34.6 °C maximum air temperature) and 14, 2009 (29.9 °C maximum air temperature). Microclimate measurements included photosynthetically active radiation, relative humidity, and air temperature. Pistil measurements included pistil surface temperature, pollen germination, pollen tube growth through the style, fertilization efficiency, fertilized ovule number, and total number of ovules per ovary. Subtending leaf measurements included leaf temperature, photosynthesis, and stomatal conductance. Under high temperatures the first measurable pollen tube growth through the style was observed earlier in the day (12:00 h) than under cooler conditions (15:00 h). Also, high temperature resulted in slower pollen tube growth through the style (2.05 mm h −1) relative to cooler conditions (3.35 mm h −1), but there were no differences in fertilization efficiency, number of fertilized ovules, or ovule number. There was no effect of sampling date on diurnal photosynthetic patterns, where the maximum photosynthetic rate was observed at 12:00 h on both dates. It is concluded that, of the measured physiological and reproductive processes, pollen tube growth rate showed the greatest sensitivity to high temperature under field conditions.

Chlorophyll fluorescence images demonstrate variable pathways in the effects of plasma membrane excitation on electron flow in chloroplasts of Chara cells

Chlorophyll fluorescence Imaging and Microscopy PAM fluorometry were applied to study spatial dynamics of photosystem II quantum yield (ΔF/F'(m)) and non-photochemical quenching (NPQ) in resting and electrically stimulated Chara corallina cells in the absence and presence of the hydrophilic electron acceptor methyl viologen (MV) in the external medium. Electrical excitation of the plasma membrane temporarily enhanced the heterogeneity of photosynthetic patterns under physiological conditions (in the absence of MV), but irreversibly eliminated these patterns in the presence of MV. These findings suggest that the action potential (AP) of the excitable plant cell affects the spatial patterns of photosynthesis and chlorophyll fluorescence through different pathways operated in the absence and presence of MV. Based on the extent of NPQ as an indicator of MV-dependent electron flow, it is supposed that MV cannot permeate into the chloroplasts of photosynthetically active "acid cell regions" but gains an immediate access to the stroma of these chloroplasts after triggering of an AP. The AP-triggered MV-dependent non-photochemical quenching in the chloroplasts of acidic cell regions was routinely observed at 0.1 mM Ca(2+) in the medium but not at elevated (2 mM) external Ca(2+) concentration. The results are interpreted in terms of competition between two permeant divalent ion species, Ca(2+) and MV(2+), for their passage through the voltage-gated calcium channels of the plasma membrane. It is proposed that the herbicidal activity of MV in characean cells, here serving as model object, can be manipulated by triggering AP and varying Ca(2+) concentration in the environmental medium.

Changes in growth and photosynthetic patterns of oil palm (Elaeis guineensis Jacq.) seedlings exposed to short-term CO2 enrichment in a closed top chamber

Three varieties of oil palm seedlings (Deli Yangambi, Deli Urt, Deli AVROS) were exposed to three levels of CO2 (400, 800, 1,200 μmol/mol) in split plot design to determine growth (net assimilation rate, NAR; relative growth rate, RGR) and photosynthetic patterns of the seedlings under short-term CO2 exposure of 15 weeks. Increasing CO2 from 400 to 800 and 1,200 μmol/mol significantly enhanced total biomass and leaf area, net photosynthesis (A) and water use efficiency (WUE) especially from weeks 9 to 15. By the end of week 15, total biomass increased by 113%, and A and WUE by one- and fivefold, respectively, while specific leaf area decreased by 37%. Both enhanced biomass and A under elevated CO2 were effective in modifying NAR and RGR as shown by high correlation coefficient values (r 2 = 0.68 and 0.72; r 2 = 0.63 and 0.67, respectively), although WUE seemed to have more influence over the NAR (r 2 = 0.97) and RGR (r 2 = 0.93). Neither interspecific preference nor its interaction with CO2 imposed any significant effect on parameters observed. Growth improvement with CO2 seemed able to produce healthy, bigger and vigorous oil palm seedlings, and the technique may have potential to be developed for use to reduce nursery period.

Action potential-induced changes in photosynthetic pattern of a plant cell

Action potential-induced changes in photosynthetic pattern of a plant cell

Comparison of light harvesting and resource allocation strategies between two rhizomatous herbaceous species inhabiting deciduous forests

Light conditions on the floor of deciduous forests are determined by the leaf dynamics of canopy trees and gap formation. Such spatiotemporal variations of light availability should affect the resource partitioning strategies of understory herbs. Although rhizomatous species are common in understory, relationships between rhizome structure, vegetative growth, and sexual reproduction are unclear in terms of carbon allocation. We compared the photosynthetic characteristics and carbon translocation patterns in the under-canopy and light-gap sites between two summer-green perennial species: Cardamine leucantha with an annual long rhizome, and Smilacina japonica with a perennial short rhizome system. Flowering of both species occurs in early summer under decreasing light availability. In the light-gap, C. leucantha maintained high photosynthetic activity due to continuous leaf production, resulting in higher seed production than in the under-canopy. In contrast, the photosynthetic rate of S. japonica, producing leaves simultaneously, decreased with time irrespective of light conditions, resulting in stable seed production in both sites. Although seasonally decreasing light availability commonly restricts carbon assimilation of understory herbs, the responses of resource partitioning to variations in light availability depend greatly on the belowground structure of individual species.

Photosynthetic Patterns of 3 Crassulacean Plants under Drought Conditions

Higher plants can be categorized as C3, C4 or CAM according to their photosynthetic pathways, and some succulent plants are known to shift their patterns of photosynthesis from C3 to CAM in response to environmental stresses such as salt treatment or water deficiency. To investigate fundamental photosynthetic patterns and the induction of pattern shifts (C3, CAM, C3-CAM etc.) as a result of environmental stresses, we measured the water content, diurnal changes in pH, net <TEX>$CO_2$</TEX> exchange, transpiration rate, total ionic contents, and osmolality of Kalancoe daigremontiana, Sedum kamschaticum and Sedum sarmentosum which belong to Crassulaceae known as representative CAM plant, after 10 days of drought treatment. S. kamschaticum and S. sarmentosum did not show a significant difference in diurnal pH variation in the treatment and control conditions. However, the pH of drought-treated Kalancoe was low at night and high in the daytime, with a pH value between 4 and 5. Typical CAM plants display a net <TEX>$CO_2$</TEX> exchange that increases at night and decreases in the daytime. Kalancoe displayed the predicted pattern. However, S. kamschaticum and S. sarmentosum showed a photosynthetic pattern more typical of C3 plants, and did not show changes in photosynthetic pattern under drought stress. Kalancoe also showed a transpiration rate typical for CAM pho-tosynthesis, whereas the transpiration rates of S. kamschaticum and S. sarmentosum were in the typical range for C3 photosynthesis. Kalancoe had high total ionic contents during the night, which decreased somewhat during the daytime, whereas S. kamschaticum and S. sarmentosum displayed the opposite pattern. This result is similar to the diurnal patterns of changes in pH in the three plant species, which suggests a relationship between pH and ionic contents. S. sarmentosum showed lower osmolality under drought stress than in the control condition, whereas the osmolality of Kalancoe and S. kamschaticum did not differ between conditions. S. sarmentosum may have maintained internal water content by lowering its osmolality and raising its total ionic contents. In conclusion, Kalancoe displayed the characteristic responses of a typical CAM plant, whereas S. kamschaticum and S. sarmentosum displayed aspects of the C3 photosynthetic pattern under drought conditions. These results suggest that S. kamschaticum and S. sarmentosum (Crassulacea) in Korea overcome drought stress by increasing solute and ionic contents internally rather than changing their photosynthetic pattern from C3 to CAM under drought stress.

(137) High Temperature Increases the Midday Depression of Net Photosynthesis in Oncidium Gower Ramsey

Photosynthetic rate is reduced during midday in some crops; this phenomenon has been termed as midday depression (MD). Oncidium also suffers greatly from MD in the summer, resulting in reduced growth and poor flowering quality. Since high radiation usually accompanies high temperature midday in the summer, it is difficult to figure out the key factor that promotes MD. We investigated the photosynthetic activities of Oncidium Gower Ramsey in the following conditions: environment-controlled and nonenvironment-controlled. In a growth chamber that simulated field growth conditions, photosynthesis declined dramatically when the temperature was higher than 32 °C. Photosynthesis was also reduced when photosynthetically active radiation (PAR) exceeded the saturating point of Oncidium. Gower Ramsey, which is about 250 μmol·m-2·s-1. However, the reduction was slight when PAR was under 500 μmol·m-2·s-1. Daily photosynthetic patterns were changed when Oncidium Gower Ramsey was grown under different environments. By regression, we found that MD was not directly associated with PAR within the range of 0–400 μmol·m-2·s-1. By contrast, photosynthesis was significantly reduced when temperature was higher than 32 °C. This explains the observation of greater photosynthetic reduction and earlier occurrence of MD when Oncidium Gower Ramsey was grown in rain-shelter rather than in phytotron and growth chamber, since temperature in the rain-shelter was not controlled, while the others were controlled at 25 °C. When Oncidium Gower Ramsey was moved from 35 °C to 25 °C, the photosynthetic depression was relieved.

Fluorescence imaging application: effect of leaf age on seagrass photokinetics

We used the Imaging-PAM fluorometer to map spatial variability of photosynthesis in three seagrass species, Halophila ovalis, Zostera capricorni and Posidonia australis. Photosynthesis was described by relative photosynthetic rate (PS/50), effective quantum yield (Φ PSII), non-photochemical quenching (NPQ and qN), electron transport rate (ETR) and leaf absorptivity. Photosynthetic patterns were linked to leaf age and light climate but patterns were not consistent across species. Longitudinal heterogeneity in photosynthesis was apparent along the leaves of all three species while lateral spatial heterogeneity was found only across Z. capricorni and H. ovalis leaves. Age of leaf tissue, determined by longitudinal location on the leaf, strongly influenced photosynthetic activity of Z. capricorni and P. australis. A comparison of H. ovalis leaves of differing maturity demonstrated the influence of leaf age on photosynthetic activity, yet a comparison of Z. capricorni leaves of differing maturity showed no leaf-age effects. Variations in stress-induced changes across a seagrass leaf can be used to identify areas or particular regions of the leaf, which are more susceptible to photodamage. Clear evidence of substantial within-leaf heterogeneity in photosynthetic activity (i.e., a two-fold variation in half saturation constant along a leaf of P. australis) has serious implications for use of small sections of leaf for photosynthetic incubations (such as O 2 or single-point chlorophyll a fluorescence measurements).

Changes in the photosynthetic pigment patterns during the synchronous life cycle of Porphyridium purpureum

Changes in the photosynthetic pigment patterns during the synchronous life cycle of Porphyridium purpureum

Expression of phosphoenolpyruvate carboxylase and phosphoenolpyruvate carboxylase kinase genes. Implications for genotypic capacity and phenotypic plasticity in the expression of crassulacean acid metabolism.

In plants with crassulacean acid metabolism (CAM), dark CO2 uptake is mediated by phosphoenolpyruvate carboxylase (PEPC), an enzyme that can be regulated at transcriptional and posttranslational levels. Reversible phosphorylation of PEPC is catalyzed by a dedicated PEPC kinase, which in turn is regulated at the transcriptional level over the 24-h cycle in CAM plants. PEPC kinase controls the day/night regulation of PEPC during the CAM cycle, thus facilitating plasticity for optimizing CO2 uptake under different environmental conditions. To understand the importance of PEPC kinase in relation to its target PEPC in terms of CAM performance, the expression of the genes encoding the two enzymes was investigated in four species of Clusia that have photosynthetic patterns ranging from C3 photosynthesis to constitutive CAM. By linking changes in the expression of PEPC and PEPC kinase to day/night patterns of leaf gas exchange, organic acid, and soluble sugar contents under different environmental conditions, the genetic and metabolic limitations to CAM plasticity were assessed. The results indicate that PEPC expression is a major factor underpinning the genotypic capacity for CAM and that PEPC kinase expression does not appear to limit CAM. The day/night regulation of Ppck transcript abundance was found to be a consequence of CAM and the day/night cycling of associated metabolites, rather than the primary controlling factor for the temporal separation of carboxylation processes.

Responses of photosynthetic rates and yield/quality of main crops to irrigation and manure application in the black soil area of Northeast China

Soil nutrients and water have long been recognized as the main determining factors influencing agricultural productivity in rain-fed agriculture. Manure application and irrigation can increase crop yield when nutrients and water are deficient. Often effects of water and nutrients are closely related and can not be easily separated in actual production. Three years of experiment were conducted in northern part of black soil area of Northeast China to investigate the responses of photosynthetic rates and yield/quality of main crops, wheat (Triticum aestivum L.), maize (May zeas L.), soybean (Glycine max L. Merr.) to irrigation and manure application. Irrigation and manure application had no effects on photosynthetic patterns during reproductive development in crops, maximum photosynthetic rates were achieved by irrigation, and manure application maintained relatively higher photosynthetic rates after the peak. On average, higher photosynthetic rates with irrigation may contribute to higher yield in soybean but not in maize and wheat. Responses of crop yield and quality to manure application and irrigation varied in the crops. Soybean yield and quality was very sensitive to irrigation and manure application. The greater supply of nutrients with sufficient water, the higher the yield. However, the high-yield of soybean achieved was accompanied with a decline of seed protein content. Maize yield mainly depended on nutrients used not the water supply, irrigation resulted in higher water content in the seed of maize and lower grain protein content in wheat at harvest, which is detrimental to seed storage in maize and processing quality in wheat. In the northern part of black soil area in Northeast China, the management of manure is critical to improve crop production, the optimum management for maize and wheat production was to apply chemical fertilizer and manure without irrigation, but for soybean was to apply fertilizer and manure with irrigation.

Depth-related variability in the photobiology of two populations of Halophila johnsonii and Halophila decipiens

The threatened seagrass Halophila johnsonii Eiseman coexists subtidally with H. decipiens Ostenfeld in southeastern Florida, but only H. johnsonii also oc- curs intertidally. Pulse amplitude modulated fluorome- try and fiber-optic spectrometry were used to investigate the photobiology of two populations of H. johnsonii and H. decipiens in an attempt to explain these distribution patterns. Maximum photosynthetic quantum yields (Fv/ Fm) were measured in situ as a function of depth dis- tribution within, and between, these two species at two sites (Jupiter Sound, 26� 57¢N; 80� 04¢W, and northern Biscayne Bay, 25� 55¢N; 80� 07¢W) along the east coast of Florida, USA, during 6-10 March 2001. Reciprocal transplants at the northern site were used to evaluate the plasticity of photosynthetic patterns and pigment absorption spectra and to gain insights into the mecha- nisms responsible for variations in the observed depth- distribution patterns. Subtidal-population Fv/Fm values were generally higher for H. johnsonii than for H. deci- piens, at both sites. At the northern site, intertidal H. johnsonii had significantly lower Fv/Fm (0.494±0.138) than both subtidal H. johnsonii (0.696±0.045) and subtidal H. decipiens (0.668±0.048). In contrast, at the southern site intertidal H. johnsonii had the highest Fv/ Fm (0.663±0.047) and were the largest plants. Fv/Fm values of subtidal plants of both species decreased when they were transplanted into shallow, intertidal beds. Correspondingly, Fv/Fm increased for intertidal H. johnsonii transplanted into the subtidal, 2 m deep beds. Rapid light curves indicated that H. decipiens had lower maximum relative electron transport rates (RE- TRmax) than did H. johnsonii. In addition, the onset of photoinhibition occurred at lower irradiances for H. decipiens (537-820 lmol photons m )2 s )1 ) compared to H. johnsonii (1141-2670 lmol photons m )2 s )1 ). RETRmax values decreased for intertidal H. johnsonii transplanted into subtidal beds, but they increased for both species when transplanted from subtidal to inter- tidal beds. Absorption spectra for the acetone-soluble leaf pigments of intertidal H. johnsonii exhibited a dominant peak near 345 nm; this UV peak was 30% lower for subtidal plants. Pigment absorption spectra for H. decipiens lacked the 345 nm peak and absorbances, normalized to leaf pairs, were lower across the spectrum. Our results indicate that photosynthetic tolerance to higher irradiances and presence of UV-absorbing pig- ments (UVP) in H. johnsonii may allow this species to exploit the shallowest waters without competition from the closely related, but UVP-lacking H. decipiens.

Leaf Pigment and Canopy Photosynthetic Response to Early Flower Removal in Cotton

Loss of reproductive organs from cotton (Gossypium hirsutum L.) often results in compensatory growth that culminates in altered morphologic, physiologic, and photosynthetic patterns. This field study examined the change in leaf chlorophyll (Chl) and anthocyanin (Ant) contents and their relationship to canopy photosynthetic patterns in response to the removal of flowers for the first 2 wk of flowering. Flower removal caused an extended flowering period in all years except 1995 when temperatures were highest. The largest yield differences occurred in 1994, while there were no significant differences in any other year. Differences in canopy photosynthesis occurred on at least one date in each year that measurements were made. In 1997, significant differences were observed on four dates and plants from the removal treatment had 15% larger area under the seasonal photosynthetic curve. Chlorophyll concentrations were higher in leaves from the flower removal treatment after 100 d after planting. Anthocyanin levels were higher in controls during the same period, indicating significant negative relationships between Ant levels and either Chl a/b ratio or Chl concentration. Pigment differences late in plant ontogeny appeared to be associated with delayed senescence of plants from the removal treatment. While pigment levels late in development were associated with canopy photosynthesis, not all treatment differences could be related to Chl loss. In 2 yr, significant differences in canopy photosynthesis occurred prior to differences in Chl concentration, implicating other morphological and physiological adaptations in response to early fruit loss.

Photosynthetic response of Populus euphratica to salt stress

P. euphratica Olive and the hybrids ( P. talassica Kom X ( P. euphratica + Salix alba L)) seedlings were subjected to low (50 mM NaCl) and high salt (200 mM NaCl) treatments to determine their photosynthetic responses to salt stress. The photosynthetic pattern indicated that P. euphratica is a C3 plant with a high CO 2 compensation point (150 μmol mol −1) and saturation point (900 μmol mol −1), but has some characteristics of C4 plants with a high light saturation point (2800 μmol m −2 s −1) in control conditions. CO 2 compensation and saturation points increased with high salt treatment for both the hybrid and P. euphratica while light saturation point decreased with salt treatment. The net photosynthesis of P. euphratica with high salt treatment declined in the first 14 days and recovered to 70% that with control in day 21 when soil salt content was about 0.7% NaCl, while that of the hybrids did not recover when soil salt content was about 0.5% NaCl with hgih salt treatment. With increasing salt levels, Chlorophyll a contents and Chlorophyll a b ratio increased, while Chlorophyll b and carotenoid contents decreased by day 10, when photosynthesis was heavily depressed for both species. Fluorescence patterns confirmed that reduction of photosynthesis under high salt treatment was not due to damage of the photosynthetic apparatus, but more likely due to inhibition of the dark reaction.

Ecology of Sargassum muticum on the North Coast of Spain. II. Physiological Differences between Sargassum muticum and Cystoseira nodicaulis

The variations of photosynthesis and C, N and mannitol content were analyzed in the co-existing invasive species Sargassum muticum and the native Cystoseira nodicaulis. Both species exhibited similar seasonal patterns of photosynthesi s, with a significant decay in P max in summer, which can be attributed to nutrient limitation. Nitrogen content was the lowest in summer (< 1.5%) and this decrease was simultaneous with a significant increase in mannitol, to a value of over 15% of the organic weight, in both species. Cystoseira nodicaulis showed higher C/N values, typical of N-limited growth, both in February and June, while in Sargassum muticum high C/N values where found only in June. The variations in N content and C/N ratio in C. nodicaulis were very similar to those in protein content, while in S. muticum there was a striking similarity between the variation in C content and that of mannitol. Although the photosynthetic pattern may be similar in both species, these differences in biochemical status are interpreted as a consequence of different growth strategies. While Sargassum shows a response to the environment, with growth confined to a short period during the favourable season, Cystoseira must have some storage ability that allows it to 'anticipate' favourable conditions and to exhibit two growth periods during the year.