Relative Photosynthetic Rate Research Articles

Predictive Modeling of Different Treatments for Physiological and Nutritional Parameters of Ocimum Sanctum

An increasing demand for superior quality crops has led to investigating the current trends in agriculture. One of the main factors impacting this is environmental stress. Even with certain plant defense mechanisms to combat stress, not all plants can tolerate the impact induced by abiotic stress, therefore compromising the overall physiological and nutritional parameters greatly. This research focuses on the effects of stress on the Ocimum sanctum plant, its corresponding parametric variation data is further processed and analyzed by predictive models. Abiotic stress: Plants were exposed to drought, jasmonic acid, potassium nitrate, hydrogen peroxide, at varied intensities, and parameters - plant height, relative water capacity, protein, chlorophyll content, and photosynthetic rate were subsequently recorded for 50 days. KNN classification model was used to predict the treatment required for any given parameter. A comparative study between Linear and Non-Linear Regression models with a common goal of predicting one parameter from the other known parameter was done and inferred that the Non-Linear Regression model performed well and had better accuracy.

Environmental Factors at Different Canopy Heights Had Significant Effects on Leaf Water-Use Efficiency in Cold-Temperate Larch Forest

It is of great significance to study short-term water-use efficiency (WUEs) at different canopy heights for accurately evaluating the adaptability of cold-temperate larch (Larix gmelinii) forest to climate change. The stable isotope method combining data of gradient meteorology, photosynthetic properties and leaf structure were used to assess the influence of different canopy heights on short-term water-use efficiency (WUEs) in larch forests in the northern Da Hinggan Mountains. The results show that: (1) The rank of leaf WUEs at different canopy heights was upper canopy > middle canopy > lower canopy. The leaf WUEs in upper canopy was significantly higher than those in the middle and lower canopy (p < 0.01), and no significant difference was found between the middle and lower canopy (p > 0.05). (2) The environmental factors, the photosynthetic characteristics, the specific leaf weight (LMA) and stomatal density (SD) had significant impact (p < 0.05) on leaf WUEs at different canopy heights of larch forest. (3) The results of the weighted random forest analysis show that the main factor affecting WUEs in larch forests at different canopy heights was vapor pressure deficit (VPD), followed by relative humidity (RH) and net photosynthetic rate (Pn), while LMA and SD made relatively small contributions. This indicates that the variation of leaf WUEs at different canopy heights is mainly due to environmental factors. Our results highlight that the difference of environmental factors at different canopy heights should be considered in the future study of leaf WUE. Our results contribute to a better understanding of water utilization strategies and carbohydrate relations in the boreal forest ecosystems, which is of great significance for improving the sustainable management measures and strategies of boreal forest resources.

Foliar application of potassium nitrate induces tolerance to water deficit in pre-flowering sorghum plants

The objective of this study was to evaluate the the ability of foliar application of potassium nitrate (KNO3) to induce water deficit tolerance in sorghum plants (Sorghum bicolor cv. P898012) subjected to water deficit at pre-flowering. The experiment was conducted under greenhouse conditions with 4 treatments: field capacity (FC), water deficit (WD), field capacity + KNO3 (FC + KNO3), and water deficit + KNO3 (WD + KNO3). Two foliar applications of 3% (m/v) KNO3 were made, the first on day zero of stress and the second on the fifth day. All analyses were performed after 12 days of stress (end of stress). Foliar application of KNO3 to irrigated plants led to increases in relative chlorophyll content, photosynthetic rate, stomatal conductance, transpiration, and carboxylation efficiency. It also induced increases in leaf concentrations of P, Mg, S, Cu, and Fe, in addition to height growth. Under water deficit conditions, plants treated with KNO3 presented higher relative chlorophyll content, leaf area, photosynthetic rate, stomatal conductance, transpiration, carboxylation efficiency, and higher levels of P, K, Mg, S, Cu, and Fe than those not treated with KNO3. The morphometry of the root system was not altered by the treatments. In addition, plants treated with KNO3 under water deficit conditions showed higher growth and a grain yield 32.2% higher than those that did not receive KNO3. These results demonstrated that KNO3 applied to the leaves induced water deficit tolerance in sorghum plants subjected to severe water stress at pre-flowering.

Physiological insights into sulfate and selenium interaction to improve drought tolerance in mung bean

The present study involved two pot experiments to investigate the response of mung bean to the individual or combined SO42− and selenate application under drought stress. A marked increment in biomass and NPK accumulation was recorded in mung bean seedlings fertilized with various SO42− sources, except for CuSO4. Compared to other SO42− fertilizers, ZnSO4 application resulted in the highest increase in growth attributes and shoot nutrient content. Further, the combined S and Se application (S + Se) significantly enhanced relative water content (16%), SPAD value (72%), photosynthetic rate (80%) and activities of catalase (79%), guaiacol peroxidase (53%) and superoxide dismutase (58%) in the leaves of water-stressed mung bean plants. Consequently, the grain yield of mung bean was markedly increased by 105% under water stress conditions. Furthermore, S + Se application considerably increased the concentrations of P (47%), K (75%), S (80%), Zn (160%), and Fe (15%) in mung bean seeds under drought stress conditions. These findings indicate that S + Se application potentially increases the nutritional quality of grain legumes by stimulating photosynthetic apparatus and antioxidative machinery under water deficit conditions. Our results could provide the basis for further experiments on cross-talk between S and Se regulatory pathways to improve the nutritional quality of food crops.

Anatomical physiological and biochemical processes involved in grapevine rootstock drought tolerance

In order to explore the drought resistance mechanism of grape rootstocks, two grape rootstock species, '1103P' (a drought-tolerant rootstock) and '101-14M' (drought-sensitive), were treated with moderate water deficit (field capacity of 45-50 %). Throughout the experimental period, the leaves of '1103P' showed a higher stomatal conductance (gs), relative water content and photosynthetic rate (Pn) than '101-14M', indicating '1103P' was more resistant to tolerant than '101-14M'. We propose that '1103P' could prevent water loss from leaves under drought conditions based on the discoveries that '1103P' had higher leaf phytohormone abscisic acid (ABA) content and leaf cuticular wax content, and smaller stomata aperture than those of '101-14M'. Additionally, the activities of H2O2-scavenging enzymes in leaves of '1103P' were higher than those of '101-14M' under drought conditions, indicating the lipid peroxidation induced by H2O2 of '1103P' was less serious than that of '101-14M'. Therefore, better water-saving and higher reactive oxygen species (ROS) scavenging abilities contributed together to stronger drought resistance of '1103P' than '101-14M'.

Mombaça grass development with partial replacement of potassium fertilizer by sodium chloride and the effects of adding calcium

The objective of this greenhouse study was to evaluate the effects on development parameters in Megathyrsus maximus cv. Mombaça of partially replacing the potassium (K) in fertilizer by sodium (Na)and the impacts of applying calcium (Ca). The experimental design was completely randomized with 4 replicates, in a 3 × 4 + 3 factorial arrangement. Three Ca sources (CaCO3, CaSO4 and CaCl2) were applied at 4 Ca doses (10, 20, 30 and 40 mg Ca/kg of soil) to the grass where 25% of the K fertilizer was replaced by NaCl. The 3 additional treatments were: application of standard fertilizer (N:P:K) with 100% of K recommendation; application of fertilizer with 25% of K replaced by Na but no Ca applied; and grass with no fertilizer of any kind as Control. The variables analyzed were: leaf area, leaf area ratio, net assimilation rate, relative growth rate and photosynthetic rate. Partial replacement of K by Na up to 25% of the K fertilizer recommendation did not cause significant change in the development of Mombaça grass or to any of the measured parameters. Addition of Ca had minimal impact on the analyzed variables regardless of level or source. These measurements helped to explain why dry matter yields of Mombaça grass were not significantly affected by partial replacement of K by Na up to 25% of the K fertilizer recommendation.

PGRs and nutrient consortium effect on water relations, photosynthesis, catalase enzyme and yield of blackgram under salinity stress

An experiment was conducted to study the effect of plant growth regulators namely jasmonic acid (50 µM), brassinolide (0.5 ppm), salicylic acid (100 ppm), ascorbic acid (100 ppm), gibberellic acid (10 ppm), benzyl amino purine (5 ppm) and nutrient consortium (K2SO4 (0.5%) + FeSO4 (0.5%) + Borax (0.3%) and TNAU Pulse Wonder (1%) on blackgram (Vigna mungo L.) variety TNAU (Blackgram) CO 6 under salinity condition. The salinity was imposed by 125 mM NaCl concentration in pot culture. Plant growth regulators and nutrient consortium were used as foliar spray at 20 and 40 days after sowing except jasmonic acid, which used as seed soaking. Under salinity stress, water potential, relative water content (RWC), photosynthetic rate, chlorophyll index and yield were significantly reduced as compared to control. Among the treatments, brassinolide and TNAU Pulse Wonder showed supremacy to enhance water potential, RWC and yield compared to other treatments. Salicylic acid performed better to stabilize the photosynthetic rate under salinity followed by TNAU Pulse Wonder. Benzyl amino purine had higher chlorophyll index than other treatments. Increased catalase activity was observed in brassinolide treated plants followed by salicylic acid and ascorbic acid under salinity.

Relationship of plant water status and leaf gas exchange with fruit cracking of pomegranate

Plant water status and leaf gas exchange as influenced by micronutrients, kaolin and water management were studied to establish a relationship with fruit cracking in pomegranate in arid regions. Observations were recorded on fruiting pomegranate trees that were maintained under different water status and leaf gas exchange through mulching of tree basins and foliar spray of borax (0.4%), zinc sulphate (0.5%), kaolin (4.0%) with respect to fruit cracking, LWP, RWC, stomatal conductance, transpiration, photosynthetic rate and difference between ambient and leaf temperature of fruiting branch. The results showed that per cent fruit cracking was associated with reduction in leaf water potential, stomatal conductance and leaf transpiration. Such a situation coupled with high relative water content and photosynthetic rate as observed under combined sprays of borax (0.4%) + ZnSO4 (0.5%) and borax (0.4%) + ZnSO4 (0.5%)+ kaolin (4%) reflects the possible relationship of fruit cracking with selected physiological parameters. Plant water status also influences leaf gas exchange parameters and subsequently growth which may indirectly affect cracking in pomegranate fruits.

Stromatolite records of environmental change in perennially ice-covered Lake Joyce, McMurdo Dry Valleys, Antarctica

Calcite-rich columnar stromatolites grew in perennially ice-covered Lake Joyce in the McMurdo Dry Valleys, Antarctica, during a period of environmental change associated with rising lake level. Stromatolite calcite contains carbon and oxygen isotope records of changes to microbial activity in response to variable light environments and water chemistry through time. The stromatolites grew synchronously with correlative calcite zones. The innermost (oldest) calcite zone has a wide range of δ13Ccalcite values consistent with variable photosynthetic effects on local DIC 13C/12C. Subsequent calcite zones preserve a progressive enrichment in δ13Ccalcite values of approximately + 2.6‰ through time, with δ13Ccalcite values becoming less variable. This enrichment likely records the removal of 12C by photosynthesis from the DIC reservoir over decades, with photosynthetic effects decreasing as light levels became lower and more consistent through time. Mean δ18Ocalcite values of the innermost calcified zone were at least 1‰ lower than those of the other calcified zones (t test p-level < 0.001). The significant difference in δ18Ocalcite values between the innermost and other calcified zones could be a product of mixing source waters with different isotopic values associated with the initiation of lake stratification associated with rising lake level. Overall, Lake Joyce stromatolites record significant lateral variability in relative photosynthetic rate and long-lived lake water stratification with microbial modification of the DIC pool. Such processes provide criteria for interpreting microbial activity within polar paleolake deposits and may shed light on variability in lake environments associated with changing climate in the McMurdo Dry Valleys.

Impact of potassium sulfate salinity on growth and development of cranberry plants subjected to overhead and subirrigation1

New recommendations in cranberry production suggest reducing overhead irrigation and the use of subirrigation as an alternative irrigation method, two strategies suspected to increase the risk of salt buildup in soil. Because very little is known about cranberry tolerance to salinity, this study was conducted to determine if deficit irrigation and subirrigation could cause salinity issues and affect plant yield. In a greenhouse, cranberry plants were submitted to eight different treatments combination from two irrigation methods (overhead irrigation and subirrigation) and four salinity levels created by increasing amounts of applied K2SO4 (125 (control), 2500, 5000, and 7500 kg K2O ha−1). Irrigation methods showed no significant difference in measured electrical conductivity of soil solution (ECss). Meanwhile, growth and yield parameters decreased significantly with soil salinity in both irrigation treatments, and an average ECss of 3.2 dS m−1 during flowering caused a 22% drop in relative photosynthetic rate and a 56% decrease in yield when compared with the control. Cranberry seems to be salt sensitive, and further work should investigate ECss levels under different field and irrigation practices to make sure that it does not reach critical levels.

DIFFERENCE IN PHOTOSYNTHESIS OF DIFFERENT POSITION LEAVES OF GREENHOUSE CUCUMBER IN AUTUMN AND WINTER

Diurnal photosynthetic changes of upper, middle and lower leaves of cucumber were measured in different dates in the middle and late of autumn and winter. The results indicated that the middle leaves had a relative high photosynthetic rate, the upper leaves took the second place and the lower leaves were the least. With the pass of time, the photosynthesis of cucumber reduced quickly in general, and the upper leaves decreased in greatest extent, the middle leaves and the lower leaves took the second and the third place respectively. The reason why cucumber photosynthesis was low in medium-late stage was that stomatal limitation and senescence of cucumber, and it is necessary to enhance the management of ventilation, lessen the time of ventilation and shorten the size of intake.

Upper Limit of Residual Chlorine in Reclaimed Wastewater

Chlorination as a disinfectant of tertiary treatment is the most common form in municipal wastewater treatment plants in China. Excess residual chlorine in reclaimed wastewater is harmful to growth of lawn grass. However, upper limit of residual chlorine aimed at reclaimed wastewater reuse for urban green land irrigation has not been promulgated. Lab-scale potted experiments of seedling tall fescue (Festuca arundinacea Schreb.)(TF) and Kentucky bluegrass (Poa pratensis L.)(KBG) were performed to evaluate the effects of residual chlorine in reclaimed wastewater on these two kinds of lawn grass. The results showed that: relative aboveground biomass, photosynthetic rate and total chlorophll (Tchl) concentration reduced to great extent with increasing of residual chlorine. The activity of catalase (CAT) of TF went up under low concentrations and decreased under higher ones, which was different from the decline trend of the same index of KBG. Considered growth of the two kinds of turf grass and disinfectant of reclaimed water, the upper limits of residual chlorine in reclaimed water for landscape irrigation should be equal to 1.0 mg/L for TF and 0.8 mg/L for KBG.

CORAL PHOTOBIOLOGY STUDIED WITH A NEW IMAGING PULSE AMPLITUDE MODULATED FLUOROMETER1

A new high‐resolution imaging fluorometer (Imaging‐PAM) was used to identify heterogeneity of photosynthetic activity across the surface of corals. Three species were examined: Acropora nobilis Dana (branching), Goniastrea australiensis Edwards &amp; Haime (massive), and Pavona decussata Dana (plate). Images of fluorescence parameters (F, Fm′, effective quantum yield, optimal quantum yield, electron transport rate, relative photosynthetic rate, and non‐photochemical quenching) allowed heterogeneity to be detected in terms of position on colony and indicated that the photosynthetic activity of polyp and coenosarc tissues responded differently to changing light for all three species. The Imaging‐PAM offers a special routine, with which images of PAR absorption (absorptivity) are obtained. In this way, for the first time it has become possible to derive images of the relative photosynthesis rate. Polyps had a lower PAR absorptivity than coenosarc tissue for A. nobilis and P. decussata, whereas G. australiensis showed the opposite pattern. Acropora nobilis showed heterogeneity along the longitudinal axis of the branch, which could be differentiated from the effect of variations in illumination across the rugose and curved surface. Diel changes were apparent and influenced the longitudinal heterogeneity along the A. nobilis branch. Images were also obtained showing the degree of photoinhibition caused by high‐light stress across a coral surface at a hitherto unobtainable level of resolution.

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).

The Effects of Rust and Anthracnose on the Photosynthetic Competence of Diseased Bean Leaves

ABSTRACT The effects of rust (caused by Uromyces appendiculatus) and anthracnose (caused by Colletotrichum lindemuthianum) and their interaction on the photosynthetic rates of healthy and diseased bean (Phaseolus vulgaris) leaves were determined by gas-exchange analysis, in plants with each disease, grown under controlled conditions. The equation P(x)/P(0) = (1 - x)() was used to relate relative photosynthetic rate (P(x)/P(0)) to proportional disease severity (x), where beta represents the ratio between virtual and visual lesion. The beta values obtained for rust were near one, indicating that the effect of the pathogen on the remaining green leaf area was minimal. The high values of beta obtained for anthracnose (8.46 and 12.18) indicated that the photosynthesis in the green area beyond the necrotic symptoms of anthracnose was severely impaired. The impact of anthracnose on bean leaf photosynthesis should be considered in assessments of the proportion of healthy tissue in diseased leaves. The accurate assessment of the healthy portion of the leaf could improve the use of concepts such as healthy leaf area duration and healthy leaf area absorption, which are valuable predictors of crop yield. The equation used to analyze the interaction between rust and anthracnose on the same leaf was P(z) = P(0) (1 - x)(x) x (1 - y)(y), where P(z) is the relative photosynthetic rate of any given leaf, P(0) is the maximum relative photosynthetic rate, x is anthracnose severity, y is rust severity, betax is the beta value for anthracnose in the presence of rust, and betay is the beta value for rust in the presence of anthracnose. From the resulting response surface, no interaction of the two diseases was observed. Dark respiration rate increased on diseased leaves compared with control leaves. The remaining green leaf area of leaves with both diseases was not a good source to estimate net photosynthetic rate because the effect of anthracnose extended far beyond the visual lesions, whereas the effect of rust on photosynthesis was essentially limited to the pustule plus halo.

Remote sensing of photosynthetic-light-use efficiency of boreal forest

Using a helicopter-mounted portable spectroradiometer and continuous eddy covariance data we were able to evaluate the photochemical reflectance index (PRI) as an indicator of canopy photosynthetic light-use efficiency (LUE) in four boreal forest species during the Boreal Ecosystem Atmosphere experiment (BOREAS). PRI was calculated from narrow waveband reflectance data and correlated with LUE calculated from eddy covariance data. Significant linear correlations were found between PRI and LUE when the four species were grouped together and when divided into functional type: coniferous and deciduous. Data from the helicopter-mounted spectroradiometer were then averaged to represent data generated by the Airborne Visible Infrared Imaging Spectrometer (AVIRIS). We calculated PRI from these data and relationships with canopy LUE were investigated. The relationship between PRI and LUE was weakened for deciduous species but strengthened for the coniferous species. The robust nature of this relationship suggests that relative photosynthetic rates may be derived from remotely-sensed reflectance measurements.

Light acquisition and use by individuals competing in a dense stand of an annual herb, Xanthium canadense.

The importance of light acquisition and utilization by individuals in intraspecific competition was evaluated by determining growth and photosynthesis of individual plants in a dense monospecific stand of an annual, Xanthium canadense. Photosynthesis of individual plants in the stand was calculated using a canopy photosynthesis model in which leaf photosynthesis was assumed to be function of leaf nitrogen content and light availability. The estimated photosynthetic rates of individuals were strongly correlated with the measured growth rates. Photosynthetic rates per unit aboveground mass (RPR, relative photosynthetic rate) increased with increasing aboveground mass, suggesting asymmetric (one-sided) competition in the stand. However, larger individuals had similar RPRs, suggesting symmetric (two-sided) competition. These results were consistent with the observation that size inequality over the whole stand increased with growth, but it remained stable among the larger individuals. The RPR of an individual was calculated as the product of absorbed photon flux per unit aboveground mass (Φmass) and light use efficiency (LUE, photosynthesis per unit absorbed photon flux). Φmass indicates the efficiency of light acquisition, and was higher in larger individuals in the stand, while LUE was highest in individuals with intermediate aboveground mass. LUE depends on leaf nitrogen content. At an early stage, leaf nitrogen contents of smaller individuals were similar to those that maximize LUE. Light availability to smaller individuals decreased as they grew, while their nitrogen contents did not change markedly, which decreased their LUE. We concluded that asymmetric competition among individuals in the stand resulted mainly from lower efficiencies in both light acquisition and light use by smaller individuals.

Photosynthesis and Productivity of Cotton under Silverleaf Whitefly Stress

The silverleaf whitefly (SLW), Bemisia argentifolii (Bellows and Perring), has been a severe pest of numerous field and vegetable crops for many years. Nevertheless, little has been reported on the complex interactions between SLW and its host plants. This study was aimed at investigating the effects of SLW on cotton (Gossypium hirsutum L.) photosynthesis and productivity under various irrigation and N fertilization regimes. Cotton plants (cv. Siv'on) were examined during an entire growing season in two factorial‐designed screenhouse experiments consisting of two irrigation regimes (I) × two N application rates × two SLW levels (noninfested vs. infested). Buildup of the SLW population was markedly higher on N‐fertilized plants than on N‐deficient plants. Seed cotton yield was reduced by SLW in festation under all combinations of I × N treatments by about 40%. Yield reduction (noninfested minus infested) was significantly correlated with the number of SLW adults on the maximally infested leaf at peak flowering (r2 = 0.94, P &lt; 0.05 in 1995; r2 = 0.91, P &lt; 0.05 in 1996). Photosynthetic rate decreased 50% at about 60 d after SLW introduction. The relative photosynthetic rate (infested/noninfested) was significantly correlated with SLW adult density on the maximally infested leaf (r2 = 0.72, P &lt; 0.001 in 1995; r2 = 0.53, P &lt; 0.01 in 1996). The reduced photosynthetic rate was associated with reductions in chlorophyll variable fluorescence (Fv/Fm) and fluorescence yield. No substantial changes were found in stomatal conductance, intercellular CO2 concentration, and leaf chlorophyll content. These findings indicate that SLW infestation impairs, either directly or indirectly, the photochemical reaction of the photosynthetic system in cotton plants.

The photochemical reflectance index: an optical indicator of photosynthetic radiation use efficiency across species, functional types, and nutrient levels.

The photochemical reflectance index (PRI), derived from narrow-band reflectance at 531 and 570 nm, was explored as an indicator of photosynthetic radiation use efficiency for 20 species representing three functional types: annual, deciduous perennial, and evergreen perennial. Across species, top-canopy leaves in full sun at midday exhibited a strong correlation between PRI and ΔF/Fm', a fluorescence-based index of photosystem II (PSII) photochemical efficiency. PRI was also significantly correlated with both net CO2 uptake and radiation use efficiency measured by gas exchange. When species were examined by functional type, evergreens exhibited significantly reduced midday photosynthetic rates relative to annual and deciduous species. This midday reduction was associated with reduced radiation use efficiency, detectable as reduced net CO2 uptake, PRI, and ΔF/Fm' values, and increased levels of the photoprotective xanthophyll cycle pigment zeaxanthin. For each functional type, nutrient deficiency led to reductions in both PRI and ΔF/Fm' relative to fertilized controls. Laboratory experiments exposing leaves to diurnal courses of radiation and simulated midday stomatal closure demonstrated that PRI changed rapidly with both irradiance and leaf physiological state. In these studies, PRI was closely correlated with both ΔF/Fm' and radiation use efficiency determined from gas exchange at all but the lowest light levels. Examination of the difference spectra upon exposure to increasing light levels revealed that the 531 nm Δ reflectance signal was composed of two spectral components. At low irradiance, this signal was dominated by a 545-nm component, which was not closely related to radiation use efficiency. At progressively higher light levels above 100 μmol m-2 s-1, the 531-nm signal was increasingly dominated by a 526-nm component, which was correlated with light use efficiency and with the conversion of the xanthophyll pigment violaxanthin to antheraxanthin and zeaxanthin. Further consideration of the two components composing the 531-nm signal could lead to an index of photosynthetic function applicable over a wide range of illumination. The results of this study support the use of PRI as an interspecific index of photosynthetic radiation use efficiency for leaves and canopies in full sun, but not across wide ranges in illumination from deep shade to full sun. The discovery of a consistent relationship between PRI and photosynthetic radiation use efficiency for top-canopy leaves across species, functional types, and nutrient treatments suggests that relative photosynthetic rates could be derived with the "view from above" provided by remote reflectance measurements if issues of canopy and stand structure can be resolved.

アナアオサの不稔性変異株の生長と光合成‐温度特性

Growth and photosynthesis temperature characteristics of the sterile Ulva pertusa (sterile type) were studied and compared with the wild U. pertusa (wild type) collected from the low water mark at Tana in Yamaguchi Prefecture and at Shimoda in Shizuoka Prefecture. The sterile type and the wild type at the Tana site in summer were cultured at 10, 15, 20, 25, 30, and 35°C. The sterile type grew faster than the wild type from 20 to 30°C. Photosynthesis temperature relationships of both types were measured with two seasons. The photosynthetic rate, measured from 5 to 35°C every 5 using the same fronds, was higher in the sterile type than in the wild type at the Tana site in autumn over 25°C. The relative photosynthetic rate, expressed as values relative to that at 20°C, was also higher in the sterile type than in the wild type both at the Tana site and at the Shimoda site in summer over 25°C, while the respiratory rate from 10 to 35°C was lower in the sterile type than in the wild type at the Shimoda site in summer. These results indicate that the rapid growth of the sterile type from 20 to 30°Cis mainly caused by a high photosynthetic rate and a low respiratory rate.