Rate Of Apparent Photosynthesis Research Articles

Efficient cotton population photosynthetic production synergistically increases seedcotton yield and fiber quality through straw incorporation with appropriate nitrogen fertilization in wheat-cotton rotation system

ContextStraw incorporation with appropriate nitrogen (N) fertilization could increase seedcotton yield, but it is unknown whether and how straw incorporation with N fertilization can synergistically improve seedcotton yield and fiber quality. ObjectiveContinuous years of positioning field wheat-cotton double cropping experiments were conducted from 2015 to 2021 to investigate the effects of straw incorporation and N fertilization on seedcotton yield and fiber quality. MethodsFour N rates (0, 75, 150 and 300 kg N ha−1) and two straw managements (wheat-cotton straw incorporation and straw removal i.e. CK) were used as experimental treatments. The canopy photosyhthetic capacity, biomass, seedcotton yield and fiber quality were measured. Meanwhile, the dynamics of cotton square nuber and boll number during the efficient photo-thermal periods (approximately from 25th July to 30th August) were monitored. ResultsIn the study from 2019 to 2021, the canopy apparent photosynthesis rate, leaf area index and chlorophyll relative content increased with straw incorporation and increasing N rates. The maximum daily square appearance rate of 6.9 × 104 no. ha−1 and the maximum daily boll setting rate of 3.4 × 104 no. ha−1 during the efficient photo-thermal periods were obtained under straw incorporation with 150 kg N ha−1. Where the maximum boll setting ratio and boll weight ratio were observed. Straw incorporation with 150 kg N ha−1 also produced the maximum boll number (87.3–98.1 × 104 no. ha−1), seedcotton yield (3998–4544 kg ha−1) and the longest fiber length of 30.3–31.2 mm across from 2019 to 2021, and the strongest fiber strength and the lowest micronaire in 2019 and 2020. The results of 13CO2 feeding to cotton plants in 2019 and 2020 showed that straw incorporation promoted 13C allocation into cotton fiber and the maximum cotton fiber 13C proportion appeared under straw incorporation with 150 kg N ha−1. Besides, straw incorporation and increasing N rates increased seed hull 13C proportion for fiber development. In addition, long-term straw incorporation could reduce chemical N fertilizer by approximatly 30% from 150 kg N ha−1 to achieve the seedcotton yield under 150 kg N ha−1 without significant influence on fiber quality. ConclusionIn wheat-cotton rotation system, straw incorporation with a 30% reduction from 150 kg N ha−1 was appropriate to increasing seedcotton yield and fiber quality synergistically by improving canopy photosynthetic capacity, increasing cotton square and boll number during the efficient photo-thermal period, and optimizing photosynthate allocation in cotton boll.

Straw returning coupled with nitrogen fertilization increases canopy photosynthetic capacity, yield and nitrogen use efficiency in cotton

Nitrogen (N) fertilization plays a pivotal role in canopy photosynthetic capacity and yield formation of cotton (Gossypium hirsutum L.), but the interaction effects with consecutive straw returning remain poorly understood. A field experiment was conducted (2015–2018) to examine the effects of N fertilization (0, 75, 150, and 300 kg N ha−1) coupled with or without barley and cotton straw supplementation on soil nutrient status, cotton canopy photosynthetic capacity, seedcotton yield, and nitrogen use efficiency (NUE) in Yancheng, China. N fertilization coupled with straw addition enhanced most cotton growth traits, showing higher canopy apparent photosynthesis rate, leaf area index, leaf N content, specific leaf area, and boll density, and progressively increased seedcotton yield annually. In 2018, straw addition increased seedcotton yield by 7.5 %, 9.6 %, 12.1 %, and 4.1 % under 0, 75, 150, and 300 kg N ha−1, respectively, compared to corresponding treatments of straw removal. The highest increase in seedcotton yield and NUE under 150 kg N ha−1 combined with straw addition was due to the greatest improvements in soil fertility, canopy photosynthetic capacity, and N uptake by cotton. In addition, the results suggested that approx. 33–44 % of chemical N fertilizer reduction would not affect seedcotton yield with straw addition. Our results demonstrated that straw returning combined with 150 kg N ha−1 had benefits on improving soil nutrient status, canopy photosynthetic capacity, seedcotton yield, and NUE of cotton.

Comparative Contribution of СО2/Н2О Exchange Components to the Process of Adaptation to Drought in Xero-Halophytes from the Family Chenopodiaceae with Different Types of Photosynthesis

Components of СО2/Н2О exchange (rates of apparent photosynthesis, transpiration, and dark respiration), as well as efficiency of photosystem I, growth rate, and proline content, were investigated in plants of the С3 species (Atriplex verrucifera M. Bieb), two populations of the С4 species (A. tatarica L.), and two populations of the intermediate С3–С4 species (Sedobassia sedoides (Pall.) Freitag & G. Kadereit), family Chenopodiaceae, in the course of adaptation to PEG-induced moderate osmotic stress (–0.4…–0.5 MPa). Two taken СО2 concentrations (400 and 200 ppm) enabled the examination of stomatal and metabolic contribution to the formation of the mechanisms of drought tolerance and estimate sensitivity of stomata. Under moderate water deficit, the С3 species showed drought tolerance and succulence and was notable for insensitive stomata. Examination of growth characteristics made it possible to reveal differences in productivity and tolerance between populations of the С4 and С3–С4 species. In spite of a different nature of carbon-concentrating mechanism (aspartate in С4 and photorespiratory in С3–С4), populations tolerant to water deficiency shared common features: less sensitive stomata and operation of the mechanism stabilizing water balance of the leaf cells probably due to proline and cyclic transport of electrons. Realization of such a strategy maintains coordination among parameters of СО2/Н2О exchange, which ensures a lower variability of dark respiration and a greater tolerance of plants to moderate osmotic stress. In nontolerant populations, adaptation mainly depends on stomatal closure, which probably results in upsetting the balance among parameters of СО2/Н2О exchange.

Growth and yield of cotton as affected by different straw returning modes with an equivalent carbon input

Crop production is greatly affected by the applications of straw and straw-biochar. However, the responses of cotton (Gossypium hirsutum L.) growth and yield to different straw returning modes with an equivalent carbon (C) input are still unclear. A four-year field experiment was conducted to investigate the effects of different straw returning modes on the soil temperature, soil water content, soil nutrient availability, cotton root growth, cotton nutrient status, cotton canopy photosynthetic properties and seedcotton yield in a barley-cotton rotation system in Yancheng, China. Based on an equivalent C input, five treatments were set: straw-biochar incorporation (SB), straw incorporation with microbial inoculant (SI), straw incorporation (S), straw mulching (SM), and the control without straw or straw-biochar (CK). Treatments with straw and straw-biochar significantly enhanced most cotton growth parameters, and consequently increased the seedcotton yield from the second year to the fourth year. Such beneficial effects induced by the applications of straw and straw-biochar tended to progressively increase annually. In the fourth year, seedcotton yields in SB, SI, S and SM were significantly increased by 24.2%, 16.1%, 14.3% and 8.2%, respectively, compared with that of the control. The highest increase in seedcotton yield in SB was due to the greatest improvements in the contents of soil available nitrogen (N), phosphorus (P) and potassium (K); root biomass; NPK uptake by cotton; partitioning percentage of NPK to bolls; and canopy apparent photosynthesis rate. The lowest increase in seedcotton yield in SM was mainly ascribed to a reduction of 2.4–3.2 ℃ in the daily maximum temperature of topsoil at the early growth stage of cotton. Overall, compared with other crop straw returning modes, converting straw into biochar and incorporating it into fields could be an appropriate practice for sustaining high seedcotton yield in the barley-cotton rotation system.

Apparent photosynthesis of terrestrial mosses: An indicator of population functional health

Abstract Terrestrial mosses dominate the ground in many vegetation types and most are long-lived perennials with highly complex canopies. Long-term population health continues through numerous wetting and drying cycles; however, extreme drought or extended wet periods may create conditions that cause some parts of the population to die or remain inactive. I examined apparent photosynthesis of fully hydrated populations of four terrestrial species of mosses occurring in leaf-free mesohabitats in temperate deciduous forests of eastern North America in order to explore photosynthetic variability of both popula-tions and species. There was high variability in rates of apparent photosynthesis among the popula-tions of mosses for all four species examined in this study. Despite this variability within species, all four species achieved similar mean rates of photosynthesis. Two years after relocation to nearly bare ground habitats, populations of three of the four species achieved similar apparent photosynthetic rates as natural popula-tions, and functioned in a similar manner.

Atmospheric CO2 mole fraction affects stand-scale carbon use efficiency of sunflower by stimulating respiration in light.

Plant carbon-use-efficiency (CUE), a key parameter in carbon cycle and plant growth models, quantifies the fraction of fixed carbon that is converted into net primary production rather than respired. CUE has not been directly measured, partly because of the difficulty of measuring respiration in light. Here, we explore if CUE is affected by atmospheric CO2 . Sunflower stands were grown at low (200 μmol mol-1 ) or high CO2 (1000 μmol mol-1 ) in controlled environment mesocosms. CUE of stands was measured by dynamic stand-scale 13 C labelling and partitioning of photosynthesis and respiration. At the same plant age, growth at high CO2 (compared with low CO2 ) led to 91% higher rates of apparent photosynthesis, 97% higher respiration in the dark, yet 143% higher respiration in light. Thus, CUE was significantly lower at high (0.65) than at low CO2 (0.71). Compartmental analysis of isotopic tracer kinetics demonstrated a greater commitment of carbon reserves in stand-scale respiratory metabolism at high CO2 . Two main processes contributed to the reduction of CUE at high CO2 : a reduced inhibition of leaf respiration by light and a diminished leaf mass ratio. This work highlights the relevance of measuring respiration in light and assessment of the CUE response to environment conditions.

Cotton responds to different plant population densities by adjusting specific leaf area to optimize canopy photosynthetic use efficiency of light and nitrogen

Appropriate plant population density (PPD) is an important crop management practice for optimizing canopy light distribution and increasing canopy photosynthetic capacity in field-grown cotton (Gossypium hirsutum L.). A 2-year field experiment was conducted to determine how the PPD (7.5, 19.5 or 31.5 plantsm−2) of cotton affects canopy photosynthetic capacity and photosynthetic use efficiency of light and N. The results indicated that PPD significantly affected both leaf morphology and canopy photosynthetic characteristics. As PPD changed, cotton maximized canopy apparent photosynthetic light use efficiency (CAPLUE) and photosynthetic capacity by adjusting specific leaf area (SLA), which in turn affected leaf N distribution in the canopy. The SLA of all three canopy layers increased as PPD increased. In the upper canopy, canopy light interception and canopy apparent photosynthetic N use efficiency (CAPNUE) rose as SLA increased, but CAPLUE declined. As PPD increased, SLA in the mid- and lower-canopy layers increased significantly. This caused canopy apparent photosynthesis rate per leaf area (CAPLeaf) and CAPNUE to decline. Medium-PPD had the highest canopy apparent photosynthesis rate (CAP) and CAPLUE in the mid- and lower-canopy layers. As a result, medium-PPD had the highest whole-canopy photosynthetic capacity and CAPLUE in this study. Overall, the results indicated that optimal spatial distribution of both light and specific leaf area is key for efficient utilization of light and N in cotton canopies.

Slight shading after anthesis increases photosynthetic productivity and grain yield of winter wheat (Triticum aestivum L.) due to the delaying of leaf senescence

The solar radiation intensity and duration are continuously decreasing in the major wheat planting area of China. As a con-sequence, leaf senescence, photosynthesis, grain filling and thus wheat yield shall be affected by light deficiency. Therefore, two winter wheat (Triticum aestivum L.) cultivars, Tainong 18 (a large-spike cultivar) and Ji'nan 17 (a multiple-spike cultivar), were subjected to shading during anthesis and maturity under field condition in 2010–2011 and 2011–2012. Under the slight shading treatment (S1, 88% of full sunshine), leaf senescence was delayed, net photosynthesis rate (Pn) and canopy apparent photosynthesis rate (CAP) were improved, and thus thousand-kernel weight (TKW) and grain yield were higher as compared with the control. However, mid and severe shading (S2 and S3, 67 and 35% of full sunshine, respectively) led to negative effects on these traits substantially. Moreover, superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT) activities in flag leaf were significantly greater under slight shading than those in other treatments, while the malondialdehyde (MDA) content was less than that under other treatments. In addition, the multiple-spike cultivar is more tolerant to shading than large-spike cultivar. In conclusion, slight shading after anthesis delayed leaf senescence, enhanced photosynthesis and grain filling, and thus resulted in higher grain yield.

Reorganization of chloroplast ultrastructure associated with low-temperature hardening of Arabidopsis plants

When following low-temperature acclimation (5 days at 2°C) of cold-resistant plants of Arabidopsis (Arabidopsis thaliana Heynh. (L.), ecotype Columbia) in relation to the changes in chloroplast ultrastructure, we registered the high efficiency of hardening and the ability of hardened plants to lower a threshold of frost damage by about 3°C. During hardening, the area of grana in the chloroplasts more than doubled, with considerably increased numbers of thylakoids per granum and thylakoids per chloroplast. The rate of apparent photosynthesis decreased to lesser extent than the rate of dark respiration, as a result the content of soluble sugars increased fourfold, ensuring an adaptive reorganization of metabolism, which enabled the hardened plants to survive even at below-zero temperatures (up to −7°C). The authors conclude that a considerable increase in the number of thylakoids in the chloroplasts helps maintain photosynthesis at low above-zero temperatures and is a prerequisite for the accumulation of soluble sugars in Arabidopsis leaves.

Oxygen and radiation effects on C02 exchange in fight and in darkness of decaploid and hexaploid tall fescue (Festuca arundinacea Schreb.)

Rates of apparent photosynthesis (APS). photorespiration (PR), CO<sub>2</sub> compensation (I) and dark respiration (DR) were determined on attached shoots of decaploid (70 chromosomes) and a hexaploid (42 chromosomes) genotype of tall fescue (Festuca arundinacea Schreb.) using an infra red CO<sub>2</sub> analyzer arranged in a closed circuit system. Plants were grown at a photon flux density 500 µmol m<sup>-2</sup>s<sup>-1</sup> (400-700 nm) and at 25°C. Measurements were made at 25°C in O<sub>2</sub> concentrations of l, 21 and 100% and at irradiance of 500 or 1800 µmol m<sup>-2</sup>s<sup>-1</sup>. The decaploid exhibited rates of APS that was from 26 to 46% higher in 1 and 21% O<sub>2</sub> but not in 100% O<sub>2</sub>, than those of hexaploid. Rates of PR were positively related to rates of APS. Values of r were very similar for both genotypes, they were little affected by irradiance, and were a linear function of O<sub>2</sub> Concentration. The percentages of PR in true photosynthesis (TPS = APS+ PR) were also similar for the two genotypes, and were a linear function of O<sub>2</sub> concentration. Alternatively, rates of DR were by 16-26% higher in the hexaploid than decaploid genotype, and were little affected by O<sub>2</sub> concentration or by previous rates of APS.

Seasonal Photoprotective Responses in Needles of Korean Fir (Abies koreana) Over an Altitudinal Gradient on Mount Halla, Jeju Island, Korea

Chloroplast pigments and chlorophyll fluorescence were characterized in needles of Korean fir (Abies koreana) in summer, winter, and spring at three altitudes on Jeju Island, Korea. High light-harvesting efficiency (intrinsic photosystem II efficiency) and indirect evidence for high photosynthetic rates (high levels ofβ-carotene and chlorophyll b) during the growing season contrasted with mid-winter downregulation of light-harvesting efficiency involving retention of high zeaxanthin levels and locked-in photoprotective thermal dissipation (from low chlorophyll fluorescence emission). Neoxanthin levels were inversely correlated with sustained photoprotection in the winter, and lutein to xanthophyll cycle carotenoid levels decreased from summer to winter, suggesting that zeaxanthin plays the prominent role in winter photoprotection of Korean fir needles. Summer was apparently most conducive to photosynthesis, consistent with high levels of summer precipitation on Jeju Island, and in contrast to fir and other conifers in a climate with dry summers at high altitudes in Colorado, U.S.A., where studies have shown that the wet spring is the season most favorable for photosynthesis. Lastly, despite there being only 300 m difference in altitude among the three sites, there were discernible differences in (i) accumulation of zeaxanthin in winter (as an indicator for the severity of conditions, with highest levels at the highest altitude), (ii) apparent photosynthesis rates in summer (from β-carotene levels, with highest levels at the highest altitude), and (iii) transition to increased photosynthesis in spring (from fluorescence emission levels, slowest at the highest altitude).

Waterlogging of cotton calls for caution with N fertilization

The main objective of this investigation was to evaluate the effects of nitrogen on waterlogging resistance in terms of changes in dry-matter accumulation, root antioxidant enzyme activities, root vigor, and photosynthesis under waterlogging during the flowering and boll-development stage. Cotton plants grown in pots with three N levels (0, 4.5, and 9.0 g N pot−1, equivalent to 0, 240, and 480 kg N ha−1, respectively) were subjected to waterlogging for eight days and then permitted to recover for fifteen days. The dry weights of root and shoot were decreased by waterlogging, and were highest at 240 kg N ha−1. In waterlogged root, the activities of superoxide dismutase and catalase decreased and that of peroxidase increased in comparison with the control. The application of N increased the activities of catalase and peroxidase of both waterlogged root and the control, but decreased superoxide dismutase activity. Malondialdehyde content, an indicator of membrane lipid peroxidation, was significantly increased, and was lowest in the 240 kg N ha−1 N treatment during waterlogging. Both root vigor and canopy apparent photosynthesis rate, which were weakened by waterlogging, reached a peak at 240 kg N ha−1. At the 15th day after termination of waterlogging, N application promoted root vigor and canopy apparent photosynthesis rate of waterlogged cotton plants. These results indicated that an appropriate N supply (240 kg N ha−1) may contribute to waterlogging resistance of cotton by adjusting the antioxidant enzyme activities of root, reducing lipid peroxidation and boosting root vigor; however, excessive N supply (480 kg N ha−1) may lead to an adverse impact on waterlogging resistance of cotton. Therefore, the application of N should be reduced to decrease stress when waterlogging occurs, and additional N fertilizer may be used to promote cotton growth after waterlogging.

PHOTOSYNTHETIC CHARACTERISTICS AND PRODUCTIVITY OF THE COCONUT PALM

Among the tree crops in the tropics the coconut palm occupies an importantposition as a food, oil, and fibre crop. Productivity of crop species depends on thecombined effect of their genetic constitution, climate, nutrition and other bioticfactors. To increase the productivity of the coconut palm it is necessary to have abasic understanding of physiological processes such as assimilation of carbon andgrowth in relation to climatic factors.In-situ photosynthetic measurement of coconut seedlings using Li-COR 6500portable photosynthesis system revealed that their maximum photosynthetic capacityis attained at photosynthetic photon flux densities (PPFD) ranging from 1400-1700u moles photons m'2 S"1. The rate of apparent photosynthesis (A) of the coconutpalm varies between 2-15 a moi C02 m"2 S"1 depending on leaf age, nutritional status.and climatic factors. The rate of leaf respiration was closely similar in young andolder leaves ranging from - 2 to -1 fi mol C02m'2S"'. The measured light-useefficiency of the coconut palm was found to be 1.2 g MJ"1 and the conversionefficiency of solar energy was approximately 2.4%.Water deficit is the major constraint causing wide fluctuations in photosynthesis.Due to height of trees, the leaves in the canopy are exposed to a high wind velocityas well as water and thermal stresses. As a result, under soil water deficit conditionscoconut palms reduce excessive water loss and gaseous exchange by mid-day closureof stomata and maintain stomatal conductance at a lower level. However, the rateof apparent photosynthesis and the ratio of intercellular to ambient partial pressureof C 0 2 (P/PJ are not decreased proportionately with the stomatal conductance.

Parameters of photosynthesis light curve in Salix dasyclados and their changes during the growth season

A dependence of the photosynthesis rate on light is characterized by a number of parameters that are often used for comparison between plant species or for finding photosynthesis interconnections with other physiological processes. In order to properly assessed these parameters, we measured the maximum apparent photosynthesis rate (P max), dark respiration rate (R d), light compensation point (LCP), quantum yield corresponding to photosynthetic efficiency (QY), and the light saturation constant (K s), taking into consideration the leaf plastochron index during vegetation of one of the willow species (Salix dasyclados Wimn.). The P max value was the highest in the beginning of the growth season when the leaf reached 65% of its full area; after that P max slowly declined. The most important cardinal value for R d is its plateau reached by the end of leaf growth, i.e., later than the photosynthesis rate maximum. This plateau value also decreased during vegetation. The LCP value changed in the same way as R d but reached its plateau simultaneously with the photosynthesis rate maximum. QY also reached its maximum at the same time with the photosynthesis rate; during vegetation it changed more than twofold. The K s value also changed almost twofold during the season, reaching its maximum together or slightly later than the photosynthesis maximum and then remained constant. Thus, we have found significant changes in the parameters of the photosynthesis light curve during growth season. This shows that they can be used only after a thorough study of leaf development in each particular plant species. Usually performed measuring gas exchange parameters in fully developed leaves does not yield their maximum values and thus does not have any physiological sense.

Suppression of the source activity affects carbon distribution and frost hardiness of vegetating winter wheat plants

Effect of suppression of the source activity on some physiological characteristics of winter wheat (Triticum aestivum L., cv. Mironovskaya 808) was studied on plants grown in water culture. The plants were examined at the mixotrophic stage of growth period, during their transition from vegetative state to relative dormancy in autumn. The average temperature over 10 days of the experiment was 6°C at 9-h photoperiod and illuminance of 8–20 klx. The source strength was suppressed successively with a series of treatments: intact control plants (V1); plants with the seed endosperm removed (V2); plants with photosynthesis inhibited (V3); plants with the seed endosperm removed and photosynthesis inhibited (V4); plants with the seed endosperm removed, photosynthesis inhibited, and the root nutrient medium replaced with distilled water (V5). On the 6th–10th day of the experiment, the relative growth rate (RGR) was determined from dry weight increments. At the same time, the distribution of biomass among organs, the CO2 exchange rates (photosynthesis and dark respiration), the content and proportions of sugars (sucrose, glucose, and fructose), the total content of phenolic compounds and flavonoids, the index of membrane stability (IMS) in leaves, and frost hardiness of plants were measured. Frost hardiness of vegetating plants was shown to be inversely related to RGR (R = −0.906), dark respiration rate (R = −0.789), the percentage of sucrose in total sugar content (R = −0.737), leaf IMS (R = −0.390), and the rate of apparent photosynthesis (R = −0.288); it was directly proportional to the content of flavonoids (R =0.973), total phenols (R = 0.743), and sugars (R = 0.385). The role of modified source-sink relations in frost hardiness of vegetating plants at the stage of their transition to cold hardening is discussed. The differences between plants undergoing this transition and cold-hardened plants are considered, as well as the importance of phenolic compounds for the development of frost hardiness.

Effect of doubled CO2 on morphology: Inhibition of stomata development in growing birch (Betula platyphylla Suk.) leaves

Two-year old birch (Betula platyphylla Suk.) seedlings were grown in climatic chambers for 7 weeks under various conditions: (1) ambient CO2 concentration (350 ppm) and an ordinary nitrogen content in soil (2 mM NH4NO3); (2) ambient CO2 concentration and a high nitrogen rate (16 mM NH4NO3); (3) doubled CO2 concentration (700 ppm) and ordinary nitrogen content, and (4) doubled CO2 concentration and a high nitrogen rate. Doubled CO2 concentration in combination with the high nitrogen rate activated mostly seedling growth, e.g., stem thickening and leaf initiation. In this treatment, the maximum rate of apparent photosynthesis (A max) was twice as high as in control seedlings. At doubled CO2 concentration and ordinary nitrogen content, we observed the phenomenon of stomata absence from the upper leaf surface and doubling their number on the lower surface, whereas, at doubled CO2 concentration and a high nitrogen rate, stomata partition was essentially similar as in control leaves. The conclusion is that, when the balance between CO2 concentration and nitrogen rate is shifted, doubled CO2 concentration exerts a morphotropic effect on differentiation of young epidermal tissue.

Comparison of the Early Growth between Sugarcane and Sweet Sorghum.

サトウキビは, 光合成能力が高いことから, 高い乾物生産力が期待されている。しかし, 実際のサトウキビ収量は, 気象災害や緩慢な初期生長のため, 長い在圃期間に関わらず, 低いものとなっている。そこで, サトウキビの緩慢な初期生長の原因を探るため, 旺盛な生育を示すスイートソルガムとサトウキビの初期生長を比較した。分げつ性の異なるサトウキビ2品種と, スイートソルガム1品種をポット栽培し, 発芽後47日までの初期生長を調査した。その結果, スイートソルガムは, 茎長, 葉数および葉面積が大きく, 発芽47日後で, その乾物重はサトウキビの5倍に達した。両作物間で, 見かけの光合成速度の指標である純同化率に差は認められなかった。発芽後20日以降のスイートソルガムの葉面積拡大は著しかったが, 両作物間で葉身への乾物分配率に大きな差異は見られなかった。スイートソルガムは, 比葉面積が大きく, 同じ乾物量でサトウキビに比べ広い葉面積を確保していた。このことから, スイートソルガムの旺盛な初期生長は, 比葉面積の大きい葉身を迅速に拡大することで実現されていることが判明した。従って, サトウキビにおける初期生長の改善には, 比葉面積が一つの重要な指標となるものと考えられた。また, 群落生長の改善に有効な密植栽培では, 茎数過剰による生育後半の枯死茎発生が問題となっているが, 分げつ発生数は個体の乾物生産速度と無関係であったことから, 分げつ数の少ない品種を用いた密植栽培で, 茎数過剰を伴うことなく初期生長の改善が可能となるものと考えられた。

Photosynthetic use of light and inorganic carbon in air and water by the intertidal alga Petalonia fascia (Scytosiphonales, Phaeophyta)

SUMMARYThe photosynthetic performance of the intertidal alga Petalonia fascia (0. F. Muller) Kuntze (Scytosiphona‐ceae, Phaeophyta) has been investigated, both in air and water, by analyzing the relationship between apparent photosynthesis rate and photon irradiance and inorganic carbon. In relation to the use of photon irradiance, it was found that the net photosynthetic capacity in water was 5.7 times that in air (fully hydrated thallus). The light compensation point was achieved at 5.9 and 3.0 μmol photons m−2 s−1 in air and water, respectively. The light onset‐saturation parameter and the photosynthetic efficiency were 77% and 25% greater in water than in air, respectively. The dark respiration rate was one‐third greater when emersed in comparison to submersion conditions. These data suggest that the photosynthetic response to irradiance in P. fascia is similar to that in infralittoral species rather than the intertidal species. This assessment can be explained by the winter seasonality of the bladed stage of growth, when storms and waves permit a permanent hydrated status of P. fascia that in the intertidal zone. Moreover, the minimum tissue water content that permitted active photosynthesis in the alga was around 20%. The net photosynthetic capacity as a function of inorganic carbon (C) concentration in water was 1.5 times that in air. Photosynthesis was saturated in both media with respect to the availability of inorganic C in natural conditions. The affinity to inorganic C, and the carbon conductance, were two orders of magnitude higher in air than in water. However, the higher photosynthetic capacity when submerged in comparison to emersion conditions suggests that P. fascia can assimilate the external HCO3,– or the occurrence of a CO2 concentrating mechanism in this species.

Response of two potato clones (S. tuberosum L.) to contrasting temperature regimes in the field

Two potato clones (S. tuberosum L.) were grown in the field under contrasting temperature regimes during the crop cycle. Differential growth and yield was observed in the clones studied. Differences in yield were due to the decreased proportion of tubers larger than 3.5 cm in length as well as to the differences in dry weight and percent of dry matter in tubers. Yield reductions per plant were 52 and 94% for Alfa and Herta, respectively, in the warmer regime compared with the cooler regime. Apparent photosynthesis rates measured in Herta were maximum (45 umol.m−2.s−1) during tuber filling. Stomatal resistance and apparent photosynthesis rate were reduced by high temperature, indicating mesophyllic inhibition of photosynthesis. Dark respiration was promoted by moderately high temperature and differed significantly between clones, with Herta showing the higher rates.

SEASONAL VARIATIONS OF PHOTOSYNTHETIC PIGMENTS, TOTAL C, N, AND P CONTENT, AND PHOTOSYNTHESIS IN PHYLLARIOPSIS PURPURASCENS: (PHAEOPHYTA) FROM THE STRAIT OF GIBRALTAR

ABSTRACT Photosynthetic pigments, C, N, and P tissue composition, and photosynthetic rate were measured from April to October in the brown alga Phyllariopsis purpurascens (C. Agardh) Henry et South (Laminariales, Phaeophyta) growing at a 30‐m depth in the Strait of Gibraltar. Ir‐radiance reaching the population ranged from 13.5 to 27.5 mol.m‐2.mo‐1. The available light for this species, expressed as a percentage of the irradiance above the water, was 1.8%. Dissolved inorganic nitrogen forms, NO3‐and NH4+, were constant from April to October, whereas phosphate was depleted in August. Chlorophyll a decreased from 520.0 ± 165.0 to 199.6 ± 159.9 μg.g‐1 dry weight; in contrast, chlorophyll c and carotenoids did not change until September but increased threefold in October. C:N and N:P ratios changed in the same way and in the same range. They were constant until July but increased from 15–17 up to 42 (C:N) and from 14 to 40 (N:P) in October, suggesting a severe P limitation of growth of this species. The dark respiration rate and the light compensation point were constant from April to October (0.5 ± 0.1 μmol O2. m‐2.s‐1 and 6.5 ± 0.2 μmol.m‐2. s‐1, respectively), whereas the maximum rate of apparent photosynthesis, light onset saturation parameter, and half saturation constant for light were maximum in April to May (3.7 μmol O2. m‐2.s‐1and 40 and 41.5 μmol.m‐2. s‐1, respectively) and October (3.6 μmol O2. m‐2.s‐1 and 50 and 53.7 μmol.m‐2. s‐1, respectively). They were minimum in August (1.2 μmol O2.m‐2.s‐1 and 11.3 and 12 μmol.m‐2.s‐1, respectively). These minimum figures yielded a negative carbon budget in August and 0 in September, whereas it was positive the rest of the year. Photosynthetic efficiency, estimated by the ratio between maximum apparent photosynthesis and light half saturation constant, showed a strong agreement with productivity measured by means of an independent method. These results indicate that lamina expansion in this species is controlled by photosynthetic efficiency.