Response of cyanobacterial carbon concentrating system to light intensity: a simulated analysis

Cyanobacteria possess a delicate system known as the carbon concentrating mechanism (CCM), which can efficiently elevate the intracellular inorganic carbon (Ci) concentration via active transportation. The system requires energy supplied by photosystems; therefore, the activity of the Ci transporter is closely related to light intensity. However, the relationship between CCM and light intensity has rarely been evaluated. Here, we present an improved quantitative model of CCM in which light is incorporated, and developed a CCM model that modified after Fridlyand et a1. in 1996. Some equations used in this model were inducted to describe the relationship between transport capacity and light intensity, by which the response of the CCM to light change is simulated. Our results indicate that the efficiency of the carbon concentrating system is sensitive to light intensity. When the external Ci concentration was low, CO₂ uptake dominated the total Ci uptake with increasing light intensity, while under high external Ci concentrations HCO₃⁻ uptake primarily contributed to the total Ci uptake. Variations in the ratio of energy allocated between the transport systems could markedly affect the operation of CCM. Indeed, our simulations suggest that various combinations of Ci fluxes can provide a possible approach to detect the way by which the cell distributes energy produced by the photosystems to the two active Ci transport processes. The proportion of the energy consumed on CCM to the total energy expenditure for the fixation of one CO₂ molecule was determined at 18%–40%.     

Impacts of CO<Subscript>2</Subscript> enrichment on growth and photosynthesis in freshwater and marine diatoms

The physiological responses of Nitzschia palea Kvtzing, a freshwater diatom, to elevated CO2 were investigated and compared with those of a marine diatom, Chaetoceros muelleri Lemmermann previously reported. Elevated CO2 concentration to 700 μl/L increased the dissolved inorganic carbon （D!C） and lowered the pH in the cultures of N. palea, thus enhancing the growth by 4%-20% during the whole growth period. High CO2-grown N. palea cells showed lower levels of dark respiration rates and higher Ik values. Light-saturated photosynthetic rates and photosynthetic efficiencies decreased in N. palea with the doubling CO2 concentration in airflow to the bottom of cultures, although the doubling CO2 concentration in airflow to the surface cultures had few effects on these two photosynthetic parameters. N. palea cells were found to be capable of using HCO5 in addition to gaseous CO2, and the CO2 enrichment decreased their affinity for HCO5 and CO2. Although doubled CO2 level would enhance the biomass of N. patea and C. muelleri to different extents, compared with the marine diatom, it had a significant effect on the specific growth rates of N. palea. In addition, the responses of photosynthetic parameters of IV. palea to doubled CO2 concentration were almost opposite to those of C. muelleri.     

Comparative studies of inorganic carbon utilization inEmiliania huxleyi and some non-calcifying marine microalgae

Inorganic carbon utilization in the non-calcifying marine microalgae,Nannochloropsis oculata, Phaeodactylum tricornutum andPorphyridium purpureum was compared with high- and low-calcifying strains ofEmiliania huxleyi grown in artificial seawater medium aerated with either air (0.03% V/V CO₂) or CO₂-free air. For high-calcifying strain ofE. oculata andP. tricornutem, similar growth patterns were observed in air-and CO₂-free air-grown cultures.P. purpureum showed a less final cell density in CO₂-free air than in air-grown culture. However, low-calcifying strain ofE. huxleyi was able to grow only in air-grown culture, but not in CO₂-free air-grown culture. Measurements of alkalinity, pH, concentration of dissolved inorganic carbon (DIC) and free CO₂ showed different patterns of DIC utilization. WithN. oculata, P. tricornutum andP. purpureum the pattern of DIC utilization was characterized by an increase of pH and a decrease of DIC but a constant alkalinity in the cultures aerated with air or CO₂-free air, suggesting that bicarbonate utilization was concomitant with an efflux of OH⁻. Both alkalinity and pH were maintained rather constant in air-grown culture of low-calcifying strain ofE. huxleyi, suggesting that diffusive entry of CO₂ could meet the requirement of DIC for its photosynthesis and growth. High-calcifying strain ofE. huxleyi, however, showed a pattern of decrease of alkalinity and DIC but an almost constant pH, indicating that bicarbonate was the major form of inorganic carbon utilised by this organism and bicarbonate uptake is unlikely to be accompanied by an efflux of OH⁻. The final pH values reached byN. oculata, P. tricornutum andP. purpureum in a closed system were 10.75, 10.60 and 9.85 respectively, showing that bicarbonate utilisation is concomitant with an efflux of OH⁻. While the final pH of 8.4 in high-calcifyingE. huxleyi suggests that bicarbonate utilization was not accompanied by an efflux of OH⁻. Contribution No. 3557 from the Institue of Oceanology, Chinese Academy of Sciences. This work was supported by NERC grant GRE3/7853 U. K. and partly supported by Bio-Engineering Center, SSTC 96-C01-05-01.     

Inorganic carbon parameters responding to summer hypoxia outside the Changjiang Estuary and the related implications

The eutrophication, hypoxia and coastal acidification are attracting more and more attention. In this study, inorganic carbon parameters, including dissolved inorganic carbon (DIC), total alkalinity (TA) and calculated partial pressure of CO₂ (pCO₂), obtained from a summer cruise in August, 2009, were used to investigate their integrated response to biological processes accompanying the oxygen depletion in the areas off the Changjiang Estuary. According to the observations, the typical hypoxia occurred in the bottom water just outside the Changjiang Estuary with Dissolved Oxygen (DO) lower than 2.00 mg L^?1. The biological uptake in the surface water and the decomposition of organic matter in the bottom water were fully coupled with each other. The high concentration of Chl_a (Chl_a = 10.9 μg L^?1) and DO (9.25 mg L^?1), profoundly decreased DIC concentration (1828 μmol kg^?1) and elevated pH (8.42) was observed in the surface water. The correspondingly increased DIC and depletion of oxygen were observed in the bottom water. The semi-quantitative analysis proved that the locally-produced phytoplankton, determined by primary productivity, was deposited to the bottom and contributed about 76% of total amount of the organic carbon decomposition in the bottom. However, in the bottom hypoxia (DO = 2.05 mg L^?1) area observed in the Southern Zhejiang coastal water, the responding patterns of inorganic carbon parameters deviated from the previous one. The expanding of Changjiang Diluted Water (CDW), the adding of Hangzhou Bay water (with high DIC concentration) and Coastal Current together modify the DIC background value in this area, and the local degeneration and upwelling process may also help to offset the local DIC removed by net biological uptake in surface water. In addition, when the mixing occurring in autumn, which may break the summer stratification, the excess release of high DIC in the bottom water to the subsurface water could have an important influence on coastal acidification and the CO₂ uptake capacity in this area.     

CARBON DYNAMICS OF WETLAND IN THE SANJIANG PLAIN

1INTRODUCTIONWetlandsplayanimportant roleintheprocessofcar-bonstorage.Thetotalcarbonstoredindifferentkindsofwetlandsisabout15%-35%ofthetotalcarboninthegloballandsoils(POSTetal.,1982;GORHAM,1991).Inaddition,wetlandsaresignificantnaturalsources fortheatmospheric CH4 (MOORE,1994).It isestimatedthatabout110×1012gCH4 originates fromanaerobicdecompositioninthenaturalwetlands,CH4 emission fromthenaturalwetlandsis15%-30%oftheglobalCH4 emission andtheCH4 emission from thepeat land at hi…     

Potential effects of future adoption of the REDD mechanism as a preventive measure against deforestation and forest degradation in North Korea

This study assesses potential effects of adaption to climate change in the future as a carbon related value using a baseline and credit approach, considering the implementation of the Reducing Emissions from Deforestation and forest Degradation(REDD) mechanism. Basic data were obtained for implementing the REDD mechanism in the Democratic People's Republic of Korea(DPRK) for scientific decision-making to prevent deforestation and forest degradation. The potential effects according to the implementation of the REDD mechanism in the DPRK based on forest status data(the latest) are as follows. If the deforestation rate is reduced to a level below 6% through a 20-year REDD mechanism beginning in 2011, 0.01–11.64 C-tons of carbon credit per ha could be issued for DPRK. Converted into CO?-tons per ha, this amounts to 0.03–42.68 CO?-tons, which translates to a minimum of 226,000 CO?-tons and a maximum of 289,082,000 CO?-tons overall for forests in DPRK. In terms of carbon price, this measures up to 1.10 million USD–1.4 billion USD, considering that the REDD carbon price in voluntary carbon markets in 2010 was around 5 USD.     

Variation in Rubisco and other photosynthetic parameters in the life cycle of Haematococcus pluvialis

Cells of Haematococcus pluvialis Flot. et Will were collected in four different growth phases. We quantified the initial and total enzyme activity of ribulose-1,5-bisphosphate carboxylase (Rubisco) in crude extracts, and the relative expression of large-subunit ribulose-1,5-bisphosphate caboxylase / oxygenase (rbcL) mRNA. We measured the ratio of photosynthetic rate to respiration rate (P/R), maximal effective quantum yield of photosystem II (Fv/Fm), electron transport rate (ETR), actual photochemical efficiency of PSII in the light (ΦPSII), and non-photochemical quenching (NPQ). Green vegetative cells were found to be in the most active state, with a relatively higher P/R ratio. These cells also displayed the lowest NPQ and the highest Fv/Fm, ETR, and ΦPSII, indicating the most effective PSII. However, both Rubisco activity and rbcL mRNA expression were the lowest measured. In orange resting cysts with relatively lower P/R and NPQ, Rubisco activity and rbcL expression reached a peak, while Fv/Fm, ETR, and ΦPSII were the lowest measured. Taking into account the methods of astaxanthin induction used in industry, we suggest that Rubisco may participate in astaxanthin accumulation in H. pluvialis. A continuous and sufficient supply of a carbon source such as CO2 may therefore aid the large scale production of astaxanthin.     

CARBON CYCLE OF MARSH IN THE SANJIANG PLAIN

Peat~hisaprocessofbeinghelpfulfordecreasingtheincrementofopcontentintheair,whichiscausedbycombustionofdineralfuelsandhumanactivitiesinterrestrialecosystem.But,exploitingrnaxsh,eSPeCiallyPeatedtObefuels,impliesthatorgbocsubstanceaccUInulatedfroma~hereduringthepastthousandsofyearsisrapidlyOxidized.aamthemarShplaysanimPOrtantroleinthecycleofbiogaxhdristry.TheSanjiangPlainisalowplainformedbythecommonreactionoftheHeilongRiver,SonghuaherandWUSuliabover.Thetotalareais10.89X104klnZandmarsharea…     

Effects of environmental conditions and aboveground biomass on CO<Subscript>2</Subscript> budget in <Emphasis Type="Italic">Phragmites australis</Emphasis> wetland of Jiaozhou Bay,China

Estuarial saline wetlands have been recognized as a vital role in CO₂ cycling. However, insufficient attention has been paid to estimating CO₂ fluxes from estuarial saline wetlands. In this study, the static chamber-gas chromatography (GC) method was used to quantify CO₂ budget of an estuarial saline reed (Phragmites australis) wetland in Jiaozhou Bay in Qingdao City of Shandong Province, China during the reed growing season (May to October) in 2014. The CO₂ budget study involved net ecosystem CO₂ exchange (NEE), ecosystem respiration (R_eco) and gross primary production (GPP). Temporal variation in CO₂ budget and the impact of air/soil temperature, illumination intensity and aboveground biomass exerted on CO₂ budget were analyzed. Results indicated that the wetland was acting as a net sink of 1129.16 g/m²during the entire growing season. Moreover, the values of R_eco and GPP were 1744.89 g/m² and 2874.05 g/m², respectively; the ratio of R_eco and GPP was 0.61. Diurnal and monthly patterns of CO₂ budget varied significantly during the study period. R_eco showed exponential relationships with air temperature and soil temperature at 5 cm, 10 cm, 20 cm depths, and soil temperature at 5 cm depth was the most crucial influence factor among them. Meanwhile, temperature sensitivity (Q₁₀) of R_eco was negatively correlated with soil temperature. Light and temperature exerted strong controls over NEE and GPP. Aboveground biomass over the whole growing season showed non-linear relationships with CO₂ budget, while those during the early and peak growing season showed significant linear relationships with CO₂ budget. This research provides valuable reference for CO₂ exchange in estuarial saline wetland ecosystem.     

Carbon dynamics in woody biomass of forest ecosystem in China with forest management practices under future climate change and rising CO2 concentration

It is critical to study how different forest management practices affect forest carbon sequestration under global climate change regime. Previous researches focused on the stand-level forest carbon sequestration with rare investigation of forest carbon stocks influ- enced by forest management practices and climate change at regional scale. In this study, a general integrative approach was used to simulate spatial and temporal variations of woody biomass and harvested biomass of forest in China during the 21st century under dif- ferent scenarios of climate and CO2 concentration changes and management tasks by coupling Integrated Terrestrial Ecosystem Carbon budget （InTEC） model with Global Forest Model （G4M）. The results showed that forest management practices have more predominant effects on forest stem stocking biomass than climate and CO2 concentration change. Meanwhile, the concurrent future changes in cli- mate and CO2 concentration will enhance the amounts of stem stocking biomass in forests of China by 12%-23% during 2001-2100 relative to that with climate change only. The task for maximizing stem stocking biomass will dramatically enhance the stem stocking biomass from 2001~100, while the task for maximum average increment will result in an increment of stem stocking biomass before 2050 then decline. The difference of woody biomass responding to forest management tasks was owing to the current age structure of forests in China. Meanwhile, the sensitivity of long-term woody biomass to management practices for different forest types （coniferous forest, mixed forest and deciduous forest） under changing climate and CO2 concentration was also analyzed. In addition, longer rotation length under future climate change and rising CO2 concentration scenario will dramatically increase the woody biomass of China during 2001~100. Therefore, our estimation indicated that taking the role of forest management in the carbon cycle into the consideration at regional or national level is very important to project the forest carbon sequestration under future climate change and rising atmospheric CO2 concentration.     

RIVERINE INORGANIC CARBON DYNAMICS： OVERVIEW AND PERSPECTIVE

1INTRODUCTION River systems are the major linkage between the land and the ocean, not only transporting carbon from terres- trial environment to the ocean, but also exchanging CO2 with the atmosphere, actively involved in the global car- bon biogeochemical cycle (RICHEY et al., 2002; COLE and CARACO, 2001). The inorganic carbon, mainly o- riginating from soil CO2, carbonate minerals and atmo- sphericCO2,constitutedthegreatpart(about 60%) ofthe riverine carbon exported to the ocean…     

Paleoproductivity evolution in the West Philippine Sea during the last 700 ka

In order to reconstruct the paleoproductivity evolution history of the West Philippine Sea during the last 700 ka,the vertical gradient of δ 13 C in dissolved inorganic carbon(δ 13 C between those of foraminifera Pulleniatina obliquiloculata and Cibicidoides wuellerstorfi) and planktonic foraminiferal assemblages were analysed in piston Core MD06-3047 retrieved from the Benham Rise(east of the Luzon Island).Paleoproductivity evolution in the West Philippine Sea during the last 700 ka is closely related to glacial-interglacial cycles and precession-controlled insolation.Controlling factors of paleoproductivity could have been both thermocline fluctuations related with ENSO-like processes and eolian input associated with East Asian winter monsoon,and the former could have been the primary factor.A higher productivity and a shallower thermocline coeval with the occurrence of low CO 2 concentrations in the EPICA Dome C ice core might indicate that biological export production in the low-latitude could act as a significant sink in the global carbon cycle,and modify atmospheric CO 2 concentrations.Spectral analysis further reveals that the paleoproductivity is mainly controlled by thermocline fluctuations subjected to ENSO processes responding to processional variability of insolation.High coherences in eccentricity,obliquity and precession periods further revealing the close link between thermocline fluctuations,paleoproductivity and atmospheric CO 2 levels.     

Carbon dioxide partial pressure and carbon fluxes of air-water interface in Taihu Lake, China

1 INTRODUCTION Carbon dioxide (CO2) is principal greenhouse gas. Its air-water exchange is important in terrestrial ecosystems for climate change (Frankignoulle et al., 1998; Schimel et al., 2001). The direction of CO2 gas movement depends on the CO2 concentration gradient between air and surface water. The amount of CO2 exchange is related to the gas exchange coefficient, k. All lakes, with their small area but large atmospheric CO2 flux are important to under-stand the CO2 fluxes …     

Effect of climate change on seasonal water use efficiency in subalpine <Emphasis Type="Italic">Abies fabri</Emphasis>

Abies fabri is a typical subalpine dark coniferous forest in southwestern China. Air temperature increases more at high elevation areas than that at low elevation areas in mountainous regions, and climate change ratio is also uneven in different seasons. Carbon gain and the response of water use efficiency (WUE) to annual and seasonal increases in temperature with or without CO₂ fertilization were simulated in Abies fabri using the atmospheric-vegetation interaction model (AVIM2). Four future climate scenarios (RCP2.6, RCP4.5, RCP6.0 and RCP8.5) from the Coupled Model Intercomparison Project Phase 5 (CMIP5) were selectively investigated. The results showed that warmer temperatures have negative effects on gross primary production (GPP) and net primary production (NPP) in growing seasons and positive effects in dormant seasons due to the variation in the leaf area index. Warmer temperatures tend to generate lower canopy WUE and higher ecosystem WUE in Abies fabri. However, warmer temperature together with rising CO₂ concentrations significantly increase the GPP and NPP in both growing and dormant seasons and enhance WUE in annual and dormant seasons because of the higher leaf area index (LAI) and soil temperature. The comparison of the simulated results with and without CO₂ fertilization shows that CO₂ has the potential to partially alleviate the adverse effects of climate warming on carbon gain and WUE in subalpine coniferous forests.     

Distribution of Dissolved Inorganic Carbon （DIC） and Its Related Parameters in Seawater of the North Yellow Sea and off the Qingdao Coast in October, 2007

Data on the distribution of dissolved inorganic carbon (DIC) were obtained from two cruises in the North Yellow Sea (NYS) and off the Qingdao Coast (QC) in October, 2007. Carbonate parameters were calculated. The concentrations of DIC are from 1.896–2.229 mmolL⁻¹ in the NYS and from 1.939–2.032 mmolL⁻¹ off the QC. In the southwest of the NYS, DIC in the upper layers decreases from the north of the SP (Shandong Peninsula) shelf to the center of the NYS; whereas in the lower layers DIC increases from the north of the SP shelf to the center of the NYS and South Yellow Sea. In the northeast of the NYS, DIC in all layers increases from the YR (Yalu River) estuary to the centre of the NYS. The distribution of DIC in NYS can be used as an indicator of Yellow Sea Cold Water Mass (YSCWM). Air-sea CO₂ fluxes were calculated using three models and the results suggest that both the NYS and the QC waters are potential sources of atmospheric CO₂ in October.     

Diurnal variation of soil CO<Subscript>2</Subscript> efflux and its optimal measuring time-window of temperate meadow steppes in western Songnen Plain,China

In order to study the diurnal variation of soil CO_2 efflux from temperate meadow steppes in Northeast China, and determine the best time for observation, a field experiment was conducted with a LI-6400 soil CO_2 flux system under five typical plant communities(Suaeda glauca(Sg), Chloris virgata(Cv), Puccinellia distans(Pd), Leymus chinensis(Lc) and Phragmites australis(Pa)) and an alkali-spot land(As) at the meadow steppe of western Songnen Plain. The results showed that the diurnal variation of soil CO_2 efflux exhibited a single peak curve in the growing season. Diurnal maximum soil respiration(Rs) often appeared between 11:00 and 13:00, while the minimum occurred at 21:00–23:00 or before dawn. Air temperature near the soil surface(Ta) and soil temperature at 10 cm depth(T10) exerted dominant control on the diurnal variations of soil respiration. The time-windows 7:00–9:00 could be used as the optimal measuring time to represent the daily mean soil CO_2 efflux at the Cv, Pd, Lc and Pa sites. The daily mean soil CO_2 efflux was close to the soil CO_2 efflux from 15:00 to 17:00 and the mean of 2 individual soil CO_2 efflux from 15:00 to 19:00 at the As and Sg sites, respectively. During nocturnal hours, negative soil CO_2 fluxes(CO_2 downwards into the soil) were frequently observed at the As and Sg sites, the magnitude of the negative CO_2 fluxes were 0.10–1.55 μmol/(m~2·s) and 0.10–0.69 μmol/(m~2·s)at the two sites. The results implied that alkaline soils could absorb CO_2 under natural condition, which might have significant implications to the global carbon budget accounting.     

Effects of temperature,soil moisture,soil type and their interactions on soil carbon mineralization in Zoigê alpine wetland,Qinghai-Tibet Plateau

Wetland stores substantial amount of carbon and may contribute greatly to global climate change debate. However, few researches have focused on the effects of global climate change on carbon mineralization in Zoigê al-pine wetland, Qinghai-Tibet Plateau, which is one of the most important peatlands in China. Through incubation ex-periment, this paper studied the effects of temperature, soil moisture, soil type (marsh soil and peat soil) and their in-teractions on CO2 and CH4 emission rates in Zoigê alpine wetland. Results show that when the temperature rises from 5℃ to 35℃, CO2 emission rates increase by 3.3-3.7 times and 2.4-2.6 times under non-inundation treatment, and by 2.2-2.3 times and 4.1-4.3 times under inundation treatment in marsh soil and peat soil, respectively. Compared with non-inundation treatment, CO2 emission rates decrease by 6%-44%, 20%-60% in marsh soil and peat soil, respec-tively, under inundation treatment. CO2 emission rate is significantly affected by the combined effects of the tempera-ture and soil type (p < 0.001), and soil moisture and soil type (p < 0.001), and CH4 emission rate was significantly af-fected by the interaction of the temperature and soil moisture (p < 0.001). Q10 values for CO2 emission rate are higher at the range of 5℃-25℃ than 25℃-35℃, indicating that carbon mineralization is more sensitive at low temperature in Zoigê alpine wetland.     

Estimating areal carbon fixation of intertidal macroalgal community based on composition dynamics and laboratory measurements

The community dynamics and potential carbon ?xation of intertidal macroalgae were investigated monthly from April 2014 to April 2015 in the northwest coast of Yellow Sea. Seasonal variations in biomass and carbon ?xation were presented and showed close relationship with community structure.The carbon ?xation rate ranged from 0.48±0.13 mg C/(g FW ·d) to 4.35±0.12 mg C/(g FW ·d). Sargassum thunbergii, Chondrus ocellatus and Ulva intestinalis were three most in?uential species which contributed27%, 21.9% and 18.5% variation of carbon ?xation rate, respectively. Standing carbon stocks ranged from7.52 g C/m~2 to 41.31 g C/m~2, and estimated carbon stocks varied from 11.77 g C/m 2 to 96.49 g C/m~2. The larger dif ference between estimated and standing carbon stocks implied that more ?xed carbon was exported from the community in summer and autumn than in winter. This study suggested that intertidal macroalgal community could provide a potential function in carbon ?xation of coastal ecosystem.     

Effect of NH4-non the pigment content ofLaminaria japonica

Experiments withLaminaria japonica were conducted in Meidao Bay and Pier Bay, Qingdao, China, Nitrogen-starved plants were fertilized intermittently with 7.1 mM NH₄−N solution for 1 hour at 3 day intervals, after which chlorophyll a, fucoxanthin, chlorophyll c and β-carotene contents were analyzed. Photosynthetic and growth rates of plants and nitrogen content of seawater were determined. their contents of chlorophyll a, fucoxanthin, chlorophyll c and β-carotene were 1.65, 0.67, 0.33 and 0.06 mg.dm⁻² respectively, or 2.46, 2.03, 1.86 and 1.81 times those of the controls. The ratio of fucoxanthin to chlorophyll a in nitrogen-enriched plants was lower than that of the controls. Normal growth rate of the plants (2 cm·day⁻¹ in length) were reached when the chlorophyll a content exceeded 0.1 mg·g⁻¹ fresh wt., indicating that chlorophyll a content can serve as an indicator of normal growth. Experimental results show that seawater is regarded as fertile for the normal growth ofLaminaria if the total inorganic nitrogen (including ammonium salt, nitrate and nitrite) content in seawater is about 2 μm, and infertile if less than 1 μm, in which case fertilizer should be applied. Contribution No. 1703 from the Institute of Oceanology, Academia Sinica     

Hydrogen photoproduction ofA. Variabilis incorporated in a photobioreactor

H₂ photoproduction and nitrogenase activities in two strains ofAnabaena variabilis marked wild type ATCC 29413 and mutant PK84 exposed to thermal stress (temperature higher than the normal incubation temperature of 30°C) were studied. Cultures of both strains collected from any interval of logarithmic growth phase exhibited high H₂ photoproduction and nitrogenase activities when exposed to limited time heat shock during the assay process. In contrast, the algal H₂ photoproduction rate of both strains fluctuated with long term thermal stress caused by increasing the growth temperature from 30°C to 36°C.

The changes of nitrogenase (the key H₂ photobiosynthetic enzyme) activities in the mutant PK84 showed variation tendency similar to that of H₂ photoproduction during exposure to thermal stress, indicating that fluctuation of H₂ photoproduction in the mutant was mainly due to the variation of nitrogenase activities. A temporary maximal H₂ photoproduction in the mutant PK84 (wild type ATCC29413) was observed when cells grew at 36°C for 14 (6) days. However, the responses of nitrogenase activities in the wild type to thermal stress were not completely similar to those in the mutant in spite of similar variations of H₂ photoproduction in both strains. The data obtained in these studies suggested that the activities of other enzymes (in the wild strain) involved in H₂ photoproduction were affected by thermal stress since H₂ photoproduction maximized or dropped to 0 without variation tendency similar to that of nitrogenase activities.

Furthermore, an enhancement of H₂ photoproduction speed of the mutant strain cultured in a 4.4 L laboratory photobioreactor was also observed when it was subjected to short time continuous charge of argon, and temperature rise.

All these results indicated that high temperature plays an important role in the photo-autotrophic H₂ photoproduction, and that long term thermal stress is unfavourable for net H₂ photoproduction in both strains ofA. variabilis though short-time heat shock is conducive to H₂ photoproduction.