Simulation of forest carbon dynamics based on a dry-matter production model

Effects of dry season upon a tropical rainforest ecosystem are analysed by employing the microcomputer model developed in a previous paper (Oikawa, 1985). Surplus production (P _s) illustrated in a three-dimensional figure linearly decreases with the length of dry season (λ). Simulation experiments demonstrate that all the three strata constituting the tropical rainforest ecosystem model are able to exist stably and perpetually unless λ exceeds four months. However, it is suggested that the dry season lasting five months brings about a transition from a tropical rainforest to a subtropical deciduous forest, because the upper story fails in a stable and perpetual occurrence at λ =5 months. Though the total living phytomass gradually decreases with prolonged dry season within four months, supplementary increase of living phytomass is observed in the middle story. A considerable amount of soil organic dead accumulated is also observed with increasing dry season, so that fairly constant ecosystem biomass including soil organic dead is predicted independent of the length of dry season so long as it is less than five months.     

Simulation of forest carbon dynamics based on a dry-matter production model

A microcomputer model for forest carbon dynamics with five functional comparments (atmosphere, foliage, woody-parts, roots and dead biomass in the soil) is constructed which incorporates dry-matter production processes of trees such as photosynthesis, respiration and allocation of photosynthate. The effect of photosynthesis rate at saturated light and dark respiration rate of a single leaf upon surplus production (P _s) is three-dimensionally illustrated as a function of cumulative leaf area index (LAI) and extinction coefficient of light. Probable values of the physiological parameters in this model are determined by repeated simulation experiments. The successional pattern during a period of 100 years is simulated, demonstrating stable and perpetual occurrence of a tropical rainforest ecosystem composed of three strata. The model is also analyzed in terms of response of relative initial density of trees, thereby displaying the law of constant final yield in a forest ecosystem. The model outputs of carbon fluxes and phytomasses at the steady state agree quite well with field data already obtained from a tropical rainforest at Pasoh.     

Photosynthetic responses to overnight frost in Eucalyptus nitens and E. globulus

Significant expansion in the area of eucalypt plantations in Tasmania has led to their establishment at altitudes that are close to the upper limits of the planting distributions of Eucalyptus nitens and E. globulus, the main species planted. This has implications for plantation productivity. We investigated the processes that limit productivity in these environments through a study of freezing-induced depression of photosynthesis of E. nitens saplings in the field and plantlets of E. nitens and E. globulus clones in a controlled environment cabinet. In the field consecutive frosts of around –4.6°C had a cumulative effect, reducing maximum net photosynthesis ( A _max) by 17%, and then a further 9%, respectively, compared with saplings insulated from the frosts. Shading saplings pre-dawn had no effect on A _max measured after 1030 hours indicating that the reduction in A _max at this time was independent of photoinhibition. Recovery of A _max to pre-frost levels required at least two consecutive frost-free nights and was dependent on the severity of frost. Photosynthetic light response curves indicated that reduced A _max was associated also with decreased quantum yield and stomatal conductance. Similar intracellular carbon dioxide concentration between exposed and insulated saplings indicated that low stomatal conductance did not limit photosynthesis through carbon dioxide limitation. The timing of frost events was critical: E. nitens saplings took less time to recover from reduced A _max in the field when they were hardened. Unhardened plantlets of E. nitens and E. globulus clones had greater reduction of A _max and took longer to recover from frost events than hardened plantlets. E. globulus was more susceptible to frost-induced reduction of A _max than E. nitens. This is consistent with its planting range which is restricted to mild sites compared with that of E. nitens.     

Changes in specific photosynthetic rate of oceanic phytoplankton from the northeast Pacific Ocean

The study is based on data (n=244) from light-saturation experiments utilizing artificial incubation under fluorescent light. Values of maximum photosynthetic rate,P _max, and the light intensity at which it takes place,I _max, are estimated by non-linear regression using stepwise Gauss-Newton iterations. Estimated values ofP _max ranged from 0.85 to 5.48 mg C (mg Chla·h)^?1;I _max varied from 2.35 to 5.52 cal (cm²·h)^?1. The effects of time (months) and depth (illumination levels) and their interaction are evaluated by analysis of covariance using a linear model. A significant time-depth interaction is noted: The maximum specific primary productivity occurred in the surface layers during March, at the 50% light level during April, and at 1% level during May. Estimates ofP _max from simulated in situ primary productivity experiments for the same period are lower than those from light-saturation experiments. A comparison of data from light-saturation and simulated in situ experiments indicated that effects of duration of experiments and the quality of available light may affect primary productivity data considerably.     

Variability of photosynthesis-irradiance curves and ecosystem respiration in a small river

• 1 We investigated photosynthesis‐irradiance relationships (P‐I curves; P = oxygen production rate due to photosynthesis, I = light irradiance rate at the water surface) and ecosystem respiration in a 9 km long reach of a river that is characterised by light conditions favouring primary production, high ambient nutrient concentrations, a high re‐aeration rate, and frequent spates. We addressed the question of how disturbances (spates) and season influence photosynthesis and ecosystem respiration.
• 2 We used an oxygen mass‐balance model of the river to identify ecosystem respiration rates and the two parameters of a hyperbolic P‐I function (P_max = maximum oxygen production rate due to photosynthesis, α = the initial slope of the P‐I function). The model was fitted to dissolved oxygen concentrations quasi‐continuously recorded at the end of the reach. We estimated parameters for 137 three‐day periods (during the years 1992–97) and subsequently explored the potential influence of season and disturbances (spates) on P_max, α and ecosystem respiration using stepwise regression analysis.
• 3 Photosynthesis‐irradiance relationships and ecosystem respiration were subject to distinct seasonal variation. Only a minor portion of the variability of P‐I curves could be attributed to disturbance (spates), while ecosystem respiration did not correlate with disturbance related parameters. Regular seasonal variation in photosynthesis and ecosystem respiration apparently prevailed due to the absence of severe disturbances (a lack of significant bedload transport during high flow).

     

Studies on the dynamic properties of terrestrial ecosystems based on a simulation model II. Tropical rainforest dynamics and stability as influenced by stem mortality

Further analysis of tropical rainforest dynamics and stability in relation to stem mortality has been conducted using a microcomputer model developed in a previous study (Oikawa, 1985). By simulation experiments covering a period of 100 years, the effects of changing stem mortality (δc) upon a tropical rainforest were investigated. Increasing stem mortality ranging from a standard value (3%yr⁻¹) to a 4-fold value (12%yr⁻¹) brings about decreases in stem biomass and thus total living biomass, and a contrasting increase of stem litterfall flux at the steady state of the forest ecosystem. At the same time, the decreased stem biomass at the steady state is predicted to result in increases of gross production (P _g) and net production (P _n), and an improvement in production efficiency of the model rainforest expressed as theP _n/P_g ratio. similar simulation experiments predict that the improved production efficiency in the forest with a 4-fold stem mortality is able to enhance tolerance to less productive environments such as a prolonged dry season or a reduced incident light flux density. On the other hand, the standard stem mortality (δ_c=3%yr⁻¹), which was estimated as a probable value for the Pasoh forest, West Malaysia, is considered to approximate the lower threshold necessary for attaining forest stability. Based on the results obtained, the significance of δ_c for the dynamics and stability of a tropical rainforest ecosystem is discussed in relation to the competition and tolerance of trees. In addition, the effectiveness of the simulation approach adopted here is emphasized. Titles are tentative translations by the author for original titles in Japanese.     

A simple calibrated model of Amazon rainforest productivity based on leaf biochemical properties

A simple ‘big leaf’ ecosystem gas exchange model was developed, using eddy covariance data collected at an undisturbed tropical rainforest in south-western Amazonia (Brazil). The model used mechanistic equations of canopy biochemistry combined with an empirical stomatal model describing responses to light, temperature and humidity. After calibration, the model was driven using hourly data from a weather station at the top of the tower at the measurement site, yielding an estimate of gross primary productivity (annual photosynthesis) in 1992/1993 of about 200 mol C m^?2 year ^?. Although incoming photon flux density emerged as the major control on photosynthesis in this forest, at a given PAR CO₂ assimilation rates were higher in the mornings than in the afternoons. This was attributable to stomatal closure in the afternoon in response to increasing canopy-to-air vapour pressure differences. Although most morning gas exchange was clearly limited by the rate of electron transport, afternoon gas exchange was generally observed to be very nearly co-limited by both Rubisco activity (V_max) and electron transport rate. The sensitivity of the model to changes in nitrogen allocation showed that the modelled ratio of V_max to electron transport (J_max) served nearly to maximize the annual carbon gain, and indeed, would have resulted in almost maximum annual carbon gain at the pre-industrial revolution atmospheric CO₂ concentration of 27 Pa. Modelled gross primary productivity (GPP) was somewhat lower at 27 Pa, being about 160 mol C m^?2 year^?1. The model suggests that, in the absence of any negative feedbacks on GPP, future higher concentrations of atmospheric CO₂ will continue to increase the GPP of this rainforest, up to about 230 mol C m^?2 year^?1 at 70 Pa.     

Small tropical forest trees have a greater capacity to adjust carbon metabolism to long-term drought than large canopy trees

The response of small understory trees to long-term drought is vital in determining the future composition, carbon stocks and dynamics of tropical forests. Long-term drought is, however, also likely to expose understory trees to increased light availability driven by drought-induced mortality. Relatively little is known about the potential for understory trees to adjust their physiology to both decreasing water and increasing light availability. We analysed data on maximum photosynthetic capacity (J_max, V_cmax), leaf respiration (R_leaf), leaf mass per area (LMA), leaf thickness and leaf nitrogen and phosphorus concentrations from 66 small trees across 12 common genera at the world's longest running tropical rainfall exclusion experiment and compared responses to those from 61 surviving canopy trees. Small trees increased J_max, V_cmax, R_leaf and LMA (71, 29, 32, 15% respectively) in response to the drought treatment, but leaf thickness and leaf nutrient concentrations did not change. Small trees were significantly more responsive than large canopy trees to the drought treatment, suggesting greater phenotypic plasticity and resilience to prolonged drought, although differences among taxa were observed. Our results highlight that small tropical trees have greater capacity to respond to ecosystem level changes and have the potential to regenerate resilient forests following future droughts.     

Photosynthetic Characteristics,Dark Respiration,and Leaf Mass Per Unit Area in Seedlings of Four Tropical Tree Species Grown Under Three Irradiances

We investigated the effect of growth irradiance (I) on photon-saturated photosynthetic rate (P _max), dark respiration rate (R _D), carboxylation efficiency (CE), and leaf mass per unit area (LMA) in seedlings of the following four tropical tree species with contrasting shade-tolerance. Anthocephalus chinensis (Rubiaceae) and Linociera insignis (Oleaceae) are light-demanding, Barringtonia macrostachya (Lecythidaceae) and Calophyllum polyanthum (Clusiaceae) are shade-tolerant. Their seedlings were pot-planted under shading nets with 8, 25, and 50 % daylight for five months. With increase of I, all species displayed the trends of increases of LMA, photosynthetic saturation irradiance, and chlorophyll-based P _max, and decreases of chlorophyll (Chl) content on both area and mass bases, and mass-based P _max, R _D, and CE. The area-based P _max and CE increased with I for the light-demanders only. Three of the four species significantly increased Chl-based CE with I. This indicated the increase of nitrogen (N) allocation to carboxylation enzyme relative to Chl with I. Compared to the two shade-tolerants, under the same I, the two light-demanders had greater area- and Chl-based P _max, photosynthetic saturation irradiance, lower Chl content per unit area, and greater plasticity in LMA and area- or Chl-based P _max. Our results support the hypothesis that light-demanding species is more plastic in leaf morphology and physiology than shade-tolerant species, and acclimation to I of tropical seedlings is more associated with leaf morphological adjustment relative to physiology. Leaf nitrogen partitioning between photosynthetic enzymes and Chl also play a role in the acclimation to I.     

Natural selection on ecophysiological traits of a fern species in a temperate rainforest

Unlike other species of the genus Blechnum, the fern Blechnum chilense occurs in a wide range of habitats in Chilean temperate rainforest, from shaded forest understories to abandoned clearings and large gaps. We asked if contrasting light environments can exert differential selection on ecophysiological traits of B. chilense. We measured phenotypic selection on functional traits related to carbon gain: photosynthetic capacity (A _max), dark respiration rate (R _d), water use efficiency (WUE), leaf size and leaf thickness in populations growing in gaps and understorey environments. We assessed survival until reproductive stage and fecundity (sporangia production) as fitness components. In order to determine the potential evolutionary response of traits under selection, we estimated the genetic variation of these traits from clonally propagated individuals in common garden experiments. In gaps, survival of B. chilense was positively correlated with WUE and negatively correlated with leaf size. In contrast, survival in shaded understories was positively correlated with leaf size. We found positive directional fecundity selection on WUE in gaps population. In understories, ferns of lower R _d and greater leaf size showed greater fecundity. Thus, whereas control of water loss was optimized in gaps, light capture and net carbon balance were optimized in shaded understories. We found a significant genetic component of variation in WUE, R _d and leaf size. This study shows the potential for evolutionary responses to heterogeneous light environments in functional traits of B. chilense, a unique fern species able to occupy a broad successional niche in Chilean temperate rainforest.     

The light-climate of Loch Leven, a shallow Scottish lake, in relation to primary production by phytoplankton

Seasonal changes in incident irradiance and underwater light penetration at Loch Leven from 1968 to 1971 are discussed in relation to the photosynthetic behaviour and crop density of phytoplankton. Light extinction was highest in the blue and lowest in the orange spectral regions, a pattern typical of other turbid waters. Euphotic depth varied between 1·2 and 7·4 m and was on average c. three times the Secchi disc transparency. Underwater light extinction depended chiefly on phytoplankton crop density (estimated as chlorophyll a). Despite the shallowness and wind-exposed situation of the loch there was no evidence of appreciable light extinction due to sediment disturbance. Possible causes of variability in the relationship between the minimum vertical extinction coefficient (k _min) and the concentration of chlorophyll a are discussed. The value of k_s, the increment in k_min per unit increment in algal concentration, was estimated from field data as 0·0086 In units per mg chl a/m² and from laboratory spectroradiometer data as 0·0079 In units per mg chl a/m². These k_s values imply theoretical upper limits for the amount of chlorophyll a in the euphotic zone (Σn _max) of 430 and 468 mg chl a/m², respectively. Observed euphotic chlorophyll a contents (Σn) were sometimes close to these upper limits. Typical photosynthesis/depth profiles are described. Profile area is shown to be related to the logarithm of the ratio between surface-penetrating irradiance (I_o') and the irradiance (I_k) defining the onset of light-saturation of photosynthesis. Standardized profiles, plotted on a common scale of ‘optical depth’, are used to illustrate the relatively minor influence of variations in I_o' and I_k on hourly rates of photosynthesis per unit area. The saturation parameter (I_k) generally increased as photosynthetic capacity (P_max) increased; the temperature-dependence of I_k is explained by the temperature-dependence of the enzyme-controlled (dark) reactions of photosynthesis, which control P_max. A spring peak in the ratio between surface penetrating irradiance (I_o') and I_k is interpreted as a result of a lag in the seasonal increase in water temperature with increase in surface irradiance. The gradient (K') of the linear light-limited region of the photosynthesis-irradiance curve showed little variation and had an average value of 0·31 mg O₂/mg chl a.h per 1 W/m² (PAR). Interactions between mixed depth, underwater light extinction and phytoplankton productivity are discussed; comparisons are made with other shallow, optically deep lakes.     

Impact of severe dry season on net ecosystem exchange in the Neotropical rainforest of French Guiana

The lack of information on the ways seasonal drought modifies the CO₂ exchange between Neotropical rainforest ecosystems and the atmosphere and the resulting carbon balance hinders our ability to precisely predict how these ecosystems will respond as global environmental changes force them to face increasingly contrasting conditions in the future. To address this issue, seasonal variations in daily net ecosystem productivity (NEP_d) and two main components of this productivity, daily total ecosystem respiration (R_Ed) and daily gross ecosystem productivity (GEP_d), were estimated over 2 years at a flux tower site in French Guiana, South America (5 °16′54″N, 52 °54′44″W). We compared seasonal variations between wet and dry periods and between dry periods of contrasting levels of intensity (i.e. mild vs. severe) during equivalent 93‐day periods. During the wet periods, the ecosystem was almost in balance with the atmosphere (storage of 9.0 g C m^?2). Seasonal dry periods, regardless of their severity, are associated with higher incident radiation and lower R_Ed combined with reduced soil respiration associated with low soil water availability. During the mild dry period, as is normally the case in this region, the amount of carbon stored in the ecosystem was 32.7 g C m^?2. Severe drought conditions resulted in even lower R_Ed, whereas the photosynthetic activity was only moderately reduced and no change in canopy structure was observed. Thus, the severe dry period was characterized by greater carbon storage (64.6 g C m^?2), emphasizing that environmental conditions, such as during a severe drought, modify the CO₂ exchange between Neotropical rainforest ecosystems and the atmosphere and potentially the resulting carbon balance.     

Intracellular responses from the photosensitive pineal organ of the teleost,Phoxinus phoxinus

Summary Intracellular potentials from the isolated dark-adapted pineal organ ofPhoxinus phoxinus were recorded by using glass microelectrodes. The majority of cells had resting potentials of 20 to 35 mV and responded to light with intensitygraded hyperpolarizations. Voltage intensity curves of responses to brief flashes followed the hyperbolic tangent functionV/V _max=Iⁿ/(I ⁿ + ⁿ ).The latency of onset for responses to light stimuli near threshold was 400 ms and decreased with saturating flashes to about 50 ms. The membrane resistance decreased during the hyperpolarization. Spectral sensitivity measurements for these cells exhibited curves with _max=530 nm. Intracellular dye injection unequivocally identified this cell type as a photoreceptor cell.A second cell type with resting potentials between 30 to 40 mV exhibited a biphasic response pattern to light stimulation. The cell depolarized with dim light flashes and hyperpolarized with bright flashes. The amplitude of the hyperpolarizing component showed no saturation over an intensity range of 5 log units. Latencies and rise times were comparable to those of photoreceptor potentials. Spectral sensitivity curves peaked at longer wavelengths ( _max=550 nm) than the action spectra of photoreceptors ( _max=530 nm). It is assumed that this rare cell type represents a small class of pineal interneurons.     

Photosynthetic and respiratory responses of <Emphasis Type="Italic">Gracilaria salicornia</Emphasis> (C. Ag.) Dawson (Gracilariales,Rhodophyta) from Thailand and Japan

The photosynthetic and respiratory responses of Gracilaria salicornia in the subtropical waters of Japan (in Okinawa) and in the tropical waters of Thailand (in Rayong and Phuket Provinces), were studied under various conditions of irradiance, salinity and temperature. This alga showed adaptability in its photosynthetic and respiratory responses to oceanic salinity as well as to subtropical to tropical temperature. Significant differences in the photosynthetic and respiratory rates among the G. salicornia populations collected from the above sites were observed. The Phuket population showed adaptability to high irradiance and temperature, characteristic of its natural sun-exposed environment, as it exhibited the highest I _k and I _c, and lowest α and higher P _max at 30–35°C. On the other hand, the Okinawa population demonstrated adaptability to low submarine irradiance as it had a lower I _k and I _c than either population from Thailand. Its P _max at 20–25°C was also higher than that of the Phuket population. The Rayong population, however, showed the highest P _max, R_d, α, I _k and I _c, suggesting its adaptability to both sun and shade light conditions in its natural environment. Presented at the 6th Meeting of the Asian Pacific Society of Applied Phycology, Manila, Philippines     

Ethanol production from sulphuric acid wood hydrolysate ofPinus radiata using free and immobilized cells ofPichia stipitis

Summary Ethanol was produced by a strain ofPichia stipitis adapted to an inhibitory acid wood hydrolysate ofPinus radiata. The best ethanol productivity for batch cultures was 0.21 g/l h at 0.7% ethanol. Varying culture conditions increased ethanol concentration to 0.76%, however the productivity decreased to 0.18 g/l h. A decrease in ethanol concentration in the culture fluid was noted late in the batch which suggested ethanol catabolism. Values of kinetic parameters (K _m,K _s, _max, andV _max) were evaluated for this system. The use of calcium alginate immobilized cells in a continuous-flow stirred tank reactor lead to enhanced fermentative performance, namely a maximum productivity of 0.27 g/l h and 1.13% ethanol yield. The immobilized cells in continuous flow reactors represent an attractive option for fermenting sugars released by sulphuric acid hydrolysis ofP. radiata wood.     

Photosynthetic responses of Miconia species to canopy openings in a lowland tropical rainforest

We examined the photosynthetic acclimation of three tropical species of Miconia to canopy openings in a Costa Rican rainforest. The response of photosynthesis to canopy opening was very similar in Miconia affinis, M. gracilis, and M. nervosa, despite differences in growth form (trees and shrubs) and local distributions of plants (understory and gap). Four months after the canopy was opened by a treefall, photosynthetic capacity in all three species had approximately doubled from closed canopy levels. There were no obvious signs of high light damage after treefall but acclimation to the gap environment was not immediate. Two weeks after treefall, A_max, stomatal conductance, apprarent quantum efficiency, and dark respiration rates had not changed significantly from understory values. The production of new leaves appears to be an important component of light acclimation in these species. The only variables to differ significantly among species were stomatal conductance at A_max and the light level at which assimilation was saturated. M. affinis had a higher stomatal conductance which may reduce its water use efficiency in gap environments. Photosynthesis in the more shade-tolerant M. gracilis saturated at lower light levels than in the other two species. Individual plant light environments were assessed after treefall with canopy photography but they explained only a small fraction of plant variation in most measures of photosynthesis and growth. In conclusion, we speculate that species differences in local distribution and in light requirements for reproduction may be more strongly related to species differences in carbon allocation than in carbon assimilation.     

The Adaptation of Plankton Algae

The variation in Skeletonema cells grown at 3 klux continuous illumination and 20°C is reported. Four different types of lamps gave no difference in the photosynthetic characteristics. The average diameter of the cells decreased from 8–3.5 μ during their six months vegetative period. The ratio between the pigment content in the largest and the smallest cells was about 2:1. A good correlation between cell volume and chlorophyll a content was found for this species. The content of chlorophyll c generally varied between 4 and 17 per cent of the chlorophyll a content. — A distinct correlation between the chlorophyll a content and the rate of photosynthesis per unit of cells at low light intensity was found. The rate of photosynthesis, in mg C per mg chlorophyll a and hour at 1 klux, varied between 0.40 and 0.70 for all 60 experiments with an average value of 0.56. The corresponding value for cells deficient in phosophorus was 0.19 and for cells deficient in nitrogen 0.09. — The material also showed a good correlation between the rate of photosynthesis per cell at 1 klux and the light-saturated rate of photosynthesis. I_k varied between 7 and 13 klux.     

On the three visual pigments in the retina of the firefly squid,Watasenia scintillans

Summary The deep-sea bioluminescent squid, Watasenia scintillans, has three visual pigments: The major one (A1 pigment) is based on retinal and has _max = 484 nm, the second one (A2 pigment) is based on 3-dehydroretinal and has _max = 500 nm, and the third one (A4 pigment) is based on 4-hydroxyretinal and has _max = 470 nm. The distribution of these 3 visual pigments in the retina was studied by HPLC analysis of the retinals in retina slices obtained by microdissection. It was found that A1 pigment was not located in the specific region of the ventral retina receiving the down-welling light which contains very long photoreceptor cells, forming two strata. A2 and A4 pigment were found exclusively in the proximal pinkish stratum and in the distal yellowish stratum. The role of these pigments in the retina is hypothesized to involve spectral discrimination. The extraction and analysis of retinoids to determine the origin of 3-dehydroretinal and 4-hydroxyretinal in the mature squid showed only a trace amount of 4-hydroxyretinol in the eggs. Similar analysis of other cephalopods collected near Japan showed the absence of A2 or A4 pigment in their eyes.Abbreviations HPLC high-performance liquid chromatography - IS inner segment - OS outer segment     

Gross Primary Productivity of a High Elevation Tropical Montane Cloud Forest

For decades, the productivity of tropical montane cloud forests (TMCF) has been assumed to be lower than in tropical lowland forests due to nutrient limitation, lower temperatures, and frequent cloud immersion, although actual estimates of gross primary productivity (GPP) are very scarce. Here, we present the results of a process-based modeling estimate of GPP, using a soil–plant–atmosphere model, of a high elevation Peruvian TMCF. The model was parameterized with field-measured physiological and structural vegetation variables, and driven with meteorological data from the site. Modeled transpiration corroborated well with measured sap flow, and simulated GPP added up to 16.2 ± SE 1.6 Mg C ha^?1 y^?1. Dry season GPP was significantly lower than wet season GPP, although this difference was 17% and not caused by drought stress. The strongest environmental controls on simulated GPP were variation of photosynthetic active radiation and air temperature (T _air). Their relative importance likely varies with elevation and the local prevalence of cloud cover. Photosynthetic parameters (V _cmax and J _max) and leaf area index were the most important non-environmental controls on GPP. We additionally compared the modeled results with a recent estimate of GPP of the same Peruvian TMCF derived by the summing of ecosystem respiration and net productivity terms, which added up to 26 Mg C ha^?1 y^?1. Despite the uncertainties in modeling GPP we conclude that at this altitude GPP is, conservatively estimated, 30–40% lower than in lowland rainforest and this difference is driven mostly by cooler temperatures than changes in other parameters.     

Growth,vitamin B12, and photopigment formations of Rhodopseudomonas sphaeroides S growing on propionate media under dark and light conditions

Summary The effects of light illumination and dissolved oxygen concentration (DO) on the growth characteristics of Rhodopseudomonas sphaeroides S and intracellular accumulations of vitamin B₁₂ and photopigments were studied in continuous cultures of aerobic-dark (S-1, DO>5 mg l^–1), aerobic-light (S-2, DO>5 mg l^–1, 4.5 klux), microaerobic-light (S-3, DO0,4.5 klux) and anaerobic-light (S-4, 4.5 klux) conditions using propionate media. Growth yields from propionic acid determined in S-3 and 4 were 1.5 to twofold greater than in S-1 and 2. Carbon dioxide evolution observed in S-3 and 4 was 0.05 to 0.1 times that in S-1 and 2. Overall carboxylase activity was maximal in S-4. Intracellular accumulations of bacteriochlorophyll and carotenoid were maximal in S-4, followed by S-3 and almost nil in S-1 and 2. The high growth yields observed in S-3 and 4 could be accounted for the high level of activity of carbon dioxide fixation and by the additional or effective utilization of light energy.Intracellular accumulation of vitamin B₁₂ in S-2, 3 and 4 was 1.5 to 1.8 times that in S-1. The maximum content of the vitamin was 74 g-B₁₂ g-cell^–1. The maximum productivity of vitamin B₁₂, g-B₁₂ l^–1 h^–1, was 6.6 in S-3 since specific growth rate, growth yield and the vitamin content of the cells were maximal in S-3.