Photosynthetic Primary Production Research Articles

Shedding of older needle age classes does not necessarily reduce photosynthetic primary production of Norway spruce

The hypothesis that the frequently observed shedding of older needle age classes in stands of Norway spruce suffering from atmospheric pollutants has minimal effect on photosynthetic primary production was assessed. Using structural parameters of young Norway spruce [Picea abies (L.) Karst.] trees, an existing 3-dimensional canopy photosynthesis model was adapted and validated for conifer canopies. This model was employed to quantitatively demonstrate that, depending on the stand density, the loss in photosynthetic active foliage area may be compensated by higher photosynthetic rates of the remaining younger foliage age classes due to higher levels of photosynthetically active radiation (PAR) within the thinned tree crowns. Under certain circumstances, beneficial effects on the tree's water use efficiency may be expected. Extrapolating the model results to mature tree stands is addressed. The potential effects of higher PAR levels on abundance and species diversity of the epiphytic and understory vegetation, as well as the general importance of the older foliage age classes for spruce trees on a long term scale, are discussed.

Gas Exchange and Carbon Partitioning in the Leaves of Celery (Apium graveolens L.) at Various Levels of Root Zone Salinity.

Both mannitol and sucrose (Suc) are primary photosynthetic products in celery (Apium graveolens L.). In other biological systems mannitol has been shown to serve as a compatible solute or osmoprotectant involved in stress tolerance. Although mannitol, like Suc, is translocated and serves as a reserve carbohydrate in celery, its role in stress tolerance has yet to be resolved. Mature celery plants exposed to low (25 mM NaCl), intermediate (100 mM NaCl), and high (300 mM NaCl) salinities displayed substantial salt tolerance. Shoot fresh weight was increased at low NaCl concentrations when compared with controls, and growth continued, although at slower rates, even after prolonged exposure to high salinities. Gas-exchange analyses showed that low NaCl levels had little or no effect on photosynthetic carbon assimilation (A), but at intermediate levels decreases in stomatal conductance limited A, and at the highest NaCl levels carboxylation capacity (as measured by analyses of the CO2 assimilation response to changing internal CO2 partial pressures) and electron transport (as indicated by fluorescence measurements) were the apparent prevailing limits to A. Increasing salinities up to 300 mM, however, increased mannitol accumulation and decreased Suc and starch pools in leaf tissues, e.g. the ratio of mannitol to Suc increased almost 10-fold. These changes were due in part to shifts in photosynthetic carbon partitioning (as measured by 14C labeling) from Suc into mannitol. Salt treatments increased the activity of mannose-6-phosphate reductase (M6PR), a key enzyme in mannitol biosynthesis, 6-fold in young leaves and 2-fold in fully expanded, mature leaves, but increases in M6PR protein were not apparent in the older leaves. Mannitol biosynthetic capacity (as measured by labeling rates) was maintained despite salt treatment, and relative partitioning into mannitol consequently increased despite decreased photosynthetic capacity. The results support a suggested role for mannitol accumulation in adaptation to and tolerance of salinity stress.

Molecular palaeontological evidence for food-web relationships.

The presence of consumer organisms in ancient ecosystems has been indicated mainly by the occurrence of fossilized mineral skeletons. In comparison with primary producers and bacteria, nonphotosynthetic enkaryotic organisms are minute contributors to organic carbon preserved in sediments. In principle, however, organic compounds produced by heterotrophs have the potential to enter the sedimentary record. The biomass of respiring heterotrophs is enriched in ¹³C relative to its carbon source, and it has been shown in the modern environment that the carbon isotopic fractionation between photosynthetic primary producers and heterotrophs increases as a function of the trophic level of the consumer. In ancient sediments, identification of organic compounds derived from specific heterotrophs and determination of their isotopic compositions are potential tools to reconstruct palaeo-food-web relationships. Here, we present unprecedented evidence of the presence in sediments of organic compounds derived from insect waxes. Analyses of the ¹³C contents of these materials indicate that insects utilized the organic material of cyanobacterial mats as their main source of carbon and, thus, demonstrate that molecular palaeontology can reveal food-web relationships in ancient communities. The observations confirm that the identification in sediments of specific refractory organic compounds from higher organisms and the determination of their stable carbon isotopic compositions provide valuable information regarding trophic relationships at the time of deposition. The molecular-isotopic approach appears likely to provide one of the only means for secure detection of products of consumer organisms and for placement of those organisms within ancient trophic systems.

GROWTH, SALT TOLERANCE AND MANNITOL ACCUMULATION IN CELERY

Mannitol, which in celery is a primary photosynthetic product, has been implicated along with other polyols in stress tolerance mechanisms as a possible osmotic regulator, compatible solute and free radical scavenger. We have characterized the growth of salt stressed celery, determined the extent of salt tolerance and showed a correlation between mannitol accumulation and salt tolerance.Six, 8 and 12 week-old pot grown celery (Apium graveolens L.) plants of two cultivars were irrigated with up to 500 mM NaCl for 3.5 and 7 weeks. After 7 weeks, 12 week-old `Giant Pascal' plants showed three major responses: 1) shoot wet wt increased as much as 30% at 25 mM NaCl but root wet wt decreased; 2) plants tolerated 500 mM NaCl, although at a severely reduced growth rate; 3) as salt concentrations increased mannitol concentrations increased in roots, leaves and petioles, while sucrose, the other photosynthetic product in celery, decreased Although all ages of both cultivars tolerated the highest salt concentration used, the beneficial effect of 25 mM NaCl occurred only in 8 and 12 week-old `Giant Pascal'. Root wet wt was reduced in all salt treated plants, irrespective of age or cultivar.Regardless of age, cultivar and length of treatment, celery tolerated high salinity and sometimes even increased wet wt at low salinity. Mannitol accumulation and the ratio of mannitol to sucrose were both positively correlated with salt tolerance

Vertical fluxes of nitrate associated with salt fingers in the world's oceans

The primary means by which the oceans serve as a sink for atmospheric carbon dioxide is through the vertical flux of sinking organic carbon. This organic material is derived from primary photosynthetic production in the upper ocean. Its rate of loss to the deep sea, the “new production”, is rigorously constrained by the upward flux of the limiting nutrient, nitrate. New production estimates have been made by using velocity microstructure measurements to infer nitrate fluxes, where it is assumed that turbulent production (mixing) balances viscous energy dissipation. However, estimates based on a salt finger convection model lead to nitrate fluxes which are as much as an order of magnitude larger than a turbulent mixing model predicts and agree much better with fluxes inferred from biological uptake measurements and tracer studies. Heat flux estimates are also higher, but by less than a factor of 3. Observations of the “scaled dissipation ratio” Γ, a quantity that is based on both velocity and temperature microstructure measurements, may provide a means of distinguishing between the two mixing hypotheses. Where both turbulent production and salt fingering contribute to the mixing this distinction is more difficult, but by using measurements of Γ the potential error in the vertical flux estimate due to an improper choice of mixing models is greatly reduced.

Box model analysis on phytoplankton production and grazing pressure in a eutrophic estuary

To determine the quantitative relationship between phytoplankton production and zooplankton grazing pressure in Atsumi Bay, a eutrophic and partially-mixed estuary, a series of investigations, including measurements of hydrographic conditions, dissolved oxygen, dissolved total nitrogen, particulate organic nitrogen, and phyto- and zooplankton biomass were conducted 13 times at intervals of 2–7 days in June and July 1984. Continuous measurements of water flow and salinity were also carried out to examine transverse flow and horizontal diffusivity. The supply of freshwater and nitrogen was estimated from given data. The changes of hydrographic condition, net photosynthetic rate and community primary production were calculated by a two-layered box model analysis. The grazing rate on phytoplankton obtained as the difference between net photosynthetic rate and community primary production was compared to the one estimated from zooplankton biomass and sardine,Sardinops melanosticta, biomass. The agreement between the data was remarkable in the upper layer, showing the grazing pressure on phytoplankton followed phytoplankton production, suggesting that a large part of produced phytoplankton was immediately grazed by zooplankton. Consequently, the community primary production was depressed to a fairly lower level. An important role of nutrient supply and water circulation, to limit phytoplankton production, was also confirmed. Dynamic response observed between the calculated grazing pressure and the biomass of phytoplankton and protozoa was also analyzed.

Reaktivierung der Photosynthese trockener Flechten durch Wasserdampfaufnahme aus dem Luftraum: Artspezifisch unterschiedliches Verhalten

Summary It is known in principle, that dry thalli of lichens are able to take up water vapor from air of high relative humidity and that this can stimulate CO2 exchange so that high rates of net photosynthesis are reached without exposing the lichens to liquid water. The present investigation compars different types of lichens from different climatic regions with respect to their ability to be activated by water vapor uptake. Thalli of dry lichens (kept in a desiccator with silicagel) were enclosed in gas exchange chambers and treated for 50 to 100 h with air of a relative humidity of 96.5% at 15°C (corresponding to a water potential of ca. —45 bar); subsequently they were sprayed with liquid water. During the course of the experiment, their rate of CO2 exchange in the light (150 μE m−2 s−1 photosynthetically active radiation) and dark respiration was monitored. With all of the heteromerous lichen species with green algae, water vapor uptake leads to reactivation of metabolism. Photosynthetic CO2-assimilation as well as mitochondrial respiration, increases during the course of treatment with moist air and reaches an equilibrium value when water potential of the thallus has equilibrated with that of the surrounding air. However, there are essential differences in the length of time required for reactivation of different species. Several fruticose and folious lichen species (e.g., Parmelia hypoleucina, Thamnolia vermicularis) reach 50% of maximum net photosynthesis already after less than 5 h treatment of the initially dry thalli with moist air. Alpine and Antarctic Umbilicaria-species need 15 to 16 h, and the Antarctic Caloplaca regalis requires approximately 34 h. Habitat adaptations are clearly recognizable. This is apparent for instance for species from a Chilean fog oasis, which depend almost entirely on air humidity as a source for water. There are also distinct differences between lichen types in the response to moistening with liquid water. With some species, spraying with water after water vapor uptake results in an increase of net photosynthesis. With other species there is often a decrease. In extreme cases, CO2 exchange decreases below the compensation point in the light, which appears to be due to a strong and reversible stimulation of mitochondrial respiration by liquid water. The gelatinous lichens are of exceptional interest. None of the investigated Collemataceae (2 Collema, 1 Leptogium species) is able to make use of water vapor for attain positive net photosynthesis rates. With these lichens, photosynthetic primary production depends solely on hydration with liquid water. This must strongly limit the distribution of these species. The results indicate that the gelatinous species must represent an independent life form among lichens. Differences in anatomical and morphological structure of their thallus appear also to be associated with differences in function which profoundly alters the way in which photosynthetic metabolism responds to available water in the environment.

Distribution and rate of disappearance of fluorene in pond ecosystems

Fluorene, an energy related polynuclear aromatic hydrocarbon, was applied to several experimental pond ecosystems to effect concentrations of 0.12, 0.5, 2.0, 5.0, and 10.0 mg/L. Water, benthic sediment, and rooted macrophytes were monitored for fluorene residues for 56 days after application. Most of the fluorene at concentrations greater than its water solubility appeared to sublime from the surface of the ponds. The rate of disappearance of fluorene from the water decreased as the application rate increased. This reduction was linked to high concentrations and a flux of fluorene from benthic sediments, macrophytes, and pond surfaces to water columns. Several parameters of photosynthetic primary production were statistically linked to the accelerated disappearance of fluorene from the water.

Epiphytische Flechten im Bereich einer chilenischen „Nebeloase“ (Fray Jorge) I. Vegetationskundliche Gliederung und Standortsbedingungen

Summary Fog formation occurs frequently along the coast of nothern Chile. The fog envelopes the slopes and the summit of the coastal ranges. Water condenses in this zone and effects the development of an usually lush vegetation known as a fog oasis in this arid or semi-arid environment. In the Fray Jorge National Park, the fog-dependent vegetation consists of evergreen forests which are surrounded by thorn scrub and succulents. Lichens play an important role in these habitats. They cover the phanerophytes of the different zones of the coastal area as epiphytic vegetation and have both high biomass and species diversity. The objective of the first part of this work was a description of the epiphytic lichen vegetation for a selected, representative area of about 10 km2 of the Fray Jorge National Park and to study the environmental relationships of these lichens with special emphasis on their water relations. Redon (1982) described 54 different epiphytic lichen species for this area. A phytosociological study resulted in the definition of 2 lichen-associations which are characterized by species combinations, dominant life forms, and species diversity. The Oropogonetum loxensis lichen community grows on shrubs and trees in the zone which is directly affected by persistent fog. On the other hand, the Ramalinetum cactacearum lichen community covers the shrubs in the region below the fog belt. Along a transect which streched from the drier inland depression without fog influence to the top of the coastal range where there is regular fog formation, the changes in the lichen vegetation and the gradation between the 2 communities were characterized. At the habitats of the Oropogonetum and the Ramalinetum, diurnal courses of light intensity, air temperature, air humidity and lichen thallus temperature were measured during characteristic wheather conditions in the different seasons throughout the year. Lichen water content of typical, selected species was followed at the same time by weighing of samples. The species of the Oropogonetum are often thoroughly moistened during the night by condensing fog which forms droplets on the thalli. In the early morning hours, maximum water contents of the lichens up to 153 and 172 % (by dry weight) respectively were measured. After disappearance of the fog during the late morning hours, the thalli increasingly dry out as temperatures increase and air humidity is decreased. Thallus water content reaches a minimum of about 16 % in the early afternoon. In contrast, water relations of the species of the Ramalinetum are much more unfavourable. Moistening by liquid water seems to be restricted to very infrequent dew condensation and to the few rain events in winter (situations, which were not observed during this study in the field). The habitats of the Ramalinetum are not reached by the fog. However, fog formation in the higher altitudes of the coastal ranges is correlated with a substantial increase in air humidity in the depression where the Ramalinetum occurs. The lichen thalli are able to absorb this water vapor from the air even though no condensation occurs. Thus, in the early morning hours after nights with high air humidity, hydration of the species of the Ramalinetum increases, and water contents up to about 37 % were measurable. Subsequently the thalli dry out again and reach their minimum water content after noon, similar to the lichens of the Oropogonetum. Water exchange between lichens and air seems to take place so quickly, that the thalli are almost in equilibrium with the water potential of the ambient air, at least during the time periods of low solar radiation before noon. The same is the case for the species of the Oropogonetum on days without fog formation but with high air humidity. In a second communication of this series, the importance of the habitat conditions for the photo-synthetic primary production of the lichens will be assessed.

Sediment—sea interaction

1. (1) The nature of sediment—sea interactions depends on the time scale considered. At a time scale commensurate with human life, one can define a water—sediment interface, and the main exchanges are solutes exchanges through this interface by concentration diffusion. This condition will be termed as “Short time-scale equilibrium interaction”. On the other hand, at a geological time scale, there is a continuous accretion to the “sediment” of suspended particulate matter, bottom-current borne materials and sometimes precipitates of previously dissolved salts; to this sediment build-up corresponds a flux of water of reverse sense, from the sediment to the water column, due to the compaction of muds and oozes which reduce their porosity (their water content) under their own load. The concept of interface is then of limited utility, since physically it is constantly changing, and since the material balance of the exchanges does not depend on its characteristics at a first order of approximation. This condition will be termed “long time-scale geological interaction”. These situations are extreme ones. In areas of present important detrital sedimentation, even for short time spans it is doubtful if the definition of an interface has some utility: we are in a situation close to “geological time scale”. On the contrary, in abyssal zones remote from continents, the rate of sedimentation is so low that even for eons an interface separating two environments in physico-chemical equilibrium exists. 2. (2) If there were no internal sources of dissolved species in the sediment, the only concentration changes to occur would be due to the decrease in porosity (in water content) following gravitational compaction of sediments. But this phenomenon is the same as sedimentation, thus transfer of matter would be unappreciable within short time spans. The fact that this transfer can be measured at human time scale shows therefore that dissolved species are actually produced in the sediment. Some of these can originate from possible inorganic chemical reactions, but all the organic molecules, and an important part of the inorganic (such as phosphates, nitrates, NH 4 +, S 2-) require processing of organic matter for their production. Whether or not this reworking is of biological origin remains controversial. On the whole, the quantities of matter thus transferred are very minute compared to the quantities present in oceanic waters. They cannot be considered in general as a significant input. But they may be important locally (nearshore restricted water bodies, or manganese nodules formation). 3. (3) At geological time scale, sedimentation, which adds solid material to the preexisting sediment, results also in the compaction of this sediment. At every depth in the sediment there exists an equilibrium value of the porosity, i.e. the fluids content, of the sediment; it tends to this value by expelling the corresponding quantity of fluids, with a rate determined by its permeability. This input may be important, but it is mainly water, and water formerly oceanic: therefore it is not a true input, but simply a delayed return. The transfer of other fluids (mainly oil and gas) is unsignificant generally speaking. Once more, it may be locally important (submarine seepages). 4. (4) On the whole, the processes of water—sediment interaction appear not to add any new matter into the oceanic pool, but rather to regulate the restitution by the sediment to the water of substances which were already present in ocean, in particulate or dissolved form, either free or combined. One can trace out two main processes, which differ in their rates and yields: 4.1. (a) the short time scale diffusion—high rate low yield restitution of organics and inorganics in dissolved state: 4.2. (b) the long time scale compaction: low rate high yield restitution of entrapped fluids, essentially water (devoid of dissolved species). Not only do these processes not bring any new matter to the ocean, but even the absolute quantities involved are modest compared either to the quantities present in the ocean or to the quantities generated by the photosynthetic primary production or brought by the rivers. In contrast to the insignificance of the water—sediment interaction in the oceanic material balance, this same interaction is one of the main sources for the material sedimented and especially the organic one, and therefore it is a fundamental key for all the subsequent sedimentary history. The significant inputs at the limit “bottom”-water come from the regions of deep tectonic activity, volcanism, creation of new oceanic crust etc… There tremendous amounts of substances can be brought into solution, changing at least locally the concentration equilibrium values of seawater. They are of course inorganic ions, but they can have important biological consequences. The buffering capacity of the world ocean is so high that only cosmic events can influence its composition.

Physiological Studies with Isolated Leaf Cells

A number of plants have been surveyed with respect to isolation by mild grinding in large quantities of leaf cells. The extent of recovery of mesophyll cells per unit leaf area was found to vary with plant species and the method of grinding. Greater than 70% recovery was obtained from the leaves of Canna indica L., Crotalaria Laburnifolia L., and Thunbergia grandiflora Roxb.By pulse-chase time course experiments, the photosynthetically fixed primary carbon compounds of bean leaf cells were not converted into the ethanol-insoluble fraction. About 25% of total (14)C-photoassimilates were found to leak out into the incubation medium. In contrast, Euglena and Chlorella cells incorporated their primary photosynthetic products into cellular macromolecules and the amount of "leak" was very little. (14)C-Leucine supplied to the bean cells was absorbed readily and incorporated into the trichloroacetic acid insoluble fraction.

Plant Species Intermediate for C 3 , C 4 Photosynthesis

Mollugo verticillata is the first plant species reported which has characteristics of both C(3) (Calvin-Benson pathway) and C(4) (Hatch-Slack pathway) plants. This plant species is intermediate between C(3) and C(4) plants in at least four features generally used to separate those two plant groups: leaf anatomy, cell ultrastructure, photorespiration, and primary photosynthetic products.

Relationship between leaf development and primary photosynthetic products in the C4 plant Portulaca oleracea L.

The photosynthetic products of Portulaca oleracea differ greatly depending on leaf age and length of exposure to (14)CO2. Mature leaves of P. oleracea fix (14)CO2 primarily into organic and amino acids during a 10-s exposure period. Less than 2% of the (14)CO2 fixed appears in phosphorylated compounds. In contrast, incorporation into amino acids can account for over 60% of the total (14)CO2 fixed by young leaves in an equal time period, and incorporation into alanine alone can account for up to one half of this amount. Senescent leaves display a quantitative shift of primary products toward phosphorylated compounds with a concomitant reduction of the label residing in malate and asparate. About 8 times more phosphoglyceric acid is produced in senescent leaves than in mature leaves. The aspartate/ malate ratio is not constant and depends on the length of time the leaves are exposed to (14)CO2 and the age of the leaves under study. It appears as if the stage of leaf development is one of the most important factors determining the operation of a particular enzyme system in C4 plants.