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1.
Alexandrium catenella (Whedon et Kofoid) Balech was isolated from Thau lagoon (northern Mediterranean) and its growth and uptake characteristics measured for nitrate, ammonium, and urea. Although affinity constants did not indicate a preference for ammonium over nitrate, there was a strong inhibition of nitrate uptake by ammonium when both nitrogen (N) sources were present. Nitrogen budgets during growth in cultures revealed major imbalances between decreases in dissolved N and increases in particulate N, indicating excretion of dissolved organic N during the early part of the growth phase and uptake during the later part. A quasi‐unialgal bloom in November 2001 (4×106 cells·L?1) allowed measurements of uptake of nitrate, nitrite, ammonium, and urea; net and gross growth rate of A. catenella; and grazing rates on this organism. The affinity constants indicate that it is not a strong competitor for the N nutrients tested when these are in low concentrations (<10 μgat N·L?1), compared with other members of the phytoplankton community. Indirect evidence from cultures indicate that dissolved organic N compounds could be important in triggering those blooms. Finally, the strongly unbalanced growth observed in the field indicates that A. catenella exhibits a storage rather than a growth response to a nutrient pulse and is adapted to low frequency events such as the passage of frontal disturbances. The disappearance of A. catenella was due to grazing that balanced growth at the peak of the bloom.  相似文献   

2.
  • 1 Picoplankton community production (0.2–2μm) was investigated over 3 months, June-September 1991, in Llyn Padarn, a mesotrophic upland lake in north Wales.
  • 2 The picoplankton was differentiated into autotrophic algae (<1–3μm) and heterotrophic bacteria (<0.2–1 μm) using differential filtration through a 1 μm pore size Nuclepore filter.
  • 3 Efficient separation of these distinct metabolic constituents of picoplankton was obtained. A good correlation (r= 0.81, P < 0.001) was found between physical separation of bacterial and picoalgal cells from fluorescence microscopy and the distribution of heterotrophic metabolic activity between different cell size fractions measured by uptake of 14C-glucose.
  • 4 Picoplankton community production was differentiated into the ‘absolute’ autotrophic production by picoalgae, corrected for overestimation due to retention of bacteria with the picoalgae, and the heterotrophic component, bacterial uptake of ‘extracellular organic carbon’ (EOC), derived from the entire phytoplankton community.
  • 5 The heterotrophic contribution to picoplankton community production ranged from 88 to 1%, mean value 55% of total. Autotrophic picoplankton production was dominant in June and July, but in August and September heterotrophic uptake of EOC was the major input to picoplankton community production.
  • 6 During the 3 months, the mean contributions to plankton production were autotrophic picoplankton 10.3%, heterotrophic bacterial uptake of EOC 9.7%, EOC in lake water 11.6% and phytoplankton (>3μm) 68.3%.
  • 7 Bacteria accounted for about half the picopfankton community production via uptake of EOC. Thus although autotrophic picoplankton were ubiquitous, it is likely that their contribution via primary production to the carbon balance of planktonic environments has been overestimated in previous studies.
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3.
4.
Recently, a novel electrogenic type of sulphur oxidation was documented in marine sediments, whereby filamentous cable bacteria (Desulfobulbaceae) are mediating electron transport over cm-scale distances. These cable bacteria are capable of developing an extensive network within days, implying a highly efficient carbon acquisition strategy. Presently, the carbon metabolism of cable bacteria is unknown, and hence we adopted a multidisciplinary approach to study the carbon substrate utilization of both cable bacteria and associated microbial community in sediment incubations. Fluorescence in situ hybridization showed rapid downward growth of cable bacteria, concomitant with high rates of electrogenic sulphur oxidation, as quantified by microelectrode profiling. We studied heterotrophy and autotrophy by following 13C-propionate and -bicarbonate incorporation into bacterial fatty acids. This biomarker analysis showed that propionate uptake was limited to fatty acid signatures typical for the genus Desulfobulbus. The nanoscale secondary ion mass spectrometry analysis confirmed heterotrophic rather than autotrophic growth of cable bacteria. Still, high bicarbonate uptake was observed in concert with the development of cable bacteria. Clone libraries of 16S complementary DNA showed numerous sequences associated to chemoautotrophic sulphur-oxidizing Epsilon- and Gammaproteobacteria, whereas 13C-bicarbonate biomarker labelling suggested that these sulphur-oxidizing bacteria were active far below the oxygen penetration. A targeted manipulation experiment demonstrated that chemoautotrophic carbon fixation was tightly linked to the heterotrophic activity of the cable bacteria down to cm depth. Overall, the results suggest that electrogenic sulphur oxidation is performed by a microbial consortium, consisting of chemoorganotrophic cable bacteria and chemolithoautotrophic Epsilon- and Gammaproteobacteria. The metabolic linkage between these two groups is presently unknown and needs further study.  相似文献   

5.
Among land plants, which generally exhibit autotrophy through photosynthesis, about 880 species are mycoheterotrophs, dependent on mycorrhizal fungi for their carbon supply. Shifts in nutritional mode from autotrophy to mycoheterotrophy are usually accompanied by evolution of various combinations of characters related to structure and physiology, e.g., loss of foliage leaves and roots, reduction in seed size, degradation of plastid genome, and changes in mycorrhizal association and pollination strategy. However, the patterns and processes involved in such alterations are generally unknown. Hybrids between autotrophic and mycoheterotrophic plants may provide a breakthrough in molecular studies on the evolution of mycoheterotrophy. We have produced the first hybrid between autotrophic and mycoheterotrophic plant species using the orchid group Cymbidium. The autotrophic Cymbidium ensifolium subsp. haematodes and mycoheterotrophic C. macrorhizon were artificially pollinated, and aseptic germination of the hybrid seeds obtained was promoted by sonication. In vitro flowering was observed five years after seed sowing. Development of foliage leaves, an important character for photosynthesis, segregated in the first generation; that is, some individuals only developed scale leaves on the rhizome and flowering stems. However, all of the flowering plants formed roots, which is identical to the maternal parent.  相似文献   

6.
Autotrophic carbon dioxide (CO2) fixation by microbes is ubiquitous in the environment and potentially contributes to the soil organic carbon (SOC) pool. However, the multiple autotrophic pathways of microbial carbon assimilation and fixation in paddy soils remain poorly characterized. In this study, we combine metagenomic analysis with 14C-labelling to investigate all known autotrophic pathways and CO2 assimilation mechanisms in five typical paddy soils from southern China. Marker genes of six autotrophic pathways are detected in all soil samples, which are dominated by the cbbL genes (67%–82%) coding the ribulose-bisphosphate carboxylase large chain in the Calvin cycle. These marker genes are associated with a broad range of phototrophic and chemotrophic genera. Significant amounts of 14C-CO2 are assimilated into SOC (74.3–175.8 mg 14C kg−1) and microbial biomass (5.2–24.1 mg 14C kg−1) after 45 days incubation, where more than 70% of 14C-SOC was concentrated in the relatively stable humin fractions. These results show that paddy soil microbes contain the genetic potential for autotrophic carbon fixation spreading over broad taxonomic ranges, and can incorporate atmospheric carbon into organic components, which ultimately contribute to the stable SOC pool.  相似文献   

7.
Ecosystem respiration (Reco) is one of the largest terrestrial carbon (C) fluxes. The effect of climate change on Reco depends on the responses of its autotrophic and heterotrophic components. How autotrophic and heterotrophic respiration sources respond to climate change is especially important in ecosystems underlain by permafrost. Permafrost ecosystems contain vast stores of soil C (1672 Pg) and are located in northern latitudes where climate change is accelerated. Warming will cause a positive feedback to climate change if heterotrophic respiration increases without corresponding increases in primary production. We quantified the response of autotrophic and heterotrophic respiration to permafrost thaw across the 2008 and 2009 growing seasons. We partitioned Reco using Δ14C and δ13C into four sources–two autotrophic (above – and belowground plant structures) and two heterotrophic (young and old soil). We sampled the Δ14C and δ13C of sources using incubations and the Δ14C and δ13C of Reco using field measurements. We then used a Bayesian mixing model to solve for the most likely contributions of each source to Reco. Autotrophic respiration ranged from 40 to 70% of Reco and was greatest at the height of the growing season. Old soil heterotrophic respiration ranged from 6 to 18% of Reco and was greatest where permafrost thaw was deepest. Overall, growing season fluxes of autotrophic and old soil heterotrophic respiration increased as permafrost thaw deepened. Areas with greater thaw also had the greatest primary production. Warming in permafrost ecosystems therefore leads to increased plant and old soil respiration that is initially compensated by increased net primary productivity. However, barring large shifts in plant community composition, future increases in old soil respiration will likely outpace productivity, resulting in a positive feedback to climate change.  相似文献   

8.
Colloidal macromolecular organic compounds are important intermediaries between solution and particle phases and play a critical role in the biogeochemistry of trace metals and organic carbon. The releases of colloidal organic carbon and trace metals (Cd, Fe, and Zn) mediated by copepod grazing and decomposition, and direct diatom exudation, were examined using a radiotracer approach. The colloidal phase was operationally defined in this study as the size fraction between 5 kDa and 0.2 μm and the dissolved phase as the ≤0.2 μm filter passing phase. About 13-60% of dissolved carbon exuded by the diatom Thalassiosira pseudonana was partitioned into the colloidal phase, and this fraction increased considerably as the diatom cells grew older. A lower fraction of dissolved 14C (12-23%) excreted by the copepods Acartia erythraea was detected in the colloidal phase compared to carcass (13-35%) and feces decomposition (21-34%). In contrast to carbon, a lower fraction of regenerated dissolved Cd (1-11%) and Zn (0-20%) from copepods and diatoms was consistently detected in the colloidal phases. Copepod excretion and carcass decomposition resulted in more colloidal Fe (51-91%) than diatom exudation (46-62% for Thalassiosira weissflogii, and 3-33% for T. pseudonana) and copepod feces decomposition (16-30%). Copepod (Calanus sinicus) grazing reduced the colloidal fraction of dissolved 14C, although a higher concentration of the diatom's (T. weissflogii) carbon was regenerated into the dissolved phase. The grazing of these copepods did not have any influence on the colloidal metal partitioning. The release of trace metals and carbon was enhanced by a higher density of copepod's grazing. Thus, different biological processes (grazing, excretion, exudation, and decomposition) may contribute differently to the production and dynamics of colloidal carbon and metals in planktonic systems.  相似文献   

9.
Light supply is one of the most important factors affecting autotrophic growth of microalgae. This study investigated the effect of the type and light intensity of artificial light sources on the cell growth of an indigenous microalga Chlorella vulgaris ESP‐31 obtained from southern Taiwan. In addition, a dissolved inorganic carbon source (i.e. sodium bicarbonate) was used to improve the biomass production of strain ESP‐31. The results show that a new fluorescent light source (TL5) was effective in indoor cultivation of microalgae. Better overall productivity of 0.029 g dry cell weight/L‐d was obtained when using TL5 lamps as the light source with a light intensity of 9 W/m2. A carbon source (sodium bicarbonate) concentration of 1000 mg/L was found to be optimal for the growth of strain ESP‐31 in terms of both biomass production and carbon source utilization. Under the optimal growth conditions, the resulting microalgal biomass consisted of 25–30% protein, 6–10% carbohydrate, and 30–40% lipid.  相似文献   

10.
Wanek  Wolfgang  Popp  Marianne 《Plant and Soil》2000,221(1):13-24
Increased levels of rhizospheric dissolved inorganic carbon have repeatedly been demonstrated to enhance plant growth by up to 80%, although carbon from dark fixation accounts for only 1–3% of total plant carbon gain. This study, therefore, aimed at investigating the effects of bicarbonate on nitrate uptake, assimilation and translocation to shoots. Clonal saplings of poplar (Populus canescens(Ait.) Sm.) and elder (Sambucus nigraL.) were grown hydroponically for 35 days in a nutrient solution containing 0, 0.5 and 1 mM bicarbonate and 2 mM nitrate as the sole nitrogen source at pH 7.0. Net nitrate uptake, root nitrate accumulation and reduction, and export of nitrogenous solutes to shoots were measured after incubating plants with 15N-labelled nitrate for 24 h. Net nitrate uptake increased non-significantly in plant species (19–61% compared to control plants) in response to 1 mM bicarbonate. Root nitrate reduction and nitrogen export to shoots increased by 80 and 95% and 15 and 44% in poplar and elder, respectively. With enhanced root zone bicarbonate, both species also exhibited a marked shift between the main nitrate utilising processes. Poplar plants increasingly utilised nitrate via nitrate reduction (73–88% of net nitrate uptake), whereas the proportions of export (20–9%) and storage in roots (7–3%) declined as plants were exposed to 1 mM external bicarbonate. On the other hand, elder plants exhibited a significant increase of root nitrate reduction (44–66%) and root nitrate accumulation (6–25%). Nitrate translocation to elder shoots decreased from 50 to 8% of net nitrate uptake. The improved supply of nitrogen to shoots did not translate into a significant stimulation of growth, relative growth rates increased by only 16% in poplar saplings and by 7% in elder plants. This revised version was published online in June 2006 with corrections to the Cover Date.  相似文献   

11.
Magnetotactic bacteria are present at the oxic–anoxic transition zone where opposing gradients of oxygen and reduced sulfur and iron exist. Growth of non‐magnetotactic lithoautotrophic Magnetospirillum strain J10 and its close relative magnetotactic Magnetospirillum gryphiswaldense was characterized in microaerobic continuous culture. Both strains were able to grow in mixotrophic (acetate + sulfide) and autotrophic (sulfide or thiosulfate) conditions. Autotrophically growing cells completely converted sulfide or thiosulfate to sulfate and produced 7.5 g dry weight per mol substrate at a maximum observed growth rate of 0.09 h?1 for strain J10 and 0.07 h?1 for M. gryphiswaldense. The respiratory activity for acetate was repressed in autotrophic and also in mixotrophic cultures, suggesting acetate was used as C‐source in the latter. We have estimated the proportions of substrate used for assimilatory processes and evaluated the biomass yields per mol dissimilated substrate. The yield for lithoheterotrophic growth using acetate as the C‐source was approximately twice the autotrophic growth yield and very similar to the heterotrophic yield, showing the importance of reduced sulfur compounds for growth. In the draft genome sequence of M. gryphiswaldense homologues of genes encoding a partial sulfur‐oxidizing (Sox) enzyme system and reverse dissimilatory sulfite reductase (Dsr) were identified, which may be involved in the oxidation of sulfide and thiosulfate. Magnetospirillum gryphiswaldense is the first freshwater magnetotactic species for which autotrophic growth is shown.  相似文献   

12.
To achieve sustainable production of biofuel from microalgae, a well-optimized and sustained biomass production is prerequisite. The major factor determining the higher productivity of algae is the availability and uptake of CO2 for biomass growth. In this study, an improved CO2 sequestration method leading to improved biomass yields has been investigated. The ability of OH? ions in fixing dissolved CO2 in form of HCO 3 ? in algal growth medium was studied using a Chlorella sp. and scaled-up in a photobioreactor. It was observed that a critical concentration of 0.005?M OH? is required for HCO 3 ? formation and utilization by algae. HCO 3 ? uptake was enhanced by 70.8% (in presence of 0.01?M NaOH) with a sixfold increase in growth rate compared with only CO2 system. In mineral carbon systems such as NaHCO3 and Na2CO3, increase in HCO 3 ? uptake was enhanced by 65.4% and 63.4%, respectively. The maximum rate of CO2 fixation of 6.6?mg?L?1?h?1 was obtained with 0.01?M NaOH which was 1.5 times compared with mineral carbon sources. The biomass from scale-up experiment contained 16.3% lipid (by weight) of which 75% is unsaturated fatty acids (in total lipids). This supports the idea that fixing the dissolved CO2 in the form of bicarbonate using alkali helps in increased biomass productivity rather than CO2 itself, forms a precursor for biodiesel, and increases CO2 sequestration in a cyclic process.  相似文献   

13.
Although the facultatively autotrophic acidophile Thiobacillus acidophilus is unable to grow on formate and formaldehyde in batch cultures, cells from glucose-limited chemostat cultures exhibited substrate-dependent oxygen uptake with these C1-compounds. Oxidation of formate and formaldehyde was uncoupler-sensitive, suggesting that active transport was involved in the metabolism of these compounds. Formate- and formaldehyde-dependent oxygen uptake was strongly inhibited at substrate concentrations above 150 and 400 M, respectively. However, autotrophic formate-limited chemostat cultures were obtained by carefully increasing the formate to glucose ratio in the reservoir medium of mixotrophic chemostat cultures. The molar growth yield on formate (Y=2.5 g ·mol-1 at a dilution rate of 0.05 h-1) and RuBPCase activities in cell-free extracts suggested that T. acidophilus employs the Calvin cycle for carbon assimilation during growth on formate. T. acidophilus was unable to utilize the C1-compounds methanol and methylamine. Formate-dependent oxygen uptake was expressed constitutively under a variety of growth conditions. Cell-free extracts contained both dye-linked and NAD-dependent formate dehydrogenase activities. NAD-dependent oxidation of formaldehyde required reduced glutathione. In addition, cell-free extracts contained a dye-linked formaldehyde dehydrogenase activity. Mixotrophic growth yields were higher than the sum of the heterotrophic and autotrophic yields. A quantitative analysis of the mixotrophic growth studies revealed that formaldehyde was a more effective energy source than formate.  相似文献   

14.
Plants typically expend a significant portion of their available carbon (C) on nutrient acquisition – C that could otherwise support growth. However, given that most global terrestrial biosphere models (TBMs) do not include the C cost of nutrient acquisition, these models fail to represent current and future constraints to the land C sink. Here, we integrated a plant productivity‐optimized nutrient acquisition model – the Fixation and Uptake of Nitrogen Model – into one of the most widely used TBMs, the Community Land Model. Global plant nitrogen (N) uptake is dynamically simulated in the coupled model based on the C costs of N acquisition from mycorrhizal roots, nonmycorrhizal roots, N‐fixing microbes, and retranslocation (from senescing leaves). We find that at the global scale, plants spend 2.4 Pg C yr?1 to acquire 1.0 Pg N yr?1, and that the C cost of N acquisition leads to a downregulation of global net primary production (NPP) by 13%. Mycorrhizal uptake represented the dominant pathway by which N is acquired, accounting for ~66% of the N uptake by plants. Notably, roots associating with arbuscular mycorrhizal (AM) fungi – generally considered for their role in phosphorus (P) acquisition – are estimated to be the primary source of global plant N uptake owing to the dominance of AM‐associated plants in mid‐ and low‐latitude biomes. Overall, our coupled model improves the representations of NPP downregulation globally and generates spatially explicit patterns of belowground C allocation, soil N uptake, and N retranslocation at the global scale. Such model improvements are critical for predicting how plant responses to altered N availability (owing to N deposition, rising atmospheric CO2, and warming temperatures) may impact the land C sink.  相似文献   

15.
Bioenergy crop cultivation on former peat extraction areas is a potential after‐use option that provides a source of renewable energy while mitigating climate change through enhanced carbon (C) sequestration. This study investigated the full C and greenhouse gas (GHG) balances of fertilized (RCG‐F) and nonfertilized (RCG‐C) reed canary grass (RCG; Phalaris arundinacea) cultivation compared to bare peat (BP) soil within an abandoned peat extraction area in western Estonia during a dry year. Vegetation sampling, static chamber and lysimeter measurements were carried out to estimate above‐ and belowground biomass production and allocation, fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) in cultivated strips and drainage ditches as well as the dissolved organic carbon (DOC) export, respectively. Heterotrophic respiration was determined from vegetation‐free trenched plots. Fertilization increased the above‐ to belowground biomass production ratio and the autotrophic to heterotrophic respiration ratio. The full C balance (incl. CO2, CH4 and DOC fluxes from strips and ditches) was 96, 215 and 180 g C m?2 yr?1 in RCG‐F, RCG‐C and BP, respectively, suggesting that all treatments acted as C sources during the dry year. The C balance was driven by variations in the net CO2 exchange, whereas the combined contribution of CH4 and DOC fluxes was <5%. The GHG balances were 3.6, 7.9 and 6.6 t CO2 eq ha?1 yr?1 in RCG‐F, RCG‐C and BP, respectively. The CO2 exchange was also the dominant component of the GHG balance, while the contributions of CH4 and N2O were <1% and 1–6%, respectively. Overall, this study suggests that maximizing plant growth and the associated CO2 uptake through adequate water and nutrient supply is a key prerequisite for ensuring sustainable high yields and climate benefits in RCG cultivations established on organic soils following drainage and peat extraction.  相似文献   

16.
Abstract Dark-grown cell suspension cultures of Chenopodium rubrum lacking chlorophyll greened strongly upon transfer to illumination and fresh medium. This greening took place both in the presence of sucrose as a carbon source and in a mineral salt medium under an atmosphere enriched in CO2. The synthesis of chlorophyll was in each case closely accompanied by the development of high levels of enzymes typical of photosynthesis. Greening in sugar-containing medium resulted in a rapid acquisition of characteristic features of photomixotrophic cultures, which have the ability to survive for a prolonged period in a minimal photoautotrophic environment in the light long after the initially present sucrose has been depleted from the medium. Greening under autotrophic conditions represented a direct transition from starvation conditions resulting from prolonged heterotrophic batch growth to successful photoautotrophy. Thus, light triggered the build-up of a competent photosynthetic apparatus irrespective of the nutritional necessity for autotrophy. Illumination and greening did not influence catabolic enzyme activities beyond that increase of metabolic activity which is required for the production of photosynthetic machinery.  相似文献   

17.
Previous studies have demonstrated that growth of marine phytoplankton, bacteria and protozoa can be limited by the availability of Fe. We report evidence that the amount of Fe assimilated by crustacean grazers is affected by the Fe status of their pry. 59Fe and 14C radiotracers were used to follow the fate of Fe and carbon during trophic transfer from diatoms to copepods. Fe assimilation efficiency was higher for copepods ingesting Fe-limited Thalassiosira weissflogii (17%) compared to diatoms that were not limited by Fe (10%), but assimilated Fe was lost more rapidly by copepods ingesting Fe-limited prey. Fe:C assimilation ratios were lower in copepods (5-12 mol Fe:mol C) than the cellular ratios of the phytoplankton prey (17-35 mol Fe:mol C), suggesting that copepods do not accumulate Fe relative to C during grazing. The largest single fate for Fe and C after grazing was regeneration to dissolved pools. Fe:C ratios in dissolved pools were approximately equal to the ratios in the original prey, but Fe:C ratios were higher in particular pools (largely fecal pellets), which should facilitate the export of Fe from the euphotic zone relative to C. Although copepod grazing does recycle cellular Fe and C, our results indicate that grazing may also tend to enhance Fe stress for lower trophic levels by removing Fe from the euphotic zone faster than C.   相似文献   

18.
Global warming has the potential to increase soil respiration (RS), one of the major fluxes in the global carbon (C) cycle. RS consists of an autotrophic (RA) and a heterotrophic (RH) component. We combined a soil warming experiment with a trenching experiment to assess how RS, RA, and RH are affected. The experiment was conducted in a mature forest dominated by Norway spruce. The site is located in the Austrian Alps on dolomitic bedrock. We warmed the soil of undisturbed and trenched plots by means of heating cables 4 °C above ambient during the snow‐free seasons of 2005 and 2006. Soil warming increased the CO2 efflux from control plots (RS) by ∼45% during 2005 and ∼47% during 2006. The CO2 efflux from trenched plots (RH) increased by ∼39% during 2005 and ∼45% during 2006. Similar responses of RS and RH indicated that the autotrophic and heterotrophic components of RS responded equally to the temperature increase. Thirty‐five to forty percent or 1 t C ha−1 yr−1 of the overall annual increase in RS (2.8 t C ha−1 yr−1) was autotrophic. The remaining, heterotrophic part of soil respiration (1.8 t C ha−1 yr−1), represented the warming‐induced C loss from the soil. The autotrophic component showed a distinct seasonal pattern. Contribution of RA to RS was highest during summer. Seasonally derived Q10 values reflected this pattern and were correspondingly high (5.3–9.3). The autotrophic CO2 efflux increase due to the 4 °C warming implied a Q10 of 2.9. Hence, seasonally derived Q10 of RA did not solely reflect the seasonal soil temperature development.  相似文献   

19.
Lakes process terrigenous carbon. The carbon load processed by lakes may partially offset estimates made for terrestrial net ecosystem exchange (NEE). The balance within lakes between carbon burial and evasion to the atmosphere determines whether lakes are net sinks or net sources of atmospheric carbon. Here we develop a model to study processing of both autochthonous and allochthonous carbon sources in lakes. We run the model over gradients of dissolved organic carbon (DOC) and total phosphorus (TP) concentrations found in the Northern Highlands Lake District of Wisconsin. In our model, lakes processed between 5 and 28 g C m?2 (watershed) yr?1 derived from the watershed, which approximates one‐tenth of NEE for similar terrestrial systems without lakes. Most lakes were net heterotrophic and had carbon evasion in excess of carbon burial, making them net sources of carbon to the atmosphere. Only lakes low in DOC and moderate to high in TP were net autotrophic and net sinks of carbon from the atmosphere.  相似文献   

20.
Increased plant biomass is observed in terrestrial systems due to rising levels of atmospheric CO2, but responses of marine macroalgae to CO2 enrichment are unclear. The 200% increase in CO2 by 2100 is predicted to enhance the productivity of fleshy macroalgae that acquire inorganic carbon solely as CO2 (non‐carbon dioxide‐concentrating mechanism [CCM] species—i.e., species without a carbon dioxide‐concentrating mechanism), whereas those that additionally uptake bicarbonate (CCM species) are predicted to respond neutrally or positively depending on their affinity for bicarbonate. Previous studies, however, show that fleshy macroalgae exhibit a broad variety of responses to CO2 enrichment and the underlying mechanisms are largely unknown. This physiological study compared the responses of a CCM species (Lomentaria australis) with a non‐CCM species (Craspedocarpus ramentaceus) to CO2 enrichment with regards to growth, net photosynthesis, and biochemistry. Contrary to expectations, there was no enrichment effect for the non‐CCM species, whereas the CCM species had a twofold greater growth rate, likely driven by a downregulation of the energetically costly CCM(s). This saved energy was invested into new growth rather than storage lipids and fatty acids. In addition, we conducted a comprehensive literature synthesis to examine the extent to which the growth and photosynthetic responses of fleshy macroalgae to elevated CO2 are related to their carbon acquisition strategies. Findings highlight that the responses of macroalgae to CO2 enrichment cannot be inferred solely from their carbon uptake strategy, and targeted physiological experiments on a wider range of species are needed to better predict responses of macroalgae to future oceanic change.  相似文献   

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