碳酸钠逐级驯化对星星草幼苗抗碱性的影响

对不同浓度Ｎａ２ＣＯ３膛级驯化星星草幼苗的研究结果表明,逐级提高对星星草幼苗的盐碱胁迫强度,在一定程度上可以缓解Ｎａ２ＣＯ３对幼苗鲜重和干重增长的抑制作用,及其对星星草幼苗细胞膜的伤害,从而提高幼苗对Ｎａ２ＣＯ３胁迫的抗性。并就星星草幼苗耐盐碱的极限进行了讨论。     

Calcium magnesium imbalance in clovers: A cause of negative yield response to liming

Three pot experiments, in which causes of negative yield responses to liming were investigated, are reported. The soil used, Waimumu silt loam (Fragiochrept), differed from others that have been reported to show negative yield response to liming, in that it is only moderately weathered and leached, only moderately acid and has previously shown positive yield responses to liming. Deficiencies of Zn and Mg were identified, but limed (pH 6.8) soils still showed a 40% yield depression even where all nutrients were supplied daily. Phosphorus availability was little affected by liming, and despite Mg and Zn addition, yields were depressed at high lime (pH 6.4) and high P while plants showed leaf symptoms of Mg deficiency. Neither plant nor soil analyses indicated low Mg levels but Ca: Mg ratios in soil were 22:1. When a pH range 5.2–6.1 was produced by liming with CaCO₃ and MgCO₃ at ratios between 100:0, and 50:50 on an equivalent basis, negative yield response was eliminated at Ca:Mg of 50:50. There was no evidence that Mg was fixed or rendered unavailable at the higher pH levels. A Ca induced Mg deficiency arising when exchangeable Ca:Mg>20 is suggested as the cause. The role of variable surface charge in converting soils that respond positively to lime to a negative response condition is discussed.     

Iron Additions Reduce Sulfide Intrusion and Reverse Seagrass (<Emphasis Type="Italic">Posidonia oceanica</Emphasis>) Decline in Carbonate Sediments

Abstract We conducted a 2-year in situ experiment to test the capacity of iron additions to reverse the decline experienced by a Posidonia oceanica meadow colonizing carbonate, iron poor sediment. Iron additions improved the sediment conditions that support seagrass growth by decreasing the sediment sulfide concentration and sulfate reduction rates, and decreased sulfide intrusion into the plants. Iron additions for 2 years did not significantly change survivorship of shoots present at the onset of the experiment, but significantly increased shoot recruitment and survivorship of shoots recruited during the experiment. After 2 years, iron additions reversed seagrass decline and yielded positive growth rates of shoots relative to control populations where seagrass continued to decline. This research demonstrates that seagrass decline in carbonate sediments may be reversed by targeting critical processes such are sediment sulfide pools and seagrass nutritional status, controlling the functioning of the ecosystem.     

Acidification effects on biofouling communities: winners and losers

How ocean acidification affects marine life is a major concern for science and society. However, its impacts on encrusting biofouling communities, that are both the initial colonizers of hard substrata and of great economic importance, are almost unknown. We showed that community composition changed significantly, from 92% spirorbids, 3% ascidians and 4% sponges initially to 47% spirorbids, 23% ascidians and 29% sponges after 100 days in acidified conditions (pH 7.7). In low pH, numbers of the spirorbid Neodexiospira pseudocorrugata were reduced ×5 compared to controls. The two ascidians present behaved differently with Aplidium sp. decreasing ×10 in pH 7.7, whereas Molgula sp. numbers were ×4 higher in low pH than controls. Calcareous sponge (Leucosolenia sp.) numbers increased ×2.5 in pH 7.7 over controls. The diatom and filamentous algal community was also more poorly developed in the low pH treatments compared to controls. Colonization of new surfaces likewise showed large decreases in spirorbid numbers, but numbers of sponges and Molgula sp. increased. Spirorbid losses appeared due to both recruitment failure and loss of existing tubes. Spirorbid tubes are comprised of a loose prismatic fabric of calcite crystals. Loss of tube materials appeared due to changes in the binding matrix and not crystal dissolution, as SEM analyses showed crystal surfaces were not pitted or dissolved in low pH conditions. Biofouling communities face dramatic future changes with reductions in groups with hard exposed exoskeletons and domination by soft‐bodied ascidians and sponges.     

盐碱胁迫对青海湖裸鲤耗氧率、血浆渗透浓度和离子浓度的影响

采用呼吸生理和血液生理的方法,探讨了性成熟青海湖裸鲤(Gymnocypris przewalskii)对盐度、碳酸盐碱度的适应性以及青海湖裸鲤在盐碱胁迫下的渗透调节和离子调节规律。将裸鲤从淡水突变到盐水(盐度14.01±0.01)、碱水(碳酸盐碱度33.03±0.01mmol·L-1)和青海湖水(盐度12.12±0.02、碳酸盐碱度29.07±0.09mmol·L-1)中,测定了在不同水质胁迫下裸鲤耗氧率、血浆渗透压和离子浓度的变化。结果表明:与淡水对照组比较,呼吸耗氧率除了盐度组在3h有显著性升高(P<0.05),其他实验组96h内均未出现显著性变化(P>0.05);裸鲤的窒息点为0.14～0.17mg·L-1,各实验组窒息点均没有显著性差异(P>0.05);碱度组血浆的渗透浓度和Na+、Cl-、Ca2+离子浓度在96h内未出现变化(P>0.05),盐度组和青海湖水组在所测时间段有显著的升高(P<0.05),并且随着胁迫时间的延长,在72h达到峰值。各实验组血浆K+浓度变化没有血浆Na+、Cl-明显,K+浓度有增高的趋势,且都在72h达到了峰值。青海湖裸鲤具有较强的盐碱耐受性,能通过渗透调节和离子调控适应高盐碱环境,而消耗能量较少。     

Biocatalytic capture of CO2 with carbonic anhydrase and its transformation to solid carbonate

Atmospheric CO₂ is well known to be a major contributor to the “green house” effect on earth and as such it deserves to be treated as any environmental pollutant. The present paper focused on its biocatalytic capture by an anhydrase carbonic enzyme to form HCO₃⁻ anions, followed by trapping as solid CaCO₃ in basic conditions, in a “one pot” process. The kinetics of CaCO₃ formation with and without enzyme were compared at 5 and 20 °C, as well as the crystalline nature of the solid formed. Depending on the temperature and the initial pH of the buffer used, two different solid phases were observed: metastable vaterite and stable rhombohedra calcite. The formation of vaterite was enhanced when a buffer stock solution at an initial pH of 10.5, without any enzyme, was used. The possible mechanisms to explain these observations are discussed. At 5 °C, the initial precipitation rate of solid CaCO₃ increased by the addition of the enzyme, by a multiplication factor >10. However, this initial rate was also found to depend on the concentration of enzyme and the buffer capacity. Depending on these two parameters, an increasing formation rate of HCO₃⁻ in a first step, may lower the reaction medium pH so quickly, that the precipitation of solid carbonate in a second step may be highly hindered. As a consequence, the overall formation rate of solid CaCO₃ may actually decrease, for instance when the mass of enzyme is increased.     

The Evolution of Calcification in Reef-Building Corals

Corals build the structural foundation of coral reefs, one of the most diverse and productive ecosystems on our planet. Although the process of coral calcification that allows corals to build these immense structures has been extensively investigated, we still know little about the evolutionary processes that allowed the soft-bodied ancestor of corals to become the ecosystem builders they are today. Using a combination of phylogenomics, proteomics, and immunohistochemistry, we show that scleractinian corals likely acquired the ability to calcify sometime between ∼308 and ∼265 Ma through a combination of lineage-specific gene duplications and the co-option of existing genes to the calcification process. Our results suggest that coral calcification did not require extensive evolutionary changes, but rather few coral-specific gene duplications and a series of small, gradual optimizations of ancestral proteins and their co-option to the calcification process.     

Strontium/Calcium ratio, carbon and oxygen stable isotopes in coccolith carbonate from different grain-size fractions in South Atlantic surface sediments

In this study, the Strontium/Calcium (Sr/Ca) ratio, and the carbon and oxygen isotopic compositions of coccoliths are investigated in three different grain-size fractions (<20 μm, 15-5 μm, <5 μm) of 17 surface sediment samples from the Equatorial and South Atlantic. The results are compared to environmental parameters in order to assess the factors controlling the observed coccolith geochemical patterns. Isotopic and geochemical composition of coccolith species in surface sediment samples from the South Atlantic greatly varies according to the different grain-size fractions. However, even if the absolute values show a great offset, the general trends are comparable. The δ¹⁸O values show a decreasing trend with increasing temperature. The δ¹³C and Sr/Ca ratio are mainly influenced by productivity of coccolithophores, which is in turn controlled by different factors, such as temperature, nutrient supply and productivity of other phytoplankton groups. Dilution and dissolution are negligible factors in these open marine samples. Therefore, coccolith abundance in bulk sediment is the best approximation for productivity of coccolithophores. The various coccolith species fractionate Sr differently, as is best shown by the 5-15 μm fraction where three species (Calcidiscus leptoporus, Helicosphaera carteri and Coccolithus pelagicus) predominantly occur.     

A BATCH CULTURE METHOD FOR MICROALGAE AND CYANOBACTERIA WITH CO2 SUPPLY THROUGH POLYETHYLENE MEMBRANES1

A new method for CO₂ supply to photoautotrophic organisms was developed, and its applicability for measuring specific growth rates in shaken batch cultures of cyanobacteria and unicellular algae was shown. Small bags containing a concentrated carbonate buffer with a CO₂ partial pressure of 32 mbar were prepared from a thin foil of low density polyethylene (LDPE). These bags were inserted as CO₂ reservoirs (CRs) into polystyrene culture flasks with gas‐permeable screw caps, which were suitable to photometric growth measurement. CO₂ was released directly into the medium with membrane‐controlled kinetics. The CRs were not depleted within 1 week, although the atmosphere in the culture vessel exchanged rapidly with the ambient air. Rates of initial growth and final densities of the cultures of six different unicellular algal species and one cyanobacterium were markedly increased by diffusive CO₂ supply from the CR. In the presence of a CR, growth was exponential during the first 2 d in all cultures studied. The method described allowed a high number of measurements of specific growth rates with relatively simple experimental setup.     

SPATIAL AND TEMPORAL VARIABILITY IN BIOMASS AND PRODUCTION OF PSAMMOPHYTIC HALIMEDA INCRASSATA (BRYOPSIDALES,CHLOROPHYTA) IN A CARIBBEAN REEF LAGOON1

Estimates for the production of calcium carbonate by Halimeda spp. have been based on limited measures in small areas or over short periods, subsequently extrapolated over larger temporal and spatial scales. The accuracy of these extrapolations depends on the variations in time and space of the parameters used for the derivations of the production, which were evaluated in the present study for Halimeda incrassata (J. Ellis) J. V. Lamour. in the Puerto Morelos reef lagoon, Mexican Caribbean. Growth, biomass, and CaCO₃ content of the branches of the thalli were determined at 1–3 monthly intervals from November 1997 until June 1999, using the marking technique with the coloring agent Alizarin Red‐S. Biomass exhibited great variability (V=25.4%), and fluctuations were closely related to changes in thallus density. Growth and CaCO₃‐content changes were related to the solar cycle, having coefficients of 15.4% and 2.5%, respectively. Additionally, calcified biomasses of the thalli were determined over a large spatial (31 stations in ～7 km² area) and time (6 y) scale. Spatial variability in calcified biomass was 59%, and the coefficient of variation attained its highest value (69%) for the samples collected over a 6 y period, from 1990 to 1996 (except 1995). Based on overall average values, branches of H. incrassata in the study area had a mean turnover of 30 d, with an annual production of 815 g CaCO₃ per square meter.