Interactive effects of salinity and elevated CO2 levels on juvenile eastern oysters, Crassostrea virginica

Rising levels of atmospheric CO2 lead to acidification of the ocean and alter seawater carbonate chemistry, which can negatively impact calcifying organisms, including mollusks. In estuaries, exposure to elevated CO2 levels often co-occurs with other stressors, such as reduced salinity, which enhances the acidification trend, affects ion and acid-base regulation of estuarine calcifiers and modifies their response to ocean acidification. We studied the interactive effects of salinity and partial pressure of CO2 (PCO2) on biomineralization and energy homeostasis in juveniles of the eastern oyster, Crassostrea virginica, a common estuarine bivalve. Juveniles were exposed for 11 weeks to one of two environmentally relevant salinities (30 or 15 PSU) either at current atmospheric PCO2 (400 µatm, normocapnia) or PCO2 projected by moderate IPCC scenarios for the year 2100 (700-800 µatm, hypercapnia). Exposure of the juvenile oysters to elevated PCO2 and/or low salinity led to a significant increase in mortality, reduction of tissue energy stores (glycogen and lipid) and negative soft tissue growth, indicating energy deficiency. Interestingly, tissue ATP levels were not affected by exposure to changing salinity and PCO2, suggesting that juvenile oysters maintain their cellular energy status at the expense of lipid and glycogen stores. At the same time, no compensatory upregulation of carbonic anhydrase activity was found under the conditions of low salinity and high PCO2. Metabolic profiling using magnetic resonance spectroscopy revealed altered metabolite status following low salinity exposure; specifically, acetate levels were lower in hypercapnic than in normocapnic individuals at low salinity. Combined exposure to hypercapnia and low salinity negatively affected mechanical properties of shells of the juveniles, resulting in reduced hardness and fracture resistance. Thus, our data suggest that the combined effects of elevated PCO2 and fluctuating salinity may jeopardize the survival of eastern oysters because of weakening of their shells and increased energy consumption.

Lack of evidence for elevated CO2-induced bottom-up effects on marine copepods: a dinoflagellate-calanoid prey-predator pair

Rising levels of atmospheric CO2 are responsible for a change in the carbonate chemistry of seawater with associated pH drops (acidification) projected to reach 0.4 units from 1950 to 2100. We investigated possible indirect effects of seawater acidification on the feeding, fecundity, and hatching success of the calanoid copepod Acartia grani, mediated by potential CO2-induced changes in the nutritional characteristics of their prey. We used as prey the autotrophic dinoflagellate Heterocapsa sp., cultured at three distinct pH levels (control: 8.17, medium: 7.96, and low: 7.75) by bubbling pure CO2 via a computer automated system. Acartia grani adults collected from a laboratory culture were acclimatized for 3 d at food suspensions of Heterocapsa from each pH treatment (ca. 500 cells/ml; 300 ?g C/l). Feeding and egg production rates of the preconditioned females did not differ significantly among the three Heterocapsa diets. Egg hatching success, monitored once per day for the 72 h, did not reveal significant difference among treatments. These results are in agreement with the lack of difference in the cellular stoichiometry (C : N, C : P, and N : P ratios) and fatty acid concentration and composition encountered between the three tested Heterocapsa treatments. Our findings disagree with those of other studies using distinct types of prey, suggesting that this kind of indirect influence of acidification on copepods may be largely associated with interspecific differences among prey items with regard to their sensitivity to elevated CO2 levels.

Calcification of the Arctic coralline red algae Lithothamnion glaciale in response to elevated CO2

Rising atmospheric CO2 concentrations could cause a calcium carbonate subsaturation of Arctic surface waters in the next 20 yr, making these waters corrosive for calcareous organisms. It is presently unknown what effects this will have on Arctic calcifying organisms and the ecosystems of which they are integral components. So far, acidification effects on crustose coralline red algae (CCA) have only been studied in tropical and Mediterranean species. In this work, we investigated calcification rates of the CCA Lithothamnion glaciale collected in northwest Svalbard in laboratory experiments under future atmospheric CO2 concentrations. The algae were exposed to simulated Arctic summer and winter light conditions in 2 separate experiments at optimum growth temperatures. We found a significant negative effect of increased CO2 levels on the net calcification rates of L. glaciale in both experiments. Annual mean net dissolution of L. glaciale was estimated to start at an aragonite saturation state between 1.1 and 0.9 which is projected to occur in parts of the Arctic surface ocean between 2030 and 2050 if emissions follow 'business as usual' scenarios (SRES A2; IPCC 2007). The massive skeleton of CCA, which consist of more than 80% calcium carbonate, is considered crucial to withstanding natural stresses such as water movement, overgrowth or grazing. The observed strong negative response of this Arctic CCA to increased CO2 levels suggests severe threats of the projected ocean acidification for an important habitat provider in the Arctic coastal ocean.

Phytoplankton-bacteria coupling under elevated CO2 levels: a stable isotope labelling study, 2010

The potential impact of rising carbon dioxide (CO2) on carbon transfer from phytoplankton to bacteria was investigated during the 2005 PeECE III mesocosm study in Bergen, Norway. Sets of mesocosms, in which a phytoplankton bloom was induced by nutrient addition, were incubated under 1x (~350 µatm), 2x (~700 µatm), and 3x present day CO2 (~1050 µatm) initial seawater and sustained atmospheric CO2 levels for 3 weeks. 13C labelled bicarbonate was added to all mesocosms to follow the transfer of carbon from dissolved inorganic carbon (DIC) into phytoplankton and subsequently heterotrophic bacteria, and settling particles. Isotope ratios of polar-lipid-derived fatty acids (PLFA) were used to infer the biomass and production of phytoplankton and bacteria. Phytoplankton PLFA were enriched within one day after label addition, whilst it took another 3 days before bacteria showed substantial enrichment. Group-specific primary production measurements revealed that coccolithophores showed higher primary production than green algae and diatoms. Elevated CO2 had a significant positive effect on post-bloom biomass of green algae, diatoms, and bacteria. A simple model based on measured isotope ratios of phytoplankton and bacteria revealed that CO2 had no significant effect on the carbon transfer efficiency from phytoplankton to bacteria during the bloom. There was no indication of CO2 effects on enhanced settling based on isotope mixing models during the phytoplankton bloom, but this could not be determined in the post-bloom phase. Our results suggest that CO2effects are most pronounced in the post-bloom phase, under nutrient limitation.

Ecophysiological characteristics of four intertidal marine macroalgae during emersion along Shantou coast of China, with a special reference to the relationship of photosynthesis and CO2

Intertidal marine macroalgae experience periodical exposures during low tide due to their zonational distribution. The duration of such emersion leads to different exposures of the plants to light and aerial CO2, which then affect the physiology of them to different extents. The ecophysiological responses to light and CO2 were investigated during emersion in two red algae Gloiopeltis furcata and Gigartina intermedia, and two brown algae Petalonia fascia and Sargassum hemiphyllum, growing along the Shantou coast of China. The light-saturated net photosynthesis in G. furcata and P. fascia showed an increase followed by slightly desiccation, whereas that in G. intermedia and S. hemiphyllum exhibited a continuous decrease with water loss. In addition, the upper-zonated G. furcata and P. fascia, exhibited higher photosynthetic tolerance to desiccation and required higher light level to saturate their photosynthesis than the lower-zonated G. intemedia and S. hemiphyllum. Desiccation had less effect on dark respiration in these four algae compared with photosynthesis. The light-saturated net photosynthesis increased with increased CO2 concentrations, being saturated at CO2 concentrations higher than the present atmospheric level in G. furcata, G. intermedia and S. hemiphyllum during emersion. It was evident that the relative enhancement of photosynthesis by elevated CO, in those three algae increased, though the absolute values of photosynthetic enhancement owing to CO2 increase were reduced when the desiccation statuses became more severe. However, in the case of desiccated P. fascia (water loss being greater than 20 %), light saturated net photosynthesis was saturated with current ambient atmospheric CO2 level. It is proposed that increasing atmospheric CO2 will enhance the daily photosynthetic production in intertidal macroalgae by varied extents that were related to the species and zonation.

Effects of CO2 enrichment on the bloom-forming cyanobacterium Microcystis aeruginosa (Cyanophyceae): Physiological responses and relationships with the availability of dissolved inorganic carbon

Microcystis aeruginosa Kutz. 7820 was cultured at 350 and 700 muL.L-1 CO2 to assess the impacts of doubled atmospheric CO2 concentration on this bloom-forming cyanobacterium. Doubling Of CO2 concentration in the airflow enhanced its growth by 52%-77%, with pH values decreased and dissolved inorganic carbon (DIC) increased in the medium. Photosynthetic efficiencies and dark respiratory rates expressed per unit chl a tended to increase with the doubling of CO2. However, saturating irradiances for photosynthesis and light-saturated photosynthetic rates normalized to cell number tended to decrease with the increase of DIC in the medium. Doubling of CO2 concentration in the airflow had less effect on DIC-saturated photosynthetic rates and apparent photosynthetic affinities for DIC. In the exponential phase, CO2 and HCO3- levels in the medium were higher than those required to saturate photosynthesis. Cultures with surface aeration were DIC limited in the stationary phase. The rate of CO2 dissolution into the liquid increased proportionally when CO2 in air was raised from 350 to 700 muL.L-1, thus increasing the availability of DIC in the medium and enhancing the rate of photosynthesis. Doubled CO2 could enhance CO2 dissolution, lower pH values, and influence the ionization fractions of various DIC species even when the photosynthesis was not DIC limited. Consequently, HCO3- concentrations in cultures were significantly higher than in controls, and the photosynthetic energy cost for the operation of CO2 concentrating mechanism might decrease.

CO2升高对土壤微生物群落影响的模拟研究

大气CO2浓度升高可以通过植物间接影响土壤生态系统。土壤生态系统的结构和功能改变将影响有机质矿化和营养物质循环，进而可能对CO2浓度升高产生正反馈或负反馈。微生物是土壤生态系统的主体，在对CO2浓度升高的反馈中起着至关重要的作用。本研究以开顶箱系统为平台，采用微生物分子生态学技术和现代酶学技术，通过对长期接受500 ppm CO2的红松幼树、长白赤松幼树和蒙古栎幼树非根际土壤连续两个生长季的测定，系统研究了高浓度CO2对温带森林土壤微生物群落的生物量和微生物活性的影响，检测了土壤微生物群落的结构和功能以及土壤化学性质变化，主要结论如下： （1）高浓度CO2处理提高了土壤有机碳含量。与对照组相比较，红松幼树土壤有机碳含量提高9.4%；长白赤松幼树土壤提高0.6%；蒙古栎幼树土壤提高1.3%。 （2）高浓度CO2处理使土壤磷酸酶（phosphatase）、几丁质酶（1,4-β-acetylglucosaminidase, 1,4-β-NAG）和多酚氧化酶（phenol oxidase）活性发生了显著变化，高浓度CO2使红松土壤 1,4-β-NAG活性提高7-25%，长白松土壤1,4-β-NAG平均活性降低14%，蒙古栎土壤1,4-β-NAG平均活性提高31%。 同时研究还发现，过氧化物酶（peroxidase）和多酚氧化酶(phenol oxidase)活性与微生物量碳和微生物量氮呈显著的正相关。相关分析还显示，土壤湿度与1,4-α-葡萄糖苷酶（1,4-α-glucosidase）活性、 微生物生物量碳和微生物生物量氮呈显著的正相关。 高浓度CO2在不同程度上改变了土壤转化酶活性和脱氢酶活性。高浓度CO2显著提高了红松和长白赤松土壤硝化酶活性；而显著降低反硝化酶活性。 （3）研究发现三种树土壤的真菌和细菌群落存在着季节性演替，并且高浓度CO2熏蒸处理使真菌群落结构发生了显著的变化，表现为一些种群优势度下降，另一些升高。虽然，细菌群落没有如真菌群落变化的明显，但研究中也发现高浓度CO2的确使个别细菌种群的优势度发生了显著改变。 亲缘关系与Calocybe carnea，Magmatodrilus obscurus密切的真菌是红松土壤优势种群，与Humicola fuscoatra关系相近的是长白松土壤的优势种群，并且此三种真菌的季节性变化不显著。研究发现高浓度CO2使红松土壤中亲缘关系与Pachyella clypeata，Cochlonema euryblastum，Lepiota cristata，Eimeriidae sp.， Trichoderma sp.相近的种群的丰富度显著提高，使蒙古栎土壤中亲缘关系与Serendipita vermifera，Calocybe carnea种群丰富度显著下降，使蒙古栎土壤中与Candida sp.，Magmatodrilus obscurus和Pachyella clypeata亲缘关系密切种群的丰富度显著提高。 （4）三种幼树叶的原位分解培养429天结果显示，红松和长白松凋落物的β-葡萄糖苷酶（1,4-β-glucosidase）和木糖苷酶（1,4-β-xylosidase）活性随着分解而逐渐增加，而这两种酶在蒙古栎凋落物分解过程中保持相对恒定；高浓度CO2显著影响叶凋落物分解磷酸酶（phosphatase），纤维二糖酶（cellobiohydrolase）, 几丁质酶(1,4-β-NAG)，多酚氧化酶（phenol oxidase）和过氧化物酶（peroxidase）的活性。研究发现，凋落物的生物化学性质变化能引起分解的微生物群落发生变化，进而引起分泌的胞外酶活性变化，科学印证了大气CO2浓度升高“通过影响凋落物质量进而影响分解叶凋落物的微生物群落的结构和功能”的猜测。 不同凋落物之间酶活性差异显著，真菌和细菌群落结构也显著不同。序列与Hyphodiscus hymeniophilus亲缘关系密切的真菌和亲缘关系与Verrucomicrobia bacterium密切的细菌是长白松凋落分解的最优势种群，序列与Lophium mytilinum亲缘关系密切的真菌是红松凋落分解的最优势种群。 另外，研究还发现，高浓度CO2使参与分解红松凋落物Beta proteobacterium OS-15A亲缘关系相近的细菌种群和与Azospirillum amazonense亲缘关系相近的种群丰富度显著降低；使与Luteibactor rhizovicina亲缘关系相近的种群和与Luteibactor rhizovicina亲缘关系相近的种群显著提高。高浓度CO2使定殖于长白松凋落物上Hyphodiscus hymeniophilus亲缘关系相近的种群和与Bionectria pityrodes亲缘关系相近的种群显著提高，而使与Neofabraea malicorticis亲缘关系相近的种群和与Hyphodiscus hymeniophilus亲缘关系相近的种群显著下降。

CO2浓度升高对三种树木叶片化学和舞毒蛾幼虫取食及生长的影响

探讨全球气候变化的生物学和生态学效应是当今生态学中的热点，研究大气CO2浓度升高对植物-昆虫相互作用关系的影响具有重要的理论和实践意义。本文使用开顶式气室（Open-top chamber，OTC）在野外条件下研究了CO2浓度升高对三种树木（小青杨、白桦和蒙古栎）叶片化学成分含量的影响，以及树木叶片品质变化对一种广食性森林昆虫（舞毒蛾）幼虫取食、生长发育和取食偏嗜性的影响。得出如下结果：（1）CO2浓度升高对3个受试树种叶片中的营养成分及次生代谢物含量均有显著影响，总体表现为氮含量降低，而碳氮比、非结构性碳水化合物、总酚和缩合丹宁含量增加。叶片中的化学成分含量可随时间发生显著变化，不同树种、甚至同一树种不同冠层高度的叶片对CO2浓度升高的响应强度也是不同的。叶片的干物质含量和比叶重对CO2浓度升高的响应不显著。（2）室内非选择性取食实验、室内选择性取食实验以及上树取食饲养方式下的多龄期取食实验，均发现高浓度CO2处理组内舞毒蛾幼虫的生长发育受到显著抑制。但对四龄舞毒蛾幼虫所进行的短期生物测定并未发现不同CO2浓度处理下幼虫的生长发育速率、对食物的取食率和转化率等昆虫营养指标存在显著差异。（3）叶片品质的降低是导致舞毒蛾幼虫生长发育受抑制的主要原因。但是总体上，CO2浓度升高导致的叶片品质变化并未显著影响幼虫的取食率和取食量。（4）舞毒蛾幼虫对不同叶片种类表现出清晰的取食选择性，这种选择性在其幼龄期就可表现出来。幼虫对小青杨上层叶片有最显著的偏嗜性，对蒙古栎下层叶片有最明显的拒食性。但是CO2浓度升高导致的叶片品质变化对舞毒蛾幼虫的取食选择性和寄主偏嗜行为并未产生显著影响。（5）检测出高浓度CO2处理组内舞毒蛾幼虫虫粪中含有浓度更高的植物次生代谢物质（总酚和缩合单宁），这很可能是昆虫整体生长发育受抑制的重要原因之一。

CO2浓度升高对红桦幼苗生理与生长的影响

大气CO2浓度的增加已经成为不可争议的事实。预计本世纪末大气CO2浓度将增加到约700µmol mol-1。森林年光合产量约占陆地生态系统年光合产量的70%。森林树木是一个巨大的生物碳库，约占全球陆地生物碳库的85%。森林树木对CO2的固定潜力是缓解由大气CO2浓度升高引起的未来全球气候变化问题的决定性因子之一。红桦（Betula albosinensis Burk.）是川西亚高山采伐迹地自然或人工恢复的重要树种。本研究以1a红桦幼苗为模式植物，采用人工模拟的方法，研究CO2浓度升高对不同种内竞争强度（种群水平）下红桦幼苗的生理特征、生长、干物质积累及其分配的影响，探讨在种内竞争生长条件下红桦幼苗的“光合适应机理”与生长特征，为西南亚高山森林生产力对未来全球变化的预测提供重要参考。 本研究的主要结果如下： 1）在种内竞争生长条件下红桦幼苗经过CO2浓度升高熏蒸4个月后，叶片出现“光合适应”现象。与对照相比，低种植密度（28株m-2）和高种植密度（84株m-2）条件下的红桦幼苗净光合速率（A）、气孔导度（gs）、蒸腾速率（E）、表观量子产量（AQY）和羧化速率（CE）显著降低，而水分利用效率（WUE）则显著提高。CO2浓度升高处理的红桦幼苗叶片Rubisco活性、单位叶面积N浓度、叶绿素a、叶绿素b和类胡萝卜素浓度都显著降低。但CO2浓度对红桦幼苗的叶绿素a与叶绿素b的比值没有显著影响。CO2浓度升高显著增加红桦幼苗单位叶面积的非结构性碳水化合物（TNC）浓度，结果是红桦幼苗的比叶面积（SLA，cm2 g-1）显著降低。 2）与对照相比，CO2浓度升高处理的红桦幼苗高、基径、单叶面积和侧枝的相对生长速率（R GR）显著提高，尤其在试验处理的早期。CO2浓度升高既增加单株红桦幼苗总叶片数量又增加单叶面积，结果是单株红桦幼苗的总叶面积比对照显著增加。 3）CO2浓度升高处理显著增加红桦幼苗干物质积累（尤其是细根生物量），改变了红桦幼苗生物量的分配格局。与对照相比，CO2浓度升高处理的红桦幼苗叶重比（LWR）、叶面积比（LAR）、叶根重比（Wl/Wr）和源汇重比（leaf weight to non-leaf weight ratio, Wsource/Wsink）显著下降（高种植密度的LWR除外），而根冠比（R/S）则显著增加。在两种种植密度条件下，CO2浓度升高显著增加红桦幼苗根生物量的分配比率，显著降低叶片的生物量分配比率，对主茎、侧枝以及地上生物量的分配比率不变或约有下降。 总之，长期生长在CO2浓度升高条件下的红桦幼苗光合能力下降，并伴随Rubisco活性、叶N浓度、光合色素浓度的显著降低以及TNC浓度的显著增加。支持树木光合速率下降与Rubisco活性、叶N浓度下降以及TNC浓度增加紧密相关的假设。CO2浓度升高处理红桦幼苗的早期相对生长速率大大高于对照，而后期迅速下降，说明红桦幼苗生物量的显著增加主要归功于CO2浓度升高的早期促进作用和叶面积的显著增加。CO2浓度升高显著增加红桦幼苗根系生物量和根冠比，表明红桦幼苗“额外”固定的C向根系转移。 The steady increae of atmospheric CO2 concentration（[CO2]）has been inevitable fact. Models predict that the atmospheric [CO2] will increase to about 700µmol mol-1 at the end of the twenty-first century. As trees constitute a majoor carbon reservoir–85% of total plant carbon is found in forest, and their ability to sequester carbon is a key determinant of future global change problems caused by increases in atmospheric CO2. In addition to the role of forests in the global carbon cycle, inceased growth could be of economic benefit, for example, offsetting deleterious effects of climatic changes. Betula albosinensis (Burk.) usually emerges as the pioneer species in initial stage and as constructive species in later stages of forest community succession of mountain forest area, and also is one of important tree species for afforestation in logged area, in southwesten China. In this experinment, Betula albosinensis seedling (one-year-old) was used as the model plant. B. albosinensis seedlings were grown under two all-day [CO2], ambient (about 350 µmol·mol-1) and elevated [CO2] (about 700 µmol·mol-1), and two planting densities of 28 plants per m2 and 84 plants per m2. The objectives were to characterize birch mature leaf photosynthesis, growth, mass accumulation and allocation responses to long-tern elevated growth [CO2] under the influences of neighbouring plants, and to assess whether elevated [CO2] regulated birch mature leaf photosynthetic capacity, in terms of leaf nitrogen concentration (leaf [N]), activity of ribulose bisphosphate carboxygenase (Rubisco), Rubisco photosynthetic efficiency, and total nonstructural carbohydrates (TNC) concentration, and also to provide a strong reference to predict the productivity of subalpine forests under the future global changes. The results are as follows: 1) B.albosinensis seedlings exposed to elevated [CO2] for 120 days, photosynthetic acclimation phenomena occurred. At two planting densities, leaves of birch seedlings grown under elevated [CO2] had lower net photosynthetic rate (A), stomatal conductance (gs), transpiration (E), apparent quantum yield (AQY) and carboxylated efficiency (CE) and higher water use efficiency (WUE), compared to those of B.albosinensis seedlings grown under ambient [CO2]. Based on the leaf area, leaf [N], Rubisco activity and photosynthetic pigments concentrations of B. albosinensis seedlings grown under elevated [CO2] were significantly lower than those grown under ambient [CO2]. The ratio of chlorophyll a to chlorophyll b concentration was not affected by elevated [CO2]. Under elevated [CO2], the TNC concentration per unit leaf area significantly increased, resulting in significant decrease in specific leaf area. Thus leaf photosynthetic capacity of B. albosinensis seedlings would perform worse under rising atmospheric [CO2] and the influences of neighbouring plants. 2) Under elevated [CO2], the relative growth rate (RGR) of B. albosinensis seedlings height, basal diameter, a leaf area and branch length significantly increased, especially at the initial stage of exposure to elevated [CO2], and a leaf area and leaf numbers per B. albosinensis seedling also significantly increased. Thus the total leaf area per B. albosinensis seedling was significantly increased under elevated [CO2]. 3) As the increase of RGR and total leaf area, biomass of B. albosinensis seedling grown elevated [CO2] was higher, compared to that of B.albosinensis seedlings grown at ambient [CO2]. Elevated [CO2] changed the biomass allocation pattern of B. albosinensis seedling. At two planting densities, B. albosinensis seedlings grown elevated [CO2] had lower leaf weight to total weight ratio (LWR), leaf area to total weight ratio (LAR) and leaf weight to non-leaf weight ratio (Wsource/Wsink), but higher root weight to shoot weight ratio (R/S), compared to those of B.albosinensis seedlings grown at ambient [CO2]. Under elevated [CO2], roots biomass to total biomass ratio was signigicantly increased, leaves biomass to total biomass ratio was significantly decreased. The main stem and branch biomass to total biomass ratio were not affected by elevated [CO2]. In conclusion, our results supported the hypothesis that the decline in photosynthetic capacity of C3 plants will appear after long-term exposure to elevated [CO2], accompanying with the significant decrease in Rubisco activity, leaf N concentration, photosynthetic pigments concentration, and significant increase in total non-structural carbohydrates concentration. Our results also have shown that the increase of biomass of B. albosinensis seedlings should be attributed to initial stimulation on RGR and total leaf area resulted from elevated [CO2]. Under elevated [CO2], the extra carbon sequestered by B.albosinensis seedlings transferred into under-ground part because of increase in root biomass and R/S.

环境CO2浓度和群落密度对红桦(Betula albosinensis Burk.)幼苗碳氮吸收和分配的影响

当前大气CO2浓度升高是全球变化的主要趋势之一，CO2浓度升高还会引起全球变暖等其它环境问题，因而CO2浓度浓度升高对植物影响的研究已经成为全球变化领域的焦点。红桦是川西亚高山地区暗针叶林演替初期的先锋树种和演替后期的建群种，在群落演替过程中它对环境因子的响应决定红桦群落的演替进程。本文通过控制CO2浓度的气候室试验，研究了CO2浓度倍增环境下，不同密度水平红桦碳氮固定、分配可能发生的改变，并探讨了升高大气CO2浓度对群体内部竞争的影响。以期通过本研究明确川西亚高山地区代表性物种红桦对未来气候变化的响应，为今后采取措施应对气候变化、妥善进行森林管理提供理论依据和科学指导。主要研究结果如下： 1.升高CO2浓度对红桦幼苗生长的影响以及树皮、树干响应的不同 (1) CO2浓度升高显著促进红桦幼苗的生物量、株高、基茎的生长，同时也改变生物量在体内的分配格局，主要是增加根和主茎、减少叶在总生物量中的比重。(2)树皮和树干对升高CO2浓度的影响有差异，它们对CO2浓度升高的反应程度不同，但反应方向一致。 2.密度的副效应 (1) 增加种植密度对单株生物量、株高和基径的生长具有副效应，也降低升高CO2浓度对红桦生长的正效应。(2) 增加种植密度，显著增加红桦幼苗的群体生物量，从而使红桦群体固定更多的大气CO2气体。可见密度在决定红桦生物量及固碳能力方面具有重要意义。探索适合未来大气CO2浓度升高条件下植物生长的密度，对未来的森林经济生产、生态恢复具有重要意义。 3. 升高CO2浓度对红桦幼苗苗冠结构及冠层内部竞争的影响 (1) 冠幅、冠高、苗冠表面积和苗冠体积等树冠特征均受CO2浓度升高的影响而增加，但是受密度增加的影响而降低。(2) 单位苗冠投影面积叶片数(LDcpa)和单位苗冠体积叶片数(LDcv)均低于相应的现行CO2浓度处理，这主要是由于冠幅和冠高的快速生长所造成的。(3) LDcpa和LDcv的降低表明，红桦在升高CO2浓度的条件下，会作出积极的响应，从而缓解由于群体和个体生长的增加所引起的竞争压力的增加。 4. 升高CO2浓度对红桦幼苗养分元素吸收与分配的影响 (1) CO2浓度升高，植株各器官N、P含量降低，但单株N、P总吸收量均增加。红桦幼苗体内N、P浓度的下降是由于生物量迅速增加引起的稀释效应造成的。(2) CO2浓度升高，N、P向主茎和根的分配增加，向叶片的分配减少，主要是由于前者在总生物量中的比重增加，而后者减少了。(3) CO2浓度升高，氮磷利用效率(NUE和PUE)提高，氮磷累积速率(NAcR和PAcR)显著增加。而NUE和PUE的提高可以有效缓解CO2浓度升高后，亚高山和高山地区森林土壤中养分元素不足对森林生产力的限制。 5. 升高CO2浓度对红桦幼苗群体碳平衡的影响 (1) 升高CO2浓度对植物的光合作用、呼吸速率和生长均具有促进作用。(2) 土壤有机碳含量在实验前期迅速增加，后期积累速率下降。(3) 升高CO2浓度以后，土壤呼吸显著增强；土壤呼吸还具有明显的季节变化。(4) 红桦群体日固碳量受到升高CO2浓度的促进作用。结果(1)-(4)说明所研究群落的碳动态对现行的气候波动是敏感的；所研究群落在作为大气CO2气体的源-汇关系方面至少存在季节间的源汇飘移。(5)种植密度的升高显著增加了群体固碳量。 6. 升高CO2浓度对红桦幼苗生长后期叶片衰老的影响 升高CO2浓度有利于减缓红桦幼苗叶片生长季节末期的衰老。生长季节末期，随着CO2浓度的升高光合速率和可溶性蛋白含量均呈上升趋势，同时MDA（丙二醛）含量下降，保护酶SOD（超氧化物岐化酶）、CAT（过氧化氢酶）活性升高。由此说明，升高CO2浓度有利于减缓生长季节后期叶片的衰老，使叶片维持较高的光合速率，也从生理学的角度支持了本文及前人有关CO2浓度升高促进植物光合和生长的假说及结果。 The increased CO2 concentration is one of the most important problems among global changes. The increase of CO2 will also cause other environmental problems, such as global warming, etc. So the effects of elevated CO2 on plant have drawn sights of many scientists in the research field of global change. Red birch (Betula albosinensis) usually emerges as the pioneer species in initial stage and as constructive species in later stages of forest community succession of the dark coniferous forests in Western Sichuan, China. It’s response to elevated CO2 may determine the succession process of the community where it lives in. By controlling CO2 at the ambient and twice as the ambient level (ambient + 350 umol mol-1) using enclosed-top chambers (ETC), possible effects of elevated CO2 on carbon fixation and allocation under two plantation densities are investigated. The effects of elevated CO2 on competition within canopy of red birch seedlings are also observed in the present paper. We hope to make sure of the effects of elevated CO2 on the representative species, red birch. And so that, our results could provide a strong theoretical evidence and scientific direction for forest management and afforestation under a future, CO2 elevated world. The results are as fowllows: 1. The effects of elevated CO2 on growth and the different responses of wood and bark of red birch seedlings (1) Elevated CO2 increases the growth of seedling biomass, seedling height and basal diameter of red birch. It also changed the biomass allocation in red birch seedlings. The ratio of root and main stem to all biomass is increased and the ratio of leaf is decreased. (2) Tree bark and wood show different response degree but similar response direction to elevated CO2. 2. Negative effects of planting density (1) The increase of planting density showes negative effects on the individual growth of seedling biomass, seedling height and basal diameter of red birch. It also eliminates the positive effects of elevated CO2 on growth of red birch seedlings. (2) Community biomass is increased by the elevated planting density, which means that the high density red birch community could fix more CO2 than the low density one. These results show that planting density plays an important role in determining biomass and carbon fixation ability of red birch community. Thus, exploring proper planting density becomes economically important for the future, CO2 elevated word. 3. The effects of elevated CO2 on crown architecture and competition within canopy of red birch seedlings (1) Crown width, crown depth, crown surface area and crown volume are all increased under the influence of elevated CO2. (2) Leaf number per unit area of projected crown area (LDcpa) and per unit volume of crown volume (LDcv) are lower under elevated CO2. This is resulted from the stimulated growth of tree crown features. (3) The decrease of LDcpa and LDcv indicate that plants will respond forwardly to reduce the possible increase of competition resulted from stimulated growth of individual plant and collectives in conditions of elevated CO2. 4. The effects of elevated CO2 on nutrition accumulation and allocation of red birch seedlings (1) Contents of N and P decrease due to the prompt increase of biomass of plant organs caused by elevated CO2. However, their accumulations increase under elevated CO2. (2) Elevated CO2 increases the allocation of N, P to main stem but reduced its allocation to leaf for that dry weight of the former increased but the dry weight of the later decreased. (3) Using efficiencies of N, P (NUE and PUE) and their accumulation rates (NAcR and PAcR) are found to increase under elevated CO2. Soil nutrition contents are always the limiting factors for plant growth at subalpine and alpine region. The increased NUE and PUE are helpful to eliminate the nutrition limitation in this area in the future world, when CO2 concentration doubles the ambient. 5. The effects of elevated CO2 on carbon balance of red birch communities (1) Net photosynthetic rates (Pn), dark respiration rates (Rd) and growth are all stimulated by elevated CO2. (2) Content soil organic carbon increases sharply at the primary stage of experiments and then the increasing rates decrease to a low level at later stages. (3) Soil respiration rates increase significantly with the elevation of CO2 concentration. (4) The daily carbon fixations of whole community are heightened by elevated CO2. The results (1)-(4) suggest that, the community being studied are sensitive to current climate change; the studied community, as a sink of atmospheric CO2, is pool-sink alternative between seasons. (5) The carbon fixations are increased along the increase of planting densities. 6. The effects of elevated CO2 on physiological features of leaf senescences of red birch seedlings at the later stage of growing season Elevated CO2 helps to postpone the leaf senescences of red birch at the end of the growth season. CO2 enrichment increases the photosynthetic rates, contents of soluble proteins and photosynthetic pigments. And meanwhile contents of malondialdehyde (MDA) decreases and activities of superoxide dismutase (SOD) and catalase (CAT) are both increased. These results suggest that the senescences of red birch leaves are delayed by elevated CO2, which keep the photosynthetic rates at relatively high levels. Our results lend supports to hypothesis and results on stimulated photosynthetic rates and growth from both other researchers and the present paper.

The role of CO2 and dynamic vegetation on the impact of temperate land use change in the HadCM3 coupled climate model

Human induced land-use change (LUC) alters the biogeophysical characteristics of the land surface influencing the surface energy balance. The level of atmospheric CO2 is expected to increase in the coming century and beyond, modifying temperature and precipitation patterns and altering the distribution and physiology of natural vegetation. It is important to constrain how CO2-induced climate and vegetation change may influence the regional extent to which LUC alters climate. This sensitivity study uses the HadCM3 coupled climate model under a range of equilibrium forcings to show that the impact of LUC declines under increasing atmospheric CO2, specifically in temperate and boreal regions. A surface energy balance analysis is used to diagnose how these changes occur. In Northern Hemisphere winter this pattern is attributed in part to the decline in winter snow cover and in the summer due to a reduction in latent cooling with higher levels of CO2. The CO2-induced change in natural vegetation distribution is also shown to play a significant role. Simulations run at elevated CO2 yet present day vegetation show a significantly increased sensitivity to LUC, driven in part by an increase in latent cooling. This study shows that modelling the impact of LUC needs to accurately simulate CO2 driven changes in precipitation and snowfall, and incorporate accurate, dynamic vegetation distribution.

Elevated CO(2) increases photosynthesis, biomass and productivity, and modifies gene expression in sugarcane

Because of the economical relevance of sugarcane and its high potential as a source of biofuel, it is important to understand how this crop will respond to the foreseen increase in atmospheric [CO(2)]. The effects of increased [CO(2)] on photosynthesis, development and carbohydrate metabolism were studied in sugarcane (Saccharum ssp.). Plants were grown at ambient (similar to 370 ppm) and elevated (similar to 720 ppm) [CO(2)] during 50 weeks in open-top chambers. The plants grown under elevated CO(2) showed, at the end of such period, an increase of about 30% in photosynthesis and 17% in height, and accumulated 40% more biomass in comparison with the plants grown at ambient [CO(2)]. These plants also had lower stomatal conductance and transpiration rates (-37 and -32%, respectively), and higher water-use efficiency (c.a. 62%). cDNA microarray analyses revealed a differential expression of 35 genes on the leaves (14 repressed and 22 induced) by elevated CO(2). The latter are mainly related to photosynthesis and development. Industrial productivity analysis showed an increase of about 29% in sucrose content. These data suggest that sugarcane crops increase productivity in higher [CO(2)], and that this might be related, as previously observed for maize and sorghum, to transient drought stress.

Coffee growth, pest and yield responses to free-air CO2 enrichment

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Soil-nutrient availability modifies the response of young pioneer and late successional trees to elevated carbon dioxide in a Brazilian tropical environment

The aim of this work was to determine the impact of three levels of [CO2] and two levels of soil-nutrient availability on the growth and physiological responses of two tropical tree species differing in their ecological group: Croton urucurana Baillon, a pioneer (P), and also Cariniana legalis (Martius) Kuntze, a late succession (LS). We aimed to test the hypothesis that P species have stronger response to elevated [CO2] than LS species as a result of differences in photosynthetic capacity and growth kinetics between both functional groups. Seedlings of both species were grown in open-top-chambers under high (HN) or low (LN) soil-nutrient supply and exposed to ambient (380 mu mol mol(-1)) or elevated (570 and 760 mu mol mol(-1)) [CO2]. Measurements of gas exchange, chlorophyll a fluorescence, seedling biomass and allocation were made after 70 days of treatment. Results suggest that elevated [CO2] significantly enhances the photosynthetic rates (A) and biomass production in the seedlings of both species, but that soil-nutrient supply has the potential to modify the response of young tropical trees to elevated [CO2]. In relation to plants grown in ambient [CO2], the P species grown under 760 mu mol mol(-1) [CO2] showed increases of 28% and 91% in A when grown in LN and HN, respectively. In P species grown under 570 mu mol mol(-1) [CO2], A increased by 16% under HN, but there was no effect in LN. In LS species, the enhancement of A by effect of 760 mu mol mol(-1) [CO2] was 30% and 70% in LN and HN, respectively. The exposure to 570 mu mol mol(-1) [CO2] stimulated A by 31% in HN, but was no effect in LN. Reductions in stomatal conductance (g(s)) and transpiration (E), as a result of elevated [CO2] were observed. Increasing the nutrient supply from low to high increased both the maximum rate of carboxylation (V-cmax) and maximum potential rate of electron transport (J(max)). As the level of [CO2] increased, both the V-cmax and the J(max) were found to decrease, whereas the J(max)/V-cmax ratio increased. In the LS species, the maximum efficiency of PSII (F-v/F-m) was higher in the 760 mu mol mol(-1) [CO2] treatment relative to other [CO2] treatments. The results suggest that when grown under HN and the highest [CO2], the performance of the P species C. urucurana, in terms of photosynthesis and biomass enhancement, is better than the LS species C. legalis. However, a larger biomass is allocated to roots when C. legalis seedlings were exposed to elevated [CO2]. This response would be an important strategy for plant survival and productivity of the LS species under drought stresses conditions on tropical environments in a global-change scenario. (C) 2011 Elsevier B.V. All rights reserved.

Temperature and CO2 estimation for the Middle Eocene section of ODP Hole 189-1172A

The long-term warmth of the Eocene (~56 to 34 million years ago) is commonly associated with elevated partial pressure of atmospheric carbon dioxide (pCO2). However, a direct relationship between the two has not been established for short-term climate perturbations. We reconstructed changes in both pCO2 and temperature over an episode of transient global warming called the Middle Eocene Climatic Optimum (MECO; ~40 million years ago). Organic molecular paleothermometry indicates a warming of southwest Pacific sea surface temperatures (SSTs) by 3° to 6°C. Reconstructions of pCO2 indicate a concomitant increase by a factor of 2 to 3. The marked consistency between SST and pCO2 trends during the MECO suggests that elevated pCO2 played a major role in global warming during the MECO.