High Atmospheric CO2 Concentrations Research Articles

High sea-surface temperatures during the early Aptian Oceanic Anoxic Event 1a in the Boreal Realm

The early Aptian was characterized by the widespread occurrence of anoxia in the oceans, known as Oceanic Anoxic Event (OAE) 1a. Intense degassing from submarine volcanic plateaus presumably resulted in high atmospheric CO2 concentrations, culminating in greenhouse conditions. OAE 1a can, therefore, be considered as a past “natural experiment” important to understand the future evolution of our climate. Paleotemperature estimates for OAE 1a are, however, predominantly based on bulk oxygen isotopes, which are susceptible to diagenetic overprinting, while TEX86 paleotemperature estimates are limited in number or derived from stratigraphically poorly constrained sections. Here we reconstructed for the first time sea-surface water temperatures (SSTs) based on the TEX86 paleothermometer from an OAE 1a section from the middle northern latitudes (39°N paleolatitude). We find a SST rise starting prior to OAE 1a and reaching a maximum during the event, with SSTs of ~31–34 °C, 4–9 °C higher than those of older Hauterivian–lower Aptian sediments from the same sedimentary basin. The end of OAE 1a is marked by relatively lower SSTs of ~30 °C. These observations are supported by belemnite-based oxygen-isotope (d18OBel) data and calcareous nannofossils. Our integrated data set clearly indicates that “super greenhouse” conditions prevailed during OAE 1a at northern latitudes. SSTs are similar to those estimated for coeval low-latitudinal sites, suggesting that an equable warm climate, with reduced latitudinal gradients, characterized the early Aptian.

The faint young Sun problem revisited with a 3-D climate–carbon model – Part 1

Abstract. During the Archaean, the Sun's luminosity was 18 to 25% lower than the present day. One-dimensional radiative convective models (RCM) generally infer that high concentrations of greenhouse gases (CO2, CH4) are required to prevent the early Earth's surface temperature from dropping below the freezing point of liquid water and satisfying the faint young Sun paradox (FYSP, an Earth temperature at least as warm as today). Using a one-dimensional (1-D) model, it was proposed in 2010 that the association of a reduced albedo and less reflective clouds may have been responsible for the maintenance of a warm climate during the Archaean without requiring high concentrations of atmospheric CO2 (pCO2). More recently, 3-D climate simulations have been performed using atmospheric general circulation models (AGCM) and Earth system models of intermediate complexity (EMIC). These studies were able to solve the FYSP through a large range of carbon dioxide concentrations, from 0.6 bar with an EMIC to several millibars with AGCMs. To better understand this wide range in pCO2, we investigated the early Earth climate using an atmospheric GCM coupled to a slab ocean. Our simulations include the ice-albedo feedback and specific Archaean climatic factors such as a faster Earth rotation rate, high atmospheric concentrations of CO2 and/or CH4, a reduced continental surface, a saltier ocean, and different cloudiness. We estimated full glaciation thresholds for the early Archaean and quantified positive radiative forcing required to solve the FYSP. We also demonstrated why RCM and EMIC tend to overestimate greenhouse gas concentrations required to avoid full glaciations or solve the FYSP. Carbon cycle–climate interplays and conditions for sustaining pCO2 will be discussed in a companion paper.

Increased water‐use efficiency does not lead to enhanced tree growth under xeric and mesic conditions

Higher atmospheric CO2 concentrations (c(a)) can under certain conditions increase tree growth by enhancing photosynthesis, resulting in an increase of intrinsic water-use efficiency (i WUE) in trees. However, the magnitude of these effects and their interactions with changing climatic conditions are still poorly understood under xeric and mesic conditions. We combined radial growth analysis with intra- and interannual δ(13)C and δ(18)O measurements to investigate growth and physiological responses of Larix decidua, Picea abies, Pinus sylvestris, Pinus nigra and Pseudotsuga menziesii in relation to rising c(a) and changing climate at a xeric site in the dry inner Alps and at a mesic site in the Swiss lowlands. (i)WUE increased significantly over the last 50 yr by 8-29% and varied depending on species, site water availability, and seasons. Regardless of species and increased (i)WUE, radial growth has significantly declined under xeric conditions, whereas growth has not increased as expected under mesic conditions. Overall, drought-induced stomatal closure has reduced transpiration at the cost of reduced carbon uptake and growth. Our results indicate that, even under mesic conditions, the temperature-induced drought stress has overridden the potential CO2 'fertilization' on tree growth, hence challenging today's predictions of improved forest productivity of temperate forests.

Do the rich always become richer? Characterizing the leaf physiological response of the high-yielding rice cultivar Takanari to free-air CO2 enrichment.

The development of crops which are well suited to growth under future environmental conditions such as higher atmospheric CO2 concentrations ([CO2]) is essential to meeting the challenge of ensuring food security in the face of the growing human population and changing climate. A high-yielding indica rice variety (Oryza sativa L. cv. Takanari) has been recently identified as a potential candidate for such breeding, due to its high productivity in present [CO2]. To test if it could further increase its productivity under elevated [CO2] (eCO2), Takanari was grown in the paddy field under season-long free-air CO2 enrichment (FACE, approximately 200 µmol mol−1 above ambient [CO2]) and its leaf physiology was compared with the representative japonica variety ‘Koshihikari’. Takanari showed consistently higher midday photosynthesis and stomatal conductance than Koshihikari under both ambient and FACE growth conditions over 2 years. Maximum ribulose-1,5-bisphosphate carboxylation and electron transport rates were higher for Takanari at the mid-grain filling stage in both years. Mesophyll conductance was higher in Takanari than in Koshihikari at the late grain-filling stage. In contrast to Koshihikari, Takanari grown under FACE conditions showed no decrease in total leaf nitrogen on an area basis relative to ambient-grown plants. Chl content was higher in Takanari than in Koshihikari at the same leaf nitrogen level. These results indicate that Takanari maintains its superiority over Koshihikari in regards to its leaf-level productivity when grown in elevated [CO2] and it may be a valuable resource for rice breeding programs which seek to increase crop productivity under current and future [CO2].

外来入侵植物飞机草和本地植物异叶泽兰对大气CO2升高的响应

PDF HTML阅读 XML下载 导出引用 引用提醒 外来入侵植物飞机草和本地植物异叶泽兰对大气CO2浓度升高的响应 DOI: 10.5846/stxb201211101581 作者: 作者单位: 中国科学院西双版纳热带植物园,中国科学院西双版纳热带植物园,中国科学院西双版纳热带植物园,中国科学院西双版纳热带植物园,沈阳农业大学生物科学技术学院 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学基金项目（30830027，31270582）；中国科学院知识创新工程重要方向性项目（KSCX2-YW-Z-1019） Responses of invasive Chromolaena odorata and native Eupatorium heterophyllum to atmospheric CO2 enrichment Author: Affiliation: Key Laboratory of Tropical Forest Ecology,Xishuangbanna Tropical Botanical Garden,Chinese Academy of Sciences,Mengla,Key Laboratory of Tropical Forest Ecology,Xishuangbanna Tropical Botanical Garden,Chinese Academy of Sciences,Mengla,Key Laboratory of Tropical Forest Ecology,Xishuangbanna Tropical Botanical Garden,Chinese Academy of Sciences,Mengla,Key Laboratory of Tropical Forest Ecology,Xishuangbanna Tropical Botanical Garden,Chinese Academy of Sciences,Mengla,College of Bioscience and Biotechnology,Shenyang Agricultural University Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:大气CO2浓度升高影响外来植物入侵，研究外来入侵植物和本地植物对大气CO2浓度升高响应的差异，有助于准确预测和管理外来植物入侵。基于封顶式CO2生长室，模拟大气CO2浓度变化（对照和700 μmol/mol），比较研究了外来入侵植物飞机草（Chromolaena odorata）和本地植物异叶泽兰（Eupatorium heterophyllum）形态、生长、生物量分配和光合特性对大气CO2浓度升高响应的差异。结果表明：（1）在当前大气CO2浓度下，飞机草总生物量、株高、基径和总叶面积高于异叶泽兰，分枝数低于异叶泽兰；CO2浓度升高，飞机的总生物量、株高、基径、分枝数和总叶面积分别增加了92%、41%、60%、325%和148%，高于异叶泽兰的32%、14%、30%、64%和79%，飞机草生长优势进一步提高。（2）无论在高或低CO2浓度下，飞机草根生物量分数（RMF）都低于异叶泽兰，叶生物量分数（LMF）和茎生物量分数（SMF）都高于异叶泽兰；CO2倍增两种植物RMF均降低，LMF和SMF均升高，但这2个参数对CO2倍增响应的种间差异不显著。（3）无论在高或低CO2浓度下，飞机草和异叶泽兰的净光合速率差异均不显著，CO2倍增对两种植物的净光合速率的促进作用相似。上述结果表明，在未来大气CO2浓度升高的条件下，飞机草的入侵性可能提高，入侵危害将加剧。 Abstract:Atmospheric CO2 concentration had increased from a pre-industrial level of 270 μmol/mol to 350 μmol/mol in 2005 and continues to increase at 1.9 μmol/mol per year on average. It is well known that atmospheric CO2 enrichment may influence the invasiveness of introduced plant species. Identifying the effects of elevated CO2 on invasiveness of exotic plants is very important for improving our ability to predict and control potentially invasive species. Four closed-top chambers were used to control CO2 concentration, ambient atmospheric CO2 concentration (control) and doubled atmospheric CO2 concentration (700 μmol/mol). To determine the effects of atmospheric CO2 enrichment on invasiveness of Chromolaena odorata, a noxious invasive perennial herb or subshrub in many countries of Asia, Oceania and Africa, we compared C. odorata and its phylogenetically related indigenous plant Eupatorium heterophyllum in terms of morphology, growth, biomass allocation, and photosynthesis at two CO2 concentrations. Fourteen traits related to morphology, growth, biomass allocation, and photosynthesis were measured when C. odorata and E. heterophyllum were treated for nearly three months.At ambient CO2 concentration, total biomass, height, stem diameter, and total leaf area were significantly higher and branch number were lower for invasive C. odorata than for native E. heterophyllum, which contribute to form dense monoculture for the invader, outshading native plant species. CO2 enrichment significantly increased total biomass, height, stem diameter, branch number, and total leaf area in both species. For C. odorata, total biomass, height, stem diameter, branch number and total leaf area were increased by 92%, 41%, 60%, 325%, and 148%, respectively, much higher than 32%, 14%, 30%, 64%, and 79% for E. heterophyllum. Consistently, growth advantage of the invader over the native became more evident at doubled atmospheric CO2 concentration.CO2 enrichment decreased root mass fraction (RMF) and increased stem mass fraction (SMF) and leaf mass fraction (LMF) for both the invasive and native species. However, the responses of these traits to CO2 enrichment were not significantly different between C. odorata and E. heterophyllum. C. odorata allocated more biomass to stems and leaves and less to roots than E. heterophyllum at either ambient CO2 concentration or doubled atmospheric CO2 concentration. Higher LMF and SMF may help C. odorata to increase carbon assimilation, and lower RMF may help C. odorata to reduce respiratory carbon loss, facilitating biomass accumulation. The more efficient strategy of biomass accumulation adopted by the invader might still provide stronger competitive ability against the native. In addition, atmospheric CO2 enrichment significantly increased net photosynthetic rate (Pmax) for both species, and the increases were not significantly different between C. odorata and E. heterophyllum. At both low and high CO2 concentration, Pmax was not significantly different between two species. This indicates that higher biomass accumulation of C. odorata may not be associated with photosynthesis, and benefit from other aspects at doubled atmospheric CO2 concentration.In conclusion, our results indicate that CO2 enrichment stimulates growth more greatly for invasive C. odorata than for native E. heterophyllum, and that in the future with high atmospheric CO2 concentration invasions by C. odorata may become more serious. 参考文献 相似文献 引证文献

A perturbed hydrological cycle during Oceanic Anoxic Event 2

Research Article| February 01, 2014 A perturbed hydrological cycle during Oceanic Anoxic Event 2 Niels A.G.M. van Helmond; Niels A.G.M. van Helmond * 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands *E-mail: n.vanhelmond@uu.nl. Search for other works by this author on: GSW Google Scholar Appy Sluijs; Appy Sluijs 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Gert-Jan Reichart; Gert-Jan Reichart 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands2NIOZ (Royal Netherlands Institute for Sea Research), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands Search for other works by this author on: GSW Google Scholar Jaap S. Sinninghe Damsté; Jaap S. Sinninghe Damsté 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands2NIOZ (Royal Netherlands Institute for Sea Research), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands Search for other works by this author on: GSW Google Scholar Caroline P. Slomp; Caroline P. Slomp 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands Search for other works by this author on: GSW Google Scholar Henk Brinkhuis Henk Brinkhuis 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands2NIOZ (Royal Netherlands Institute for Sea Research), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands Search for other works by this author on: GSW Google Scholar Author and Article Information Niels A.G.M. van Helmond * 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands Appy Sluijs 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands Gert-Jan Reichart 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands2NIOZ (Royal Netherlands Institute for Sea Research), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands Jaap S. Sinninghe Damsté 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands2NIOZ (Royal Netherlands Institute for Sea Research), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands Caroline P. Slomp 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands Henk Brinkhuis 1Department of Earth Sciences, Faculty of Geosciences, Utrecht University, Budapestlaan 4, 3584 CD Utrecht, Netherlands2NIOZ (Royal Netherlands Institute for Sea Research), P.O. Box 59, 1790 AB Den Burg, Texel, Netherlands *E-mail: n.vanhelmond@uu.nl. Publisher: Geological Society of America Received: 11 Jul 2013 Revision Received: 19 Oct 2013 Accepted: 22 Oct 2013 First Online: 09 Mar 2017 Online ISSN: 1943-2682 Print ISSN: 0091-7613 © 2014 Geological Society of America Geology (2014) 42 (2): 123–126. https://doi.org/10.1130/G34929.1 Article history Received: 11 Jul 2013 Revision Received: 19 Oct 2013 Accepted: 22 Oct 2013 First Online: 09 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Niels A.G.M. van Helmond, Appy Sluijs, Gert-Jan Reichart, Jaap S. Sinninghe Damsté, Caroline P. Slomp, Henk Brinkhuis; A perturbed hydrological cycle during Oceanic Anoxic Event 2. Geology 2014;; 42 (2): 123–126. doi: https://doi.org/10.1130/G34929.1 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyGeology Search Advanced Search Abstract The Late Cretaceous Oceanic Anoxic Event 2 (OAE2; ca. 94 Ma) was one of the largest global carbon cycle perturbations during the Phanerozoic. OAE2 represents an important, although extreme, case study for modern trends because widespread anoxia and enhanced organic carbon burial during OAE2 were linked to exceptionally warm climates and high atmospheric CO2 concentrations. However, the consequences of this warmth for the hydrological cycle remain poorly understood, hampering our understanding of its impact on biogeochemical cycles during this greenhouse episode. Here we show evidence for changes in the hydrological cycle during OAE2 based on combined geochemical and palynological data for the stratigraphically expanded coastal OAE2 succession at Bass River, located on the New Jersey shelf (Ocean Drilling Program Leg 174AX), eastern United States. Paleothermometry, based on TEX86, indicates sea-surface warming at the onset of OAE2 and a subsequent pronounced cooling event. Palynological data show that these changes in temperature were associated with strong variations in precipitation and runoff. We suggest that an acceleration of the hydrological cycle during OAE2 played a key role in supplying nutrients to coastal waters and enhancing stratification, thus contributing to the development of ocean anoxia. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Forward into the Past

Climate Science It has been well established that high concentrations of atmospheric CO2 caused by anthropogenic emissions will persist for thousands of years after those emissions cease and that the consequences for climate will last even longer than that. Suggestions have been made that CO2 could

Adaptation of an Antarctic lichen to Martian niche conditions can occur within 34 days

Stresses occurring on the Martian surface were simulated in a Mars Simulation Chamber (MSC) and included high UV fluxes (Zarnecki and Catling, 2002), low temperatures, low water activity, high atmospheric CO2 concentrations, and an atmospheric pressure of about 800Pa (Kasting, 1991; Head et al., 2003). The lichen Pleopsidium chlorophanum is an extremophile that lives in very cold, dry, high-altitude habitats, which are Earth's best approximation of the Martian surface. Samples with P. chlorophanum were exposed uninterruptedly to simulated conditions of the unprotected Martian surface (i.e. 6344kJm−2) and protected niche conditions (269kJm−2) for 34 days. Under unprotected Martian surface conditions the fungal symbiont decreases its metabolic activity and it was unclear if the algal symbiont of the lichen was still actively photosynthesizing. However, under “protected site” conditions, the entire lichen not only survived and remained photosynthetically active, it even adapted physiologically by increasing its photosynthetic activity over 34 days.

Paleoenvironmental and Paleoclimatic Interpretations of the Late Paleocene Goler Formation, Southern California, U.S.A., Based On Paleosol Geochemistry

The Paleocene was characterized by high global temperatures and elevated concentrations of atmospheric CO2. Paleoclimate records of this epoch are of particular interest to understanding the effects of anthropogenic climate forcing as well as linkages between the Paleocene climate and major tectonic and evolutionary events. However, terrestrial paleoclimatic records of the Paleocene are limited in their spatial extent, and few such records are known from western North America. In this study, paleosols from two members in the late Paleocene Goler Formation of Southern California were used to investigate local paleoclimatic conditions. The paleosols were described in detail and analyzed for morphology, clay mineralogy, and bulk geochemistry. Carbonate nodules present in paleosols from the upper member (member 4a) were characterized using petrographic and cathodoluminescence microscopy and were analyzed for carbon and oxygen stable-isotope composition. Enrichment and retention of soluble elements (Ca, Mg, and Na) and the mobilization of Fe and Mn in the paleosol profiles suggest a climate with strongly seasonal precipitation. This interpretation is further supported by the presence of pedogenic slickensides and the clay minerals smectite and illite. The appearance of pedogenic carbonate nodules in paleosols from the upper member is suggestive of a shift to more arid or more seasonal conditions that is coincident with a prominent change in sediment provenance and an inferred increase in sedimentation rate. Uplift of the ancestral Sierra Nevada during the late Paleocene was likely an important control on regional paleoclimate due to the effects of elevated topography on mean annual precipitation and seasonal distribution of precipitation. The correlation of a shift in pedogenic processes with changes in provenance and sedimentation rate suggests that the evolution of regional tectonic activity was an important control on these processes during the deposition of the Goler Formation.

Lithium isotope evidence for enhanced weathering during Oceanic Anoxic Event 2

The Ocean Anoxic Event 2 (OAE2) about 93.5 million years ago was marked by high atmospheric CO2 concentration, rapid global warming and marine anoxia and euxinia. The event lasted for about 440,000 years and led to habitat loss and mass extinction. The marine anoxia is thought to be linked to enhanced biological productivity, but it is unclear what triggered the increased production and what allowed the subsequent rapid climate recovery. Here we use lithium isotope measurements from carbonates spanning the interval including OAE2 to assess the role of silicate weathering. We find the lightest values of the Li isotope ratio (δ7Li) during OAE2, indicating high levels of weathering—and therefore atmospheric CO2 removal—which we attribute to an enhanced hydrological cycle. We use a geochemical model to simulate the evolution of δ7Li and the Ca, Sr and Os isotope tracers. Our simulations suggest a scenario in which the eruption of a large igneous province led to high atmospheric CO2 concentrations and rapid global warming, which initiated OAE2. The simulated warming was accompanied by a roughly 200,000 year pulse of accelerated weathering of mafic silicate rocks, which removed CO2 from the atmosphere. The weathering also delivered nutrients to the oceans that stimulated primary productivity. We suggest that this process, together with the burial of organic carbon, allowed the rapid recovery and stabilization from the greenhouse state.

Earliest record of megaphylls and leafy structures, and their initial diversification

Evolutionary changes in the structure of leaves have had far-reaching effects on the anatomy and physiology of vascular plants, resulting in morphological diversity and species expansion. People have long been interested in the question of the nature of the morphology of early leaves and how they were attained. At least five lineages of euphyllophytes can be recognized among the Early Devonian fossil plants (Pragian age, ca. 410 Ma ago) of South China. Their different leaf precursors or “branch-leaf complexes” are believed to foreshadow true megaphylls with different venation patterns and configurations, indicating that multiple origins of megaphylls had occurred by the Early Devonian, much earlier than has previously been recognized. In addition to megaphylls in euphyllophytes, the laminate leaf-like appendages (sporophylls or bracts) occurred independently in several distantly related Early Devonian plant lineages, probably as a response to ecological factors such as high atmospheric CO2 concentrations. This is a typical example of convergent evolution in early plants.

Climate change effects on macrofaunal litter decomposition: the interplay of temperature, body masses and stoichiometry

Macrofauna invertebrates of forest floors provide important functions in the decomposition process of soil organic matter, which is affected by the nutrient stoichiometry of the leaf litter. Climate change effects on forest ecosystems include warming and decreasing litter quality (e.g. higher C : nutrient ratios) induced by higher atmospheric CO(2) concentrations. While litter-bag experiments unravelled separate effects, a mechanistic understanding of how interactions between temperature and litter stoichiometry are driving decomposition rates is lacking. In a laboratory experiment, we filled this void by quantifying decomposer consumption rates analogous to predator-prey functional responses that include the mechanistic parameters handling time and attack rate. Systematically, we varied the body masses of isopods, the environmental temperature and the resource between poor (hornbeam) and good quality (ash). We found that attack rates increased and handling times decreased (i) with body masses and (ii) temperature. Interestingly, these relationships interacted with litter quality: small isopods possibly avoided the poorer resource, whereas large isopods exhibited increased, compensatory feeding of the poorer resource, which may be explained by their higher metabolic demands. The combination of metabolic theory and ecological stoichiometry provided critically important mechanistic insights into how warming and varying litter quality may modify macrofaunal decomposition rates.

Growth under elevated atmospheric CO2 concentration accelerates leaf senescence in sunflower (Helianthus annuus L.) plants

Some morphogenetic and metabolic processes were sensitive to a high atmospheric CO2 concentration during sunflower primary leaf ontogeny. Young leaves of sunflower plants growing under elevated CO2 concentration exhibited increased growth, as reflected by the high specific leaf mass referred to as dry weight in young leaves (16days). The content of photosynthetic pigments decreased with leaf development, especially in plants grown under elevated CO2 concentrations, suggesting that high CO2 accelerates chlorophyll degradation, and also possibly leaf senescence. Elevated CO2 concentration increased the oxidative stress in sunflower plants by increasing H2O2 levels and decreasing activity of antioxidant enzymes such as catalase and ascorbate peroxidase. The loss of plant defenses probably increases the concentration of reactive oxygen species in the chloroplast, decreasing the photosynthetic pigment content as a result. Elevated CO2 concentration was found to boost photosynthetic CO2 fixation, especially in young leaves. High CO2 also increased the starch and soluble sugar contents (glucose and fructose) and the C/N ratio during sunflower primary leaf development. At the beginning of senescence, we observed a strong increase in the hexoses to sucrose ratio that was especially marked at high CO2 concentration. These results indicate that elevated CO2 concentration could promote leaf senescence in sunflower plants by affecting the soluble sugar levels, the C/N ratio and the oxidative status during leaf ontogeny. It is likely that systemic signals produced in plants grown with elevated CO2, lead to early senescence and a higher oxidation state of the cells of these plant leaves.

Growth Responses of Nutrient-Stressed Cenchrus ciliaris Under Carbon Dioxide Enrichment

The response of plants to carbon dioxide (CO2) enrichment is an important aspect to be thoroughly investigated in order to accurately predict the impact on resource use as well ecosystem level responses. But the extent of response of individual plant species is dependent on the underlying biotic and abiotic stresses. In the current project, the response of Cenchrus ciliaris, a C4 grass, was investigated under CO2 enrichment conditions under nutrient stress. Eco-physiological growth parameters were assessed within two plastic chambers with one chamber kept at ambient CO2 conditions (500ppm) and the second enriched with CO2 (1000ppm). Three treatments were studied: ambient (ACO2), enriched (ECO2) and alternating (alternating two weeks in each chamber; ALCO2). High atmospheric CO2 concentrations did increase shoot and inflorescence production under nutrient stress. The blade area of ECO2 plants was significantly larger than that of ALCO2 plants on the 31st of March 2010 at P=0.06 and on the 7th of April 2010 (P=0.074). Stomatal density of C.ciliaris, however, did decrease for ECO2 and ALCO2. Under ACO2, average sheath biomass was signcantly higher under nutrient stressed condition than under non-stressed condition (65.81% vs. 52.96%; respectively). Growth allocations results revealed a rush toward reproductive production for ECO2 under nutrient stress conditions.

The stomatal CO2 proxy does not saturate at high atmospheric CO2 concentrations: evidence from stomatal index responses of Araucariaceae conifers

The inverse relationship between the number of stomata on a leaf surface and the atmospheric carbon dioxide concentration ([CO(2)]) in which the leaf developed allows plants to optimise water-use efficiency (WUE), but it also permits the use of fossil plants as proxies of palaeoatmospheric [CO(2)]. The ancient conifer family Araucariaceae is often represented in fossil floras and may act as a suitable proxy of palaeo-[CO(2)], yet little is known regarding the stomatal index (SI) responses of extant Araucariaceae to [CO(2)]. Four Araucaria species (Araucaria columnaris, A. heterophylla, A. angustifolia and A. bidwillii) and Agathis australis displayed no significant relationship in SI to [CO(2)] below current ambient levels (~380 ppm). However, representatives of the three extant genera within the Araucariaceae (A. bidwillii, A. australis and Wollemia nobilis) all exhibited significant reductions in SI when grown in atmospheres of elevated [CO(2)] (1,500 ppm). Stomatal conductance was reduced and WUE increased when grown under elevated [CO(2)]. Stomatal pore length did not increase alongside reduced stomatal density (SD) and SI in the three araucariacean conifers when grown at elevated [CO(2)]. These pronounced SD and SI reductions occur at higher [CO(2)] levels than in other species with more recent evolutionary origins, and may reflect an evolutionary legacy of the Araucariaceae in the high [CO(2)] world of the Mesozoic Era. Araucariacean conifers may therefore be suitable stomatal proxies of palaeo-[CO(2)] during periods of "greenhouse" climates and high [CO(2)] in the Earth's history.

Effects of CO<sup>2</sup>, continental distribution, topography and vegetation changes on the climate at the Middle Miocene: a model study

Abstract. The Middle Miocene was one of the last warm periods of the Neogene, culminating with the Middle Miocene Climatic Optimum (MMCO, approximatively 17–15 Ma). Several proxy-based reconstructions support warmer and more humid climate during the MMCO. The mechanisms responsible for the warmer climate at the MMCO and particularly the role of the atmospheric carbon dioxide are still highly debated. Here we carried out a series of sensitivity experiments with the model of intermediate complexity Planet Simulator, investigating the contributions of the absence of ice on the continents, the opening of the Central American and Eastern Tethys Seaways, the lowering of the topography on land, the effect of various atmospheric CO2 concentrations and the vegetation feedback. Our results show that a higher than present-day CO2 concentration is necessary to generate a warmer climate at all latitudes at the Middle Miocene, in agreement with the terrestrial proxy reconstructions which suggest high atmospheric CO2 concentrations at the MMCO. Nevertheless, the changes in sea-surface conditions, the lowering of the topography on land and the vegetation feedback also produce significant local warming that may, locally, even be stronger than the CO2 induced temperature increases. The lowering of the topography leads to a more zonal atmospheric circulation and allows the westerly flow to continue over the lowered Plateaus at mid-latitudes. The reduced height of the Tibetan Plateau notably prevents the development of a monsoon-like circulation, whereas the reduction of elevations of the North American and European reliefs strongly increases precipitation from northwestern to eastern Europe. The changes in vegetation cover contribute to maintain and even to intensify the warm and humid conditions produced by the other factors, suggesting that the vegetation-climate interactions could help to improve the model-data comparison.

The occurrence of plants with crassulacean acid metabolism (CAM) photosynthesis in tropical and subtropical rain forests with very high rainfall.

Crassulacean acid metabolism (CAM) is a photosynthetic pathway that conserves water by restricting stomatal opening, hence water loss, to the night. Thus, it is not surprising to find that floras of arid regions include a large number of CAM plants. In addition, CAM is common among epiphytes in tropical and subtropical environments, where water is plentiful. Despite the latter, evidence exists that comparatively short periods of drought, coupled with the unusual morphology and/or microhabitat of such epiphytes, comprise stress substantial enough that the CAM pathway proves highly adaptive. It is more difficult to explain the adaptive significance of CAM in tropical and subtropical rain forests with exceedingly high annual rainfall, i.e., in excess of 4 meters per year. This review explores a variety of hypotheses proffered as explanations for this apparent conundrum. Such hypotheses include: 1. CAM allows an epiphytic CAM plant to capitalize on the high concentrations of atmospheric CO2 at night in the canopies of its host trees; 2. even in such rain forests, rainless periods are long enough and/or frequent enough that CAM proves advantageous as a water conservation adaptation. 3. The ability of many CAM plants to assimilate CO2 during both the day and night is advantageous in such environments. 4. The increase in daytime CO2 levels in CAM photosynthetic tissue prevents photoinhibition and minimizes CO2 losses during the day. 5. The high acid content of CAM photosynthetic tissue, at least early in the day, deters herbivory. 6. The stimulation of CO2 uptake following wetting of the leaves reported for at least one epiphytic CAM plant is advantageous in such high-rainfall environments. 7. The low demand for essential elements observed in at least one CAM plant increases the nutrient efficiency of such plants, which is adaptive in rain forests with excessive rainfall and, hence, high levels of nutrient leaching from the leaf tissues. 8. Guttation resulting from osmotically-driven high tissue water contents benefits CAM plants several ways. 9. Epiphytic CAM plants are well-adapted to shady microhabitats, comprising a valuable adaptation to the cloudy environment of high-rainfall rain forests. 10. CAM is not beneficial for such plants in these environments for at least 3 possible reasons. All of the hypotheses have only rarely been examined in past studies. Thus, all are in need of further investigation.

Conservation and possible reintroduction of an endangered plant based on an analysis of community ecology: a case study of Primulina tabacum Hance in China

AbstractThe distribution of the rare and endangered perennial herb Primulina tabacum Hance is restricted to eight karst caves in southern China. To conserve P. tabacum and to evaluate possible reintroduction, we studied its historical distribution and conducted field surveys of both its biotic and physical environment. We used detrended correspondence analysis and canonical correspondence analysis to investigate the plant community structure and to identify the major environmental factors associated with its presence at eight sites and absence from three other sites where it formerly grew. The results revealed differences in community structure among sites and close correlations between species composition and environmental conditions. The data indicate that P. tabacum has special ecological requirements, including alkaline soil, low soil content of N, P, K and organic matter, low light, a high soil water content and high relative humidity, and a high atmospheric CO2 concentration. Soil K content, relative humidity and atmospheric CO2 concentration were the three variables most strongly associated with the vegetation composition and structure of the 11 sites. It appears that as a result of reductions in humidity, some of the historical localities of P. tabacum may no longer be suitable for reintroduction. Pilea notata, Pteris cretica var. nervosa and two moss species, Heteroscyphus coalitus and Gymnostomiella longinervis, were strongly associated with P. tabacum. The first two plants could be useful as indicators of suitable environments for P. tabacum, and the moss species could be useful as nurse plants for the reintroduction of P. tabacum into wild habitats.

Efeito do aumento da concentração de CO2 atmosférico sobre o oídio e o crescimento de plantas de soja

O aumento da concentracao de dioxido de carbono (CO2) atmosferico, como resultado da acao antropica, pode causar alteracoes na morfologia e nos processos fisiologicos das plantas, assim como no ciclo dos patogenos e na sua interacao com os hospedeiros. O presente estudo teve por objetivo avaliar o efeito do aumento da concentracao de CO2 atmosferico sobre a severidade do oidio (Microsphaera diffusa) da soja e sobre o crescimento e a nodulacao da planta.O experimento foi conduzido em estufas de topo aberto (OTC) com e sem injecao de CO2 e teve como testemunha o tratamento sem estufa, correspondendo, em media, as concentracoes de 504 ppm, 429 ppm e 424 ppm, respectivamente, durante o periodo diurno. Durante 83 dias, foram avaliadas quatro cultivares de soja com diferentes niveis de resistencia ao oidio: FT-Estrela (altamente suscetivel), Embrapa 48 (suscetivel), FT-Cometa (moderadamente resistente) e FT-5 (Formosa) (resistente). O aumento da concentracao de CO2 resultou em aumento da severidade da doenca, nas quatro cultivares quando analisadas em conjunto, mas nao houve efeito na esporulacao do patogeno. Alem disso, houve incremento da altura, massa seca de raizes e nodulacao por Bradyrhizobium spp., exceto na cultivar Formosa. No entanto, a massa seca da parte aerea das plantas nao diferiu significativamente com o aumento da concentracao de CO2. O desenvolvimento da doenca e o crescimento das plantas foi maior nas OTCs do que fora das estufas. Os resultados demonstram que o aumento da concentracao de CO2 afeta a doenca e ha diferencas nas respostas das cultivares.

CO<sub>2</sub> enrichment increases nutrient leaching from model forest ecosystems in subtropical China

Abstract. The effect of high atmospheric CO2 concentrations on the dynamics of mineral nutrient is not well documented, especially for subtropical China. We used model forest ecosystems in open-top chambers to study the effects of CO2 enrichment alone and together with N addition on the dynamics of soil cations and anions. Two years of exposure to a 700 ppm CO2 atmospheric concentration resulted in increased annual nutrient losses by leaching below 70 cm soil profile. Compared to the control, net Mg2+ losses increased by 385%, K+ by 223%, Ca2+ by 167% and NO3−-N by 108%, respectively. Increased losses following exposure to elevated CO2 were related to both faster weathering of minerals/organic matter decomposition and greater amounts of leaching water. Net annual nutrient losses in the high CO2 concentration chambers reached 22.2 kg ha−1 year−1 for K+, 171.3 kg ha−1 year−1 for Ca2+, 8.2 kg ha−1 year−1 for Mg2+ and about 2 kg ha−1 year−1 for NO3−-N. The N addition alone had no significant effect on the mineral nutrient leaching losses. However, addition of N together with the high CO2 treatment significantly reduced mineral nutrient losses.We hypothesize that forests in subtropical China might suffer from nutrient limitation and reduction in plant biomass under elevated CO2 concentration due to mineral leaching losses in the future.