183 research outputs found
Evolution of leaf-form in land plants linked to atmospheric CO2 decline in the Late Palaeozoic era
The widespread appearance of megaphyll leaves, with their branched veins and planate form, did not occur until the close of the Devonian period at about 360 Myr ago. This happened about 40 Myr after simple leafless vascular plants first colonized the land in the Late Silurian/Early Devonian, but the reason for the slow emergence of this common feature of present-day plants is presently unresolved. Here we show, in a series of quantitative analyses using fossil leaf characters and biophysical principles, that the delay was causally linked with a 90% drop in atmospheric pCO2 during the Late Palaeozoic era. In contrast to simulations for a typical Early Devonian land plant, possessing few stomata on leafless stems, those for a planate leaf with the same stomatal characteristics indicate that it would have suffered lethal overheating, because of greater interception of solar energy and low transpiration. When planate leaves first appeared in the Late Devonian and subsequently diversified in the Carboniferous period, they possessed substantially higher stomatal densities. This observation is consistent with the effects of the pCO2 on stomatal development and suggests that the evolution of planate leaves could only have occurred after an increase in stomatal density, allowing higher transpiration rates that were sufficient to maintain cool and viable leaf temperatures
Limited response of peatland CH4 emissions to abrupt Atlantic Ocean circulation changes in glacial climates
Ice-core records show that abrupt DansgaardâOeschger (DâO) climatic warming events
of the last glacial period were accompanied by large increases in the
atmospheric CH4 concentration (up to 200 ppbv). These abrupt changes
are generally regarded as arising from the effects of changes in the Atlantic
Ocean meridional overturning circulation and the resultant climatic impact on
natural CH4 sources, in particular wetlands. We use two different
ecosystem models of wetland CH4 emissions to simulate northern CH4
sources forced with coupled general circulation model simulations of five
different time periods during the last glacial to investigate the potential
influence of abrupt ocean circulation changes on atmospheric CH4 levels
during DâO events. The simulated warming over Greenland of 7â9 °C
in the different time periods is at the lower end of the range of
11â15 °C derived from ice cores, but is associated with strong
impacts on the hydrological cycle, especially over the North Atlantic and
Europe during winter. We find that although the sensitivity of CH4
emissions to the imposed climate varies significantly between the two
ecosystem emissions models, the model simulations do not reproduce sufficient
emission changes to satisfy ice-core observations of CH4 increases
during abrupt events. The inclusion of permafrost physics and peatland carbon
cycling in one model (LPJ-WHyMe) increases the climatic sensitivity of CH44
emissions relative to the Sheffield Dynamic Global Vegetation Model (SDGVM) model, which does not incorporate these
processes. For equilibrium conditions this additional sensitivity is mostly
due to differences in carbon cycle processes, whilst the increased
sensitivity to the imposed abrupt warmings is also partly due to the effects
of freezing on soil thermodynamics. These results suggest that alternative
scenarios of climatic change could be required to explain the abrupt glacial
CH4 variations, perhaps with a more dominant role for tropical wetland
CH4 sources
Functional complementarity of ancient plantâfungal mutualisms: contrasting nitrogen, phosphorus and carbon exchanges between Mucoromycotina and Glomeromycotina fungal symbionts of liverworts
Liverworts, which are amongst the earliest divergent plant lineages and important ecosystem pioneers, often form nutritional mutualisms with arbuscular mycorrhizaâforming Glomeromycotina and fineâroot endophytic Mucoromycotina fungi, both of which coevolved with early land plants. Some liverworts, in common with many later divergent plants, harbour both fungal groups, suggesting these fungi may complementarily improve plant access to different soil nutrients.
We tested this hypothesis by growing liverworts in single and dual fungal partnerships under a modern atmosphere and under 1500 ppm [CO2], as experienced by early land plants. Access to soil nutrients via fungal partners was investigated with 15Nâlabelled algal necromass and 33P orthophosphate. Photosynthate allocation to fungi was traced using 14CO2.
Only Mucoromycotina fungal partners provided liverworts with substantial access to algal 15N, irrespective of atmospheric CO2 concentration. Both symbionts increased 33P uptake, but Glomeromycotina were often more effective. Dual partnerships showed complementarity of nutrient pool use and greatest photosynthate allocation to symbiotic fungi.
We show there are important functional differences between the plantâfungal symbioses tested, providing new insights into the functional biology of Glomeromycotina and Mucoromycotina fungal groups that form symbioses with plants. This may explain the persistence of the two fungal lineages in symbioses across the evolution of land plants
Legumeâmicrobiome interactions unlock mineral nutrients in regrowing tropical forests
Legume trees form an abundant and functionally important component of tropical forests worldwide with N2-fixing symbioses linked to enhanced growth and recruitment in early secondary succession. However, it remains unclear how N2-fixers meet the high demands for inorganic nutrients imposed by rapid biomass accumulation on nutrient-poor tropical soils. Here, we show that N2-fixing trees in secondary Neotropical forests triggered twofold higher in situ weathering of fresh primary silicates compared to non-N2âfixing trees and induced locally enhanced nutrient cycling by the soil microbiome community. Shotgun metagenomic data from weathered minerals support the role of enhanced nitrogen and carbon cycling in increasing acidity and weathering. Metagenomic and marker gene analyses further revealed increased microbial potential beneath N2-fixers for anaerobic iron reduction, a process regulating the pool of phosphorus bound to iron-bearing soil minerals. We find that the Fe(III)-reducing gene pool in soil is dominated by acidophilic Acidobacteria, including a highly abundant genus of previously undescribed bacteria, Candidatus Acidoferrum, genus novus. The resulting dependence of the Fe-cycling gene pool to pH determines the high iron-reducing potential encoded in the metagenome of the more acidic soils of N2-fixers and their nonfixing neighbors. We infer that by promoting the activities of a specialized local microbiome through changes in soil pH and C:N ratios, N2-fixing trees can influence the wider biogeochemical functioning of tropical forest ecosystems in a manner that enhances their ability to assimilate and store atmospheric carbon
Paleoclimate Implications for Human-Made Climate Change
Paleoclimate data help us assess climate sensitivity and potential human-made
climate effects. We conclude that Earth in the warmest interglacial periods of
the past million years was less than 1{\deg}C warmer than in the Holocene.
Polar warmth in these interglacials and in the Pliocene does not imply that a
substantial cushion remains between today's climate and dangerous warming, but
rather that Earth is poised to experience strong amplifying polar feedbacks in
response to moderate global warming. Thus goals to limit human-made warming to
2{\deg}C are not sufficient - they are prescriptions for disaster. Ice sheet
disintegration is nonlinear, spurred by amplifying feedbacks. We suggest that
ice sheet mass loss, if warming continues unabated, will be characterized
better by a doubling time for mass loss rate than by a linear trend. Satellite
gravity data, though too brief to be conclusive, are consistent with a doubling
time of 10 years or less, implying the possibility of multi-meter sea level
rise this century. Observed accelerating ice sheet mass loss supports our
conclusion that Earth's temperature now exceeds the mean Holocene value. Rapid
reduction of fossil fuel emissions is required for humanity to succeed in
preserving a planet resembling the one on which civilization developed.Comment: 32 pages, 9 figures; final version accepted for publication in
"Climate Change at the Eve of the Second Decade of the Century: Inferences
from Paleoclimate and Regional Aspects: Proceedings of Milutin Milankovitch
130th Anniversary Symposium" (eds. Berger, Mesinger and Sijaci
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The uronic acid content of coccolith-associated polysaccharides provides insight into coccolithogenesis and past climate
Unicellular phytoplanktonic algae (coccolithophores) are among the most prolific producers of calcium carbonate on the planet, with a production of âŒ1026 coccoliths per year. During their lith formation, coccolithophores mainly employ coccolith-associated polysaccharides (CAPs) for the regulation of crystal nucleation and growth. These macromolecules interact with the intracellular calcifying compartment (coccolith vesicle) through the charged carboxyl groups of their uronic acid residues. Here we report the isolation of CAPs from modern day coccolithophores and their prehistoric predecessors and we demonstrate that their uronic acid content (UAC) offers a species-specific signature. We also show that there is a correlation between the UAC of CAPs and the internal saturation state of the coccolith vesicle that, for most geologically abundant species, is inextricably linked to carbon availability. These findings suggest that the UAC of CAPs reports on the adaptation of coccolithogenesis to environmental changes and can be used for the estimation of past CO2 concentrations
Flammable biomes dominated by eucalypts originated at the Cretaceous-Palaeogene boundary
Fire is a major modifier of communities, but the evolutionary origins of its prevalent role in shaping current biomes are uncertain. Australia is among the most fire-prone continents, with most of the landmass occupied by the fire-dependent sclerophyll and savanna biomes. In contrast to biomes with similar climates in other continents, Australia has a tree flora dominated by a single genus, Eucalyptus, and related Myrtaceae. A unique mechanism in Myrtaceae for enduring and recovering from fire damage likely resulted in this dominance. Here, we find a conserved phylogenetic relationship between post-fire resprouting (epicormic) anatomy and biome evolution, dating from 60 to 62 Ma, in the earliest Palaeogene. Thus, fire-dependent communities likely existed 50 million years earlier than previously thought. We predict that epicormic resprouting could make eucalypt forests and woodlands an excellent long-term carbon bank for reducing atmospheric CO2 compared with biomes with similar fire regimes in other continents
Biogenic Volatile Organic Compound and Respiratory CO2 Emissions after 13C-Labeling: Online Tracing of C Translocation Dynamics in Poplar Plants
Globally plants are the primary sink of atmospheric CO(2), but are also the major contributor of a large spectrum of atmospheric reactive hydrocarbons such as terpenes (e.g. isoprene) and other biogenic volatile organic compounds (BVOC). The prediction of plant carbon (C) uptake and atmospheric oxidation capacity are crucial to define the trajectory and consequences of global environmental changes. To achieve this, the biosynthesis of BVOC and the dynamics of C allocation and translocation in both plants and ecosystems are important.We combined tunable diode laser absorption spectrometry (TDLAS) and proton transfer reaction mass spectrometry (PTR-MS) for studying isoprene biosynthesis and following C fluxes within grey poplar (Populus x canescens) saplings. This was achieved by feeding either (13)CO(2) to leaves or (13)C-glucose to shoots via xylem uptake. The translocation of (13)CO(2) from the source to other plant parts could be traced by (13)C-labeled isoprene and respiratory (13)CO(2) emission.In intact plants, assimilated (13)CO(2) was rapidly translocated via the phloem to the roots within 1 hour, with an average phloem transport velocity of 20.3±2.5 cm h(-1). (13)C label was stored in the roots and partially reallocated to the plants' apical part one day after labeling, particularly in the absence of photosynthesis. The daily C loss as BVOC ranged between 1.6% in mature leaves and 7.0% in young leaves. Non-isoprene BVOC accounted under light conditions for half of the BVOC C loss in young leaves and one-third in mature leaves. The C loss as isoprene originated mainly (76-78%) from recently fixed CO(2), to a minor extent from xylem-transported sugars (7-11%) and from photosynthetic intermediates with slower turnover rates (8-11%).We quantified the plants' C loss as respiratory CO(2) and BVOC emissions, allowing in tandem with metabolic analysis to deepen our understanding of ecosystem C flux
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