Global vegetation change through the Miocene/Pliocene boundary (original) (raw)
Related papers
Global vegetation change through the Miocene/Pliocene boundary: Nature
1997
Between 8 and 6 million years ago, there was a global increase in the biomass of plants using C 4 photosynthesis as indicated by changes in the carbon isotope ratios of fossil tooth enamel in Asia, Africa, North America and South America. This abrupt and widespread increase in C 4 biomass may be related to a decrease in atmospheric CO 2 concentrations below a threshold that favoured C 3 -photosynthesizing plants. The change occurred earlier at lower latitudes, as the threshold for C 3 photosynthesis is higher at warmer temperatures. 157
Earth and Planetary Science Letters, 1997
6 j3C values in paleosols and fossil teeth have been used to document the expansion of C, plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C, vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the S13C values of soil carbonate rise above a threshold of-8%0, suggesting the presence of C, plants, starting at 7.3-6.7 Ma. Sr3C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C, plants in the diets of large herbivores. These results show that the late Miocene expansion of C, plants was global, but occurred at different rates in each region. While it is has been suggested that declining pC0, levels during the late Neogene caused C, plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The 6 "0 soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3-4%~ in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.
Oligocene CO 2 Decline Promoted C 4 Photosynthesis in Grasses
Current Biology, 2008
C 4 photosynthesis is an adaptation derived from the more common C 3 photosynthetic pathway that confers a higher productivity under warm temperature and low atmospheric CO 2 concentration . C 4 evolution has been seen as a consequence of past atmospheric CO 2 decline, such as the abrupt CO 2 fall 32-25 million years ago (Mya) . This relationship has never been tested rigorously, mainly because of a lack of accurate estimates of divergence times for the different C 4 lineages . In this study, we inferred a large phylogenetic tree for the grass family and estimated, through Bayesian molecular dating, the ages of the 17 to 18 independent grass C 4 lineages. The first transition from C 3 to C 4 photosynthesis occurred in the Chloridoideae subfamily, 32.0-25.0 Mya. The link between CO 2 decrease and transition to C 4 photosynthesis was tested by a novel maximum likelihood approach. We showed that the model incorporating the atmospheric CO 2 levels was significantly better than the null model, supporting the importance of CO 2 decline on C 4 photosynthesis evolvability. This finding is relevant for understanding the origin of C 4 photosynthesis in grasses, which is one of the most successful ecological and evolutionary innovations in plant history.
Scientific Reports, 2017
Pyrogenic carbon (PyC) and n-alkane data from sediments in the northern South China Sea reveal variations in material from C 4 plants in East Asia over the last ~19 Ma. These data indicate the likely presence of C 4 taxa during the earliest part of the record analysed, with C 4 species also prominent during the mid and late Miocene and especially the mid Quaternary. Notably the two records diverge after the mid Quaternary, when PyC data indicate a reduced contribution of C 4 taxa to biomass burning, whereas plant-derived n-alkanes indicate a greater abundance of C 4 plants. This divergence likely reflects differences in the predominant source areas of organic materials accumulating at the coring site, with PyC representing a larger source area that includes material transported in the atmosphere from more temperate (relatively cooler and drier) parts of East Asia. Variations in the relative abundances of C 3 and C 4 taxa appear to be linked to a combination of environmental factors that have varied temporally and geographically and that are unique to East Asia. A major expansion of C 4 biomass in warmer subtropical parts of eastern Asia from ~1 Ma and particularly from ~0.4 Ma is later than other parts of the world. The Calvin-Benson cycle, the process through which plants convert inorganic carbon (C) and water to three C (C 3) sugar molecules, originated when atmospheric composition was very different from present 1, 2. One modification to the cycle, leading to reduced photorespiration effects and improved photosynthetic efficiency under certain conditions (e.g. moisture stress and relatively low pCO 2), involves production of four C (C 4) oxaloacetate as the first-formed product of photosynthesis. Uncertainty surrounds the exact date of origin of this modification. That said, there is no widely accepted evidence of C 4 taxa pre-dating the Oligocene 3 , with molecular studies indicating that the C 4 photosynthetic pathway first appeared between 35 and 30 Ma 4 , a period that includes a major decline in pCO 2 5
Ecology, 2015
Various environmental factors, including atmospheric CO 2 ( pCO 2 ), regional climate, and fire, have been invoked as primary drivers of long-term variation in C 4 grass abundance. Evaluating these hypotheses has been difficult because available paleorecords often lack information on past C 4 grass abundance or potential environmental drivers. We analyzed carbon isotope ratios (d 13 C) of individual grains of grass pollen in the sediments of two East African lakes to infer changes in the relative abundance of C 3 vs. C 4 grasses during the past 25 000 years. Results were compared with concurrent changes in pCO 2 , temperature, moisture balance, and fire activity. Our grass-pollen d 13 C analysis reveals a dynamic history of grass-dominated vegetation in equatorial East Africa: C 4 grasses have not consistently dominated lowland areas, and high-elevation grasses have not always been predominantly C 3. On millennial timescales, C 4 grass abundance does not correlate with charcoal influx at either site, suggesting that fire was not a major proximate control of the competitive balance between C 3 and C 4 grasses. Above the present-day treeline on Mt. Kenya, C 4 grass abundance declined from an average of ;90% during the glacial period to less than ;60% throughout the Holocene, coincident with increases in pCO 2 and temperature, and shifts in moisture balance. In the lowland savanna southeast of Mt. Kilimanjaro, C 4 grass abundance showed no such directional trend, but fluctuated markedly in association with variation in rainfall amount and seasonal-drought severity. These results underscore spatiotemporal variability in the relative influence of pCO 2 and climate on the interplay of C 3 and C 4 grasses and shed light on an emerging conceptual model regarding the expansion of C 4 -dominated grasslands in Earth's history. They also suggest that future changes in the C 3 /C 4 composition of grass-dominated ecosystems will likely exhibit striking spatiotemporal variability as a result of varying combinations of environmental controls.
… Society of America …, 2007
6 j3C values in paleosols and fossil teeth have been used to document the expansion of C, plants in South Asia, Africa, and North America during the late Miocene. However, the exact timing and rate of expansion of C, vegetation is unclear outside the Old World because of a lack of high-resolution records. We present a high-resolution record from northwest Argentina in which the S13C values of soil carbonate rise above a threshold of -8%0, suggesting the presence of C, plants, starting at 7.3-6.7 Ma. Sr3C values of fossil teeth from well dated sections in South and North America display a concomitant increase of C, plants in the diets of large herbivores. These results show that the late Miocene expansion of C, plants was global, but occurred at different rates in each region. While it is has been suggested that declining pC0, levels during the late Neogene caused C, plant expansion, climate change, such as an increase in summer-dominated rainfall regimes globally, is an alternative explanation. The 6 "0 soil carbonate records from South Asia, East Africa and now also northwest Argentina all show an increase of at least 3-4%~ in the late Neogene, either the result of climate change or of greater evaporation in average grassland soils.
Consequences of the evolution of C 4 photosynthesis for surface energy and water exchange
Journal of Geophysical Research, 2007
Although comprising less than 4% of all terrestrial plant species, C 4 plants are an essential component of low-latitude ecosystems, and in recent modeling simulations have been shown to strongly influence the stable carbon isotope ratio of the atmosphere. We used a fully coupled Earth system model (HadCM3LC) to evaluate the contribution of C 4 plants to the exchange of energy and water between the biosphere and atmosphere. Our simulations indicate that the presence or absence of C 4 plants is important for understanding regional climate, specifically with respect to seasonal climate patterns. When C 4 plants are absent from simulated tropical ecosystems, the percentage of bare soil increases regionally, Amazonia becomes warmer during the dry season, South Africa becomes drier during the dry season, the African Sahara-Sahel boundary becomes hotter during the dry season, and yet temperatures cool in central Australia during the Austral winter. Our modeling study provides the first insights into the potential climate feedbacks of late-Miocene C 4-C 3 ecosystems on surface energy and water exchange.
Palaeogeography, Palaeoclimatology, Palaeoecology, 2013
The abrupt spread of grasslands using C4 photosynthesis, sometimes referred to as the rapid increase in C4 ecosystems (RICE), occurred in the late Miocene in North America. While fossil plant specimens from the Miocene Dove Spring Formation of California as well as data from phylogenetic studies and molecular clocks show that C4 grasses evolved prior to the RICE, most isotopic data from paleosols and mammal tooth enamel suggest that its abundance on the landscape was minimal. However, a few recent studies from the Great Plains suggest that C4 grasslands may have been more prominent prior to the RICE event. Here we examine stable carbon isotope values from ungulate tooth enamel from the Barstow Formation of southern California, which is geographically and temporally close to the Dove Spring Formation, and records a diverse and abundant paleofauna of medial Miocene age. Tooth enamel δ13C values were examined in seven ungulate genera including the hypsodont equids; Acritohippus sp. and Scaphohippus sp.; the camelids, Aepycamelus sp., Hesperocamelus sp., and Procamelus sp.; the antilocaprid, Merycodus sp.; and the proboscidean, Gomphotherium sp. More positive δ13C values observed within the equids, camelids, and antilocaprids are suggestive of C4 grasses being included in the diets of these taxa. The equids exhibited the most positive mean δ13C values, which indicate a higher component of dietary C4 grasses (up to 18%) when compared to the other sampled ungulate taxa. The tooth enamel isotope values presented in this study show the presence of C4 grasses as a significant component of ungulate diets millions of years before the RICE. The abundance of C4 plants earlier in the Miocene may imply a more significant role in the major ungulate diversification events than previously suspected. The few pre-RICE localities showing evidence of C4 abundance suggests that these grasslands were geographically restricted which limits, but may not exclude, the possibility that a world-wide mechanism controlled its spread.