Glacial trees from the La Brea tar pits show physiological constraints of low CO 2 (original) (raw)
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Carbon starvation in glacial trees recovered from the La Brea tar pits, southern California
Proceedings of the National Academy of Sciences, 2005
The Rancho La Brea tar pit fossil collection includes Juniperus (C 3 ) wood specimens that 14 C date between 7.7 and 55 thousand years (kyr) B.P., providing a constrained record of plant response for southern California during the last glacial period. Atmospheric CO 2 concentration ([CO 2 ]) ranged between 180 and 220 ppm during glacial periods, rose to ≈280 ppm before the industrial period, and is currently approaching 380 ppm in the modern atmosphere. Here we report on δ 13 C of Juniperus wood cellulose, and show that glacial and modern trees were operating at similar leaf-intercellular [CO 2 ]( c i )/atmospheric [CO 2 ]( c a ) values. As a result, glacial trees were operating at c i values much closer to the CO 2 -compensation point for C 3 photosynthesis than modern trees, indicating that glacial trees were undergoing carbon starvation. In addition, we modeled relative humidity by using δ 18 O of cellulose from the same Juniperus specimens and found that glacial humidity was ≈10...
Oecologia, 1998
To evaluate how the land carbon reservoir has been responding to the rising CO 2 concentration of the atmosphere, it is important to study how plants in natural forests adjust physiologically to the changing atmospheric conditions. Many experimental studies have addressed this issue, but it has been dicult to scale short-term experimental observations to long-term ecosystem-level responses. This paper derives carbon-isotope-related variables for the past 100±200 years from measurements on trees from natural forests. Calculations show that the c i /c a ratios [c i /c a is the ratio of the CO 2 concentration (lmol mol A1) in the intercellular space of leaves to that in the atmosphere] of the trees were constant or increased slightly before the 20th century, but changed more rapidly in the 20th century; some increased, some decreased, and some stayed constant. In contrast, the CO 2 concentration inside plant leaves increased monotonically for all trees. Key words Atmospheric CO 2 concentration á Tree rings á Long-term changes á Carbon isotopes á c i /c a ratios
Changes in biomass allocation buffer low CO2 effects on tree growth during the last glaciation
Scientific reports, 2017
Isotopic measurements on junipers growing in southern California during the last glacial, when the ambient atmospheric [CO2] (ca) was ~180 ppm, show the leaf-internal [CO2] (ci) was approaching the modern CO2 compensation point for C3 plants. Despite this, stem growth rates were similar to today. Using a coupled light-use efficiency and tree growth model, we show that it is possible to maintain a stable ci/ca ratio because both vapour pressure deficit and temperature were decreased under glacial conditions at La Brea, and these have compensating effects on the ci/ca ratio. Reduced photorespiration at lower temperatures would partly mitigate the effect of low ci on gross primary production, but maintenance of present-day radial growth also requires a ~27% reduction in the ratio of fine root mass to leaf area. Such a shift was possible due to reduced drought stress under glacial conditions at La Brea. The necessity for changes in allocation in response to changes in [CO2] is consisten...
Ecology Letters, 2014
Assessing family- and species-level variation in physiological responses to global change across geologic time is critical for understanding factors that underlie changes in species distributions and community composition. Here, we used stable carbon isotopes, leaf nitrogen content and stomatal measurements to assess changes in leaf-level physiology in a mixed conifer community that underwent significant changes in composition since the last glacial maximum (LGM) (21 kyr BP). Our results indicate that most plant taxa decreased stomatal conductance and/or maximum photosynthetic capacity in response to changing conditions since the LGM. However, plant families and species differed in the timing and magnitude of these physiological responses, and responses were more similar within families than within co-occurring species assemblages. This suggests that adaptation at the level of leaf physiology may not be the main determinant of shifts in community composition, and that plant evolutionary history may drive physiological adaptation to global change over recent geologic time.
Impact of climate and CO 2 on a millennium-long tree-ring carbon isotope record
Geochimica Et Cosmochimica Acta, 2009
We present one millennium-long (1171-year), and three 100 year long annually resolved d 13 C tree-ring chronologies from ecologically varying Juniperus stands in the Karakorum Mountains (northern Pakistan), and evaluate their response to climatic and atmospheric CO 2 changes. All d 13 C records show a gradual decrease since the beginning of the 19th century, which is commonly associated with a depletion of atmospheric d 13 C due to fossil fuel burning. Climate calibration of high-frequency d 13 C variations indicates a pronounced summer temperature signal for all sites. The low-frequency component of the same records, however, deviates from long-term temperature trends, even after correction for changes in anthropogenic CO 2 . We hypothesize that these high-elevation trees show a response to both climate and elevated atmospheric CO 2 concentration and the latter might explain the offset with target temperature data. We applied several corrections to tree-ring d 13 C records, considering a range of potential CO 2 discrimination changes over the past 150 years and calculated the goodness of fit with the target via calibration/verification tests (R 2 , residual trend, and Durbin-Watson statistics). These tests revealed that at our sites, carbon isotope fixation on longer timescales is affected by increasing atmospheric CO 2 concentrations at a discrimination rate of about 0.012&/ppmv. Although this statistically derived value may be site related, our findings have implications for the interpretation of any long-term trends in climate reconstructions using tree-ring d 13 C, as we demonstrate with our millennium-long d 13 C Karakorum record. While we find indications for warmth during the Medieval Warm Period (higher than today's mean summer temperature), we also show that the low-frequency temperature pattern critically depends on the correction applied. Patterns of long-term climate variation, including the Medieval Warm Period, the Little Ice Age, and 20th century warmth are most similar to existing evidence when a strong influence of increased atmospheric CO 2 on plant physiology is assumed.
Palaeobotany: Atmospheric CO2 from fossil plant cuticles
Nature, 2002
The link between atmospheric CO 2 levels and global warming is an axiom of current public policy, and is well supported by physicochemical experiments, by comparative planetary climatology and by geochemical modelling. Geological tests of this idea seek to compare proxies of past atmospheric CO 2 with other proxies of palaeotemperature. For at least the past 300 Myr, there is a remarkably high temporal correlation between peaks of atmospheric CO 2 , revealed by study of stomatal indices of fossil leaves of Ginkgo, Lepidopteris, Tatarina and Rhachiphyllum, and palaeotemperature maxima, revealed by oxygen isotopic (δ 18 O) composition of marine biogenic carbonate. Large and growing databases on these proxy indicators support the idea that atmospheric CO 2 and temperature are coupled. In contrast, CO 2 -temperature uncoupling has been proposed from geological time-series of carbon isotopic composition of palaeosols and of marine phytoplankton compared with foraminifera, which fail to indicate high CO 2 at known times of high palaeotemperature. Failure of carbon isotopic palaeobarometers may be due to episodic release of CH 4 , which has an unusually light isotopic value (down to −110 % % , and typically −60 % % δ 13 C) and which oxidizes rapidly (within 7-24 yr) to isotopically light CO 2 . Past CO 2 highs (above 2000 ppmv) were not only times of catastrophic release of CH 4 from clathrates, but of asteroid and comet impacts, flood basalt eruptions and mass extinctions. The primary reason for iterative return to low CO 2 was carbon consumption by hydrolytic weathering and photosynthesis, perhaps stimulated by mountain uplift and changing patterns of oceanic thermohaline circulation. Sequestration of carbon was promoted in the long term by such evolutionary innovations as the lignin of forests and the sod of grasslands, which accelerated physicochemical weathering and delivery of nutrients to fuel oceanic productivity and carbon burial.
Impact of CO2 and climate on Last Glacial maximum vegetation – a factor separation
Biogeosciences, 2013
The factor separation of Stein and Alpert (1993) is applied to simulations with the MPI Earth system model to determine the factors which cause the differences between vegetation patterns in glacial and pre-industrial climate. The factors firstly include differences in the climate, caused by a strong increase in ice masses and the radiative effect of lower greenhouse gas concentrations; secondly, differences in the ecophysiological effect of lower glacial atmospheric CO 2 concentrations; and thirdly, the synergy between the pure climate effect and the pure effect of changing physiologically available CO 2. It is has been shown that the synergy can be interpreted as a measure of the sensitivity of ecophysiological CO 2 effect to climate. The pure climate effect mainly leads to a contraction or a shift in vegetation patterns when comparing simulated glacial and pre-industrial vegetation patterns. Raingreen shrubs benefit from the colder and drier climate. The pure ecophysiological effect of CO 2 appears to be stronger than the pure climate effect for many plant functional types-in line with previous simulations. The pure ecophysiological effect of lower CO 2 mainly yields a reduction in fractional coverage, a thinning of vegetation and a strong reduction in net primary production. The synergy appears to be as strong as each of the pure contributions locally, but weak on global average for most plant functional types. For tropical evergreen trees, however, the synergy is strong on global average. It diminishes the difference between glacial and pre-industrial coverage of tropical evergreen trees, due to the pure climate effect and the pure ecophysiological CO 2 effect, by approximately 50 per cent.