Carbon starvation in glacial trees recovered from the La Brea tar pits, southern California (original) (raw)
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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...
Low atmospheric CO2 levels before the rise of forested ecosystems
Nature Communications
The emergence of forests on Earth (~385 million years ago, Ma)1has been linked to an order-of-magnitude decline in atmospheric CO2levels and global climatic cooling by altering continental weathering processes, but observational constraints on atmospheric CO2before the rise of forests carry large, often unbound, uncertainties. Here, we calibrate a mechanistic model for gas exchange in modern lycophytes and constrain atmospheric CO2levels 410–380 Ma from related fossilized plants with bound uncertainties of approximately ±100 ppm (1 sd). We find that the atmosphere contained ~525–715 ppm CO2before continents were afforested, and that Earth was partially glaciated according to a palaeoclimate model. A process-driven biogeochemical model (COPSE) shows the appearance of trees with deep roots did not dramatically enhance atmospheric CO2removal. Rather, shallow-rooted vascular ecosystems could have simultaneously caused abrupt atmospheric oxygenation and climatic cooling long before the r...
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.
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
Estimation of past atmospheric carbon dioxide levels using tree-ring cellulose δ13 C
We study the applicability of the Farquhar model for carbon isotopic discrimination (change in carbon isotopic composition from air CO 2 to tree-ring cellulose) in C 3 plants to trees growing in the field. Two new carbon isotope datasets from Himalayan conifers with published data from another eight sites across the world show disparate trends in the plot of carbon isotope discrimination versus atmospheric carbon dioxide concentration, in contrast to the model prediction of absence of any trend. This is because the model assumes that the tree adjusts its stomatal conductance for water-use efficiency to maintain a constant ratio of carbon dioxide concentrations inside and outside the leaf and treats the diffusive and biochemical fractionation factors as constants. By introducing a simple linear dependence of these fractionation factors with ambient temperature and humidity, we have enhanced the applicability of the model to naturally growing trees. Further, despite the disparate trends exhibited by the 10 trees, we show using the inverse modelling that it is possible to derive a unique record of past atmospheric CO 2 concentrations using tree cellulose 13 C data. The reconstructions also replicate the summer pCO 2 gradient from tropics to mid-latitudes. We also discuss the merits and demerits of the model, and compare the model-derived pCO 2 with that of the ice core-based records from Law Dome.
Quaternary Science Reviews, 2004
In order to predict accurately how elevated atmospheric CO 2 concentrations will affect the global carbon cycle, it is necessary to know how trees respond to increasing CO 2 concentrations. In this paper we examine the response over the period AD 1895 -1994 of three tree species growing across northern Europe to increases in atmospheric CO 2 concentrations using parameters derived from stable carbon isotope ratios of trunk cellulose. Using the isotope data we calculate values of intrinsic water-use efficiency (IWUE) and intercellular CO 2 concentrations in the leaf (c i ).