Changes in biomass allocation buffer low CO2 effects on tree growth during the last glaciation (original) (raw)
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Glacial trees from the La Brea tar pits show physiological constraints of low CO 2
New Phytologist, 2011
• While studies of modern plants indicate negative responses to low [CO 2 ] that occurred during the last glacial period, studies with glacial plant material that incorporate evolutionary responses are rare. In this study, physiological responses to changing [CO 2 ] were compared between glacial (La Brea tar pits) and modern Juniperus trees from southern California. • Carbon isotopes were measured on annual rings of glacial and modern Juniperus. The intercellular : atmospheric [CO 2 ] ratio (c i ⁄ c a) and intercellular [CO 2 ] (c i) were then calculated on an annual basis and compared through geologic time. • Juniperus showed constant mean c i ⁄ c a between the last glacial period and modern times, spanning 50 000 yr. Interannual variation in physiology was greatly dampened during the last glacial period relative to the present, indicating constraints of low [CO 2 ] that reduced responses to other climatic factors. Furthermore, glacial Juniperus exhibited low c i that rarely occurs in modern trees, further suggesting limiting [CO 2 ] in glacial plants. • This study provides some of the first direct evidence that glacial plants remained near their lower carbon limit until the beginning of the glacial-interglacial transition. Our results also suggest that environmental factors that dominate carbon-uptake physiology vary across geologic time, resulting in major alterations in physiological response patterns through time.
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...
Global change biology, 2015
Theory predicts that the postindustrial rise in the concentration of CO2 in the atmosphere (ca ) should enhance tree growth either through a direct fertilization effect or indirectly by improving water use efficiency in dry areas. However, this hypothesis has received little support in cold-limited and subalpine forests where positive growth responses to either rising ca or warmer temperatures are still under debate. In this study, we address this issue by analyzing an extensive dendrochronological network of high-elevation Pinus uncinata forests in Spain (28 sites, 544 trees) encompassing the whole biogeographical extent of the species. We determine if the basal area increment (BAI) trends are linked to climate warming and increased ca by focusing on region- and age-dependent responses. The largest improvement in BAI over the past six centuries occurred during the last 150 years affecting young trees and being driven by recent warming. Indeed, most studied regions and age classes p...
Tree physiology
In this review, I focus on modeling studies of tree responses to CO(2) enrichment. First, I examine leaf-scale models of assimilation with respect to the interaction between low temperature and CO(2) enrichment. Second, because changes in allocation within a tree may be significant in determining the growth response of trees to CO(2) enrichment and low temperatures, I review models of the control of allocation in plants. Finally, models of stand-scale processes are discussed with respect to their ability to make reliable estimates of likely vegetation responses to predicted climate change. I conclude that our ability to make reliable predictions is hindered by our lack of understanding of several processes, namely: the interaction between increased atmospheric CO(2) concentration and low temperatures; the control of allocation in plants; and the modeling of stand-scale processes.
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.
HISTORICAL CO 2 GROWTH ENHANCEMENT DECLINES WITH AGE IN QUERCUS AND PINUS
Ecological Monographs, 2006
Despite experimental evidence showing that elevated CO 2 levels increase growth in most plants, the isolation of a signal consistent with anthropogenically caused increases in atmospheric CO 2 from the dendrochronological record has shown mixed results. Our extensive sets of tree ring data from the Ozark Mountains in Missouri showed that since 1850, Quercus velutina Lam., Quercus coccinea Muench., and Pinus echinata Mill. trees increased in stem growth coincidently with increases in atmospheric CO 2 . Those long-term increases in radial growth appear unrelated to historical disturbance levels for the region, to long-term changes in relevant climatic variables, or to productivity of sites sampled for the purpose of creating a time sequence of tree ring growth. It is still unclear what the potential role of nitrogen deposition might have been for tree growth. We cross-dated a large number of increment cores and aligned the ring width data by pith date for accurate age constant assessments of growth over the past 150 years. Thus, we circumvented changes in growth trend associated with differences in physiological functioning during development, as well as the need for statistical detrending that removes an unknown degree of long-term environmental signal, the so called segment length curse that applies to standard dendrochronological investigations. When the positive relationship between CO 2 and ring width was examined at different ages, an ontogenetic decline in the rate of growth stimulation was found. Specifically, both the pooled Quercus spp. and P. echinata were characterized by a negative exponential pattern of response over a developmental sequence through age 50. Further knowledge of an intrinsic decline in CO 2 sensitivity with tree age or size such as this may be important for increased accuracy in estimating terrestrial carbon stocks across successional landscapes.
Response of Lodgepole Pine Growth to Co 2 Degassing at Mammoth Mountain, California
Ecology, 1999
We conducted dendroclimatic and stable isotope analyses of lodgepole pines (Pinus contorta) located in high-mortality sites at Mammoth Mountain (California, USA) to test for tree responses to magmatic degassing. Existing climatic and tree-ring data from nearby Yellowstone National Park were used for comparison. Sampled trees were scarcely sensitive to climate, and their growth showed an overall decline during the 20th century. Past growth rates of currently dead and stressed pines plummeted after 1990, when degassing of magmatic CO 2 was first reported in the area. No consistent or strong correlation was found with monthly and seasonal climatic parameters. Stable carbon isotopes were measured on holocellulose extracted from annual rings of a dead pine, a stressed pine, and a live pine. The ␦ 13 C signature of the dead and stressed pines showed enrichment in heavy carbon beginning in 1990, which could be related to stomatal closure following impairment of root systems by high levels of magmatic CO 2 in the soil.
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
Soil warming and CO 2 enrichment induce biomass shifts in alpine tree line vegetation
Global Change Biology, 2015
Responses of alpine treeline ecosystems to increasing atmospheric CO2 concentrations and global warming are poorly understood. We used an experiment at the Swiss treeline to investigate changes in vegetation biomass after 9 years of free air CO2 enrichment (+200 ppm; 2001-2009) and 6 years of soil warming (+4°C; 2007-2012). The study contained two key treeline species, Larix decidua and Pinus uncinata, both approximately 40 years old, growing in heath vegetation dominated by dwarf shrubs. In 2012, we harvested and measured biomass of all trees (including root systems), above-ground understorey vegetation and fine roots. Overall, soil warming had clearer effects on plant biomass than CO2 enrichment, and there were no interactive effects between treatments. Total plant biomass increased in warmed plots containing Pinus but not in those with Larix. This response was driven by changes in tree mass (+50%), which contributed an average of 84% (5.7 kg m-2) of total plant mass. Pinus coarse root mass was especially enhanced by warming (+100%), yielding an increased root mass fraction. Elevated CO2 led to an increased relative growth rate of Larix stem basal area but no change in the final biomass of either tree species. Total understory above-ground mass was not altered by soil warming or elevated CO2. However, Vaccinium myrtillus mass increased with both treatments, grass mass declined with warming, and forb and nonvascular plant (moss and lichen) mass decreased with both treatments. Fine roots showed a substantial reduction under soil warming (-40% for all roots <2 mm in diameter at 0-20 cm soil depth) but no change with CO2 enrichment. Our findings suggest that enhanced overall productivity and shifts in biomass allocation will occur at the treeline, particularly with global warming. However, individual species and functional groups will respond differently to these environmental changes, with consequences for ecosystem structure and functioning.