Publications
Found 22 publication(s)
- of type
Seibert, R.; Grünhage, L.; Müller, C.; Otte, A. & Donath, T.W. (2018): Raised atmospheric CO2 levels affect soil seed bank composition of temperate grasslands. Journal of Vegetation Science 30, 86-97
DOI: http://dx.doi.org/10.1111/jvs.12699.
Andresen, L.C.; Yuan, N.; Seibert, R.; Moser, G.; Kammann, C.; Luterbacher, J.; Erbs, M. & Müller, C. (2018): Biomass responses in a temperate European grassland through 17 years of elevated CO2. Global Change Biology 24, 3875-3885
DOI: http://dx.doi.org/10.1111/gcb.13705.
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DOI: 10.1111/gcb.13705
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Abstract:
Abstract:
Future increase in atmospheric CO2 concentrations will potentially enhance grassland
biomass production and shift the functional group composition with consequences
for ecosystem functioning. In the “GiFACE” experiment (Giessen Free Air Carbon
dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2
(eCO2) year-round during daylight hours since 1998, at a level of +20% relative to
ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014,
aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually
through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of
C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass
(TAB) was significantly increased under eCO2 (p = .045 and .025, at first and
second harvest). The dominant plant functional group grasses responded positively at
the start, but for forbs, the effect of eCO2 started out as a negative response. The
increase in TAB in response to eCO2 was approximately 15% during the period from
2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time,
tentatively a consequence of the fertilization management. Biomass and soil moisture
responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested
in the latter years was associated with a positive biomass response of both functional
groups. The direction of the biomass response of the functional group forbs changed
over the experimental duration, intensified by extreme weather conditions, pointing
to the need of long-term field studies for obtaining reliable responses of perennial
ecosystems to eCO2 and as a basis for model development.
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Keywords: |
climate change |
soil moisture |
forbs |
frost |
Giessen free air carbon dioxide enrichment |
grasses |
long-term response |
Free air carbon dioxide enrichment |
Obermeier, W.; Lehnert, L.W.; Ivanov, M.; Luterbacher, J. & Bendix, J. (2018): Reduced summer aboveground productivity in temperate C3 grasslands under future climate regimes. Earth's Future 6, 1-14
DOI: http://dx.doi.org/10.1029/2018EF000833.
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DOI: 10.1029/2018EF000833
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Abstract:
Abstract:
Temperate grasslands play globally an important role, for example, for biodiversity conservation, livestock forage production, and carbon storage. The latter two are primarily controlled by biomass
production, which is assumed to decrease with lower amounts and higher variability of precipitation, while increasing air temperature might either foster or suppress biomass production. Additionally, a higher atmospheric CO2 concentration ([CO2]) is supposed to increase biomass productivity either by directly
stimulating photosynthesis or indirectly by inducing water savings (CO2 fertilization effect). Consequently, future biomass productivity is controlled by the partially contrasting effects of changing climatic conditions and [CO2], which to date are only marginally understood. This results in high uncertainties of future
biomass production and carbon storage estimates. Consequently, this study aims at statistically estimating mid-21st century grassland aboveground biomass (AGB) based on 18 years of data (1998–2015) from a free air carbon enrichment experiment. We found that lower precipitation totals and a higher precipitation variability
reduced AGB. Under drier conditions accompanied by increasing air temperature, AGB further decreased. Here AGB under elevated [CO2] was partly even lower compared to AGB under ambient [CO2], probably because elevated [CO2] reduced evaporative cooling of plants, increasing heat stress. This indicates a higher susceptibility
of AGB to increased air temperature under future atmospheric [CO2]. Since climate models for Central Europe project increasing air temperature and decreasing total summer precipitation associated with an increasing variability, our results suggest that grassland summer AGB will be reduced in the future, contradicting the widely expected positive yield anomalies from increasing [CO2].
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Keywords: |
biomass |
climate change |
elevated CO2 |
FACE |
precipitation |
warming |
Andresen, L.C.; Yuan, N.; Seibert, R.; Moser, G.; Kammann, C.; Luterbacher, J.; Erbs, M. & Müller, C. (2017): Biomass reponses in a temperate European grassland through 17 years of elevated CO2. Global Change Biology 2017, 1-11
DOI: http://dx.doi.org/10.1111/gcb.13705.
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DOI: 10.1111/gcb.13705
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Abstract:
Abstract:
Future increase in atmospheric CO2 concentrations will potentially enhance grassland biomass production and shift the functional group composition with consequences for ecosystem functioning. In the “GiFACE” experiment (Giessen Free Air Carbon dioxide Enrichment), fertilized grassland plots were fumigated with elevated CO2(eCO2) year-round during daylight hours since 1998, at a level of +20% relative to ambient concentrations (in 1998, aCO2 was 364 ppm and eCO2 399 ppm; in 2014, aCO2 was 397 ppm and eCO2 518 ppm). Harvests were conducted twice annually through 23 years including 17 years with eCO2 (1998 to 2014). Biomass consisted of C3 grasses and forbs, with a small proportion of legumes. The total aboveground biomass (TAB) was significantly increased under eCO2 (p = .045 and .025, at first and second harvest). The dominant plant functional group grasses responded positively at the start, but for forbs, the effect of eCO2 started out as a negative response. The increase in TAB in response to eCO2 was approximately 15% during the period from 2006 to 2014, suggesting that there was no attenuation of eCO2 effects over time, tentatively a consequence of the fertilization management. Biomass and soil moisture responses were closely linked. The soil moisture surplus (c. 3%) in eCO2 manifested in the latter years was associated with a positive biomass response of both functional groups. The direction of the biomass response of the functional group forbs changed over the experimental duration, intensified by extreme weather conditions, pointing to the need of long-term field studies for obtaining reliable responses of perennial ecosystems to eCO2 and as a basis for model development.
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Keywords: |
climate change |
soil moisture |
forbs |
free air carbon dioxide enrichment |
frost |
Giessen free air carbon dioxide enrichment |
grasses |
long-term response |
Obermeier, W. (2017-07-04). Future summer aboveground biomass in a temperate C3 grassland. Presented at General Assembly - FACE2FACE, Giessen.
Obermeier, W.; Lehnert, L.W.; Kammann, C.; Müller, C.; Grünhage, L.; Luterbacher, J.; Erbs, M.; Moser, G.; Seibert, R.; Yuan, N. & Bendix, J. (2016): Reduced CO2 fertilization effect in temperate C3 grasslands under more extreme weather conditions. Nature Climate Change 7(2), 137-141
DOI: http://dx.doi.org/10.1038/nclimate3191.
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DOI: 10.1038/nclimate3191
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Abstract:
Abstract:
The increase in atmospheric greenhouse gas concentrations from anthropogenic activities is the major driver of recent global climate change1. The stimulation of plant photosynthesis due to rising atmospheric carbon dioxide concentrations ([CO2]) is widely assumed to increase the net primary productivity (NPP) of C3 plants—the CO2 fertilization effect (CFE). However, the magnitude and persistence of the CFE under future climates, including more frequent weather extremes, are controversial. Here we use data from 16 years of temperate grassland grown under ‘free-air carbon dioxide enrichment’ conditions to show that the CFE on above-ground biomass is strongest under local average environmental conditions. The observed CFE was reduced or disappeared under wetter, drier and/or hotter conditions when the forcing variable exceeded its intermediate regime. This is in contrast to predictions of an increased CO2 fertilization effect under drier and warmer conditions. Such extreme weather conditions are projected to occur more intensely and frequently under future climate scenarios. Consequently, current biogeochemical models might overestimate the future NPP sink capacity of temperate C3 grasslands and hence underestimate future atmospheric [CO2] increase.
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Keywords: |
climate change |
grassland |
GiFACE |
CO2 fertilization |
Elevated carbon dioxide |
grassland ecology |
ecophysiology |
Grünhage, L.; Kammann, C. & Moser, G. (2016-01-07). GiFACE Sampling Design. Presented at Internal Presentation, Giessen.
Yuan, N.; Xoplaki, E.; Zhu, C. & Luterbacher, J. (2016): A novel way to detect correlations on multi-time scales, with temporal evolution and for multi-variables. Scientific Reports 6, 27707
DOI: http://dx.doi.org/10.1038/srep27707.
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DOI: 10.1038/srep27707
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Abstract:
In this paper, two new methods, Temporal evolution of Detrended Cross-Correlation Analysis (TDCCA)
and Temporal evolution of Detrended Partial-Cross-Correlation Analysis (TDPCCA), are proposed
by generalizing DCCA and DPCCA. Applying TDCCA/TDPCCA, it is possible to study correlations on
multi-time scales and over different periods. To illustrate their properties, we used two climatological
examples: i) Global Sea Level (GSL) versus North Atlantic Oscillation (NAO); and ii) Summer Rainfall
over Yangtze River (SRYR) versus previous winter Pacific Decadal Oscillation (PDO). We find significant
correlations between GSL and NAO on time scales of 60 to 140 years, but the correlations are nonsignificant
between 1865–1875. As for SRYR and PDO, significant correlations are found on time
scales of 30 to 35 years, but the correlations are more pronounced during the recent 30 years. By
combining TDCCA/TDPCCA and DCCA/DPCCA, we proposed a new correlation-detection system,
which compared to traditional methods, can objectively show how two time series are related (on
which time scale, during which time period). These are important not only for diagnosis of complex
system, but also for better designs of prediction models. Therefore, the new methods offer new
opportunities for applications in natural sciences, such as ecology, economy, sociology and other
research fields.
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Keywords: |
Correlation |
multi-time scales |
multi-variables |
nonliear interactions |
temporal evolution |
Yuan, N.; Fu, Z.; Zhang, H.; Piao, L.; Xoplaki, E. & Luterbacher, J. (2015): Detrended partial-cross-correlation analysis: A new method for analyzing correlations in complex system. Scientific Reports 5, 08143
DOI: http://dx.doi.org/10.1038/srep08143.
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DOI: 10.1038/srep08143
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Abstract:
In this paper, a new method, detrended partial-cross-correlation analysis (DPCCA), is proposed. Based on
detrended cross-correlation analysis (DCCA), this method is improved by including partial-correlation
technique, which can be applied to quantify the relations of two non-stationary signals (with influences of
other signals removed) on different time scales. We illustrate the advantages of this method by performing
two numerical tests. Test I shows the advantages of DPCCA in handling non-stationary signals, while Test II
reveals the ‘‘intrinsic’’ relations between two considered time series with potential influences of other
unconsidered signals removed. To further show the utility of DPCCA in natural complex systems, we
provide new evidence on the winter-time Pacific Decadal Oscillation (PDO) and the winter-time Nino3 Sea
Surface Temperature Anomaly (Nino3-SSTA) affecting the Summer Rainfall over the middle-lower reaches
of the Yangtze River (SRYR). By applying DPCCA, better significant correlations between SRYR and
Nino3-SSTA on time scales of 6 , 8 years are found over the period 1951 , 2012, while significant
correlations between SRYR and PDO on time scales of 35 years arise. With these physically explainable
results, we have confidence that DPCCA is an useful method in addressing complex systems.
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Keywords: |
Complex system |
Correlation |
DPCCA |
Zhang, H.; Yuan, N.; Esper, J.; Werner, J.P.; Xoplaki, E.; Büntgen, U.; Treydte, K. & Luterbacher, J. (2015): Modified climate with long term memory in tree ring proxies. Environmental Research Letters 10, 084020
DOI: http://dx.doi.org/10.1088/1748-9326/10/8/084020.
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DOI: 10.1088/1748-9326/10/8/084020
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Abstract:
Abstract:
Long term memory (LTM) scaling behavior in worldwide tree-ring proxies and subsequent climate
reconstructions is analyzed for and compared with the memory structure inherent to instrumental
temperature and precipitation data. Detrended fluctuation analysis is employed to detect LTM, and its
scaling exponent ? is used to evaluate LTM. The results show that temperature and precipitation
reconstructions based on ringwidthmeasurements (mean ? = 0.8) containmorememory than
records based onmaximumlatewood density (mean ? = 0.7). Both exceed thememory inherent to
regional instrumental data (? = 0.6 for temperature, ? = 0.5 for precipitation) in the time scales
ranging from1 year up to 50 years.We comparememory-free (? = 0.5) pseudo-instrumental
precipitation datawith pseudo-reconstructed precipitation datawith LTM (? > 0.5), and demonstrate
the biasing influences ofLTMon climate reconstructions. Wecall for attention to statistical
analysis with regard to the variability of proxy-based chronologies or reconstructions, particularly
with respect to the contained (i) trends, (ii) past warm/cold period and wet/dry periods; and (iii)
extreme events.
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Keywords: |
climate reconstructions |
tree-ring width |
maximum latewood density |
frequency domains |
Untenecker, J.; Tiemeyer, B.; Freibauer, A.; Laggner, A. & Luterbacher, J. (2017): Tracking changes in the land use, management and drainage status of organic soils as indicators of the effectiveness of mitigation strategies for climate change. Ecological Indicators 72, 459-472
DOI: http://dx.doi.org/10.1016/j.ecolind.2016.08.004.
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DOI: 10.1016/j.ecolind.2016.08.004
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tThe tracking of land use since 1990 presents a major challenge in greenhouse gas (GHG) reporting underthe United Nations Framework Convention on Climate Change (UNFCCC) and the Kyoto Protocol becausethere is often limited availability of data, especially for the base year of 1990. There is even less landmanagement and soil moisture data, which are needed to track climate change mitigation activities sincesoil moisture is one of the main drivers of GHG emissions of organic soils. Information is also needed for thereporting of land-based activities such as grazing land management or wetland drainage and rewetting oforganic soils. Different spatial and thematic resolutions of land-use data produce inconsistent time serieswith a strong overestimation of land-use change (LUC) if not adequately accounted for. Our aim was tocreate a consistent time series of land use since 1990 that is in line with GHG reporting under the UNFCCCand the Kyoto Protocol by combining official cadastral data with colour-infrared aerial photography usedfor biodiversity monitoring in six federal states in northern and eastern Germany. We developed a generichierarchical classification by land use, management and drainage status, and a translation key for dataharmonisation into a consistent time series. This time series enabled the quantification of LUC on organicsoils between 1992 and 2013 in a spatially explicit manner. Furthermore we used this time series todevelop indicators for changes in land management and drainage to evaluate the success of protectionstatuses on peatland restoration.The study area encompassed one million hectares, half of which had some type of legal nature pro-tection status. Areas with no protection status tended to become more intensively farmed and drier,while highly protected areas (e.g. Natura 2000) showed the opposite trend. Land-use trends also dif-fered greatly between federal states. In Schleswig-Holstein organic soils tended to become drier duringthe study period, while in Mecklenburg-Western Pomerania they tended to become wetter overall. Thetrends and differences in LUC between federal states were linked to German reunification, changes in theEuropean Common Agricultural Policy (CAP) and Germany’s Renewable Energy Act (EEG). A large-scalepeatland protection programme also had major impact.In conclusion, our study demonstrates how data derived for biodiversity monitoring and other highlydetailed land-use data can be used to track changes in land use, management and drainage status inaccordance with the reporting requirements under the UNFCCC and the Kyoto Protocol.
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Keywords: |
Land-use change |
Time series consistency |
Peatland |
Rewetting |
Kyoto Protocol |
Greenhouse gas inventory |
Lehnert, L.W.; Meyer, H.; Obermeier, W.; Silva, B.; Regeling, B.; Thies, B. & Bendix, J. (2016): Hyperspectral data analysis in R: the hsdar-package. Journal of Statistical Software online, online.
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Abstract:
Hyperspectral remote sensing is a promising tool for a variety of applications including ecology and geology but also analytical chemistry and medical research. Here, the new hsdar-package for R statistical software is presented, which allows to perform a large variety of analysis steps during a typical hyperspectral remote sensing approach. Therefore, the package introduces a new class to e?ciently store even large hyperspectral datasets such as hyperspectral cubes within R. The package includes several important hyperspectral analysis tools such as continuum removal, normalized ratio indices and integrates two widely used radiation transfer models. Besides this, the package provides methods to directly use the functionality of the caret-package for machine learning tasks. To demonstrate the range of functions of the hsdar-package, two case studies are included. The ?rst one shows the estimation of plant leave chlorophyll content and the second one the ability to detect cancer in the human larynx from hyperspectral data.
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Keywords: |
Hyperspectral remote sensing |
hyperspectral imaging |
spectroscopy |
continuum removal |
normalized ratio indices |
Jansen-Willems, A.B.; Lanigan, G.J.; Grünhage, L. & Müller, C. (2016): Carbon cycling in temperate grassland under elevated temperature. Ecology and Evolution In press, In press
DOI: http://dx.doi.org/In press.
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DOI: In press
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Abstract:
Abstract:
An increase in mean soil surface temperature has been observed over the last century and it is predicted to further increase in the future. The effect of increased temperature on ecosystem carbon fluxes in a permanent temperate grassland, was studied in a long term (6 years) field experiment, using multiple temperature increments induced by IR-lamps. Ecosystem respiration (R-eco) and net ecosystem exchange (NEE) were measured, and modelled by a modified Lloyd and Taylor model including a soil moisture component for R-eco (average R2 of 0.78) and inclusion of a photosynthetic component based on temperature and radiation for NEE (R2=0.65). Modelled NEE values ranged between 2.3 and 5.3 kg CO2 m-2 year-1, depending on treatment. An increase of 2 or 3°C led to increased carbon losses, lowering the carbon storage potential by around 4 tonnes of C ha-1 year-1. The majority of significant NEE differences were found during night-time compared to daytime. This suggests that during daytime the increased respiration could be offset by an increase in photosynthetic uptake. This was also supported by differences in ?13C and ?18O, indicating prolonged increased photosynthetic activity associated with the higher temperature treatments. However, this increase in photosynthesis was insufficient to counteract the 24hr increase in respiration, explaining the higher CO2 emissions due to elevated temperature.
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Keywords: |
CO2 |
grassland |
Heating |
elevated temperature |
respiration |
net ecosystem exchange |
isotopes |
Moser, G.; Müller, C. & Grünhage, L. (2016-01-07). Klimawandel vor der Haustür. Presented at UKL, UKL.
Keidel, L.; Kammann, C.; Grünhage, L.; Moser, G. & Müller, C. (2015): Long term CO2 enrichment in a temperate grassland increases soil respiration during late autumn and winter. Biogeoscience 12, 1257-1269
DOI: http://dx.doi.org/10.5194/bg-12-1257-2015.
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DOI: 10.5194/bg-12-1257-2015
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Abstract:
Soil respiration of terrestrial ecosystems, a major component in the global carbon cycle is affected by elevated atmospheric CO2 concentrations. However, seasonal differences of feedback effects of elevated CO2 have rarely been studied. At the Gießen Free-Air CO2 Enrichment (GiFACE) site, the effects of +20% above ambient CO2 concentration have been investigated since 1998 in a temperate grassland ecosystem. We defined five distinct annual seasons, with respect to management practices and phenological cycles. For a period of 3 years (2008–2010), weekly measurements of soil respiration were carried out with a survey chamber on vegetation-free subplots. The results revealed a pronounced and repeated increase of soil respiration under elevated CO2 during late autumn and winter dormancy. Increased CO2 losses during the autumn season (September–October) were 15.7% higher and during the winter season (November–March) were 17.4% higher compared to respiration from ambient CO2 plots.
However, during spring time and summer, which are characterized by strong above- and below-ground plant growth, no significant change in soil respiration was observed at the GiFACE site under elevated CO2. This suggests (1) that soil respiration measurements, carried out only during the growing season under elevated CO2 may underestimate the true soil-respiratory CO2 loss (i.e. overestimate the C sequestered), and (2) that additional C assimilated by plants during the growing season and transferred below-ground will quickly be lost via enhanced heterotrophic respiration outside the main growing season.
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Keywords: |
temperature |
soil |
aCO2 |
climate change |
elevated CO2 |
FACE |
soil respiration |
grassland |
Haworth, M.; Moser, G.; Raschi, A.; Kammann, C.; Grünhage, L. & Müller, C. (2016): Carbon dioxide fertilisation and supressed respiration induce enhanced spring biomass production in a mixed species temperate meadow exposed to moderate carbon dioxide enrichment. Functional Plant Biology FP15232, A-N
DOI: http://dx.doi.org/10.1071/FP15232.
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DOI: 10.1071/FP15232
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Abstract:
Abstract:
The rising concentration of carbon dioxide in the atmosphere ([CO2]) has a direct effect on terrestrial vegetation
through shifts in the rates of photosynthetic carbon uptake and transpirational water-loss. Free Air CO2 Enrichment (FACE)
experiments aim to predict the likely responses of plants to increased [CO2] under normal climatic conditions. The Giessen
FACE system operates a lower [CO2] enrichment regime (480 mmol mol–1) than standard FACE (550–600 mmol mol–1),
permitting the analysis of a mixed species temperate meadow under a [CO2] level equivalent to that predicted in 25–30 years.
We analysed the physiological and morphological responses of six species to investigate the effect of moderate [CO2] on
spring biomass production. Carbon dioxide enrichment stimulated leaf photosynthetic rates and supressed respiration,
contributing to enhanced net assimilation and a 23% increase in biomass. The capacity for photosynthetic assimilation was
unaffected by [CO2] enrichment, with no downregulation of rates of carboxylation of Rubisco or regeneration of ribulose-
1,5-bisphosphate. Foliar N content was also not influenced by increased [CO2]. Enhanced [CO2] reduced stomatal size, but
stomatal density and leaf area index remained constant, suggesting that the effect on gas exchange was minimal.
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Keywords: |
ring |
biomass |