| 1. |
- Eckert, Diana, et al.
(författare)
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CO2 refixation is higher in leaves of woody species with high mesophyll and stomatal resistances to CO2 diffusion
- 2021
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Ingår i: Tree Physiology. - : Oxford University Press. - 0829-318X .- 1758-4469. ; 41:8, s. 1450-1461
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Tidskriftsartikel (refereegranskat)abstract
- The percentage of respiratory and photorespiratory CO2 refixed in leaves (P-r) represents part of the CO2 used in photosynthesis. The importance of P-r as well as differences between species and functional types are still not well investigated. In this study, we examine how P-r differs between six temperate and boreal woody species: Betula pendula, Quercus robur, Larix decidua, Pinus sylvestris, Picea abies and Vaccinium vitis-idaea. The study covers early and late successional species, deciduous broadleaves, deciduous conifers, evergreen conifers and evergreen broadleaves. We investigated whether some species or functional types had higher refixation percentages than others, whether leaf traits could predict higher P-r and whether these traits and their impact on P-r changed during growing seasons. Photosynthesis CO2 response (A/C-i)-curves, measured early, mid and late season, were used to estimate and compare P-r, mesophyll resistance (r(m)) and stomatal resistance (r(s)) to CO2 diffusion. Additionally, light images and transmission electron microscope images were used to approximate the fraction of intercellular airspace and cell wall thickness. We found that evergreens, especially late successional species, refixed a significantly higher amount of CO2 than the other species throughout the entire growing season. In addition, r(m), r(s) and leaf mass per area, traits that typically are higher in evergreen species, were also significantly, positively correlated with P-r. We suggest that this is due to higher r(m) decreasing diffusion of (photo) respiratory CO2 out of the leaf. Cell wall thickness had a positive effect on P-r and r(m), while the fraction of intercellular airspace had no effect. Both were significantly different between evergreen conifers and other types. Our findings suggest that species with a higher r(m) use a greater fraction of mitochondria-derived CO2, especially when stomatal conductance is low. This should be taken into account when modeling the overall CO2 fertilization effect for terrestrial ecosystems dominated by high r(m) species.
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| 2. |
- Eckert, Diana, et al.
(författare)
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The maximum carboxylation rate of Rubisco affects CO2 refixation in temperate broadleaved forest trees
- 2020
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Ingår i: Plant physiology and biochemistry (Paris). - : Elsevier. - 0981-9428 .- 1873-2690. ; 155, s. 330-337
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Tidskriftsartikel (refereegranskat)abstract
- Mesophyll resistance to CO2 diffusion (rm) and the maximum carboxylation rate of Rubisco (Vcmax) affect photosynthetic rates, and can potentially also influence the percentage of respiratory and photorespiratory CO2 being refixated (Pr) by mesophyll cells. Here we investigated how various leaf anatomical traits (e.g. leaf mass per area [LMA] and leaf dry matter content [LDMC]) influenced rm in leaves of mature forest trees. We further explored how rm and Vcmax in turn affected Pr, and if these traits varied among species and leaves along a light gradient. Photosynthetic CO2 response of leaves grown in high-, medium-, and low-light environments was measured, from Pinus sylvestris [Scots pine], Picea abies [Norway spruce], Quercus robur [English oak], and Betula pendula [Silver birch] in southern Sweden. A modified version of the Farquhar-von Caemmerer-Berry model was fitted to the leaf gas exchange data to estimate Vcmax, rm and Pr. We found that of all leaf traits measured, only LMA for Q. robur was significantly higher in leaves from high-light environments. When comparing species, both rm and LMA were significantly higher in the conifers, and rm had a negative correlation with Vcmax. We found that Pr was similar between different species and functional groups, with an average of 73.2% (and SD of ±10.4) across all species. There was a strong, positive correlation between Pr and Vcmax in broadleaves, and we hypothesise that this effect might derive from a higher CO2 drawdown near Rubisco in leaves with high Vcmax.
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| 3. |
- Niu, Shuli, et al.
(författare)
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Thermal optimality of net ecosystem exchange of carbon dioxide and underlying mechanisms.
- 2012
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Ingår i: New Phytologist. - : Wiley. - 1469-8137 .- 0028-646X. ; 194:3, s. 775-783
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Tidskriftsartikel (refereegranskat)abstract
- • It is well established that individual organisms can acclimate and adapt to temperature to optimize their functioning. However, thermal optimization of ecosystems, as an assemblage of organisms, has not been examined at broad spatial and temporal scales. • Here, we compiled data from 169 globally distributed sites of eddy covariance and quantified the temperature response functions of net ecosystem exchange (NEE), an ecosystem-level property, to determine whether NEE shows thermal optimality and to explore the underlying mechanisms. • We found that the temperature response of NEE followed a peak curve, with the optimum temperature (corresponding to the maximum magnitude of NEE) being positively correlated with annual mean temperature over years and across sites. Shifts of the optimum temperature of NEE were mostly a result of temperature acclimation of gross primary productivity (upward shift of optimum temperature) rather than changes in the temperature sensitivity of ecosystem respiration. • Ecosystem-level thermal optimality is a newly revealed ecosystem property, presumably reflecting associated evolutionary adaptation of organisms within ecosystems, and has the potential to significantly regulate ecosystem-climate change feedbacks. The thermal optimality of NEE has implications for understanding fundamental properties of ecosystems in changing environments and benchmarking global models.
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| 4. |
- Norby, Richard J., et al.
(författare)
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Informing models through empirical relationships between foliar phosphorus, nitrogen and photosynthesis across diverse woody species in tropical forests of Panama
- 2017
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Ingår i: New Phytologist. - : Wiley-Blackwell. - 0028-646X .- 1469-8137. ; 215:4, s. 1425-1437
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Tidskriftsartikel (refereegranskat)abstract
- Our objective was to analyze and summarize data describing photosynthetic parameters and foliar nutrient concentrations from tropical forests in Panama to inform model representation of phosphorus (P) limitation of tropical forest productivity.Gas exchange and nutrient content data were collected from 144 observations of upper canopy leaves from at least 65 species at two forest sites in Panama, differing in species composition, rainfall and soil fertility. Photosynthetic parameters were derived from analysis of assimilation rate vs internal CO2 concentration curves (A/Ci), and relationships with foliar nitrogen (N) and P content were developed.The relationships between area-based photosynthetic parameters and nutrients were of similar strength for N and P and robust across diverse species and site conditions. The strongest relationship expressed maximum electron transport rate (Jmax) as a multivariate function of both N and P, and this relationship was improved with the inclusion of independent data on wood density.Models that estimate photosynthesis from foliar N would be improved only modestly by including additional data on foliar P, but doing so may increase the capability of models to predict future conditions in P-limited tropical forests, especially when combined with data on edaphic conditions and other environmental drivers.
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| 5. |
- Sun, Ying, et al.
(författare)
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Asymmetrical effects of mesophyll conductance on fundamental photosynthetic parameters and their relationships estimated from leaf gas exchange measurements
- 2014
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Ingår i: Plant, Cell and Environment. - : John Wiley & Sons. - 0140-7791 .- 1365-3040. ; 37:4, s. 978-994
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Tidskriftsartikel (refereegranskat)abstract
- Worldwide measurements of nearly 130 C3 species covering all major plant functional types are analysed in conjunction with model simulations to determine the effects of mesophyll conductance (gm) on photosynthetic parameters and their relationships estimated fromA/Ci curves. We find that an assumption of infinite gm results in up to 75% underestimation for maximum carboxylation rate Vcmax, 60% for maximum electron transport rate Jmax, and 40% for triose phosphate utilization rate Tu. Vcmax is most sensitive, Jmax is less sensitive, and Tuhas the least sensitivity to the variation of gm. Because of this asymmetrical effect of gm, the ratios of Jmax to Vcmax, Tu to Vcmax and Tu toJmax are all overestimated. An infinite gm assumption also limits the freedom of variation of estimated parameters and artificially constrains parameter relationships to stronger shapes. These findings suggest the importance of quantifying gm for understanding in situphotosynthetic machinery functioning. We show that a nonzero resistance to CO2 movement in chloroplasts has small effects on estimated parameters. A non-linear function with gm as input is developed to convert the parameters estimated under an assumption of infinite gm to proper values. This function will facilitate gm representation in global carbon cycle models.
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| 6. |
- Walker, Anthony P., et al.
(författare)
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Integrating the evidence for a terrestrial carbon sink caused by increasing atmospheric CO2
- 2021
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Ingår i: New Phytologist. - : John Wiley & Sons. - 0028-646X .- 1469-8137. ; 229:5, s. 2413-2445
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Tidskriftsartikel (refereegranskat)abstract
- Atmospheric carbon dioxide concentration ([CO2]) is increasing, which increases leaf‐scale photosynthesis and intrinsic water‐use efficiency. These direct responses have the potential to increase plant growth, vegetation biomass, and soil organic matter; transferring carbon from the atmosphere into terrestrial ecosystems (a carbon sink). A substantial global terrestrial carbon sink would slow the rate of [CO2] increase and thus climate change. However, ecosystem CO2 responses are complex or confounded by concurrent changes in multiple agents of global change and evidence for a [CO2]‐driven terrestrial carbon sink can appear contradictory. Here we synthesize theory and broad, multidisciplinary evidence for the effects of increasing [CO2] (iCO2) on the global terrestrial carbon sink. Evidence suggests a substantial increase in global photosynthesis since pre‐industrial times. Established theory, supported by experiments, indicates that iCO2 is likely responsible for about half of the increase. Global carbon budgeting, atmospheric data, and forest inventories indicate a historical carbon sink, and these apparent iCO2 responses are high in comparison to experiments and predictions from theory. Plant mortality and soil carbon iCO2 responses are highly uncertain. In conclusion, a range of evidence supports a positive terrestrial carbon sink in response to iCO2, albeit with uncertain magnitude and strong suggestion of a role for additional agents of global change.
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| 7. |
- Yi, Chuixiang, et al.
(författare)
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Climate control of terrestrial carbon exchange across biomes and continents
- 2010
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 5:3
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Tidskriftsartikel (refereegranskat)abstract
- Understanding the relationships between climate and carbon exchange by terrestrial ecosystems is critical to predict future levels of atmospheric carbon dioxide because of the potential accelerating effects of positive climate-carbon cycle feedbacks. However, directly observed relationships between climate and terrestrial CO2 exchange with the atmosphere across biomes and continents are lacking. Here we present data describing the relationships between net ecosystem exchange of carbon (NEE) and climate factors as measured using the eddy covariance method at 125 unique sites in various ecosystems over six continents with a total of 559 site-years. We find that NEE observed at eddy covariance sites is (1) a strong function of mean annual temperature at mid-and high-latitudes, (2) a strong function of dryness at mid-and low-latitudes, and (3) a function of both temperature and dryness around the mid-latitudinal belt (45 degrees N). The sensitivity of NEE to mean annual temperature breaks down at similar to 16 degrees C (a threshold value of mean annual temperature), above which no further increase of CO2 uptake with temperature was observed and dryness influence overrules temperature influence.
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