1
|
Haworth M, Marino G, Loreto F, Centritto M. The evolution of diffusive and biochemical capacities for photosynthesis was predominantly shaped by [CO 2] with a smaller contribution from [O 2]. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 840:156606. [PMID: 35691351 DOI: 10.1016/j.scitotenv.2022.156606] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/08/2022] [Revised: 05/18/2022] [Accepted: 06/06/2022] [Indexed: 06/15/2023]
Abstract
The atmospheric concentration of carbon dioxide ([CO2]) and oxygen ([O2]) directly influence rates of photosynthesis (PN) and photorespiration (RPR) through the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase (RubisCO). Levels of [CO2] and [O2] have varied over Earth history affecting rates of both CO2 uptake and loss, alongside associated transpirative water-loss. The availability of CO2 has likely acted as a stronger selective pressure than [O2] due to the greater specificity of RubisCO for CO2. The role of [O2], and the interaction of [O2] and [CO2], in plant evolutionary history is less understood. We exposed twelve phylogenetically diverse species to combinations of sub-ambient, ambient and super-ambient [O2] and [CO2] to examine the biochemical and diffusive components of PN and the possible role of [O2] as a selective pressure. Photosynthesis, photosynthetic capacity and stomatal, mesophyll and total conductance to CO2 were higher in the derived eudicot and monocot angiosperms than the more basal ferns, gymnosperms and basal angiosperms which originated in atmospheres characterised by higher CO2:O2 ratios. The ratio of RPR:PN was lower in the monocots, consistent with greater carboxylation capacity and higher stomatal and mesophyll conductance making easier CO2 delivery to chloroplasts. The effect of [O2] and [CO2] on PN/RPR was less evident in more derived species with a higher conductance to CO2. The effect of [O2] was less apparent at high [CO2], suggesting that atmospheric [O2] may only have exerted a strong selective pressure on plant photosynthetic processes during periods characterised by low atmospheric CO2:O2 ratios. Current rising [CO2] will predominantly enhance PN rates in species with low diffusive conductance to CO2.
Collapse
Affiliation(s)
- Matthew Haworth
- National Research Council of Italy - Institute of Sustainable Plant Protection (CNR - IPSP), Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy.
| | - Giovanni Marino
- National Research Council of Italy - Institute of Sustainable Plant Protection (CNR - IPSP), Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy
| | - Francesco Loreto
- Department of Biology, University of Naples Federico II, Naples, Italy
| | - Mauro Centritto
- National Research Council of Italy - Institute of Sustainable Plant Protection (CNR - IPSP), Via Madonna del Piano 10, 50019 Sesto Fiorentino (FI), Italy; ENI-CNR Water Research Centre "Hypatia of Alexandria", Research Centre Metapontum Agrobios, Metaponto, Italy
| |
Collapse
|
2
|
Poorter H, Knopf O, Wright IJ, Temme AA, Hogewoning SW, Graf A, Cernusak LA, Pons TL. A meta-analysis of responses of C 3 plants to atmospheric CO 2 : dose-response curves for 85 traits ranging from the molecular to the whole-plant level. THE NEW PHYTOLOGIST 2022; 233:1560-1596. [PMID: 34657301 DOI: 10.1111/nph.17802] [Citation(s) in RCA: 34] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/27/2021] [Accepted: 09/03/2021] [Indexed: 05/20/2023]
Abstract
Generalised dose-response curves are essential to understand how plants acclimate to atmospheric CO2 . We carried out a meta-analysis of 630 experiments in which C3 plants were experimentally grown at different [CO2 ] under relatively benign conditions, and derived dose-response curves for 85 phenotypic traits. These curves were characterised by form, plasticity, consistency and reliability. Considered over a range of 200-1200 µmol mol-1 CO2 , some traits more than doubled (e.g. area-based photosynthesis; intrinsic water-use efficiency), whereas others more than halved (area-based transpiration). At current atmospheric [CO2 ], 64% of the total stimulation in biomass over the 200-1200 µmol mol-1 range has already been realised. We also mapped the trait responses of plants to [CO2 ] against those we have quantified before for light intensity. For most traits, CO2 and light responses were of similar direction. However, some traits (such as reproductive effort) only responded to light, others (such as plant height) only to [CO2 ], and some traits (such as area-based transpiration) responded in opposite directions. This synthesis provides a comprehensive picture of plant responses to [CO2 ] at different integration levels and offers the quantitative dose-response curves that can be used to improve global change simulation models.
Collapse
Affiliation(s)
- Hendrik Poorter
- Plant Sciences (IBG-2), Forschungszentrum Jülich GmbH, D-52425, Jülich, Germany
- Department of Biological Sciences, Macquarie University, North Ryde, NSW, 2109, Australia
| | - Oliver Knopf
- Plant Sciences (IBG-2), Forschungszentrum Jülich GmbH, D-52425, Jülich, Germany
| | - Ian J Wright
- Department of Biological Sciences, Macquarie University, North Ryde, NSW, 2109, Australia
- Hawkesbury Institute for the Environment, Western Sydney University, Richmond, NSW, 2753, Australia
| | - Andries A Temme
- Albrecht Daniel Thaer-Institute of Agricultural and Horticultural Sciences, Humboldt Universität zu Berlin, 14195, Berlin, Germany
| | | | - Alexander Graf
- Agrosphere (IBG-3), Forschungszentrum Jülich GmbH, D-52425, Jülich, Germany
| | - Lucas A Cernusak
- College of Science and Engineering, James Cook University, Cairns, Qld, 4879, Australia
| | - Thijs L Pons
- Plant Ecophysiology, Institute of Environmental Biology, Utrecht University, 3512 PN, Utrecht, the Netherlands
| |
Collapse
|
3
|
Waigwa AN, Mwangi BN, Gituru RW, Omengo F, Zhou Y, Wang Q. Altitudinal variation of leaf carbon isotope for
Dendrosenecio keniensis
and
Lobelia gregoriana
in Mount Kenya alpine zone. Biotropica 2021. [DOI: 10.1111/btp.12990] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Affiliation(s)
- Antony Njogu Waigwa
- Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture Wuhan Botanical Garden Chinese Academy of Sciences Wuhan China
- University of Chinese Academy of Sciences Beijing China
- Sino‐Africa Joint Research Center (SAJOREC) Jomo Kenyatta University of Agriculture and Technology Juja Kenya
| | - Brian Njoroge Mwangi
- Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture Wuhan Botanical Garden Chinese Academy of Sciences Wuhan China
- University of Chinese Academy of Sciences Beijing China
| | - Robert Wahiti Gituru
- Sino‐Africa Joint Research Center (SAJOREC) Jomo Kenyatta University of Agriculture and Technology Juja Kenya
| | - Fred Omengo
- Department of Biodiversity Research Kenya Wildlife Service Nairobi Kenya
| | - Yadong Zhou
- Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture Wuhan Botanical Garden Chinese Academy of Sciences Wuhan China
- Center of Conservation Biology Core Botanical Gardens Chinese Academy of Sciences Wuhan China
- Sino‐Africa Joint Research Center (SAJOREC) Chinese Academy of Sciences Wuhan China
| | - Qingfeng Wang
- Key Laboratory of Plant Germplasm Enhancement and Specialty Agriculture Wuhan Botanical Garden Chinese Academy of Sciences Wuhan China
- Center of Conservation Biology Core Botanical Gardens Chinese Academy of Sciences Wuhan China
- Sino‐Africa Joint Research Center (SAJOREC) Chinese Academy of Sciences Wuhan China
| |
Collapse
|
4
|
Tedla B, Dang QL, Inoue S. Longer photoperiods negate the CO 2 stimulation of photosynthesis in Betula papyrifera Marsh: Implications to climate change-induced migration. PHYSIOLOGIA PLANTARUM 2021; 172:106-115. [PMID: 33280131 DOI: 10.1111/ppl.13298] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/25/2020] [Revised: 10/20/2020] [Accepted: 12/01/2020] [Indexed: 06/12/2023]
Abstract
In response to global warming, trees are expected to shift their distribution ranges to higher latitudes. The range shift will expose them to novel environmental conditions, such as new photoperiod regimes. These factors can interact with rising atmospheric CO2 ([CO2 ]) to affect trees' physiology and growth. This study simulated future environmental conditions to investigate photosynthetic responses to changes in photoperiod regimes (seed origin [48°N], 52, 55, and 58°N) and [CO2 ] (ambient 400 vs. elevated 1000 μmol mol-1 ) in white birch (Betula papyrifera Marsh.) seedlings. Our results show that elevated [CO2 ] stimulated leaf photosynthesis (Pn ) at the two lower latitudes (48 and 52°N). However, this stimulation by elevated [CO2 ] was lost in the two higher latitudes (55 and 58°N). Elevated [CO2 ] led to the downregulation of maximum Rubisco activity (Vcmax ) for the two higher latitudes, and maximum electron transport rate (Jmax ) and triose phosphate utilization (TPU) at 58°N, while it enhanced Jmax and TPU for the two lower latitudes. Increased instantaneous water-use efficiency (IWUE) for the two lower latitudes was primarily attributed to the CO2 stimulation of Pn while the higher IWUE under the photoperiod regimes of 55 and 58°N latitudes was explained by reduced water loss. Photoperiod effects varied with [CO2 ]: Pn increased at the photoperiod regimes of 55 and 58°N in ambient [CO2 ] while it tended to decline under these photoperiods in elevated [CO2 ]. Our study suggests that the photosynthesis of white birch will likely respond negatively to northward migration or seed transfer in response to climate change.
Collapse
Affiliation(s)
- Binyam Tedla
- Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Ontario, Canada
- Northern Alberta Institute of Technology, Centre for Boreal Research, Peace River, Alberta, Canada
| | - Qing-Lai Dang
- Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Ontario, Canada
| | - Sahari Inoue
- Faculty of Natural Resources Management, Lakehead University, Thunder Bay, Ontario, Canada
- Northern Alberta Institute of Technology, Centre for Boreal Research, Peace River, Alberta, Canada
| |
Collapse
|
5
|
Yiotis C, McElwain JC. A Novel Hypothesis for the Role of Photosynthetic Physiology in Shaping Macroevolutionary Patterns. PLANT PHYSIOLOGY 2019; 181:1148-1162. [PMID: 31484680 PMCID: PMC6836816 DOI: 10.1104/pp.19.00749] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Accepted: 08/25/2019] [Indexed: 05/08/2023]
Abstract
The fossil record and models of atmospheric concentrations of O2 and CO2 suggest that past shifts in plant ecological dominance often coincided with dramatic changes in Earth's atmospheric composition. This study tested the effects of past changes in atmospheric composition on the photosynthetic physiology of a limited range of early-diverging angiosperms (eight), gymnosperms (three), and ferns (two). We performed physiological measurements on all species and used the results to parameterize simulations of their photosynthetic paleophysiology using three independent modeling approaches. Unique physiological attributes were identified for the three evolutionary groups: angiosperm taxa displayed significantly higher mesophyll conductance (g m), yet their stomatal conductance (g s) was lower than that of ferns. Gymnosperm taxa displayed low g s and g m, but they partially offset their significant diffusional limitations on photosynthesis through their higher maximum Rubisco carboxylation rate. Despite their high total conductance to CO2, fern taxa lacked an optimized control of g s, which was reflected in their low intrinsic water use efficiency. Simulations of the photosynthetic physiology of ferns, angiosperms, and gymnosperms through Earth's history demonstrated that past fluctuations in O2 and CO2 concentrations may have resulted in significant shifts in the relative competitiveness of the three evolutionary groups. Although preliminary because of limited species sampling, these findings hint at a potential mechanistic basis for the observed broad temporal correlation between atmospheric change and shifts in plant evolutionary group-level richness observed in the fossil record and are presented as a framework to be tested with paleophotosynthetic proxies and through increased species sampling.
Collapse
Affiliation(s)
- Charilaos Yiotis
- Botany Department, School of Natural Sciences, Trinity College, Dublin 2, Ireland
| | - Jennifer C McElwain
- Botany Department, School of Natural Sciences, Trinity College, Dublin 2, Ireland
| |
Collapse
|
6
|
Haworth M, Belcher CM, Killi D, Dewhirst RA, Materassi A, Raschi A, Centritto M. Impaired photosynthesis and increased leaf construction costs may induce floral stress during episodes of global warming over macroevolutionary timescales. Sci Rep 2018; 8:6206. [PMID: 29670149 PMCID: PMC6049339 DOI: 10.1038/s41598-018-24459-z] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2017] [Accepted: 03/21/2018] [Indexed: 11/30/2022] Open
Abstract
Global warming events have coincided with turnover of plant species at intervals in Earth history. As mean global temperatures rise, the number, frequency and duration of heat-waves will increase. Ginkgo biloba was grown under controlled climatic conditions at two different day/night temperature regimes (25/20 °C and 35/30 °C) to investigate the impact of heat stress. Photosynthetic CO2-uptake and electron transport were reduced at the higher temperature, while rates of respiration were greater; suggesting that the carbon balance of the leaves was adversely affected. Stomatal conductance and the potential for evaporative cooling of the leaves was reduced at the higher temperature. Furthermore, the capacity of the leaves to dissipate excess energy was also reduced at 35/30 °C, indicating that photo-protective mechanisms were no longer functioning effectively. Leaf economics were adversely affected by heat stress, exhibiting an increase in leaf mass per area and leaf construction costs. This may be consistent with the selective pressures experienced by fossil Ginkgoales during intervals of global warming such as the Triassic - Jurassic boundary or Early Eocene Climatic Optimum. The physiological and morphological responses of the G. biloba leaves were closely interrelated; these relationships may be used to infer the leaf economics and photosynthetic/stress physiology of fossil plants.
Collapse
Affiliation(s)
- Matthew Haworth
- The Italian National Research Council - Tree and Timber Institute (CNR-IVALSA) Via Madonna del Piano 10, Sesto Fiorentino, 50019, Florence, Italy.
| | - Claire M Belcher
- University of Exeter wildFIRE Lab, Hatherly Labs Prince Wales Road Exeter, EX PS, Devon, England
| | - Dilek Killi
- Department of Agrifood Production and Environmental Sciences (DiSPAA), University of Florence Piazzale delle Cascine, 28 50144, Florence, Italy
| | - Rebecca A Dewhirst
- University of Exeter wildFIRE Lab, Hatherly Labs Prince Wales Road Exeter, EX PS, Devon, England
| | - Alessandro Materassi
- The Italian National Research Council - Institute of Biometeorology (CNR-IBIMET) Via Giovanni Caproni, 8 50145, Florence, Italy
| | - Antonio Raschi
- The Italian National Research Council - Institute of Biometeorology (CNR-IBIMET) Via Giovanni Caproni, 8 50145, Florence, Italy
| | - Mauro Centritto
- The Italian National Research Council - Tree and Timber Institute (CNR-IVALSA) Via Madonna del Piano 10, Sesto Fiorentino, 50019, Florence, Italy
| |
Collapse
|
7
|
Lundgren MR, Christin PA, Escobar EG, Ripley BS, Besnard G, Long CM, Hattersley PW, Ellis RP, Leegood RC, Osborne CP. Evolutionary implications of C3 -C4 intermediates in the grass Alloteropsis semialata. PLANT, CELL & ENVIRONMENT 2016; 39:1874-1885. [PMID: 26524631 DOI: 10.1111/pce.12665] [Citation(s) in RCA: 50] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/13/2015] [Revised: 10/21/2015] [Accepted: 10/25/2015] [Indexed: 06/05/2023]
Abstract
C4 photosynthesis is a complex trait resulting from a series of anatomical and biochemical modifications to the ancestral C3 pathway. It is thought to evolve in a stepwise manner, creating intermediates with different combinations of C4 -like components. Determining the adaptive value of these components is key to understanding how C4 photosynthesis can gradually assemble through natural selection. Here, we decompose the photosynthetic phenotypes of numerous individuals of the grass Alloteropsis semialata, the only species known to include both C3 and C4 genotypes. Analyses of δ(13) C, physiology and leaf anatomy demonstrate for the first time the existence of physiological C3 -C4 intermediate individuals in the species. Based on previous phylogenetic analyses, the C3 -C4 individuals are not hybrids between the C3 and C4 genotypes analysed, but instead belong to a distinct genetic lineage, and might have given rise to C4 descendants. C3 A. semialata, present in colder climates, likely represents a reversal from a C3 -C4 intermediate state, indicating that, unlike C4 photosynthesis, evolution of the C3 -C4 phenotype is not irreversible.
Collapse
Affiliation(s)
- Marjorie R Lundgren
- Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
| | - Pascal-Antoine Christin
- Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
| | - Emmanuel Gonzalez Escobar
- Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
| | - Brad S Ripley
- Botany Department, Rhodes University, Grahamstown, 6139, South Africa
| | - Guillaume Besnard
- CNRS, Université de Toulouse, ENFA, UMR5174 EDB (Laboratoire Évolution and Diversité Biologique), 118 Route de Narbonne, Toulouse, 31062, France
| | - Christine M Long
- Department of Primary Industry and Fisheries, Northern Territory Government, Darwin, NT, 0801, Australia
| | - Paul W Hattersley
- School of Chemistry and Biochemistry (honorary research fellow), University of Western Australia, Crawley, WA, 6009, Australia
| | | | - Richard C Leegood
- Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
| | - Colin P Osborne
- Department of Animal and Plant Sciences, University of Sheffield, Western Bank, Sheffield, S10 2TN, UK
| |
Collapse
|
8
|
Pan S, Zhang W, Zhao M, Li Y, Xu S, Wang G. Altitude Patterns of Leaf Carbon Isotope Composition in a Subtropical Monsoon Forest. POLISH JOURNAL OF ECOLOGY 2016. [DOI: 10.3161/15052249pje2016.64.2.003] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
9
|
Pan S, Zhang W, Zhao M, Li Y, Xu S, Wang G. Altitude Patterns of Leaf Carbon Isotope Composition in a Subtropical Monsoon Forest. POLISH JOURNAL OF ECOLOGY 2015. [DOI: 10.3161/15052249pje2015.63.4.004] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
|
10
|
Hagopian WM, Schubert BA, Jahren AH. Large-scale plant growth chamber design for elevated pCO2 and δ13C studies. RAPID COMMUNICATIONS IN MASS SPECTROMETRY : RCM 2015; 29:440-446. [PMID: 26349466 DOI: 10.1002/rcm.7121] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/17/2014] [Revised: 12/09/2014] [Accepted: 12/10/2014] [Indexed: 06/05/2023]
Abstract
RATIONALE Throughout at least the next century, CO(2) fertilization and environmental stresses (e.g. nutrient, moisture, insect herbivory) are predicted to affect yields of economically important crop species. Stable isotopes of carbon are used to study plant stresses, which affect yields, but a growth chamber design that can be used to isolate the effects of environmental stresses on crop-sized species through precise maintenance of pCO(2) levels and the δ(13)C values of atmospheric CO(2) (δ(13) C(CO2)) is lacking. METHODS We designed and built low-cost plant growth chambers for growing staple crop species under precise pCO(2) and δ(13) C(CO2) conditions. Over the course of 14 hours, we assessed for pCO(2) stability at two targeted levels (ambient, ~400 ppm; and 2×, ~800 ppm) and measured the δ(13) C(CO2) value within the two chambers using a stable isotope ratio mass spectrometer. We also compared the temperature and relative humidity conditions within the two growth chambers, and in the ambient, outside air. RESULTS Across our experimental period, we achieved δ(13) C(CO2) stability (ambient: -8.05 ± 0.17‰; elevated: -12.99 ± 0.29‰) that showed nearly half the variability of any previously reported values for other chamber designs. The stability of the pCO(2) conditions (ambient: 406 ± 3 ppm; elevated: 793 ± 54 ppm) was comparable with that in previous studies, but our design provided ~8 times more growing space than previous chamber designs. We also measured nearly identical temperature and relative humidity conditions for the two chambers throughout the experiment. CONCLUSIONS Our growth chamber design marks a significant improvement in our ability to test for plant stress across a range of future pCO(2) scenarios. Through significant improvement in δ(13) C(CO2) stability and increased chamber size, small changes in carbon isotope fractionation can be used to assess stress in crop species under specific environmental (temperature, relative humidity, pCO(2)) conditions.
Collapse
Affiliation(s)
- William M Hagopian
- Department of Geology and Geophysics, University of Hawaii, Honolulu, HI, 96822, USA
| | - Brian A Schubert
- School of Geosciences, University of Louisiana at Lafayette, Lafayette, LA, 70504, USA
| | - A Hope Jahren
- Department of Geology and Geophysics, University of Hawaii, Honolulu, HI, 96822, USA
| |
Collapse
|
11
|
Ogaya R, Llorens L, Peñuelas J. Density and length of stomatal and epidermal cells in "living fossil" trees grown under elevated CO2 and a polar light regime. ACTA OECOLOGICA-INTERNATIONAL JOURNAL OF ECOLOGY 2011. [DOI: 10.1016/j.actao.2011.04.010] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
|
12
|
Wilson JP, Fischer WW. Hydraulics of Asteroxylon mackei, an early Devonian vascular plant, and the early evolution of water transport tissue in terrestrial plants. GEOBIOLOGY 2011; 9:121-130. [PMID: 21244621 DOI: 10.1111/j.1472-4669.2010.00269.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/30/2023]
Abstract
The core of plant physiology is a set of functional solutions to a tradeoff between CO(2) acquisition and water loss. To provide an important evolutionary perspective on how the earliest land plants met this tradeoff, we constructed a mathematical model (constrained geometrically with measurements of fossils) of the hydraulic resistance of Asteroxylon, an Early Devonian plant. The model results illuminate the water transport physiology of one of the earliest vascular plants. Results show that Asteroxylon's vascular system contains cells with low hydraulic resistances; these resistances are low because cells were covered by scalariform pits, elliptical structures that permit individual cells to have large areas for water to pass from one cell to another. Asteroxylon could move a large amount of water quickly given its large pit areas; however, this would have left these plants particularly vulnerable to damage from excessive evapotranspiration. These results highlight a repeated pattern in plant evolution, wherein the evolution of highly conductive vascular tissue precedes the appearance of adaptations to increase water transport safety. Quantitative insight into the vascular transport of Asteroxylon also allows us to reflect on the quality of CO(2) proxy estimates based on early land plant fossils. Because Asteroxylon's vascular tissue lacked any safety features to prevent permanent damage, it probably used stomatal abundance and behavior to prevent desiccation. If correct, low stomatal frequencies in Asteroxylon reflect the need to limit evapotranspiration, rather than adaptation to high CO(2) concentrations in the atmosphere. More broadly, methods to reveal and understand water transport in extinct plants have a clear use in testing and bolstering fossil plant-based paleoclimate proxies.
Collapse
Affiliation(s)
- J P Wilson
- Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA, USA.
| | | |
Collapse
|