Nitrogen inputs and losses in response to chronic CO&lt;sub&gt;2&lt;/sub&gt; exposure in  a sub-tropical oak woodland

Abstract. Rising atmospheric CO2 concentrations could alter the nitrogen (N) content of ecosystems by changing N inputs and N losses, but responses vary in field experiments, possibly because multiple mechanisms are at play. We measured N fixation and N losses in a subtropical oak woodland exposed to 11 yr of elevated atmospheric CO2 concentrations. We also explored the role of herbivory, carbon limitation, and competition for light and nutrients in shaping response of N fixation to elevated CO2. Elevated CO2 did not significantly alter gaseous N losses, but lower recovery and deeper distribution in the soil of a long-term 15N tracer indicated that elevated CO2 increased leaching losses. Elevated CO2 had no effect on asymbiotic N fixation, and had a transient effect on symbiotic N fixation by the dominant legume. Elevated CO2 tended to reduce soil and plant concentrations of iron, molybdenum, phosphorus, and vanadium, nutrients essential for N fixation. Competition for nutrients and herbivory likely contributed to the declining response N fixation to elevated CO2. These results indicate that positive responses of N fixation to elevated CO2 may be transient, and that chronic exposure to elevated CO2 can increase N leaching. Models that assume increased fixation or reduced N losses with elevated CO2 may overestimate future N accumulation in the biosphere.

Download Full-text

Nitrogen inputs and losses in response to chronic CO2 exposure in a subtropical oak woodland

Biogeosciences ◽

10.5194/bg-11-3323-2014 ◽

2014 ◽

Vol 11 (12) ◽

pp. 3323-3337 ◽

Cited By ~ 8

Author(s):

B. A. Hungate ◽

B. D. Duval ◽

P. Dijkstra ◽

D. W. Johnson ◽

M. E. Ketterer ◽

...

Keyword(s):

Elevated Co2 ◽

Atmospheric Co2 ◽

15N Tracer ◽

Carbon Limitation ◽

N Fixation ◽

Oak Woodland ◽

N Losses ◽

Co2 Concentrations ◽

Nitrogen Inputs ◽

Atmospheric Co2 Concentrations

Abstract. Rising atmospheric CO2 concentrations may alter the nitrogen (N) content of ecosystems by changing N inputs and N losses, but responses vary in field experiments, possibly because multiple mechanisms are at play. We measured N fixation and N losses in a subtropical oak woodland exposed to 11 years of elevated atmospheric CO2 concentrations. We also explored the role of herbivory, carbon limitation, and competition for light or nutrients in shaping the response of N fixation to elevated CO2. Elevated CO2 did not significantly alter gaseous N losses, but lower recovery and deeper distribution in the soil of a long-term 15N tracer indicated that elevated CO2 increased leaching losses. Elevated CO2 had no effect on nonsymbiotic N fixation, and had a transient effect on symbiotic N fixation by the dominant legume. Elevated CO2 tended to reduce soil and plant concentrations of iron, molybdenum, phosphorus, and vanadium, nutrients essential for N fixation. Competition for nutrients and herbivory likely contributed to the declining response of N fixation to elevated CO2. These results indicate that positive responses of N fixation to elevated CO2 may be transient and that chronic exposure to elevated CO2 can increase N leaching. Models that assume increased fixation or reduced N losses with elevated CO2 may overestimate future N accumulation in the biosphere.

Download Full-text

Parallel between the isotopic composition of coccolith calcite and carbon levels across Termination II: Developing a new paleo-CO2 probe

10.5194/cp-2021-76 ◽

2021 ◽

Author(s):

Camille Godbillot ◽

Fabrice Minoletti ◽

Franck Bassinot ◽

Michaël Hermoso

Keyword(s):

Transfer Function ◽

Isotopic Composition ◽

Ice Core ◽

Cellular Growth ◽

Atmospheric Co2 ◽

Small Cells ◽

Carbon Limitation ◽

Co2 Concentrations ◽

Atmospheric Co2 Concentrations ◽

Ambient Co2

Abstract. Beyond the pCO2 records provided by ice core measurements, the quantification of atmospheric CO2 concentrations and changes thereof relies on proxy data, the development of which represents a foremost challenge in paleoceanography. In the paleoceanographic toolbox, the coccolithophores occupy a notable place, as the magnitude of the carbon isotopic fractionation between ambient CO2 and a type of organic compounds that these photosynthetic microalgae synthesize (the alkenones) represents a relatively robust proxy to reconstruct past atmospheric CO2 concentrations during the Cenozoic. The isotopic composition of coeval calcite biominerals found in the sediments and also produced by the coccolithophores (the coccoliths) have been found to record an ambient CO2 signal through culture and sediment analyses. These studies have, however, not yet formalized a transfer function that quantitatively ties the isotopic composition of coccolith calcite to the concentrations of aqueous CO2, and, ultimately, to atmospheric CO2 levels. Here, we make use of a micro-separation protocol to compare the isotopic response of two size-restricted coccolith assemblages from the North Atlantic to changes in surface ocean CO2 during Termination II (ca. 130–140 ka). Performing paired measurements of the isotopic composition (δ13C and δ18O) of relatively large and small coccoliths provides an isotopic offset that can be designated as a “differential vital effect”. We find that the evolution of this offset follows that of aqueous CO2 concentrations computed from the ice core CO2 curve and an independent temperature signal. We interpret this biogeochemical feature to be the result of converging carbon fixation strategies between large and small cells as the degree of carbon limitation for cellular growth decreases across the deglaciation. We are therefore able to determine a transfer function between the coccolith differential vital effects and aqueous CO2 in the range of Quaternary CO2 concentrations. We here consolidate a new coccolith ∆δ13C proxy that overtakes the strong assumptions that have to be made pertaining to the chemistry of the carbonate system in seawater, as required in CO2 proxy methods such as the boron isotope and alkenone proxies.

Download Full-text

Elevated atmospheric CO2 concentrations increase wheat root phosphatase activity when growth is limited by phosphorus

Functional Plant Biology ◽

10.1071/pp97045 ◽

1998 ◽

Vol 25 (1) ◽

pp. 87 ◽

Cited By ~ 27

Author(s):

Damian J. Barrett ◽

Alan E. Richardson ◽

Roger M. Gifford

Keyword(s):

Phosphatase Activity ◽

Elevated Co2 ◽

Atmospheric Co2 ◽

Organic P ◽

Wheat Seedlings ◽

P Deficiency ◽

Co2 Concentrations ◽

Wide Range ◽

Atmospheric Co2 Concentrations ◽

Ambient Co2

Wheat seedlings were grown in solution culture under adequate and limited phosphorus treatments at current ambient and elevated (approximately 2× ambient) CO2 concentrations. Acid phosphomonoesterase (‘phosphatase’) activity of root segments was measured using p-nitrophenyl phosphate as substrate. When plant growth was P-limited, elevated CO2 concentrations increased phosphatase activity more than at ambient CO2. This result (1) was evident when expressed on a unit root dry weight or root length basis, indicating that increased root enzyme activity was unlikely to be associated with CO2-induced changes in root morphology; (2) occurred when plants were grown aseptically, indicating that the increase in phosphatase activity originated from root cells rather than root- associated microorganisms; (3) was associated with shoot P concentrations below 0.18%; (4) occurred only when wheat roots were grown under P deficiency but not when a transient P deficiency was imposed; and (5) suggest that a previously reported increase in phosphatase activity at elevated CO2 by an Australian native pasture grass (Gifford, Lutze and Barrett 1996; Plant and Soil 187, 369–387) was also a root mediated response. The observed increase in phosphatase activity by plant roots at elevated CO2, if confirmed for a wide range of field pasture and crop species, is one factor which may increase mineralisation of soil organic P as the anthropogenic increase of atmospheric CO2 concentrations continues. But, whether a concomitant increase in plant uptake of P occurs will depend on the relative influence of root and microbial phosphatases, and soil geochemistry in determining the rate of mineralisation of soil organic P for any given soil.

Download Full-text

Effects of water availability, nitrogen supply and atmospheric CO2 concentrations on plant nitrogen natural abundance values

Functional Plant Biology ◽

10.1071/fp05188 ◽

2006 ◽

Vol 33 (3) ◽

pp. 219 ◽

Cited By ~ 15

Author(s):

William D. Stock ◽

John R. Evans

Keyword(s):

Stomatal Conductance ◽

Water Supply ◽

Elevated Co2 ◽

Water Availability ◽

Atmospheric Co2 ◽

Co2 Concentrations ◽

Atmospheric Co2 Concentrations ◽

Cape Gooseberry ◽

Foliar Δ15n ◽

Leaf N

The relative effects of soil N, water supply and elevated atmospheric CO2 on foliar δ15N values were examined. Phalaris arundinacea L. (Holdfast) and Physalis peruviana L. (Cape Gooseberry) were grown for 80 d with three water availability treatments, two atmospheric CO2 concentrations and four N supply rates. Elevated CO2 increased total plant biomass and N for each treatment and decreased allocation to roots, leaf N concentrations and stomatal conductance. Leaves had less negative leaf δ13C values under low water supply associated with decreased stomatal conductance and increased leaf N concentration, which decreased the ratio of intercellular to ambient CO2 concentration. The δ15N value of the supplied nitrate (4.15‰) was similar to the value for Phalaris leaves (4.11‰), but Cape Gooseberry leaves were enriched (6.52‰). The effects of elevated CO2 on leaf δ15N values were small, with Phalaris showing no significant change, while Cape Gooseberry showed a significant (P < 0.05) decline of 0.42 ‰. Variation in δ15N values was unrelated to stomatal conductance, transpiration, differential use of N forms or denitrification. Plants with low foliar N concentrations tended to be depleted in 15N. We suggest that changes in N allocation alter foliar δ15N values under different CO2 and water treatments.

Download Full-text

Pest and disease abundance and dynamics in wheat and oilseed rape as affected by elevated atmospheric CO2 concentrations

Functional Plant Biology ◽

10.1071/fp12162 ◽

2013 ◽

Vol 40 (2) ◽

pp. 125 ◽

Cited By ~ 5

Author(s):

Viktoriya Oehme ◽

Petra Högy ◽

Jürgen Franzaring ◽

Claus P. W. Zebitz ◽

Andreas Fangmeier

Keyword(s):

Elevated Co2 ◽

Oilseed Rape ◽

Spring Wheat ◽

Co2 Enrichment ◽

Plant Phenology ◽

Plant Diseases ◽

Atmospheric Co2 ◽

Pest Species ◽

Co2 Concentrations ◽

Atmospheric Co2 Concentrations

Future atmospheric CO2 concentrations are predicted to increase, and directly affect host plant phenology, which, in turn, is assumed to mediate the performance of herbivorous insects indirectly as well as the abundance and epidemiology of plant diseases. In a 4-year field experiment, spring wheat (Triticum aestivum L. cv. Triso) and spring oilseed rape (Brassica napus L. cv. Campino) were grown using a mini- free-air CO2 enrichment (FACE) system, which consisted of a control (CON), an ambient treatment (AMB) and FACE treatments. The CON and AMB treatments did not receive additional CO2, whereas the FACE plots were moderately elevated by 150 μL L–1 CO2. The impact of elevated CO2 was examined with regard to plant phenology, biomass, leaf nitrogen and carbon, abundance of insect pest species and their relative population growth by either direct counts or yellow sticky traps. Occurrence and damage of plants by pathogens on spring wheat and oilseed rape were directly assessed. Disease infestations on plants were not significantly different between ambient and elevated CO2 in any of the years. Plant phenology, aboveground biomass, foliar nitrogen and carbon concentrations were also not significantly affected by CO2 enrichment. In contrast, the abundance of some species of insects was significantly influenced by elevated CO2, showing either an increase or a decrease in infestation intensity.

Download Full-text