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  • 1
    Electronic Resource
    Electronic Resource
    Sucrose-phosphate synthase responds differently to source-sink relations and to photosynthetic rates: Lolium perenne L. growing at elevated pCO2 in the field (2000)
    Oxford, UK : Blackwell Science Ltd
    Plant, cell & environment 23 (2000), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Lolium perenne, a main component species in managed grassland, is well adapted to defoliation, fertilization, and regrowth cycles; and hence, to changes in the assimilatory carbon source-sink ratio. In the Swiss Free Air CO2 Enrichment experiment the source-sink ratio is (i) increased by elevated partial pressure of CO2 (pCO2), (ii) decreased by enhanced carbon use under high N fertilization, and (iii) gradually increased during regrowth after defoliation. Since sucrose synthesis plays a central role in leaf carbohydrate metabolism in this fructan-accumulating species, we investigated how sucrose-phosphate synthase (SPS) responds to the differing assimilatory carbon fluxes and source-sink ratios in the field. Assimilatory carbon flux, as estimated by leaf gas exchange, strongly depended on pCO2. Surprisingly, the SPS content per leaf area did not increase with pCO2, but increased with N fertilization. During later regrowth, when a dense canopy had formed, the SPS content decreased; in particular, SPS was decreased at high N under elevated pCO2. Further, the higher assimilatory carbon flux through SPS at elevated pCO2 was accompanied by a higher activation state of SPS. The SPS content correlated very strongly with the ratio of free sucrose to free amino acid in leaves, which represents the carbon source-sink ratio. Hence, SPS content in L. perenne appears to be regulated by the current, strongly nitrogen-dependent, source-sink relation.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.2000.00583.x
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  • 2
    Electronic Resource
    Electronic Resource
    Source-sink relations in Lolium perenne L. as reflected by carbohydrate concentrations in leaves and pseudo-stems during regrowth in a free air carbon dioxide enrichment (FACE) experiment (1997)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 20 (1997), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: The effect of an elevated partial pressure of CO2 (pCO2) on carbohydrate concentrations in source leaves and pseudo-stems (stubble) of Lolium perenne L. (perennial ryegrass) during regrowth was studied in a regularly defoliated grass sward in the field. The free air carbon dioxide enrichment (FACE) technology enabled natural environmental conditions to be provided. Two levels of nitrogen (N) supply were used to modulate potential plant growth. Carbohydrate concentrations in source leaves were increased at elevated pCO2, particularly at low N supply. Elevated leaf carbohydrate concentrations were related to an increased structural carbon (C) to N ratio and thus reflected an increased C availability together with a N-dependent sink limitation. Immediately after defoliation, apparent assimilate export rates (differences in the carbohydrate concentrations of young source leaves measured in the evening and on the following morning) showed a greater increase at elevated pCO2 than at ambient pCO2; however, replenishment of carbohydrate reserves was not accelerated. Distinct, treatment-dependent carbohydrate concentrations in pseudo-stems suggested an increasing degree of C-sink limitation from the treatment at ambient pCO2 with high N supply to that at elevated pCO2 with low N supply. During two growing seasons, no evidence of a substantial change in the response of the carbohydrate source in L. perenne to elevated pCO2 was found. Our results support the view that the response of L. perenne to elevated pCO2 is restricted by a C-sink limitation, which is particularly severe at low N supply.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1997.d01-131.x
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  • 3
    Electronic Resource
    Electronic Resource
    Photosynthetic acclimation to elevated CO2 is modified by source:sink balance in three component species of chalk grassland swards grown in a free air carbon dioxide enrichment (FACE) experiment (1998)
    Oxford, UK : Blackwell Publishing Ltd
    Plant, cell & environment 21 (1998), S. 0 
    Details
    ISSN: 1365-3040
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology
    Notes: Artificial chalk grassland swards were exposed to either ambient air or air enriched to 600 μmol mol–1 CO2, using free-air CO2 enrichment technology, and subjected to an 8 week simulated grazing regime. After 14 months of treatment, ribulose-1,5-bisphosphate carboxylase (Rubisco) activity (Vc,max) and electron transport mediated ribulose-1,5-bisphosphate (RuBP) regeneration capacity (Jmax), estimated from leaf gas exchange, were significantly lower in fully expanded leaves of Anthyllis vulneraria L. (a legume) and Sanguisorba minor Scop. grown in elevated CO2. After a change in source:sink balance brought about by defoliation, photosynthetic capacity was fully restored in A. vulneraria and S. minor, but acclimation continued in the grass Bromopsis erecta (Hudson) Fourr. Changes in net photosynthesis (Pn) with growth at elevated CO2 ranged from a 1·6% reduction in precut leaves of A. vulneraria to a 47·1% stimulation in postcut leaves of S. minor. Stomatal acclimation was observed in leaves of A. vulneraria (reduced stomatal density) and B. erecta (reduced stomatal conductance). The results are discussed in terms of whole-plant resource-use optimization and chalk grassland community competitive interactions at elevated CO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1046/j.1365-3040.1998.00265.x
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  • 4
    Electronic Resource
    Electronic Resource
    Does nitrogen nutrition restrict the CO2 response of fertile grassland lacking legumes? (1997)
    Springer
    Oecologia 112 (1997), S. 17-25 
    Details
    ISSN: 1432-1939
    Keywords: Key words Nitrogen nutrition ; Elevated partial pressure of carbon dioxide ; Lolium perenne ; Trifolium repens ; Transfer of symbiotically fixed nitrogen
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology
    Notes: Abstract The extent of the response of plant growth to atmospheric CO2 enrichment depends on the availability of resources other than CO2. An important growth-limiting resource under field conditions is nitrogen (N). N may, therefore, influence the CO2 response of plants. The effect of elevated CO2 (60 Pa) partial pressure (pCO2) on the N nutrition of field-grown Lolium perenne swards, cultivated alone or in association with Trifolium repens, was investigated using free air carbon dioxide enrichment (FACE) technology over 3 years. The established grassland ecosystems were treated with two N fertilization levels and were defoliated at two frequencies. Under elevated pCO2, the above-ground plant material of the L. perenne monoculture showed a consistent and significant decline in N concentration which, in general, led to a lower total annual N yield. Despite the decline in the critical N concentration (minimum N concentration required for non-N-limited biomass production) under elevated pCO2, the index of N nutrition (ratio of actual N concentration and critical N concentration) was lower under elevated pCO2 than under ambient pCO2 in frequently defoliated L. perenne monocultures. Thus, we suggest that reduced N yield under elevated pCO2 was evoked indirectly by a reduction of plant-available N. For L. perenne grown in association with T. repens and exposed to elevated pCO2, there was an increase in the contribution of symbiotically fixed N to the total N yield of the grass. This can be explained by an increased apparent transfer of N from the associated N2-fixing legume species to the non-fixing grass. The total annual N yield of the mixed grass/legume swards increased under elevated pCO2. All the additional N yielded was due to symbiotically fixed N. Through the presence of an N2-fixing plant species more symbiotically fixed N was introduced into the system and consequently helped to overcome N limitation under elevated pCO2.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/s004420050278
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