Is stimulation of leaf photosynthesis by elevated carbon dioxide concentration maintained in the long term? A test with Lolium perenne grown for 10 years at two nitrogen fertilization levels under Free Air CO₂Enrichment (FACE)

Abstract

Photosynthesis is commonly stimulated in grasslands with experimental increases in atmospheric CO2 concentration ([CO2]), a physiological response that could significantly alter the future carbon cycle if it persists in the long term. Yet an acclimation of photosynthetic capacity suggested by theoretical models and short‐term experiments could completely remove this effect of CO2. Perennial ryegrass (Lolium perenne L. cv. Bastion) was grown under an elevated [CO2] of 600 µmol mol−1 for 10 years using Free Air CO2Enrichment (FACE), with two contrasting nitrogen levels and abrupt changes in the source : sink ratio following periodic harvests. More than 3000 measurements characterized the response of leaf photosynthesis and stomatal conductance to elevated [CO2] across each growing season for the duration of the experiment. Over the 10 years as a whole, growth at elevated [CO2] resulted in a 43% higher rate of light‐saturated leaf photosynthesis and a 36% increase in daily integral of leaf CO2 uptake. Photosynthetic stimulation was maintained despite a 30% decrease in stomatal conductance and significant decreases in both the apparent, maximum carboxylation velocity (Vc,max) and the maximum rate of electron transport (Jmax). Immediately prior to the periodic (every 4–8 weeks) cuts of the L. perenne stands, Vc,max and Jmax, were significantly lower in elevated than in ambient [CO2] in the low‐nitrogen treatment. This difference was smaller after the cut, suggesting a dependence upon the balance between the sources and sinks for carbon. In contrast with theoretical expectations and the results of shorter duration experiments, the present results provide no significant change in photosynthetic stimulation across a 10‐year period, nor greater acclimation in Vc,max and Jmax in the later years in either nitrogen treatment.

Will Elevated Carbon Dioxide Concentration Amplify the Benefits of Nitrogen Fixation in Legumes?

“…4). Perennial ryegrass grown at elevated [CO 2 ] displayed photosynthetic acclimation with a lower maximum photosynthetic carboxylation capacity (V c,max ) and a lower maximum capacity for electron transport leading to ribulose-1,5-bisP regeneration ( J max ) when compared with plants grown at current [CO 2 ] (Ainsworth et al, 2003a). This results in a less-steep initial slope and lower asymptote on the A-c i curve at elevated [CO 2 ] compared to current [CO 2 ] (Fig.…”

Differential long-term effects of climate change and management on stocks and distribution of soil organic carbon in productive grasslands

“…Published estimates of D CO−2,v for species in INT and EXT range from 20-40 % and estimates of individual species typically differ as much as those between species (Aeschlimann et al, 2005;Ainsworth et al, 2003;Casella and Soussana, 1997;Ryle et al, 1992). In the present model applications, we used D CO 2 =33 % for both grasses and legumes (C3 plants) based on an extensive literature review by Wand et al (1999).…”

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“…Low N fertilization limited N uptake during vegetative growth, which constrained any increase in spikelet number, thereby limiting the yield response (Kim et al, 2003). Low N may also cause more pronounced acclimation of the photosynthesis which elevated CO 2 that can limit total dry matter and leaf area increases at elevated CO 2 (Suter et al, 2001;Ainsworth et al, 2003).…”