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Gas exchange and photosynthetic acclimation over subambient to elevated CO 2 in a C 3 –C 4 grassland
Author(s) -
Anderson Laurel J.,
Maherali Hafiz,
Johnson Hyrum B.,
Polley H. Wayne,
Jackson Robert B.
Publication year - 2001
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1046/j.1354-1013.2001.00438.x
Subject(s) - perennial plant , photosynthesis , stomatal conductance , acclimatization , plant functional type , botany , biology , photosynthetically active radiation , lolium perenne , dactylis glomerata , ecology , poaceae , ecosystem
Atmospheric CO 2 (C a ) has risen dramatically since preglacial times and is projected to double in the next century. As part of a 4‐year study, we examined leaf gas exchange and photosynthetic acclimation in C 3 and C 4 plants using unique chambers that maintained a continuous C a gradient from 200 to 550 µmol mol −1 in a natural grassland. Our goals were to characterize linear, nonlinear and threshold responses to increasing C a from past to future C a levels. Photosynthesis ( A ), stomatal conductance ( g s ), leaf water‐use efficiency ( A / g s ) and leaf N content were measured in three common species: Bothriochloa ischaemum , a C 4 perennial grass, Bromus japonicus , a C 3 annual grass, and Solanum dimidiatum , a C 3 perennial forb. Assimilation responses to internal CO 2 concentrations ( A /C i curves) and photosynthetically active radiation ( A /PAR curves) were also assessed, and acclimation parameters estimated from these data. Photosynthesis increased linearly with C a in all species ( P < 0.05). S. dimidiatum and B. ischaemum had greater carboxylation rates for Rubisco and PEP carboxylase, respectively, at subambient than superambient C a ( P < 0.05). To our knowledge, this is the first published evidence of A up‐regulation at subambient C a in the field. No species showed down‐regulation at superambient C a . Stomatal conductance generally showed curvilinear decreases with C a in the perennial species ( P < 0.05), with steeper declines over subambient C a than superambient, suggesting that plant water relations have already changed significantly with past C a increases. Resource‐use efficiency ( A / g s and A /leaf N) in all species increased linearly with C a . As both C 3 and C 4 plants had significant responses in A , g s , A / g s and A /leaf N to C a enrichment, future C a increases in this grassland may not favour C 3 species as much as originally thought. Non‐linear responses and acclimation to low C a should be incorporated into mechanistic models to better predict the effects of past and present rising C a on grassland ecosystems.