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Photosynthetic acclimation and resource use by the C 3 and C 4 subspecies of A lloteropsis semialata in low CO 2 atmospheres
Author(s) -
Ripley Brad S.,
Cunniff Jennifer,
Osborne Colin P.
Publication year - 2013
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 - 10.1111/gcb.12091
Subject(s) - photosynthesis , subspecies , acclimatization , biomass (ecology) , nitrogen , stomatal conductance , biology , botany , photosynthetic capacity , ecology , chemistry , organic chemistry
During the past 25 Myr, partial pressures of atmospheric CO 2 ( C a ) imposed a greater limitation on C 3 than C 4 photosynthesis. This could have important downstream consequences for plant nitrogen economy and biomass allocation. Here, we report the first phylogenetically controlled comparison of the integrated effects of subambient C a on photosynthesis, growth and nitrogen allocation patterns, comparing the C 3 and C 4 subspecies of A lloteropsis semialata . Plant size decreased more in the C 3 than C 4 subspecies at low C a , but nitrogen pool sizes were unchanged, and nitrogen concentrations increased across all plant partitions. The C 3, but not C 4 subspecies, preferentially allocated biomass to leaves and increased specific leaf area at low C a . In the C 3 subspecies, increased leaf nitrogen was linked to photosynthetic acclimation at the interglacial C a , mediated via higher photosynthetic capacity combined with greater stomatal conductance. Glacial C a further increased the biochemical acclimation and nitrogen concentrations in the C 3 subspecies, but these were insufficient to maintain photosynthetic rates. In contrast, the C 4 subspecies maintained photosynthetic rates, nitrogen‐ and water‐use efficiencies and plant biomass at interglacial and glacial C a with minimal physiological adjustment. At low C a , the C 4 carbon‐concentrating mechanism therefore offered a significant advantage over the C 3 type for carbon acquisition at the whole‐plant scale, apparently mediated via nitrogen economy and water loss. A limiting nutrient supply damped the biomass responses to C a and increased the C 4 advantage across all C a treatments. Findings highlight the importance of considering leaf responses in the context of the whole plant, and show that carbon limitation may be offset at the expense of greater plant demand for soil resources such as nitrogen and water. Results show that the combined effects of low CO 2 and resource limitation benefit C 4 plants over C 3 plants in glacial–interglacial environments, but that this advantage is lessened under anthropogenic conditions.