Biochemical and molecular characteristics of leaf photosynthesis and relative seed yield of two contrasting rice cultivars in response to elevated [CO₂

Chunwu Zhu,Qian Jiang,Lewis H Ziska,Jing Cao,Gang Liu,Jianguo Zhu

doi:10.1093/jxb/eru344

Abstract

Understanding the basis for intraspecific yield variability may be important in elucidating biological mechanisms that are associated with superior yield performance in response to projected increases in carbon dioxide concentration, [CO₂]. Using a free-air CO₂ enrichment (FACE) facility, two rice lines, S63 and W14, which differed consistently in their enhancement of seed yield when grown at elevated [CO₂] in multiple field trials, were examined. To determine if the different cultivar responses were linked to changes in photosynthetic characteristics at elevated [CO₂], spatial and temporal changes in photosynthetic stimulation and the occurrence of down-regulation, or acclimation, in relation to panicle sink development were quantified for the uppermost canopy leaves. Changes in photosynthetic capacity were determined by quantifying changes in the sink:source ratio, leaf nitrogen (N) content, the concentration and mRNA expression of the large Rubisco subunit, and changes in V c,max, the maximum ribulose bisphosphate (RuBP)-saturated rate of carboxylation. For the W14 cultivar, significant reductions in photosynthesis at the elevated, relative to ambient [CO₂], signalling photosynthetic acclimation, were observed following panicle initiation. The observance of photosynthetic acclimation was consistent with significant reductions in N, Rubisco content and expression, and V c,max. In contrast, for the cultivar S63, elevated [CO₂] resulted in increased spikelet number and grain weight, increased sink:source ratios, and continued stimulation of photosynthesis up to grain maturity. Overall, these data suggest that the greater response of the S63 line to elevated [CO₂] may be associated with enhanced carbon sinks relative to sources, and the ability to maintain photosynthetic capacity during grain development.

Highlights

Since 1959, concentrations of atmospheric carbon dioxide,[CO2], have increased from 318 to ~400 ppm, and, depending on anthropogenic emission rates, may reach 1000 μmol mol–1 by the end of the century (Meinshausen et al, 2011)
If high temperatures or low N limited sink development, any stimulatory response to elevated [CO2] may be negated as lack of sinks could result in a reduction in photosynthetic capacity (e.g. Lin et al, 1997; Kim et al, 2003)
Some experiments suggest that allocation of additional carbon for increased sink development, through either panicle size or increased tiller production, may be associated with yield stimulation at elevated [CO2] (e.g. Shimono et al, 2009; Shimono, 2011; Hasegawa et al, 2013; Shimono and Okada, 2013)

Summary

Introduction

Since 1959, concentrations of atmospheric carbon dioxide,[CO2], have increased from 318 to ~400 ppm, and, depending on anthropogenic emission rates, may reach 1000 μmol mol–1 by the end of the century (Meinshausen et al, 2011). Since 1959, concentrations of atmospheric carbon dioxide,. Widely recognized as a global warming gas, [CO2] is the sole source of carbon for photosynthesis, and its increased availability can directly enhance plant growth. The degree of enhancement, has been found to vary between plant species and within a given species. Such intraspecific enhancement is of obvious interest in agricultural research because it represents a potential means to begin selection of crop cultivars that could show superior yield performance in response to rising atmospheric [CO2] (Tausz et al, 2013).

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