Abstract
. Mesophyll conductance (gm) has been shown to vary between genotypes of a number of species and with growth environments, including nitrogen availability, but understanding of gm variability in legumes is limited. We might expect gm in legumes to respond differently to limited nitrogen availability, due to their ability to fix atmospheric N2. Using online stable carbon isotope discrimination method, we quantified genetic variability in gm under ideal conditions, investigated gm response to N source (N2-fixation or inorganic N) and determined the effects of N source and water availability on the rapid response of gm to photosynthetic photon flux density (PPFD) and radiation wavelength in three genotypes of chickpea (Cicer arietinum). Genotypes varied 2-fold in gm under non-limiting environments. N-fed plants had higher gm than N2-fixing plants in one genotype, while gm in the other two genotypes was unaffected. gm response to PPFD was altered by N source in one of three genotypes, in which the gm response to PPFD was statistically significant in N-fed plants but not in N2-fixing plants. There was no clear effect of moderate water stress on the gm response to PPFD and radiation wavelength. Genotypes of a single legume species differ in the sensitivity of gm to both long- and short-term environmental conditions, precluding utility in crop breeding programmes.
Highlights
IntroductionMesophyll conductance to CO2 (gm), which regulates the diffusion of CO2 from substomatal cavities to the sites of carboxylation, is recognized as a significant and variable limitation to photosynthesis (Flexas et al 2008, 2012). gm is a combination of gaseous diffusion through the intercellular airspaces and diffusion in the liquid phase through the mesophyll cell walls, plasma membrane, cytosol and chloroplast envelope to chloroplast stroma (Evans et al 2009). gm has been shown to be influenced by different growth environments including water availability, photosynthetic photon flux density (PPFD), temperature, CO2 concentration and nitrogen nutrition (Warren et al 2007; Flexas et al 2008; Loreto et al 2009; Bunce 2010; Douthe et al 2011; Perez-Martin et al 2014; Xiong et al 2015; Olsovska et al 2016). gm variability within and among species and in response to growth conditions has been associated with leaf structure and anatomical properties, the licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.AoB PLANTS https://academic.oup.com/aobplaShrestha et al – gm response to environmental changes in chickpea surface area of chloroplasts exposed to the intercellular spaces (Sc), cell wall and chloroplast thickness (Evans et al 2009; Tosens et al 2012; Tomás et al 2013), but see (Hanba et al 2002; Tomás et al 2014; Shrestha2017). gm variability may result from the changes in leaf enzymatic processes including membrane permeability through aquaporins, AQPs (Terashima andOno 2002; Hanba et al 2004; Flexas et al 2006, 2008, 2012) and CO2/bicarbonate equilibration though carbonic anhydrase, CA (Gillon and Yakir 2000; Perez-Martin et al 2014; Momayyezi and Guy 2017). gm has been suggested as an appropriate selection target to improve crop water-use efficiency (Flexas et al 2013)while maintaining photosynthetic rate
Mesophyll conductance has been found to respond to short-term changes in environmental conditions such as temperature and CO2 concentration (Flexas et al 2008; von Caemmerer and Evans 2015; Xiong et al 2015); there are conflicting results between studies regarding the short-term response of gm to light environment
We attempted to address three questions: (i) Do chickpea genotypes differ in mesophyll conductance? (ii) Does the source of N influence gm in chickpea and are there genotypic differences in this effect? (iii) Are there genotypic differences in the growth environment effects on the gm response to PDF and radiation wavelength? Three experiments were conducted to answer these questions
Summary
Mesophyll conductance to CO2 (gm), which regulates the diffusion of CO2 from substomatal cavities to the sites of carboxylation, is recognized as a significant and variable limitation to photosynthesis (Flexas et al 2008, 2012). gm is a combination of gaseous diffusion through the intercellular airspaces and diffusion in the liquid phase through the mesophyll cell walls, plasma membrane, cytosol and chloroplast envelope to chloroplast stroma (Evans et al 2009). gm has been shown to be influenced by different growth environments including water availability, photosynthetic photon flux density (PPFD), temperature, CO2 concentration and nitrogen nutrition (Warren et al 2007; Flexas et al 2008; Loreto et al 2009; Bunce 2010; Douthe et al 2011; Perez-Martin et al 2014; Xiong et al 2015; Olsovska et al 2016). gm variability within and among species and in response to growth conditions has been associated with leaf structure and anatomical properties, the licenses/by/4.0/), which permits unrestricted reuse, distribution, and reproduction in any medium, provided the original work is properly cited.AoB PLANTS https://academic.oup.com/aobplaShrestha et al – gm response to environmental changes in chickpea surface area of chloroplasts exposed to the intercellular spaces (Sc), cell wall and chloroplast thickness (Evans et al 2009; Tosens et al 2012; Tomás et al 2013), but see (Hanba et al 2002; Tomás et al 2014; Shrestha2017). gm variability may result from the changes in leaf enzymatic processes including membrane permeability through aquaporins, AQPs (Terashima andOno 2002; Hanba et al 2004; Flexas et al 2006, 2008, 2012) and CO2/bicarbonate equilibration though carbonic anhydrase, CA (Gillon and Yakir 2000; Perez-Martin et al 2014; Momayyezi and Guy 2017). gm has been suggested as an appropriate selection target to improve crop water-use efficiency (Flexas et al 2013)while maintaining photosynthetic rate. Gm has been shown to be influenced by different growth environments including water availability, photosynthetic photon flux density (PPFD), temperature, CO2 concentration and nitrogen nutrition (Warren et al 2007; Flexas et al 2008; Loreto et al 2009; Bunce 2010; Douthe et al 2011; Perez-Martin et al 2014; Xiong et al 2015; Olsovska et al 2016). Mesophyll conductance has been found to respond to short-term changes in environmental conditions such as temperature and CO2 concentration (Flexas et al 2008; von Caemmerer and Evans 2015; Xiong et al 2015); there are conflicting results between studies regarding the short-term response of gm to light environment. There has been speculation that rapid changes in gm with PPFD are methodological artefacts
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